Shedding Light on a Fast-Melting Glacier

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Like runaway tooth decay, a large and growing cavity of warm water is eating away at the base of the fastest-melting glacier in West Antarctica.

Using satellite data and measurements from a robotic "autonomous underwater vehicle" to explore the dark depths beneath the Antarctic ice shelf, British and US scientists have constructed a detailed new picture of rapidly changing geometry where Pine Island Glacier discharges into the Amundsen Sea.

The melting and thinning of the floating ice shelf — like an ice cube in a glass — does not change the level of the sea, but the shelf serves as an outlet dam that controls the flow from the upstream glacier.

This graphical depiction, left, from Nature Geoscience shows how warmer "circumpolar deep water" has progressively melted the base of the glacier beyond a ridge on the seabed and continues to erode inland.

What the new picture tells researchers about what is happening under the ice shelf could have far-flung implications for estimates of the future of sea level around the world — one of the most serious consequences of our changing climate. Estimating the rate of future sea level rise is one of the most difficult problems in climate science and is a subject of continuing debate. Scientists figure that glacial meltwater flow from West Antarctica contributes about 10 percent of the current rise in global sea level.

In just a few decades — since the 1970s — the relatively warm deep ocean water flowing beneath the cold, buoyant glacier meltwater has encroached inland under the glacier some 30 km, or 18.6 miles, and the pace of the outflow of Pine Island Glacier continues to accelerate.

"The pace and ultimate extent of such potentially unstable retreat are central to the debate over the possibility of widespread ice-sheet collapse triggered by climate change," Adrian Jenkins of the British Antarctic Survey in Cambridge, UK, and colleagues write in the new online edition of the journal Nature Geoscience.

In a separate analysis, Canadian scientist Christian Schoof of the University of British Columbia writes that the "completely new observational picture" provides "direct confirmation of what had been inferred from models" and raises "the spectre of further retreat of the glacier."