OCEAN CIRCULATION MODELING IN SUPPORT OF ECOHAB PNW

Amy MacFadyen¹, Michael Foreman², Angelica Peña² and Barbara Hickey¹

¹University of Washington, School of Oceanography, Seattle, WA, 98195, USA
²Department of Fisheries and Oceans, Institute of Ocean Sciences, Sidney, BC,
V8L 4B2, Canada

Recent studies suggest that the Juan de Fuca Eddy, a seasonal nutrient-rich retentive feature off the Washington and British Columbia coasts, may be an initiation site for the toxic Pseudo-nitzschia blooms that impact shellfish along the Washington coast. As part of ECOHAB PNW, ocean circulation models are being utilized i) to simulate the ocean circulation during and after field surveys, ii) to conduct process studies into the mechanisms underlying the generation and collapse of the eddy and iii) to couple with a biological model to investigate mechanisms of bloom formation in the Juan de Fuca Eddy and the regional scale transport of Pseudo-nitzschia to the coast.

A diagnostic model has been used for the hindcasting of flow fields from all surveys to date. Results show a more developed Juan de Fuca eddy later in the upwelling season contributing to a broader region of high nutrients off the mouth of the Juan de Fuca Strait.
Under intermittent upwelling/downwelling conditions (September 2004), a much tighter recirculation is observed in the eddy and residence time increases dramatically.

Studies are also being carried out with the prognostic numerical model, ROMS. This model will provide flow fields for the biological model and be used for both process studies looking at the dynamics of eddy generation and collapse, and hindcasts of the circulation during field surveys. It will also be the primary tool for examining mechanisms that transport HABs to the coast and the viability of providing a HAB forecasting capability, when combined with UW MM5 atmospheric model forecasts and boundary conditions from a basin scale ocean model.