Subsurface iceberg melt key to Greenland fjord freshwater budget

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Liquid freshwater fluxes from the Greenland ice sheet affect ocean water properties and circulation on local, regional and basin-wide scales, with associated biosphere effects. The exact impact, however, depends on the volume, timing and location of freshwater releases, which are poorly known. In particular, the transformation of icebergs, which make up roughly 30–50% of the loss of the ice-sheet mass to liquid freshwater, is not well understood. Here we estimate the spatial and temporal distribution of the freshwater flux for the Helheim–Sermilik glacier–fjord system in southeast Greenland using an iceberg-melt model that resolves the subsurface iceberg melt. By estimating seasonal variations in all the freshwater sources, we confirm quantitatively that iceberg melt is the largest annual freshwater source in this system type. We also show that 68–78% of the iceberg melt is released below a depth of 20 m and, seasonally, about 40–100% of that melt is likely to remain at depth, in contrast with the usual model assumptions. Iceberg melt also peaks two months after all the other freshwater sources peak. Our methods provide a framework to assess individual freshwater sources in any tidewater system, and our results are particularly applicable to coastal regions with a high solid-ice discharge in Greenland.

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We thank M. van den Broeke and B. Noël for downscaled RACMO2.3 data, I. Joughin for TerraSAR-X ice-velocity data through the NASA-funded MEaSUREs Program (NNX13AI21A) and S. Powell for illustrations. T.M. was in part supported by National Science Foundation (NSF) Ocean Sciences (OCE) 1420096. D.A.S. was partially supported by NSF grant 1552232. L.K. was supported by a National Defense Science & Engineering Graduate Fellowship. F.S. was supported by NSF PLR 1418256 and OCE 1434041. Synthesis of the Sermilik Fjord data was supported by EarthCube GRISO RCN NSF ICER 1541390.

Author information

Author notes

    • D. Carroll

    Present address: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    • F. Straneo

    Present address: Scripps Institution of Oceanography, University of California, San Diego, CA, USA


  1. National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA

    • T. Moon
  2. Department of Earth Sciences, University of Oregon, Eugene, OR, USA

    • D. A. Sutherland
    •  & D. Carroll
  3. Institute for Geophysics, University of Texas at Austin, Austin, TX, USA

    • D. Felikson
  4. Polar Science Center, Applied Physics Lab and Department of Earth & Space Sciences, University of Washington, Seattle, WA, USA

    • L. Kehrl
  5. Dept. of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

    • F. Straneo


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T.M. and D.A.S. designed the study and led the analysis and writing. L.K. contributed glacier discharge data and analysis, D.F. contributed hydrology-catchment basins and data sampling, D.C. modelled buoyant plumes and terminus melt, and F.S. contributed oceanographic data and interpretation. All of the authors contributed to the final manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to T. Moon.

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