Seawater Can Intrude Even Under “Grounded” Ice to Accelerate Ice Sheet Retreat

The Cryosphere, 8 February 2022

New modeling suggests that warm seawater can slip underneath grounded ice sheets — ice resting on land or bedrock — and travel tens of kilometers inland beneath the grounded ice. When the ground below the ice is flat or slopes downward and is impermeable, such as bedrock; seawater can mix with the channels of meltwater flowing beneath the surface of the ice sheet. This mixing pushes warm saltwater against the bottom of the ice, accelerating melt rates and ice loss. These findings suggest that the “grounding line” – where the ice sheet transitions to float on the surface of water – is not an impenetrable barrier between ice sheet and ocean. If seawater sneaks underneath and flows just several hundred meters past the grounding line, ice loss from that ice sheet could increase by 10-50% over a century. Should this seawater flow tens of kilometers inland, it can double or triple projected ice loss. Understanding the extent to which ice sheets and outlet glaciers are affected by seawater intrusion is critical to predicting how quickly Antarctic ice sheet loss may contribute to sea-level rise.