Ocean mixing and circulation response in the marginal ice zone.

Abstract

The purpose of this research was to develop a coupled sea ice-ocean model capable of simulating the upper ocean circulation features of the Marginal Ice Zone (MIZ) . A sea ice model using the Rossby-similarity method was added to a two-dimensional, embedded ocean general circulation— mixed layer model. Advection, diffusion, and mixing of buoyancy and momentum were included in the model to determine their effects on the ocean response. In particular, the case of Northern Hemisphere ice edge upwelling was investigated. Ice edge upwelling was created for a down-ice geostrophic wind and varying surface buoyancy flux forcing. It appeared in model solutions for both stationary and moving ice covers and is driven by a divergence in the oceanic surface transport across the ice edge. These results are supported by the observations of the NORSEX group in the Greenland Sea MIZ (Johannessen et.al. 1983) . For an up-ice geostrophic wind, the upper ocean response was modified by the buoyancy forcing and ice motion. The combined effects of the wind forcing and ice motion due to a nonstationary ice cover caused weak downwelling at the ice edge. Application of a downward surface buoyancy flux (simulating ice melting) resulted in a 8 m elevation of the mixed layer depth at the ice edge, or upwelling, next to the downwelling. The existence of this dual (upwelling and downwelling) feature at the ice edge differs from the weak downwelling predicted by Roed and O'Brien (1983) . Adding the effects of mixing had a significant impact on the upper ocean circulation response and should be incorporated in future models of dynamical MIZ processes.