The Impact of Surface Mixing on the Arctic River Water Distribution and Stratification in a Global Ice-Ocean Model

The impact of oceanic vertical mixing on the near-surface vertical structure of the Arctic Ocean is investigated in a global ice-ocean model with a passive tracer. Lowering surface background vertical diffusivity and ignoring the effects of surface wave breaking under sea ice improves the model simulation of the horizontal Arctic river water distribution. This improvement is largely responsible for the freshening of the Arctic surface salinity in the model. Although these modifications in the model vertical mixing scheme are applied over the whole global ocean, the change in the surface salinity over the Arctic is larger than that in the rest of the global ocean by one to two orders of magnitude. In contrast, when a reduced background vertical diffusivity is used at all depths, the Arctic vertical salinity stratification is improved below the surface as well as in the surface layer, but the vertical structure and deep circulation in the rest of the global ocean are also strongly affected. Weaker surface vertical mixing in the Arctic Ocean also causes sea ice to thicken even without changes in the parameters for the sea ice component.