Seasonably Variable Estuarine Exchange Through Interconnected Channels in the Salish Sea

Abstract The Salish Sea is a semi‐enclosed estuary whose largest basin (Strait of Georgia (SoG)) is connected to the north‐eastern Pacific Ocean through regions with tight constructions and sills that cause intense tidal mixing. The estuarine circulation is complicated through the tidally mixed region around the San Juan and Gulf Islands, which consists of three different straits: Haro Strait, Rosario Strait, and San Juan Channel (SJC). Haro Strait, as the largest and deepest of the channels, is the dominant pathway; however, we determine that Rosario Strait also has an important influence in this region. To examine the differences in water transport through the different channels, Lagrangian particle tracking experiments were performed for a 4‐year hindcast (from 2018 to 2022) using the 3‐dimensional numerical model SalishSeaCast. While Haro Strait has southward surface flow and northward deep flow, the flux making it through Rosario Strait and SJC is primarily southward. The proportion of the total southward flux through these two channels is higher from May to October and this increase is attributed to the influence of both the Fraser River and the river discharge from Puget Sound. Rosario Strait is the dominant pathway of southward exchange from the SoG to Puget Sound, while the majority of deep northward flux to the SoG is through Haro Strait.