Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends

Recent trends in Southern Ocean (SO) climate – of surface cooling, freshening and sea-ice expansion – are not captured in historical simulations of state-of-the-art coupled climate models, suggesting that there may be a singular or multiple missing process(s). Here we demonstrate that the addition of plausible discharges of Antarctic meltwater to a coupled climate model can produce a closer match to a wide range of climate trends found in observational records. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth System Model (GISS-E2.1-G) to compute ‘Climate Response Functions’ (CRFs) for the addition of Antarctic meltwater. These imply a cooling and freshening of the SO, an expansion of winter sea ice and an increase in steric height, all consistent with observed trends since 1992. The CRF framework allows one to compare the efficacy of Antarctic meltwater as a driver of SO climate trends, relative to greenhouse gas and surface wind forcing. The meltwater CRFs presented here strongly suggest that interactive Antarctic ice melt must be included in models in order to correctly hindcast the historical record and, by implication, make realistic future predictions.