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A profound global climate shift took place at the Eocene-Oligocene transition ( approximately 33.5 million years ago) when Cretaceous/early Palaeogene greenhouse conditions gave way to icehouse conditions. During this interval, changes in the Earth's orbit and a long-term drop in atmospheric carbon dioxide concentrations resulted in both the growth of Antarctic ice sheets to approximately their modern size and the appearance of Northern Hemisphere glacial ice. However, palaeoclimatic studies of this interval are contradictory: although some analyses indicate no major climatic changes, others imply cooler temperatures, increased seasonality and/or aridity. 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 approximately 5 degrees C in cold-month (winter) mean temperatures to 0-2 degrees C, and a concomitant increased seasonality before the Oi-1 glaciation event. These data indicate that a cooling component is indeed incorporated in the delta(18)O 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.

The Eocene and Oligocene epochs (approximately 55 to 23 million years ago) comprise a critical phase in Earth history. An array of geological records supported by climate modelling indicates a profound shift in global climate during this interval, from a state that was largely free of polar ice caps to one in which ice sheets on Antarctica approached their modern size. However, the early glaciation history of the Northern Hemisphere is a subject of controversy. Here we report stratigraphically extensive ice-rafted debris, including macroscopic dropstones, in late Eocene to early Oligocene sediments from the Norwegian-Greenland Sea that were deposited between about 38 and 30 million years ago. Our data indicate sediment rafting by glacial ice, rather than sea ice, and point to East Greenland as the likely source. Records of this type from one site alone cannot be used to determine the extent of ice involved. However, our data suggest the existence of (at least) isolated glaciers on Greenland about 20 million years earlier than previously documented, at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher.

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