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Arctic sea ice at lowest point in thousands of years

Warming at the North Pole caused by the buildup of atmospheric greenhouse gases has reduced the ice that normally covers the Arctic Ocean at its lowest point in a few thousand years, a new study suggests.

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The shrinking amount of sea ice that covers the Arctic Ocean today is the smallest it has been in the last few thousand years, a new study suggests.

The sea ice that normally covers huge swaths of the Arctic Ocean has been retreating and thinning over the last few decades, due to the amplified warming at the North Pole, which is a consequence of the buildup of greenhouse gases in Earth's atmosphere.

The most dramatic sea-ice melt in recent years came in 2007, when sea-ice extent (or the area of ocean covered by the ice) dropped to its lowest level since 1979, when satellite measurements began. This event also opened up the fabled Northwest Passage.

While satellite images are useful in looking at the changes in sea-ice extent over the last few years to decades, scientists also want to know how conditions today compare with those further back in the past. To get this information, scientists can look at sediment cores — long cylinders of the Earth's crust — drilled from the Arctic Ocean floor.

"Sediment cores are essentially a record of sediments that settled at the sea floor, layer by layer, and they record the conditions of the ocean system during the time that they settled," explained researcher Leonid Polyak of the Byrd Polar Research Center at Ohio State University in Columbus, who led a study looking at these sediment records, which are like fossils of the ocean's climate.

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