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Bottom waters of the northeast Pacific continental shelf naturally experience localized hypoxic conditions, with significant influences on food webs and biogeochemical cycling. In August 2021, extreme hypoxia was detected from several measurement platforms along the southern British Columbia continental shelf, with oxygen concentration <60 μmol kg−1, and a difference from the seasonal climatology of more than 2 standard deviations. Early and intense remote upwelling and local density shifts were associated with an anomalously strong spring phytoplankton bloom, which likely stimulated localized respiration of subsurface organic matter. This event was concurrent with unsuitable habitat for Pacific halibut and calcite and aragonite undersaturation throughout most of the water column. The drivers of this extreme low oxygen event could be enhanced under future climate change, with potentially significant impacts on marine ecology and biogeochemistry. Plain Language Summary: Most marine organisms consume oxygen, and are therefore impacted when seawater oxygen concentrations reach low values. Extreme low oxygen concentrations are rare in the coastal waters of British Columbia, Canada. However, unusually strong oxygen depletion was observed off the coast of Vancouver Island during summer 2021. Unusually strong, early season upwelling winds along the California coast impacted Vancouver Island by causing nutrient‐rich water to be mixed into the surface, stimulating a large and earlier than usual spring phytoplankton bloom. Decomposition of the bloom‐derived organic carbon consumed local subsurface oxygen throughout the spring and summer. These subtle changes in timing and intensity of seasonal processes likely caused this low oxygen event, which was also associated with high concentrations of inorganic carbon, leading to ocean acidification. Such extreme low oxygen events, even if short‐lived, can have a significant impact on marine ecosystems, restricting the habitat available for groundfish species, such as Pacific halibut, and impacting the formation of carbonate shells by various organisms. The drivers of extreme low oxygen events are projected to intensify as climate change progresses. Key Points: Widespread extreme hypoxia was observed throughout the water column along the southern British Columbia continental shelf in summer 2021Early and intense upwelling followed by a strong biological response contributed to oxygen depletion in subsurface watersMultiple indices suggest that this extreme event was concurrent with unsuitable habitat conditions for groundfish and calcifying organisms [ABSTRACT FROM AUTHOR]

We present inorganic carbon data from the coastal upwelling region west of Vancouver Island, Canada (∼48.5°N, 126°W) directly after an upwelling event and during summer downwelling in July 1998. The inner-shelf buoyancy current, the outer-shelf and the slope regions are contrasted for both wind regimes (up- and downwelling). Results show strong biological drawdown of the partial pressure of carbon dioxide (pCO2) in response to upwelling over the outer-shelf. In contrast, measured pCO2 is exceptionally high (pCO2>1000 ppm) in the inner-shelf current, where biological uptake of carbon is consistently large. The biological C:N uptake ratio appears to increase when nitrogen becomes limiting (during downwelling), while the POC:PON ratio is relatively constant (slightly lower than the Redfield ratio) suggesting that excess carbon uptake does not go into the POC pool. As expected, large cells dominate where measured primary productivity is greatest. Sub-surface inorganic carbon (and pCO2) is high over the shelf. We suggest that carbon concentrations may be higher in coastal waters because of remineralization associated with high productivity that is confined to a smaller volume of water by bathymetry. At the coast these sub-surface concentrations are more efficiently mixed into the surface (especially during winter) relative to deeper offshore regions. Thus, despite high primary production, coastal waters may not aid in sequestration of atmospheric carbon. [Copyright &y& Elsevier]

Ocean warming and deoxygenation are already modifying the habitats of many aerobic organisms. Benthic habitat in the Northeast Pacific is sensitive to deoxygenation, as low oxygen concentrations occur naturally in continental shelf bottom waters. Here, we examine the potential impacts of deoxygenation and ocean warming on the habitat distribution of Pacific halibut (Hippoglossus stenolepis), one of the most commercially important groundfish in North America. We combine fisheries‐independent Pacific halibut survey data (1998–2020) with oceanographic measurements and a regional ocean circulation model to investigate current and future (end of 21st century) influences of deoxygenation and warming on optimal Pacific halibut habitat. We use the observations and model output to derive a metabolic index of Pacific halibut‐specific suitable habitat. Our results show high Pacific halibut counts in regions where the metabolic index is greatest and demonstrate that interannual variability in Pacific halibut abundance is coherent with the Pacific Decadal Oscillation. Working with model projections, we examine potential future changes in suitable Pacific halibut habitat by the end of the century under a high carbon dioxide emissions scenario. These projections indicate that suitable Pacific halibut habitat may largely disappear off the coast of Washington state, retreating approximately 5° latitude northward. In bottom waters along coastal British Columbia and Alaska continental shelf, Pacific halibut habitat is projected to decrease by about 50%. Such habitat changes may potentially drive a northward shift in Pacific halibut, with significant implications for commercial fisheries. [ABSTRACT FROM AUTHOR]

Abstract: Oceanographic surveys of surface water hydrography, pCO2, biological O2 saturation (ΔO2/Ar) and dimethylsulfide (DMS) were conducted around Vancouver Island, B.C. during late spring of 2007 and 2010. Winter El Niño conditions during early 2010 resulted in strong downwelling and decreased sub-surface nutrient inventories relative to 2007, while reduced Fraser River input, high wind speeds and greater cloud cover led to relatively weak vertical stratification and decreased sea surface irradiance during the 2010 survey. Phytoplankton biomass (Chla) was significantly higher along the west coast of Vancouver Island (WCVI) during late May 2007, and we observed a strong biological imprint on surface gas distributions during this survey, with biologically induced O2 saturation in excess of 40%. Minimum pCO2 along the WCVI was 100ppm during the 2007 survey, and this region served as a moderate CO2 sink at the time of our sampling (mean sea-air flux of -3.2mmolCO2 m−2 d−1). By comparison, both pCO2 and ΔO2/Ar were much closer to atmospheric equilibrium during our 2010 survey. Despite these lower sea-air gradients, high wind speeds led to a significantly larger CO2 sink (13.4mmolm−2 d−1) during the 2010 survey, and a greater uncoupling of ΔO2/Ar and pCO2 through differential gas exchange. Relative to the WCVI, pCO2 and ΔO2/Ar distributions showed smaller differences among cruises along the east coast of Vancouver Island (ECVI), where surface water properties were largely driven by physical circulation. Nonetheless, we did observe lower pCO2 and higher ΔO2/Ar in the Strait of Georgia during the 2010 survey, possibly due to a wind-driven mixing event which may have stimulated local primary productivity. DMS concentrations exhibited large ranges and significant small-scale spatial variability for both cruises, but mean DMS concentrations were more than three-fold higher along the WCVI during late May 2007. Higher wind speeds in late May 2010 led to greater DMS fluxes during our 2010 survey (10 vs. 5μmolm−2 d−1 for 2010 and 2007, respectively) despite lower sea-air concentration gradients. For both cruises, about 40% of the variability in surface water DMS concentrations was explained by Chla/mixed layer depth ratios when data were binned to a spatial resolution of 0.25°. Based on our results, we discuss the potential linkages between regional climate variability and surface gases in coastal B.C. waters. [Copyright &y& Elsevier]

Abstract: Sea-air carbon dioxide (CO2) fluxes have been analyzed from recently-collected winter, summer and autumn surface ocean CO2 partial pressure (pCO2) data spanning a large portion of the western Canadian coastal ocean, and historical underway pCO2 measurements from the southwest Vancouver Island shelf and the Strait of Juan de Fuca. Sea-air CO2 fluxes from the recent data for specific subregions of the coastal ocean, selected based on geography or bathymetry, were used to make seasonal area-specific estimates of CO2 exchange. These show significant differences between subregions, which have important consequences for estimating seasonal area-weighted fluxes on the margin. Climatologies of sea-air CO2 flux were calculated from the historical data using two approaches: One based on fluxes calculated from temporally-averaged values of sea-air pCO2 differences, solubility and gas transfer velocities, and the other from temporally-averaged instantaneous flux estimates. Seasonal flux estimates from our recently-collected data are consistent with the climatological estimates, in that both show stronger outgassing of CO2 in autumn relative to winter, and both reveal straits as important atmospheric CO2 source regions. Taken together, both analyses of recent and historical data suggest that the transition seasons (spring and autumn) contain the largest (positive and negative) fluxes because of the coincidence of high gas transfer velocities and large surface seawater disequilibria with the atmosphere. By combining the results from these analyses, and making some assumptions where data are missing, we estimate moderate net annual sea-air CO2 influx in the western Canadian coastal ocean of −6mmolm−2 d−1. [Copyright &y& Elsevier]