Earth, Atmospheric, and Planetary Sciences Faculty Publications Copyright (c) 2013 Purdue University All rights reserved. http://docs.lib.purdue.edu/easpubs Recent documents in Earth, Atmospheric, and Planetary Sciences Faculty Publications en-us Sat, 16 Mar 2013 01:38:29 PDT 3600 Contrails and Induced Cirrus: Optics and Radiation http://docs.lib.purdue.edu/easpubs/155 http://docs.lib.purdue.edu/easpubs/155 Thu, 14 Mar 2013 14:32:17 PDT This paper summarizes the assessment of the current state of knowledge, areas of uncertainties, and recommendations for future efforts, regarding the optical and radiative properties of contrails and contrail cirrus, which have been reported in two detailed subject-specific white papers for the Aviation Climate Change Research Initiative undertaken by the U.S. Federal Aviation Administration. To better estimate the radiative forcing of aircraft-induced cloudiness, there is a pressing need to improve the present understanding of the optical properties of nonspherical ice crystals within contrails and contrail cirrus, and to enhance the global satellite detection and retrieval of these clouds. It is also critical to develop appropriate parameterizations of ice crystal bulk optical properties for climate models on the basis of state-of-the-art scattering simulations and available in situ measurements of ice crystal size and habit distributions within contrails and contrail cirrus. More accurate methods are needed to retrieve the bulk radiative properties of contrails and contrail cirrus to separate natural from anthropogenic ice cloud effects. Such refined techniques should be applied to past and future satellite imagery to develop a contrail climatology that would serve to evaluate contrail radiative forcing more accurately, to determine trends in contrail cirrus, and to guide and validate parameterizations of contrails in numerical weather and climate models. To point the way forward, we recommend four near-term and three long-term research priorities.

]]> Ping Yang et al. The influence of drinking water on the $ẹlta$D and $ẹlta$18O values of house sparrow plasma, blood and feathers http://docs.lib.purdue.edu/easpubs/153 http://docs.lib.purdue.edu/easpubs/153 Thu, 14 Mar 2013 14:32:16 PDT We investigated the relationships between the δdeuterium (δD) and the δ18oxygen (δ18O) of drinking water and the δD and δ18O of blood plasma, red blood cells and feathers in house sparrows (Passer domesticus) fed on diets with identical hydrogen and oxygen isotopic compositions and five isotopically distinct drinking water treatments. We expected and, with only one exception (18O in blood plasma), found linear relationships between the δD and δ18O values of drinking water and those of bird tissues. The slopes of these relationships, which estimate the percentage contributions of drinking water to the tissue isotopic signatures, were lower than those of previous studies. We found significant differences in the δD and δ18O values of feathers, red blood cells and plasma solids. In feathers and red blood cells, δD and δ18O values were linearly correlated. Our results have three implications for isotopic field studies: (1) if the isotopic composition of drinking water differs from that of food, its effect on tissue isotope values can confound the assignment of animals to a site of origin; (2) comparisons of the δD and δ18O values of different tissues must account for inter-tissue discrimination factors; and (3) δD/δ18O linear relationships are probably as prevalent in animal systems as they are in geohydrological systems. These relationships may prove to be useful tools in animal isotopic ecology.

]]> N. Wolf et al. Mid-upper tropospheric methane in the high Northern Hemisphere: Spaceborne observations by AIRS, aircraft measurements, and model simulations http://docs.lib.purdue.edu/easpubs/154 http://docs.lib.purdue.edu/easpubs/154 Thu, 14 Mar 2013 14:32:16 PDT Spaceborne measurements by the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua satellite provide a global view of the methane (CH4) distribution in the mid-upper troposphere (MUT-CH4). The focus of this study is to examine the spatiotemporal variation of MUT-CH4 in the high Northern Hemisphere (HNH) using AIRS retrievals, aircraft measurements, and simulations from a forward chemistry-transport model (i.e., ACTM). Data from 2004 and 2005 focusing over two regions (Alaska and Siberia) are analyzed. An important feature in the seasonal variation of CH4 we found is the summer increase of MUT-CH4, which is nearly opposite to the summer minimum of CH4 in the marine boundary layer (MBL). This study also demonstrated an apparent increase of CH4 over Alaska associated with the 2004 Alaska forest fire and a negative bias of the ACTM simulations in the HNH. The larger bias of the model simulations in the late winter to early spring may indicate possible unidentified CH4 emission sources (e.g., the use of energy or gas leakage) during this period, but more studies will be needed due to the retrieval uncertainties in the polar winter season. The summer increase of MUT-CH4 is related to surface emission, but the enhanced convection in summer is likely the most important driver.

]]> X. Xiong et al. Impacts of cloud-system resolving regional modeling on the simulation of monsoon depressions http://docs.lib.purdue.edu/easpubs/152 http://docs.lib.purdue.edu/easpubs/152 Thu, 14 Mar 2013 14:32:15 PDT The impacts of high-resolution (<10 km) and cloud-system-resolving regional modeling (CSRM) on the simulation of an intense south Asian monsoon depression (MD) were examined using the WRF-ARW model. Spatial resolution in this range was necessary to realistically simulate the MD's propagation, intensity, and precipitation. Simulations were however highly sensitive to the moist convection and cloud microphysics. The best scenarios were created by the microphysics parameterization (MP) that generated the most robust post-landfall condensation associated with the MD, alone or in combination with the cumulus parameterization that triggered vigorous convection overland in the coarser setup. A sensitivity study of the MP schemes in CSRM suggested that more sophisticated mixed-phased schemes contributed to higher simulation fidelity. Insufficient condensation and weak convection overland might induce spurious low systems over the Bay of Bengal through low-level moisture advection, which further interfered with the MD and degraded several simulations.

]]> Y. C. Wang et al. Quantifying the quality of coral bleaching predictions http://docs.lib.purdue.edu/easpubs/150 http://docs.lib.purdue.edu/easpubs/150 Thu, 14 Mar 2013 14:32:14 PDT Techniques that utilize sea surface temperature (SST) observations to predict coral reef bleaching are in common use and form the foundation for predicted global coral reef ecosystem demise within this century. Yet, quality assessments of these methods are typically qualitative or anecdotal. Quality is the correspondence of forecasts with observations and has standard quantitative measures. Here a forecast verification method, commonly used in meteorology, is presented and used to measure the quality of the degree heating weeks (DHW) technique as an exploration of insights that can be gleaned from this methodology. DHW values were calculated from NOAA Optimum Interpolation SST version 2 data and compared to a database of bleaching observations from 1990–2007. Quality is expressed with an objective measure, the Peirce Skill Score (PSS). The quality at varying DHW thresholds above which bleaching was projected to occur is calculated. By selecting the thresholds that maximize quality, the predictive technique is objectively optimized. This results in optimal threshold maps, showing reefs more prone and more resistant to bleaching. Optimization increases the quality of DHW as a predictor of bleaching from PSS = 0.55 to PSS = 0.83, in global average, but the optimal PSS and corresponding DHW values vary significantly from location to location. The coral reef research and management community are urged to adopt the simple, but rigorous tools of forecast verification routinely used in other disciplines so that bleaching forecasts can be quantitatively compared and their quality improved.

]]> R. van Hooidonk et al. Equivocal evidence for a thermostat and unusually low levels of coral bleaching in the Western Pacific Warm Pool http://docs.lib.purdue.edu/easpubs/151 http://docs.lib.purdue.edu/easpubs/151 Thu, 14 Mar 2013 14:32:14 PDT An ocean “thermostat” was recently proposed that limits Western Pacific Warm Pool (WPWP) sea surface temperature (SST) causing anomalously low coral bleaching rates. We analyze WPWP SST trends and bleaching using HadISST data and a coral bleaching database and find no strong evidence for a thermostat or for anomalously low bleaching. A region within the WPWP has a trend of maximum SST near zero, but this signal is not robust – by using different data or periods the signal disappears. We do find a negative correlation between the average warmest month for the years 1950–1969 (average SST max) and the linear trend of maximum monthly temperatures for the years 1950–2006 (linear trend SST max). However this correlation is not unique to the WPWP, it is also observed in a cooler region. Consequently it can not be explained by a thermostat. The observed sparsity of bleaching observations in the WPWP is not in agreement with estimated bleaching likelihood. The sparsity of observations is more likely due to the WPWP's remoteness.

]]> R. van Hooidonk et al. Technical Note: Propagating correlations in atmospheric inversions using different Kalman update smoothers http://docs.lib.purdue.edu/easpubs/148 http://docs.lib.purdue.edu/easpubs/148 Thu, 14 Mar 2013 14:32:13 PDT The scheme to propagate correlations between on-line and off-line state variables in atmospheric inversions using the fixed-lag Kalman smoother proposed in Bruhwiler et al. (2005) is explained as a process to impose a balanced constraint on the on-line state variables. It is then extended to the fixed-lag ensemble square root Kalman smoother and fixed-lag square root sigma-point Kalman smoother, allowing us to treat nonlinear observation operators easily. Further, to constrain the posterior fluxes within their feasible ranges, the constrained fixed-lag Kalman smoother is presented and the variable transform technique is proposed for the other two smoothers. Comparisons between various methods and observational data are conducted using a synthetic inversion of atmospheric CH4 fluxes. The results indicate that our developed methods are good alternatives to existing methods for conducting sequential inversion of atmospheric trace gases. It is also shown that the benefit to include the correlations between on-line and off-line state variables is case dependent.

]]> Jinyun Tang et al. Quantifying wetland methane emissions with process-based models of different complexities http://docs.lib.purdue.edu/easpubs/149 http://docs.lib.purdue.edu/easpubs/149 Thu, 14 Mar 2013 14:32:13 PDT Bubbling is an important pathway of methane emissions from wetland ecosystems; however the concentration-based threshold function approach in current biogeochemistry models of methane is not sufficient to represent the complex ebullition process. Here we revise an extant process-based biogeochemistry model, the Terrestrial Ecosystem Model into a multi-substance model (CH4, O2, CO2 and N2) to simulate methane production, oxidation, and transport (particularly ebullition) with different model complexities. When ebullition is modeled with a concentration-based threshold function and if the inhibition effect of oxygen on methane production and the competition for oxygen between methanotrophy and heterotrophic respiration are retained, the model is a two-substance system. Ignoring the role of oxygen, while still modeling ebullition with a concentration-based threshold function, reduces the model to a one-substance system. These models were tested through a group of sensitivity analyses at two temperate peatland sites in Michigan. We demonstrate that only the four-substance model with a pressure-based ebullition algorithm is able to capture the episodic emissions induced by a sudden decrease in atmospheric pressure. All models captured the retardation effect on methane efflux from an increase in surface standing water which results from the inhibition of diffusion and the increase in rhizospheric oxidation. We conclude that to more accurately account for the effects of atmospheric pressure dynamics and standing water on methane effluxes, the multi-substance model with a pressure-based ebullition algorithm should be used in the future to quantify global wetland CH4 emissions. Further, to more accurately simulate the pore water gas concentrations and different pathways of methane transport, an exponential root distribution function should be used and the phase-related parameters should be treated as temperature dependent.

]]> Jinyun Tang et al. A global sensitivity analysis and Bayesian inference framework for improving the parameter estimation and prediction of a process-based Terrestrial Ecosystem Model http://docs.lib.purdue.edu/easpubs/147 http://docs.lib.purdue.edu/easpubs/147 Thu, 14 Mar 2013 14:32:12 PDT A global sensitivity analysis and Bayesian inference framework was developed for improving the parameterization and predictability of a monthly time step process-based biogeochemistry model. Using a Latin Hypercube sampler and an existing Terrestrial Ecosystem Model (TEM), a set of 500,000 Monte Carlo ensemble simulations was conducted for a black spruce forest ecosystem. A global sensitivity analysis was then conducted to identify the key model parameters and examine the interaction structures among TEM parameters. Bayesian inference analysis was also performed using these ensemble simulations and eddy flux data of carbon, latent heat flux, and MODIS gross primary production (GPP) to reduce the uncertainty of parameter estimation and prediction of TEM. We found that (1) the simulated carbon fluxes are mostly affected by parameters of the maximum rate of photosynthesis (CMAX), the half-saturation constant for CO2 uptake by plants (kc), the half-saturation constant for Photosynthetically Active Radiation used by plants (ki), and the change in autotrophic respiration due to 10°C temperature increase (RHQ10); (2) the effect of parameters on seasonal carbon dynamics varies from one parameter to another during a year; (3) to well constrain the uncertainties of TEM predictions and parameters using the Bayesian inference technique, at least two different fluxes of NEP, GPP, and ecosystem respiration (RESP) are required; and (4) different assumptions of the error structures of the flux data used in the Bayesian inference analysis result in different uncertainty bounds of the posterior parameters and model predictions. We further found that, using the Bayesian framework and eddy flux and satellite data, the uncertainty of simulated carbon fluxes has been remarkably reduced. The developed global sensitivity analysis and Bayesian framework could further be used to analyze and improve the predictability and parameterization of relatively coarse time step biogeochemistry models when the eddy flux and satellite data are available for other terrestrial ecosystems.

]]> Jinyun Tang et al. Numerical study of 1998 late summer flood in East Asia http://docs.lib.purdue.edu/easpubs/145 http://docs.lib.purdue.edu/easpubs/145 Thu, 14 Mar 2013 14:32:11 PDT Wen Yih Sun et al. Ecosystem effects of non-native earthworms in Mid-Atlantic deciduous forests http://docs.lib.purdue.edu/easpubs/146 http://docs.lib.purdue.edu/easpubs/146 Thu, 14 Mar 2013 14:32:11 PDT In many mid-Atlantic forests where both native and non-native earthworms exist, it is the non-native species that are the dominant component of the soil macrofauna. Few earthworm ecology studies, however, focus attention on these forest systems in order to determine the relative ecological roles and potential interactions of the native and non-native earthworms. In a series of field samplings and experimental manipulations we collected data on the effects of earthworms on below-and aboveground ecosystem processes. Earthworm abundance and the ecological processes measured were dynamic in space and time across the range of study sites. Leaf litter decay rates doubled at sites that had abundant non-native earthworms. Earthworms also altered the abundance of soil fungi, the activity of extracellular enzymes, soil respiration, and the growth of tree seedlings but the effects varied among sites depending on differences in land-use history and forest age. Red oak seedling growth was less at sites that had abundant earthworms but tulip poplar and red maple seedlings grew equally well with and without abundant earthworms. These preliminary results suggest that non-native earthworms have significant ecosystem effects, even in forests where native earthworms still occur. Land use history, however, plays an important role in determining what those effects will be, and these effects are likely to be dynamic, depending on the abundance of non-native earthworms.

]]> Katalin Szlavecz et al. One-Dimensional Sea Ice-Ocean Model Applied to SHEBA Experiment in 1997-1998 Winter http://docs.lib.purdue.edu/easpubs/144 http://docs.lib.purdue.edu/easpubs/144 Thu, 14 Mar 2013 14:32:10 PDT Wen Yih Sun et al. Artificial neural network approach for mapping contrasting tillage practices http://docs.lib.purdue.edu/easpubs/143 http://docs.lib.purdue.edu/easpubs/143 Thu, 14 Mar 2013 14:32:09 PDT K. P. Sudheer et al. Lithospheric buoyancy forces in Africa from a thin sheet approach http://docs.lib.purdue.edu/easpubs/142 http://docs.lib.purdue.edu/easpubs/142 Thu, 14 Mar 2013 14:32:08 PDT D. S. Stamps et al. Selection and placement of best management practices used to reduce water quality degradation in Lincoln Lake watershed http://docs.lib.purdue.edu/easpubs/141 http://docs.lib.purdue.edu/easpubs/141 Thu, 14 Mar 2013 14:32:07 PDT Hector German Rodriguez et al. Geologic problem solving in the field: Analysis of field navigation and mapping by advanced undergraduates http://docs.lib.purdue.edu/easpubs/140 http://docs.lib.purdue.edu/easpubs/140 Thu, 14 Mar 2013 14:32:06 PDT E. M. Riggs et al. Effectiveness in problem solving during geologic field examinations: Insights from analysis of GPS tracks at variable time scales http://docs.lib.purdue.edu/easpubs/139 http://docs.lib.purdue.edu/easpubs/139 Thu, 14 Mar 2013 14:32:05 PDT Eric M. Riggs et al. A simplified in situ cosmogenic 14C extraction system http://docs.lib.purdue.edu/easpubs/138 http://docs.lib.purdue.edu/easpubs/138 Thu, 14 Mar 2013 14:32:03 PDT Jeffrey S. Pigati et al. Seismic images of crustal variations beneath the East Anatolian Plateau (Turkey) from teleseismic receiver functions http://docs.lib.purdue.edu/easpubs/137 http://docs.lib.purdue.edu/easpubs/137 Thu, 14 Mar 2013 14:32:01 PDT Arda A. Özacar et al. Scaling laws for fractional Brownian motion with power-law clock http://docs.lib.purdue.edu/easpubs/136 http://docs.lib.purdue.edu/easpubs/136 Thu, 14 Mar 2013 14:32:00 PDT Daniel O’Malley et al. THE PROPAGATION OF Pn IN WESTERN CHINA http://docs.lib.purdue.edu/easpubs/134 http://docs.lib.purdue.edu/easpubs/134 Thu, 14 Mar 2013 14:31:59 PDT Robert L. Nowack et al. The Gouy phase anomaly for harmonic and time-domain paraxial Gaussian beams http://docs.lib.purdue.edu/easpubs/135 http://docs.lib.purdue.edu/easpubs/135 Thu, 14 Mar 2013 14:31:59 PDT Robert L. Nowack et al. Seismic interferometry and estimation of the Green’s function using Gaussian beams http://docs.lib.purdue.edu/easpubs/133 http://docs.lib.purdue.edu/easpubs/133 Thu, 14 Mar 2013 14:31:58 PDT Robert L. Nowack Observational evidence that agricultural intensification and land use change may be reducing the Indian summer monsoon rainfall http://docs.lib.purdue.edu/easpubs/132 http://docs.lib.purdue.edu/easpubs/132 Thu, 14 Mar 2013 14:31:57 PDT Dev Niyogi et al. GPS/INS navigation precision and its effect on airborne radio occultation retrieval accuracy http://docs.lib.purdue.edu/easpubs/131 http://docs.lib.purdue.edu/easpubs/131 Thu, 14 Mar 2013 14:31:56 PDT Paytsar Muradyan et al. A regional scale assessment of land use/land cover and climatic changes on water and energy cycle in the upper Midwest United States http://docs.lib.purdue.edu/easpubs/130 http://docs.lib.purdue.edu/easpubs/130 Thu, 14 Mar 2013 14:31:56 PDT Vimal Mishra et al. Isotope modeling of nitric acid formation in the atmosphere using ISO-RACM: testing the importance of NO oxidation, heterogeneous reactions, and trace gas chemistry http://docs.lib.purdue.edu/easpubs/129 http://docs.lib.purdue.edu/easpubs/129 Thu, 14 Mar 2013 14:31:54 PDT G. Michalski et al. Summer monsoon convection in the Himalayan region: Terrain and land cover effects http://docs.lib.purdue.edu/easpubs/128 http://docs.lib.purdue.edu/easpubs/128 Thu, 14 Mar 2013 14:31:53 PDT Socorro Medina et al. Open Loop Tracking of Radio Occultation Signals from an Airborne Platform http://docs.lib.purdue.edu/easpubs/127 http://docs.lib.purdue.edu/easpubs/127 Thu, 14 Mar 2013 14:31:53 PDT Tyler Delfield Lulich et al. Possible decline of the carbon sink in the Mongolian Plateau during the 21st century http://docs.lib.purdue.edu/easpubs/126 http://docs.lib.purdue.edu/easpubs/126 Thu, 14 Mar 2013 14:31:52 PDT Y. Lu et al. Evaluating climate impacts on carbon balance of the terrestrial ecosystems in the Midwest of the United States with a process-based ecosystem model http://docs.lib.purdue.edu/easpubs/125 http://docs.lib.purdue.edu/easpubs/125 Thu, 14 Mar 2013 14:31:50 PDT Xiaoliang Lu et al. Urbanization signature in the observed heavy rainfall climatology over India http://docs.lib.purdue.edu/easpubs/124 http://docs.lib.purdue.edu/easpubs/124 Thu, 14 Mar 2013 14:31:49 PDT C. M. Kishtawal et al. Temporal variation of oxygen isotope ratios ([delta] 18O) in drinking water: Implications for specifying location of origin with human scalp hair http://docs.lib.purdue.edu/easpubs/123 http://docs.lib.purdue.edu/easpubs/123 Thu, 14 Mar 2013 14:31:48 PDT Casey D. Kennedy et al. Geo-complexity and Earthquake Prediction http://docs.lib.purdue.edu/easpubs/122 http://docs.lib.purdue.edu/easpubs/122 Thu, 14 Mar 2013 14:31:48 PDT V. Keilis-Borok et al. Characterization of wildfire regimes in Canadian boreal terrestrial ecosystems http://docs.lib.purdue.edu/easpubs/121 http://docs.lib.purdue.edu/easpubs/121 Thu, 14 Mar 2013 14:31:47 PDT Jiang Yueyang et al. Jurassic Chronostratigraphic Database and the TimeScale Creator Visualization System http://docs.lib.purdue.edu/easpubs/120 http://docs.lib.purdue.edu/easpubs/120 Thu, 14 Mar 2013 14:31:46 PDT A joint project of the International Commission on Stratigraphy (ICS) and CHRONOS database program

]]> James Ogg et al. Multiscale analysis of heart rate variability: a comparison of different complexity measures http://docs.lib.purdue.edu/easpubs/119 http://docs.lib.purdue.edu/easpubs/119 Thu, 14 Mar 2013 14:31:45 PDT Heart rate variability (HRV) is an important dynamical variable of the cardiovascular function. There have been numerous efforts to determine whether HRV dynamics are chaotic or random, and whether certain complexity measures are capable of distinguishing healthy subjects from patients with certain cardiac disease. In this study, we employ a new multiscale complexity measure, the scale-dependent Lyapunov exponent (SDLE), to characterize the relative importance of nonlinear, chaotic, and stochastic dynamics in HRV of healthy, congestive heart failure (CHF), and atrial fibrillation subjects. We show that while HRV data of all these three types are mostly stochastic, the stochasticity is different among the three groups. Furthermore, we show that for the purpose of distinguishing healthy subjects from patients with CHF, features derived from SDLE are more effective than other complexity measures such as the Hurst parameter, the sample entropy, and the multiscale entropy.

]]> Jing Hu et al. Probabilistic Seismic Hazard Estimates Incorporating Site Effects–An Example from Indiana, USA http://docs.lib.purdue.edu/easpubs/118 http://docs.lib.purdue.edu/easpubs/118 Thu, 14 Mar 2013 14:31:44 PDT The U.S. Geological Survey (USGS) has published probabilistic earthquake hazard maps for the United States based on current knowledge of past earthquake activity and geological constraints on earthquake potential. These maps for the central and eastern United States assume standard site conditions with S-wave velocities of 760 m/s in the top 30 m. For urban and infrastructure planning and long-term budgeting, the public is interested in similar probabilistic seismic hazard maps that take into account near-surface geological materials. We have implemented a probabilistic method for incorporating site effects into the USGS seismic hazard analysis that takes into account the first-order effects of the surface geologic conditions. The thicknesses of sediments, which play a large role in amplification, were derived from a P-wave refraction database with over 13,000 profiles, and a preliminary geology-based velocity model was constructed from available information on S-wave velocities. An interesting feature of the preliminary hazard maps incorporating site effects is the approximate factor of two increases in the 1-Hz spectral acceleration with 2 percent probability of exceedance in 50 years for parts of the greater Indianapolis metropolitan region and surrounding parts of central Indiana. This effect is primarily due to the relatively thick sequence of sediments infilling ancient bedrock topography that has been deposited since the Pleistocene Epoch. As expected, the Late Pleistocene and Holocene depositional systems of the Wabash and Ohio Rivers produce additional amplification in the southwestern part of Indiana. Ground motions decrease, as would be expected, toward the bedrock units in south-central Indiana, where motions are significantly lower than the values on the USGS maps.

]]> Jennifer S. Haase et al. Earthquake Scenario Ground Motions for the Urban Area of Evansville, Indiana http://docs.lib.purdue.edu/easpubs/117 http://docs.lib.purdue.edu/easpubs/117 Thu, 14 Mar 2013 14:31:43 PDT Jennifer S. Haase et al. Probabilistic Seismic-Hazard Assessment Including Site Effects for Evansville, Indiana, and the Surrounding Region http://docs.lib.purdue.edu/easpubs/115 http://docs.lib.purdue.edu/easpubs/115 Thu, 14 Mar 2013 14:31:41 PDT Evansville, Indiana, is one of the closest large urban areas to both the New Madrid Seismic Zone, where large earthquakes occurred in 1811–1812, and the Wabash Valley Seismic Zone, where there is evidence of several large prehistoric earthquakes in the last 14,000 yr. For this reason, Evansville has been targeted as a priority region for urban seismic-hazard assessment. The probabilistic seismic-hazard methodology used for the Evansville region incorporates new information from recent surficial geologic mapping efforts, as well as information on the depth and properties of near-surface soils and their associated uncertainties. The probabilistic seismic-hazard calculation applied here follows the method used for the 2008 United States Geological Survey (USGS) national seismic-hazard maps, with modifications to incorporate estimates of local site conditions and their uncertainties, in a completely probabilistic manner. The resulting analysis shows strong local variations of acceleration with 2% probability of exceedance in 50 yr, which are clearly correlated with variations in the thickness of unconsolidated soils above bedrock. Spectral accelerations at 0.2-s period range from 0.6 to 1.5g, values that are much greater than those of the USGS national seismic-hazard map, which assume B/C site conditions with an average shear-wave velocity of 760 m/s in the top 30 m. The presence of an ancient bedrock valley underlying the current Ohio River flood plain strongly affects the spatial pattern of accelerations. For 1.0-s spectral acceleration, ground motions are significantly amplified due to deeper soils within this structure, to a level comparable to that predicted by the national seismic-hazard maps with D site conditions assumed. For PGA and 0.2-s spectral acceleration, ground motions are significantly amplified outside this structure, above the levels predicted by the national seismic-hazard maps with uniform D site conditions assumed.

]]> Jennifer S. Haase et al. Liquefaction Hazard near the Ohio River from Midwestern Scenario Earthquakes http://docs.lib.purdue.edu/easpubs/116 http://docs.lib.purdue.edu/easpubs/116 Thu, 14 Mar 2013 14:31:41 PDT Evansville, Indiana, and Henderson, Kentucky, located on the banks of the Ohio River, are susceptible to liquefaction-induced damage in the event of significant earthquake shaking. A sequence of three earthquakes with magnitudes greater than 7 occurred near New Madrid, MO, in 1811–1812, producing ground motions with Modified Mercalli Intensity VII in the Evansville-Henderson area near the Ohio River, 180 km away from the source. In addition, liquefaction evidence has been documented less than 40 km from Evansville from two large earthquakes that occurred within the past 12,000 years in the Wabash Valley. As a complement to recent work on the probabilistic seismic hazard analysis and scenario earthquake ground motions, we have calculated the liquefaction hazard within the 33 × 42–km2area containing Evansville and Henderson, based on scenario earthquakes from each of these source regions. Cone penetrometer test data were used to estimate the factor of safety against liquefaction at 58 sites in the study region. Liquefaction potential index (LPI) maps were calculated using a probabilistic method to account for the uncertainty due to spatial variability of soil profiles. The site response and peak ground accelerations for the scenario earthquakes vary across the study area, resulting in significant variations inLPI. The LPI is highest in the outwash terraces at the edges of the Ohio River Valley for both scenario earthquakes. However, the probability of liquefaction severe enough to produce lateral spreading (LPI > 12) was less than 20 percent in most of the study area for both scenarios.

]]> Jennifer S. Haase et al. Regionalization of SWAT Model Parameters for Use in Ungauged Watersheds http://docs.lib.purdue.edu/easpubs/114 http://docs.lib.purdue.edu/easpubs/114 Thu, 14 Mar 2013 14:31:40 PDT There has been a steady shift towards modeling and model-based approaches as primary methods of assessing watershed response to hydrologic inputs and land management, and of quantifying watershed-wide best management practice (BMP) effectiveness. Watershed models often require some degree of calibration and validation to achieve adequate watershed and therefore BMP representation. This is, however, only possible for gauged watersheds. There are many watersheds for which there are very little or no monitoring data available, thus the question as to whether it would be possible to extend and/or generalize model parameters obtained through calibration of gauged watersheds to ungauged watersheds within the same region. This study explored the possibility of developing regionalized model parameter sets for use in ungauged watersheds. The study evaluated two regionalization methods: global averaging, and regression-based parameters, on the SWAT model using data from priority watersheds in Arkansas. Resulting parameters were tested and model performance determined on three gauged watersheds. Nash-Sutcliffe efficiencies (NS) for stream flow obtained using regression-based parameters (0.53–0.83) compared well with corresponding values obtained through model calibration (0.45–0.90). Model performance obtained using global averaged parameter values was also generally acceptable (0.4 ≤ NS ≤ 0.75). Results from this study indicate that regionalized parameter sets for the SWAT model can be obtained and used for making satisfactory hydrologic response predictions in ungauged watersheds.

]]> Margaret W. Gitau et al. Denoising Nonlinear Time Series by Adaptive Filtering and Wavelet Shrinkage: A Comparison http://docs.lib.purdue.edu/easpubs/112 http://docs.lib.purdue.edu/easpubs/112 Thu, 14 Mar 2013 14:31:39 PDT Time series measured in real world is often nonlinear, even chaotic. To effectively extract desired information from measured time series, it is important to preprocess data to reduce noise. In this Letter, we propose an adaptive denoising algorithm. Using chaotic Lorenz data and calculating root-mean-square-error, Lyapunov exponent, and correlation dimension, we show that our adaptive algorithm more effectively reduces noise in the chaotic Lorenz system than wavelet denoising with three different thresholding choices. We further analyze an electroencephalogram (EEG) signal in sleep apnea and show that the adaptive algorithm again more effectively reduces the Electrocardiogram (ECG) and other types of noise contaminated in EEG than wavelet approaches.

]]> Jianbo Gao et al. Stable Isotopes in Large Scale Hydrological Applications http://docs.lib.purdue.edu/easpubs/113 http://docs.lib.purdue.edu/easpubs/113 Thu, 14 Mar 2013 14:31:39 PDT Measurement and modeling of the stable isotope signature of water in continental runoff provides unique information for large scale hydrological process studies and global water budget assessment. This chapter presents theory and case studies that illustrate isotopic signals relevant to understanding large scale hydrological processes. We provide examples illustrating isotopic labeling arising from isotopically varying runoff sources, open-water evaporation from lakes and wetlands, and river channel evaporation. Incorporation of isotopes in global and regional distributed runoff models may support the formal implementation of water isotopes as tools for monitoring large scale changes in continental water budgets and for model validation, but this work will require more comprehensive monitoring efforts for both surface water and meteoric precipitation isotopic composition.

]]> John J. Gibson et al. Approximation of definable sets by compact families, and upper bounds on homotopy and homology http://docs.lib.purdue.edu/easpubs/111 http://docs.lib.purdue.edu/easpubs/111 Thu, 14 Mar 2013 14:31:38 PDT We prove new upper bounds on homotopy and homology groups of o-minimal sets in terms of their approximations by compact o-minimal sets. In particular, we improve the known upper bounds on Betti numbers of semialgebraic sets defined by quantifier-free formulae and obtain, for the first time, a singly exponential bound on Betti numbers of sub-Pfaffian sets.

]]> Andrei Gabrielov et al. Predictability of extreme events in a branching diffusion model http://docs.lib.purdue.edu/easpubs/110 http://docs.lib.purdue.edu/easpubs/110 Thu, 14 Mar 2013 14:31:37 PDT Andrei Gabrielov et al. Temperature and equivalent temperature over the United States (1979–2005) http://docs.lib.purdue.edu/easpubs/108 http://docs.lib.purdue.edu/easpubs/108 Thu, 14 Mar 2013 14:31:36 PDT Temperature (T) and equivalent temperature (TE) trends over the United States from 1979 to 2005 and their correlation to land cover types are investigated using National Centers for Environmental Prediction North American Regional Reanalysis data, the Advanced Very High Resolution Radiometer (AVHRR) land use/cover classification, the National Land Cover Database (NLCD) 1992–2001 Retrofit Land Cover Change and the Normalised Difference Vegetation Index (NDVI) derived from AVHRR. Even though most of the magnitude of TE is explained by T, the moisture component induces larger trends and variability of TE relative to T. The contrast between pronounced temporal and spatial differences between T and TE at the near-surface level (2 m) and minor-to-no differences at 300–200 mb is a consistent pattern. This study therefore demonstrates that in addition to temperature, atmospheric heat content may help to quantify the differences between surface and tropospheric heating trends, and hence the impact of land cover types on the surface temperature changes. Correlations of T and TE with NDVI reveal that TE shows a stronger relationship to vegetation cover than T, especially during the growing season, with values that are significantly different and of opposite signs (−0.31 for Tvs NDVI; 0.49 for TEvs NDVI). Our results suggest that land cover types influence both moisture availability and temperature in the lower atmosphere and that TE is larger in areas with higher physical evaporation and transpiration rates. As a result, TE can be used as an additional metric for analysing near-surface heating trends with respect to land cover types. Moreover, TE can be tested as a complementary variable for assessing the impact of land surface and boundary layer processes in re-analysis and weather/climate model studies.

]]> Souleymane Fall et al. Impacts of land use land cover on temperature trends over the continental United States: assessment using the North American Regional Reanalysis http://docs.lib.purdue.edu/easpubs/109 http://docs.lib.purdue.edu/easpubs/109 Thu, 14 Mar 2013 14:31:36 PDT We investigate the sensitivity of surface temperature trends to land use land cover change (LULC) over the conterminous United States (CONUS) using the observation minus reanalysis (OMR) approach. We estimated the OMR trends for the 1979–2003 period from the US Historical Climate Network (USHCN), and the NCEP-NCAR North American Regional Reanalysis (NARR). We used a new mean square differences (MSDs)-based assessment for the comparisons between temperature anomalies from observations and interpolated reanalysis data. Trends of monthly mean temperature anomalies show a strong agreement, especially between adjusted USHCN and NARR (r = 0.9 on average) and demonstrate that NARR captures the climate variability at different time scales. OMR trend results suggest that, unlike findings from studies based on the global reanalysis (NCEP/NCAR reanalysis), NARR often has a larger warming trend than adjusted observations (on average, 0.28 and 0.27 °C/decade respectively).

OMR trends were found to be sensitive to land cover types. We analysed decadal OMR trends as a function of land types using the Advanced Very High Resolution Radiometer (AVHRR) and new National Land Cover Database (NLCD) 1992–2001 Retrofit Land Cover Change. The magnitude of OMR trends obtained from the NLDC is larger than the one derived from the ‘static’ AVHRR. Moreover, land use conversion often results in more warming than cooling.

Overall, our results confirm the robustness of the OMR method for detecting non-climatic changes at the station level, evaluating the impacts of adjustments performed on raw observations, and most importantly, providing a quantitative estimate of additional warming trends associated with LULC changes at local and regional scales. As most of the warming trends that we identify can be explained on the basis of LULC changes, we suggest that in addition to considering the greenhouse gases–driven radiative forcings, multi-decadal and longer climate models simulations must further include LULC changes.

]]> Souleymane Fall et al. Singular perturbation of polynomial potentials in the complex domain with applications to PT-symmetric families http://docs.lib.purdue.edu/easpubs/107 http://docs.lib.purdue.edu/easpubs/107 Thu, 14 Mar 2013 14:31:35 PDT In the first part of the paper, we discuss eigenvalue problems of the form -w"+Pw=Ew with complex potential P and zero boundary conditions at infinity on two rays in the complex plane. We give sufficient conditions for continuity of the spectrum when the leading coefficient of P tends to 0. In the second part, we apply these results to the study of topology and geometry of the real spectral loci of PT-symmetric families with P of degree 3 and 4, and prove several related results on the location of zeros of their eigenfunctions.

]]> Alexandre Eremenko et al. Biofuels and water quality: challenges and opportunities for simulation modeling http://docs.lib.purdue.edu/easpubs/105 http://docs.lib.purdue.edu/easpubs/105 Thu, 14 Mar 2013 14:31:34 PDT Quantification of the various impacts of biofuel feedstock production on hydrology and water qualityis complex. Mathematical models can be used to efficiently evaluate various what if scenarios related to biofeedstock production and their impacts on hydrology and water quality at various spatial and temporal scales. Currently available models, although having the potential to serve such purposes, have many limitations. In this paper, we review the strengths and weaknesses of such models in light of short- and long term biofeedstock production scenarios. The representation of processes in the currently available models and how these processes need to be modified to fully evaluate various complex biofeedstock production scenarios are discussed. Similarly, issues related to availability of data that are needed to parameterize and evaluate these models are presented. We have presented a vision for the development of decision support tools and ecosystem services that can be used to make watershed management decisions to minimize any potentially adverse environmental impacts while meeting biofeedstock demands. We also discuss a case study of biofeedstock impact simulation in relation to watershed management policy implications for various state and federal agencies in the USA.

]]> Bernard Engel et al. Tangencies between holomorphic maps and holomorphic laminations http://docs.lib.purdue.edu/easpubs/106 http://docs.lib.purdue.edu/easpubs/106 Thu, 14 Mar 2013 14:31:34 PDT Alexandre Eremenko et al. A framework for the incorporation of isotopes and isoscapes in geospatial forensic investigations http://docs.lib.purdue.edu/easpubs/104 http://docs.lib.purdue.edu/easpubs/104 Thu, 14 Mar 2013 14:31:33 PDT A field that will likely benefit from the developments of isoscapes is forensic sciences, where there is an interest in understanding where evidentiary material might have originated from. This chapter focuses on one small aspect of this large field through exploration of how analyses of hydrogen and oxygen isotopes in water and in human body tissues may be applied to forensic applications where spatially relevant information is required as part of an investigation. The applications of isocapes to forensic sciences are broad, including wildlife, food sourcing, and murder investigations. While the focus of this chapter is on hydrogen and oxygen isotopes, the analyses of heavy elements are an equally important component that can be scaled to include broad geo-spatial patterns.

]]> James R. Ehleringer et al. Quantifying rock uplift rates using channel steepness and cosmogenic nuclide-determined erosion rates: Examples from northern and southern Italy http://docs.lib.purdue.edu/easpubs/102 http://docs.lib.purdue.edu/easpubs/102 Thu, 14 Mar 2013 14:31:32 PDT Rock uplift rates can be difficult to measure over 103–105 yr time scales. If, however, a landscape approaches steady state, where hillslope erosion and rock uplift rates are steady and locally similar, then it should be possible to quantify rock uplift rates from hillslope erosion rates. Here, we test this prediction by comparing channel steepness index values and 10Be catchment-averaged erosion rates to well-constrained rock uplift rates in two landscapes in Italy. The first field area is the Romagna Apennines, northern Italy, where rock uplift rates are relatively uniform, between 0.2 and 0.5 mm/yr (regional mean 0.40 ± 0.15 [SE] mm/yr), and have been steady since 0.9 Ma. The second area is the region around northeastern Sicily and the southernmost Italian peninsula, where rock uplift rates are higher and exhibit a strong spatial gradient, from ∼0.7 to ∼1.6 mm/yr (regional mean 1.09 ± 0.13 [SE] mm/yr). In both regions, channel steepness indices and 10Be erosion rates vary directly with rock uplift rates. Although there is considerable variability in erosion rates, regionally averaged rates in both the northern (0.46 ± 0.04 [SE] mm/yr) and southern (1.21 ± 0.24 [SE] mm/yr) areas accurately measure rock uplift rates. Although channel steepness indices do not quantify rock uplift rates, they are useful for (1) identifying regional patterns of rock uplift, (2) identifying areas where uplift rates might be expected to be uniform, and (3) informing 10Be sampling strategies. This study demonstrates that, together, channel steepness and hillslope erosion rates can provide a powerful tool for determining rock uplift rates.

]]> Andrew J. Cyr et al. Impacts of land use change on climate http://docs.lib.purdue.edu/easpubs/103 http://docs.lib.purdue.edu/easpubs/103 Thu, 14 Mar 2013 14:31:32 PDT Paul A. Dirmeyer et al. Analysis of the hydrogen and oxygen stable isotope ratios of beverage waters without prior water extraction using isotope ratio infrared spectroscopy http://docs.lib.purdue.edu/easpubs/100 http://docs.lib.purdue.edu/easpubs/100 Thu, 14 Mar 2013 14:31:31 PDT Hydrogen (δ2H) and oxygen (δ18O) stable isotope analysis is useful when tracing the origin of water in beverages, but traditional analytical techniques are limited to pure or extracted waters. We measured the isotopic composition of extracted beverage water using both isotope ratio infrared spectroscopy (IRIS; specifically, wavelength-scanned cavity ring-down spectroscopy) and isotope ratio mass spectrometry (IRMS). We also analyzed beer, sodas, juices, and milk ‘as is’ using IRIS. For IRIS analysis, four sequential injections of each sample were measured and data were corrected for sample-to-sample memory using injections (a) 1-4, (b) 2-4, and (c) 3-4. The variation between δ2H and δ18O values calculated using the three correction methods was larger for unextracted (i.e., complex) beverages than for waters. The memory correction was smallest when using injections 3-4. Beverage water δ2H and δ18O values generally fit the Global Meteoric Water Line, with the exception of water from fruit juices. The beverage water stable isotope ratios measured using IRIS agreed well with the IRMS data and fit 1:1 lines, with the exception of sodas and juices (δ2H values) and beers (δ18O values). The δ2H and δ18O values of waters extracted from beer, soda, juice, and milk were correlated with complex beverage δ2H and δ18O values (r = 0.998 and 0.997, respectively) and generally fit 1:1 lines. We conclude that it is possible to analyze complex beverages, without water extraction, using IRIS although caution is needed when analyzing beverages containing sugars, which can clog the syringe and increase memory, or alcohol, a known spectral interference. Copyright © 2010 John Wiley & Sons, Ltd.

]]> Lesley A. Chesson et al. Sensitivity and identifiability of stream flow generation parameters of the SWAT model http://docs.lib.purdue.edu/easpubs/101 http://docs.lib.purdue.edu/easpubs/101 Thu, 14 Mar 2013 14:31:31 PDT Implementation of sensitivity analysis (SA) procedures is helpful in calibration of models and also for their transposition to different watersheds. The reported studies on SA of Soil and Water Assessment Tool (SWAT) model were mostly focused on identifying parameters for pruning or modifying during the calibration process. This paper presents a sensitivity and identifiability analysis of model parameters that influence stream flow generation in SWAT. The analysis was focused on evaluating the sensitivity of the parameters in different climatic settings, temporal scales and flow regimes. The global sensitivity analysis (GSA) technique based on classical decomposition of variance, Sobol', was employed in this study. The results of the study indicate that modeled stream flow show varying sensitivity to parameters in different climatic settings. The results also suggest that the identifiability of a parameter for a given watershed is a major concern in calibrating the model for the specific watershed, as it might lead to equifinality of parameters. The SWAT model parameters show varying sensitivity in different years of simulation suggesting the requirement for dynamic updation of parameters during the simulation. The sensitivity of parameters during various flow regimes (low, medium and high flow) is also found to be uneven, which suggests the significance of a multi-criteria approach for the calibration of models.

]]> R. Cibin et al. Transpressional rupture of an unmapped fault during the 2010 Haiti earthquake http://docs.lib.purdue.edu/easpubs/99 http://docs.lib.purdue.edu/easpubs/99 Thu, 14 Mar 2013 14:31:30 PDT On 12 January 2010, a Mw 7.0 earthquake struck the Port-au-Prince region of Haiti. The disaster killed more than 200,000 people and caused an estimated $8 billion in damages, about 100% of the country’s gross domestic product1. The earthquake was initially thought to have ruptured the Enriquillo–Plantain Garden fault of the southern peninsula of Haiti, which is one of two main strike-slip faults inferred to accommodate the 2 cm yr−1relative motion between the Caribbean and North American plates2, 3. Here we use global positioning system and radar interferometry measurements of ground motion to show that the earthquake involved a combination of horizontal and contractional slip, causing transpressional motion. This result is consistent with the long-term pattern of strain accumulation in Hispaniola. The unexpected contractional deformation caused by the earthquake and by the pattern of strain accumulation indicates present activity on faults other than the Enriquillo–Plantain Garden fault. We show that the earthquake instead ruptured an unmapped north-dipping fault, called the Léogâne fault. The Léogâne fault lies subparallel to—but is different from—the Enriquillo–Plantain Garden fault. We suggest that the 2010 earthquake may have activated the southernmost front of the Haitian fold-and-thrust belt4 as it abuts against the Enriquillo–Plantain Garden fault. As the Enriquillo–Plantain Garden fault did not release any significant accumulated elastic strain, it remains a significant seismic threat for Haiti and for Port-au-Prince in particular.

]]> Eric Calais et al. Refining oxygen isotope analysis in the Nasca region of Peru: An investigation of water sources and archaeological samples http://docs.lib.purdue.edu/easpubs/98 http://docs.lib.purdue.edu/easpubs/98 Thu, 14 Mar 2013 14:31:29 PDT The development of complex societies, irrigation agriculture and sociopolitical transitions are of interest to researchers working in the Nasca region on the south coast of Peru. Occupied for thousands of years, many questions regarding the circumstances of these changes in the area are being investigated. Oxygen isotope analysis provides a method for exploring residential mobility of past peoples during these transitions. This study presents new δ18O data from water sources that would have been used by the ancient inhabitants, providing important information regarding the oxygen isotope variability in the region and the necessary baseline data for migration studies in this region. Our results suggest that the isotopic composition of water sources in the Nasca region is not highly variable. In addition, archaeological human tooth enamel samples from the sites of La Tiza and Pajonal Alto are analysed. The δ18Oc results of the human enamel samples confirm the local nature of the burial population, as suggested by previous strontium isotope analysis (87Sr/86Sr).

]]> M. R. Buzon et al. Isoscapes to address large-scale Earth science challenges http://docs.lib.purdue.edu/easpubs/97 http://docs.lib.purdue.edu/easpubs/97 Thu, 14 Mar 2013 14:31:29 PDT Sugar cane cropping for biofuel production reduces water discharge from a northern Indian basin and threatens downstream communities. Regulators want to partition blame between climate change—induced declines in mountain snowpack and excessive evaporation from poorly managed fields. In the same basin, a tiger is found shot. Is it the nuisance animal that has been tormenting local communities, or is it a different animal poached from the upland forests?

]]> Gabriel J. Bowen et al. Statistical and geostatistical mapping of precipitation water isotope ratios http://docs.lib.purdue.edu/easpubs/96 http://docs.lib.purdue.edu/easpubs/96 Thu, 14 Mar 2013 14:31:28 PDT More than 5 decades of monitoring has documented wide and systematic variation in the stable isotopic composition of precipitation across the globe. This variation is controlled by climatological processes that govern the source, transport and precipitation of atmospheric moisture. Given the ordered and spatially continuous nature of these processes, variation in precipitation isotopic composition represents a near-ideal system for spatial analysis using geostatistical methods. Spatial analysis of precipitation isotopic composition has a long history, and a wide range of methodologies have been applied to the problem of mapping and predicting isotopic compositions at scales ranging from 102 to 104 km. These range from basic space-only interpolation approaches to more quantitative regression and coupled geostatistical/regression techniques, each with particular benefits and drawbacks. Within the last decade, improved methods for generating quantitative predictions of precipitation isotope ratio distributions and the widespread dissemination of precipitation isoscapes via the world wide web have help spur the development of numerous applications of these data products in climatology, hydrology, ecology, and forensics. Current and future research emphasis on continued improvements in water isotope ratio monitoring and novel isoscapes model parameterizations should help lead to the development of dynamic precipitation isoscapes, incorporating both spatial and temporal variation, and enable new research and applications.

]]> Gabriel J. Bowen et al. Sources of Terrestrial Organic Carbon in the Mississippi Plume Region: Evidence for the Importance of Coastal Marsh Inputs http://docs.lib.purdue.edu/easpubs/95 http://docs.lib.purdue.edu/easpubs/95 Thu, 14 Mar 2013 14:31:27 PDT High sedimentation rates along river-dominated margins make these systems important repositories for organic carbon derived from both allochthonous and autochthonous sources. Using elemental carbon/nitrogen ratios, molecular biomarker (lignin phenol), and stable carbon isotopic (bulk and compound-specific) analyses, this study examined the sources of organic carbon to the Louisiana shelf within one of the primary dispersive pathways of the Mississippi River. Surface sediment samples were collected from stations across the inner, mid, and outer Louisiana shelf, within the Mississippi River plume region, during two cruises in the spring and fall of 2000. Lignin biomarker data showed spatial patterns in terrestrial source plant materials within the river plume, such that sediments near the mouth of the Mississippi River were comparatively less degraded and richer in C 4 plant carbon than those found at mid-depth regions of the shelf. A molecular and stable isotope-based mixing model defining riverine, marsh, and marine organic carbon suggested that the highest organic carbon inputs to the shelf in spring were from marine sources (55–61% marine organic carbon), while riverine organic carbon was the highest (63%) in fall, likely due to lower inputs of marine organic carbon at this time compared with the spring season. This model also indicated that marsh inputs, ranging from 19 to 34% and 3–15% of the organic carbon in spring and fall, respectively, were significantly more important sources of organic carbon on the inner Louisiana shelf than previously suggested. Finally, we propose that the decomposition of terrestrial-derived organic carbon (from the river and local wetlands sources) in mobile muds may serve as a largely unexplored additional source of oxygen-consuming organic carbon in hypoxic bottom waters of the Louisiana shelf.

]]> Thomas S. Bianchi et al. Spectroscopy of sulfates, clays, and iron oxides in the Jurassic Navajo Sandstone http://docs.lib.purdue.edu/easpubs/94 http://docs.lib.purdue.edu/easpubs/94 Thu, 14 Mar 2013 14:31:27 PDT Analysis of the history of fluid flow and diagenesis in sandstone deposits can potentially furnish insight into how these deposits function as reservoirs. Imaging spectroscopy provides a way to examine surface mineralogy in order to better understand how this mineralogy might have resulted from past fluid flow and diagenesis. Aerially-acquired spectral data, along with spectral data from field samples, are used to help map the mineralogy of a site located within the Jurassic Navajo Sandstone in southern Utah. This site, “Mollies Nipple”, is unusual as it is a butte containing jarosite; an atypical mineral for this area. Mapping the butte's mineralogy in conjunction with its morphology may help provide additional knowledge as to the geologic history of this area. In addition, the presence of hematite concretions as well as the mineral jarosite may potentially make this butte a terrestrial analog for sediments on Mars.

]]> Julianne Bell et al. Simulation of the Middle Miocene climate optimum: implications for future climate http://docs.lib.purdue.edu/easpubs/92 http://docs.lib.purdue.edu/easpubs/92 Thu, 14 Mar 2013 14:31:26 PDT Proxy data constraining land and ocean surface paleo-temperatures indicate that the Middle Miocene Climate Optimum (MMCO), a global warming event at ∼15 Ma, had a global annual mean surface temperature of 18.4°C, about 3°C higher than present and equivalent to the warming predicted for the next century. We apply the latest National Center for Atmospheric Research (NCAR) Community Atmosphere Model CAM3.1 and Land Model CLM3.0 coupled to a slab ocean to examine sensitivity of MMCO climate to varying ocean heat fluxes derived from paleo sea surface temperatures (SSTs) and atmospheric carbon dioxide concentrations, using detailed reconstructions of Middle Miocene boundary conditions including paleogeography, elevation, vegetation and surface temperatures. Our model suggests that to maintain MMCO warmth consistent with proxy data, the required atmospheric CO2 concentration is about 460–580 ppmv, narrowed from the most recent estimate of 300–600 ppmv.

]]> Y. You et al. Global methane emissions from wetlands, rice paddies, and lakes http://docs.lib.purdue.edu/easpubs/93 http://docs.lib.purdue.edu/easpubs/93 Thu, 14 Mar 2013 14:31:26 PDT The current concentration of atmospheric methane is 1774±1.8 parts per billion, and it accounts for 18% of total greenhouse gas radiative forcing [Forster et al., 2007]. Atmospheric methane is 22 times more effective, on a per-unit-mass basis, than carbon dioxide in absorbing long-wave radiation on a 100-year time horizon, and it plays an important role in atmospheric ozone chemistry (e.g., in the presence of nitrous oxides, tropospheric methane oxidation will lead to the formation of ozone). Wetlands are a large source of atmospheric methane, Arctic lakes have recently been recognized as a major source [e.g., Walter et al., 2006], and anthropogenic activities—such as rice agriculture—also make a considerable contribution.

]]> Qianlai Zhuang et al. Changes of urban wetlands in Wuhan, China, from 1987 to 2005 http://docs.lib.purdue.edu/easpubs/91 http://docs.lib.purdue.edu/easpubs/91 Thu, 14 Mar 2013 14:31:25 PDT Urban wetlands play a significant role in the sustainable development of the urban eco-environment. However, accelerated urbanization has caused rapid changes in urban wetland landscape patterns, which may seriously affect their functions. Based on land-use maps, TM images, and field data from the Wuhan wetlands, the spatiotemporal evolution and wetland landscape pattern were quantitatively analyzed, with reference to landscape ecology indices of diversity, fragmentation, dominance, shape, and dimension. The results showed that: (1) the natural wetland area decreased: lakewetlands andmarshwetlands decreased by 18.71% and 50.3% from1987 to 2005, respectively; (2) artificial wetland area increased by 47.75% in Wuhan over the same period; (3) the lake wetland area ofWuhan declined due to the conversion of large lakes tosmaller ones; (4) the value of the diversity index (H), evenness index (E), and fragmentation index (F) decreased,while the value of the dominance index (D) increased from1987 to 2005; (5) the landscape shape index (LSI) and fractal dimension (FD) of the river wetlands, lake wetlands, bottomland wetlands, and marsh wetlands decreased, while the LSI and FD of the reservoir and pond wetlands increased from1987 to 2005; and (6) natural, societal, and economic, as well as human, activities are major factors for the structural changes in the Wuhan wetland landscape, as revealed by canonical correlation analysis.Results suggest that the ecological environment of urban wetlands should be protected to maximize the services of urban wetland ecosystems in Wuhan, China. [ABSTRACT FROM AUTHOR]

]]> Kai Xu et al. Twentieth-century droughts and their impacts on terrestrial carbon cycling in China http://docs.lib.purdue.edu/easpubs/90 http://docs.lib.purdue.edu/easpubs/90 Thu, 14 Mar 2013 14:31:24 PDT Midlatitude regions experienced frequent droughts during the twentieth century, but their impacts on terrestrial carbon balance are unclear. This paper presents a century-scale study of drought effects on the carbon balance of terrestrial ecosystems in China. The authors first characterized the severe extended droughts over the period 1901–2002 using the Palmer drought severity index and then examined how these droughts affected the terrestrial carbon dynamics using tree-ring width chronologies and a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM). It is found that China suffered from a series of severe extended droughts during the twentieth century. The major drought periods included 1920–30, 1939–47, 1956–58, 1960–63, 1965–68, 1978–80, and 1999–2002. Most droughts generally reduced net primary productivity (NPP) and net ecosystem productivity (NEP) in large parts of drought-affected areas. Moreover, some of the droughts substantially reduced the countrywide annual NPP and NEP. Out of the seven droughts, three (1920–30, 1965–68, and 1978–80) caused the countrywide terrestrial ecosystems to switch from a carbon sink to a source, and one (1960–63) substantially reduced the magnitude of the countrywide terrestrial carbon sink. Strong decreases in NPP were mainly responsible for the anomalies in annual NEP during these drought periods. Changes in heterotrophic respiration happened in the same direction, but mostly with smaller magnitude. The results show that severe extended droughts had significant effects on terrestrial carbon cycling in China, although future studies should consider other important processes such as drought-induced mortality and regrowth, land-use change, disturbances (e.g., fire), human management (e.g., fertilization and irrigation), and environmental pollution (e.g., ozone pollution, nitrogen deposition). These drought effects are of particular importance in light of projected widespread summer drying in midlatitude regions during the twenty-first century. Future droughts could lead to a reduced terrestrial carbon sink or even a source and exert a positive feedback to the global climate system.

]]> Jingfeng Xiao et al. Orbitally forced climate changes in the Tasman sector during the Middle Eocene http://docs.lib.purdue.edu/easpubs/88 http://docs.lib.purdue.edu/easpubs/88 Thu, 14 Mar 2013 14:31:23 PDT The influence of orbital precession on early Paleogene climate and ocean circulation patterns in the southeast Pacific region is investigated by combining environmental analyses of cyclic Middle Eocene sediments and palynomorph records recovered from ODP Hole 1172A on the East Tasman Plateau with climate model simulations. Integration of results indicates that in the marine realm, direct effects of precessional forcing are not pronounced, although increased precipitation/runoff could have enhanced dinoflagellate cyst production. On the southeast Australian continent, the most pronounced effects of precessional forcing were fluctuations in summer precipitation and temperature on the Antarctic Margin. These fluctuations resulted in vegetational changes, most notably in the distribution of Nothofagus (subgenus Brassospora). The climate model results suggest significant fluctuations in sea ice in the Ross Sea, notably during Austral summers. This is consistent with the influx of Antarctic heterotrophic dinoflagellates in the early part of the studied record. The data demonstrate a strong precessionally driven climate variability and thus support the concept that precessional forcing could have played a role in early Antarctic glaciation via changes in runoff and/or precipitation.

]]> Jeroen Warnaar et al. Global warming, convective threshold and false thermostats http://docs.lib.purdue.edu/easpubs/89 http://docs.lib.purdue.edu/easpubs/89 Thu, 14 Mar 2013 14:31:23 PDT We demonstrate a theoretically expected behavior of the tropical sea surface temperature probability density function (PDF) in future and past (Eocene) greenhouse climate simulations. To first order this consists of a shift to warmer temperatures as climate warms, without change of shape of the PDF. The behavior is tied to a shift of the temperature for deep convection onset. Consequently, the threshold for appearance of high clouds and associated radiative forcing shifts along with temperature. An excess entropy coordinate provides a reference to which the onset of deep convection is invariant, and gives a compact description of SST changes and cloud feedbacks suitable for diagnostics and as a basis for simplified climate models. The results underscore that the typically skewed appearance of tropical SST histograms, with a sharp drop-off above some threshold value, should not be taken as evidence for tropical thermostats.

]]> Ian N. Williams et al. Regional climate of hazardous convective weather through high-resolution dynamical downscaling http://docs.lib.purdue.edu/easpubs/87 http://docs.lib.purdue.edu/easpubs/87 Thu, 14 Mar 2013 14:31:22 PDT We explore the use of high-resolution dynamical downscaling as a means to simulate the regional climatology and variability of hazardous convective-scale weather. Our basic approach differs from a traditional regional climate model application in that it involves a sequence of daily integrations. We use the weather research and forecasting (WRF) model, with global reanalysis data as initial and boundary conditions. Horizontal grid lengths of 4.25 km allow for explicit representation of deep convective storms and hence a compilation of their occurrence statistics over a large portion of the conterminous United States. The resultant 10-year sequence of WRF model integrations yields precipitation that, despite its positive bias, has a diurnal cycle consistent with observations, and otherwise has a realistic geographical distribution. Similarly, the occurrence frequency of short-duration, potentially flooding rainfall compares well to analyses of hourly rain gauge data. Finally, the climatological distribution of hazardous-thunderstorm occurrence is shown to be represented with some degree of skill through a model proxy that relates rotating convective updraft cores to the presence of hail, damaging surface winds, and tornadoes. The results suggest that the proxy occurrences, when coupled with information on the larger-scale atmosphere, could provide guidance on the reliability of trends in the observed occurrences. [ABSTRACT FROM AUTHOR]

]]> Robert J. Trapp et al. Modeling soil thermal and hydrological dynamics and changes of growing season in Alaskan terrestrial ecosystems http://docs.lib.purdue.edu/easpubs/85 http://docs.lib.purdue.edu/easpubs/85 Thu, 14 Mar 2013 14:31:21 PDT Abundant evidence indicates the growing season has been changed in the Alaskan terrestrial ecosystems in the last century as climate warms. Reasonable simulations of growing season length, onset, and ending are critical to a better understanding of carbon dynamics in these ecosystems. Recent ecosystem modeling studies have been slow to consider the interactive effects of soil thermal and hydrological dynamics on growing season changes in northern high latitudes. Here, we develop a coupled framework to model these dynamics and their effects on plant growing season at a daily time step. In this framework, we (1) incorporate a daily time step snow model into our existing hydrological and soil thermal models and (2) explicitly model the moisture effects on soil thermal conductivity and heat capacity and the effects of active layer depth and soil temperature on hydrological dynamics. The new framework is able to well simulate snow depth and soil temperature profiles for both boreal forest and tundra ecosystems at the site level. The framework is then applied to Alaskan boreal forest and tundra ecosystems for the period 1923-2099. Regional simulations show that (1) for the historical period, the growing season length, onset, and ending, estimated based on the mean soil temperature of the top 20 cm soils, and the annual cycle of snow dynamics, agree well with estimates based on satellite data and other approaches and (2) for the projected period, the plant growing season length shows an increasing trend in both tundra and boreal forest ecosystems. In response to the projected warming, by year 2099, (1) the snow-free days will be increased by 41.0 and 27.5 days, respectively, in boreal forest and tundra ecosystems and (2) the growing season lengths will be more than 28 and 13 days longer in boreal forest and tundra ecosystems, respectively, compared to 2010. Comparing two sets of simulations with and without considering feedbacks between soil thermal and hydrological dynamics, our analyses suggest coupling hydrological and soil thermal dynamics in Alaskan terrestrial ecosystems is important to model ecosystem dynamics, including growing season changes.

]]> Jinyun Tang et al. Stable isotope analysis of modern human hair collected from Asia (China, India, Mongolia, and Pakistan) http://docs.lib.purdue.edu/easpubs/86 http://docs.lib.purdue.edu/easpubs/86 Thu, 14 Mar 2013 14:31:21 PDT We report isotopic data (δ2H, δ18O n = 196; δ13C, δ15N n = 142; δ34S n = 85) from human hair and drinking water (δ2H, δ18O n = 67) collected across China, India, Mongolia, and Pakistan. Hair isotope ratios reflected the large environmental isotopic gradients and dietary differences. Geographic information was recorded in H and O and to a lesser extent, S isotopes. H and O data were entered into a recently developed model describing the relationship between the H and O isotope composition of human hair and drinking water in modern USA and pre-globalized populations. This has anthropological and forensic applications including reconstructing environment and diet in modern and ancient human hair. However, it has not been applied to a modern population outside of the USA, where we expect different diet. Relationships between H and O isotope ratios in drinking water and hair of modern human populations in Asia were different to both modern USA and pre-globalized populations. However, the Asian dataset was closer to the modern USA than to pre-globalized populations. Model parameters suggested slightly higher consumption of locally producedfoods in our sampled population than modern USA residents, but lower than pre-globalized populations. The degree of in vivo amino acid synthesis was comparable to both the modern USA and pre-globalized populations. C isotope ratios reflected the predominantly C3-based regional agriculture and C4 consumption in northernChina. C, N, and S isotope ratios supported marine food consumption in some coastal locales. N isotope ratios suggested a relatively low consumption of animal-derived products compared to western populations. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc.

]]> A. H. Thompson et al. Instability in Leapfrog and Forward-Backward Schemes, Part II-Numerical Simulations of Dam Break http://docs.lib.purdue.edu/easpubs/84 http://docs.lib.purdue.edu/easpubs/84 Thu, 14 Mar 2013 14:31:20 PDT Following Sun’s approach [17], Shuman smoothing instead of conventional diffusion terms is used in a simple two-time step semi-implicit finite volume scheme to simulate dam break. When the Courant number is less than one, the absolute value of amplification factor of the 1D linearized shallow-water equations is 1 in this new scheme. Compared with the characteristic-based semi-Lagrangian schemes and the Riemann solver, this scheme produces excellent results of free water depth and speed of the shock. Numerical simulations show that the water inside the dam initially moves away radially until water almost depletes near the center; then the water moves back to the center and forms a vertical water column there. This paper proves that Shuman smoothing can be used not only in the linearized shallow-water equations discussed in Sun [17] but also in the nonlinear wave equations to control instability around shocks.

]]> Wen Yih Sun Instability in Leapfrog and Forward-Backward Schemes http://docs.lib.purdue.edu/easpubs/83 http://docs.lib.purdue.edu/easpubs/83 Thu, 14 Mar 2013 14:31:19 PDT This paper shows that in the linearized shallow-water equations, the numerical schemes can become weakly unstable for the 2Δx wave in the C grid when the Courant number is 1 in the forward–backward scheme and 0.5 in the leapfrog scheme because of the repeated eigenvalues in the matrices. The instability can be amplified and spread to other waves and smaller Courant number if the diffusion term is included. However, Shuman smoothing can control the instability.

]]> Wen Yih Sun Modeled sensitivity of upper thermocline properties to tropical cyclone winds and possible feedbacks on the Hadley circulation http://docs.lib.purdue.edu/easpubs/81 http://docs.lib.purdue.edu/easpubs/81 Thu, 14 Mar 2013 14:31:18 PDT The sensitivity of upper thermocline properties, and global climate, to tropical cyclone (TC) winds is examined using global ocean and atmosphere general circulation models. We combine seven years of global, satellite-based TC wind records with a standard surface wind input data set derived from reanalysis, and we apply idealized factors to TC winds in order to model the ocean's equilibrium response to increases in TC intensities. We find TC-induced vertical ocean mixing impacts upper thermocline properties, such as temperature and mixed layer depth, and the effects are amplified for increasing intensities. The model's ocean heat transport is also affected, but only when TC winds are increased substantially compared to present-day values. Atmospheric model simulations show altered ocean temperature can lead to changes in the mean Hadley circulation. Results suggest increased TC activity may affect global climate by altering the ocean's thermal structure, which could be important for large scale ocean-atmosphere feedbacks.

]]> Ryan L. Sriver et al. Application of a pseudo simulator to evaluate the sensitivity of parameters in complex watershed models http://docs.lib.purdue.edu/easpubs/82 http://docs.lib.purdue.edu/easpubs/82 Thu, 14 Mar 2013 14:31:18 PDT In this paper, the issue of nonlinear sensitivity analysis for dimensionality reduction in hydrologic model calibration is discussed, and a novel method to quantify the sensitivity of each parameter that considers the nonlinear relationship in the model is presented. The method is based on computing the absolute variation of the nonlinear function represented by the model in its parameter space. The paper discusses the theoretical background of the method and presents the algorithm. The algorithm employs neural network as a pseudo simulator to reduce the computational burden of the analysis. The proposed approach of sensitivity analysis is illustrated through a case study on a physically based distributed hydrologic model. The results indicate that the method is able to rank the parameters effectively, and the ranking can be interpreted in the context of the physical processes being considered by the model.

]]> K. P. Sudheer et al. Modeling the influence of a reduced equator-to-pole sea surface temperature gradient on the distribution of water isotopes in the Early/Middle Eocene http://docs.lib.purdue.edu/easpubs/80 http://docs.lib.purdue.edu/easpubs/80 Thu, 14 Mar 2013 14:31:17 PDT Proxy-based climate reconstructions suggest the existence of a strongly reduced equator-to-pole temperature gradient during the Azolla interval in the Early/Middle Eocene, compared to modern. Changes in the hydrological cycle, as a consequence of a reduced temperature gradient, are expected to be reflected in the isotopic composition of precipitation (δD, δ18O). The interpretation of water isotopic records to quantitatively reconstruct past precipitation patterns is, however, hampered by a lack of detailed information on changes in their spatial and temporal distribution. Using the isotope-enabled version of the National Center for Atmospheric Research (NCAR) atmospheric general circulation model, Community Atmosphere Model v.3 (isoCAM3), relationships between water isotopes and past climates can be simulated. Here we examine the influence of an imposed reduced meridional sea surface temperature gradient on the spatial distribution of precipitation and its isotopic composition in an Early/Middle Eocene setting. As a result of the applied forcings, the Eocene simulation predicts the occurrence of less depleted high latitude precipitation, with δD values ranging only between 0 and −140‰ (compared to Present-day 0 to −300‰). Comparison with Early/Middle Eocene-age isotopic proxy data shows that the simulation accurately captures the main features of the spatial distribution of the isotopic composition of Early/Middle Eocene precipitation over land in conjunction with the aspects of the modeled Early/Middle Eocene climate. Hence, the included stable isotope module quantitatively supports the existence of a reduced meridional temperature gradient during this interval.

]]> Eveline N. Speelman et al. Students’ conceptions about the greenhouse effect, global warming, and climate change http://docs.lib.purdue.edu/easpubs/78 http://docs.lib.purdue.edu/easpubs/78 Thu, 14 Mar 2013 14:31:16 PDT The purpose of this study was to investigate students' conceptions of the greenhouse effect, global warming, and climate change. The study was descriptive in nature and reflected a cross-age design involving the collection of qualitative data from 51 secondary students from three different schools in the Midwest, USA. These data were analyzed for content in an inductive manner to identify student's conceptions. The categories that emerged from the students' responses reflected different degrees of sophistication of students' conceptions about the greenhouse effect, global warming, and climate change. Based on these findings we make curricular recommendations that build on the students' conceptions, the IPCC Findings, the NRC (1996) science education standards, and NOAA's climate literacy framework.

]]> Daniel P. Shepardson et al. An adaptability limit to climate change due to heat stress http://docs.lib.purdue.edu/easpubs/79 http://docs.lib.purdue.edu/easpubs/79 Thu, 14 Mar 2013 14:31:16 PDT Despite the uncertainty in future climate-change impacts, it is often assumed that humans would be able to adapt to any possible warming. Here we argue that heat stress imposes a robust upper limit to such adaptation. Peak heat stress, quantified by the wet-bulb temperature TW, is surprisingly similar across diverse climates today. TW never exceeds 31 °C. Any exceedence of 35 °C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7 °C, calling the habitability of some regions into question. With 11–12 °C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12 °C are possible from fossil fuel burning. One implication is that recent estimates of the costs of unmitigated climate change are too low unless the range of possible warming can somehow be narrowed. Heat stress also may help explain trends in the mammalian fossil record.

]]> Steven C. Sherwood et al. Seventh grade students' mental models of the greenhouse effect http://docs.lib.purdue.edu/easpubs/77 http://docs.lib.purdue.edu/easpubs/77 Thu, 14 Mar 2013 14:31:15 PDT This constructivist study investigates 225 student drawings and explanations from three different schools in the midwest in the US, to identify seventh grade students' mental models of the greenhouse effect. Five distinct mental models were derived from an inductive analysis of the content of the students' drawings and explanations: Model 1, a 'greenhouse' for growing plants; Model 2, greenhouse gases cause ozone depletion or formation, causing the Earth to warm; Model 3, greenhouse gases, but no heating mechanism, simply gases in the atmosphere; Model 4, greenhouse gases 'trap' the sun's rays, heating the Earth; and Model 5, the sun's rays are 'bounced' or reflected back and forth between the Earth's surface and greenhouse gases, heating the Earth. Science textbooks are critiqued in light of the students' mental models and curricular and instructional implications are explored. [ABSTRACT FROM AUTHOR]

]]> Daniel P. Shepardson et al. Ambiguous Hydraulic Heads and 14C Activities in Transient Regional Flow http://docs.lib.purdue.edu/easpubs/76 http://docs.lib.purdue.edu/easpubs/76 Thu, 14 Mar 2013 14:31:14 PDT A regional flow and transport model is used to explore the implications of significant variability in Pleistocene and Holocene climates on hydraulic heads and 14C activity. Simulations involve a 39 km slice of the Death Valley Flow System through Yucca Mountain toward the Amargosa Desert. The long-time scale over which infiltration has changed (tens-of-thousands of years) is matched by the large physical extent of the flow system (many tens-of-kilometers). Estimated paleo-infiltration rates were estimated using a juniper pollen percentage that extends from the last interglacial (LIG) period (approximately 120 kyrbp) to present. Flow and 14C transport simulations show that groundwater flow changes markedly as a function of paleoclimate. At the last glacial maximum (LGM, 21 kyrbp), the recharge to the flow system was about an order-of-magnitude higher than present, and water table was more than 100 m higher. With large basin time constants, flow is complicated because hydraulic heads at a given location reflect conditions of the past, but at another location the flow may reflect present conditions. This complexity is also manifested by processes that depend on flow, for example 14C transport. Without a model that accounts for the historical transients in recharge for at least the last 20,000 years, there is no simple way to deconvolve the 14C dates to explain patterns of flow.

]]> Franklin W. Schwartz et al. The minor importance of giant aerosol to precipitation development within small trade wind cumuli observed during RICO http://docs.lib.purdue.edu/easpubs/74 http://docs.lib.purdue.edu/easpubs/74 Thu, 14 Mar 2013 14:31:13 PDT The present study examines the importance of giant aerosol to precipitation development in marine trade wind cumuli with a new analysis method of a new extensive dataset collected during the Rain in Cumulus over the Ocean (RICO) field campaign. Giant aerosol particles were quantified from clear-air aircraft data, and the precipitation development in the clouds was tracked with dual-polarization radar data. For six different days and multiple clouds on each day, the evolution of the maximum reflectivity, and its associated differential reflectivity, was analyzed. These data were compared with the results of microphysical calculations run within an adiabatic parcel model initialized with the environmental conditions and giant aerosol concentrations on each day of interest. Despite all clouds having formed in a similar maritime environment, this study found substantial variability in the radar echo development both in clouds observed during the same day, and across other days. The maximum reflectivity attained by the clouds appeared to be largely a function of their depth. The radar echo evolution could be represented fairly well by the microphysical parcel model initialized with the observed giant aerosol in some cases but not others. The importance of the giant aerosol to precipitation formation in the small trade wind cumuli appears to be minor: the early radar echoes appear to be more consistent with the development of precipitation by collision and coalescence among droplets formed on the more numerous and smaller cloud condensation nuclei, although the number of giant aerosol appears to have some effect on the actual radar reflectivity values.

]]> C. H. Reiche et al. White-rot basidiomycete-mediated decomposition of C60 fullerol http://docs.lib.purdue.edu/easpubs/75 http://docs.lib.purdue.edu/easpubs/75 Thu, 14 Mar 2013 14:31:13 PDT Industrially produced carbon-based nanomaterials (CNM), including fullerenes and nanotubes, will be introduced into the environment in increasing amounts in the next decades. One likely environmental chemical transformation of C60 is oxidation to C60 fullerol through both abiotic- and biotic-mediated means. Unfortunately, knowledge of the environmental fate of oxidized CNM is lacking. This study used bulk and compound-specific 13C stable isotope ratio mass spectrometry techniques and spectroradiometry analysis to examine the ability of two white rot basidiomycete fungi (Phlebia tremellosa and Trametes versicolor) to metabolize and degrade an oxygenated CNM, C60 fullerol. After 32 weeks of decay, both fungi were able to bleach and oxidize fullerol to CO2. Additionally, the fungi incorporated minor amounts of the fullerol carbon into lipid biomass. These findings are significant in that they represent the first report of direct biodegradation and utilization of any fullerene derivative and provide valuable information about the possible environmental fates of other CNM.

]]> Kathryn M. Schreiner et al. Roles of atmospheric and land surface data in dynamic regional downscaling http://docs.lib.purdue.edu/easpubs/73 http://docs.lib.purdue.edu/easpubs/73 Thu, 14 Mar 2013 14:31:12 PDT In studies dealing with the impact of land use changes on atmospheric processes, a key methodological step is the validation of simulated current conditions. However, regions lacking detailed atmospheric and land use data provide limited information with which to accurately generate control simulations. In this situation, the difference between baseline control simulations and different land use change simulations can be quite different owing to the quality of the atmospheric and land use data sets. Using multiple simulations at the Monteverde cloud forest region of Costa Rica as an example, we show that when a regional climate model is used to study the effect of land use change, it can produce distinctly different results at regional scales, depending on the amount of data available to run the climate simulations. We show that for the specific case of land use change impact studies, the simulation results are very sensitive to the prescribed atmospheric information (e.g., lateral boundary conditions) compared to the land use (surface boundary) information.

]]> Deepak K. Ray et al. Magnetostratigraphic correlation of the Oxfordian-Kimmeridgian boundary http://docs.lib.purdue.edu/easpubs/71 http://docs.lib.purdue.edu/easpubs/71 Thu, 14 Mar 2013 14:31:11 PDT A magnetic polarity pattern for Boreal and Sub-Boreal ammonite zones of the Upper Oxfordian to Lower Kimmeridgian was established and confirmed in four British sections, including the proposed Global Boundary Stratotype Section and Point (GSSP) on the Isle of Skye (Scotland) to define the base of the international Kimmeridgian Stage. A coeval pattern for Sub-Mediterranean ammonite zones was compiled from seven sections in Poland, one German section and multi-section composites from France and Spain. The mean paleopole for the European Craton (excluding Spain) at the Oxfordian–Kimmeridgian boundary is 74.2°N, 181.3°E (Α95 = 3.8°). The common magnetic polarity scale enables inter-correlation of ammonite subzones among these three faunal provinces and to the marine magnetic-anomaly M-Sequence. The proposed GSSP at the base of the Pictonia baylei Zone is near the base of an extended interval dominated by reversed polarity, which is interpreted to be Chron M26r. This GSSP level projects to the lower to middle part of the Epipeltoceras bimammatum Subzone, which is the middle subzone of this E. bimammatum Zone in the Sub-Mediterranean standard zonation. In contrast, the traditional placement of the Oxfordian–Kimmeridgian boundary in that Sub-Mediterranean standard zonation (base of Sutneria platynota Zone) is at the base of Chron M25r, or nearly 1 million years younger.

]]> Piotr A. Przybylski et al. The Concordiasi Project in Antarctica http://docs.lib.purdue.edu/easpubs/72 http://docs.lib.purdue.edu/easpubs/72 Thu, 14 Mar 2013 14:31:11 PDT The Concordiasi project is making innovative observations of the atmosphere above Antarctica. The most important goals of the Concordiasi are as follows: 1. To enhance the accuracy of weather prediction and climate records in Antarctica through the assimilation of in situ and satellite data, with an emphasis on data provided by hyperspectral infrared sounders. The focus is on clouds, precipitation, and the mass budget of the ice sheets. The improvements in dynamical model analyses and forecasts will be used in chemical-transport models that describe the links between the polar vortex dynamics and ozone depletion, and to advance the understanding of the Earth system by examining the interactions between Antarctica and lower latitudes. 2. To improve our understanding of microphysical and dynamical processes controlling the polar ozone, by providing the first quasi-Lagrangian observations of stratospheric ozone and particles, in addition to an improved characterization of the 3D polar vortex dynamics. Techniques for assimilating these Lagrangian observations are being developed. A major Concordiasi component is a field experiment during the austral springs of 2008–10. The field activities in 2010 are based on a constellation of up to 18 long-duration stratospheric super-pressure balloons (SPBs) deployed from the McMurdo station. Six of these balloons will carry GPS receivers and in situ instruments measuring temperature, pressure, ozone, and particles. Twelve of the balloons will release drop-sondes on demand for measuring atmospheric parameters. Lastly, radiosounding measurements are collected at various sites, including the Concordia station.

]]> Florence Rabier et al. Oxfordian magnetostratigraphy of Poland and its correlation to Sub-Mediterranean ammonite zones and marine magnetic anomalies http://docs.lib.purdue.edu/easpubs/70 http://docs.lib.purdue.edu/easpubs/70 Thu, 14 Mar 2013 14:31:10 PDT A nearly continuous magnetostratigraphic polarity pattern was compiled from several ammonite-zoned carbonate successions of southern Poland and from a composite magnetostratigraphy from the Iberian Range of Spain. The array of sections spans the middle two-thirds of the Oxfordian within the Sub-Mediterranean Province (Cordatum through Bifurcatus ammonite zones). The average paleopole calculated from eight of these Polish sections is at 78.5°N, 184.9°E (δp = 2.6°, δm = 3.5°). The Sub-Mediterranean polarity pattern is consistent with an independent polarity pattern derived from the Boreal-realm sections of the British Isles, and improves the inter-correlation between these faunal realms. Cycle stratigraphy published for these ammonite subzones from southern France enabled temporal scaling of the polarity pattern, thereby facilitating correlation to marine magnetic anomalies M28 through M33 as modeled from deep-tow magnetometer surveys in the Western Pacific. The bases of the Middle and Upper Oxfordian substages as defined in the Sub-Mediterranean zonation in Poland correspond approximately to chrons M33 and M29 of that Pacific M-sequence model.

]]> Piotr A. Przybylski et al. Effects of sample size and position from monolith and core methods on the estimation of total root biomass in a temperate grassland ecosystem in Inner Mongolia http://docs.lib.purdue.edu/easpubs/69 http://docs.lib.purdue.edu/easpubs/69 Thu, 14 Mar 2013 14:31:08 PDT Development of an appropriate scheme to accurately sample root biomass is essential for accurate estimation of biomass and carbon budget of grassland. This study evaluated measurement accuracy of the monolith and core methods with different sample sizes and positions in a temperate grassland ecosystem in Inner Mongolia, China. The results indicated that the small core method (3.8-cm-diameter) significantly underestimated total root biomass compared with the large core method (10-cm-diameter), small monolith method (0.25 m2) and large monolith method (1 m2). Total root biomass estimated from the small core method was about 52% less than that from the large monolith method (1 m2). At 95% confidence interval, 10% relative precision could be obtained with five small monoliths, 15 large cores and 65 small cores. The coefficient of variation (CV) for total root biomass decreased logarithmically with increasing sample size for both the monolith and core methods. Compared with the stratified random sampling, core sampling with different fixed positions could not provide reliable estimate of total root biomass. Washing damage and soil lost during extraction might be the major factors controlling the measurement accuracy of total root biomass by core method with small sample size.

]]> Xiaoyan Ping et al. The Complexity of Brownian Processes Run with Nonlinear Clocks http://docs.lib.purdue.edu/easpubs/68 http://docs.lib.purdue.edu/easpubs/68 Thu, 14 Mar 2013 14:31:07 PDT Anomalous diffusion occurs in many branches of physics. Examples include diffusion in confined nanofilms, Richardson turbulence in the atmosphere, near-surface ocean currents, fracture flow in porous formations and vortex arrays in rotating flows. Classically, anomalous diffusion is characterized by a power law exponent related to the mean-square displacement of a particle or squared separation of pairs of particles: 〈|X(t)|2〉 ~tγ. The exponent γ is often thought to relate to the fractal dimension of the underlying process. If γ > 1 the flow is super-diffusive, if it equals 1 it is classical, otherwise it is sub-diffusive. In this work we illustrate how time-changed Brownian position processes can be employed to model sub-, super-, and classical diffusion, while time-changed Brownian velocity processes can be used to model super-diffusion alone. Specific examples presented include transport in turbulent fluids and renormalized transport in porous media. Intuitively, a time-changed Brownian process is a classical Brownian motion running with a nonlinear clock (Bm-nlc). The major difference between classical and Bm-nlc is that the time-changed case has nonstationary increments. An important novelty of this approach is that, unlike fractional Brownian motion, the fractal dimension of the process (space filling character) driving anomalous diffusion as modeled by Bm-nlc positions or velocities does not change with the scaling exponent, γ.

]]> Moongyu Park et al. The Role of Carbon Dioxide during the Onset of Antarctic Glaciation http://docs.lib.purdue.edu/easpubs/67 http://docs.lib.purdue.edu/easpubs/67 Thu, 14 Mar 2013 14:31:06 PDT Earth’s modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation ~33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth’s climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO2) during major climatic change. Previously published records of alkenone-based CO2 from high- and low-latitude ocean localities suggested that CO2 increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO2 levels, biasing long-term trends. Our results show that CO2 declined before and during Antarctic glaciation and support a substantial CO2 decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO2 thresholds.

]]> Markus Pagani et al. Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition http://docs.lib.purdue.edu/easpubs/65 http://docs.lib.purdue.edu/easpubs/65 Thu, 14 Mar 2013 14:31:00 PDT Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ2H values in the early spring to autochthonous particulate matter with significantly lower δ2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

]]> Kristine E. Nielson et al. Oxfordian magnetostratigraphy of Britain and its correlation to Tethyan regions and Pacific marine magnetic anomalies http://docs.lib.purdue.edu/easpubs/66 http://docs.lib.purdue.edu/easpubs/66 Thu, 14 Mar 2013 14:31:00 PDT A suite of 11 sections through the Oxfordian (Upper Jurassic) strata in the Dorset and Yorkshire regions of England and the Isle of Skye in Scotland yielded magnetic polarity patterns directly calibrated to the ammonite biostratigraphy of the Boreal and the Subboreal faunal provinces. The sections include the leading candidate for the global stratotype (GSSP) for the Callovian–Oxfordian stage boundary. The mean Oxfordian paleomagnetic pole derived from the Dorset and Yorkshire sections is 71.3°N, 172.6°E (δp = 4.2°, δm = 6.1°). The integrated magneto-biostratigraphic scale is consistent with results from the Sub-Mediterranean faunal province and extends the polarity pattern to the base of the Oxfordian. After adjusting for the estimated durations of ammonite subzones from cycle stratigraphy, the magnetostratigraphy confirms models for marine magnetic anomalies M30 through to M37, including some of the short-duration features recorded by deep-tow magnetic surveys in the western Pacific. The Callovian–Oxfordian boundary (base of Quenstedtoceras mariae Zone) occurs in a normal-polarity zone that is correlated to the youngest part of polarity chron M37n of this extension to the M-sequence.

]]> James G. Ogg et al. Lake Ice phenology of small lakes: Impacts of climate variability in the Great Lakes region http://docs.lib.purdue.edu/easpubs/64 http://docs.lib.purdue.edu/easpubs/64 Thu, 14 Mar 2013 14:30:59 PDT Formation of lake ice is common in lakes located in mid and high latitudes. Lake ice plays a vital role in heat storage, controlling lake water temperature, survival of aquatic ecosystems, and maintaining the bio diversity of lakes. Significant warming in air temperature during the cold season (October–May) may lead to reduced ice cover of lakes and eventually disturb the lake's seasonal dynamics. We examined the role of climate variability on lake ice phenology for small inland lakes in the Great Lakes region. The Variable Infiltration Capacity (VIC) model with a physically based lake algorithm was implemented to simulate long term (i.e. 1916–2007) changes in lake ice phenology, as described by the date of ice break-up, date of ice freeze-up, and number of ice-free days. Model performance was evaluated against observed lake ice phenology. A statistically significant increase (0.08–0.21 °C) in air temperature resulted in a significant change (0.2–2.0 days/decade) in lake ice freeze-up and break-up dates. While lake ice freeze-up was strongly associated (correlation > 0.60) with air temperature of the early (October–December) cold season, lake ice break-up was highly associated (correlation = − 0.80) with air temperature during the late (March–May) cold season. The number of ice-free days was affected by the temperature changes during the entire cold season. Lakes located in the southern part of the study domain experienced stronger trends in ice phenology than those located in the northern part. Inter-decadal to decadal scale variability in the number of ice-free days not associated with long-term trends in air temperature were largely driven by the Atlantic Multi-decadal Oscillation (AMO), El-Niño Southern Oscillation (ENSO), and Pacific Decadal Oscillation (PDO).

]]> Vimal Mishra et al. Multiple isotope forensics of nitrate in a wild horse poisoning incident http://docs.lib.purdue.edu/easpubs/63 http://docs.lib.purdue.edu/easpubs/63 Thu, 14 Mar 2013 14:30:59 PDT Multiple stable isotope analysis can be a powerful technique in forensic sciences. Oxygen and nitrogen isotopes were used to determine the source of nitrate that was responsible for the poisoning deaths of 71 wild horses in the Nevada desert. The nitrate was present in a water-filled hole known as ‘the Main Lake depression.’ Nitrate from the Main Lake depression had δ18O and δ15N values that were very positive (+32‰, +37‰), and Δ17O values of approximately +2‰. The isotopic data suggested that the most probable source of the nitrate was nitrification of nitrogen from horse manure and urine that had leached into the pond. The δ18O signal suggested that extreme evaporative concentration had occurred, resulting in toxic levels of nitrate accumulating in the Main Lake depression. The study demonstrates the utility of the multiple stable isotope analysis approach for characterizing sources of nitrate.

]]> Greg Michalski et al. The role of symmetry in the mass independent isotope effect in ozone http://docs.lib.purdue.edu/easpubs/62 http://docs.lib.purdue.edu/easpubs/62 Thu, 14 Mar 2013 14:30:58 PDT Understanding the internal distribution of “anomalous” isotope enrichments has important implications for validating theoretical postulates on the origin of these enrichments in molecules such as ozone and for understanding the transfer of these enrichments to other compounds in the atmosphere via mass transfer. Here, we present an approach, using the reaction NO2− + O3, for assessing the internal distribution of the Δ17O anomaly and the δ18O enrichment in ozone produced by electric discharge. The Δ17O results strongly support the symmetry mechanism for generating mass independent fractionations, and the δ18O results are consistent with published data. Positional Δ17O and δ18O enrichments in ozone can now be more effectively used in photochemical models that use mass balance oxygen atom transfer mechanisms to infer atmospheric oxidation chemistry.

]]> Greg Michalski et al. Evaluating evapotranspiration and water-use efficiency of terrestrial ecosystems in the conterminous United States using MODIS and AmeriFlux data http://docs.lib.purdue.edu/easpubs/61 http://docs.lib.purdue.edu/easpubs/61 Thu, 14 Mar 2013 14:30:57 PDT In this study, we used the remotely-sensed data from the Moderate Resolution Imaging Spectrometer (MODIS), meteorological and eddy flux data and an artificial neural networks (ANNs) technique to develop a daily evapotranspiration (ET) product for the period of 2004–2005 for the conterminous U.S. We then estimated and analyzed the regional water-use efficiency (WUE) based on the developed ET and MODIS gross primary production (GPP) for the region. We first trained the ANNs to predict evapotranspiration fraction (EF) based on the data at 28 AmeriFlux sites between 2003 and 2005. Five remotely-sensed variables including land surface temperature (LST), normalized difference vegetation index (NDVI), normalized difference water index (NDWI), leaf area index (LAI) and photosynthetically active radiation (PAR) and ground-measured air temperature and wind velocity were used. The daily ET was calculated by multiplying net radiation flux derived from remote sensing products with EF. We then evaluated the model performance by comparing modeled ET with the data at 24 AmeriFlux sites in 2006. We found that the ANNs predicted daily ET well (R2 = 0.52–0.86). The ANNs were applied to predict the spatial and temporal distributions of daily ET for the conterminous U.S. in 2004 and 2005. The ecosystem WUE for the conterminous U.S. from 2004 to 2005 was calculated using MODIS GPP products (MOD17) and the estimated ET. We found that all ecosystems' WUE-drought relationships showed a two-stage pattern. Specifically, WUE increased when the intensity of drought was moderate; WUE tended to decrease under severe drought. These findings are consistent with the observations that WUE does not monotonously increase in response to water stress. Our study suggests a new water-use efficiency mechanism should be considered in ecosystem modeling. In addition, this study provides a high spatial and temporal resolution ET dataset, an important product for climate change and hydrological cycling studies for the MODIS era.

]]> Xiaoliang Lu et al. Global cooling during the Eocene-Oligocene climate transition http://docs.lib.purdue.edu/easpubs/60 http://docs.lib.purdue.edu/easpubs/60 Thu, 14 Mar 2013 14:30:57 PDT About 34 million years ago, Earth's climate shifted from a relatively ice-free world to one with glacial conditions on Antarctica characterized by substantial ice sheets. How Earth's temperature changed during this climate transition remains poorly understood, and evidence for Northern Hemisphere polar ice is controversial. Here, we report proxy records of sea surface temperatures from multiple ocean localities and show that the high-latitude temperature decrease was substantial and heterogeneous. High-latitude (45 degrees to 70 degrees in both hemispheres) temperatures before the climate transition were ∼20°C and cooled an average of ∼5°C. Our results, combined with ocean and ice-sheet model simulations and benthic oxygen isotope records, indicate that Northern Hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time.

]]> Zhonghui Liu et al. Pacific/North American teleconnection controls on precipitation isotope ratios across the contiguous United States http://docs.lib.purdue.edu/easpubs/59 http://docs.lib.purdue.edu/easpubs/59 Thu, 14 Mar 2013 14:30:56 PDT Large-scale climate teleconnections such as the Pacific/North American (PNA) pattern strongly influence atmospheric processes and continental climate. Here we show that precipitation δ18O values in the contiguous United States are correlated with an index of the PNA pattern. The δ18O/PNA relationship varies across the study region and exhibits two prominent modes, with positive correlation in the western USA and negative correlation in the east. This spatial pattern appears not to reflect variation in local climate variables, but rather primarily reflects differences in atmospheric circulation and moisture sources associated with PNA. Our results suggest that strong antiphase variation in paired paleo-water δ18O proxy records from regions characterized by the two modes of δ18O/PNA correlation, especially in the Midwest and southwestern USA, may provide a robust basis for reconstruction of past variation in the PNA pattern. --------------------------------------------------------------------------------

]]> Zhongfang Liu et al. Old and stable soil organic matter is not necessarily chemically recalcitrant: implications for modeling concepts and temperature sensitivity http://docs.lib.purdue.edu/easpubs/58 http://docs.lib.purdue.edu/easpubs/58 Thu, 14 Mar 2013 14:30:55 PDT Soil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. Although these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use near edge X-ray absorption fine structure (NEXAFS) spectroscopy in combination with differential scanning calorimetry (DSC) and alkaline cupric oxide (CuO) oxidation to explore this assumption. Specifically, we examined material from the 2.3-2.6 kg L density fraction of three soils of different type (Oxisol, Alfisol, Inceptisol). The density fraction with the youngest C age (Oxisol, 107 years) showed the highest relative abundance of aromatic groups and the lowest O-alkyl C/aromatic C ratio as determined by NEXAFS. Conversely, the fraction with the oldest C (Inceptisol, 680 years) had the lowest relative abundance of aromatic groups and highest O-alkyl C/aromatic C ratio. This sample also had the highest proportion of thermally labile materials as measured by DSC, and the highest ratio of substituted fatty acids to lignin phenols as indicated by CuO oxidation. Therefore, the organic matter of the Inceptisol sample, with a C age associated with 'passive' pools of carbon (680 years), had the largest proportion of easily metabolizable organic molecules with low thermodynamic stability, whereas the organic matter of the much younger Oxisol sample (107 years) had the highest proportion of supposedly stable organic structures considered more difficult to metabolize. Our results demonstrate that C age is not necessarily related to molecular structure or thermodynamic stability, and we suggest that soil carbon models would benefit from viewing turnover rate as codetermined by the interaction between substrates, microbial actors, and abiotic driving variables. Furthermore, assuming that old carbon is composed of complex or 'recalcitrant' compounds will erroneously attribute a greater temperature sensitivity to those materials than they may actually possess. [ABSTRACT FROM AUTHOR].

]]> Markus Kleber et al. Characterizing heart rate variability by scale-dependent Lyapunov exponent http://docs.lib.purdue.edu/easpubs/57 http://docs.lib.purdue.edu/easpubs/57 Thu, 14 Mar 2013 14:30:55 PDT Previous studies on heart rate variability (HRV) using chaos theory, fractal scaling analysis, and many other methods, while fruitful in many aspects, have produced much confusion in the literature. Especially the issue of whether normal HRV is chaotic or stochastic remains highly controversial. Here, we employ a new multiscale complexity measure, the scale-dependent Lyapunov exponent (SDLE), to characterize HRV. SDLE has been shown to readily characterize major models of complex time series including deterministic chaos, noisy chaos, stochastic oscillations, random 1/f processes, random Levy processes, and complex time series with multiple scaling behaviors. Here we use SDLE to characterize the relative importance of nonlinear, chaotic, and stochastic dynamics in HRV of healthy, congestive heart failure, and atrial fibrillation subjects. We show that while HRV data of all these three types are mostly stochastic, the stochasticity is different among the three groups.

]]> Jing Hu et al. Characterizing subdiurnal extreme precipitation in the midwestern United States http://docs.lib.purdue.edu/easpubs/55 http://docs.lib.purdue.edu/easpubs/55 Thu, 14 Mar 2013 14:30:54 PDT This research establishes a methodology to quantify the characteristics of convective cloud systems that produce subdiurnal extreme precipitation. Subdiurnal extreme precipitation events are identified by examining hourly precipitation data from 48 rain gauges in the midwestern United States during the period 1956–2005. Time series of precipitation accumulations for 6-h periods are fitted to the generalized Pareto distribution to determine the 10-yr return levels for the stations. An extreme precipitation event is one in which precipitation exceeds the 10-yr return level over a 6-h period. Return levels in the Midwest vary between 54 and 93 mm for 6-h events. Most of the precipitation contributing to these events falls within 1–2 h. Characteristics of the precipitating systems responsible for the extremes are derived from the National Centers for Environmental Prediction stage II and stage IV multisensor precipitation data. The precipitating systems are treated as objects that are identified using an automated procedure. Characteristics considered include object size and the precipitation mean, variance, and maximum within each object. For example, object sizes vary between 96 and 34 480 km2, suggesting that a wide variety of convective precipitating systems can produce subdiurnal extreme precipitation.

]]> Nathan M. Hitchens et al. Tropical sea temperatures in the high-latitude South Pacific during the Eocene http://docs.lib.purdue.edu/easpubs/56 http://docs.lib.purdue.edu/easpubs/56 Thu, 14 Mar 2013 14:30:54 PDT Sea-surface temperature (SST) estimates of ~30 °C from planktic foraminifera and archaeal membrane lipids in bathyal sediments in the Canterbury Basin, New Zealand, support paleontological evidence for a warm subtropical to tropical climate in the early Eocene high-latitude (55°S) southwest Pacific. Such warm SSTs call into question previous estimates based on oxygen isotopes and present a major challenge to climate modelers. Even under hypergreenhouse conditions (2240 ppm CO2), modeled summer SSTs for the New Zealand region do not exceed 20 °C.

]]> Christopher J. Hollis et al. Early to Middle Miocene monsoon climate in Australia http://docs.lib.purdue.edu/easpubs/54 http://docs.lib.purdue.edu/easpubs/54 Thu, 14 Mar 2013 14:30:53 PDT The present-day Australian monsoon delivers substantial moisture to the northern regions of a predominantly arid continent. However, the pre-Quaternary history of the Australian monsoon is poorly constrained due to sparse and often poorly dated paleoclimate proxy evidence. Sedimentological and paleontological data suggest that warm, humid, and seasonal environments prevailed in central and north Australia during the Miocene, though it is unclear whether these were products of the Australian monsoon. We perform a series of sensitivity experiments using an atmospheric general circulation model, combined with an offline equilibrium vegetation model, to quantitatively constrain the areal extent of the Miocene monsoon. Our results suggest a weaker than modern monsoon climate during the Miocene. This result is insensitive to atmospheric CO2, although somewhat sensitive to vegetation interactions and the presumed distribution of inland water bodies. None of our Miocene experiments exhibit precipitation rates greater than modern over north Australia, in disagreement with paleoclimate record interpretations. Vegetation modeling indicates that inferred precipitation values from fossil flora and fauna could only support Miocene vegetation patterns if atmospheric CO2 was twice the modern concentration. This suggests that elevated CO2 was critical for sustaining Miocene vegetation.

]]> Nicholas Herold et al. Interpreting finite strain: Analysis of deformation in analog models http://docs.lib.purdue.edu/easpubs/52 http://docs.lib.purdue.edu/easpubs/52 Thu, 14 Mar 2013 14:30:52 PDT We investigate the accuracy of strain rates calculated directly from a robust set of velocity measurements that were obtained in controlled experimental settings. We compare the calculated strains and strain rates, and the corresponding deformation style, determined from sets of three vs. four velocity measurements obtained by tracking a dense set of surface markers during experiments. The density of our measurements, in conjunction with a well-understood model deformational setting, allows us to relate the style and magnitude of strains to the underlying structures. We demonstrate that calculating strain values from three measurements can be irrelevant to the geologic structures even if they are mathematically correct, but that one can avoid some of these deceptive results by using quadrangles to calculate strain. We demonstrate the utility of such strain calculations in interpreting strain partitioning in obliquely convergent analog models for continuously and discontinuously deforming materials. In addition, we compare direct calculations with those obtained by determining strains from the derivatives of continuous spline functions that have been fit to the velocity field.

]]> Saad S. B. Haq et al. Nitrous Oxide Production in an Eastern Corn Belt Soil: Sources and Redox Range http://docs.lib.purdue.edu/easpubs/53 http://docs.lib.purdue.edu/easpubs/53 Thu, 14 Mar 2013 14:30:52 PDT Nitrous oxide derived from soils is a main contributor to the greenhouse gas effect and a precursor to ozone-depleting substrates; however, the source processes and interacting controls are not well established. This study was conducted to estimate the magnitude and source (nitrification vs. denitrification) of N^sub 2^O production as affected by the form of N fertilizer, soil water content, and redox potential (Eh). Soils from continuous corn (Zea mays L.) experimental plots with a history of eight consecutive years of either side-dressed urea-NH^sub 4^NO^sub 3^ (UAN) or fall liquid swine manure (FM) were collected and N^sub 2^O evolution was traced in both aerobic and anaerobic incubations using ^sup 15^N labeling. Partitioning results were highly variable but suggested that enhanced denitrification occurred after an extreme increase in soil water content (from 45 to 90% water-filled pore space [WFPS]) while a more coupled nitrification-denitrification process drove N^sub 2^O evolution at moderate water content (55% WFPS). Manured soils at high water contents registered shorter duration peaks but with higher overall N^sub 2^O production rates than those observed at moderate water content (7-d weighted average of 0.61 vs. 0.09 μg N^sub 2^O kg^sup -1^ soil h^sup -1^). Under anoxic conditions, manured soils showed higher N^sub 2^O production rates than UAN soils (up to 336 and 145 μg N^sub 2^O kg^sup -1^ soil h^sup -1^, respectively) shortly after flooding, which coincided with a sharp drop in Eh (from 575 to 466 mV). Irrespective of the N source, a narrow, consistent Eh range for N^sub 2^O production occurred under moderate reducing conditions (420-575 mV). These results indicate that soils receiving repeated manure application that are subject to intensive, recurrent soil rewetting events may be prone to higher N^sub 2^O emissions. [PUBLICATION ABSTRACT]

]]> Guillermo B. Hernandez-Ramirez et al. Propagation of plasma bubbles observed in Brazil from GPS and airglow data http://docs.lib.purdue.edu/easpubs/51 http://docs.lib.purdue.edu/easpubs/51 Thu, 14 Mar 2013 14:30:51 PDT Equatorial spread-F is a common occurrence in the equatorial ionosphere that is associated with large variations in plasma density that often cause scintillation and interference in communication signals. These events are known to result from Rayleigh–Taylor instability, but the day-to-day variability of their occurrence is not well understood. The triggering mechanism of plasma depletions is still a matter of debate, but may be linked to gravity waves that under favorable conditions propagate to the middle atmosphere. Understanding the triggering of ESF was the focus of the SpreadFEx campaign near Brasilia, Brazil in 2005. The campaign provided co-located airglow and GPS observations to study the onset of plasma depletions and their evolution as they traversed the region. Comparisons between the 630.0 nm airglow data and GPS data demonstrate the ability of the compact dual frequency GPS array to detect the plasma bubbles and retrieve reliable propagation characteristics of the depletions. In this case study, a plasma depletion was detected and moved over the array at velocities of 85–110 m/s, slowing as it moved towards the east. Correlation of consecutive airglow images gives consistent estimates of the eastward drift over the same time period. Mapping the airglow data to the GPS line-of-sight geometry allows direct comparison and reveals a resolvable westward tilt of the plasma depletion that may be due to vertical shear. The uniqueness of this study is the ability to resolve locally the characteristics of the plasma depletion without relying on assumptions about the mapping of the depletion along magnetic field lines to large latitudinal distances. It presents new information for understanding ESF development and the development of depletions strong enough to produce scintillation.

]]> Jennifer S. Haase et al. Impacts of land-use change and best management practice implementation in a Conservation Effects Assessment Project watershed: Northwest Arkansas http://docs.lib.purdue.edu/easpubs/50 http://docs.lib.purdue.edu/easpubs/50 Thu, 14 Mar 2013 14:30:50 PDT A study was conducted to quantify land use and management changes and their effects on water quality as part of an effort to evaluate the effects of best management practices under the Conservation Effects Assessment Project. This study was focused on the Lincoln Lake watershed, a primarily pastured watershed in northwest Arkansas and one of the watersheds funded under the Conservation Effects Assessment Project competitive grants program. As with a number of other Conservation Effects Assessment Project watersheds, this watershed has undergone substantial land-use change over the past few years. These changes have occurred concurrently with best management practice implementation. Thus, the need has arisen to determine their impacts on watershed water quality. Land-use analyses covering a 12-year period revealed a rapidly changing landscape, with the various land uses experiencing gains and losses at different times. Furthermore, a systematic trend for pastured areas to be replaced by urban land uses was identified, with pastures experiencing a net decline of about 12% during the analyses period. With regard to water quality, downward trends were observed under base and storm flow conditions in the upper reaches (Upper Moores Creek) with significant changes in total phosphorus and total suspended solids (p-values = 0.0153 and 0.0135, respectively). Significant increases in flow and nitrate-nitrogen (p-values = 0.0465 and 0.0927, respectively) were observed in the lower reaches (Lower Moores Creek), while no appreciable changes were observed in one part of the watershed. We conclude that the concurrent implementation of best management practices served to protect water quality from otherwise adverse effects that might have occurred due to a rapid urbanization in the watershed.

]]> Margaret W. Gitau et al. Contribution of gravitational potential energy differences to the global stress field http://docs.lib.purdue.edu/easpubs/49 http://docs.lib.purdue.edu/easpubs/49 Thu, 14 Mar 2013 14:30:50 PDT Modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics. Both these sources of buoyancies are important in generating the lithospheric stress field. However, these sources and the contribution that they make are dependent on a number of variables, such as the role of lateral strength variation in the lithosphere, the reference level for computing the gravitational potential energy per unit area (GPE) of the lithosphere, and even the definition of deviatoric stress. For the mantle contribution, much depends on the mantle convection model, including the role of lateral and radial viscosity variations, the spatial distribution of density buoyancies, and the resolution of the convection model. GPE differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography. The global lithospheric stress field can thus be divided into (1) stresses associated with GPE differences (including the contribution from radial basal tractions) and (2) stresses associated with the contribution of horizontal basal tractions. In this paper, we investigate only the contribution of GPE differences, both with and without the inferred contribution of radial basal tractions. We use the Crust 2.0 model to compute GPE values and show that these GPE differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes, as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the Earth's plate boundary zones. We argue that GPE differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere; shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection. Deviatoric stress magnitudes arising from GPE differences are in the range of 1–4 TN m−1, a part of which is contributed by dynamic topography. The EGM96 geoid data set is also used as a rough proxy for GPE values in the lithosphere. However, GPE differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators. GPE values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography. Another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating GPE. We also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2-D approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress.

]]> Attreyee Ghosh et al. A computationally efficient inverse modelling approach of inherent optical properties for a remote sensing model http://docs.lib.purdue.edu/easpubs/48 http://docs.lib.purdue.edu/easpubs/48 Thu, 14 Mar 2013 14:30:49 PDT Inverse modelling of inherent optical properties (IOP) is an alternative to the in situ measurements of IOP requiring specialized instruments. However, inverse modelling using Monte Carlo models may require very large computational time due to a large number of dynamic model runs needed to search the optimum parameter values. We present a new approach to reduce this computational time. Mathematical relationships were developed for wavelength and concentration dependence of IOP values of suspended mineral based on four parameters. Optimal values of these four parameters were calculated by minimizing the mean sum of error between the physical hyperspectral optical-Monte Carlo (PHO-MC) model predicted reflectance to measured reflectance values for selected 33 reflectance measurements for a set of 11 wavelengths and three suspended sediment concentrations. The computation time was significantly reduced by several orders of magnitude by: (1) replacing the PHO-MC model with 11 wavelengths specific pseudo-simulator models developed by applying artificial neural network approach; and (2) using a nondominated sorted genetic algorithm –II (NSGA II) to search the global optimal solution of four parameters of IOP equations. Determined IOP values of suspended minerals were then successfully validated by using them as input to PHO-MC model to predict reflectance values for an independent set of 287 combinations of 41 wavelengths and seven suspended sediment concentrations.

]]> Vijay Garg et al. Inverse Modeling of Beaver Reservoir's Water Spectral Reflectance http://docs.lib.purdue.edu/easpubs/47 http://docs.lib.purdue.edu/easpubs/47 Thu, 14 Mar 2013 14:30:48 PDT Estimation of inherent optical properties (IOP) needed for water quality evaluation by remote sensing models is very complex, primarily due to the large number of model simulations needed to find optimal parameter values. This study presents an approach for optimally parameterizing the IOP values of a physical hyperspectral optical - Monte Carlo (PHO-MC) model. An artificial neural network (ANN) based pseudo simulator combined with the Nondominated Sorted Genetic Algorithm II (NSGA II) was used to efficiently perform a large number of model simulations and to search the optimal parameter values for IOP determination. Concentrations of suspended matter (sm), chlorophyll-a (chl), and total dissolved organic matter (DOM) along with the reflectance data at 16 different wavelengths were measured at 48 sampling stations in the Beaver Reservoir, Arkansas, between 2003 and 2005 and were used to evaluate the IOP values. Measured concentrations and reflectance data from 24 sampling stations were used to optimize IOP parameter values for sm, chl, and DOM. The data collected from the remaining 24 sampling stations were used for the validation of PHO-MC model-predicted reflectance by using optimized IOP values. PHO-MC predicted reflectance values were significantly correlated (r = 0.90, p < 0.01) with the corresponding measured reflectance values, indicating that the pseudo simulator combined with the NSGA II accurately estimated the IOP values. An estimated 10 10 years of calculation time was reduced to less than 3 min by using the pseudo simulator and NSGA II to supplement the PHO-MC model for estimating the IOP values.

]]> Vijay Garg et al. Density profiles of oceanic slabs and surrounding mantle: integrated thermodynamic and thermal modeling, and implications for the fate of slabs at the 660 km discontinuity http://docs.lib.purdue.edu/easpubs/46 http://docs.lib.purdue.edu/easpubs/46 Thu, 14 Mar 2013 14:30:48 PDT We have calculated the mineralogical properties of the Earth's mantle and the lithological units constituting the subducting oceanic slabs within a wide range of P–T conditions within the CaO–FeO–MgO–Al2O3–SiO2 system, except for the basalt top-layer of a slab, for which the system is extended to include Na2O. The mineralogical data are then converted, using the appropriate P–V–T relations, to bulk densities. The calculated adiabatic density vs. depth profile of the mantle between 200 and 725 km depths is in good agreement with geophysical and experimental data. The density data of the different compositional units are combined with calculated thermal structures for a variety of slab–mantle systems to construct equilibrium density profiles as a function of depth. The mean equilibrium densities of the slabs within the transition zone (400–660 km depth) are found to be ∼0.04–0.05 g/cm3 greater than those of the ambient mantle within the same depth interval. For the entire upper mantle, density differences between slabs and ambient mantle are slightly less, but the slabs still remain denser than the latter. At 670 km depth, slabs have lower density than the ambient lower mantle because of the commencement of perovskite forming reactions within the mantle, and displacements of these reaction boundaries to higher pressures within the slabs as a consequence of their negative P–T slopes. If perovskite forming reactions within slabs are hindered for kinetic sluggishness, then neutral buoyancy would be achieved when the slabs have penetrated ∼100 km into the lower mantle. However, using the available data on the kinetics of spinel to perovskite plus periclase reaction, we conclude that the reaction would go to completion in a Peru-type young slab (41 Myr), and very likely also in a Tonga-type old slab (110 Myr), before these penetrated 100 km into the lower mantle. Thus, slabs should always remain negatively buoyant, and therefore continue to subduct through the lower mantle once it penetrates through the 660 km discontinuity. Despite a negative buoyancy force, a slab could deflect at the top of the lower mantle (660 km) because of factors resisting subduction, namely viscosity jump, low dip angle, slab roll back, and metastable persistence of olivine in cold slabs. If published scale model experiments represent realistic approximations of the factors affecting plate subduction, then according to our density data, any slab with a dip angle of ≤40–50° would bend at the 660 km discontinuity if there is a viscosity jump of at least by a factor of ∼10 and trench migration. The basalt top-layer of a slab is denser than other slab components and the ambient mantle at all depths to 660 km, and therefore should continue to sink into the lower mantle, especially if a slab directly penetrates the 660 km barrier, instead of peeling off in the transition zone to form a “perched eclogite” or “piclogite” layer, as previously proposed. The harzburgite layer, which is sandwiched between denser basalt and lherzolite layers, faces greater resistance to subduction, especially in a young slab, and thus could significantly contribute to the deformation of a slab near the 660 km discontinuity.

]]> Jibamitra Ganguly et al. Could Pantheon Fossae be the result of the Apollodorus crater-forming impact within the Caloris basin, Mercury? http://docs.lib.purdue.edu/easpubs/45 http://docs.lib.purdue.edu/easpubs/45 Thu, 14 Mar 2013 14:30:47 PDT The ~ 40-km-diameter Apollodorus impact crater lies near the center of Pantheon Fossae, a complex of radiating linear troughs itself at the approximate center of the 1500-km-diameter Caloris basin on Mercury. Here we use a series of finite element models to explore the idea that the Apollodorus crater-forming impact induced the formation of radially oriented graben by altering a pre-existing extensional stress state. Graben in the outer portions of the Caloris basin, which display predominantly circumferential orientations, have been taken as evidence that the basin interior was in a state of horizontal extensional stress as a result of uplift. If the Apollodorus crater formed at the time of such a stress state, impact-induced damage to basin fill material would have caused basin material to move radially outward, leading to a decrease in the radial extensional stress and an increase in the circumferential stress. If this change in differential stress was sufficient to induce failure, the predicted style of faulting would be radial graben extending outward from the exterior crater rim. The ~ 230-km radial extent of Pantheon Fossae implies, by this scenario, that the Apollodorus impact generated a large damage zone, extending to perhaps three crater radii (~ 60 km) or more. The calculations also suggest, under this scenario, that the Caloris basin fill had greater strength than the surrounding crust and that the basin uplift and extensional stress field prior to the Apollodorus impact were close to azimuthally symmetric. The location of Pantheon Fossae very near the center of the Caloris basin appears to be coincidental; any crater similar in size to Apollodorus and located within ~ 300 km of the basin center could have produced a radiating set of graben by the mechanism explored here.

]]> Andrew M. Freed et al. Improved imaging with phase-weighted common conversion point stacks of receiver functions http://docs.lib.purdue.edu/easpubs/43 http://docs.lib.purdue.edu/easpubs/43 Thu, 14 Mar 2013 14:30:46 PDT Broad-band array studies frequently stack receiver functions to improve their signal-to-noise ratio while mapping structures in the crust and upper mantle. Noise may produce spurious secondary arrivals that obscure or mimic arrivals produced by P-to-S conversions at large contrasts in seismic impedance such as the Moho. We use a Hilbert transform to calculate phase-weights, which minimize the constructive stacking of erroneous signal in receiver function data sets. We outline this approach and demonstrate its application through synthetic data combined with different types of noise, a previously published example of signal-generated noise, and a large data set from the Sierra Nevada EarthScope Project. These examples show that phase-weighting reduces the presence of signal-generated noise in receiver functions and improves stacked data sets.

]]> A. Frassetto et al. Steady-state laboratory flow laws alone fail to explain postseismic observations http://docs.lib.purdue.edu/easpubs/44 http://docs.lib.purdue.edu/easpubs/44 Thu, 14 Mar 2013 14:30:46 PDT We test whether laboratory derived steady-state flow laws for wet olivine can be used to explain postseismic relaxation in the upper mantle following the 1999 Hector Mine earthquake. This is accomplished using rate changes in GPS observed displacement time-series at far-field stations as constraints on the parameters associated with laboratory derived temperature- and stress-dependent flow laws for diffusion and dislocation creep of olivine. We primarily concentrate on the influences of temperature, grain size, and background strain rate to explain observed fast early displacement rates that slow rapidly in the 7 years of postseismic observations. We find that a reasonable fit to the observed time-series cannot be achieved by any combination of flow law parameters and plausible assumptions for the tectonic environment of the mantle beneath the Mojave Desert. We conclude that postseismic relaxation within the mantle following the Hector Mine earthquake likely includes an initial transient weakening phase, suggesting that steady-state flow laws by themselves are insufficient to characterize the flow of mantle rocks when stress conditions evolve.

]]> Andrew M. Freed et al. Gravitational potential energy and regional stress and strain rate fields for continental plateaus: Examples from the central Andes and Colorado Plateau http://docs.lib.purdue.edu/easpubs/42 http://docs.lib.purdue.edu/easpubs/42 Thu, 14 Mar 2013 14:30:45 PDT The commonly observed extension in areas of elevated and thickened crust is an expected consequence of having excess gravitational potential energy (GPE) compared to the low GPE of the surrounding crust. While this conceptual model is well founded, it is less clear how well GPE-related stress orientations compare quantitatively to observed stress and strain rate orientations and what any inconsistency tells us about the presence of other competing forces. We estimate the GPE distribution for the central Andes and the greater Colorado Plateau area using topography and crustal thickness variations, respectively, and compare the related stress fields with the World Stress Map as well as with a geodetic strain rate field (for the Colorado Plateau only). In both areas, deviatoric stresses associated with GPE variations alone cannot fully account for the observed deformation rate field. For the central Andes only a combination of deviatoric stresses associated with GPE and relative plate motions can account for the near N–S tensional stress observed in the Peruvian Andes and the margin–normal compressional stress along the eastern Cordillera and sub-Andean fold-and-thrust belt. The observed deformation field around the Colorado Plateau shows E–W extension, largely inconsistent with the deviatoric stresses associated with GPE variations except for the area east of the Rio Grande Rift. The NE–SW oriented stress observed on the southwestern Colorado Plateau is consistent with the orientations of tensional deviatoric stresses associated with GPE variations. We argue that this consistency could be haphazard; stress observations may not reflect the current state of stress due to inherited structure, or could result from the relative high strength of Colorado Plateau that allows for regional GPE variations (and possibly basal shear) to be more significant forces than far-field plate interactions. For the central Andes and Colorado Plateau, stresses associated with GPE variations have a strong influence on the total stress field, and can thus be used to calibrate the overall level of deviatoric stress acting within the lithosphere.

]]> Lucy M. Flesch et al. Analytic continuation of eigenvalues of a quartic oscillator http://docs.lib.purdue.edu/easpubs/41 http://docs.lib.purdue.edu/easpubs/41 Thu, 14 Mar 2013 14:30:45 PDT We consider the Schrödinger operator on the real line with even quartic potential x4 + α x2 and study analytic continuation of eigenvalues, as functions of parameter α. We prove several properties of this analytic continuation conjectured by Bender, Wu, Loeffel and Martin. 1. All eigenvalues are given by branches of two multi-valued analytic functions, one for even eigenfunctions and one for odd ones. 2. The only singularities of these multi-valued functions in the complex α-plane are algebraic ramification points, and there are only finitely many singularities over each compact subset of the α-plane. [ABSTRACT FROM AUTHOR].

]]> Alexandre Eremenko et al. Increased seasonality through the Eocene to Oligocene transition in northern high latitudes http://docs.lib.purdue.edu/easpubs/40 http://docs.lib.purdue.edu/easpubs/40 Thu, 14 Mar 2013 14:30:44 PDT A profound global climate shift took place at the Eocene–Oligocene transition (33.5 million years ago) when Cretaceous/early Palaeogene greenhouse conditions gave way to icehouse conditions1, 2, 3. During this interval, changes in the Earth's orbit and a long-term drop in atmospheric carbon dioxide concentrations4, 5, 6 resulted in both the growth of Antarctic ice sheets to approximately their modern size2, 3 and the appearance of Northern Hemisphere glacial ice7, 8. However, palaeoclimatic studies of this interval are contradictory: although some analyses indicate no major climatic changes9, 10, others imply cooler temperatures11, increased seasonality12, 13 and/or aridity12, 13, 14, 15. Climatic conditions in high northern latitudes over this interval are particularly poorly known. Here we present northern high-latitude terrestrial climate estimates for the Eocene to Oligocene interval, based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the Norwegian–Greenland Sea. Our data indicate a cooling of 5 °C in cold-month (winter) mean temperatures to 0–2 °C, and a concomitant increased seasonality before the Oi-1 glaciation event. These data indicate that a cooling component is indeed incorporated in the 18O isotope shift across the Eocene–Oligocene transition. However, the relatively warm summer temperatures at that time mean that continental ice on East Greenland was probably restricted to alpine outlet glaciers.

]]> James S. Eldrett et al. New paleomagnetic and stable-isotope results from the Nanxiong Basin, China: Implications for the K/T boundary and the timing of Paleocene mammalian turnover http://docs.lib.purdue.edu/easpubs/39 http://docs.lib.purdue.edu/easpubs/39 Thu, 14 Mar 2013 14:30:43 PDT The Nanxiong Basin (Guangdong Province, China) preserves the most complete Asian stratigraphic record of the Cretaceous-Paleogene (K/Pg) boundary extinction and the subsequent Paleocene mammalian radiation. Despite extensive study, the precise placement of the K/Pg boundary in the Nanxiong Basin sequence has been controversial, and the timing of subsequent mammalian turnover is poorly constrained. We present new paleomagnetic and geochemical data from the Late Cretaceous Pingling Formation (Nanxiong Group) and the overlying Paleocene Shanghu, Nongshan, and Guchengcun formations (Luofozhai Group). Our samples are directly correlated with previous geochemical and paleontological sampling localities, allowing for easy comparison with other local proxy records. Results indicate that the traditional placement of the K/Pg boundary at the base of a chaotic channel sandstone bed marking the highest stratigraphic appearance of dinosaur eggshell fragments and lowest stratigraphic appearance of Paleocene mammalian fossils lies about two-thirds of the way up Chron C29R, consistent with the placement of the boundary in all other well-documented sections. The average carbon isotope composition of paleosol carbonates decreases by 12‰ in the Early Paleocene, consistent with a major disruption to global carbon cycling after the K/Pg boundary. Constraints on the age of the first major Cenozoic mammalian turnover event in Asia (the Shanghuan-Nongshanian Asian Land Mammal Age boundary) support its placement near the top of Chron C27N, which coincides with a similar turnover in North America and geochemical changes recorded in several deep sea cores. [ABSTRACT FROM AUTHOR]

]]> William C. Clyde et al. Differentiating impacts of land use changes from pasture management in a CEAP watershed using SWAT model http://docs.lib.purdue.edu/easpubs/37 http://docs.lib.purdue.edu/easpubs/37 Thu, 14 Mar 2013 14:30:42 PDT Due to intensive farm practices, nonpoint-source (NPS) pollution has become one of the most challenging environmental problems in agricultural and mixed land use watersheds. Usually, various conservation practices are implemented in the watershed to control the NPS pollution problem. However, land use changes can mask the water quality improvements from the conservation practices implemented in the watershed. The objectives of this study were to evaluate the linkage between nutrient input from various pasture management practices and water quality, and to quantify the impacts of land use changes and pasture management on water quality in a pasture-dominated watershed. Land use data from 1992, 1994, 1996, 1999, 2001, and 2004 were evaluated for the land use changes in the watershed, and the corresponding implemented management practices were also incorporated into the Soil and Water Assessment Tool (SWAT) model. The individual impacts of land use change and pasture management were quantified by comparing the SWAT simulation results for different land use change and pasture management scenarios. The results indicated that land use changes resulted in greater total sediment (499 kg ha -1 ) and nitrogen losses (3.8 kg ha -1 ) in the Moores Creek subwatershed, whereas pasture management resulted in greater total nitrogen losses (4.3 kg ha -1 ) in the Beatty Branch subwatershed. Overall, the combined impacts of land use changes and pasture management resulted in greater total sediment (28 to 764 kg ha -1 of cumulative combined impacts between 1992 and 2007) and nitrogen losses (5.1 to 6.1 kg ha -1 ) and less total phosphorus losses (1.5 to 2.1 kg ha -1 ) in the Beatty Branch, Upper Moores Creek, and Moores Creek subwatersheds. By quantifying the individual impacts of land use changes and pasture management, we found that an increase in total nitrogen losses in the Beatty Branch subwatershed was mainly due to an increase in nutrient inputs in the pasture areas, and total sediment and nitrogen losses in the Moores Creek subwatershed were mainly due to an increase in urban lands. Therefore, the individual impacts of land use changes and conservation practices should be quantified to get a true picture of the success of CEAP programs in watersheds experiencing significant land use changes.

]]> Li-Chi Chiang et al. Do Earth anD EnvironmEntal SciEncE tExtbookS PromotE miDDlE anD high School StuDEntS’concEPtual DEvEloPmEnt about climatE changE? http://docs.lib.purdue.edu/easpubs/38 http://docs.lib.purdue.edu/easpubs/38 Thu, 14 Mar 2013 14:30:42 PDT Misconceptions or a lack of relevant prior concepts can hinder students from developing an understanding of scientific concepts. Science education research suggests that building on students' prior concepts is an effective way to develop students' scientific knowledge. This study reports the results of an analysis of earth and environmental science textbooks' representations of climate change concepts and an examination of these presentations for possible contribution to students' common misconceptions of climate change. A literature review was conducted to identify students' common misconceptions of climate change. Textbooks' conceptual coverage and their ways of presenting scientific conceptions were examined concerning their potential influence on further reinforcing and adding greater confidence to students' misconceptions. Our results indicate that the reviewed textbooks were not designed based on careful consideration of students' common misconceptions of climate change. We made recommendations for improving the conceptual clarity and organization of climate change concepts in Earth and environmental science textbooks.

]]> Soyoung Choi et al. Shear-wave birefringence and current configuration of converging lithosphere under Tibet http://docs.lib.purdue.edu/easpubs/36 http://docs.lib.purdue.edu/easpubs/36 Thu, 14 Mar 2013 14:30:41 PDT New data from west-central Tibet show that birefringence of S-waves has two pronounced increases in magnitude toward the hinterland. Null birefringence persists to about 75 km north of the Indus–Yarlung suture (IYS) between the Indian shield and the Lhasa terrane of southern Tibet. A second, rapid increase occurs about 100 km farther north of the Bangong–Nujiang sutures between the Lhasa terrane and the Qiangtang terrane in central Tibet. The latter feature is consistently observed along three long transects that collectively span a lateral (orogen-parallel) distance of about 600 km and is likely to mark the northern, leading edge of sub-horizontally advancing mantle lithosphere of the Indian shield (the “Greater India”) — an interpretation consistent with the latest results of finite-frequency tomography using both P- and S-wave travel-times, previous results of modeling gravity anomalies, and a host of other seismic observations. Similarly, complementary constraints indicate that the sudden onset of significant birefringence north of the IYS is likely to be the southern termination of Eurasian mantle lithosphere. Curiously, the shortest of three transects showed null birefringence through much of the Lhasa terrane, a pattern inconsistent with those of He isotopes and gravity.

]]> Wang-Ping Chen et al. A Proposed Model-Based Methodology for Feature-Specific Prediction for High-Impact Weather http://docs.lib.purdue.edu/easpubs/34 http://docs.lib.purdue.edu/easpubs/34 Thu, 14 Mar 2013 14:30:40 PDT A feature-specific forecasting method for high-impact weather events that takes advantage of high-resolution numerical weather prediction models and spatial forecast verification methodology is proposed. An application of this method to the prediction of a severe convective storm event is given.

]]> Jacob R. Carley et al. Effectiveness of best management practices in improving water quality in a pasture-dominated watershed http://docs.lib.purdue.edu/easpubs/35 http://docs.lib.purdue.edu/easpubs/35 Thu, 14 Mar 2013 14:30:40 PDT The nonpoint source pollution problem can be controlled by implementing various best management practices (BMPs) in the watershed. However, before such practices are adopted, their effectiveness at various spatial and temporal scales must be evaluated. The objective of this research was to evaluate a suite of BMPs in a pasture-dominated watershed in their effectiveness at controlling nutrient losses. A total of 171 different BMP combinations incorporating grazing and pasture management, riparian and buffer zones, and poultry litter applications were evaluated for their effectiveness using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was parameterized using detailed farm and watershed-scale data. The stochasticity in weather was captured by generating 250 various possible weather realizations for a 25-year period, using measured historical climate data for the watershed. Model results indicated that losses of both total nitrogen, mineral phosphorus, and total phosphorus increased with an increase in litter application rates. For the same application rates, greatest losses were predicted for fall application timings compared to spring and summer applications. Overgrazing resulted in greater nutrient losses compared to baseline conditions for all application rates, timings, and litter characteristics, indicating that overgrazing of pasture areas must be avoided if any improvement in the water quality is to be expected. Variability in weather conditions significantly affected BMP performance; under certain weather conditions, an increase in pollutant losses can be greater than reductions due to BMPs implemented in the watershed. Buffer strips and grazing management were two most important BMPs affecting the losses of total nitrogen and total phosphorus from the pasture areas.

]]> Indrajeet Chaubey et al. Triggering of New Madrid seismicity by late-Pleistocene erosion http://docs.lib.purdue.edu/easpubs/33 http://docs.lib.purdue.edu/easpubs/33 Thu, 14 Mar 2013 14:30:39 PDT Eric Calais et al. Spontaneous transition to superrotation in warm climates simulated by CAM3 http://docs.lib.purdue.edu/easpubs/32 http://docs.lib.purdue.edu/easpubs/32 Thu, 14 Mar 2013 14:30:38 PDT Recent paleoclimate proxy reconstructions show that tropical surface temperatures may have been as high as 35°–40°C in the Early Cenozoic. Here, we study the tropical atmospheric circulation's response to temperatures in this range using a full-complexity atmospheric general circulation model (AGCM). We find that when equatorial surface temperatures exceed ∼33°C, the model undergoes a transition to equatorial superrotation, a state with strong annual- and zonal-mean westerlies on the equator. The transition is driven by zonal momentum convergence due to large-amplitude transient eddies on the equator. These eddies have a structure similar to the observed Madden-Julian Oscillation (MJO). The model's MJO variability is weaker than observed when simulating the modern climate but increases sharply with temperature, coming to dominate the tropical variability and mean state of the warmest climates.

]]> Rodrigo Caballero et al. Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone http://docs.lib.purdue.edu/easpubs/31 http://docs.lib.purdue.edu/easpubs/31 Thu, 14 Mar 2013 14:30:37 PDT A first-order process in the growth of continents is the collision and accretion of terranes against continental margins. Collision leads to the formation of a suture zone between the accreted terrane and the former continental margin. New insights on the suturing process are observed from two receiver function transects across the Mesozoic Alaska Range suture zone. Three distinct crustal sections are identified from observations of crustal thickness, intracrustal discontinuities, and Vp/Vs: a northern section with ∼27 km thick crust of felsic to intermediate composition, a central section that is ∼37 km thick that exhibits intracrustal discontinuities and has felsic to intermediate composition, and a southern section that is ∼30 km thick and has a more mafic composition. We interpret these sections to correspond with the former continental margin (Yukon composite terrane), the suture zone proper, and the allochthonous oceanic terrane (Wrangellia composite terrane). The boundary between the Yukon composite terrane and the suture zone appears to be a subhorizontal discontinuity that accommodated underthrusting of crust from the suture zone beneath the former continental margin. The boundary between the suture zone and the Wrangellia composite terrane, in contrast, appears to be a relatively discrete, vertical boundary. The observed variability in the crust across the Alaska Range suture zone is likely controlled by the differing compositions of the terranes involved, which influences how each section responds to precollisional, syncollisional, and postcollisional deformation.

]]> Patrick P. K. Brennan et al. Dietary and physiological controls on the hydrogen and oxygen isotope ratios of hair from mid-20th century indigenous populations http://docs.lib.purdue.edu/easpubs/30 http://docs.lib.purdue.edu/easpubs/30 Thu, 14 Mar 2013 14:30:37 PDT A semimechanistic model has recently been proposed to explain observed correlations between the H and O isotopic composition of hair from modern residents of the USA and the isotopic composition of drinking water, but the applicability of this model to hair from non-USA and preglobalization populations is unknown. Here we test the model against data from hair samples collected during the 1930s–1950s from populations of five continents. Although C and N isotopes confirm that the samples represent a much larger range of dietary “space” than the modern USA residents, the model is able to reproduce the observed δ2H and δ18O values given reasonable adjustments to 2 model parameters: the fraction of dietary intake derived from locally produced foods and the fraction of keratin H fixed during the in vivo synthesis of amino acids. The model is most sensitive to the local dietary intake, which appears to constitute between 60% and 80% of diet among the groups sampled. The isotopic data are consistent with a trophic-level effect on protein H isotopes, which we suggest primarily reflects mixing of 2H-enriched water and 2H-depleted food H in the body rather than fractionation during biosynthesis. Samples from Inuit groups suggest that humans with marine-dominated diets can be identified on the basis of coupled δ2H and δ18O values of hair. These results indicate a dual role for H and O isotopic measurements of keratin, including both biological (diet, physiology) and environmental (geographic movement, paleoclimate) reconstruction. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc.

]]> Gabriel J. Bowen et al. Isoscapes: Spatial Pattern in Isotopic Biogeochemistry http://docs.lib.purdue.edu/easpubs/29 http://docs.lib.purdue.edu/easpubs/29 Thu, 14 Mar 2013 14:30:36 PDT Isotope ratios of actively cycled elements vary as a function of the biogeochemical processes in which they participate and the conditions under which those processes occur. The resultant spatiotemporal distribution of isotopes in environmental materials can be predicted using models of isotope-fractionating processes and data describing environmental conditions across space and time, and it has been termed an isoscape, or isotopic landscape. Analysis of isoscapes and comparison of isoscape predictions with observational data have been used to test biogeochemical models, calculate aerially integrated biogeochemical fluxes based on isotope mass balance, and determine spatial connectivity in biogeochemical, ecological, and anthropological systems. Isoscape models of varying quality are available for stable H, C, N, and O isotopes in a range of Earth surface systems, but significant opportunities exist to refine our understanding of biogeochemical cycles and our ability to predict isoscapes through the development of more mechanistic and more comprehensive isoscape models.

]]> Gabriel J. Bowen Geochemical characteristics of naturally acid and alkaline saline lakes in southern Western Australia http://docs.lib.purdue.edu/easpubs/28 http://docs.lib.purdue.edu/easpubs/28 Thu, 14 Mar 2013 14:30:36 PDT Abundant shallow saline lakes on the Archean Yilgarn Craton in southern Western Australia exhibit a rare spectrum of geochemical conditions. Here the field geochemistry over three seasons (pH, salinity, and temperature), as well as major ions, trace elements, and H, O, and S stable isotopes of surface waters and shallow groundwaters from 59 ephemeral lakes in southern Western Australia (WA) are reported. Approximately 40% of the lakes and 84% of the measured groundwaters in WA are extremely acidic (pH < 4) and pHs are observed as low as 1.7. The salinity of lake waters and groundwaters ranges from rare freshwaters to common saline waters and brines with total dissolved solids >28%. The fluids are typically Na–Cl to Na–Mg–Cl–SO4 brines with variable yet locally high amounts of Ca, K, Al, Fe, Si, and Br. The acid brine fluid compositions are unusual. For example, in some fluids the amount of Al≫Ca, the amount of Br > K, and comparison of total S to

]]> Brenda Beitler. Bowen et al. Milankovitch and sub-Milankovitch forcing of the Oxfordian (Late Jurassic) Terres Noires Formation (SE France) and global implications http://docs.lib.purdue.edu/easpubs/27 http://docs.lib.purdue.edu/easpubs/27 Thu, 14 Mar 2013 14:30:35 PDT High-resolution analysis (2277 samples) of magnetic susceptibility (MS) was performed on ∼700-m-thick Early–Middle Oxfordian marine marls of the Terres Noires Formation, SE France. MS variations within these sediments record sub-Milankovitch to Milankovitch frequencies with long-term eccentricity (405 kyr and ∼2 Myr) being the most prominent. The 405 kyr cycle was used as a high-resolution geochronometer for astronomical calibration of this poorly constrained interval of Late Jurassic time. The estimated duration of this Early–Middle Oxfordian interval concurs with the current International Geologic Time Scale GTS2004 (∼4 Myr), but the estimated durations of the corresponding ammonite zones are notably different. The calibration improves the resolution and accuracy of the M-sequence magnetic anomaly block model that was previously used to establish the Oxfordian time scale. Additionally, the 405 kyr cyclicity is linked to third-order sea-level depositional sequences observed for Early–Middle Oxfordian time. Strong ∼2 Myr cycles are consistent with long-term eccentricity modulation predicted for the Late Jurassic. These cycles do not match second-order sequences that have been documented for European basins; this raises questions about the definition and hierarchy of depositional sequences in the Mesozoic eustatic chart. Our results require substantial revisions to the chart, which is frequently used as a reference for the correlation of widely separated palaeogeographic domains. Finally, a long-term trend in the MS data reflects a progressive carbonate enrichment of the marls expressing an Early Oxfordian global cooling followed gradually by a warming in the Middle Oxfordian. This trend also records a major transgressive interval likely peaking at the Transversarium ammonite zone of the Middle Oxfordian.

]]> S. Boulila et al. Some lower bounds in the B. and M. Shapiro conjecture for flag varieties http://docs.lib.purdue.edu/easpubs/25 http://docs.lib.purdue.edu/easpubs/25 Thu, 14 Mar 2013 14:30:34 PDT Monique Azar et al. Imaging spectroscopy of jarosite cement in the Jurassic Navajo Sandstone http://docs.lib.purdue.edu/easpubs/26 http://docs.lib.purdue.edu/easpubs/26 Thu, 14 Mar 2013 14:30:34 PDT Imaging spectroscopy is a powerful tool for mapping surface mineralogy. Interactions of energy and surface materials on atomic and molecular levels result in specific absorption features that are diagnostic of mineralogy. Hyperspectral airborne sensors such as HyMap have sufficient spectral resolution to identify subtle features over narrow wavelength ranges. An anomalous zone of jarosite cement within the Jurassic Navajo Sandstone in southern Utah was identified with airborne hyperspectral data. To date no other locations of sulfate-rich cements such as this have been documented in the Navajo Sandstone. Here, we use multiple spectral analysis techniques over a micro to macro spatial continuum in order to focus our evaluation on the distribution and relative abundance of jarosite in this area. In this study, imaging spectroscopy is used to help determine the extent of the distribution of jarosite [KFe3(SO4)2(OH)6], at “Mollie's Nipple” (MN), a significant geomorphic landmark located within the Grand Staircase-Escalante National Monument, in the Jurassic Navajo Sandstone of south central Utah. The extent of the jarosite across the butte is identified in this study by mapping two diagnostic absorption features, referred to as the ∼ 2.26 μm and near-infrared ferric iron absorption features (∼ 0.70–1.15 μm), independently. This analysis shows that there is a single circular zone of abundant jarosite ∼ 1 km in diameter that includes both in-situ and weathered out accumulations. Jarosite formation requires acidic and sulfate-rich fluids, which are unusual for the Navajo Sandstone. Imaging and field spectroscopy provides the spectral resolution needed to map and analyze the mineralogic characteristics of this area; characteristics that may help constrain the conditions under which this atypical butte formed.

]]> Julianne H. Bell et al. A New Three-Dimensional Visualization System for Combining Aircraft and Radar Data and Its Application to RICO Observations http://docs.lib.purdue.edu/easpubs/23 http://docs.lib.purdue.edu/easpubs/23 Thu, 14 Mar 2013 14:30:33 PDT Dan K. Arthur et al. Suppression of south Asian summer monsoon precipitation in the 21st century http://docs.lib.purdue.edu/easpubs/24 http://docs.lib.purdue.edu/easpubs/24 Thu, 14 Mar 2013 14:30:33 PDT We used a high-resolution nested climate modeling system to investigate the response of South Asian summer monsoon dynamics to anthropogenic increases in greenhouse gas concentrations. The simulated dynamical features of the summer monsoon compared well with reanalysis data and observations. Further, we found that enhanced greenhouse forcing resulted in overall suppression of summer precipitation, a delay in monsoon onset, and an increase in the occurrence of monsoon break periods. Weakening of the large-scale monsoon flow and suppression of the dominant intraseasonal oscillatory modes were instrumental in the overall weakening of the South Asian summer monsoon. Such changes in monsoon dynamics could have substantial impacts by decreasing summer precipitation in key areas of South Asia.

]]> Moetasim Ashfaq et al. Estimating methane emissions from northern lakes using ice-bubble surveys http://docs.lib.purdue.edu/easpubs/22 http://docs.lib.purdue.edu/easpubs/22 Thu, 14 Mar 2013 14:30:32 PDT The magnitude and variability in methane (CH4) emissions from lakes are uncertain due to limitations in methods for quantifying the patchiness of ebullition (bubbling). We present a field method to estimate an important and highly uncertain source: ebullition from northern lakes. We defined four classes of CH4 bubble clusters trapped in lake ice representing distinct types of biogenic ebullition seeps that differed in flux rate. Mean annual ebullition determined through long-term (up to 700 d) continuous flux measurements of 31 seeps in three Siberian and one Alaskan lake was (mean ± standard error, 4-10 seeps per class; g CH4 seep –1 y –1): A, 6 ± 4; B, 48 ± 11; C, 354 ± 52; Hotspot, 1167 ± 177. Discrete-seep ebullition comprised up to 87% of total emissions from Siberian lakes when diffusive flux and background and seep ebullition were considered together. Including seep ebullition increased previous estimates of lake CH4 emissions based on traditional methods 5- to 8-fold for Siberian and Alaskan lakes. Linking new ebullition estimates to an established biogeochemical model, the Terrestrial Ecosystem Model, increased previous estimates of regional terrestrial CH4 emissions 3- to 7-fold in Siberia. Assessment of the method revealed that ebullition seeps are an important component of the terrestrial CH4 budget. They are identifiable by seep type by independent observers; they are consistent predictors of flux rate in both Siberia and Alaska; and they allow quantification of what was previously a large source of uncertainty in upscaling CH4 emissions from lakes to regions.

]]> Katey W. Anthony et al. Developing a process model for visual penetrative ability http://docs.lib.purdue.edu/easpubs/20 http://docs.lib.purdue.edu/easpubs/20 Thu, 14 Mar 2013 14:30:31 PDT Visual penetrative ability (VPA) is a basic skill for any geology undergraduate student and is also required in many introductory laboratory exercises designed for nonmajors. This is the ability to visualize the three-dimensional (3-D) underground structure of folded sedimentary rocks from two-dimensional (2-D) surface clues. This study seeks to understand the origins of difficulties that introductory geology students encounter with this task. Problem-solving interviews were conducted with students representing the range of performance on the GeoSAT, a semiquantitative instrument designed to measure VPA. We conducted think-aloud, discursive interviews where participants solved similar 3-D visualization tasks. The interviewers interacted with participants to probe their problem-solving difficulties and thought processes while they were working. Analysis of interviews and videotapes of student gestures yielded insight into the nature of the difficulties faced by students in solving this style of spatial problem, and explained the origin of many of the common incorrect responses seen by previous workers using the GeoSAT. Students with high VPA appear to rapidly construct a 3-D internal visual model, and readily produced gestures and physical expressions illustrating their spatial understanding. Students with poor VPA tend to view external information as merely a type of "gift wrapping" over the cubic volume and do not perceive the internal structure. They also do not typically address spatial concepts through physical expression. We construct a process model for VPA that describes the origin of commonly observed errors at crucial steps, and associated accommodation strategies used by students struggling with spatial visualization of this type.

]]> Mathew Alles et al. Flat-slab subduction and crustal models for the seismically active Sierras Pampeanas region of Argentina http://docs.lib.purdue.edu/easpubs/21 http://docs.lib.purdue.edu/easpubs/21 Thu, 14 Mar 2013 14:30:31 PDT Patricia Alvarado et al. Mammalian biodiversity on Madagascar controlled by ocean currents http://docs.lib.purdue.edu/easpubs/18 http://docs.lib.purdue.edu/easpubs/18 Thu, 14 Mar 2013 14:30:30 PDT Madagascar hosts one of the world’s most unusual, endemic, diverse and threatened concentrations of fauna1. To explain its unique, imbalanced biological diversity, G. G. Simpson proposed the ‘sweepstakes hypothesis’, according to which the ancestors of Madagascar’s present-day mammal stock rafted there from Africa2. This is an important hypothesis in biogeography and evolutionary theory for how animals colonize new frontiers1, 3, 4, 5, but its validity is questioned5, 6, 7, 8, 9. Studies suggest that currents were inconsistent with rafting to Madagascar9 and that land bridges provided the migrants’ passage5, 6, 7, 8. Here we show that currents could have transported the animals to the island and highlight evidence inconsistent with the land-bridge hypothesis. Using palaeogeographic reconstructions and palaeo-oceanographic modelling, we find that strong surface currents flowed from northeast Mozambique and Tanzania eastward towards Madagascar during the Palaeogene period, exactly as required by the ‘sweepstakes process’. Subsequently, Madagascar advanced north towards the equatorial gyre and the regional current system evolved into its modern configuration with flows westward10 from Madagascar to Africa. This may explain why no fully non-aquatic land mammals have colonized Madagascar since the arrival of the rodents and carnivorans during the early-Miocene epoch. One implication is that rafting may be the dominant means of overseas dispersal in the Cenozoic era when palaeocurrent directions are properly considered.

]]> Jason R. Ali et al. Contemporary deformation and stressing rates in Southern Alaska http://docs.lib.purdue.edu/easpubs/19 http://docs.lib.purdue.edu/easpubs/19 Thu, 14 Mar 2013 14:30:30 PDT Syed Tabrez Ali et al. Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches http://docs.lib.purdue.edu/easpubs/17 http://docs.lib.purdue.edu/easpubs/17 Thu, 14 Mar 2013 14:30:29 PDT Tile drainage is a common water management practice in many agricultural landscapes in the Midwestern United States. Drainage ditches regularly receive water from agricultural fields through these tile drains. This field-scale study was conducted to determine the impact of tile discharge on ambient nutrient concentration, nutrient retention and transport in drainage ditches. Grab water samples were collected during three flow regimes for the determination of soluble phosphorus (SP), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3-N) concentrations and their retention in three drainage ditches. Measured nutrient concentration indicated lower SP and NH4+-N, and greater NO3-N concentrations in tile effluents compared to the ditch water. Net uptake lengths were relatively long, especially for NO3-N, indicating that nutrients were generally not assimilated efficiently in these drainage systems. Results also indicated that the study reaches were very dynamic showing alternating increases or decreases in nutrient concentration across the flow regimes. The drainage ditches appeared to be nutrient-rich streams that could potentially influence the quality of downstream waters. --------------------------------------------------------------------------------

]]> L. M. Ahiablame et al. An Extended Solar Cycle 23 with Deep Minimum Transition to Cycle 24: Assessments and Climatic Ramifications http://docs.lib.purdue.edu/easpubs/15 http://docs.lib.purdue.edu/easpubs/15 Thu, 14 Mar 2013 14:30:28 PDT The extended length of solar cycle 23 and the associated deep quiet period (QP) between cycles 23 and 24 have been examined using the international sunspot record from 1755 to 2010. This study has also introduced a QP definition based on a (beginning and ending) mean monthly threshold value of less than 10 for the sunspot number. Features addressed are the length and intensity of cycle 23, the length of the QP and the associated number of spotless days, and the respective relationships between cycle intensity, length, and QP. The length of cycle 23 (153 months) is second only to cycle 4 (164 months), with an average of 132.5 months for the 11-yr cycle. The length of the QP between cycles 23 and 24 ranks eighth, extending from October 2005 through November 2009 (but subject to continued weakness in cycle 24). The number of spotless days achieved within this QP was 751 (and for all days within the transition from cycle 23 to cycle24, a record number of 801 spotless days had been observed through May 2010). Shortcomings of solar-convection-model predictions of sunspot activity and intensity are also noted, including the failure in the initial predictions of cycle-24 onset. The relevance of an extended quiet solar period and the potential reduction of total solar irradiance (TSI) are also discussed, both in the context of climate-model simulations of future climate change as well as with regard to future satellite measurements of TSI.

]]> Ernest M. Agee et al. Nutrient Content at the Sediment-Water Interface of Tile-Fed Agricultural Drainage Ditches http://docs.lib.purdue.edu/easpubs/16 http://docs.lib.purdue.edu/easpubs/16 Thu, 14 Mar 2013 14:30:28 PDT Extensive network of tile drains present in the Midwest USA accelerate losses of nutrients to receiving ditches, rivers and eventually to the Gulf of Mexico. Nutrient inputs from agricultural watersheds and their role in affecting water quality have received increased attention recently; however, benthic sediment-nutrient interactions in tile-fed drainage ditches is still a matter of active research in consideration to nutrient discharge from tile drains. In this study, phosphorus (P) and nitrogen (N) contents and variability of nutrient retention ability of benthic sediments upstream and downstream from tile drain outlets were evaluated in managed agricultural drainage ditches in Indiana. Sediment samples were collected every three months upstream and downstream from selected tile drains in three ditches in northwest Indiana. Sediment equilibrium P concentrations (EPC0) were measured to examine P adsorption-desorption and equilibrium characteristics of benthic sediments in the ditches. P sorption index (PSI), exchangeable P (ExP), and exchangeable NH4+-N (ExN) were measured to evaluate nutrient retention ability and readily available nutrient content of benthic sediments. Results indicated a dynamic interaction between benthic sediment and overlying water column where sediments were acting as a sink or a source of P. There were no differences in nutrient retention ability between sediments collected upstream and sediments collected downstream from the selected tile drains. While the data, except for ExN, was comparable to reported values by previous studies in Indiana’s drainage ditches, there was no particular seasonal pattern in the content of exchangeable nutrient content in sediments at all three sites. This study also suggested that nutrient uptake by benthic sediments in these drainage ditches is not always efficient; therefore watershed management should focus on minimizing the delivery of nutrients into ditches while maintaining their drainage functionality.

]]> Laurent Ahiablame et al. High-CO2 cloud radiative forcing feedback over both land and ocean in a global climate model http://docs.lib.purdue.edu/easpubs/14 http://docs.lib.purdue.edu/easpubs/14 Thu, 14 Mar 2013 14:30:27 PDT A positive feedback on high-latitude winter marine climate change involving convective clouds has recently been proposed using simple models. This feedback could help explain data from equable climates, e.g., the Eocene, and might be relevant for future climate. Here this convective cloud feedback is shown to be active in an atmospheric GCM in modern configuration (CAM) at CO2 = 2240 ppm and in a coupled GCM in Eocene configuration (CCSM) at CO2 = 560 ppm. Changes in boundary conditions that increase surface temperature have a similar effect as increases in CO2 concentration. It is also found that the high-latitude winter cloud radiative forcing over land increases with increases in surface temperature due to either increased CO2 or changes in boundary conditions, which could represent an important part of the explanation for warm continental interior winter surface temperatures during equable climates. This is due to increased low-level layered clouds caused by increased relative humidity.

]]> Dorian S. Abbot et al. Transpressional rupture of an unmapped fault during the 2010 Haiti earthquake http://docs.lib.purdue.edu/easpubs/13 http://docs.lib.purdue.edu/easpubs/13 Thu, 14 Mar 2013 14:10:16 PDT E. Calais et al.