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.

[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.

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Momentum balances in the near-field region of a large, tidally pulsed river plume are examined. The authors concentrate on a single ebb tide of the Columbia River plume, using the Regional Ocean Modeling System (ROMS) configured to hindcast flow conditions on the Washington and Oregon shelves and in the Columbia River estuary. During ebb, plume-interior streamwise balances are largely between advection, pressure gradient, and frictional forces. Stream-normal balances in this region reduce to centrifugal, crossstream pressure gradient, and Coriolis terms (i.e., the ''gradient wind'' balance commonly assumed in river plume bulge investigations). Temporal derivatives are most important at the plume front and as the ebb progresses. Winds were light and contributed little to the force balance. Midebb stress and vertical salt flux were largest at a midplume depth, where stratification and vertical shear were also high, consistent with shearinduced mixing. Internal stress slows the spreading plume considerably. A kinematic description of the spreading process relates lateral spreading to the momentum dynamics and illustrates that plume spreading is largely a competition between the cross-stream pressure gradient and Coriolis forces. However, the very nearfield dome of buoyant water is instrumental in setting initial flow pathways.

[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.