The change in the ice mass covering Antarctica is a critical factor in global climate events. Scientists at the GFZ German Research Center for Geosciences have now found that the year by year mass variations in the western Antarctic are mainly attributable to fluctuations in precipitation, which are controlled significantly by the climate phenomenon El Nino. Gravity data collected from space using NASA's Grace satellite show that Antarctica has been losing more than a hundred cubic kilometers (24 cubic miles) of ice each year since 2002. The latest data reveal that Antarctica is losing ice at an accelerating rate, too. How is it possible for surface melting to decrease, but for the continent to lose mass anyway? The answer boils down to the fact that ice can flow without melting.
The change in the ice mass covering Antarctica is a critical factor in global climate events. Scientists at the GFZ German Research Center for Geosciences have now found that the year by year mass variations in the western Antarctic are mainly attributable to fluctuations in precipitation, which are controlled significantly by the climate phenomenon El Nino. Gravity data collected from space using NASA's Grace satellite show that Antarctica has been losing more than a hundred cubic kilometers (24 cubic miles) of ice each year since 2002. The latest data reveal that Antarctica is losing ice at an accelerating rate, too. How is it possible for surface melting to decrease, but for the continent to lose mass anyway? The answer boils down to the fact that ice can flow without melting.
!ADVERTISEMENT!Antarctica is Earth's southernmost continent (including ice and underlying land), encapsulating the South Pole. It is situated in the Antarctic region of the southern hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. At 5.4 million square miles), it is the fifth-largest continent in area after Asia, Africa, North America, and South America.
Two-thirds of Antarctica is a high, cold desert. Known as East Antarctica, this section has an average altitude of about 1.2 miles, higher than the American Colorado Plateau. There is a continent about the size of Australia underneath all this ice; the ice sheet sitting on top averages at a little over 1.2 miles thick. If all of this ice melted, it would raise global sea level by about 197 feet.
West Antarctica is very different. Instead of a single continent, it is a series of islands covered by ice. Because it's a group of islands, much of the West Antarctic Ice Sheet (WAIS, in the jargon) is actually sitting on the floor of the Southern Ocean, not on dry land. Parts of it are more than 1 mile below sea level. Pine Island is the largest of these islands and the largest ice stream in West Antarctica is called Pine Island Glacier. The WAIS, if it melted completely, would raise sea level by 16 to 23 feet.
Two areas in Antarctica are of particular interest because of their potential sensitivity to global climate change: the Antarctic Peninsula (which reaches up towards the tip of South America), and the Amundsen Sector of West Antarctica. The peninsula is currently experiencing a warming exceeding the global mean and the disappearance of large ice shelf areas. In the Amundsen Sector there are currently the largest flow rates and mass loss of the Antarctic Ice Sheet.
Glaciers can both melt and move or flow. Both results lead to a faster overall mass loss. Satellite images of more than 300 glaciers on the Antarctic Peninsula have already showed that they were flowing some 12 percent faster in 2003 than they were in 1993. Current data indicates that the "flow rate" is increasing though not in a linear fashion.
In the latest study, the mass balance of both regions is reevaluated from gravity data of the satellite mission GRACE. As a result, the estimates were lower than those of conventional mass balance methods. "With the GRACE time series, it was for the first time possible to observe how the large-scale ice mass varies in the two areas due to fluctuations in rainfall from year to year," said the GFZ scientists Ingo Sasgen.
It has long been known that the Pacific El Niño climate phenomenon and the snowfall in Antarctica are linked. The complementary piece to the warm phase El Nino, the cold phase known as La Nina, also affects the Antarctic climate:
"The cooler La Nina years lead to a strong low pressure area over the Amundsen Sea, which favors heavy rainfall along the Antarctic Peninsula - the ice mass is increasing there. In contrast, the Amundsen area is dominated by dry air from the interior during this time.
El Nino years with their warm phase lead to precisely the opposite pattern: reduced rainfall and mass loss in the Antarctic Peninsula, and an increase in the Amundsen Sector field, respectively" explains Professor Maik Thomas.
The recording of the entire ice mass of the South Pole and its variations is a central task in climate research and still raises many unanswered questions. In principle, the study could show that the continuous gravity data of the GRACE satellite mission contain another important medium-term climate signal.
For further information: http://www.eurekalert.org/pub_releases/2010-10/haog-iti102910.p
