Seasonal and Interannual Salish Sea Inflow Origins Using Lagrangian Tracking

Abstract The Salish Sea is a semi‐enclosed sea between Vancouver Island and the coast of British Columbia and Washington State, invaluable from both an economic and ecologic perspective. Here we explore the contribution of Pacific water masses to the flow through Juan de Fuca Strait (JdF), the Salish Sea's primary connection to the Pacific Ocean. Quantitative Lagrangian particle tracking within Ariane, an offline Lagrangian tool capable of volume transport calculations, was applied to two numerical ocean models to track the paths and physical properties of water parcels before entering JdF (CIOPS) and within the Salish Sea (SalishSeaCast). During summer upwelling, flow from the north shelf and offshore dominate Pacific inflow, while during winter downwelling, flow from the south shelf and surface flow from the Columbia River plume are the dominant Pacific sources. A weaker and less consistent estuarine flow regime in the winter leads to less Pacific inflow overall and a smaller percentage of said inflow reaching the Salish Sea's inner basins than in the summer. Nevertheless, it was found that winter dynamics are a large driver of interannual variability. This analysis extends the knowledge on the dynamics of Pacific inflow to the Salish Sea and highlights the importance of winter inflow to interannual variability.