Warm Ocean Currents Cause Majority of Ice Loss from Antarctica

Warm ocean currents attacking the underside of ice shelves are the dominant cause of recent ice loss from Antarctica, a new study using measurements from NASA's Ice, Cloud, and land Elevation Satellite (ICESat) revealed.An international team of scientists used a combination of satellite measurements and models to differentiate between the two known causes of melting ice shelves: warm ocean currents thawing the underbelly of the floating extensions of ice sheets and warm air melting them from above. The finding, published today in the journal Nature, brings scientists a step closer to providing reliable projections of future sea level rise.

The researchers concluded that 20 of the 54 ice shelves studied are being melted by warm ocean currents. Most of these are in West Antarctica, where inland glaciers flowing down to the coast and feeding into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise. This ocean-driven thinning is responsible for the most widespread and rapid ice losses in West Antarctica, and for the majority of Antarctic ice sheet loss during the study period."We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt," said the study's lead author Hamish Pritchard of the British Antarctic Survey in Cambridge, United Kingdom. "The oceans can do all the work from below."

To map the changing thickness of almost all the floating ice shelves around Antarctica, the team used a time series of 4.5 million surface height measurements taken by a laser instrument mounted on ICESat from October 2003 to October 2008. They measured how the ice shelf height changed over time and ran computer models to discard changes in ice thickness because of natural snow accumulation and compaction. The researchers also used a tide model that eliminated height changes caused by tides raising and lowering the ice shelves.

NASA Airborne Mission Maps Remote, Deteriorating Glaciers

NASA's airborne expedition over Antarctica this October and November has measured the change in glaciers vital to sea level rise projections and mapped others rarely traversed by humans.Operation IceBridge, nearing completion of its third year, is the largest airborne campaign ever flown over the world's polar regions. Bridging a gap between two ice elevation mapping satellites, and breaking new scientific ground on its own, IceBridge this fall has charted the continued rapid acceleration and mass loss of Pine Island Glacier.

IceBridge has now generated three years of laser altimetry data over certain locations to continue the record from NASA's Ice Climate and Elevation Satellite (ICESat), which stopped operating in 2009. IceBridge measurements show Pine Island following its rapid deterioration that began around 2006. Combined IceBridge and ICESat data show the glacier is losing more than six times as much mass per year -- mass loss was measured at 7 gigatons a year in 2005 and about 46 gigatons a year in 2010 – making it one of the most significant climate change response trends that scientists see worldwide. For comparison, the Chesapeake Bay holds about 70 gigatons of water.

Satellites still operating, such as NASA's Gravity Recovery and Climate Experiment (GRACE), can provide a large-scale picture of this trend. But it takes a more focused mission such as Operation IceBridge to gather higher-resolution data near the surface to piece together the dynamic interactions of ice, bedrock and ocean currents behind specific changes, and to improve the models that scientists use to predict how much an unstable ice sheet like West Antarctica will contribute to sea level rise.