Positive and Negative Feedbacks to Antarctic Ice Shelf Melt in an Eddy Rich Global Ocean–Sea-Ice Model

Ruth Moorman1, Adele K Morrison2 and Andrew M Hogg1, (1)Australian National University, Research School of Earth Sciences, Canberra, ACT, Australia, (2)Australian National University, Research School of Earth Sciences, Canberra, Australia
Water-mass exchange across the Antarctic shelf margin plays a crucial role in abyssal ocean ventilation and the transport of ocean heat to Antarctic glaciers. Coastal freshening from accelerating Antarctic land-ice melt may alter dynamics at the shelf margin, with implications for deep ocean heat storage and future ice shelf melt rates. Due to the scarcity of observations near the Antarctic coast and difficulties associated with resolving high latitude processes in ocean models, such responses are poorly constrained and confer large uncertainties to projections of future sea level.

Using a high resolution (0.1º) global ocean–sea-ice model with a realistic representation of near-Antarctic water mass properties, we investigate the response of near-Antarctic waters to increased meltwater. We conduct two freshwater perturbation experiments using spatially variable projected ice-loss rates under RCP 4.5 and RCP 8.5 emissions scenarios at 2100. Within 10 years of the onset of 2100 meltwater forcing, formation of Dense Shelf Water and its export to the abyssal ocean ceases. On the shelf, increased ocean stratification in Dense Shelf Water formation regions leads to subsurface warming, suggesting a local positive feedback to ice shelf melt. In contrast, we find that coastal freshening strengthens the subsurface lateral density gradients of the Antarctic Slope Front, inhibiting the transport of warm Circumpolar Deep Water onto the shelf and accelerating geostrophic currents along the coast and shelf break. Thus, freshening acts to isolate cool shelf waters from open ocean heat, indicating a negative feedback to ice melt, and to homogenize shelf waters, enhancing remote feedbacks. The net effect over the continental shelf is cooling over both experiments, however, this signal is comprised of strong positive and negative regional temperature responses with complex implications for future melt rates.