Impact of surface waves on sea ice and ocean in the polar regions
Wave height in the Arctic is increasing and this is expected to continue as summer sea ice cover declines. The summer Marginal Ice Zone (MIZ), an area consisting of severely fragmented sea ice undergoing frequent collisions, is also expanding in the Arctic. Current climate and forecasting models are not adapted to these conditions, yet accurate models are required because of climate change and the increasing human activity in the region.
This project aims to improve such models by including wave-related processes that are currently lacking. First, a Combined Collisional, reflecting the granular behaviour of MIZ sea ice, and Elastic-Viscous-Plastic (EVP) rheology is implemented in a global sea ice-ocean model. This replaces the EVP rheology currently used in models, which is appropriate for pack ice conditions. The effect of sea ice floe size, determined by wave break-up and thermodynamics, is examined using a new floe size distribution (FSD) formulation. Finally, an existing wave mixing formulation is adapted to use consistent wave information from the model rather than parameterisations that ignore sea ice presence.
The combined rheology affects sea ice distribution and motion. Using an FSD results in a decreased ice thickness and concentration through increased lateral melting. The new wave mixing formulation gives a large decrease in surface roughness under sea ice, resulting in a decreased mixed layer depth. The associated reductions in heat diffusion cause an increased ice thickness in large parts of the Arctic. Both through the effect of floe size and wave mixing, the increasing wave height in the Arctic can accelerate sea ice decline. The wave information available in this model can also be used for practical applications and to parameterise other processes that are currently lacking in earth system models. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 607476.