from the did-they-find-aliens? dept.
We are all aware that Antarctica's ice shelves are thinning, but recently scientists have also discovered huge canyons cutting through the underbelly of these shelves, potentially making them even more fragile. Thanks to the CryoSat and Sentinel-1 missions, new light is being shed on this hidden world.
Antarctica is surrounded by ice shelves, which are thick bands of ice that extend from the ice sheet and float on the coastal waters. They play an important role in buttressing the ice sheet on land, effectively slowing the sheet's flow as it creeps seaward.
The ice sheet that covers Antarctica is, by its very nature, dynamic and constantly on the move. Recently, however, there has been a worrying number of reports about its floating shelves thinning and even collapsing, allowing the grounded ice inland to flow faster to the ocean and add to sea-level rise.
While scientists continue to study the changing face of Antarctica, monitor cracks in the surface of the ice that might signal the demise of a shelf and learn how these changes are affecting the biology of coastal waters, they are also aware of dramatic changes taking place below the surface, hidden from view.
A Sword of Damocles hanging over the heads of the Earth's coastal populations?
Scientists now have their best view yet of where Antarctica is giving up ground to the ocean as some of its biggest glaciers are eaten away from below by warm water.
Researchers using Europe's Cryosat radar spacecraft have traced the movement of grounding lines around the continent. These are the places where the fronts of glaciers that flow from the land into the ocean start to lift and float. The new study reveals an area of seafloor the size of Greater London that was previously in contact with ice is now free of it.
[...] On the face of it, the results are pretty much as expected. Of the 1,463km² of grounded ice that has been given up, most of it is in well documented areas of West Antarctica where warm ocean water is known to be infiltrating the undersides of glaciers to melt them.
Dr Konrad explained: "If you take 25m per year as a threshold, which is sort of the average since the end of the last ice age, and you say anything below this threshold is normal behaviour and anything above it is faster than normal - then in West Antarctica, almost 22% of grounding lines are retreating more rapidly than 25m/yr. "That's a statement we can only make now because we have this wider context."
The new data-set confirms other observations that show the mighty Pine Island Glacier, one of the biggest and fast-flowing glaciers on Earth, and whose grounding line has been in retreat since the 1940s, appears now to have stabilised somewhat.