Greenland More Exposed to Melt from Beneath

Washington Post:

Two new studies of Greenland, using sophisticated technologies and large scientific teams to pull together and process the data, have now gone further in taking the full measure of the island through that ever-so-basic scientific act: mapping.

The first, a comprehensive seabed mapping project, relying in part on new data from NASA’s OMG (“Oceans Melting Greenland”) mission, concludes that the Greenland ice sheet is far more exposed to the planet’s warming oceans than previously known — and has more ice to give up than, until now, has been recognized.

The massive study, published last month in Geophysical Research Letters, pulls together a large number of data records to provide a comprehensive map of the shape of the seabed around and lying beneath Greenland’s glaciers, based on state of the art soundings taken by ships and other data sources.

The research — which pulls together a body of evidence that has now been accumulating for a while — measures the depth and contours of the ocean floor both beneath liquid water in Greenland’s fjords and beneath ice in places where the ocean may someday flow. The work was led by Mathieu Morlighem of the University of California at Irvine, with no less than 31 other authors from institutions in the United States, Canada, Britain and across Europe.

The researchers have found that Greenland contains more total ice above sea level than previously thought — the entire ice mass is capable of raising sea levels by 24.3 feet, about three inches more than previously realized.

Still more significant is how much of that ice is vulnerable to warm water that reaches the bases of the ice sheet’s deeper glaciers. The new research finds that “between 30 and 100% more glaciers are potentially exposed to [warm Atlantic water] than suggested by previous mapping, which represents 55% of the ice sheet’s total drainage area.” In other words, more than half of Greenland’s ice lies in or flows through areas that could be influenced by warming seas.

“The typical result is that we find these fjords to be much deeper than represented in previous maps,” said Eric Rignot, a NASA and UCI scientist who has been working on mapping Greenland for a decade and is a co-author on the work. “They’re deeper because they’ve been carved by glacial cycles, multiple times.”

The study, which catalogues 243 separate Greenland glaciers, also underscores that the island has several vulnerable points where a submerged passageway penetrates into the center of the ice sheet, where the bedrock also lies below sea level. One is at Jakobshavn Isbrae (or Jakobshavn Glacier), the fastest flowing of all Greenland glaciers, racing outward at over eight miles per year, and lying over a deep channel that cuts into the center of Greenland from its western flank.

Another is at Petermann Glacier in northwest Greenland. Petermann is not flowing as rapidly as Jakobshavn, and isn’t currently as deep. But both glaciers have vast drainage areas, accounting for the potential for large sea level rise.

And those are just the goliaths of Greenland. There are hundreds of other glaciers and, the new research finds, 134 of them currently sit in the ocean waters, and thus are resting on a bed below sea level. Of those, 89 rest 200 or more meters below sea level, and 59 rest 300 meters or more below sea level, including some of Greenland’s fastest flowing glaciers (and Jakobshavn and Petermann). For dozens of these glaciers, the new study calculates a deeper depth than previously realized, which means they are all more potentially exposed than previously thought to warm seas.

All of this new data, Rignot said, will now be fed into sophisticated models that, he thinks, will probably lead to higher estimates of Greenland’s sea level rise potential in this century and beyond. “I think when they’re going to use these new bed models, the projections are going to change,” he said.