Tropical Controls on West Antarctic Ice Sheet Surface Mass Balance Interannual Variability in the Twentieth Century

Abstract The West Antarctic Ice Sheet (WAIS) contains an ice volumetric equivalent of 5.3 m of global mean sea‐level rise. Understanding the climate mechanisms that influence WAIS surface mass balance (SMB) can help reduce uncertainties in sea‐level rise projections. Previous work has focused on trends related to temperature and the roles of well‐known climate phenomena in the Pacific sector, including the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode. Here, the focus is on interannual variability of precipitation associated with Rossby wave trains emanating from tropical convection regions in the Indian Ocean and the central tropical Pacific. Objective clustering of SMB measurements from 25 WAIS ice and firn cores from 1900 through 1999 indicated oppositely signed mean SMB trends in the East and West sectors of WAIS, and these trends were removed to focus on year‐to‐year variations. Climatically important months for each sector were identified by correlating reanalysis precipitation with ice core SMB. Tropical Rossby wave source regions that produced anomalous WAIS SMB were identified by analyzing composite convection, geopotential height, and wave activity flux. East WAIS SMB variability was controlled by anomalously low geopotential height over the Ross and Amundsen Seas. West WAIS SMB variability was driven by ENSO and non‐uniformity in the phase distribution of the Madden‐Julian Oscillation. These results provide a deeper understanding of the drivers of WAIS SMB variability and may improve projections of future sea‐level rise.