CASSANDRA - Accelerating mass loss of Greenland: firn and the shifting runoff limit

Meltwater running off the flanks of the Greenland ice sheet contributes roughly 60% to its mass loss, the rest being due to calving. Only meltwater originating from below the elevation of the runoff limit leaves the ice sheet, contributing to mass loss; melt at higher elevations refreezes in the porous firn and does not drive mass loss. Therefore any shift in the runoff limit modifies mass loss and subsequent sea level rise. Recent evidence shows surface runoff at increasingly high elevations, but the properties and changes to the runoff limit remain enigmatic. This research proposal focuses on the runoff limit as a powerful yet poorly understood modulator of Greenland mass balance. We will track the runoff limit over the full satellite era, using two of the largest and oldest remote sensing archives, to identify the mechanisms driving fluctuations in the runoff limit. This newly gained process understanding will then be used to build firn hydrology models capable of simulating runoff and the associated runoff limit over time. The firn hydrology models will be used to reconcile estimates of Greenland past, present and future mass balance.


Study area: Greenland ice sheet


  • Illustrations

    a) Firn core drilling on the Greenland ice sheet (Photo H. Machguth). b) Stratigraphy of cores drilled along an elevation transect (lowest elevation to the left, highest to the right). Ice lenses are in blue, porous firn is white, density is in black. The dotted vertical line indicates the density of pure ice (917 kg m-3); the thin inclined line denotes dry firn density according to Herron and Langway (1980). Dashed areas mark the end of the cores (Source: Machguth et al., 2016)

  • Publications
    • Machguth, H., M. MacFerrin, D. van As, J.E. Box, C. Charalampidis, W. Colgan, R.S. Fausto, H.A.J. Meijer, R.S.W. van de Wal and E. Mosley-Thompson (2016): Greenland meltwater storage in firn limited by near-surface ice formation, Nature Climate Change, 6, 390-393.
    • Machguth H., J.E. Box, R.S. Fausto and W.T. Pfeffer (2018): Editorial: Melt Water Retention Processes in Snow and Firn on Ice Sheets and Glaciers, Observations and Modeling, Frontiers in Earth Science, 6:105.
    • Vandecrux, B., M. MacFerrin, H. Machguth, W.T. Colgan, D. van As, A. Heilig, C. M. Stevens, C. Charalampidis, R. Fausto, E. Morris, E. Mosley-Thompson, L. Koenig, L.N. Montgomery, C. Miège, S. B. Simonsen, T. Ingeman-Nielsen and J.E. Box (2019): Firn data compilation reveals widespread decrease of firn air content in West Greenland, The Cryosphere, 13, 845-859.

Duration: 2019-2024

Funded by: The European Research Council (ERC), grant 818994

Collaborators:  IMAU Utrecht, the Netherlands; University of Liège, Belgium; GEUS, Copenhagen, Denmark; TU Delft, The Netherlands; ETH Zurich, Switzerland; University of Bern, Switzerland; CIRES, Boulder, Colorado, US; University of Utah, US.




Horst Machguth

Department of Geosciences

University of Fribourg
Chemin du Musée 4

CH–1700 Fribourg

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