Preprints
https://doi.org/10.5194/tc-2021-170
https://doi.org/10.5194/tc-2021-170

  16 Jun 2021

16 Jun 2021

Review status: this preprint is currently under review for the journal TC.

Seasonal evolution of basal conditions within Russell sector, West Greenland, inverted from satellite observations of surface flow

Anna Derkacheva1,, Fabien Gillet-Chaulet1,, Jeremie Mouginot1,2,, Eliot Jager1, Nathan Maier1, and Samuel Cook1 Anna Derkacheva et al.
  • 1Université Grenoble Alpes, CNRS, IRD, INP, 38400 Grenoble, Isère, France
  • 2Department of Earth System Science, University of California, Irvine, 92697 CA, USA
  • These authors contributed equally to this work.

Abstract. Increasing surface melting on the Greenland ice sheet requires better constraints on seasonally evolving basal water pressure and sliding speed. Here we assess the potential of using inverse methods on a dense time series of surface speeds to recover the seasonal evolution of the basal conditions in a well-documented region in southwest Greenland. Using data compiled from multiple satellite missions, we document seasonally evolving surface velocities with a temporal resolution of two weeks. We then apply the inverse control method using Elmer/Ice to infer the basal sliding and friction corresponding to each of the 24 surface-velocity data sets. Near the margin where the uncertainty in the velocity and bed topography are small, we obtain clear seasonal variations that can be mostly interpreted in terms of a effective-pressure based hard-bed friction law. We find for valley bottoms or "troughs" in the bed topography, the changes in basal conditions directly respond to local water pressure variations, while the link is more complex for subglacial "ridges" which are often non-locally forced. At the catchment scale, in-phase variations of the water pressure, surface velocities, surface-runoff variations are found.Our results show that time-series inversions of observed surface velocities can be used to understand the evolution of basal conditions over different timescales and could therefore serve as an intermediate validation for subglacial hydrology models to achieve better coupling with ice-flow models.

Anna Derkacheva et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-170', Anonymous Referee #1, 04 Aug 2021
    • AC1: 'Reply on RC1', Anna Derkacheva, 13 Sep 2021
  • RC2: 'Comment on tc-2021-170', Anonymous Referee #2, 12 Aug 2021
    • AC2: 'Reply on RC2', Anna Derkacheva, 13 Sep 2021
  • CC1: 'Comment on tc-2021-170', Conrad Koziol, 18 Aug 2021
    • AC3: 'Reply on CC1', Anna Derkacheva, 13 Sep 2021

Anna Derkacheva et al.

Anna Derkacheva et al.

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Short summary
Along the edges of the Greenland Ice Sheet surface melt lubricates the bed and causes large seasonal fluctuations in ice speeds during summer. Accurately understanding how these ice speed changes occur is difficult due to the inaccessibility of the glacier bed. We show that by using surface velocity maps with high temporal resolution and numerical modelling we can infer the basal conditions that control seasonal fluctuations in ice speed and gain insight into seasonal dynamics over large areas.