Effects of small-scale heterogeneities on the bulk mechanical properties of sea ice

Abstract:

The Arctic ice cover is riddled with cracks, ridges, and melt ponds leading to spatial heterogeneities that manifest as sharp transitions in thickness, porosity, salinity, etc., that in turn affect the bulk mechanical behavior of the ice pack. In regions within and near the marginal ice zone, where ice survives the summer melt and break-up as discrete floes with length scales on the order of hundreds of meters to a kilometer, the freeze up subsequent to the melt season forms a patchwork of thick perennial ice bound together by thinner and smoother first-year ice with a coherence of varying length scales. Remote sensing has shown that the fracture patterns in these patchy ice regions, which may be more representative of marginal ice zone and coastal areas, tend to form in preferential pathways in the thinner ice, therefore modifying the rhomboidal pattern that is characteristic of more homogeneous ice. Using a sea ice model based on the discrete element method (DEM) and remotely sensed images, we examine the effect that heterogeneities in the ice cover have on the derivation of constitutive behavior at scales relevant to climate models by representing the observed heterogeneities explicitly. This model allows us to not only measure the mechanical response of a sample domain, but to also look at the break-up behavior for regions of varying melt pond coverage, thickness, etc. Our hope is that our results can be used to extend existing sea ice rheologies that already incorporate the spatial discontinuities of the ice cover due to lead formation [Moritz & Ukita, 2000; Schreyer et al., 2006; Wilchinsky & Feltham, 2004; Sedlacek et al., 2007].