A recent study of the Greenland ice sheet found that glaciers are retreating in almost every sector of the island while undergoing other physical changes as well. Some of those changes divert freshwater rivers beneath the ice.
In a study led by Twila Moon of the National Snow and Ice Data Center, researchers took a closer look at the physical changes in 225 of Greenland’s ocean-terminating glaciers – narrow fingers of ice that flow from the interior of the ice sheet to the ocean. They found that none of those glaciers have progressed substantially since the year 2000, and 200 of them have retreated.
The map at the top of this page shows ice speed measurements over Greenland as measured by satellites. The data was collected through the Inter-mission Time Series of Land Ice Velocity and Elevation project (ITS_LIVE), which gathers observations of glaciers collected between 1985 and 2015 by multiple Landsat satellites into one dataset open to scientists and the public .
About 80 percent of Greenland is covered by an ice sheet, also known as a continental glacier, that reaches a thickness of up to 3 kilometers (2 miles). As glaciers flow to the sea, they are usually replenished by new snowfall on the inside of the ice sheet that condenses into ice. Multiple studies have shown that the balance between melting and replenishing glaciers is changing, as is the rate at which the iceberg is calving. Rising air and ocean temperatures cause the ice sheet to lose mass at an accelerated rate and additional meltwater to flow into the sea.
“Greenland’s coastal environment is undergoing a major transformation,” said Alex Gardner, snow and ice scientist at NASA’s Jet Propulsion Laboratory and co-author of the study. “We are already seeing new parts of the ocean and fjords opening as the ice sheet recedes, and now we have indications of changes in these freshwater flows. So losing ice isn’t just about changing sea levels, it’s also about reshaping Greenland’s coastline and changing coastal ecology. “
While the findings of Moon, Gardner and colleagues are in agreement with other Greenland observations, the new survey records a trend that was not apparent in previous work. As individual glaciers retreat, they also change in ways likely to divert freshwater flows under the ice. Glaciers, for example, not only change in thickness as warmer air melts the ice from their surface, but also as their flow rate changes. Both scenarios can lead to changes in the pressure distribution under the ice. This, in turn, can change the path of subglacial rivers, as water will always follow the path of least resistance (lowest pressure).
Referring to previous studies on Greenland’s ecology, the authors note that freshwater rivers below the ice sheet provide nutrients to bays, deltas, and fjords around Greenland. In addition, the rivers under the ice enter the ocean where the ice and rock meet, which is often far below the ocean’s surface. The relatively floating freshwater rises and carries nutrient-rich deep ocean water to the surface, where the nutrients can be consumed by phytoplankton. Research has shown that glacial meltwater rivers have a direct impact on the productivity of phytoplankton, which serves as the basis for the marine food chain. Combined with the opening of new fjords and parts of the ocean as glaciers and ice shelves recede, these changes amount to a transformation of the local environment.
“The rate of ice loss in Greenland is astonishing,” said Moon. “As the edge of the ice sheet responds to rapid ice loss, the character and behavior of the system as a whole changes, with the potential to affect ecosystems and people who depend on it.”
NASA Earth Observatory image by Joshua Stevens, using Landsat data from the US Geological Survey and the Inter-mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) project at NASA / JPL-Caltech, and the General Bathymetric Chart of the Oceans (GEBCO). Story by Calla Cofield, Jet Propulsion Laboratory, with Mike Carlowicz.