As the global climate warms, increased surface meltwater production on ice shelves may trigger ice-shelf collapse and enhance global sea-level rise. The formation of surface rivers could help prevent ice-shelf collapse if they can efficiently evacuate meltwater. Here we present observations of the evolution of a surface river into an ice-shelf estuary atop the Petermann Ice Shelf in northwest Greenland and identify a second estuary at the nearby Ryder Ice Shelf. This surface-hydrology process can foster fracturing and enhance calving. At the Petermann estuary, sea ice was observed converging at the river mouth upstream, indicating a flow reversal. Seawater persists in the estuary after the surrounding icescape is frozen. Along the base of Petermann estuary, linear fractures were initiated at the calving front and propagated upstream along the channel. Similar fractures along estuary channels shaped past large rectilinear calving events at the Petermann and Ryder ice shelves. Increased surface melting in a warming world will enhance fluvial incision, promoting estuary development and longitudinal fracturing orthogonal to ice-shelf fronts, and increase rectilinear calving. Estuaries could develop in Antarctica within the next half-century, resulting in increased calving and accelerating both ice loss and global sea-level rise.
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Except for DigitalGlobe constellation data, all datasets used in this analysis are freely available. DigitalGlobe satellite imagery was provided by the PGC under National Science Foundation grant 1644869 and is available from the PGC upon request with eligible active research awards. Imagery-derived river widths and fracture length developed in this analysis are available at http://wonder.ldeo.columbia.edu/data/publicationData/Boghosian/Estuary/, along with MAR data used. Landsat data are available at https://earthexplorer.usgs.gov and the Landsat Image Mosaic of Antarctica is available at https://nimbus.cr.usgs.gov/landing/. OIB data are provided by the National Snow and Ice Data Center at https://nsidc.org/. The 1978 orthophotos are provided by the National Oceanic and Atmospheric Administration National Centers for Environmental Information at https://www.nodc.noaa.gov/archive/arc0088/0145405/1.1/data/0-data/G150AERODEM/Orthorectified/. Ice-shelf elevation data are available at https://sealevel.nasa.gov/data/dataset/?identifier=SLCP_ice_shelf_dhdt_v1_1. REMA data are available through the PGC at https://www.pgc.umn.edu/data/rema/.
This analysis does not depend on specific code. All results can be reproduced through the equations and procedures outlined in the Methods section of this manuscript.
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We thank D. MacAyeal for helpful discussions about this manuscript. We also would like to acknowledge R. Fishman for providing imagery of the estuary, as well as M. Vogt of Volcano Heli, Iceland, for piloting the expedition to Petermann, enabling documentation of the estuary and providing imagery of the estuary. We also thank R. Boghosian for proofreading. We would have preferred to refer to the study site and features with Greenlandic/Indigenous names but were unable to find them; ‘Petermann’ was used as it is consistent with the literature39. Funding was provided by National Science Foundation grant 1644869 (A.L.B), the Old York Foundation (R.E.B.), the Heising-Simons Foundation grant PG009346_HSFOUND 2019-1160 (M.T.), the National Aeronautics and Space Administration Cryospheric Sciences Program grant 80NSSC19K0942 (L.C.S. and L.H.P.) and the National Aeronautics and Space Administration Modeling, Analysis and Prediction program award 16-MAP 16-0137 (P.M.A. and M.T.).
The authors declare no competing interests.
Peer review information Primary Handling Editor: Thomas Richardson, in collaboration with the Nature Geoscience team. Nature Geoscience thanks Knut Christianson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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a Modèle Atmosphérique Regional v. 3.9 (MAR) average daily ice-surface melt averaged across the Petermann Ice Shelf from 2010 to 2017. The red dotted lines show earliest indication of seawater in the channel after the melt season as identified in high resolution WorldView-1 and WorldView-2 satellite imagery (Extended Data Table 2). b The first evidence of water atop the ice shelf was collected by WorldView-1 in 2013 (top). Note that break in the shadow cast by the ice-shelf terminus at the Petermann river channel confirms a direct connection between the ice shelf and the ocean. Multispectral WorldView-2 images collected in 2014 (middle) and 2016 (bottom) show water in the channel directly connected to the ocean and an absence of surface meltwater elsewhere on the ice shelf. Credit: b, (2013, 2014, 2016) DigitalGlobe, Inc.
Top: MAR simulation of daily surface melt (blue) and snowfall (gray) averaged across the Petermann Ice Shelf from 2010 to 2017. Melt and snowfall are reported in millimeters water equivalent (mmwe), which is used to represent snow or ice mass in terms of its equivalent water volume. Bottom: estuary wetted widths measured at 25 m from calving front as in Extended Data Fig. 3 from 2010 to 2017. This demonstrates the lack of correlation between estuary widening and surface runoff.
a Location of wetted width measurements at 1 km increments along the Petermann river set against pan-chromatic WorldView-2 image (30 August 2018). Blue line denotes the maximum extent of sea ice found in the channel, (24 July 2018). Purple line denotes the maximum extent of the longitudinal fracture (25 July 2017). Red box shows the location of Extended Data Fig. 3b. b The mouth of the Petermann estuary widened from 2012 (left) to 2018 (right). Left panel: 2012 image with river widths shown as colored lines at 25 m increments from the ice-shelf front (QuickBird image July 19th). Right panel: 2018 image with river widths at 25m increments as in left panel. The estuary is approximately three times wider in 2018. c Wetted width measurements along channel from 2010 to 2018. The channel widens at the mouth of the estuary and within 2 km from the ice-shelf front. Width measurements (points) and trendlines are colored by locations marked in Extended Data Fig. 3a,b. Fracture growth and flow reversal evidence are coincident with this widening as shown in a. Credit: a,b (left): (2012, 2018) DigitalGlobe, Inc.
(a) The Ryder estuary in a WorldView-2 image collected on 25 August 2014. Red boxes mark the location of (b) and (c), and gold star marks the approximate location of the 2019 estuary (Fig. 2c). (b) Detailed image of the downstream portion of the estuary shows water in the channel directly connected to the ocean and an absence of surface meltwater elsewhere on the ice shelf. (c) Detailed image of the upstream portion of the estuary shows water in the channel directly connected to ocean water in the rift and an absence of surface meltwater elsewhere on the ice shelf. Credit: (2014) DigitalGlobe, Inc.
WorldView imagery at the Petermann estuary from which fractures were digitized (Fig. 2a). Red boxes show location of detail views. Fractures are identified as dark linear features along the bottom of the channel. Images collected on 14 July 2014; 17 July 2015; 15 July 2016; and 25 July 2017. Credit: (2014, 2015, 2016, 2017) DigitalGlobe Inc.
MAR outputs of runoff, snowfall and melt in millimeters water equivalent (mmwe). Also available for download in .mat and NetCDF at: http://wonder.ldeo.columbia.edu/data/publicationData/Boghosian/Estuary/
Digitized river widths and fractures. All original shapefiles are available at: http://wonder.ldeo.columbia.edu/data/publicationData/Boghosian/Estuary/
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Boghosian, A.L., Pitcher, L.H., Smith, L.C. et al. Development of ice-shelf estuaries promotes fractures and calving. Nat. Geosci. 14, 899–905 (2021). https://doi.org/10.1038/s41561-021-00837-7