Greenland glaciers' varied vulnerability to melting

"The undersides of glaciers in deeper valleys are exposed to warm, salty Atlantic water, while the others are perched on sills, protected from direct exposure to warmer ocean water," said Romain Millan, lead author of the study, available online in the American Geophysical Union journal Geophysical Research Letters. "We have been able to demonstrate unequivocally that glacier retreat in southeast Greenland is controlled by the topography of the bedrock under the ice and by ocean temperature."

Millan, a UCI graduate student researcher in Earth system science, and his colleagues analyzed 20 major outlet glaciers in southeast Greenland using high-resolution airborne gravity measurements and ice thickness data from NASA's Operation IceBridge mission; bathymetry information from NASA's Oceans Melting Greenland project; and results from the BedMachine version 3 computer model, developed at UCI.

They found glacial fjords hundreds of meters deeper than previously estimated; the full extent of the marine-based portions of the glaciers; deep troughs enabling Atlantic Ocean water to reach the glacier fronts and melt them from below; and few shallow sills that limit contact with this warmer water.

"It's important to understand the physical processes controlling the retreat in order to improve projections of sea level rise from this region in a warming climate," Millan said. "Until recently, we had little information on ocean temperature and water depth in these fjords to quantify these processes, so the interpretation of glacier evolution on a case-by-case basis was difficult."

Co-author Eric Rignot, UCI professor of Earth system science, added, "Now that the picture is clear, the role of the ocean in glacier evolution is overwhelming."

Rignot, who has led dozens of research expeditions to Earth's polar regions, said that southeast Greenland -- with its fast-moving glaciers, deep fjords and harsh climate conditions -- poses significant challenges to researchers.

"Thanks to the newest NASA missions, such as Oceans Melting Greenland and Operation IceBridge, we have been able to make great advances in understanding the evolution of this very dynamic sector of Greenland and its impact on sea level rise now and in decades to come," he said.