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IACS

JCMP08 - Connecting Polar to lower latitudes: A global perspective on climate change and impacts for Future Earth Strategies

Antarctic Ice Sheet Surface Mass Balance; impact of the Southern Annular Mode and El Nino Southern Oscillation on accumulation and melt

The Antarctic Ice Sheet has been losing mass for several decades due to regional ocean-driven increases in basal melting of ice shelves, iceberg calving and associated dynamic changes in ice discharge. Snow accumulation, the major control on surface mass balance in Antarctica, has been increasing over this period. Surface melt in Antarctica remains a minor component of the mass balance, but surface melting can be significant on the northernmost ice shelves in Antarctica and has led to ice shelf collapse. Both surface melt and accumulation are characterised by significant spatial and temporal variability, and though previous work has demonstrated relationships between the Southern Annular Mode (SAM), the El Ni?o Southern Oscillation (ENSO), and Antarctic climate, the links with ice sheet mass balance remain poorly understood. Here, we focus on two recent PhD papers by Dominic Saunderson (1) and Jess Macha (2), as part of Securing Antarctica��s Environmental Future (SAEF), an Australian Research Council Special Research Initiative involving Australian universities and partner organisations. Our work ulilises RACMO regional climate model outputs and ERA5 reanalysis to demonstrate that (1) variability in surface melting of East Antarctic ice shelves is strongly related to the SAM, and (2) that surface accumulation in West Antarctica is significantly influenced by ENSO, and particularly whether El Ni?o activity is centred in the Eastern or Central Pacific Ocean. We show that on East Antarctic ice shelves, a decreasing SAM index is associated with increased melt in Dronning Maud Land primarily owing to reduced precipitation and greater absorption of solar radiation in early summer. Conversely, in Wilkes Land, a decreasing SAM index corresponds to increased melt because of greater incoming longwave radiation from a warmer atmosphere. In West Antarctica, we show that Central Pacific El Ni?o results in significantly increased winter and spring snow accumulation in the western Ross Sea sector and decreased accumulation in the Amundsen Sea sector. The distinct impacts of Central and Eastern Pacific El Ni?o also extend beyond West Antarctica into parts of East Antarctica. Together, these results demonstrate important and clear influences of two major modes of climate variability on both surface melt and accumulation in Antarctica. The magnitude and spatial signature of these influences make it necessary to realistically include climate variability in future projections of Antarctic surface mass balance to better predict the impacts of anthropogenic climate change. 1. Saunderson, D., Mackintosh, A. N., McCormack, F. S., Jones, R. S., & van Dalum, C. T. (2024). How does the Southern Annular Mode control surface melt in East Antarctica? Geophysical Research Letters, https://doi.org/10.1029/2023GL105475 2. J. Macha, A. Mackintosh, F. McCormack, B. Henley, H. McGregor, C.T. van Dalum, A. Purich. Distinct Central and Eastern Pacific El Ni?o influence on Antarctic Surface Mass Balance. Geophysical Research Letters https://doi.org/10.1029/2024GL109423