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Abstract The dynamics of ocean‐estuary exchange depend on a variety of local and remote ocean forcing mechanisms where local mechanisms include those directly forcing the estuary such as tides, river discharge, and local wind stress; remote forcing includes forcing from the ocean such as coastal wind stress and coastal stratification variability. We use a numerical model to investigate the limits of oceanic influence, such as wind‐driven upwelling, on the Salish Sea exchange flow and salt transport. We find that along‐shelf winds substantially modulate flow throughout the Strait of Juan de Fuca until flow reaches sill‐influenced constrictions. At these constrictions the exchange flow variability becomes sensitive to local tidal and river forcing. The salt exchange variability is tidally dominated at Admiralty Inlet and upwelling has little impact on seasonal salt exchange variability. While within Haro Strait, the salt exchange variability is driven by a mix of coastal upwelling and local forcing including river discharge. There, the transition from oceanic to local control of salt exchange occurs over a longer distance and is primarily identifiable in the increasing variability of bulk outflowing salinity values. The differences between the two locations highlight how ocean variability interacts with both tidal pumping and gravitational circulation. We also distinguish between transient ocean forcing which can modify fjord properties near the mouth of the strait and seasonal ocean forcing which primarily affects along‐strait pressure gradients. The results have implications for understanding the transport variability of biogeochemical variables that are influenced by both along‐shelf winds and local sources. 

Abstract The exchange between estuaries and the coastal ocean is a key dynamical driver impacting nutrient and phytoplankton concentrations and regulating estuarine residence time, hypoxia, and acidification. Estuarine exchange flows can be particularly challenging to monitor because many systems have strong vertical and lateral velocity shear and sharp gradients in water properties that vary over space and time, requiring high‐resolution measurements in order to accurately constrain the flux. The total exchange flow (TEF) method provides detailed information about the salinity structure of the exchange, but requires observations (or model resolution) that resolve the time and spatial co‐variability of salinity and currents. The goal of this analysis is to provide recommendations for measuring TEF with the most efficient spatial sampling resolution. Results from three realistic hydrodynamic models were investigated. These model domains included three estuary types: a bay (San Diego Bay), a salt‐wedge (Columbia River), and a fjord (Salish Sea). Model fields were sampled using three different mooring strategies, varying the number of mooring locations (lateral resolution) and sample depths (vertical resolution) with each method. The exchange volume transport was more sensitive than salinity to the sampling resolution. Most (>90%) of the exchange flow magnitude was captured by three to four moorings evenly distributed across the estuarine channel with a minimum threshold of 1–5 sample depths, which varied depending on the vertical stratification. These results can improve our ability to observe and monitor the exchange and transport of water masses efficiently with limited resources. 

The two-way exchange of water and properties such as heat and salinity as well as other suspended material between estuaries and the coastal ocean is important to regulating these marine habitats. This exchange can be challenging to measure. The Total Exchange Flow (TEF) method provides a way to organize the complexity of this exchange into distinct layers based on a given water property. This method has primarily been applied in numerical models that provide high resolution output in space and time. The goal here is to identify the minimum horizontal and vertical sampling resolutions needed to measure TEF depending on estuary type. Results from three realistic hydrodynamic models were investigated. These models included three estuary types: bay (San Diego Bay: data/SDB_*.mat files), salt-wedge (Columbia River: data/CR_*.mat files), and fjord (Salish Sea: data/SJF_*.mat files). The models were sampled using three different mooring strategies, varying the number of mooring locations and sample depths with each method. This repository includes the Matlab code for repeating these sampling methods and TEF calculations using the data from the three estuary models listed above. 

This folder contains  model extractions for the manuscript "The Limits of Oceanic Forcing on the Exchange Flow of the Salish Sea" by Robert Sanchez, Sarah Giddings, and Emily Lemagie. At the moment, data is still being uploaded. The model extractions contain hourly fields of ssh, wind stress, u,v,temp,and salt. Feel free to reach out to the corresponding author (Robert Sanchez) for code or clarifications. Code to produce TEF from these sections will be available on GitHub soon. The data comes from the LiveOcean model (here), with other extractions available here. Model details can be found here.