Main Text:
The rate at which the mass of the Antarctic Ice Sheet (AIS) has reduced over recent decades has fluctuated, resulting in changes to the rate of contribution to sea-level change over time(1, 2 ). This is reflected in analyses of satellite observations shifting from quantification of a single linear rate of change(3, 4 ) to estimating time-varying rates of change that vary over months to decades(1, 2, 5, 6 ). These changing rates are in response to external and internal forcing that is not fully understood but understanding them, and attributing them to different drivers, would provide important insight into the extent these changes will extend into the future. Using near-continuous records of ice volume change since the early 1990s, and of mass change since 2002, studies have begun to explore the potential large-scale climatological forcing(7 ) of the ice-sheet’s change through comparing observed high frequency or single event changes with climate indices that reflect climate variability, notably with the El Niño Southern Oscillation (ENSO)(5, 8-11 ).
The degree to which the relationship between ENSO and recent ice-sheet mass change has been explored is in contrast with the limited study of the contribution of the dominant mode of Southern Hemisphere climate variability, the Southern Annular Mode (SAM), to variations observed in time series of mass change. Comparisons(9, 12 ) of satellite gravimetric mass-change time series from the Gravity Recovery and Climate Experiment (GRACE) mission and its Follow-On (GRACE-FO) to SAM indices suggest that SAM is not a primary influence on the observed inter-annual variability, although one study suggests secondary modes of variability are moderately correlated with SAM(13 ). This lack of clarity is somewhat surprising given that SAM is known to strongly influence the pattern of surface mass balance (SMB)(14 ) and its variability(15, 16 ) and, with SAM’s strong trend since the ~1940s(17, 18 ), contributing to regional multi-decadal trends(19 ) in SMB. These SMB mass changes should be evident in time series of ice sheet mass change in addition to any oceanographic response to SAM(20-22 ).