"We were surprised to discover this abrupt cooling, which is a marked contrast to the long-term regional ocean warming we've observed in the influx to the glacier," said Dr. Rebecca McPherson, a researcher at AWI and lead author of the study. "Since the ocean water in the glacier cavern grew colder, it means less oceanic warmth was transported under the ice in this period - and in turn, the glacier melted more slowly."
The researchers traced this cooling to changes in circulation patterns in the Fram Strait and Norwegian Sea. From 2016 to 2021, they used an oceanographic mooring to monitor the water temperature and flow speed at the calving front of the 79N Glacier. While Atlantic water temperatures initially rose to 2.1 degrees Celsius by December 2017, they dropped by 0.65 degrees by early 2018.
"We were able to track down the source of this temporary cooling from 2018 to 2021 upstream, to Fram Strait and the vast Norwegian Sea," explained McPherson. "Circulation changes in these remote waters can directly affect the melting of the 79N Glacier."
This cooling trend resulted from atmospheric blocking, where stationary high-pressure systems disrupted usual air currents. Over Europe, these blocks allowed cold Arctic air to flow through Fram Strait, slowing the Atlantic water moving toward the Arctic, leading it to cool. This cooler water then reached Greenland's continental shelf and the 79N Glacier.
"We assume that atmospheric blocks will remain an important factor for multiyear cooling phases in the Norwegian Sea," McPherson added. "They provide the atmospheric and oceanic conditions that influence temperature variability in Atlantic Ocean water, and in turn the glaciers of Northeast Greenland."
In 2025, AWI researchers plan to return to the glacier on the icebreaker 'Polarstern' to monitor water temperatures, which are now rising again slightly. This could provide more data on how these changes impact glacier melting.
McPherson emphasized the importance of understanding these dynamics for better predicting future sea-level rise: "Our study offers new insights into the behavior of Northeast Greenland's glaciers in a changing climate. This will allow forecasts for rising sea levels to be refined."
Prof. Torsten Kanzow from AWI highlighted the broader significance: "Generally speaking, we consider the warm-water inflow into the cavern below the 79N Glacier to be part of the Atlantic Meridional Overturning Circulation (AMOC). Forecasts indicate that this thermal conveyor belt could weaken in the future. One key challenge will be to establish long-term observation systems capable of capturing the effects of macro-scale ocean circulation extending as far as the fjords of Greenland."
Research Report:Atmospheric blocking slows ocean-driven melting of Greenland's largest glacier tongue
Related Links
Alfred Wegener Institute
Beyond the Ice Age
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