Modelling wave-induced sea ice break-up in the marginal ice zone.

F Montiel,V A Squire

doi:10.1098/rspa.2017.0258

Abstract

A model of ice floe break-up under ocean wave forcing in the marginal ice zone (MIZ) is proposed to investigate how floe size distribution (FSD) evolves under repeated wave break-up events. A three-dimensional linear model of ocean wave scattering by a finite array of compliant circular ice floes is coupled to a flexural failure model, which breaks a floe into two floes provided the two-dimensional stress field satisfies a break-up criterion. A closed-feedback loop algorithm is devised, which (i) solves the wave-scattering problem for a given FSD under time-harmonic plane wave forcing, (ii) computes the stress field in all the floes, (iii) fractures the floes satisfying the break-up criterion, and (iv) generates an updated FSD, initializing the geometry for the next iteration of the loop. The FSD after 50 break-up events is unimodal and near normal, or bimodal, suggesting waves alone do not govern the power law observed in some field studies. Multiple scattering is found to enhance break-up for long waves and thin ice, but to reduce break-up for short waves and thick ice. A break-up front marches forward in the latter regime, as wave-induced fracture weakens the ice cover, allowing waves to travel deeper into the MIZ.

Highlights

The Arctic marginal ice zone (MIZ) that separates open ocean from the interior pack ice is experiencing rapid changes as a result of high-latitude climate change
It is unclear how waves contribute to the emergence of these observed power-law regimes, as flexural failure is not expected to occur below a critical floe size of order O(10 m) [21], which would suggest that the floe number distribution should decrease to zero as floes become small unless other break-up mechanisms are imposed. We address this question by modelling the break-up of an ice cover under a sustained wave event, with the goal of establishing the floe size distribution (FSD) emerging from wave forcing alone, i.e. isolated from wind, collisions and any other sources of sea ice break-up
We focus our analysis on gaining a theoretical understanding of how ocean waves may influence sea ice break-up in the MIZ and the associated FSD

Summary

Introduction

The Arctic marginal ice zone (MIZ) that separates open ocean from the interior pack ice is experiencing rapid changes as a result of high-latitude climate change. In particular, have been observed to break up the sea ice under flexural failure and, to contribute to the increasing extent of the MIZ, which is, in turn, more sensitive to summer melting because of the increased total perimeter of the ice floes created [2]. It is unclear which physical processes have contributed to the observed changes in the FSD, as it is not possible to isolate the effect of waves For this reason, we focus our analysis on gaining a theoretical understanding of how ocean waves may influence sea ice break-up in the MIZ and the associated FSD

Preliminaries

Break-up model

Results

Conclusion