Toward a complete extinction of the last ice shelves of the Greenland ice sheet

In northern Greenland, glaciers contain enough ice to raise sea levels by more than 2 meters. In this region, glaciers naturally flow from the interior of the ice sheet to the ocean, where they start to float and form ice shelves several tens or even hundreds of kilometers long. "These ice shelves play a crucial role, similar to giant "dams" that regulate the quantity of icebergs discharged into the ocean by the glaciers" explains Romain Millan, lead author of the study. When these ice shelves thin and fracture, the dam weakens, inevitably impacting the contribution of the ice caps to sea level rise.

In Greenland, most glaciers began losing mass in the early 1980s and 1990s, specifically in the northwest and southeast part of the ice sheet. The glaciers located in the north are the last glaciers in Greenland with large floating extensions. Unlike their neighbors, these glaciers had remained very stable until now.

Researchers from CNRS (IGE, Grenoble), in collaboration with the University of Copenhagen, the National Geological Survey of Denmark and Greenland (Copenhagen, Denmark), and Moss Land Marine Laboratories (San Jose, USA), published a study in Nature Communications showing the first signs of weakening of these glaciers. Using a large collection of satellite images, scientists calculated that these shelves had lost more than a third of their volume.

By combining data from satellites, aircraft, and numerical models, researchers were able to trace the melting occurring beneath the floating ice. They observed for the first time that this melting had drastically increased since the 2000s. "When we first had the maps, we saw that the rates of underwater melting were incredibly high, reaching more than a hundred meters of melt per year in some cases !" explains Romain Millan. By collecting ocean temperature measurements over the past 40 years and comparing them with physical reanalyses, researchers determined that this increase in melting was largely due to significant warming of ocean waters throughout the region.

The problem is that this basal ice shelf melting affects the glaciers upstream. "Over the entire observation period, we have seen a significant retreat of the glaciers’ grounding lines, more than 8 kilometers for the strongest retreats," says Romain Millan. The grounding line marks the boundary where the ice becomes floating. The retreat of this natural boundary is a sensitive indicator of the glacier’s response to climate warming and instability.

By measuring glacier flow and thickness, researchers were also able to calculate the amount of ice discharged into the ocean. "On some glaciers, the discharge has increased by more than 25% in response to changes affecting the ice shelves," worries Eliot Jager, a co-author of the study and a doctoral student at the Institute of Environmental Geosciences. In other words, more and more icebergs are being discharged into the sea, directly impacting sea level rise.

"Under current climatic conditions, polar regions will inevitably continue to warm at far too high rates," comments Dr. Millan. A continuous increase in air and ocean temperatures could therefore pose a lasting threat to the last ice shelves in northern Greenland. "If these ice shelves collapse, as has happened to neighboring glaciers, there is a real risk that this region could become the largest contributor to sea level rise in the entire Greenland ice sheet," concludes Anders Bjørk from the University of Copenhagen.

In Antarctica, the majority of the ice sheet flows into the ocean from large floating platforms. The rapid changes observed in Greenland could thus be considered as a first glimpse of processes that could affect Antarctica in the near future.

Video presenting the main results

Reference :
Rapid disintegration and weakening of ice shelves in northern Greenland. R. Millan, et al. Nature Communications, November 7, 2023.
https://www.nature.com/articles/s41467-023-42198-2

Contact :
Romain Millan, CNRS | T + 33 6 16 42 16 14 | romain.millan univ-grenoble-alpes.fr