Biophysical Modelling off the Entrance of Juan de Fuca Strait

A. Pena¹, J. Morrison¹, M. Foreman¹

¹Institute of Ocean Sciences, Fisheries and Oceans Canada, PO Box 6000, 9860 West Saanich Rd, Sidney, BC V8L 4B2 Canada

Large phytoplankton blooms are often found on the continental shelf off Vancouver Island during summer associated with the Juan de Fuca Eddy situated southwest of Vancouver Island and offshore of northern Washington. Results from a biological/circulation model (ROMS) developed to study factors influencing bloom dynamics will be presented. The biological model includes two size classes of phytoplankton, nitrate and silicate limitation, and grazing by small flagellates and copepods. The sensitivity of the model output to several assumptions of uptake ratio of Si and N by diatoms, food preference of microzooplankton (grazing of flagellates on diatoms) and physical forcing will be presented. We will discuss whether these assumptions are compatible with the observed distribution of phytoplankton and nutrients. This study is part of ECOHAB PNW, a project funded by the Ecology and Oceanography of Harmful Algal Blooms program to investigate factors influencing the formation and toxicity of Pseudo-nitzschia spp. that periodically bloom in the Juan de Fuca Eddy.