Preprints
https://doi.org/10.5194/tc-2021-391
https://doi.org/10.5194/tc-2021-391
 
23 Dec 2021
23 Dec 2021
Status: this preprint is currently under review for the journal TC.

Wave-triggered breakup in the marginal ice zone generates lognormal floe size distributions

Nicolas Guillaume Alexandre Mokus and Fabien Montiel Nicolas Guillaume Alexandre Mokus and Fabien Montiel
  • Department of mathematics and Statistics, University of Otago, Dunedin, New Zealand

Abstract. Fragmentation of the sea ice cover by ocean waves is an important mechanism impacting ice evolution. Fractured ice is more sensitive to melt, leading to a local reduction in ice concentration, facilitating wave propagation. A positive feedback loop, accelerating sea ice retreat, is then introduced. Despite recent efforts to incorporate this process and the resulting floe size distribution (FSD) into the sea ice components of global climate models (GCM), the physics governing ice breakup under wave action remains poorly understood, and its parametrisation highly simplified. We propose a two-dimensional numerical model of wave-induced sea ice breakup to estimate the FSD resulting from repeated fracture events. This model, based on linear water wave theory and viscoelastic sea ice rheology, solves for the scattering of an incoming time-harmonic wave by the ice cover and derives the corresponding strain field. Fracture occurs when the strain exceeds an empirical threshold. The geometry is then updated for the next iteration of the breakup procedure. The resulting FSD is analysed for both monochromatic and polychromatic forcings. For the latter results, FSDs obtained for discrete frequencies are combined appropriately following a prescribed wave spectrum. We find that under realistic wave forcing, lognormal FSDs emerge consistently in a large variety of model configurations. Care is taken to evaluate the statistical significance of this finding. This result contrasts with the power-law FSD behaviour often assumed by modellers. We discuss the properties of these modelled distributions, with respect to the ice rheological properties and the forcing waves. The projected output will be used to improve empirical parametrisations used to couple sea ice and ocean waves GCM components.

Nicolas Guillaume Alexandre Mokus and Fabien Montiel

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-2021-391', Anonymous Referee #1, 16 Feb 2022
    • AC1: 'Reply on RC1', Nicolas Mokus, 16 May 2022
  • RC2: 'Comment on tc-2021-391', Anonymous Referee #2, 07 Mar 2022
    • AC2: 'Reply on RC2', Nicolas Mokus, 16 May 2022
  • RC3: 'Comment on tc-2021-391', Anonymous Referee #3, 07 Apr 2022
    • AC3: 'Reply on RC3', Nicolas Mokus, 16 May 2022
  • CC1: 'Comment on tc-2021-391', Elie Dumas-Lefebvre, 08 Apr 2022
    • AC4: 'Reply on CC1', Nicolas Mokus, 16 May 2022

Nicolas Guillaume Alexandre Mokus and Fabien Montiel

Data sets

Model code and simulation results for the investigation of a wave-generated floe size distribution Mokus, Nicolas; Montiel, Fabien https://doi.org/10.6084/m9.figshare.17303927

Model code and software

Model code and simulation results for the investigation of a wave-generated floe size distribution Mokus, Nicolas; Montiel, Fabien https://doi.org/10.6084/m9.figshare.17303927

Nicolas Guillaume Alexandre Mokus and Fabien Montiel

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Short summary
On the fringes of polar oceans, sea ice is easily broken by waves. As small pieces of ice, or floes, are more easily melted by the warming waters than a continuous ice cover, it is important to incorporate these floe sizes in climate models. These models simulate climate evolution at the century scale and are built by combining specialised modules. We study the statistical distribution of floe sizes under the impact of waves to better understand how to connect sea ice modules to wave modules.