A novel view on the key factors controlling the long term response of the Greenland Ice-Sheet flow to surface melt water

Ice flowing from the interior to the lower elevated edges of Greenland exerts a key control on how much the Ice-Sheet will lose mass as temperatures rise. The faster the ice flows, the faster it reaches the edges where it can be discharged in the ocean or melt. Predicting ice flow, however, is a challenging task. In Greenland, ice flow is mainly controlled by the sliding of ice over its underlying bedrock and the modulation of it by surface melt water supplied to the base through vertical conduits called moulins. Previous theories suggest increased surface melt rates actually reduce basal slipperiness by enlarging subglacial tunnels that can efficiently evacuate lubricating melt water at the bed, thus strengthening contacts between the ice and its bed. This mechanism limits the potential of melt forcing to increase mass loss as temperatures rise into the future.

In the present study published in Nature, researchers from the Grenoble Institute of Environmental Geosciences (IGE, France) developed an innovative approach combining satellite observations and numerical modelling to test how surface melt influences basal slipperiness over the entirety of western Greenland.

Surprisingly, the authors find that surface melt rates do not control basal slipperiness. Instead, they demonstrate that conditions at the ice edge, whether the ice flows directly into the ocean or terminates on land, has the largest difference on how melt influences basal slipperiness including far into the interior of Greenland. The authors suggest this different response is due to marine terminating glaciers having a different morphology than land terminating glaciers. They are consistently faster and steeper, which eases the removal of lubricating basal water compared to land terminating glaciers, which are slower and flatter.

This new insight suggests unforeseen dynamic changes which increase mass loss are likely to occur as marine terminating glaciers retreat into the future. Yet, the study suggests ways that the findings could be incorporated into ice sheet models, which will enable researchers to improve predictions of mass-loss and ice sheet evolution through the end of the century.

Reference

Maier, N., Gimbert, F. & Gillet-Chaulet, F. Threshold response to melt drives large-scale bed weakening in Greenland. Nature 607, 714–720 (2022). https://doi.org/10.1038/s41586-022-04927-3

See also: Livingstone, S.J. Trapped meltwater affects mass loss of Greenland ice sheet. Nature 607, 659-660 (2022)

See the main results in this video

Updated on 22 August 2022