Warm ocean rapidly melting antarctic ice shelf from below

NASA: 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. ... 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."

The measurements also detected differences in melt rates across the channel system that runs underneath the ice shelf, Stanton said. Such features are important for adjusting models so they can accurately predict ice melt and its contribution to sea level rise.

“Our direct measurements are consistent with the larger scale averages that remote sensing data have provided, but our data capture an enormous fine scale variability of the basal melting rate that remote sensing can't resolve,” Bindschadler said. “Using only the average melt rates would not lead to a correct understanding of the actual ocean-ice interaction processes taking place in the boundary layer.”

...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....

Drilling station and remote field camp on the Pine Island Glacier in 2012. Image Credit: Salvatore Consalvi