Northeast Greenland is the site of the 79° N Glacier, the largest floating glacier tongue in the country, which faces serious threats from climate change as warm Atlantic waters erode it from underneath. Researchers from the Alfred Wegener Institute have found that the temperature of water entering the glacier cavity decreased between 2018 and 2021, contrasting with the ongoing ocean warming seen in the region over the last few decades. This unusual cooling might stem from temporary shifts in atmospheric circulation patterns. A recent study published in the journal Science explores the implications of these findings for Greenland’s glaciers and the ocean environment.
The Greenland Ice Sheet has been losing mass over the years, compromising its stability, primarily due to rising atmospheric and ocean temperatures that accelerate ice melting, contributing to higher sea levels. If the Northeast Greenland Ice Stream, which supplies the massive Nioghalvfjerdsfjorden Glacier (also known as the 79° N Glacier), were to melt completely, it could lead to a sea-level rise of one meter. The glacier’s tongue contains a cavern where ocean water flows in, and recent data from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) shows that the temperature of this incoming water dropped from 2018 to 2021. Dr. Rebecca McPherson, a primary author of the study, expressed surprise at this sudden cooling, noting it stood in sharp contrast to the long-term warming trend seen in the region. “The colder ocean water signifies that less heat was transferred under the glacier during this period, resulting in a slower melting rate of the glacier,” she said.
The question remains: where did this cold water below the glacier originate if surrounding ocean temperatures kept rising? To answer this, AWI researchers gathered data from 2016 to 2021 using an oceanographic mooring system that continuously recorded thermodynamic parameters at the glacier’s calving front, where water enters the cavern. While the temperature of Atlantic water initially increased, peaking at 2.1 degrees Celsius in December 2017, it subsequently decreased by 0.65 degrees starting in early 2018.
“We traced the source of this temporary cooling to the Fram Strait and the Norwegian Sea,” explained Rebecca McPherson. “This indicates that changes in circulation patterns in these distant waters can have a direct impact on the melting processes of the 79° N Glacier.” The cooler water temperatures in Fram Strait were likely caused by atmospheric blocking, which involves stationary high-pressure systems altering the typical air currents. During this event, atmospheric blocks over Europe enabled more cold Arctic air to enter the Fram Strait and the Norwegian Sea, which slowed down the warm Atlantic water traveling towards the Arctic, allowing it to cool more than usual before flowing to Greenland’s continental shelf and the glacier. This entire cycle—from the formation of atmospheric blocks to the cooler Atlantic water reaching the glacier cavern—spanned two to three years.
“We expect that atmospheric blocks will play a significant role in future multiyear cooling phases in the Norwegian Sea,” noted Rebecca McPherson. “These blocks contribute to the atmospheric and oceanic conditions that shape temperature variations in Atlantic waters, which ultimately affect the glaciers of Northeast Greenland.” The northward-flowing water not only reaches further into the Arctic, impacting sea ice extent and thickness; approximately half of this water diverts westward at Fram Strait, influencing the melting of Greenland’s glaciers. “In the summer of 2025, our research team will return to the 79° N Glacier aboard the research icebreaker Polarstern. We’ve observed that water temperatures in Fram Strait are rising slightly again, and we are eager to assess whether this will lead to increased melting of the glacier,” she added.
To accurately predict the future of the 79° N Glacier, it is crucial to grasp the factors driving changes within it, as emphasized by Rebecca McPherson: “Our study sheds new light on the dynamics of Northeast Greenland’s glaciers amid climate change. This will facilitate improved predictions for sea level rise.” As stated by their colleague Prof Torsten Kanzow from AWI, “In general, we regard the warm water entering the cavern beneath the 79° N Glacier as part of the Atlantic Meridional Overturning Circulation (AMOC). Projections suggest that this critical thermal system could weaken in coming years. It will be a major challenge to implement long-term monitoring systems that can capture the effects of broader ocean circulation patterns that extend to Greenland’s fjords.”
