Saturday, April 16, 2016

Greenland's Ice Melt

You probably saw some news stories full of histrionics over Greenland's ice sheets melting earlier than normal (e.g., CNN and Washington Post). Reading these articles, you would be left with the impression that the situation was solely the result of global warming. That is incorrect, of course. In a paper recently published in Nature Geoscience, researchers published their findings showing that Greenland's ice sheets were subject to geothermal heating from below. From the abstract:
Ice-penetrating radar and ice core drilling4 have shown that large parts of the north-central Greenland ice sheet are melting from below. It has been argued that basal ice melt is due to the anomalously high geothermal flux that has also influenced the development of the longest ice stream in Greenland. Here we estimate the geothermal flux beneath the Greenland ice sheet and identify a 1,200-km-long and 400-km-wide geothermal anomaly beneath the thick ice cover. We suggest that this anomaly explains the observed melting of the ice sheet’s base, which drives the vigorous subglacial hydrology and controls the position of the head of the enigmatic 750-km-long northeastern Greenland ice stream. Our combined analysis of independent seismic, gravity and tectonic data implies that the geothermal anomaly, which crosses Greenland from west to east, was formed by Greenland’s passage over the Iceland mantle plume between roughly 80 and 35 million years ago. We conclude that the complexity of the present-day subglacial hydrology and dynamic features of the north-central Greenland ice sheet originated in tectonic events that pre-date the onset of glaciation in Greenland by many tens of millions of years.
(Footnotes omitted). Or, as reported in layman's terms in The Irish Times:
A geothermal “hot spot” deep under the Greenland ice sheet is combining with global warming to cause the three kilometre thick slab of ice to melt from below as well as from above. 
The melting at the bottom of the ice has caused the formation of a river network with water acting as a lubricant in some areas to help speed up the flow of ice into the North Atlantic. 
This is the first confirmation that a geological process deep in the Earth can exert such influence over glacial movement and water release from the ice sheets, said Dr Alan Vaughan, a research associate at Trinity College Dublin. 
“It adds uncertainty to what happens as we warm the Earth,” said the structural geologist. “We have to take that into account if we want to predict what will happen in Greenland as the planet warms.” 
The hot spot is nothing new and formed as much as three million years ago, says Dr Vaughan, who is co author of a research report published on Monday in Nature Geoscience. 
What is going on three kilometres down at the base of the ice sheet has grown in importance given climate change. 
“It is as if Greenland was riding over a blowtorch to cause the melting,” he said.
(See also "Greenland Ice Sheet Melting Increased Due To Ancient Geothermal Hot Spots"--News Everyday).

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