Mar 26, 2019

The fastest-melting Greenland glacier has made a temporary U-turn

Iceberg from the Jakobshavn Glacier is seen in Disko Bay, Greenland, in 2017. Photo: Andrew Freedman

The Jakobshavn Glacier in west-central Greenland, which has been the fastest-flowing and thinning glacier on the vast ice island during the past 20 years, has temporarily slowed its retreat and thickened in the past few years, scientists say.

The big picture: Using new, high-resolution data of ocean currents at and near the glacier's floating ice shelf, NASA researchers were able to show that an influx of cooler waters since 2016 has slowed — but not completely halted — Jakobshavn's rapid melt. The glacier is still adding to global sea level rise, since it continues to lose more ice to the ocean than it gains from snow accumulation, but at a slower rate.

Scientists do not expect this slowing trend to continue. A natural climate cycle in the North Atlantic Ocean is likely to switch gears and bring warmer waters back into contact with the ice shelf, melting it from below at the same time that increasing air temperatures weaken it from above.

Details: The study, published in the journal Nature Geoscience, found that a plume of relatively cold waters has encroached on the Jakobshavn Glacier from the southwest, starting about 600 miles away.

  • The study is based in part on high-resolution data gathered during NASA's Oceans Melting Greenland (OMG) mission, as well as other observations.
  • The OMG mission is aimed at obtaining temperature and salinity data in the vicinity of rapidly melting Greenland glaciers, since it's been shown that relatively mild ocean waters are eroding glaciers' ice shelves from below in both Greenland and Antarctica.
  • These ice shelves act like a door stop, holding back inland ice. Once the ice shelves melt and collapse, the inland ice can flow faster into the sea, raising sea levels.
  • Between 2003 and 2016, the Jakobshavn lost about 160 meters, or 525 feet in thickness at the glacial front, which is where the ice meets the ocean.

The intrigue: A key suspect in causing the glacier's slowdown is a regional climate pattern that causes the North Atlantic Ocean to alternate between warm and cold temperatures. Ocean temperatures in Disko Bay's near-surface waters have cooled to levels last seen during the mid-1980s, the study found.

The study traces this cooling to unusual loss of heat from the ocean during the winter months as the waters circulate around the southern half of Greenland.

What they're saying: "At first we didn't believe it. We had pretty much assumed that Jakobshavn would just keep going on as it had over the last 20 years," says lead author Ala Khazendar of NASA's Jet Propulsion Laboratory in California, in a press release. However, the OMG data showed cold water near Jakobshavn for three years in a row.

"Jakobshavn is getting a temporary break from this climate pattern. But in the long run, the oceans are warming. And seeing the oceans have such a huge impact on the glaciers is bad news for Greenland's ice sheet," Josh Willis of JPL, the principal investigator of OMG, explained.

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