Effects of freshwater forcing on the Antarctic slope current in a warmer climate using coupled climate model

The Antarctic slope current (ASC) is a westward flow around the Antarctic continental shelf. The ASC plays a key role in regulating the heat transport onto the shelf and thereby affects the ice-shelf melt. However, estimating changes in the ASC in response to greenhouse warming and attributing their potential drivers remain uncertain due to a lack of observations and the limitations of high-resolution coupled climate modeling. Previous equilibrium simulations using the ultra-high-resolution Community Earth System Model, comparing present-day (PD) and quadruple CO₂ (4×CO₂) simulations, showed the strengthening of the ASC in 4×CO₂ relative to the PD simulation mainly due to a decrease in salinity. This enhanced freshening was primarily driven by reduced brine rejection associated with sea-ice formation in mainly austral winter-spring and by enhanced precipitation minus evaporation in year-round. To examine transient changes in the ASC and associated freshwater forcings that could not be captured in the equilibrium experiments, we also used Alfred Wegener Institute Climate Model, version 3 (AWI-CM3) coupled climate model with SSP5-8.5 greenhouse gas emission scenario. We analyzed transient experiment with 31 km and 10 km horizontal resolution for atmosphere and ocean, respectively (TCo319). Since the 2020s, the ASC has rapidly strengthened and expanded meridionally. At the same time, salinity and sea ice concentration began to decrease abruptly, and the freshened region also expanded similarly to the ASC. Compared to the historical period (1981–2010), the future period (2071–2100) showed a strengthened ASC, with increased mean temperatures from the surface to 200 m depth confined to the continental slope. Precipitation also increased along the Antarctic coast region and over the continental slope. By using both equilibrium and transient simulations, we better understand future changes in ASC and the mechanisms linking freshwater factors to the ASC change. Our study has important implications for mesoscale ocean circulation, ocean heat exchanges, and marine ecosystems around Antarctica.