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Antarctic basal environment shaped by high-pressure flow through a subglacial river system

Abstract

The stability of ice sheets and their contributions to sea level are modulated by high-pressure water that lubricates the base of the ice, facilitating rapid flow into the ocean. In Antarctica, subglacial processes are poorly characterized, limiting understanding of ice-sheet flow and its sensitivity to climate forcing. Here, using numerical modelling and geophysical data, we provide evidence of extensive, up to 460 km long, dendritically organized subglacial hydrological systems that stretch from the ice-sheet interior to the grounded margin. We show that these channels transport large fluxes (~24 m3 s−1) of freshwater at high pressure, potentially facilitating enhanced ice flow above. The water exits the ice sheet at specific locations, appearing to drive ice-shelf melting in these areas critical for ice-sheet stability. Changes in subglacial channel size can affect the water depth and pressure of the surrounding drainage system up to 100 km either side of the primary channel. Our results demonstrate the importance of incorporating catchment-scale basal hydrology in calculations of ice-sheet flow and in assessments of ice-shelf melt at grounding zones. Thus, understanding how marginal regions of Antarctica operate, and may change in the future, requires knowledge of processes acting within, and initiating from, the ice-sheet interior.

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Fig. 1: Schematic of subglacial hydrology drainage characteristics for Greenland and Antarctica.
Fig. 2: Modelled subglacial hydrology.
Fig. 3: Impact of channel efficiency on system pressure and water depth.

Data availability

BedMachine basal and surface topography DEMs are available at NSIDC. Airborne radar data used in this study are freely available at the CReSIS website (http://data.cresis.ku.edu/). Model outputs and reflectivity data are available from the Zenodo repository: https://doi.org/10.5281/zenodo.6785041.

Code availability

The Glacier Drainage System (GlaDS) model code is available by contacting Mauro Werder (werder@vaw.baug.ethz.ch) and is also now included in the Ice-Sheet and Sea-Level System Model (ISSM), which is freely available.

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Acknowledgements

We thank M. Werder for use of the Glacier Drainage System (GlaDS) model and M. Morlighem for provision of ISSM basal ice velocity and melt rates. C.F.D. was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC; RGPIN-03761-2017) and the Canada Research Chairs Program (950-231237). M.J.S. and N.R. acknowledge support by the UK Natural Environment Research Council AFI grant NE/G013071/1. N.R. acknowledges funding from the Newcastle University Humanities and Social Science (HASS) bid preparation fund. K.S. was supported by NSERC and the University of Waterloo. We thank Compute Canada for provision of supercomputer resources. We acknowledge the use of data and/or data products from CReSIS generated with support from the University of Kansas, NSF grant ANT-0424589 and NASA Operation IceBridge grant NNX16AH54G.

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Contributions

C.F.D., N.R., and M.J.S. designed and developed the project and wrote the manuscript. C.F.D. and K.S. ran the model simulations. C.F.D. conducted the analysis and produced the figures. H.J. provided radar data and figures. All authors contributed to editing the manuscript.

Corresponding author

Correspondence to C. F. Dow.

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Nature Geoscience thanks Ian Willis and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Tom Richardson, in collaboration with the Nature Geoscience team.

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Extended data

Extended Data Fig. 1 Channel discharge compared to radar reflectivity.

Channel discharge for the FIS-AG catchment for the standard (base) model run. The dots show regions of positive radar reflectivity (calculated as relative values with a zero mean22) at the ice-bed interface assumed to indicate the presence of water50; negative relative reflectivity values are not plotted. Background image is the ice surface MODIS mosaic43. The extent of this region is shown by the grey box in Fig. 2c.

Extended Data Fig. 2 Basal melt and hydrology catchments.

Basal melt rate from ISSM15 with basal drainage catchments outlined for IIS (red), MIS (yellow), FIS-AG (green) and SFG (blue).

Extended Data Fig. 3 Location of radar transects shown in Extended Data Fig. 4.

MODIS ice-surface imagery of the Weddell Sea (WS) sector of West Antarctica43. The location of radar transects for IIS (A-A’), MIS (B-B’), and FIS-AG (C-C’) are plotted with white dashed lines. These radar transects are shown in Extended Data Fig. 4. The red dots are the location of modelled channel outlets over the grounding line (Fig. 2c, d) and the yellow squares, the location of sub ice-shelf channels (shown as yellow bars in Extended Data Fig. 4).

Extended Data Fig. 4 Ice shelf radar transects with incised basal channels.

Channels are incised upwards beneath floating ice for the following ice streams: (a,b) IIS (A–A’), (c,d) MIS (B–B’), and (e,f) FIS-AG (C–C’), with transects shown in Extended Data Fig. 3. Surface elevation profiles from an aircraft altimeter are plotted above each radargram (a,c,e) with depressions as a result of hydrostatic adjustment from the incised basal channels. Yellow bars show the location of the ice shelf channel as indicated by the yellow boxes in Extended Data Fig. 3.

Extended Data Table 1 GlaDS model parameters (base model run)
Extended Data Table 2 Grounding line discharge rates for model sensitivity tests
Extended Data Table 3 Catchment and grounding zone calculations

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Dow, C.F., Ross, N., Jeofry, H. et al. Antarctic basal environment shaped by high-pressure flow through a subglacial river system. Nat. Geosci. 15, 892–898 (2022). https://doi.org/10.1038/s41561-022-01059-1

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