Collaborative Research: Dynamics of Ocean Climate Changes in the Gulf of Alaska

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OCE-0452692/0452743/0452654The Gulf of Alaska is a complicated physical oceanographic system that supports economically important fisheries and ecologically important wildlife areas. The Alaska Current, which runs northwestward along the eastern shelf-slope boundary, and the Alaskan Stream, which runs southwestward along the western shelf-slope boundary, both support an energetic open-ocean mesoscale circulation. These mean flows are thought to be driven mainly by wind-stress curl forcing, while the eddies develop as a consequence of baroclinic instability of the mean flows, fluctuating wind stress forcing, and the arrival of remotely driven coastal waves. The Alaska Coastal Current, which winds and meanders along the shelf through numerous straights and islands, is thought to be driven by both coastal fresh-water discharge and wind stresses. An interesting aspect of the large-scale circulation of the Gulf of Alaska is that the open ocean interior is generally an upwelling region, while the coastal regions are generally downwelling. Even so, primary productivity is highest in the coastal regions, which sustain a rich and diverse ecosystem. The mechanisms by which the physical environment affects the productivity of this biological system are complicated and poorly understood. Some of these mechanisms involve cross-shelf mixing processes in which mesoscale eddy variability mix open-ocean nutrient rich waters with shelf waters that contain iron.Intellectual Merit: The ocean circulation of the Gulf of Alaska will be studied using a combination of eddy resolving ocean models, observational analyses and ocean data assimilation products to elucidate the dynamics that control the mean, mesoscale variability and interannual to interdecadal climate variations of the Alaska Current, the Alaskan Stream, as well as the broader-scale interior gyre flows. The eddy-resolving model runs (using the Regional Ocean Modeling System) will incorporate the effects of wind stresses, surface heat fluxes, surface/coastal fresh-water fluxes, and open-ocean boundary fluxes in various combinations to establish the sensitivity of the model mean and mesoscale fields to changes in these forcings as part of the seasonal cycle and as components of climate variations. The study of the ocean analysis products will provide a baseline of model-data compatibility to help link the very limited hydrographic dataset to the dynamically consistent eddy-resolving simulations. The results of the physical oceanographic analysis will be applied in several ways to understand the complicated biological oceanography of the region. This will include analyzing mixed-layer depth variations, computing cross-shelf particle transports, allowing passive tracers to advect and diffuse laterally and vertically, and incorporating simple ecosystem models in the physical model runs. The results will help us to understand the mechanisms that control the seasonal variability of the productivity of the Gulf, the processes that maintain high productivity on the shelf, and the reasons for interannual to interdecadal variations in productivity that affect higher trophic levels, like pelagic fish populations and Steller sea lions.Broader Impact: This research has broader impacts in that it is relevant to commercially important fisheries management (which must deal with decadal variations in fish populations), it may help to untangle the mysteries behind the decline of Steller sea lion populations (a protected marine mammal), which in the 1990's were reduced to 20% of their numbers of the 1970's, and it may contribute to a better understanding of climate variability and predictability (which may influence socially important industries like agriculture and energy production). A graduate student and post-doc will receive training is sophisticated numerical modeling and data assimilation techniques.