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Abstract

Southern Ocean surface freshening has been observed in recent decades and is projected to continue over the 21st Century. Surface freshening due to precipitation and sea ice changes are represented in coupled climate models, however Antarctic ice sheet/shelf meltwater contributions are not. As Antarctic melting is projected to accelerate over the 21st Century this constitutes a fundamental shortcoming in present-day projections of high-latitude climate. Southern Ocean surface freshening has been shown to cause a surface cooling by reducing both ocean convection and the entrainment of warm subsurface waters to the surface. Over the 21st Century Antarctic meltwater is expected to alter the pattern of projected surface warming as well as having other climatic effects. However, there remains considerable uncertainty in projected Antarctic meltwater amounts, and previous findings could be model-dependent. Here, we use the ACCESS-ESM1.5 coupled model to investigate global climate responses to low and high Antarctic meltwater additions over the 21st Century under a high-emissions climate scenario. Our high meltwater simulations produce anomalous surface cooling, increased Antarctic sea ice, subsurface warming and hemispheric differences in precipitation. Our low meltwater simulations suggest the magnitude of surface temperature and Antarctic sea ice responses are strongly dependent on the applied meltwater amount. These findings highlight the importance of constraining Antarctic melt projections to better project global surface climate changes over the 21st Century. Our work also motivates the Southern Ocean freshwater release model experiments initiative (SOFIA), a standardised meltwater intercomparison designed to improve our understanding of Antarctic meltwater impacts on climate.