Tuesday, 29 November 2016

Two miles of ice melt in one day?

Did Föhn Winds Just Melt Two Miles of East Antarctic Surface Ice in One Day? 


28 November, 2016
It’s right there in the satellite image. A swatch of blue that seems to indicate an approximate 2-mile long melt lake formed over the surface of East Antarctica in just one day. If confirmed, this event would be both odd and concerning. A part of the rising signal that melt stresses for the largest mass of land ice on the planet are rapidly increasing.
melt-pond-scott-coast-antarctica-november-27-2016
(Possible large melt lake on the surface of an ice shelf along the Scott Coast appears in thisNASA satellite image. The melt lake seems to have formed after just one day during which föhn winds ran downslope from the Transantarctic Mountain Range — providing a potential period of rapid heating of the glacier surface.)

Surface Melt Now Showing Up in East Antarctica

While scientists and environmentalists are understandably concerned about ocean warming melting the undersides of sea-fronting West Antarctic glaciers — resulting in risks for rapid sea level rise for the near future, another consequence of global warming is also starting have a more visible impact on the frozen and now thawing continent. Surface melt, which was hitherto unheard of for most of East Antarctica, is now starting to pop up with increasing frequency.

East Antarctica, according to Stewart Jamieson, a glaciologist at Durham University in the U.K., is “the part of the continent where people have for quite a long time assumed that it’s relatively stable, there’s not a huge amount of change, it’s very, very cold, and so, it’s only very recently that the first supraglacial lakes, on top of the ice, were identified.”

But now, even in austral springtime, we find evidence of surface melt in the satellite record.
On November 27, 2016, what looks like an approximate 2 mile long melt pond appeared in a section of ice shelf along the Scott Coast and just North of the Drygalski Ice Tongue in the region of McMurdo Sound. The lake — which is visible as a light blue swatch at center mass in the NASA-MODIS satellite image above — suddenly showed up in November 27 satellite image along a region where only white ice was visible before. And it appears in a region of East Antarctica that, before human-forced warming altered the typically-stable Antarctic climate, had rarely, if ever, seen surface melt.

near-freezing-temps-scott-coast-fohn-winds
(Near melting point temperatures appear along the Scott Coast in conjunction with an apparent föhn wind event. Image source: Earth Nullschool.)

The pond shows up coordinate with recorded near 0 C surface temperatures in the GFS monitor for November 26-27 and along with evidence of downsloping (föhn) winds. GFS indicators show downsloping winds gusting to in excess of 50 mph over the period. Such winds have the potential in increase surface temperatures by as much as 14 degrees Celsius in a matter of minutes. And they have, increasingly, produced surface glacial melt events in regions of Greenland and Antarctica during recent years.

Surface Melt as a Feature of Glacial Destabilization

Supraglacial lake is just another word for a surface glacial melt lake. And these new lakes pose a big issue for ice sheet stability. Surface melt lakes are darker than white glacier surfaces. They act as lenses that focus sunlight. And the comparatively warm waters of these lakes can flood into the glacier itself — increasing the overall heat energy of the ice mass.
nasa-greenland-surface-melt
(A NASA researcher investigates a surface melt pond in Greenland. During recent years, these climate change related features have become more common in Antarctica. Image source: NASA.)

But water at the glacier surface doesn’t just sit there. It often bores down into the ice sheet — producing impacts for months and years after the surface lake’s formation. Sub surface lakes can form in the shadow of surface ponds. Transferring heat into the glacier year after year. In other cases, water from these lakes punches all the way to the glacier’s base. There the added lubrication of water speeds the glacier’s flow. All of these processes generate stresses and make glaciers less stable. And it is the presence of surface melt ponds that has been responsible for so much of Greenland’s speeding melt during recent years.
Now, a similar process is impacting the largest concentration of land ice on the planet. And while Greenland holds enough ice to raise sea levels by around 21 feet, East Antarctica contains enough to lift the world’s oceans by about 195 feet. Surface melt there, as a result, produces considerably more risk to the coastal cities of the world.
Links:

Hat tip to Shawn Redmond (and a special thanks for being the first here to ID the rather odd apparent melt pond forming along the Scott Coast.)

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