EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term

Nanna Bjørnholt Karlsson1, Anne Munck Solgaard1, Kenneth D. Mankoff1, Jason E. Box1, Michele Citterio1, William T. Colgan1, Kristian K. Kjeldsen1, Niels J. Korsgaard1, Baptiste Vandecrux1, Douglas Benn2, Ian Hewitt3, and Robert S. Fausto1
Nanna Bjørnholt Karlsson et al.
  • 1Geological Survey of Denmark and Greenland, Glaciology and Climate, Copenhagen, Denmark (
  • 2School of Geography & Sustainable Development, University of St. Andrews, St. Andrews, UK
  • 3Oxford Centre for Industrial and Applied Mathematics, University of Oxford, Oxford, UK

The Greenland ice sheet has been one of largest sources of sea-level rise since the early 2000s. The total mass balance of the ice sheet is typically determined using one of the following methods: estimates of ice volume change from satellite altimetry, measurements of changes in gravity, and by considering the difference between solid ice discharge and surface mass balance (often referred to as the input–output method). In spite of an overall agreement between the different methods, uncertainties remain regarding the relative contribution from individual processes, and to date the basal melt has never been explicitly included in total mass balance estimates. Here, we present the first estimate of the contribution from basal melting to the total mass balance. We partition the basal melt into three terms; melt caused by frictional heat, geothermal heat and viscous heat dissipation, respectively. Combined, the three terms contribute approximately 25 Gt per year of basal melt to the total mass loss equivalent to 5% of the average solid ice discharge (average value of 1986-2018 discharge). This is equivalent to the ice discharge from the entire northeastern sector. We find that basal melting also accounts for between 5% and 30% of observed thinning in most major glacier outlets. Over our observation period (winter 2017/18), close to 2/3 of the basal melt is due to frictional heating from fast moving ice. This term is expected to increase in the future, as ice streams are likely to expand and speed up in response to rising temperatures.

How to cite: Karlsson, N. B., Solgaard, A. M., Mankoff, K. D., Box, J. E., Citterio, M., Colgan, W. T., Kjeldsen, K. K., Korsgaard, N. J., Vandecrux, B., Benn, D., Hewitt, I., and Fausto, R. S.: Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6943,, 2020

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Display material version 1 – uploaded on 06 May 2020
  • CC1: Comment on EGU2020-6943, Kerim Nisancioglu, 07 May 2020

    - seeing yoiu did not get to answer everything in chat:

    Kerim Nisancioglu (University of Bergen) (14:51)

    @Nanna Nice work! Any indications/data on changes in basal melt in the (recent) past?

    Also, what is uncertainty in basal melt esimate for NE Greenland? Are you confident that this is much less than for CW Jakobshavn area?


  • AC1: Comment on EGU2020-6943, Nanna Bjørnholt Karlsson, 07 May 2020

    Thank you! Yes, I am writing it up at the moment (hoping to submit something very soon!). There is definitely an increase in basal discharge due to glacier speed up. We do have a caveat for the NE sector because of a (probable) high geothermal flux in localised areas (you know, onset of NEGIS etc.). Overall, we are confident that the melt is lower in NW than CW because most of the NE sector is quite slow-flowing.