Annual and interannual patterns of physical oceanographic properties in the San Juan Channel: effects of external drivers

Abstract

The San Juan Channel (SJC) lies within the Salish Sea between Washington state, USA and British Columbia, Canada. As an estuary, the physical oceanographic conditions of the SJC change constantly over small and large periods of time. It is important to understand how and why these changes occur in order to understand what influences the biota of the SJC. The purpose of this study was to determine the physical oceanographic conditions of 2013, compare them to the 10 previous years of PEF research, and to evaluate the effect of external drivers. The external drivers evaluated were the discharge of the Fraser River, the fall transition from upwelling to downwelling, El Niño Pacific Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and the North Pacific Gyre Oscillation (NPGO). Weekly cruises were conducted during the fall of 2013, during which a CTD was used to measure temperature and salinity and to collect water samples for the determination of dissolved oxygen. Results revealed that the Fraser River influence on salinity was heavily affected by wind direction and strength, though the fall transition did not occur within our study period. Additionally, both ENSO and the PDO contribute to seawater temperature and the NPGO was loosely correlated with surface dissolved oxygen. The fall of 2013 was a year that clearly showed multiple sources influencing one physical oceanographic characteristic.