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January 7th, 2011

New study ties warm North Atlantic water to heating Arctic

North Atlantic water flowing into the Arctic Ocean is warmer than it has been in at least 2,000 years, which is likely amplifying global warming in the Arctic, says a new international study involving INSTAAR fellow Tom Marchitto.

"modern Fram Strait water temperatures are well outside the natural bounds.” - Tom Marchitto

The study showed that water from the Fram Strait, a major carrier of oceanic heat to the Arctic Ocean, has warmed roughly 3.5 degrees Fahrenheit in the past century. Fram Strait water temperatures today are about 2.5 degrees F warmer than during the Medieval Warm Period that affected the climate in Europe and North America. The team believes that the rapid warming of the Arctic and recent decrease in sea ice extent are tied to the enhanced heat transfer from the North Atlantic Ocean, said Robert Spielhagen of the Academy of Sciences, Humanities and Literature in Mainz and Leibniz Institute of Marine Sciences in Keil, Germany, who led the study.

German research vessel Maria S. Merian moving through sea ice in Fram Strait northwest of Svalbard. The research team discovered the water there was the warmest in at least 2,000 years, which has implications for a warming and melting Arctic. Photo by Nicolas van Nieuwenhove (IFM-GEOMAR, Kiel).

According to Marchitto, the new observations are crucial for putting the current warming trend of the North Atlantic in the proper context. “We know that the Arctic is the most sensitive region on the Earth when it comes to warming, but there has been some question about how unusual the current Arctic warming is compared to the natural variability of the last thousand years,” said Marchitto. “We found that modern Fram Strait water temperatures are well outside the natural bounds.”

The team drilled ocean sediment cores dating back 2,000 years to determine past water temperatures. The researchers used microscopic organisms called foraminifera--which prefer specific water temperatures at depths of roughly 150 to 650 feet--as tiny thermometers. In addition, the team used a second, independent method that involved analyzing the chemical composition of the foraminifera shells to reconstruct past water temperatures in the Fram Strait.

Spielhagen concludes, “We must assume that the accelerated decrease of the Arctic sea ice cover and the warming of the ocean and atmosphere of the Arctic measured in recent decades are in part related to an increased heat transfer from the Atlantic.”

A paper on the study is in the Jan. 28 issue of Science.

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