Jakobshavn Isbrae has been the single largest source of mass loss from the Greenland Ice Sheet over the last 20 years. During that time, it has been retreating, accelerating and thinning. Here we use airborne altimetry and satellite imagery to show that since 2016 Jakobshavn has been re-advancing, slowing and thickening. We link these changes to concurrent cooling of ocean waters in Disko Bay that spill over into Ilulissat Icefjord. Ocean temperatures in the bay’s upper 250 m have cooled to levels not seen since the mid 1980s. Observations and modelling trace the origins of this cooling to anomalous wintertime heat loss in the boundary current that circulates around the southern half of Greenland. Longer time series of ocean temperature, subglacial discharge and glacier variability strongly suggest that ocean-induced melting at the front has continued to influence glacier dynamics after the disintegration of its floating tongue in 2003. We conclude that projections of Jakobshavn’s future contribution to sea-level rise that are based on glacier geometry are insufficient, and that accounting for external forcing is indispensable.
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Data are available in the following public repositories, or upon request from the indicated authors. The GLISTIN ice data and the airborne expendable CTD oceanographic data are available at the OMG website: https://omg.jpl.nasa.gov/portal/browse/. The Operation IceBridge ATM data are available from the NSIDC website at https://nsidc.org/data/icebridge/data_summaries.html. The flow speed data used in this study are available from A.G. (Alex.S.Gardner@jpl.nasa.gov) upon request. The Landsat 4, 5, 7 and 8 data, used in inferring glacier flow speeds and front locations, are available at https://cloud.google.com/storage/docs/public-datasets/landsat. The Sentinel-2a/b data used in inferring flow speeds are available at https://cloud.google.com/storage/docs/public-datasets/sentinel-2. The International Council for the Exploration of the Sea oceanographic data are available at http://ices.dk/Pages/default.aspx and http://ices.dk/marine-data/data-portals/Pages/ocean.aspx. The ECCO Version 4 Release 3 and Version 5 Release alpha ocean and sea-ice products are available at http://ecco.jpl.nasa.gov and ftp://ecco.jpl.nasa.gov/Version5/Alpha/. The RACMO2.3p2 data are available from B.P.Y.N. (B.P.Y.Noel@uu.nl) and M.R.v.d.B. (M.R.vandenBroeke@uu.nl) upon request. Bed topography and fjord bathymetry BedMachine Version v3 data are available at http://sites.uci.edu/morlighem/dataproducts/bedmachine-greenland.
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The authors acknowledge support from the following sources. A.K.: NASA’s Cryospheric Sciences Program; and the Oceans Melting Greenland mission. I.G.F., I.F., O.W. and H.Z.: NASA’s Physical Oceanography; Cryospheric Sciences; and Modeling, Analysis and Prediction programmes. C.M.L.: NSF grant ARC-1022472 and NASA’s Physical Oceanography programme. H.S.: NASA’s Cryospheric Sciences; and Modeling, Analysis and Prediction programmes; and JPL’s Research and Technology Development programme. M.R.v.d.B. and B.P.Y.N.: the Netherlands Earth System Science Centre. The authors thank JPL’s UAVSAR group for ongoing support for the processing and use of the GLISTIN-A data. The authors thank J. Gobat, A. Huxtable, B. Jokinen and E. Boget (APL-UW) and the captains and crews of R/V Knorr and R/V Atlantis for their efforts in supporting the Davis Strait array. The authors thank the Greenland Institute of Natural Resources, Nuuk Greenland, for collection of hydrographic data in Disko Bay prior to 2015 as part of its Standard Hydrographic Coastal Monitoring Program. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
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