Antarctic Bottom Water Sensitivity to Spatio‐Temporal Variations in Antarctic Meltwater Fluxes

Ice sheet melting into the Southern Ocean can change the formation and properties of the Antarctic Bottom Water (AABW). Ocean models often mimic ice sheet melting by adding freshwater fluxes in the Southern Ocean under diverse spatial distributions. We use a global ocean and sea‐ice model to explore whether the spatial distribution and magnitude of meltwater fluxes can alter AABW properties and formation. We find that a realistic spatially varying meltwater flux sustains AABW with higher salinities compared to simulations with uniform meltwater fluxes. Finally, we show that increases in ice sheet melting above 12% since 1958 can trigger AABW freshening rates similar to those observed in the Southern Ocean since 1990, suggesting that the increasing Antarctic meltwater discharge can drive the observed AABW freshening. Previous research suggests that increased Antarctic ice sheet (AIS) melting may be driving freshening in the abyssal Southern Ocean, and Antarctic sea ice expansion since 1978. However, the main tools we have to assess abyssal ocean changes are ocean models, and they often misrepresent Antarctic ice melting by assuming it occurs uniformly along the Antarctic coast. In this study, we use a global ocean model to assess if correcting the spatial distribution of Antarctic ice melting (from uniform to spatially varying), and increasing its magnitude, can change the salinity in the abyssal Southern Ocean. We show that correcting the spatial representation of the AIS melting results in abyssal waters with higher salinities, correcting 30% the ocean model fresh bias in the abyssal cells. We also show that a 12% increase in Antarctic ice melting can trigger freshening of the abyssal Southern Ocean at rates similar to the trends observed since the 1990s, thus suggesting that enhanced melting of Antarctic land ice may be the main driver of the recently observed AABW freshening. An ocean and sea‐ice model is used to explore how spatiotemporal variations in meltwater fluxes affect the Antarctic Bottom Water (AABW)Spatially varying meltwater fluxes reduces the low‐salinity bias of AABW in the ocean and sea‐ice model used by 30%Increasing meltwater fluxes by 12% over 60 years induces AABW freshening at rates consistent to observed AABW trends since 1990 An ocean and sea‐ice model is used to explore how spatiotemporal variations in meltwater fluxes affect the Antarctic Bottom Water (AABW) Spatially varying meltwater fluxes reduces the low‐salinity bias of AABW in the ocean and sea‐ice model used by 30% Increasing meltwater fluxes by 12% over 60 years induces AABW freshening at rates consistent to observed AABW trends since 1990