Near Term Ocean Warming Around Antarctica Affects Long Term Rate of Sea Level Rise
A highly-resolved model of the West Antarctic Ice Sheet is used to examine the processes regulating basin-wide ice mass loss. This study finds that rates of mass loss are especially sensitive near the point the system transitions into a regime of self-sustained retreat where the effects of anomalous forcing and larger driving stresses are sustained by the dynamics of a retreating ice sheet, and even small differences in the initial forcing rates can translate into large differences in long-term rates of mass loss from the Thwaites Glacier system.
The marine-grounded portions of the West Antarctica Ice Sheet contain enough vulnerable ice to raise global sea level by 3 meters. Recent incursions of warmer water and resultant mass loss from this region will be exacerbated by projected changes in global climate, so understanding the response of this system to different marine forcings is crucial to projections of longer-term sea level rise.
We applied a highly-resolved model (the SciDAC-sponsored BISICLES ice-sheet model) to the West Antarctic Ice Sheet to examine the processes regulating basin-wide ice mass loss. In the experiment we ramped up ocean melting of the shelves very slowly to identify the point at which mass loss begins to accelerate due to the Marine Ice Sheet Instability. We then cut off this additional ocean melt forcing and allowed the system to evolve to its new equilibrium configuration where the grounding line is deep into the interior. Near the point of instability, small differences in ocean forcing have a long term effect on discharge rates, even after the external forcing is removed -- grounding line retreats that begin faster proceed more rapidly throughout the entire experiment. We did two experiments that only differed by 0.5 m/year in melt rate. The one with the higher melt rate sustained a significantly higher discharge rate for the entire collapse of West Antarctica This result is due to the role of added forcing to create steeper slopes at the grounding line which in turn causes higher discharge rates. This positive feedback for the MISI means that details concerning how the ocean forces ice sheets across the threshold for instability will be critical for determining the rate of sea level rise