Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves


Ocean-driven basal melting of Antarctica’s floating ice shelves accounts for about half of their mass loss in steady state, where gains in ice-shelf mass are balanced by losses. Ice-shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level, and the changing meltwater fluxes influence climate processes in the Southern Ocean. Existing continent-wide melt-rate datasets have no temporal variability, introducing uncertainties in sea level and climate projections. Here, we combine surface height data from satellite radar altimeters with satellite-derived ice velocities and a new model of firn-layer evolution to generate a high-resolution map of time-averaged (2010–2018) basal melt rates and time series (1994–2018) of meltwater fluxes for most ice shelves. Total basal meltwater flux in 1994 (1,090 ± 150 Gt yr–1) was similar to the steady-state value (1,100 ± 60 Gt yr–1), but increased to 1,570 ± 140 Gt yr–1 in 2009, followed by a decline to 1,160 ± 150 Gt yr–1 in 2018. For the four largest ‘cold-water’ ice shelves, we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.

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Fig. 1: Basal melt rates of Antarctic ice shelves estimated using CryoSat-2 altimetry.
Fig. 2: Vertical structure of melting and refreezing rates for selected ice shelves.
Fig. 3: Variations in Antarctic ice-shelf mass between 1994 and 2018.
Fig. 4: Time-dependent basal melt rates for different modes of melting.

Data availability

ERS‐1, ERS‐2, Envisat and CryoSat‐2 radar altimetry data are available from the European Space Agency (ERS‐1 and ERS‐2 data from, Envisat data from and CryoSat‐2 level‐2 SARIn‐mode data from We provide two datasets at (1) basal melt rates at high spatial resolution, posted on a 500 m grid, for the period 2010–2018 and (2) changes in height from satellite altimetry, firn air content from GSFC-FDMv0 and precipitation minus evaporation from MERRA-2 at 10-km grid cells and three-month intervals for 1994–2018; (2) can be used to estimate time-varying basal melt rates using Equation (7).

Code availability

The Matlab, Python and shell scripts used for the analyses described in this study can be obtained from the corresponding author upon reasonable request. Code to read and visualize the derived data products described in this manuscript, and to reproduce the major elements of Figs. 1 to 4, is available at


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This study was funded by NASA grants NNX17AI03G and NNX17AG63G, and NSF grant 1744789. S.A. was also supported by the NASA Earth and Space Science Fellowship. B.M was supported by the ICESat-2 Project Science Office. We thank members of the Scripps Polar Center, S. Howard, and K. Nicholls for their important contributions to this manuscript.

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S.A., H.A.F., L.P. and M.R.S. conceptualized the study. S.A. and M.R.S. performed altimetry data processing. B.M. conducted climate and firn modelling. All authors contributed to the writing and editing of the manuscript. H.A.F., B.M., L.P. and M.R.S. contributed equally to this work.

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Correspondence to Susheel Adusumilli.

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Adusumilli, S., Fricker, H.A., Medley, B. et al. Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves. Nat. Geosci. 13, 616–620 (2020).

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