9712889 Churchill 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 investigators from several 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, eval uate 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. The basic objective of this component of the Project is to better understand and model the dynamics of sediments off the Keweenaw Peninsula. The field program will focus on factors controlling the movement of solids along the Peninsula as well as processes which carry solids from shallower to deeper waters of the lake. Processes to be examined include storm-induced currents, surface and internal wave motions, variations in the strength of the Keweenaw current and instabilities of the Keweenaw current. Special attention will be given to the influence of thermal bar circulation. The study will also include an investigation of small-scale processes influencing sediment resuspension and motion in the bottom boundary layer. A modeling effort will build on the findings of the field observations in developing a 3-D model of fine sediment transport. Also to be addressed as part of our modeling program are issues of how settling particles become incorporated into the bottom, and how sediment movement influence the long-term fluxes and distribution of constituents within the lake.
