A recent Greenland ice sheet analysis showed that glaciers are melting and undergoing other physical changes in virtually all areas of the island. The detour of freshwater flows under the ice is triggered by some of these changes.
Researchers analyzed in detail the physical changes in 225 Greenland glaciers that flow into the ocean – small fingers of ice that flow into the ocean from inside the ice sheet – in an analysis led by Twila Moon of the National Snow and Ice Data Center.
They find that since 2000, none of these glaciers have progressed considerably, and 200 of them have retreated.
The chart at the top of this page displays ice speed measurements taken by satellites over Greenland.
The data was compiled as part of the Land Ice Velocity and Elevation (ITS-LIVE) Inter-mission Time Series project, which incorporates glacier observations collected between 1985 and 2015 by various Landsat satellites into a single dataset accessible to scientists and the public.
Around 80 percent of Greenland is covered by an ice sheet that reaches up to 3 kilometers in thickness, also known as a continental glacier.
They are normally replenished by fresh snowfall within the ice cap, which is compressed into ice, as the glaciers flow into the sea. Several studies have shown that, like the rate of iceberg calving, the equilibrium between glacier melt and replenishment is shifting.
The ice sheet is losing mass quicker and faster due to rising air and ocean temperatures, and additional meltwater is pouring into the sea.
“The coastal environment in Greenland is undergoing a major transformation,”The coastal environment in Greenland is undergoing major transformation. “We’re already seeing new sections of ocean and fjords opening up as the ice sheet retreats, and now we have evidence of changes in these freshwater streams. So ice loss is not only changing sea level, it’s also changing the Greenland coastline and coastal ecology.”
While the results of Moon, Gardner, and colleagues are consistent with other Greenland observations, the new research illustrates a pattern not seen in previous work.
They often move in ways that possibly redirect freshwater flows underneath the ice as individual glaciers withdraw.
For instance, not only when warmer air melts ice from its surface, but also when its flow rates change, glaciers change their thickness.
Both scenarios can result in changes in the distribution of pressure underneath the ice.
In essence, this will alter the direction of subglacial flows, since water still takes the path of least resistance (lowest pressure).
The authors note that freshwater rivers under the ice sheet provide nutrients for bays, deltas, and fjords around Greenland, citing previous studies of Greenland’s ecology.
In addition, the rivers beneath the ice join the water, which is mostly just below the surface of the ocean, where the ice and bedrock meet.
The relatively buoyant freshwater rises and brings deep water rich in nutrients to the surface, where phytoplankton can pick up the nutrients. Research has shown that the flow of glacial meltwater has a direct effect on phytoplankton production, which acts as the base of the marine food chain.
These changes lead to a transformation of the local climate, coupled with the opening of new fjords and ocean parts due to glacier and ice shelf retreat.
“The rate of ice loss in Greenland is staggering,” Moon says. “As the edge of the ice sheet responds to rapid ice loss, the character and behavior of the entire system is changing, with the potential to affect ecosystems and the people who depend on them.”
Image of the NASA Earth Observatory by Joshua Stevens, using US Landsat data Geological Survey and the NASA/JPL-Caltech Land Ice Velocity and Elevation Inter-mission Time Series (ITS-LIVE) project and the Oceans General Bathymetric Map (GEBCO). Contributed by Mike Carlowicz from Calla Cofield, Jet Propulsion Laboratory.