Greenland's small peripheral glaciers are rapidly melting and accelerating sea-level rise

According to new data published by the American Geophysical Union, Greenland's northernmost glaciers are rapidly melting. The small peripheral glaciers of the northernmost regions of the massive ice sheet contribute to sea-level rise. These glaciers are not attached to the larger ice sheet though they contribute disproportionally to mass ice loss on the island despite heavy snowfall falling in the higher elevations. The smaller glaciers' melt rate is currently not factored into any climate models, even though the Arctic is melting up to seven times faster than the rest of the planet. 

The unrelenting rise of air temperatures that melts the surface ice is uneven in Greenland, which according to the study authors, means that the fate of these marine-terminating clusters in the north is critical in getting an accurate picture of how much freshwater is pouring into the ocean. 

DTU Space collaborated with the Geological Survey of Denmark and Greenland, NASA Goddard Space Flight Center, Utrecht University, University of Bristol, Technical University Munich, and the University of Copenhagen to research the small glaciers. The glaciers make up only 4% of the ice in Greenland but account for 11% of the total ice loss.

The lead author, Professor Shfaqat Abbas Khan from DTU Space, is quoted, "The loss of ice from these small glaciers occurs because they are more sensitive to ongoing temperature changes and therefore melt faster than we see in many other places in the Arctic."

WASHINGTON—Greenland’s many small glaciers are melting more rapidly as the Arctic warms, contributing to sea level rise, yet they are less well-studied than the main Greenland Ice Sheet. A new study documents about a 50% increase in melting in these small but important glaciers over the past two decades.

The new study, published today in the AGU journal Geophysical Research Letters, focused on “peripheral” glaciers, which are glaciers with areas smaller than 0.05 km2 and do not receive ice flow or accumulation from the Greenland Ice Sheet.

There are around 20,300 peripheral glaciers in Greenland, and while they make up only about four percent of Greenland’s ice-covered areas, they contribute as much as 11 percent of the total loss of ice from Greenland’s ice-covered areas. This outsize melt rate means an outsize contribution to sea level rise.

Melting of peripheral glaciers has increased by more than 50% over the past two decades, as recorded by altimetry data from ICESat and ICESat-2, the study found. On average, 42.3 gigatons of ice melted per year from October 2018 to December 2021. In comparison, 27.2 gigatons melted annually from February 2003 to October 2009.

Calving on Greenland's more enormous glaciers.

Seismometers detect small icebergs produced by Greenland's glaciers.

When a large chunk of ice at the end of a glacier that flows into the sea breaks off, an iceberg is born. Heralding its birth is often a glacial earthquake that is detected by the Global Seismographic Network (GSN), an array of over 150 seismometers distributed around the world. The iceberg-calving process is a key mechanism by which large volumes of ice are lost from Greenland and Antarctica. Yet, many details remain concealed because permanent cameras are installed at the ends of very few glaciers. Poor visibility, caused by either bad weather or dark winters, further limits the utility of imagery of to understand iceberg calving. Fortunately, scientists can now keep a close eye on this process using seismic data from the Greenland Ice Sheet Monitoring Network (GLISN), which provides continuous coverage of seismicity that is too faint to be detected by global networks.

Using IRIS-curated data from both the GSN and GLISN, scientists Kira Olsen, now at the NASA Goddard Space Flight Center, and Meredith Nettles, of Columbia University’s Lamont-Doherty Earth Observatory, investigated calving at Greenland’s three largest glaciers, which have also produced the majority of recorded glacial earthquakes since 1993—Jakobshavn Isbræ, Helheim Glacier, and Kangerdlugssuaq Glacier. Olsen and Nettles found that GLISN data revealed numerous smaller seismic events in the minutes before, and sometimes after, over a third of the globally detectable quakes. The results of this study were published in the July 2019 issue of the Journal of Geophysical Research-Earth Surface.

According to lead author Olsen, who completed this work as part of her doctoral studies at Columbia University, the focus of the study is on buoyancy-driven calving, which happens when the front end of a glacier sits “too low” in the water and is subsequently bent upward because ice is less dense than liquid water (Figure 1). That bending applies a torque to the ice, causing it to fracture from the bottom up. She says “buoyancy-driven calving then occurs when the fracture has propagated all the way up to the surface and a tall, thin, block of ice has detached.” A vertically perched iceberg is unstable in the water, so it capsizes away from the glacier. As the iceberg accelerates into the water, a glacial earthquake is produced, she says.

Some of the largest icebergs in Greenland form this way, producing earthquakes detectable globally via the GSN. Yet, according to Olsen, “until this point we have had less information on when and where small icebergs calve.” She explains that the GSN stations, located outside of Greenland, are far enough away from the glaciers that they do not detect seismic signals that small icebergs should produce when they form. She says, "The advantage of the GLISN stations is that they are located closer to the large glaciers we study. When we focus on these nearby stations, we can investigate seismic signals from smaller iceberg-calving events.” In other words, before this work, whether calving of small icebergs caused glacial earthquakes was an open question, which led to uncertainty in estimates of total volume of ice lost through iceberg calving.

Scientists have documented a previously unknown subpopulation of polar bears living in Southeast Greenland. The polar bears survive with limited access to sea ice by hunting from freshwater ice that pours into the ocean from Greenland’s glaciers. Because this isolated population is genetically distinct and uniquely adapted to its environment, studying it could shed light on the future of the species in a warming Arctic.

“We wanted to survey this region because we didn’t know much about the polar bears in Southeast Greenland, but we never expected to find a new subpopulation living there,” said lead author Kristin Laidre, a polar scientist at the University of Washington’s Applied Physics Laboratory. “We knew there were some bears in the area from historical records and Indigenous knowledge. We just didn’t know how special they were.”