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East Antarctic ice shelves melting at surprising pace, study suggests

Breakup of the shelves can accelerate the flow of continental ice to the sea, contributing to sea-level rise, and the Antarctic shelves 'are melting too fast,' the study's lead author says.

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Research over the past several years has uncovered the important role relatively warm seawater plays in melting shelves from underneath. Dr. Rignot, also a senior researcher at NASA's Jet Propulsion Laboratory, and colleagues gathered data on ice shelves all around the continent's perimeter to look at whether melting from underneath or calving, which can occur without intensified undersea melting, held the most sway over the melting ice shelves.

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The team found that the mix varied by location. Averaged over the entire coastline, however, the team found that calving accounted for the loss of 1.1 trillion tons of ice loss a year, while melting from below accounted for 1.3 trillion tons a year of lost shelf ice.

Moreover, the three largest ice shelves – which together comprise two-thirds of all shelf ice at the bottom of the world – only accounted for 15 percent of the melting. The balance came from the smaller shelves. Half of the meltwater comes from 8 percent of the continent's total shelf area – essentially along the West Antarctic coast through the Antarctic Peninsula. These represent shelves most seriously affected by warm, upwelling water.

But the unexpected melt rates on several East Antarctic shelves also stood out.

While warm waters remain a suspect there as well, the few expeditions that have gone there to take measurements haven't found the extensive incursions of warm water onto the continental shelf that appear along the West Antarctic Coast, Dr. Jacobs says.

A US-led expedition to East Antarctica's Totten Ice Shelf currently is being planned for early next year to help build up the data needed to pinpoint the causes, he adds.

In addition, the combination of different data sets the team used – something unavoidable given the questions the team was asking – may have yielded somewhat larger uncertainties in the results than the team sets out in its research paper, adds Robert Bindschadler, a polar scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

Still, he adds, the study performs a useful service setting ice-shelf changes into a continental context and demonstrating that melting from underneath plays the dominant role in ice-shelf melting.

In the end, the observation of some unexpectedly high melt rates in East Antarctica represents "a tap on the shoulder" to remind colleagues that East Antartica's shelves may require more attention than they have received so far.

"East Antarctica is so big that even relatively small changes around that immense coastline could have a notable impact on sea level," says Richard Alley, a polar researcher at Penn State University in University Park, Pa.

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