Danny Feltham

Sea ice dynamics and its representation in climate models

In the polar oceans seawater freezes to form a floating layer of sea ice. Sea ice acts as a partial barrier to transports of heat, moisture, and momentum between the atmosphere and ocean and is an important component of the climate system, being both an agent and indicator of change on various timescales, including climatic. Depending upon season and location, sea ice approximates a close packed tessellation of floes and floe aggregates or a more dilute mixture of isolated floes and open ocean. The sea ice floes are wide (0.1-10 km), thin (0.1-5 m) plates. The movement and mechanical deformation of sea ice is primarily driven by the wind and ocean currents, and are resisted by internal ice forces that develop as the ice is deformed. Here, I describe some aspects of sea ice mechanics and a discrete element modelling study investigating the emergent, large scale (>~ 50 km) deformation characteristics of sea ice from a consideration of forces operating at the floe scale. These insights have informed the formulation of a continuum, anisotropic sea ice rheology model that accounts for the history of past deformation through a structure tensor. This model is beginning to be incorporated into large-scale climate models.