Variability of Dissolved Oxygen in the Strait of Georgia: Seasonal, Intraseasonal, and Interannual Changes Based on the SalishSeaCast Model

Abstract Dissolved oxygen (DO) variability in the Salish Sea is driven by circulation, deep‐water renewal (DWR), and biological activity across multiple timescales. Using an updated version of the SalishSeaCast model, we investigate these drivers of DO in its largest basin, the Strait of Georgia, from 2012 to 2020. The model's refined parameterizations better resolve the near‐bottom DO dynamics. Sediment oxygen demand peaks in spring, consuming up to 50% of surface production, primarily due to organic matter deposition. Seasonal intrusions of dense, oxygen‐rich water from Juan de Fuca and Haro Straits ventilate the Srait of Georgia, elevating deep DO from winter minima (<100 mmol ) to summer maxima (>120 mmol ). Advection dominates this renewal, while mixing and organic matter remineralization shape the vertical DO profile. Interannually, years with weak DWR (e.g., 2017) experience 25%–30% greater deep DO drawdown than strong renewal years (e.g., 2020). This result confirms that while the Haro Strait mixing buffer prevents hypoxia, the threshold can still be approached when renewal fails. The 2017 depletion was stagnation‐driven, not production‐driven: weak renewal prolonged residence times, allowing near‐bottom remineralization to deplete DO despite no increase in primary production. These findings provide a three‐dimensional, process‐resolving assessment of how interannual variability in DWR influences hypoxia development in the Strait of Georgia, demonstrating the critical interaction between physical transport and biogeochemical processes for understanding and predicting DO dynamics.