Preprints
https://doi.org/10.5194/tc-2021-327
https://doi.org/10.5194/tc-2021-327

  19 Oct 2021

19 Oct 2021

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

Shear-margin melting causes stronger transient ice discharge than ice-stream melting according to idealized simulations

Johannes Feldmann1, Ronja Reese1,2, Ricarda Winkelmann1,3, and Anders Levermann1,3,4 Johannes Feldmann et al.
  • 1Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany
  • 2Department of Geography and Environmental Sciences, Northumbria University, Newcastle, UK
  • 3Institute of Physics, University of Potsdam, Potsdam, Germany
  • 4LDEO, Columbia University, New York, USA

Abstract. Basal ice-shelf melting is the key driver of Antarctica's increasing sea-level contribution. In diminishing the buttressing force of the ice shelves that fringe the ice sheet the melting increases the solid-ice discharge into the ocean. Here we contrast the influence of basal melting in two different ice-shelf regions on the time-dependent response of an idealized, inherently buttressed ice-sheet-shelf system. Carrying out three-dimensional numerical simulations, the basal-melt perturbations are applied close to the grounding line in the ice-shelf's 1) ice-stream region, where the ice shelf is fed by the fastest ice masses that stream through the upstream bed trough and 2) shear margins, where the ice flow is slower. The results show that melting below one or both of the shear margins can cause a decadal to centennial increase in ice discharge that is more than twice as large compared to a similar perturbation in the ice-stream region. We attribute this to the fact that melt-induced ice-shelf thinning in the central grounding-line region is attenuated very effectively by the fast flow of the central ice stream. In contrast, the much slower ice dynamics in the lateral shear margins of the ice shelf facilitate sustained ice-shelf thinning and thereby foster buttressing reduction. Regardless of the melt location, a higher melt concentration toward the grounding line generally goes along with a stronger response. Our results highlight the vulnerability of outlet glaciers to basal melting in stagnant, buttressing-relevant ice-shelf regions, a mechanism that may gain importance under future global warming.

Johannes Feldmann et al.

Status: open (until 14 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2021-327', Anonymous Referee #1, 16 Nov 2021 reply
  • RC2: 'Comment on tc-2021-327', Anonymous Referee #2, 16 Nov 2021 reply

Johannes Feldmann et al.

Johannes Feldmann et al.

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Short summary
We use a numerical model to simulate the flow of a simplified Antarctic-type outlet glacier with an attached ice shelf. We find that after a few years of perturbation such a glacier responds much stronger to melting in the lateral parts of its ice shelf than to melting in the central part of its ice shelf. Since continued global warming likely will increase the melt rates under the Antarctic ice shelves the mechanism found and explained in this study might gain importance in the future.