Increased seasonality through the Eocene to Oligocene transition in northern high latitudes


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.

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