Northeast Greenland is home to the 79° N Glacier—the country’s largest floating glacier tongue, but also one seriously threatened by global warming. Warm water from the Atlantic is melting it from below. However, experts from the Alfred Wegener Institute have now determined that the temperature of the water flowing into the glacier cavern declined from 2018 to 2021, even though the ocean has steadily warmed in the region over the past several decades. This could be due to temporarily changed atmospheric circulation patterns.

In a study just released in the journal Science, the researchers discuss how this affects the ocean and what it could mean for the future of Greenland’s glaciers.

Over the past few decades, the Greenland Ice Sheet has lost more and more mass, which has also lessened its stability. This is chiefly due to the warming of the atmosphere and oceans, which accelerates the melting of ice, contributing in turn to an increase in mean sea level. The Northeast Greenland Ice Stream alone, which feeds into the massive Nioghalvfjerdsfjorden Glacier—also known as the 79° N Glacier—could produce a meter of sea-level rise if it melted completely.

Beneath the glacier tongue lies a cavern, into which ocean water flows. Data gathered by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) now indicates that the temperature of the water flowing into the cavern declined between 2018 and 2021.

“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,” says Dr. Rebecca McPherson, a researcher at the AWI and the study’s first author. “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.”

But where did this cold water below the glacier come from if temperatures in the surrounding ocean continued to climb? To find out, the AWI researchers collected data from 2016 to 2021, using an oceanographic mooring to do so.

The monitoring platform continually took readings on parameters like the temperature and flow speed of the seawater at the calving front of the 79° N Glacier, which is where water flows into the cavern. Whereas the temperature of the Atlantic water initially rose, topping out at 2.1 degrees Celsius in December 2017, it dropped by 0.65 degrees again from 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,” McPherson explains. “In other words, circulation changes in these remote waters can directly affect the melting of the 79° N Glacier.”

As such, the lower water temperatures in Fram Strait were the result of atmospheric blocking. When this blocking occurs, stationary high-pressure systems in the atmosphere force the normally dominant air currents to deviate. That’s also what happened over Fram Strait: Several atmospheric blocks over Europe allowed more cold air from the Arctic to flow through Fram Strait into the Norwegian Sea. This slowed water from the Atlantic that was flowing toward the Arctic, so that it cooled more than usual along the way.

The cooled water then flowed through Fram Strait to Greenland’s continental shelf and the 79° N Glacier. The whole process—from the appearance of the atmospheric blocks to the inflow of the cooler Atlantic water in the glacier cavern—took two to three years.

“We assume that atmospheric blocks will remain an important factor for multiyear cooling phases in the Norwegian Sea,” says McPherson. “They provide the atmospheric and oceanic conditions that influence temperature variability in Atlantic Ocean water, and in turn the glaciers of Northeast Greenland.”

Why? Because the northward-flowing water mass not only continues farther into the Arctic, where it affects the extent and thickness of sea ice; in Fram Strait, roughly half of the water veers to the west, where it determines the oceanic melting of Greenland’s glaciers.

“In the summer of 2025, we’ll be returning to the 79° N Glacier on board the research icebreaker Polarstern. We already know that water temperatures in Fram Strait are now rising again slightly, and we’re anxious to see if the glacier melting increases as a result.”

To more accurately predict the fate of the 79° N Glacier, it’s important to understand what is driving changes within it, as McPherson stresses: “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.”

As their colleague, Prof. Torsten Kanzow from the AWI, adds, “Generally speaking, we consider the warm-water inflow into the cavern below the 79° N 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.”

University of Adelaide researchers have developed a new theoretical model to predict the distances ocean waves can travel to break up sea ice.

Monitoring of ocean wave propagation is important to predict how ice covering the Arctic and Antarctic seas responds to climate change, but the incumbent model was initially developed in the 1970s and 1980s.

Dr. Luke Bennetts and Jordan Pitt from the University of Adelaide’s School of Computer and Mathematical Sciences investigated how the changes in breaking up the ice affect wave propagation, and published their findings in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

“Previously, distances ocean waves can break up sea ice cover were only considered in terms of gradual reductions in wave energy over distance,” said Dr. Bennetts.

“Our results show that large reductions can occur over a small distance until an unbroken ice cover begins to break up, and that this additional consideration can alter interpretations of field observations.”

When waves travel into frozen areas of the ocean surface, it can cause the break-up of the ice cover into discrete chunks known as floes, which drift away and melt rapidly.

“At the same time, waves become less intense over distance due to the ice cover, so that the break-up only occurs over a finite distance,” said Dr. Bennetts.

“Changes have been observed in the way waves travel through regions of sea ice before and after break-up events, but it is very difficult to measure the changes in the challenging polar seas.

“We used a mathematical model to understand the changes and were able to quantify local changes which occur where the ice cover begins and changes that occur over long distances.”

Dr. Bennetts said the findings have the potential to inform how wave–sea ice interactions are handled in numerical models used for climate studies.

“The main goal in this research field is to predict the distances over which ocean waves can break up a sea ice cover,” he said.

“The long-term aim is to advance predictions of numerical climate models about the future of the world’s sea ice.

“In the shorter-term, we aim to combine the model of the ice effect on the waves with a model of ice break-up due to waves, to generate predictions of the extent of ice break-up.”