Future Response of Antarctic Continental Shelf Temperatures to Ice Shelf Basal Melting and Calving

We investigate feedbacks between subsurface continental shelf ocean temperatures and Antarctic glacial melt using a coupled climate model. The model was forced with SSP5-8.5 and an uncoupled projection of basal melt and calving fluxes. SSP5-8.5 forcing with fixed pre-industrial glacial melt warms all continental shelves, such that historically "cool" and "fresh" shelves transition to "warm." Additional glacial melt, added at depth, cools the Eastern Ross, Amundsen, and Bellingshausen seas, suggesting a negative feedback on basal melt-a novel result for a coarse resolution coupled model. From the Weddell Sea, along East Antarctica, and into the western Ross Sea-where continental shelves transition to a "warm" state-additional glacial melt increases temperatures at the continental shelf sea floor, suggesting a positive feedback. The sign of the glacial melt-subsurface temperature feedback is critically dependent on continental shelf properties, climate state, and the vertical distribution of glacial melt inputs. Antarctic ice shelves lose mass as freshwater-primarily from melting at their base and when icebergs break off. We know that the rate at which Antarctic ice shelves are losing mass is increasing and we expect this freshwater input into the ocean to increase further in a warmer world. Most climate models do not include a representation of this changing freshwater input, and its climatic impacts are uncertain. One particularly important climate impact is how the additional freshwater changes the subsurface ocean temperature. If freshwater warms/cools the coastal ocean it could increase/decrease melt in a positive/negative feedback loop. But existing studies disagree about this effect and even about the sign of the feedback. We added a timeseries of freshwater input to a climate model and ran experiments with strong climate warming to investigate this feedback. The sign of the feedback varies by region. Where climate change drives a cold coastal ocean to transition to a new warmer state, we find that freshwater causes a strong additional warming (a positive feedback). Where the coastal ocean is already warm in the present day and warms in future, freshwater reduces this warming (a negative feedback). To achieve the negative feedback freshwater must be added at depth. A glacial melt projection is added to a 1 & DEG; coupled climate model under SSP5-8.5 to investigate ocean temperature feedbacksAdditional glacial melt cools the Eastern Ross, Amundsen, and Bellingshausen seas at depth, but warms elsewhereThe addition of glacial melt at depth is necessary to generate the cooling response