Collaborative Research: Coastal Ocean Advances in Shelf Transport (COAST): Iron Input and Wind-driven Circulation along the Oregon Coast

9907953

van Geen

Investigators at Oregon State University, University of North Carolina, and Columbia University will collaborate on an intensive five-year study to combine a unique set of observational tools and ocean and atmosphere models to investigate the circulation, biology, and chemistry of the Oregon coastal ocean. This project is under the auspices of the Coastal Ocean Processes (CoOP) Program and is in response to an Announcement of Opportunity for Wind-Driven Process Studies in the Northeast Pacific. The area to be studied on the Oregon shelf responds strongly to wind forcing during both summer, when mean winds favor upwelling, and winter, when mean winds favor downwelling.

A set of scientific hypotheses related to cross-shelf transport processes in a wind-driven system will be addressed by conducting field experiments together with coordinated ocean circulation/ ecosystem and atmospheric modeling. The hypotheses are: (1) the presence of upwelling and downwelling jets and fronts locally alters cross-shelf circulation in the surface and bottom boundary layers and in the interior; (2) alongshore topographic variations dictate the relative importance of two-dimensional versus three-dimensional cross-shelf transport processes; (3) patterns of turbulence on the shelf during upwelling and downwelling are influenced by fronts and jets, and the levels of turbulence can reach sufficient intensity to influence the mesoscale circulation; (4) the magnitude and distribution of primary production on the shelf and its subsequent transport offshore is controlled solely by the geometry of upwelling; (5) alongshore variations in turbulent mixing control the magnitude and distribution of primary production; and (6) the reduced cross-shelf transport implied by the presence of a downwelling front allows nutrients, trace metals and seed stocks of phytoplankton and zooplankton to accumulate in the mid- to inner shelf, thus priming the system for a strong biological response at the outset of upwelling.

To address the hypotheses, intensive observations will be made in two regions: one in a region of relatively simple topography and one in a region of abrupt topography. High-resolution sampling will be conducted using ships, an instrumented aircraft, a set of moorings, and a land-based coastal radar to make high -spatial resolution surface current maps. A high-resolution, three-dimensional shelf circulation and coupled ecosystem ocean model will be used in direct support of the field experiments by contributing to the dynamical synthesis of the observations and for relevant process studies. A mesoscale atmospheric modeling effort will provide estimates of surface forcing, continuous in space and time, for the ocean model and for interpretation of the oceanic observations.

These measurements bring together a unique set of observational tools not previously applied simultaneously to the study of coastal dynamics. Coordinated with ocean circulation/ecosystem and atmospheric modeling, the proposed effort will significantly advance our understanding of cross-shelf transport processes on wind-driven continental shelves.