Variability of Water Properties and Circulation in the Juan de Fuca Eddy Region - June and September 2003

Amy MacFadyen^1*, Barbara Hickey¹, Michael Foreman² and William Cochlan³

¹ School of Oceanography, University of Washington, Seattle, 98195, USA.
² Institute of Ocean Sciences, Sidney B.C., V8L 4B2, Canada.
³Romberg Tiburon Center, San Francisco State University, Tiburon, CA, 94920, USA
^*Corresponding author, email: amoreena@ocean.washington.edu

Recent ECOHAB PNW surveys, conducted in the summer of 2003, have supported the project's initial hypothesis that the Juan de Fuca eddy is an initiation site for toxic Pseudo-nitzschia blooms which impact the Washington coast. Examination of both inter-seasonal and inter-annual variability in the physical properties and circulation in the eddy region will aid in determining the environmental factors associated with toxin production as well as in predicting likelihood of transport to coastal shellfish sites.

Surveys in June and September of 2003 show marked differences in the structure of the eddy. In September, a distinct eddy located off the mouth of the strait and clearly delineated from the upwelled water at the WA coast is evident in almost all measured physical and biological water properties. Paths of drifters deployed in June and September also suggest a stronger, more developed eddy later in the summer. A diagnostic model, forced with a baroclinic pressure gradient derived from the hydrographic survey data, tides and winds representative of the survey period is used to illustrate difference in circulation between the two cruises.