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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 ).