Impact of the Keweenaw Current on Cross Margin Transport in Lake Superior: Contribution to a Study of Physics Processes

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9712846 Aagaard Research will be undertaken in response to an Announcement of Opportunity (NSF 97-38) for Coastal Studies in the Great Lakes. This is a collaborative research project involving eleven investigators from five academic research institutions. The research is being conducted under the auspices of the NSF Coastal Ocean Processes (CoOP) program and the NOAA Coastal Ocean Program. This collaborative, interdisciplinary 5-year research program will entail an integrated program of field and laboratory studies and mathematical modeling to quantify the role of coastal currents and thermal fronts in mediating cross-margin transport in Lake Superior. The western shore of Lake Superior's Keweenaw Peninsula exhibits a dramatic coastal jet known as the Keweenaw Current. A strong, shore-parallel density front, the thermal bar, also is characteristic of this region and persists long into the summer. The goal of the proposed work is to determine the physical, chemical, and biological effects that arise from the intense physical forcing on this system, and specifically, to elucidate how these effects interact temporally and spatially to define distinct nearshore and offshore environments in Lake Superior. This project represents the first effort to model coupled physical, chemical, and biological processes in the coastal zone of Lake Superior where both vertical and horizontal thermal structure and transport processes are important. The research team is divided into three subgroups: Physical Processes, Chemical Gradients, and Biological Communities. The Physical Processes group will examine the relative importance of all forcing factors (e.g., wind-driven variability, baroclinic instability) that govern cross margin transport using in situ observations, numerical modeling, and satellite observations. The Chemical Gradients group will characterize nearshore-offshore differences in distributions of chemical species, evaluate chemical tracers of water and sediment movement, and investigate differences (inshore vs. offshore) in chemical cycles induced by the current. The Biological Communities group will determine how gradients in primary production, trophic structure, and rates of material transformation develop. All three groups will interact closely throughout the project to obtain and share complementary data sets and to derive a coupled physical/chemical/biological model of the system. The detailed, process-level understanding achieved by this project will advance our quantitative understanding of the processes that regulate the transport, transformation and fate of biologically, chemically and geologically important matter in coastal regions and provide a firm basis for future management decisions on how best to preserve the pristine nature of Lake Superior. This particular project will contribute to the activities of the Physical Processes subgroup that will measure currents, thermal, and density structure in order to define the spatial and temporal extent of the Keweenaw Current and thermal bar. Moorings will be deployed through three full years so that conditions in all seasons, including under the ice, can be monitored. Ground-based measurements will be enhanced by concurrent satellite determination of surface temperature; archived images (1987-96) will be employed to obtain a record of interannual variability in thermal structure.