A team of researchers from NYU Abu Dhabi’s Center for Global Sea Level Change have found that unusually warm ocean water is causing rapid melt at the Greenland outlet glacier Helheim, one of the largest in the region. For the first time, warm waters that originate in the tropics have been found at uniform depth, displacing the cold polar water at the Helheim calving front, causing an unusually high melt rate. Typically, ocean waters near the terminus of an outlet glacier like Helheim are at the freezing point and cause little melting.
Video and photos are available from this dropbox. (Credit: Denise Holland, NYU Abu Dhabi Center for Global Sea Level Change).
On August 5, 2019, researchers, led by Professor of Mathematics at NYU’s Courant Institute of Mathematical Sciences and Principal Investigator for NYU Abu Dhabi’s Center for Sea Level Change David Holland, deployed a helicopter-borne ocean temperature probe into a pond-like opening, created by warm ocean waters, in the usually thick and frozen mélange in front of the glacier terminus. Typically, warm, salty waters from the tropics travel north with the Gulf Stream, where at Greenland they meet with cold, fresh water coming from the polar region. Because the tropical waters are so salty, they normally sink beneath the polar waters. But Holland and his team discovered that the temperature of the ocean water at the base of the glacier was a uniform plus four degrees centigrade from top to bottom at depth to 800 meters. The finding was also recently confirmed by NASA’s OMG (Oceans Melting Greenland) project.
“This is unsustainable from the point of view of glacier mass balance as the warm waters are melting the glacier much faster than they can be replenished,” said Holland.
Surface melt drains through the ice sheet and flows under the glacier and into the ocean. Such fresh waters input at the calving front at depth have enormous buoyancy and want to reach the surface of the ocean at the calving front. In doing so, they draw the deep warm tropical water up to the surface, as well.
All around Greenland, at depth, warm tropical waters can be found at many fjord locations. Their presence over time changes depending on the behavior of the Gulf Stream. Over the last two decades, the warm tropical waters at depth have been found in abundance. Greenland outlet glaciers like Helheim have been melting rapidly and retreating since the arrival of these warm waters.
“We are surprised to learn that increased surface glacier melt due to warming atmosphere can trigger increased ocean melting of the glacier,” added Holland. “Essentially, the warming air and warming ocean water are delivering a troubling ‘one-two punch’ that is rapidly accelerating glacier melt.”
The research was supported, in part, by the National Science Foundation's Office of Polar Programs.