GLOBEC-NEP: Topographic Control of Mesoscale Variability in the Gulf of Alaska

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This project addresses studies of the physical and biological distributions and processes and their effect on juvenile salmon recruitment on the Gulf of Alaska shelf. The overriding theme of the project is that along-shelf and cross-shelf mesoscale structures are due to bathymetric control of the currents. Physical oceanographic characteristics associated with this are the Alaska Coastal Current, its offshore excursions in the Seward Eddy and Seward Counter Eddy, the shelfbreak front, slope eddies and meanders and the deep flow. These features affect the transport and distribution of deep-water zooplankton that are alleged to be an important food source for juvenile salmon and may determine their survival. An undulating, underwater, towed vehicle (SeaSoar) is being used to continuously map salinity, temperature, depth and bio-optical properties. Surface samples of the above, nutrients, and chlorophyll fluorescence are being measured continuously using similar sensors. The PIs are using an Acoustic Doppler Current Profiler (ADCP) to measure along- and cross-track current velocities to 150 m depth. The PIs will calibrate the above with on-station samples of salinity, temperature, nutrients and phytoplankton. The broader impacts of this study include training of two PhD students in multidisciplinary oceanography and a better understanding of the effects of oceanographic effects on salmon variability in the Gulf of Alaska.