Calving fluxes and basal melt rates of Antarctic ice shelves

A Corrigendum to this article was published on 23 October 2013

Abstract

Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 gigatonnes per year1,2. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3,4,5. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321 ± 144 gigatonnes per year and a total basal mass balance of −1,454 ± 174 gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1,2,7. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing.

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Figure 1: Basal mass loss and calving fluxes of Antarctic ice shelves.
Figure 2: Mean basal mass-loss rates of Antarctic ice shelves.
Figure 3: Ice-shelf surface lowering rates versus mean basal mass-loss rates.

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Acknowledgements

This work was supported by funding from the ice2sea programme of the European Union Seventh Framework Programme, grant number 226375. This work is ice2sea contribution number 139. M.R.v.d.B., J.T.M.L. and S.R.M.L. acknowledge funding from the Netherlands Polar Programme. J.L.B. was supported by NERC grant NE/I027401/1.

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M.A.D. produced the results, led the development of the study and wrote the manuscript. J.L.B. had the idea for the study and contributed to the development of the methods, to the discussion of results and, extensively, to writing the manuscript. J.A.G. produced the calving-front elevation error and provided the ice-shelf elevation. J.T.M.L. and M.R.v.d.B. provided the SMB data and error analysis. S.R.M.L. and M.R.v.d.B. provided the firn data and error analysis. G.M. provided the grounding-line and ice-shelf mask data and discussion. All authors commented on the manuscript.

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Correspondence to M. A. Depoorter or J. L. Bamber.

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Depoorter, M., Bamber, J., Griggs, J. et al. Calving fluxes and basal melt rates of Antarctic ice shelves. Nature 502, 89–92 (2013). https://doi.org/10.1038/nature12567

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