Antarctic Meltwater‐Stratification Feedback Is Less Pronounced Under High Climate Forcing

Abstract Several studies have shown sub‐surface warming in the Southern Ocean via an increase in meltwater flux from the Antarctic Ice Sheet (AIS), which can lead to a positive feedback through enhanced basal melting. In this study, we investigate how the feedback strength is related to the prevailing climate in a coupled climate–ice‐sheet model. We find that sub‐surface temperature increase due to Antarctic meltwater is more pronounced under pre‐industrial climate compared to a strong global warming scenario. This is explained by a climate‐change induced reduction of vertical overturning in the Southern Ocean, which already leads to strong sub‐surface warming without additional meltwater. While in the pre‐industrial climate additional meltwater substantially reduces vertical mixing, the additional ice‐sheet mass flux into the ocean has less impact when the overturning is already suppressed by climate change. Sub‐surface warming due to meltwater flux increase thereby shows a saturation effect under climate warming.