Unsupervised classification of the Antarctic marginal ice zone

The Antarctic marginal ice zone is the regularly wave-affected outer band of the sea ice covered Southern Ocean. The ice cover in the marginal ice zone is typically unconsolidated and contains smaller, thinner ice floes than the inner ice pack, which makes it a highly dynamic region and susceptible to rapid expansion or contraction. Here, an unsupervised statistical method is used to cluster sea ice data from 2010–2019 simulated by a global sea ice model (CICE6 combined with a waves propagation module), such that it defines a sea ice region with marginal ice zone characteristics. Floe size is shown to be the key variable in classifying the marginal ice zone in the statistical method. The method is shown to give marginal ice zone widths similar to those derived from satellite observations of wave penetration distances, but contrasts with those using the 15–80\% areal sea ice concentration definition, particularly during austral winter. Using the proposed definition, the marginal ice zone is found to undergo a seasonal transition due to new ice formation in winter, increased drift in spring, and increased rates of wave-induced breakup and melting in summer. The study motivates incorporation of wave and floe-scale processes in sea ice models, and the methods are available for application to outputs from high-resolution and coupled sea ice–ocean–wave models for more detailed studies of the marginal ice zone (in both hemispheres).