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Warm Ocean Melting Antarctic Ice Shelf - NASA Study

 

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Warm ocean rapidly melting Antarctic ice shelf from below

After trying for five years, scientific instruments were finally installed on Pine Island Glacier ice shelf in Dec. 2012. Their first scientific results, determining the rate at which warm sea water is eating away the ice from underneath the floating portion of the glacier, were published today.

For five years, a scientific expedition tried reaching Pine Island Glacier ice shelf in a remote, wind-ridden corner of Antarctica. The obstacles to get to the ice shelf were extreme, but the science goal was simple: to measure how fast the sea was melting the 37-mile long ice tongue from underneath by drilling through the ice shelf.


The international team, led by NASA's emeritus glaciologist Robert Bindschadler and funded by the National Science Foundation and NASA, had to abort their mission in 2007 due to logistical challenges after becoming the first people to ever land on the ice shelf. On their next try, in 2011, bad weather prevented the scientists from reaching the ice shelf until it was too late in the field season to carry out their science. It wasn't until December 2012 that the team was finally able to install scientific instruments.


Those measurements taken on and below the Pine Island Glacier ice shelf have yielded their first scientific results, determining the rate at which warm sea water is eating away the ice from underneath the floating portion of the glacier.


In a paper published in the journal Science on Sept. 13, the team describes how at one of their study sites, halfway down the ice shelf, the melt rate was as high as 2.36 inches (6 centimeters) per day.


"This is the first observation of the actual melt rate underneath the ice shelf," said Timothy Stanton, an oceanographer at the Naval Postgraduate School in Monterey, Calif., and lead author of the paper. "We have observations using remote sensing of various kinds, but these are actual in situ measurements."


Ice shelves buttress seaward glaciers, slowing the speed at which these rivers of ice dump their contents into the sea. If an ice shelf is weakened at its grounding line, the point where the glacier loses its grip on the land and starts floating, it allows the ice to flow faster, which impacts sea level. Pine Island Glacier and its neighbor, Thwaites Glacier, drain a large fraction of the West Antarctic ice shelf and are of great importance to its stability.


Research shows that melting of the underside of Antarctic ice shelves is ultimately driven by changes in the southernmost atmospheric circulation. Strong westerly winds push the frigid top water layer of the Southern Ocean away from land, which allows deeper, warmer water to raise and spill over the border of the Antarctic continental shelf. Since the weight of land ice tilts the continental shelf inland, streams of warm water can travel all the way to the ice shelf's grounding line, where they melt the ice. The resulting warm, fresh melt water rises against the underside of the ice shelf along the length of the ice shelf and carves melt channels that look like inverted river valleys.

 

Cheers - Allan Barker

September 17th 2013

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