Studies of the Arctic ice cover and upper ocean with a coupled ice‐ocean model

Abstract

An ice‐ocean model has been developed by coupling the Hibler ice model to a three‐dimensional ocean model that consists of a turbulent mixed layer model and an inverse geostrophic model. The coupled model has a horizontal grid spacing of 127 km and has 17 vertical levels extending to the ocean bottom. The model is forced with 12‐hourly general circulation model‐derived atmospheric fluxes for the year 1986, for which good quality ice edge analyses and buoy tracks were available for comparisons. The results are presented for the fifth year of a repetitive simulation with the 1986 fluxes, at which time the system has reached a statistical equilibrium. The seasonal and geographical variations of the ice cover and the upper few hundred meters of the ocean have been examined, including the heat and salt budgets. The computed heat fluxes and mixed layer depths (MLDs) fall in the observed seasonal ranges, with winter heat fluxes ranging from 15 W m−2 in the central Arctic to about 500 W m−2 in the Barents Sea area, and summer fluxes from about 5 W m−2 under the ice to about 30 W m−2 in the various marginal ice zone (MIZ) edge areas. The corresponding winter MLDs are found to be about 25–75 m in the central Arctic to a deep 800 m in the Greenland Sea; typical summer MLDs are between 5 and 30 m. In all seasons, the MIZ was found to be the center of flux activity for both heat and salt, with the processes of advection, diffusion, atmospheric forcing, and vertical oceanic fluxes having their largest values here, and of comparable magnitudes. Values of the heat flux components in the MIZ exceed those found under the ice by an order of magnitude or more, and those in the open water region by a factor of 2. For salt, the situation is similar except in the summer (June through September), when a lot of salt flux activity takes place under the ice. Comparisons are made with Naval Polar Oceanography Center (NPOC) analyses for ice concentration and ice edge, and with observed Arctic buoy tracks, in the same 1986 time period. The computed ice edge positions have comparable accuracy to previous three‐dimensional coupled ice‐ocean studies, with too much ice growth during the winter in the Barents Sea and too little ice east of Greenland. The ice thickness distributions, however, are much better, with a monotonic increase of the ice thickness from the Siberian coast east toward the Canadian archipelago with maximum winter values of about 5–6 m.