1985 – 2015
A recent study of Greenland’s ice sheet found that glaciers in almost every sector of the island are retreating, while undergoing other physical changes. Some of these changes lead to the diversion of freshwater rivers under the ice.
In a study led by Twila Moon of the National Snow and Ice Data Center, researchers conducted a detailed study of physical changes to 225 of Greenland’s ocean-bending glaciers – narrow fingers of ice flowing from the ice sheet to the ocean. They found that none of the glaciers had made significant progress since 2000, and 200 of them had retreated.
The map at the top of this page shows measurements of the ice speed over Greenland, as measured by satellites. The data was compiled by the Inter-Mission Time Series of Land Ice Velocity and Elevation Project (ITS_LIVE), which brings together observations of glaciers collected by several Landsat satellites between 1985 and 2015 in a single data set open to scientists and the public.
About 80 percent of Greenland is covered by an ice sheet, also known as a continental glacier, which reaches a thickness of up to 3 kilometers (2 miles). As glaciers flow into the sea, they are usually supplemented by new snowfall on the inside of the ice sheet that is compacted into ice. Several studies have shown that the balance between melting glaciers and replenishment changes, as does the rate of iceberg calf. Due to rising air and ocean temperatures, the ice sheet is losing mass at a faster rate and additional meltwater is flowing into the sea.
“The coastal environment in Greenland is undergoing a major transformation,” said Alex Gardner, a snow and ice scientist. NASA‘s Jet Propulsion Laboratory and co-author of the study. ‘We’re already seeing new parts of the ocean and fjords open up as the ice shelf retreats, and now we have evidence of changes to these freshwater streams. Losing ice is not just about changing sea levels; it is also about reforming Greenland’s coastline and changing coastal ecology. ”
Although the findings by Moon, Gardner and colleagues are consistent with other observations from Greenland, the new survey records a trend that was not yet clear in previous work. As individual glaciers retreat, they also change in ways that are likely to divert freshwater flow under the ice. Glaciers, for example, change in thickness not only as warmer air melts ice from their surfaces, but also as their flow rate changes. Both scenarios can lead to changes in the distribution of pressure under the ice. This in turn can change the path of subglacial rivers, because water will always take the path of least resistance (lowest pressure).
Referring to previous studies on the ecology of Greenland, the authors note that freshwater rivers under the ice sheet supply nutrients to bays, deltas and fjords around Greenland. In addition, the rivers beneath the ice enter the ocean where the ice and rock meet, often far below the surface of the ocean. The relatively living fresh water rises, and carries deep, ocean water to the surface, where nutrients can be consumed by phytoplankton. Research has shown that glacial meltwater rivers directly affect the productivity of phytoplankton, which serve as the foundation of the marine food chain. Combined with the opening of new fjords and retreating parts of the ocean such as glaciers and ice planes, these changes are a transformation of the local environment.
“The speed of ice loss in Greenland is incredible,” Moon said. “As the ice edge 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 them.”
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, starring Mike Carlowicz.