On roles of mesoscale variability and fresh water flux on deep water formation

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As a time scale becomes longer, the ocean plays more important roleson climate variability. The North Atlantic Deep Water formed in the Greenland Sea originates the global conveyor belt in the deep ocean, andits presence and formation rates influence global climate. The surface layr of the Greenland Sea could not become dense enough to be convected with the lower layr, depending on the amount of fresh water plus sea ice from the Arctic Ocean. However, brine rejection from ice formation may increase the surface layr density and yield deepconvection. The surface layr is not horizontally uniform, but contains variability at spatial scales of 10-100km. The horizontal variability is another important aspect for deep convection, because convection can occur in more weakly stratified areas. In addition to open water deepconvection, dense water is formed over the shelf regions, leading to the Arctic Water at the mid-depth.A coupled ice-ocean model was constructed in the present study. We aimed at reconstructing dense water formation in the model as well as understanding several important processes such as convection, mesoscale eddies and internal waves. The model was applied to the Labrador Shelf and the Okhotsk Sea, for simulating seasonal formation/decay of sea ice along with dense water formation. Using a nonhydrostatic model, we examined vertical mixing caused by ice formation in open leads and polynyas. The dense water is dependent on sizes, distribution and movement of the open water areas. It was suggested that baroclinic instability plays a major role in transporting dense water to the offshore region. Internal waves were found to be important for vertical mixing in a stably stratofied ocean. These results provide useful information for predicting global climate change.