Assessment of Nutrient Supply by a Tidal Jet in the Northern Strait of Georgia Based on a Biogeochemical Model

Abstract

We present a coupled three‐dimensional biological‐physical model for the Salish Sea and evaluate it by comparison to nitrate, silicate, and chlorophyll observations. It accurately reproduces nitrate concentrations with Willmott skill scores, root‐mean‐square error, and bias ranging from 0.84–0.95, 4.02–6.5 μM, and −2.33–1.84 μM, respectively, compared to three independent discrete sample data sets. A prominent feature of the model output is a tidal jet emanating from Discovery Passage producing a downstream plume of elevated surface nitrate. The signal is present from April to September, when surface nitrate is otherwise drawn down. It has a weak but statistically significant correlation to Discovery Passage tidal velocity (R=0.37, p<0.01). Within the turbulent jet and associated plume, the average rate of vertical nitrate supply due to mixing and advection across a depth of roughly 6 m is 0.46 μmol m−2 s−1 between 15 May and 20 August 2015, compared to 0.10 μmol m−2 s−1 for the northern Strait of Georgia as a whole. Close to Discovery Passage, where velocities and shear are strongest, the majority of the vertical nitrate flux is due to mixing. As velocities weaken downstream, vertical advection becomes more important relative to mixing, but vertical velocities also decrease. The tidal pulses out of Discovery Passage drive waves that contribute net upward nitrate flux as far south as Cape Lazo, 40 km away. The nitrate supply drives new production, consistent with existing observations. Similar dynamics have been described in many other tidally influenced coastal systems.

Estuarine Circulation, Mixing, and Residence Times in the Salish Sea

“…Realistic models of the Salish Sea were also attempted in past decades but were significantly hampered by lack of computing power. Modern, realistic models of the Salish Sea only appeared in the last decade (Khangaonkar et al., 2017; Khangaonkar et al., 2011; Moore et al., 2015; Olson et al., 2020; Peña et al., 2016; Soontiens et al., 2015; D. A. Sutherland et al., 2011). The present model continues this realistic numerical approach.…”

A clustering approach to determine biophysical provinces and physical drivers of productivity dynamics in a complex coastal sea

“…Nutrient delivery via episodic tidal mixing events near Discovery Passage has been linked to increased biomass (e.g. Parsons et al (1981); Haigh and Taylor (1991)) and modelled primary productivity (Olson et al (2020)). Though this phenomenon has been recorded in the CSoG as well (Yin et al (1997); St.…”

“…The mixotroph M. rubrum has intermediate growth parameters while grazing on the flagellate class in addition to photosynthesizing. Details of phytoplankton growth rate and nutrient and light level preference are available in Olson et al (2020).…”

“…In summary, the model shows consistently high skill in across all clusters (Tables A1-A2), with Willmott skill scores for temperature and salinity ranging from 0.957-0.971 and 0.959-0.971 respectively across the clusters, while comparisons with log-transformed total chlorophyll data yield scores of 0.599-0.712. A summary of minor updates to the model tuning since publication in Olson et al (2020) is provided in Appendix B.…”

Zooplankton variability in the Strait of Georgia, Canada, and relationships with the marine survivals of Chinook and Coho salmon

“…We have begun working with researchers at the University of British Columbia to understand the processes driving zooplankton populations in the Strait of Georgia (e.g. [ 67 ]). The correlations of the latent zooplankton trends with sea surface salinity and flow from the Fraser River suggest the retention process of Bakun’s Triad would be a good initial focus for these modelling studies.…”