Preprints
https://doi.org/10.5194/tc-2020-256
https://doi.org/10.5194/tc-2020-256

  06 Nov 2020

06 Nov 2020

Review status: a revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

Surges of Harald Moltke Bræ, north-west Greenland: Seasonal modulation and initiation at the terminus

Lukas Müller1,2, Martin Horwath1, Mirko Scheinert1, Christoph Mayer3, Benjamin Ebermann1, Dana Floricioiu4, Lukas Krieger4, Ralf Rosenau1, and Saurabh Vijay5,6 Lukas Müller et al.
  • 1Technische Universität Dresden, Institut für Planetare Geodäsie, Dresden, Germany
  • 2ETH Zurich, Institute of Geodesy and Photogrammetry, Zurich, Switzerland
  • 3Bavarian Academy of Sciences and Humanities, Munich, Germany
  • 4German Aerospace Center, Wessling, Germany
  • 5DTU Space - National Space Institute, Kongens Lyngby, Denmark
  • 6Byrd Polar & Climate Research Center, Columbus, USA

Abstract. Harald Moltke Bræ, a marine-terminating glacier in north-west Greenland, shows episodic surges. A recent surge from 2013 to 2019 lasted significantly longer (6 years) than previously observed surges (2–4 years) and exhibits a pronounced seasonality with flow velocities varying by one order of magnitude (between about 0.5 and 10 m/day) in the course of a year. During this six-year period, the velocity always peaked in the early melt season and decreased abruptly when meltwater runoff was maximum. Our data suggest that the seasonality has been similar during previous surges, and, to a much lesser extent, during the intermediate quiescent phases. It is peculiar to Harald Moltke Bræ that the seasonal amplitude is amplified episodically to constitute glacier surges. The surge from 2013 to 2019 was preceded by a rapid frontal retreat and a pronounced thinning at the glacier front (30 m within 3 years).

We discuss possible causal mechanisms of the seasonally modulated surge behaviour by involving various system inherent factors (e.g. glacier geometry) and external factors (e.g. surface mass balance). The seasonality may be caused by a transition of an inefficient subglacial system to an efficient one, as known for many glaciers in Greenland. The patterns of flow velocity and ice thickness variations indicate that the surges are initiated at the terminus and develop through an up-glacier propagation of ice flow acceleration. Possibly, this is facilitated by a simultaneous up-glacier spreading of surface crevasses and weakening of subglacial till. Once a large part of the ablation zone has accelerated, conditions may favour substantial seasonal flow acceleration through seasonally changing meltwater availability. Thus the seasonal amplitude remains high for two or more years until the fast ice flow has flattened the ice surface and the glacier stabilizes again.

Lukas Müller et al.

 
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Lukas Müller et al.

Lukas Müller et al.

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Short summary
Harald Moltke Bræ, a marine-terminating glacier in northwest Greenland, undergoes remarkable surges of episodic character. Our data show that a recent surge from 2013 to 2019 was initiated at the glacier front and exhibits a pronounced seasonality with flow velocities varying by one order of magnitude which has not been observed at Harald Moltke Bræ in this way before. These findings are crucial for understanding surge mechanisms at the Harald Moltke Bræ and other marine-terminating glaciers.