Arctic has undergone unexpectedly warm periods, core data shows
New data from a core drilled into a Russian lake provide the longest continuous record of Arctic conditions and show that the pole had periods of unexpectedly high temperatures and rainfall, much higher than researchers thought possible. The warm periods may have melted most of the Arctic ice sheet and coincide with periods when parts of the Antarctic were also ice-free and warm, researchers said Thursday. The findings indicate that climate changes at the two poles are more closely linked than expected and that the polar regions are much more vulnerable to change than had been expected.
An international team of researchers drilled a core more than 444 feet into the bed of Lake El’gygytgyn -- pronounced El’gee-git-gin, but generally called just Lake E -- in northeastern Russia about 60 miles north of the Arctic Circle. Lake E was formed about 3.6 million years ago by a meteor that hit the region, leaving an 11-mile wide crater that has since been filling with sediment. The region is not glaciated, so the bottom of the lake has not been disturbed. The core yielded data about conditions in the region for the last 2.8 million years, almost 30 times as long as the 110,000 years covered by cores drilled in the Arctic ice sheets.
Individual layers of the core can be dated from magnetic field data left behind by the regular shifts in the Earth’s magnetic field. Data from pollen yields information about annual temperatures and rainfall.
Researchers know that there have been recurring periods of higher temperatures and increased rainfall in the Arctic, called interglacials, but those have been relatively modest, involving temperature increases of a couple of degrees Fahrenheit. The team reported in the journal Science that they found periods with much more extreme changes, which they called super interglacials.
They found that temperatures in two of the super interglacials, one 400,000 years ago and one 1.1 million years ago, were as much as 9 degrees Fahrenheit warmer than during normal interglacials about 12,000 and 125,000 years ago. There was also about 12 inches more rainfall during the super interglacials. With such increased temperatures and rainfall, the team said,Greenland’sice sheet could not have existed in its current form.
Simulations using state-of-the-art computer climate models show that neither changes in the Earth’s orbit nor high levels of greenhouse gases could produce such changes alone.
The team compared their results to those from the Antarctic Geological Drilling Project and found that periods when the West Antarctic ice sheet melted coincided with the super interglacials in the Arctic. They offered two potential explanations for how the two polar regions could be connected:
First, reduced glacial ice cover and loss of ice shelves in Antarctica could have limited formation of cold bottom water masses that flow into the North Pacific Ocean and upwell to the surface. Fewer movements of such masses could lead to warmer surface waters, higher temperatures and increased precipitation on land.
A second possibility, they say, is that disintegration of the West Antarctic ice sheet may have led to significant increases in global sea level, allowing more warm surface waters to reach the Arctic Ocean through the Bering Strait.
Whatever the cause, they concluded, it is clear we need to learn much more about the Earth’s climatic past.
The El’gygytgyn Drilling Project is part of the International Continental Drilling Project sponsored by the U.S., Germany, Austria and Russia.
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