Simulation of the mixed-layer circulation in the Arctic Ocean

A numerical simulation of the mixed-layer circulation of the Arctic Ocean is presented using Oberhuber's [1993a] coupled sea ice-mixed layer-isopycnal ocean general circulation model. The model domain includes the Arctic Ocean and the Greenland-Iceland-Norwegian (GIN) Sea. The horizontal resolution is 2°. The vertical is resolved using five isopycnal layers, of which the uppermost layer is a turbulent mixed layer. The sea ice is modeled using a thermodynamic-dynamic model which includes a viscous-plastic rheology. Monthly climatological atmospheric forcing is used to spin up the model into a cyclostationary equilibrium. Model results are presented and discussed with respect to observational and previous modeling studies. The mixed layer shows a circulation pattern similar to that inferred from indirect observations and other modeling studies. In an attempt to determine the main driving mechanism for the mixed-layer circulation as produced by the Oberhuber model, a set of sensitivity experiments is carried out. In particular, the relative importance of (1) ice cover, (2) atmospheric winds, (3) surface freshwater fluxes, and (4) initialization with Levitus [1982] data is examined to determine the contribution each makes to the modeled circulation. The key conclusion is that buoyancy forcing is critical to maintaining the mixed-layer circulation.