Earth & Environment - Posted by Vince Stricherz-UW on Tuesday, June 26, 2012 10:43 - 0 Comments
Sediment core reveals Arctic warm spells
U. WASHINGTON (US) — The Arctic has gone through intensely warm periods—warmer than scientists thought was possible—in the last 2.8 million years, new research shows.
The extreme interglacial warm periods correspond to times when parts of Antarctica were ice-free and warm, indicating a strong climate connection between the northern and southern hemispheres.
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The findings, which stem from examination of the longest sediment core ever collected on land in the Arctic, show that the polar regions are much more vulnerable to change than previously thought, say the three lead scientists on the project, Martin Melles of the University of Cologne in Germany, Julie Brigham-Grette of the University of Massachusetts Amherst, and Pavel Minyuk of Russia’s North-East Interdisciplinary Scientific Research Institute in Magadan.
The core was collected in 2009 from under ice-covered Lake El’gygytgyn in the northeast Russian Arctic. “Lake E,” as it is known, formed 3.6 million years ago after a meteorite gouged an 11-mile-wide crater, and it has collected layers of sediment since then. The cores stretch nearly 30 times farther back in time than ice cores from Greenland that cover the last 110,000 years.
The scientists suspect that the trigger for intense interglacials might actually be in Antarctica. Earlier research found recurring periods when the West Antarctic Ice Sheet melted, and the new study shows that some of those events match very well with the pronounced interglacial warm periods in the Arctic.
In the paper, they discuss four warm phases in detail; two of the oldest warm interglacials from about 1.1 million years ago and 400,000 years ago, and two of the youngest from 125,000 and about 12,000 years ago.
Pollen-based climate reconstructions suggest that summer temperatures during the exceptional interglacial periods were about 7 to 9 degrees F warmer and annual precipitation about 12 inches wetter than in other interglacials, the scientists say.
Modeling and other tests suggest it is virtually impossible that Greenland’s ice sheet existed in its present form during those times.
Anderson, a paleoecologist who studies pollen and spores to interpret past vegetation and climate, teamed with Anatoly V. Lozhkin of the Russian Academy of Sciences Far East Branch to provide the pollen data, which served as a basis for paleoclimate reconstructions included in the Science paper.
“These pollen data provide the first records that are definitively from warm periods of about 400,000 and 1.1 million years ago,” she says. “They also provide the first quantitative temperature and precipitation estimates for these intervals for the region.”
Despite differences in interglacial vegetation types during periods of different climate conditions, the transition from glacial to interglacial climates is marked by the same vegetation response—establishment of plant communities dominated by deciduous species, particularly birch, Anderson says.
The pattern suggests that with continued global warming, evergreen conifers may not simply move northward as intact communities but rather that tundra regions will become dominated by deciduous trees or shrubs, including birch, alder, and willow.
The work was funded by the International Continental Scientific Drilling Program, the National Science Foundation, the German Federal Ministry for Education and Research, the Alfred Wegener Institute, GeoForschungsZentrum-Potsdam, the Russian Academy of Sciences Far East Branch, the Russian Foundation for Basic Research, and the Austrian Ministry for Science and Research.
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