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A realistic numerical model is used to study the circulation and mixing of the Salish Sea, a large, complex estuarine system on the United States and Canadian west coast. The Salish Sea is biologically productive and supports many important fisheries but is threatened by recurrent hypoxia and ocean acidification, so a clear understanding of its circulation patterns and residence times is of value. The estuarine exchange flow is quantified at 39 sections over 3 years (2017–2019) using the Total Exchange Flow method. Vertical mixing in the 37 segments between sections is quantified as opposing vertical transports: the efflux and reflux. Efflux refers to the rate at which deep, landward-flowing water is mixed up to become part of the shallow, seaward-flowing layer. Similarly, reflux refers to the rate at which upper layer water is mixed down to form part of the landward inflow. These horizontal and vertical transports are used to create a box model to explore residence times in a number of different sub-volumes, seasons, and years. Residence times from the box model are generally found to be longer than those based on simpler calculations of flushing time. The longer residence times are partly due to reflux, and partly due to incomplete tracer homogenization in sub-volumes. The methods presented here are broadly applicable to other estuaries.

A coastwide bloom of the toxigenic diatom Pseudo‐nitzschia in spring 2015 resulted in the largest recorded outbreak of the neurotoxin, domoic acid, along the North American west coast. Elevated toxins were measured in numerous stranded marine mammals and resulted in geographically extensive and prolonged closures of razor clam, rock crab, and Dungeness crab fisheries. We demonstrate that this outbreak was initiated by anomalously warm ocean conditions. Pseudo‐nitzschia australis thrived north of its typical range in the warm, nutrient‐poor water that spanned the northeast Pacific in early 2015. The seasonal transition to upwelling provided the nutrients necessary for a large‐scale bloom; a series of spring storms delivered the bloom to the coast. Laboratory and field experiments confirming maximum growth rates with elevated temperatures and enhanced toxin production with nutrient enrichment, together with a retrospective analysis of toxic events, demonstrate the potential for similarly devastating ecological and economic disruptions in the future., Key Points The 2015 U.S. West Coast wide toxic Pseudo‐nitzschia australis bloom was facilitated by anomalous ocean conditionsThe seasonal transition to upwelling provided nutrients for the bloom, and spring storms delivered toxic cells to the nearshore environmentWest Coast toxic Pseudo‐nitzschia events are triggered by warm anomalies associated with El Niño and the Pacific Decadal Oscillation

Received 6 April 2011; revised 14 November 2011; accepted 3 January 2012; published 10 March 2012. [1] Simultaneous in situ measurements of waves, currents and turbulence are presented to describe dissipation rates of wave energy and turbulent kinetic energy in the windward coral reef-lagoon system at Lady Elliot Island (LEI), Australia. The dissipation of wave energy in the lagoon is tidally modulated and strongly correlates with frictional dissipation due to the presence of the extremely rough bottom boundary. The observed turbulent kinetic energy (TKE) dissipation rate, ɛ, in this wave-dominated lagoon is much larger than recently reported values for unidirectional flows over natural fringing coral reefs. The correlation between the wave dissipation and ɛ is examined. The average rate of dissipation induced by the rough turbulent flow was estimated directly from the observed ɛ coupled with both a depth-integrated approach and with a bottom boundary layer scaling. Rates of TKE dissipation estimated using the two approaches approximate well, within a factor of 1.5 to 2.4, to the surface-wave energy dissipation rate. The wave dissipation and friction factor in the lagoon can be described by a spectral wave-frictional model with a bottom roughness length scale that is approximately constant across the lagoon. We also present estimates of dissipation induced by the canopy drag force of the coral heads. The dissipation in this case is enhanced and becomes more significant for the total energy dissipation when the water depth in the lagoon is comparable to the height of the coral heads.

[1] Temperature data collected in the shallow, tidally isolated reef flat/lagoon of Lady Elliot Island off Queensland, Australia, show marked variability under solar and tidal forcing. Sea level drops below the height of the protective lagoon rim for a few hours during low tide, effectively isolating the remaining water. Because the lagoon is shallow, its temperature change (from diurnal solar forcing and cooling) is amplified. We develop a simple analytical model to predict the time evolution of mean lagoon temperature, beginning with a well-mixed control volume. This approach highlights the asymmetric flood/ebb physics of tidally isolated lagoons. After discussing the response of this model, we compare it with results from two idealized numerical simulations that illustrate differing aspects of lagoon temperature variability under “potential flow” and “prevailing current” situations. The conceptual model captures the essence of lagoon temperature variability and underscores the importance of solar-lunar phasing. However, because of the well-mixed assumption, it cannot reproduce sudden temperature transitions associated with new incoming water masses. Observations show that a slowly progressing thermal wave inundates the lagoon on rising tides. This wave is similar to our “potential flow” simulation in that it is approximately radially symmetric. On the other hand, it appears to advectively replace resident lagoon water, similar to our “prevailing current” simulations. We attempt to account for this behavior with a simple “frontal” modification to our conceptual model. Results show that this frontal model is able to capture the sudden temperature transitions present in the data and offers improved predictive capabilities over the well-mixed model.

[1] Large rivers represent gateways for the transport of terrigenous and anthropogenic material to the coastal ocean. Here we document a ∼700 km2 recirculation or bulge associated with the Columbia River plume that retains recently discharged river water sufficiently to create a regional bioreactor. Fueled by a fluvial nitrate source, this feature stimulated growth across three trophic levels and may buffer this gateway system during periods of increased warming and stratification that lead to decreased ocean productivity, potentially enhancing production at multiple trophic levels and enriching surface waters far from the river mouth.

[1] River Influences on Shelf Ecosystems (RISE) is the first comprehensive interdisciplinary study of the rates and dynamics governing the mixing of river and coastal waters in an eastern boundary current system, as well as the effects of the resultant plume on phytoplankton standing stocks, growth and grazing rates, and community structure. The RISE Special Volume presents results deduced from four field studies and two different numerical model applications, including an ecosystem model, on the buoyant plume originating from the Columbia River. This introductory paper provides background information on variability during RISE field efforts as well as a synthesis of results, with particular attention to the questions and hypotheses that motivated this research. RISE studies have shown that the maximum mixing of Columbia River and ocean water occurs primarily near plume liftoff inside the estuary and in the near field of the plume. Most plume nitrate originates from upwelled shelf water, and plume phytoplankton species are typically the same as those found in the adjacent coastal ocean. River-supplied nitrate can help maintain the ecosystem during periods of delayed upwelling. The plume inhibits iron limitation, but nitrate limitation is observed in aging plumes. The plume also has significant effects on rates of primary productivity and growth (higher in new plume water) and microzooplankton grazing (lower in the plume near field and north of the river mouth); macrozooplankton concentration (enhanced at plume fronts); offshelf chlorophyll export; as well as the development of a chlorophyll ‘‘shadow zone’’ off northern Oregon.

[1] The northern California Current System is impacted by two primary freshwater sources: the Strait of Juan de Fuca and the Columbia River. The Columbia is frequently bidirectional in summer, with branches both north and south of the river mouth simultaneously. We describe the interaction of these two warm Columbia plumes with each other and with the colder plume originating from the strait. The interactions occurred when a period of strong downwelling-favorable winds and high Columbia River discharge was followed by persistent and strong upwelling-favorable winds. The northward plume that developed under the downwelling winds extended over 200 km along the coast to the Strait of Juan de Fuca and into the strait. The plume subsequently wrapped around Juan de Fuca Strait water in the counterclockwise seasonal eddy just offshore of the strait. Inspection for similar wind and outflow conditions (>0.15 N m−2 and 104 m3 s−1, respectively) suggest that these events might have occurred in roughly half the years since 1994. Surface drifters deployed in the Columbia plume near its origin tracked this plume water northward along the coast, then reversed direction at the onset of upwelling-favorable winds, tracking plume water southward past the river mouth once again. “Recent” (∼1–2 day old) and “Aged” (>14 day old) plume water folded around the newly emerging southwest tending Columbia plume, forming a distinctive “sock” shaped plume. This plume was a mixture of ∼10% “New” (

[1] Observational estimates of entrainment and vertical salt flux into the tidally pulsed Columbia River plume are presented. Drifting buoys deployed in ebbing plume water downstream of the lift-off region are used to make measurements of velocity, salinity, and horizontal divergence in the surface layer. Drifters released near the river mouth, shoreward of the propagating ocean-plume front, catch up to the front, consistent with classical models of plume front circulation. During their offshore transit, drifter streamwise velocities decrease while salinities increase. Assuming drifter-measured quantities are representative of plume-averaged quantities, conservation equations evaluated between adjacent spreading drifters are used to determine the plume depth and entrainment velocity throughout the experiment. This approach provides knowledge of the mixing involved between the active lift-off region and the offshore ocean-plume front as the flow evolves. Because the surface drifters do not downwell at the ocean-plume front, we do not estimate mixing in that region. We find that entrainment and vertical salt flux are largest near the river mouth, as expected, with typical values of O(10−3 m s−1) and O(10−2 practical salinity units (psu) m s−1), respectively, and that these quantities steadily decrease as the drifters move offshore. Profiles of water properties following the drifters provide knowledge of vertical stratification (0.5–4 psu m−1 at the plume base) allowing for discrete estimates of the eddy diffusivity of salt KS. Typical plume values of KS are O(10−3 m2 s−1), similar to estimates made in other plume systems and 2 orders of magnitude larger than open ocean eddy diffusivity estimates.

[1] The lifespan of a barotropic tidal eddy generated by flow around a coastal headland in deep (∼200 m) stratified water is examined. Field observations recorded the evolution of the flood tide eddy from its generation, through the eddy release at the turn of the tide, until its dissipation during subsequent tidal cycles. Ship-based acoustic profiling reveals vortical structure that extends throughout the flow depth. Tracks from subsurface drifters from successive days indicated that flow structure was repeatable. Vorticity decay times, estimated from combined set of drifter tracks, are less than a tidal period. These are significantly shorter than simple estimates using boundary friction would imply, and it is suggested that baroclinic mechanisms associated with tilted vorticity in the deep stratified flow over the sloping headland may play a significant role in the dissipation of vorticity.