Arctic could be ice-free in future
Washington: Analyses of the longest continental sediment core ever collected in the Arctic has provided "absolutely new knowledge" of Arctic climate from 2.2 to 3.6 million years ago.
Results of analyses by an international team led by Julie Brigham-Grette of the University of Massachusetts Amherst provides "an exceptional window into environmental dynamics" and 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 data for the study came from analyzing sediment cores collected in the winter of 2009 from ice-covered Lake El'gygytgyn, the oldest deep lake in the northeast Russian Arctic, located 100 km north of the Arctic Circle.
It was formed 3.6 million years ago when a meteorite, perhaps a kilometer in diameter, hit the Earth and blasted out an 11-mile (18 km) wide crater.
It lies in one of the few Arctic areas not eroded by continental ice sheets during ice ages, so a thick, continuous sediment record was left remarkably undisturbed and cores from Lake E reach back in geologic time nearly 25 times farther than Greenland ice cores that span only the past 140,000 years.
The study authors said that one of their 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.
They said that this could tell 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.
Important to the story are the fossil pollen found in the core, including Douglas fir and hemlock. These allow the reconstruction of vegetation around the lake in the past, which in turn paints a picture of past temperatures and precipitation.
Another significant finding is documentation of sustained warmth in the Middle Pliocene, with summer temperatures of about 59 to 61 degrees F [15 to 16 degrees C], about 14.4 degrees F [8 degrees C] warmer than today, and regional precipitation three times higher.
Brigham-Grette said that their team shows that the 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 Ant arctic Ice Sheet did not exist.
Brigham-Grette said that the Lake E cores provide a terrestrial perspective on the stepped pacing of several portions of the climate system through the transition from a warm, forested Arctic to the first occurrence of land ice, and the eventual onset of major glacial/interglacial cycles.
Co-author Pavel Minyuk of Russia's Northeast Interdisciplinary Scientific Research Institute notes that they also observed a major drop in Arctic precipitation at around the same time large Northern Hemispheric ice sheets first expanded and ocean conditions changed in the North Pacific.
The sediment core also reveals that even during the first major "cold snap" to show up in the record 3.3 million years ago, temperatures in the western Arctic were similar to recent averages of the past 12,000 years.
The authors added that 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 study has been published in Science.