Wednesday, April 27, 2016

East Antarctica beginning to melt like Greenland did less than a decade ago.

This is not good news. I certainly did not expect to see photos of ice-melt runoff in that place, even in its East End, like this this so soon.

(Note: the East End, a term I'm nicking from London geography, is the side of West Antarctica that fronts the sea next to the Ross Ice Shelf; the West End of course would be next to the West Antarctic Peninsula south of South America.)

From the Robertscribbler:

Melt Expanding into East Antarctica as Nansen Ice Shelf Crack Produces 20 Kilometer Long Iceberg
Ever since 1999 a gigantic crack has been growing in the Nansen Ice Shelf in East Antarctica. By 2014, expansion of the crack accelerated. As of early 2016, the crevice had grown to 40 kilometers in length. Flooded by melt along the Ice Shelf’s warming surface and weakened by the heating of ocean waters from below, on April 7th, according to ESA reports, this East Antarctic Ice Shelf produced an immense 20 kilometer long iceberg. A towering block of ice covering an area larger than Manhattan floating on out toward the world’s shipping lanes.

Nansen Ice Shelf in the East End of East Antarctica.
(Image source. ESA via Robertscribbler.)
Surface melt water flooding into a great crack along the Nansen Ice Shelf. Large volumes of melt water flooding into ice shelf cracks forces them to widen even as they dive toward union with the warming waters below.

The Nansen Ice Shelf, before this most recent very large iceberg calving event, was a 10 mile wide and 30 mile long ice shelf that buttressed the Presley and Reeve Glaciers of East Antarctica. It abuts the north side of the Drygalski Ice Tongue, and runs out from Mount Nansen just inland of the coast of Victoria Land, Antarctica. And it’s yet another large shelf of ice that appears to be facing severe weakening as global average temperatures are driven above 1 C warmer than those experienced during the late 19th Century by an ongoing and reckless fossil fuel emission.

Nansen occupies a region of the world that has come under increasingly intense observation due to a number of scientific studies highlighting its accelerating rates of melt and a related risk of rapidly rising global sea levels.  Human-forced heating of the world’s ocean has caused waters warm enough to accelerate glacial melt to encroach upon Antarctica from the Southern Ocean. These warmer waters are drawn along beneath the floating ice shelves as fresh melt water flooding out along the ocean surface generates a landward-moving bottom current. These warmer waters eventually push beneath the ice shelves — eating away at their undersides.
And here is a map of Antarctica to show you exactly where the Nansen Ice Shelf is:

Image source: Science, via Robertscribbler.)
Though the most rapid rates of glacial melt dominate the Antarctic Peninsula and the region near the Pine Island and Thwaites glaciers, increasing rates of volume loss from Antarctic ice shelves have been creeping into a section of East Antarctica near the Nansen Ice Shelf along the coastline of the Ross Sea [just below where the abbreviation DRY for Drygalski Ice Tongue appears on the map]. With global average temperatures now exceeding 1 C above pre-industrial, we can expect melt and net volume loss to expand along the Antarctic coastline.
And here an enlargement of the above map showing the East End of East Antarctica where the Nansen Ice Shelf is, just to the north of the DRY [Drygalski Ice Tongue]:

What makes matter worse, is that the under-the-ice slopes of Antarctica are in retrograde; that is, the ice gets deeper the more inland you go. So the warmer waters underneath gets to melt more ice as they advance under the ice shelves and glaiciers, making them all the more unstable, so that huge pieces will break off and float away, as in this spectacular gif that I won't post in this article, you have to go to Robertscribbler to go see it, here.

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