Rising ocean temperature threatens Greenland ice sheet

Scientific progress, provides a clearer picture of the melting of the ice sheets of the massive island and the impact on world sea level. Credit: NASA “width =” 768 “height =” 432 “/>

Scientists at the University of California, Irvine and NASA’s Jet Propulsion Laboratory have quantified for the first time how warm coastal waters affect individual glaciers in the fjords of Greenland. Their work is the subject of a recent study in Scientific progress.

The researchers have been working under the auspices of the Oceans Melting Greenland mission for the past five years, using ships and aircraft to examine 226 glaciers in all sectors of one of the Earth’s largest islands. They found that 74 glaciers in deep, steep-walled valleys accounted for almost half of Greenland’s total ice loss between 1992 and 2017.

Such fjord-bound glaciers have been found to undergo the greatest subjection, a process by which hot, salt water at the bottom of the gorges melts the ice from below, causing the masses to break apart faster than usual. In contrast, the team found that 51 glaciers placed in shallower ditches experienced less undercamping and contributed only about 15 percent of the total ice loss.

“I was amazed at how skewed it was. The largest and deepest glaciers are submerged much faster than the smaller glaciers in shallow fjords,” said lead author Michael Wood, a doctoral researcher at NASA’s Jet Propulsion Laboratory in Southern California. start. this research as a doctoral student at the UCI. “In other words, the largest glaciers are the most sensitive to the hot water, and they are the ones that are really driving Greenland’s ice loss.”

The study highlighted the dynamics by which deeper fjords allow the penetration of warmer seawater than level, which accelerates the interruption process with some of Greenland’s largest glaciers.

Greenland is home to one of the only two ice sheets on earth, the largest of which is Antarctica. The ice in Greenland is more than three kilometers thick in places. At the edge of the land mass, the expansive glaciers that stretch from the ice sheet slowly move down into valleys like icy conveyor belts, which thumbs into the fjords and then melt or break down like icebergs. The ice is supplemented by snowfall that is eventually compressed in the ice pack.

If the ice sheet were in balance, the amount of snow on top would be approximately equal to the ice lost through melting, evaporation and calving – pieces that break loose from anchored masses and float in the ocean.

But the ice sheet has been out of balance since the 1990s. Melt accelerated and calving increased, causing glaciers extending into the sea to return to land. Together this leads to the shrinkage of the ice sheet.

According to the research team, the build-up of hot salt water at the bottom of the fjords was accelerated by the rising temperatures in the summer months, which heated the surfaces of glaciers and created pools of meltwater. This liquid leaks through cracks in the ice to form freshwater rivers beneath the surface that flow into the sea where it interacts with saltwater under fjords.

Melting water from glaciers is free of salt, so it is lighter than seawater and rises like a plume to the surface, drawing up hot water and placing it in contact with the bottom of glaciers. Fjord depth is a fairly unchanging factor, but other factors such as seawater temperature and the amount of meltwater from glacier surfaces are strongly influenced by climate warming. All three factors are causing accelerated deterioration of Greenland’s ice sheet, the researchers said.

As the prediction of water temperature around the Greenland coastline will continue to increase in the future, these findings suggest that some climate models may underestimate ice loss by at least a factor of two if it does not take into account the warming of a warm ocean. .

The study also provides insight into why many of Greenland’s glaciers never recovered after a sudden ocean warming between 1998 and 2007, which caused an increase in ocean temperature by almost 2 degrees Celsius. Although ocean warming stopped between 2008 and 2017, the glaciers had already experienced so much disruption in the previous decade that they were able to retreat at a faster rate.

“We have known for more than a decade that the warmer oceans play a major role in the evolution of Greenlandic glaciers,” said Eric Rignot, deputy principal investigator at JPL and UCI. “But for the first time, we were able to quantify the undercutting effect and show its dominant impact on the glacier retreat over the past twenty years.”