Cosmogenic radionuclides in precipitation
Abstract
A combination of three-hundred and fifty event and sub-event ($\sim$3 mm resolution) ground level precipitation samples were collected near West Lafayette, IN. They included most of the significant precipitation events occurring between April 18, 1992 and August 31, 1993. The cosmogenic radionuclide ($\rm\sp7Be(t\sb{1/2} = 53 d),\ \sp{10}Be(t\sb{1/2} = 1.5\ My),\ and\ \sp{36}Cl(t\sb{1/2} = 0.3\ My)),\ anion\ (Cl\sp-,\ NO\sb3\sp-,\ SO\sb4\sp{2-}),\ and\ cation\ (Na\sp+,\ K\sp+,\ Mg\sp{2+},\ and\ Ca\sp{2+})$ concentrations were measured in selected samples. Accelerator mass spectrometry was used to determine the $\rm\sp{10}Be\ and\ \sp{36}Cl$ content. We used these data along with other standard meteorological data bases to investigate relationships between the cosmogenic radionuclides in mid-latitude wet deposition and storm type, air mass history, and season. Understanding the circumstances that lead to local variations in the ratio of $\rm\sp{10}Be\ to\ \sp{36}Cl$ should aid other investigators in unlocking information stored in form of this ratio in the ice sheets, and thereby gain a better understanding of paleoclimates. In addition, the source functions for these radionuclides and how they vary with differing meteorological conditions are needed for ground water ($\rm\sp{36}Cl)$ and erosion rate ($\rm\sp{10}Be)$ studies. A departure from the $\rm\sp{10}Be/\sp{36}Cl$ ratio of 40 predicted by Lal et al. 1967 is seen. Using a new semiempirical cross section formula, we estimated the production ratio to be $\sim$9. Our mean $\rm\sp{10}Be/\sp{36}Cl$ ratio is 11.4 and typically varies from 4 to 40. We see a higher mean $\rm\sp{10}Be/\sp{36}Cl$ ratio in stratiform precipitation (14), and a lower mean ratio in convective precipitation (9.7). The estimated $\rm\sp{10}Be$ flux from re-suspended soil is 10% of the total $\rm\sp{10}Be$ flux.
Degree
Ph.D.
Advisors
Elmore, Purdue University.
Subject Area
Physics|Hydrology|Geochemistry|Atmosphere
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