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Wednesday
Apr252018

Antarctic Ice Melt "Under Way"

This is information that we have read, and wondered about for some time. Now, it appears to have eventuated, and the real "bottom-warming" is under-way. This appeared today in the Washington Post.

Pick up the remainder of the article to get the full picture. It is not pretty, and the warnings given at last week's meeting here with the the Chair of the Insurance council should not be ignored. I was unfortunately in Taranaki, and unable to attend, but Denis Tegg has reported fully on it.

"Two years ago, former NASA climate scientist James Hansen and a number of colleagues laid out a dire scenario in which gigantic pulses of fresh water from melting glaciers could upend the circulation of the oceans, leading to a world of fast-rising seas and even superstorms.

Hansen's scenario was based on a computer simulation, not hard data from the real world, and met with skepticism from a number of other climate scientists. But now, a new oceanographic study appears to have confirmed one aspect of this picture - in its early stages, at least.

The new research, based on ocean measurements off the coast of East Antarctica, shows that melting Antarctic glaciers are indeed freshening the ocean around them. And this, in turn, is blocking a process in which cold and salty ocean water sinks below the sea surface in winter, forming "the densest water on the Earth," in the words of study lead author Alessandro Silvano, a researcher with the University of Tasmania in Hobart, Australia.

This so-called Antarctic bottom water has stopped forming in two key regions of Antarctica, the research shows - the West Antarctic coast and the coast around the enormous Totten glacier in East Antarctica.

These are two of Antarctica's fastest-melting regions, and no wonder: When cold surface water no longer sinks into the depths, a deeper layer of warm ocean water can travel across the continental shelf and reach the bases of glaciers, retaining its heat as the cold waters remain above. This warmer water then rapidly melts the glaciers and the large floating ice shelves connected to them.

In other words, the melting of Antarctica's glaciers appears to be triggering a "feedback" loop in which that melting, through its effect on the oceans, triggers still more melting. The melting water stratifies the ocean column, with cold fresh water trapped at the surface and warmer water sitting below Then, the lower layer melts glaciers and creates still more melt water - not to mention rising seas as glaciers lose mass.

"What we found is not only a modeling study but is something that we observed in the real ocean," said Silvano, who conducted the research in Science Advances with colleagues from several other institutions in Australia and Japan. "Our study shows for the first time actual evidence of this mechanism. Our study shows that it is already happening."

Hansen said that "this study provides a nice small-scale example of processes that we talk about in our paper."

 

 


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