Improved modeling of the Arctic halocline with a subgrid-scale brine rejection parameterization

The halocline in the Arctic Ocean plays an important role in regulating heat exchange at the bottom of the mixed layer and it has a direct effect on the ocean sea ice energy balance and sea ice mass balance. Modeling the halocline, however, remains a challenge in current state-of-the-art coupled ocean sea ice models including those that participated in the Arctic Ocean Model Intercomparison Project. In this study, we successfully reproduce a cold halocline in the Canada Basin by implementing a subgrid-scale brine rejection parameterization in an ocean general circulation model. The brine rejection scheme improves the solution by redistributing surface salts rejected during sea ice formation to their neutral buoyancy depths. The depths are based on salt plume physics and published laboratory and numerical experiments. Compared with hydrographic data from 1993 to 2004, distribution of most of the rejected salt to the bottom of the mixed layer seems to yield the lowest model-data misfits. We also show that the model's mixed layer depth is sensitive to the background diffusivity nu used in the k-profile parameterization vertical mixing scheme. A background diffusivity of 10(-6) m(2)/s in combination with brine rejection scheme described herein yield the best simulation of the Arctic halocline.