The work “identifies for the first time a long, continuous story of that history from the Arctic and what I call the Arctic borderlands,” says Julie Brigham-Grette, a geologist at the University of Massachusetts at Amherst who focuses on the Arctic's ancient climate, referring to adjacent regions. Dr. Brigham-Grette is the lead author of a formal report of the results, which are being published in Friday's issue of the journal Science.
The evidence is captured in a 1,034-foot core sample the team drew from the bottom of Lake El'gygytgyn, known informally as Lake E. It formed 3.6 billion years ago after a meteor punched a crater in Russia's northeastern Arctic. The crater filled to form a lake 7 miles across and some 560 feet deep. The area around the lake managed to remain ice free during the ebb and flow of continental ice sheets during the Pleistocene ice ages, allowing sediment layers – and the pollen and other climate indicators they contain – to build up uninterrupted for the last 3.56 million years.
The team published initial results from the Lake E core last year, focusing on the Pleistocene. This latest effort focuses on the climate from the earlier, mid Pliocene through the onset of the glacial cycles.