Modelling sensitivities to mixing and advection in a sill-basin estuarine system

Soontiens, Nancy; Allen, Susan E.

doi:10.1016/j.ocemod.2017.02.008

Cited by 50 publications

(51 citation statements)

References 42 publications

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“…The genetic break coincides with the Victoria Sill, a shallow submarine feature that divides the Strait of Juan de Fuca from the interior Salish Sea (Ebbesmeyer & Barnes, 1980). This sill rises to depths of 55 m to 100 m and causes considerable vertical mixing during strong tidal currents in the Strait of Juan de Fuca (Ebbesmeyer & Barnes, 1980; Khangaonkar, Long, & Xu, 2017; Soontiens & Allen, 2017). This mixing creates spatial discontinuities in sediment load (Johannessen, Masson, & Macdonald, 2006), salinity (Masson & Cummins, 2000), nutrient load (Peña, Masson, & Callendar, 2016), and primary production (Masson & Peña, 2009).…”

Section: Discussionmentioning

confidence: 99%

Population assignment and local adaptation along an isolation‐by‐distance gradient in Pacific cod (Gadus macrocephalus)

Drinan

Gruenthal

Canino

et al. 2018

Evolutionary Applications

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The discernment of populations as management units is a fundamental prerequisite for sustainable exploitation of species. A lack of clear stock boundaries complicates not only the identification of spatial management units, but also the assessment of mixed fisheries by population assignment and mixed stock analysis. Many marine species, such as Pacific cod, are characterized by isolation by distance, showing significant differentiation but no clear stock boundaries. Here, we used restriction‐site‐associated DNA (RAD) sequencing to investigate population structure and assess power to genetically assign Pacific cod to putative populations of origin. Samples were collected across the species range in the eastern Pacific Ocean, from the Salish Sea to the Aleutian Islands. A total of 6,425 putative biallelic single nucleotide polymorphisms were identified from 276 individuals. We found a strong isolation‐by‐distance signal along coastlines that mirrored previous microsatellite results and pronounced genetic differentiation between coastal samples and those from the inland waters of the Salish Sea, with no evidence for hybridization between these two populations. Individual assignment success based on two methods was high overall (≥84%) but decreased from south to north. Assignment to geographic location of origin also was successful, with average distance between capture and assignment location of 220 km. Outlier analyses identified more loci potentially under selection along the coast than between Salish Sea and coastal samples, suggesting more diverse adaptation to latitudinal environmental factors than inshore vs. offshore environments. Our results confirm previous observations of sharp genetic differentiation of the Salish Sea population and isolation by distance along the coast, but also highlight the feasibility of using modern genomic techniques to inform stock boundaries and fisheries management in a low F ST marine species.

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Section: Discussionmentioning

confidence: 99%

Population assignment and local adaptation along an isolation‐by‐distance gradient in Pacific cod (Gadus macrocephalus)

Drinan

Gruenthal

Canino

et al. 2018

Evolutionary Applications

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“…The estuarine circulation that prevails throughout much of the Salish Sea and adjoining waterways has two primary components: A barotropic component forced by the seaward‐directed hydraulic head arising from freshwater discharge from bordering rivers and streams, and a baroclinic component generated by vigorous tidal mixing of the fresh surface water with salty ocean‐derived bottom water (Crean et al, 1988; Khangaonkar et al, 2017; MacCready et al, 2018; Soontiens & Allen, 2017; Sutherland et al, 2011). The circulation is modified by regional winds and oceanic processes at the coastal boundaries.…”

Section: Introductionmentioning

confidence: 99%

A Role for Gravity Currents in Cross‐Sill Estuarine Exchange and Subsurface Inflow to the Southern Strait of Georgia

et al. 2020

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Multiyear current meter records from five sites are used to examine subsurface renewal processes in the southern Strait of Georgia. The lower layer inflow of dense oceanic-derived water over the~100-m deep sill in Boundary Pass near the entrance to the strait reaches peak velocities during spring tides and rarely reverses direction. Corresponding changes in water density over the sill are inversely correlated with inflow velocity and, it is assumed, with temporal (t) variations in bottom layer thickness, h(t), arising from the fortnightly variations in tidal-mixing. The dense bottom water crossing the sill transforms into a gravity current whose velocity is dependent on both h and sill depth, H. Gravity flow velocities, which peak at h(t)/H~0.3 and weaken for h → 0 (neap tides) and h → H (spring tides), modulate the cross-sill exchange with the strait. The density anomaly, Δρ, of the gravity flow determines its terminal depth and along-strait extent. Lower-density gravity flows generated during spring tides separate from the sloping bottom of the southern strait, but the higher-density flows formed during neap tides can penetrate over 100 km northward to the deep central basin. The most extensive bottom intrusions occur monthly near neap tides in summer, when the underlying estuarine circulation delivers dense upwelled water from the coast to the sill. These deep inflows are accompanied by strong middepth outflow. There are typically three to five monthly replacement episodes each summer, but fewer during strong El Niño years due to reduced coastal upwelling.

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“…The model reproduces seasonal and interannual variability in temperature and salinity and has previously been shown to capture important physical dynamics such as deep water renewal events in the Strait of Georgia (Soontiens & Allen, 2017; Soontiens et al., 2016). As we will show in the sections that follow, it also effectively captures temporal and spatial variability in nitrate concentrations, in the contexts of both high frequency variability (section 3.1) and the seasonal cycle (section 3.2).…”

Section: Model Evaluationmentioning

confidence: 94%

“…The physical model is described in detail by Soontiens and Allen (2017) and Soontiens et al. (2016).…”

Section: Methodsmentioning

confidence: 99%

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

Olson

Allen

et al. 2020

JGR Oceans

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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.

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Modelling sensitivities to mixing and advection in a sill-basin estuarine system

Cited by 50 publications

References 42 publications

Population assignment and local adaptation along an isolation‐by‐distance gradient in Pacific cod (Gadus macrocephalus)

Population assignment and local adaptation along an isolation‐by‐distance gradient in Pacific cod (Gadus macrocephalus)

A Role for Gravity Currents in Cross‐Sill Estuarine Exchange and Subsurface Inflow to the Southern Strait of Georgia

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

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