No Longer Anchored, Antarctic Ice Stream Surges to Sea

Autosub being launched

Autosub being launched from the R/V Nathaniel B. Palmer.
Credit: James Perrett, National Oceanography Centre, Southampton, UK.


Satellite tracking has shown that the Pine Island Glacier, one of Antarctica's largest ice streams, is accelerating and thus contributing a growing share of the melt water raising sea levels worldwide.

A team of scientists visiting the region last year discovered one reason for the speed-up: warm ocean water eating away at the glacier’s base has lifted the ice off a rocky underwater ridge that once slowed the glacier’s advance into the sea.

Discovery of the submarine ridge, standing about 300 meters tall, and 30 kilometers from where the glacier currently meets the sea floor, is detailed in a paper published this week in Nature Geoscience.

Aboard the research ship Nathaniel B. Palmer, the team of British and American scientists took water measurements to track how West Antarctica’s thinning glaciers are affecting the ocean and sent a robot submarine, Autosub 3, into the deep cavity beneath Pine Island Glacier's floating ice shelf to chart the seafloor's hidden contours.

The ridge came as a surprise, the scientists say, and helped explain why the glacier has accelerated, and its grounding line—the place where the glacier stops being anchored to land and becomes an ice shelf, floating in the sea—has retreated over recent decades.

The glacier used to scrape across this ridge, which probably slowed it down, said Stan Jacobs, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory.

"Once the thinning glacier moved off the ridge, the relatively warm ocean water in this region began to melt deeper ice on the back side of the ridge," he said.

Unlike the ice sheets of Greenland and eastern Antarctica, much of West Antarctica’s ice sheet lies below sea level, and so may be particularly vulnerable to fast erosion by seawater.

Read the rest of the story here.

Related Story:

NSF Press Release: British, NSF-funded Researchers Deploy Automated Submarine to Better Understand the Mechanics of Antarctic Ice Sheets, March 17, 2009.