Basal melting of Ross Ice Shelf from solar heat absorption in an ice-front polynya

Abstract

Ice–ocean interactions at the bases of Antarctic ice shelves are rarely observed, yet have a profound influence on ice sheet evolution and stability. Ice sheet models are highly sensitive to assumed ice shelf basal melt rates; however, there are few direct observations of basal melting or the oceanographic processes that drive it, and consequently our understanding of these interactions remains limited. Here we use in situ observations from the Ross Ice Shelf to examine the oceanographic processes that drive basal ablation of the world’s largest ice shelf. We show that basal melt rates beneath a thin and structurally important part of the shelf are an order of magnitude higher than the shelf-wide average. This melting is strongly influenced by a seasonal inflow of solar-heated surface water from the adjacent Ross Sea Polynya that downwells into the ice shelf cavity, nearly tripling basal melt rates during summer. Melting driven by this frequently overlooked process is expected to increase with predicted surface warming. We infer that solar heat absorbed in ice-front polynyas can make an important contribution to the present-day mass balance of ice shelves, and potentially impact their future stability.

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Fig. 1: Basal melt rates of the north-western RIS.
Fig. 2: Oceanographic conditions and melt rate variability.
Fig. 3: SST and sea-ice concentration around Antarctica.

Data availability

Data for coastlines and ice shelves in Figs. 2 and 3 are from the Antarctic Digital Database (https://www.add.scar.org/). The RIS frontal line was modified to reflect recent changes in frontal position. MODIS images in Figs. 1a and 3c were sourced from the NSIDC Images of Antarctic Ice Shelves archive (http://nsidc.org/data/iceshelves_images/index_modis.html). SST data are from the GHRSST Multi-scale Ultra-high Resolution (MUR) SST record, obtained from the NASA EOSDIS Physical Oceanography Distributed Active Archive Center at the Jet Propulsion Laboratory (https://doi.org/10.5067/GHGMR-4FJ01). Sea-ice concentration data are from the NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 3 (https://doi.org/10.7265/N59P2ZTG). Offshore CTD data are from the Calibrated Hydrographic Data from the Ross Sea acquired with a CTD during the RV Nathaniel B. Palmer expedition NBP1101 (2011) dataset (https://doi.org/10.1594/IEDA/317595), downloaded from http://www.marine-geo.org/tools/search/Files.php?data_set_uid=17595. Mooring data are archived at https://figshare.com/s/1c92fe8eb227b878e344. ApRES radar data are archived at https://figshare.com/s/1255b7d76ed69e015c3a.

Code availability

Computer code used to process the radar observations is available from the corresponding author on request.

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Acknowledgements

The authors acknowledge T. Arnold, B. Grant and R. Benson for assistance with the radar survey fieldwork, and Antarctica New Zealand, the Andrill programme and the Woods Hole Oceanographic Institute for field support, hot-water drilling at the mooring site and assistance with the mooring deployment, respectively. We thank J. Kohut for the use of CTD data gathered by during the RV Nathaniel B. Palmer Ross Sea Expedition 2011 funded by NSF grant no. ANT08-39039, and thank C. Stevens for comments that improved the manuscript. C.L.S. was supported by the Rutherford Foundation and Antarctica New Zealand through the Scott Centenary Scholarship.

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C.L.S. and M.J. M.W. designed and deployed the sub-ice shelf mooring. C.L.S. designed the radar survey, and C.L.S. and P.C. undertook the radar fieldwork. C.L.S. analysed the radar data with advice from K.W.N. All authors contributed to the manuscript.

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Correspondence to Craig L. Stewart.

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Stewart, C.L., Christoffersen, P., Nicholls, K.W. et al. Basal melting of Ross Ice Shelf from solar heat absorption in an ice-front polynya. Nat. Geosci. 12, 435–440 (2019). https://doi.org/10.1038/s41561-019-0356-0

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