Antarctic ice shelf potentially stabilized by export of meltwater in surface river

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Abstract

Meltwater stored in ponds1 and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration2. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers3 and ice streams, thereby raising sea level globally4. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks—interconnected streams, ponds and rivers—on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf’s meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models1, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration.

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Figure 1: Surface hydrology and topography of Nansen Ice Shelf.
Figure 2: Photographs of the Nansen Ice Shelf taken by the 1912 Northern Party.
Figure 3: Evolution of the extent and depth of meltwater during the melt season.
Figure 4: Surface meltwater routing on Antarctic ice shelves.

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Acknowledgements

This work benefited from input on the Northern Party historical documents from M. Hopper and D. Webster, in addition to assistance from the staff of the Scott Polar Research Institute, University of Cambridge, UK. This work was supported by the National Science Foundation under Rosetta Project award 1443534; a National Science Foundation Graduate Research Fellowship award (DGE-16-44869); a National Science Foundation award (1341688); two NASA awards (IceBridge NNX16AJ65G and NNX14AH79G); a NASA Earth and Space Science fellowship (NNX15AN28H); a grant from the Old York Foundation; and a grant from the Korean Ministry of Oceans and Fisheries (PM16020).

Author information

R.E.B assembled the archival material and wrote the manuscript. All authors contributed to the manuscript and the overall interpretation. W.C. conducted the catchment analysis and the drainage, and assembled the laser and radar data. J.K. analysed the water area and depths. M.T. determined the water area and depth. I.D. conducted the sensitivity analysis of the water depths and distribution. K.J.T. developed the surface slope products required for the flux calculations. C.J.Z. determined the velocity and volume flow rate of the shear-margin river. M.F. collected the ablation and temperature data. A.B. mapped the water on the ice shelf in front of Petermann Glacier. W.S.L. collected the helicopter video of the river and waterfall that was used for the velocity analysis.

Correspondence to Robin E. Bell.

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The authors declare no competing financial interests.

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Reviewer Information Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Locations of Northern Party campsites.

Detailed information is included in Extended Data Table 1.

Extended Data Figure 2 Firn- and mélange-terminating surface drainage on the Nansen Ice Shelf.

a, Aerial photograph of a firn-terminating system, showing a water-filled ravine and surface streams (TMA identifier CA073631L021, https://earthexplorer.usgs.gov/; 15 January 1961). b, Aerial photograph of a firn-terminating system, showing ponds, a water-filled ravine and surface streams (TMA identifier CA238432V0020; 8 January 1975,). c, Aerial photograph of a firn-terminating system, showing surface streams that terminate in firn (TMA identifier CA238433R0030; 9 January 1975. d, Surface meltwater drainage into rifted mélange, with red arrows locating drainage points. (Aerial photograph from 1975; TMA identifier CA238332V0060.) e, Surface meltwater drainage into rifted mélange. (Worldview satellite photograph from 10 February 2014.) f, Location of the surface drainage images shown atop a Landsat image. Fig. 2d is shown as a red diamond and Fig. 2e as a green diamond.

Extended Data Figure 3 Shear-margin river and waterfall in 1974–1975.

Top, a Landsat image from 16 January 1974 (Landsat scene identifier LM10641141974016AAA02, from https://earthexplorer.usgs.gov/), and shows a well defined surface drainage network, including a calving-front waterfall. Bottom, TMA image of the 1975 waterfall, shot on 8 January 1975 (vertical-camera image reference is TMA photograph CA238432V0063).The TMA photograph is overlain on the Landsat image in the upper panel.

Extended Data Figure 4 NDWI sensitivity.

a, NDWI values obtained for six days, over the ocean (rectangular boxes) and the ice shelf (specifically, a lake, identified by a red star), showing how NDWI changes as summer progresses. The variability in the ocean values reflects the varying extent of sea ice on Terra Nova Bay, and the spectral properties of the atmospheric column above it. Numbers above each image are the year followed by the Julian day. b, Means of NDWI for the 2013–2014 melt season over the ocean (black star) and over a ‘deep’ lake/pond (red circle; located in c). This panel shows the validity of our >0.25 threshold for locating deeper water over the Nansen Ice Shelf. c, Map of Landsat-8 red-channel reflectance (636–673 nm, unitless) for the image acquired on 4 January 2014. The black box shows the region for which our quantitative analysis of NDWI-based water extent and depth was performed.

Extended Data Figure 5 Water extent and depth.

a, Maps of NDWI-based water-extent values over the area contained within the black box of Extended Data Fig. 4. The date for each image is given at the top of each panel. b, Maps of derived water-depth values over the same area.

Extended Data Figure 6 Waterfall export and duration.

a, Duration of waterfall export in the eight years for which there is adequate satellite imagery, plotted against the number of days in which the minimum temperature was above 0 °C, at Mario Zucchelli Station on Terra Nova Bay. Error bars for waterfall duration are 9.4 days. The duration of export increases with increasing temperature. b, Estimates of the volume of surface melt water exported. The export line for the observed waterfall export durations is calculated using the Manning flux estimate (260 m3 s−1). This line is compared with the melt volume produced at present in the calving-front catchment at a surface melt rate of 0.5 m yr−1, and the melt volume that would be produced if the surface melt rate were 1.5 m yr−1. The present-day melt volume of 0.16 km3 is shown in blue; the damaging melt volume of 0.49 km3 is shown in tan. The melt volume of 1.5 m yr−1 is considered damaging in the present ice-sheet models.

Extended Data Figure 7 Temperature record for Mario Zucchelli Station on Terra Nova Bay for 1986–2016.

The brown line indicates the number of days for which the temperature was positive during this period. Black bars show the number of days when the maximum temperature exceeded 0 °C, and the red bars indicate the number of days when the minimum temperature exceeded 0 °C. There is no statistically significant increase in the temperature at Terra Nova Bay over this time period. The line at the bottom indicates the years for which we have sufficient satellite imagery to resolve whether the surface hydrology was exporting water off the ice shelf. The years during which we identified export at a waterfall are indicated with a waterfall symbol. These temperature data are available at http://www.climantartide.it.

Extended Data Figure 8 Petermann Glacier and adjacent ice shelf with river.

a, Landsat image of the Petermann Ice Shelf River, taken on 15 July 2014. The red outline shows that area that is expanded in b. b, Expanded image of the Peterman Ice Shelf River at the calving front. c, NDWI analysis of water distribution in b, obtained using the methodology used for the Nansen Ice Shelf.

Extended Data Table 1 Location of the major camps of the Northern Party 1912
Extended Data Table 2 Satellite coverage available for specific melt seasons (December and January)

Supplementary information

Development of 2008-2009 Waterfall export from LANDSAT data

Development of 2008-2009 Waterfall export from LANDSAT data (MOV 4325 kb)

Development of 2013-2014 Waterfall export from LANDSAT data

Development of 2013-2014 Waterfall export from LANDSAT data. (MOV 1971 kb)

Waterfall video shot from research helicopter on January 12, 2014 by Won Sang of Korea Polar Research Institute (KOPRI)

This video was used to develop the estimate of water flux in river. (MOV 8968 kb)

Waterfall video shot from research helicopter on January 12, 2014 by Won Sang of Korea Polar Research Institute (KOPRI).

This video was used to develop the estimate of water flux in river. (MOV 9124 kb)

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Bell, R., Chu, W., Kingslake, J. et al. Antarctic ice shelf potentially stabilized by export of meltwater in surface river. Nature 544, 344–348 (2017) doi:10.1038/nature22048

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