Estuary‐enhanced upwelling of marine nutrients fuels coastal productivity in the U.S. Pacific Northwest

Abstract

The Pacific Northwest (PNW) shelf is the most biologically productive region in the California Current System. A coupled physical-biogeochemical model is used to investigate the influence of freshwater inputs on the productivity of PNW shelf waters using realistic hindcasts and model experiments that omit outflow from the Columbia River and Strait of Juan de Fuca (outlet for the Salish Sea estuary). Outflow from the Strait represents a critical source of nitrogen to the PNW shelf-accounting for almost half of the primary productivity on the Vancouver Island shelf, a third of productivity on the Washington shelf, and a fifth of productivity on the Oregon shelf during the upwelling season. The Columbia River has regional effects on the redistribution of phytoplankton, but does not affect PNW productivity as strongly as does the Salish Sea. A regional nutrient budget shows that nitrogen exiting the Strait is almost entirely (98%) of oceanorigin-upwelled into the Strait at depth, mixed into surface waters by tidal mixing, and returned to the coastal ocean. From the standpoint of nitrogen availability in the coastal euphotic zone, the estuarine circulation driven by freshwater inputs to the Salish Sea is more important than the supply of terrigenous nitrogen by rivers. Nitrogen-rich surface waters exiting the Strait follow two primary pathways-to the northwest in the Vancouver Island Coastal Current and southward toward the Washington and Oregon shelves. Nitrogen flux from the Juan de Fuca Strait and Eddy Region to these shelves is comparable to flux from local wind-driven upwelling.

Experiments with Seasonal Forecasts of ocean conditions for the Northern region of the California Current upwelling system

“…Compared to other regions in the CCS, this region has a more linear coastline, and stronger seasonal variability in the winds232425. These characteristics shape the predictable seasonal response of the ocean environment.…”

Present-day and future climate pathways affecting Alexandrium blooms in Puget Sound, WA, USA

“…First, even small variations in temperature and salinity at depth may indicate large changes in biogeochemical properties. For example, Davis et al (2015) summarized the observed deep nitrate-salinity relationship in Washington coastal waters with a piecewise-linear fit that suggests 0.1-0.2 change in salinity near 34 (i.e., matching the scale of change below 50 m in Juan de Fuca canyon and Strait of Juan de Fuca in our model) is loosely equivalent to a change of 3-7 mmol N m À3 in incoming nitrate concentration, if the salinity change is interpreted as a change in the depth from which incoming water is drawn. This is on the order of 10-20% of the total nutrient supply in the Salish Sea (Mackas and Harrison, 1997), potentially enough to have effects on primary production as a whole.…”

Feeding Ecology of Pacific Sand Lance in the San Juan Archipelago

“…While active foraging and schooling may occur throughout the day, it appears that pelagic activity increases in periods of low light (i.e., crepuscular behavior). The euphotic zone in the inland waters of the Pacific Northwest is between 0 and 30 m (the true euphotic zone, defined by the depth at which light intensity falls to 1% of surface levels, varies from 10 to 100 m in PAR data collected by conductivity, temperature, and depth measurements in the Juan de Fuca Strait and Eddy Region; NOAA Fisheries NWFS and Puget Sound Institute 2012; Davis et al 2014). Therefore, Pacific Sand Lances that use this particular sand wave field in daylight hours are not only protected by the sediment but also by darkness, thus deterring visual predators.…”