Projected Impacts of Antarctic Meltwater Anomalies over the Twenty-First Century

Antarctic margin and Southern Ocean surface freshening has been observed in recent decades and is projected to continue over the twenty-first century. Surface freshening due to precipitation and sea ice changes is represented in coupled climate models; however, Antarctic ice sheet/shelf meltwater contributions are not. Because Antarctic melting is projected to accelerate over the twenty-first century, this constitutes a fundamental shortcoming in present-day projections of high-latitude climate. Southern Ocean surface freshening has been shown to cause surface cooling by reducing both ocean convection and the entrainment of warm subsurface waters to the surface. Over the twenty-first 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 twenty-first century under a high-emissions climate scenario. Our high-meltwater simulations produce anomalous surface cooling, increased Antarctic sea ice, subsurface ocean warming, and hemispheric differences in precipitation. Our low-meltwater simulations suggest that the magnitude of surface temperature and Antarctic sea ice responses is strongly dependent on the applied meltwater amount. Taken together, these findings highlight the importance of constraining projections of Antarctic ice sheet/shelf melt to better project global surface climate changes over the twenty-first century.

This work was supported by the Australian Research Council (ARC) including the ARC Center of Excellence for Climate Extremes (CE17010023) and the ARC Centre for Excellence in Antarctic Science (SR200100008). This research was undertaken with the assistance of resources and services from the National Computational Infrastructure (NCI), which is supported by the Australian government. Figures were produced using the NCAR Command Language (https://doi.org/10.5065/ D6WD3XH5). We thank the CMS team at the ARC Center of Excellence for Climate Extremes and Tilo Ziehn and Chloe Mackallah at CSIRO for their help in configuring ACCESSESM1.5. We thank Kaitlin Naughten and Nick Golledge for helpful discussions. We also thank Shaina Sadai and two anonymous reviewers for their constructive comments.