An international team of scientists, led by Julie Brigham-Grette of the University of Amherst, has analyzed the longest continental sediment core ever collected in the Arctic to provide “absolutely new knowledge” of Arctic climate from 2.2 million to 3.6 million years ago.
“While existing geologic records from the Arctic contain important hints about this time period, what we are presenting is the most continuous archive of information about past climate change from the entire Arctic borderlands. As if reading a detective novel, we can go back in time and reconstruct how the Arctic evolved with only a few pages missing here and there,” says Brigham-Grette.
The results of this study, published in Science, provide “an exceptional window into environmental dynamics” never before possible. Brigham-Grette claims that their findings have “major implications for understanding how the Arctic transitioned from a forested landscape without ice sheets to the ice- and snow-covered land we know today.”
The sediment cores used in this study were collected in the winter of 2009 from ice-covered Lake El’gygytgyn, the oldest deep lake in the northeast Russian Arctic. “Lake E”, located 62 miles north of the Arctic Circle, was formed 3.6 million years ago when a meteorite of approximately a half mile in diameter hit the Earth, blasting out an 11-mile wide crater. Fortunately for geologists, the lake lies in one of the few Arctic areas not eroded by continental ice sheets during the ice ages. This leaves a thick, continuous sediment record remarkably undisturbed along the lake bed. Cores obtained from Lake E reach nearly 25 times farther back in geologic time than the Greenland ice cores, which only span the past 140,000 years.
“One of our major findings is that the Arctic was very warm in the middle Pliocene and Early Pleistocene [~ 3.6 to 2.2 million years ago] when others have suggested atmospheric CO2 was not much higher than levels we see today. This could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier climate models,” stated Brigham-Grette.
The team also found that the cores supplied documentation of sustained warmth in the middle Pliocene, with summer temperatures of about 59 to 61 degrees Fahrenheit – approximately 14.4 degrees Fahrenheit warmer than today. Regional precipitation was about three times higher than now, as well.
“We show that this exceptional warmth well north of the Arctic Circle occurred throughout both warm and cold orbital cycles and coincides with a long interval of 1.2 million years when other researchers have shown the West Antarctic Ice Sheet did not exist,” Brigham-Grette notes. This indicates that while both poles share some common history, the pace of change differed between them.
Research teams on the project were led by Martin Melles of the University of Cologne and Pavel Minyuk of Russia’s Northeast Interdisciplinary Scientific Research Institute, Magadan, while the modeling efforts were led by Robert DeConto, at UMass Amherst. Collaborators at the universities of Bern and Cologne performed ecosystem reconstructions which were compared to the data of both the research teams and the modeling team.
Brigham-Grette says the Lake E cores provide a terrestrial perspective on the stepped pacing of several portions of the climate system. The cores demonstrate the transition from a warm, forested Arctic to the first occurrence of land ice and the eventual onset of major glacial/interglacial cycles. “It is very impressive that summer temperatures during warm intervals even as late as 2.2 million years ago were always warmer than in our pre-Industrial reconstructions.”
The team also observed a major drop in Arctic precipitation at around the same time large Northern Hemispheric ice sheets first expanded, according to Minyuk, and ocean conditions changed in the North Pacific. These findings have major implications for understanding what drove the onset of the ice ages.
During the first major “cold snap” to show up in the record 3.3 million years ago, the sediment core also revealed that temperatures in the western Arctic were similar to recent averages of the past 12,000 years. “Most importantly, conditions were not ‘glacial,’ raising new questions as to the timing of the first appearance of ice sheets in the Northern Hemisphere,” the authors add.
This is the second article published by the team based on the Lake E project. The first covered the time period from the present to 2.8 million years ago. The most recent paper covers the record from 2.2 to 3.6 million years ago.
Melles says, “This latest paper completes our goal of providing an overview of new knowledge of the evolution of Arctic change across the western borderlands back to 3.6 million years and places this record into a global context with comparisons to records in the Pacific, the Atlantic and Antarctica.”
The findings of the Lake E paleoclimate reconstructions and climate modeling are consistent with estimates made by other research groups, supporting the idea that Earth’s climate sensitivity to CO2 might be higher than suggested by the 2007 Intergovernmental Panel on Climate Change (IPCC). Much of the funding for this project was obtained from the National Science Foundation (NSF).
Note : The above story is reprinted from materials provided by April Flowers for redOrbit