Between 2018 and 2021, the water flow from Greenland’s 79° north latitude glacier cooled, slowing down its melting rate. This cooling is due to atmospheric blocking patterns that alter ocean currents, even as the overall ocean temperature rises. Researchers will return to the glacier in 2025 to observe whether rising water temperatures will again exacerbate glacier melt, providing insights into climate-driven glacier behavior and sea level rise predictions.
Atmospheric processes are cooling Atlantic water entering the ice cave under the 79°N glacier in northeastern Greenland. The 79°N Glacier in northeast Greenland, the country's largest floating glacier tongue, is under severe threat from global warming as warm Atlantic waters erode the glacier from below. However, experts from the Alfred Wegener Institute recently discovered that the temperature of the water flowing into the glacier caves dropped between 2018 and 2021, despite continued warming of the region's oceans in recent decades. This may be related to temporary changes in atmospheric circulation patterns.
In a study just published in the journal Science, researchers discuss the impact this has on the ocean, and what it means for the future of Greenland's glaciers.
Over the past few decades, the Greenland ice sheet has lost increasing amounts of mass, which has also reduced its stability. This is largely due to atmospheric and ocean warming that accelerates the melting of ice, which in turn causes mean sea levels to rise. If the glacier flow in northeastern Greenland alone melts completely, it will cause sea levels to rise by one meter, and the source of the glacier flow is the huge Nioghalvfjerdsfjorden glacier (also known as the 79th North Latitude Glacier). There is a cave under the tongue of the glacier into which sea water can flow.
Surprising discovery: cooling water
Data collected by the Alfred Wegener Institute and the Helmholtz Center for Polar and Marine Research (AWI) show that the temperature of the water flowing into the cave dropped between 2018 and 2021.
"We were surprised to find this sudden cooling, which is in stark contrast to the long-term regional warming we observed in the water flowing into the glacier," said AWI researcher Dr. Rebecca McPherson, first author of the study. "Because the water in the glacier caves is getting colder, this means that less warm ocean currents were transported under the glacier during this period - and in turn, the glacier melted slower and slower."
But if temperatures in the surrounding ocean continue to climb, where does the cold water beneath the glacier come from? To find out, researchers at AWI collected data from 2016 to 2021 using oceanographic moorings. The monitoring platform continuously reads parameters such as the temperature and flow rate of the seawater at the front of the glacier fissure at 79° north latitude. The temperature of Atlantic Ocean waters initially increased, reaching a maximum of 2.1 degrees Celsius in December 2017, but has dropped by 0.65 degrees Celsius since early 2018.
"We were able to trace the source of this temporary cooling from 2018 to 2021, to the upper Fram Strait and the vast Norwegian Sea," explains Rebecca Macpherson. "In other words, changes in circulation in these remote waters will directly affect the melting of the 79° north latitude glacier."
The lower water temperatures in Fram Strait are therefore a result of atmospheric blocking. When this blocking occurs, stationary high-pressure systems in the atmosphere force the normally dominant flow to deviate. The same is true over the Fram Strait: several atmospheric obstructions over Europe allow more cold air from the Arctic to flow through the Fram Strait and into the Norwegian Sea. This slows down the flow of water from the Atlantic to the Arctic, causing it to cool more than usual along the way.
The cooled water flows through the Fram Strait to the Greenland continental shelf and the 79° north latitude glacier. The entire process takes two to three years from the onset of the atmospheric barrier to the flow of cooler Atlantic water into the glacial caves.
Effects of atmospheric blocking
Rebecca-McPherson said: "We believe that atmospheric barriers will remain an important factor in the multi-year cooling phase of the Norwegian Sea. They provide the atmospheric and oceanic conditions that influence changes in Atlantic seawater temperatures, and in turn affect the glaciers in northeast Greenland. Why? Because the north-flowing water mass not only continues to penetrate deeper into the Arctic, affecting the extent and thickness of sea ice; In the Fram Strait, about half of the water mass turns to the west, determining the ocean melt of the Greenland glacier. In the summer of 2025, we will return to the 79°N glacier on the research icebreaker Polarstern. We already know that the water temperature in the Fram Strait is now rising slightly, and we are eager to know whether the glacier melt will be intensified as a result. "
In order to more accurately predict the fate of the 79°N glacier, it is important to understand the drivers of changes within the glacier, as Rebecca McPherson emphasizes: "Our study provides new insights into the behavior of northeast Greenland's glaciers in a changing climate. This will help refine predictions of sea level rise."
Their colleague Professor Torsten Kanzow from AWI added: "In general, we think that the warm currents flowing into the caves beneath the 79°N glacier are part of the Atlantic Meridional Overturning Circulation (AMOC). Projections indicate that this heat transport belt may weaken in the future. A key challenge is to establish long-term observing systems that can capture the effects of large-scale ocean circulation as far away as the Greenland fjords."
Compiled from /ScitechDaily