A two‐dimensional coupled ice‐ocean model of the Bering Sea marginal ice zone

Abstract

A two‐dimensional coupled ice‐ocean model has been formulated and applied to the wintertime Bering Sea marginal ice zone. The oceanic component is a multilevel model that incorporates second‐moment closure for turbulent mixing in the water column. The ice cover is modeled as a viscous‐plastic continuum. Melting at the ice‐ocean interface is computed using well‐known law‐of‐the‐wall concepts in a turbulent boundary layer, with particular attention to the disparate momentum and scalar transfer resistance coefficients over rough walls. The thermodynamic and dynamical interactions between the ocean and the ice cover and the energy balances at the air‐ice and air‐sea interfaces are modeled according to the companion paper (Mellor and Kantha, this issue). The model incorporates barotropic tides, both diurnal and semidiurnal, for application to the Bering Shelf. Double‐diffusive fluxes across the interface between the colder, fresher layer beneath the melting ice and the warmer, more saline water underneath are prescribed from laboratory data on double‐diffusive convection. During winter, sea ice in the central Bering Sea is transported toward the shelf break by off‐ice winds, where it encounters northward flowing warmer north Pacific waters and melts. It is this situation to which the two‐dimensional model has been applied by neglecting all variations in the along‐ice‐edge direction. The water conditions downstream of the ice edge, the ice conditions upstream, and the wind stress are the primary inputs to the model. The model simulates transition from ice‐covered to open ocean conditions and the associated ice edge front and the two‐layer circulation underneath the ice cover. Sensitivity studies indicate that the density structure and the circulation beneath the ice and the position of the ice edge are rather sensitive to the parameters affecting the dynamics and the thermodynamics of the coupled ice‐ocean system. Even small changes in the relevant parameters can cause a substantial retreat or advance of the ice edge, which may help explain why marginal ice zones are such dynamically active regions.