Warm water under Antarctic glacier spurs astonishing rate of melting

[Rhiannon12866]

A two-month-long expedition to one of the most remote sites on the planet — the sprawling Pine Island Glacier in Antarctica — has revealed that currents of warm water beneath the glacier are melting the ice at a staggering rate of about 2.4 inches (6 centimeters) per day.

An international team of researchers journeyed to the southernmost continent to study the Pine Island Glacier, which is the longest and fastest-changing glacier on the West Antarctic Ice Sheet. This region, in the far reaches of Antarctica, has been of particular interest to scientists because it is among the most rapidly melting ice masses in the world, thinning as it flows to the Amundsen Sea at a rate of about 2.5 miles (4 kilometers) each year.

Since warm seawater flows beneath the ice shelf (the part of the glacier that floats on the ocean), scientists have known that the Pine Island Glacier was melting from below. Now, using sensors deployed across the 31-mile-long (50-km-long) glacier, the researchers have gauged the rate of glacial melt beneath the solid ice. [Album: Stunning Photos of Antarctic Ice]

The results demonstrate the crucial need to better understand melting processes underneath massive glaciers, including how this undersea process will affect global sea-level rise in the future.


http://www.nbcnews.com/science/warm-water-under-antarctic-glacier-spurs-astonishing-rate-melting-8C11140007




Researchers from the Naval Postgraduate School deployed multiple, unique sensors through 1,640 feet (500 meters) of solid ice to determine how quickly warm water was melting Antarctica's massive Pine Island Glacier from beneath.

[Cooley Hurd]

1. Melting @ 2.4" a day???

That seems excessive.

[muriel_volestrangler]

2. That's the rate in some channels, not over all of its base

Ice shelves play a key role in the mass balance of the Antarctic ice sheets by buttressing their seaward-flowing outlet glaciers; however, they are exposed to the underlying ocean and may weaken if ocean thermal forcing increases. An expedition to the ice shelf of the remote Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet that has rapidly thinned and accelerated in recent decades, has been completed. Observations from geophysical surveys and long-term oceanographic instruments deployed down bore holes into the ocean cavity reveal a buoyancy-driven boundary layer within a basal channel that melts the channel apex by 0.06 meter per day, with near-zero melt rates along the flanks of the channel. A complex pattern of such channels is visible throughout the Pine Island Glacier shelf.

http://www.sciencemag.org/content/341/6151/1236.abstract

The editor's summary:

Active Ice

How, exactly, does warm ocean water erode an ice shelf? In a field study of an ice shelf at Pine Island, Antarctica, Stanton et al. (p. 1236) collected data from radar, seismic surveys, and oceanographic sensors inserted in holes bored through the ice shelf. The results show that localized, intensive melting occurs in a complex network of discreet channels that are formed on the underside of the shelf. This pattern of melting may limit the absolute rate of ice-shelf mass loss.

[OKIsItJustMe]

3. Measurements of Antarctic ice-shelf melt help to greatly refine models of global climate change

http://www.nsf.gov/news/news_summ.jsp?cntn_id=129075&WT.mc_id=USNSF_51&WT.mc_ev=click

[font face=Serif]Press Release 13-156
[font size=5]Measurements of Antarctic ice-shelf melt help to greatly refine models of global climate change[/font]
[font size=4]Ability of ice shelves to regulate movement of Antarctic glaciers directly affects potential sea-level rise[/font]
[font size=3]September 13, 2013

In a finding that is expected to vastly improve models of the global effects of climate change on sea-level rise, a National Science Foundation- (NSF) funded research team, working in one of Antarctica's most challenging environments, has produced the first direct measurements of how relatively warm sea water undercuts a floating ice shelf that normally retards the movement of glaciers from the Antarctic continent to the sea.

Tim Stanton, of the Naval Postgraduate School's Department of Oceanography and lead author of the study, and Martin Truffer, a co-author at the University of Alaska, published their team's findings in the Sept. 13 edition of Science magazine.

The paper documents the mechanism by which seawater eats away at the underside of the 50-kilometer (31-mile) long Pine Island Glacier, which regulates the seaward movement of a portion of the West Antarctic Ice Sheet (WAIS). WAIS contains roughly 10 percent of all Antarctica's ice mass.

When the ice shelves interacting with the oceans melt, the flow of the ice sheets speeds up, releasing fresh water into the ocean and raising sea level.

Given the flow of relatively warm seawater below the glacier, scientists have long known that Pine Island Glacier was melting from below. The accelerated flow of WAIS glacial ice into the Amundsen Sea has been a concern since the late 1980s.

"What we have brought to the table are detailed measurements of melt rates that will allow simple physical models of the melting processes to be plugged into computer models of the coupled ocean/glacier system," Stanton said. "These improved models are critical to our ability to predict future changes in the ice shelf, and glacier melt rates of the potentially unstable Western Antarctic Ice Sheet in response to changing ocean forces."

…

The measured glacial melt rates at the Pine Island Glacier site were highly variable, reaching rates as high as six centimeters (two inches) per day within the channel on the underside of the ice, with near zero melt rates on the flanks of the channel. The study results reveal a critical need to understand channelized melting underneath massive glaciers, as they are major contributors to global sea-level rise now and into the future, the authors said.

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