Warm seas melting Antarctic ice sheet faster than expected

April Flowers in Red Orbit: The West Antarctica ice sheet is melting faster than expected. An international group of oceanographers led by the University of Gothenburg has published new observations in the journal Nature Geoscience that may improve our ability to predict future changes in ice sheet mass.

The water levels of the oceans would be affected globally by a reduction of the ice sheets in Antarctica and Greenland, making it problematic that current information concerning the ocean circulation near large glaciers in West Antarctica is insufficient. Researchers are unable to predict how water levels will change in the future with any large degree of certainty.

“There is a clear reduction in the ice mass in West Antarctica, especially around the glaciers leading into the Amundsen Sea,” says researcher Lars Arneborg from the Department of Earth Sciences at the University of Gothenburg.

Arneborg and his team have been studying ocean circulation in the Amundsen Sea. According to the team, West Antarctica is particularly sensitive because the majority of the ice rests on areas that are below sea level where warm water penetrates beneath the ice. This causes increased melting from underneath.

“It is therefore probably a change in the ocean circulation in the Amundsen Sea that has caused this increased melting,” continues Arneborg. Previously, scientists have been referred to studies that use high-resolution computer models.

“But there have been very few oceanographic measurements from the Amundsen Sea to confirm or contradict the results from the computer models. Nor has there been any winter data. Sea ice and icebergs have made it impossible to get there in the winter, and it isn’t easy to have instruments in place all year round,” he explains….

Pine Island Bay on the West Antarctic Coast, shot by NASA

Why Antarctic sea ice cover has increased under the effects of climate change

Science Daily: The first direct evidence that marked changes to Antarctic sea ice drift have occurred over the last 20 years, in response to changing winds, is published this week in the journal Nature Geoscience. Scientists from NERC's British Antarctic Survey (BAS) and NASA's Jet Propulsion Laboratory (JPL), Pasadena California explain why, unlike the dramatic losses reported in the Arctic, the Antarctic sea ice cover has increased under the effects of climate change.

Maps created by JPL using over 5 million individual daily ice motion measurements captured over a period of 19 years by four US Defense Meteorological satellites show, for the first time, the long-term changes in sea ice drift around Antarctica.

Lead author, Dr Paul Holland of BAS says: "Until now these changes in ice drift were only speculated upon, using computer models of Antarctic winds. This study of direct satellite observations shows the complexity of climate change. The total Antarctic sea-ice cover is increasing slowly, but individual regions are actually experiencing much larger gains and losses that are almost offsetting each other overall. We now know that these regional changes are caused by changes in the winds, which in turn affect the ice cover through changes in both ice drift and air temperature. The changes in ice drift also suggest large changes in the ocean surrounding Antarctica, which is very sensitive to the cold and salty water produced by sea-ice growth.

"Sea ice is constantly on the move; around Antarctica the ice is blown away from the continent by strong northward winds. Since 1992 this ice drift has changed. In some areas the export of ice away from Antarctica has doubled, while in others it has decreased significantly."

...The new research also helps explain why observed changes in the amount of sea-ice cover are so different in the two Polar Regions. The Arctic has experienced dramatic ice losses in recent decades while the overall ice extent in the Antarctic has increased slightly. However, this small Antarctic increase is actually the result of much larger regional increases and decreases, which are now shown to be caused by wind-driven changes. In places, increased northward winds have caused the sea-ice cover to expand outwards from Antarctica. The Arctic Ocean is surrounded by land, so changed winds cannot cause Arctic ice to expand in the same way....

An iceberg off the Antarctic coast, shot by Jerzy Strzelecki, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license