Ocean currents, not warm air, are driving Antarctic ice loss

West Antarctica loses ice to the sea even if a summer isn’t warm enough to melt snow on top of the glaciers. The oceans do the work from below, a study shows.

There are two ways to melt an ice shelf, which is a large sheet of ice floating in the ocean but attached to land. The first way is via warm air melting the ice from above. The second way is via warm ocean currents thawing the ice shelf from below. The results of a new NASA study suggest that recent accelerating ice loss from West Antarctica is being caused by warm ocean currents attacking the underside of ice shelves. The international team of scientists that conducted this study published their results today (April 25, 2012) in the science journal Nature, and they also released the video below.

The study – which uses measurements from NASA’s ICESat (Ice, Cloud, and land Elevation Satellite) – used a combination of satellite measurements and models to differentiate between the two known causes of melting ice shelves. The research team concluded that 20 of the 54 ice shelves studied – mostly in West Antarctica – are being melted by warm ocean currents.

Map of West Antarctica Map derived from Marble via Jeroenvrp via Wikimedia Commons

Unlike the Arctic, which is an ocean, Antarctica is a land mass. Ice from the interior of Antarctica flows to the sea, as new ice and snow fall down from above each Antarctic winter. In recent years, the rate of ice loss from West Antarctica has been accelerating, according to scientists’ measurements. The floating ice shelves have a major role to play in this acceleration, because they act as a brake against the loss of land-bound rivers of ice, or glaciers, that flow to the sea. In other words, as the ice shelves melt due to warm ocean currents, West Antarctic glaciers have begun to spill more and more ice into the ocean, contributing to sea-level rise.

The scientists determined that the thinning of West Antarctic ice shelves is primarily ocean-driven for the most of the Antarctic ice sheet loss during the study period (October 2003 to October 2008). The study’s lead author Hamish Pritchard of the British Antarctic Survey in Cambridge, United Kingdom, said:

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. The oceans can do all the work from below.

Photo credit: <a href='https://www.flickr.com/photos/cloudzilla/2090315785/' target='_blank'>cloudzilla</a>

Bottom line: An international team of scientists using NASA ICESat data and computer modeling have shown that – from October 2003 to October 2008 – ice shelves in West Antarctica melted primarily due to warm ocean currents.

Read more from NASA

Sophie Nowicki on weak underbelly of West Antarctic Ice Sheet

What a crack in a glacier looks like

More emperor penguin colonies in Antarctica

Deborah Byrd

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