Thursday 21 June 2012

Arctic once had extreme warm periods: study


The team lead by Martin Melles of the University of Cologne, Germany, drilled into an iced-over lake formed by a meteorite collision on

the Chukchi Peninsula in Siberia for the longest residue core still collected in the terrestrial Arctic.

Since the meteorite strike an area of Lake El’gygytgyn that was not battered by glaciers, the sediment record reaches back nearly 30 times further in time than ice core from Greenland that cover the history 110,000 years.

The sediment reveals periods of extreme warmness that show the polar regions are much more vulnerable to change than previously consideration, and are difficult to explain by greenhouse gases alone, said the study in the periodical Science.

Scientists have long known that the Arctic went from side to side climate cycles, but the latest research shows some of these warm phases were “outstanding,” with temperatures four to five degrees Celsius (7.2 to nine degrees Fahrenheit) warmer and 12 inches (30 centimeters) wetter than through normal interglacials, the study supposed.

Two of these “super-interglacials” happened about 400,000 years before and 1.1 million years ago, and the data suggest it was almost impossible for Greenland’s ice sheet to have existed in its present form at those times.

But just what caused these great changes remains a mystery.

Since some of the Arctic changes echo variations in the Antarctic discovered by preceding studies, events at one pole may have triggered events at the other, the researchers supposed.

One possibility is that abridged ice cover in Antarctica led to less cold bottom water mass in the northern Pacific, triggering heater surface waters, higher temperatures and more rainfall.

Another is that the dissolving Antarctic ice piece led to global sea level rise that sent warm water rushing into the Arctic Ocean, the study supposed.

Co-authors of the learn included expert from the University of Massachusetts and the Far East Branch of the Russian Academy of Sciences.

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