Preprints
https://doi.org/10.5194/gmd-2022-21
https://doi.org/10.5194/gmd-2022-21
Submitted as: model evaluation paper
01 Mar 2022
Submitted as: model evaluation paper | 01 Mar 2022
Status: this preprint is currently under review for the journal GMD.

Evaluation of an emergent feature of sub-shelf melt oscillations from an idealised coupled ice-sheet/ocean model using FISOC(v1.1)-ROMSIceShelf(v1.0)-Elmer/Ice(v9.0)

Chen Zhao1, Rupert Gladstone2, Ben Galton-Fenzi3,1,4, David Gwyther5,6, and Tore Hattermann7,8 Chen Zhao et al.
  • 1Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
  • 2Arctic Centre, University of Lapland, Rovaniemi, Finland
  • 3Australian Antarctic Division, Kingston, Australia
  • 4The Australian Centre for Excellence in Antarctic Science, University of Tasmania, Hobart, Australia
  • 5Centre for Applications in Natural Resource Mathematics, School of Mathematics and Physics, University of Queensland, Australia
  • 6Coastal and Regional Oceanography Lab, School of Biological, Earth and Environmental Sciences, UNSW Sydney, Australia
  • 7Norwegian Polar Institute, Tromsø Norway
  • 8Energy and Climate Group, Department of Physics and Technology, The Arctic University - University of Tromsø, Norway

Abstract. Changes in ocean-driven basal melting have a key influence on the stability of ice shelves, the mass loss from the ice sheet, ocean circulation and global sea level rise. Coupled ice sheet – ocean models have a critical role in understanding future ice sheet evolution and examining the processes governing ice sheet response to basal melting. However, as a new approach, coupled ice-sheet/ocean systems come with new challenges, and the impacts of solutions implemented to date have not been investigated. An emergent feature in several contributing coupled models to the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) was a time-varying oscillation in basal melt rates. Here we use a recently developed coupling framework, FISOC (v1.1), to connect the modified ocean model ROMSIceShelf (v1.0) and ice-sheet model Elmer/Ice (v9.0), to investigate the origin and implications of the feature and more generally the impact of coupled modelling strategies on the simulated basal melt in an idealised ice shelf cavity, based on the MISOMIP setup. We found the spatial-averaged basal melt rates (3.56 m yr-1) oscillated with an amplitude ~ 0.7 m yr-1 and approximate period of ~ 6 years between year 30 and 100, depending on the experimental design. The melt oscillations emerged in the coupled system and the stand-alone ocean model using a prescribed change of cavity geometry. We found that the oscillation feature is closely related to the discretised ungrounding of the ice sheet, exposing new ocean, and is likely strengthened by a combination of positive buoyancy-melt feedback and/or melt-geometry feedback near the grounding line, and the frequent coupling of ice geometry and ocean evolution. Sensitivity tests demonstrate that the response is insensitive to the choice of coupling interval, vertical resolution in the ocean model, tracer properties of immediately ungrounded cells by the retreating ice sheet, or the dependency of friction velocities to the vertical resolution. However, we were unable to ultimately determine if the feature is as a result of either numerical issues due to discritisation, or a compounding of multiple physical processes. We suggest a pathway and choices of physical parameters to help other efforts understand the coupled ice-sheet/ocean system using numerical models.

Chen Zhao 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 gmd-2022-21', Nicolas Jourdain, 31 Mar 2022
  • RC2: 'Comment on gmd-2022-21', Anonymous Referee #2, 04 Apr 2022

Chen Zhao et al.

Data sets

FISOC_ElmerIce_ROMS_MISOMIP1_GMD: FISOC_ElmerIce_ROMS_v1.0 Chen Zhao https://doi.org/10.5281/zenodo.5908713

Model code and software

ROMSIceShelf Ben Galton-Fenzi https://doi.org/10.5281/zenodo.3526801

Elmer/Ice CSC - IT Center for Science https://github.com/ElmerCSC/elmerfem

FISOC Rupert Gladstone https://doi.org/10.5281/zenodo.4507182

Chen Zhao et al.

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Short summary
Coupled ice ocean models are significant in exploring how glaciers response to ice shelf basal melting. Here we use a coupled model to explore an oscillation feature found in several contributing models to the Marine Ice Sheet–Ocean Model Intercomparison Project. It is closely related to the discretised grounding line retreat and likely strengthened by the positive buoyancy-melt feedback and/or melt-geometry feedback near the grounding line, and the frequent coupling of ice/ocean evolution.