Rapid melt is reshaping coastal Greenland, potentially altering the human and animal ecosystems along the country's coast.
New research published in the Journal of Geophysical Research: Earth Surface on Oct. 27 finds that the ice retreat in Greenland has changed the way glaciers flow and where they dump into the sea. These changes could impact ice loss from Greenland in the future, the researchers wrote.
Recent studies have shown that Greenland is losing 500 gigatons of ice each year, more than can be replenished by new snowfall. Annual ice loss is 14 percent greater today than it was between 1985 and 1999. And the meltwater from this ice loss is lubricating the ice sheet so that it slides more easily on its underlying bedrock, hastening the continued melt.
The new study, led by National Snow and Ice Data Center research scientist Twila Moon, breaks down the changes in more detail.
Moon and her colleagues combined two types of data from satellite imagery: how fast the ice sheet is moving and where glaciers terminate on their path downhill. When a glacier retreats, its terminus doesn't reach as far down-valley as it once did.
They found, first, that glacier retreat is now the norm in Greenland. Eighty-nine percent of glaciers had retreated substantially within the last decade, the researchers wrote in their paper. Virtually none had advanced.
However, this reshaping of glaciers translated into a variety of changes in glacier movement. Some glaciers were speeding up, flowing more rapidly toward the sea, the researchers found; others were flowing more slowly. And over several years to a decade, a single glacier could do both, depending on the topography around it.
Glaciers are rivers of ice, so their flow is partially determined not just by how quickly they're melting, but by what's underneath them.
For example, the Kjer and Hayes glaciers in northwestern Greenland sped up at their primary outlets to the sea from the 1990s to 2010, but other ice outlets to the ocean nearby slowed down. In one case, the southerly portion of one of those outlets sped up, then slowed again.
The researchers saw evidence of ice channels narrowing, of re-routing meltwater paths, and even of the slowing of new ice so that glaciers are stranded in place, more like lakes than rivers.
All of this local variation may be very important for predicting how quickly Greenland's ice will disappear in the future. The changes will also likely affect how and where nutrients enter the water, where there are open fjords versus ice, and where freshwater is available.
"As the Arctic ocean and atmosphere warm, we can clearly see the flow of ice into the ocean accelerate and the ice edge retreat," study co-author Alex Gardner, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, said in a statement.
"When we look more closely, however, we can see the complexity of how individual glaciers respond, owing to differences in the properties of the ocean water that reach the glacier front, the bedrock and till that lie below, and in how meltwater runoff is routed beneath. Understanding the complexity of individual glacier response is critical to improving projections of ice sheet change and the associated sea level rise that will arrive at our shores."