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Ocean Acidification (OA) creates corrosive conditions that impact organisms that produce calcium carbonate shells, such as clams and oysters. The Salish Sea, a body of water where much of British Columbia's shellfish farming sector operates, has been growing more corrosive. We present a case study of reporting on OA and the shellfish farming sector in British Columbia, Canada. We convey results from a survey with shellfish farmers and a thematic analysis that sought to understand how the science and local implications of OA were presented in a sample of media articles. All articles employed narratives of crisis, and slightly over 75% conveyed scientific uncertainty. Just over 55% incorporated interviews with one or more of scientists, shellfish sector representatives, and shellfish farmers. Survey findings reveal that respondents saw OA as a threat but often deprioritized it relative to a wider range of operational challenges. We introduce "situatedness" and draw in ideas from "solutions journalism" to expand. While telling stories about people and places is important, we conclude that new opportunities for locally salient climate change reporting stand to be unlocked by looking beyond boundaries typically drawn around "the local" and the sorts of credentials typically ascribed to "environmental experts". [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) reduces seawater pH and calcium carbonate saturation states (Ω), which can have detrimental effects on calcifying organisms such as shellfish. Nearshore areas, where shellfish aquaculture typically operates, have limited data available to characterize variability in key ocean acidification parameters pH and Ω , as samples are costly to analyze and difficult to collect. This study collected samples from four nearshore locations at shellfish aquaculture sites on the Canadian Pacific coast from 2015–2018 and analyzed them for dissolved inorganic carbon (DIC) and total alkalinity (TA), enabling the calculation of pH and Ω for all seasons. The study evaluated the diel and seasonal variability in carbonate chemistry conditions at each location and estimated the contribution of drivers to seasonal and diel changes in pH and Ω. Nearshore locations experience a greater range of variability and seasonal and daily changes in pH and Ω than open waters. Biological uptake of DIC by phytoplankton is the major driver of seasonal and diel changes in pH and Ω at our nearshore sites. The study found that freshwater is not a key driver of diel variability, despite large changes over the day in some locations. We find that during summer at mid-depth (5–20 m), where it is cooler, pH, Ω , and oxygen conditions are still favourable for shellfish. These results suggest that if shellfish are hung lower in the water column, they may avoid high sea surface temperatures, without inducing OA and oxygen stress. [ABSTRACT FROM AUTHOR]

The global ocean takes up nearly a quarter of anthropogenic CO 2 emissions annually, but the variability in this uptake at regional scales remains poorly understood. Here we use a neural network approach to interpolate sparse observations, creating a monthly gridded seawater partial pressure of CO 2 (p CO 2) data product from January 1998 to December 2019, at 1/12 ∘ × 1/12 ∘ spatial resolution, in the northeast Pacific open ocean, a net sink region. The data product (ANN-NEP; NCEI Accession 0277836) was created from p CO 2 observations within the 2021 version of the Surface Ocean CO 2 Atlas (SOCAT) and a range of predictor variables acting as proxies for processes affecting p CO 2 to create nonlinear relationships to interpolate observations at a spatial resolution 4 times greater than leading global products and with better overall performance. In moving to a higher resolution, we show that the internal division of training data is the most important parameter for reducing overfitting. Using our p CO 2 product, wind speed, and atmospheric CO 2 , we evaluate air–sea CO 2 flux variability. On sub-decadal to decadal timescales, we find that the upwelling strength of the subpolar Alaskan Gyre, driven by large-scale atmospheric forcing, acts as the primary control on air–sea CO 2 flux variability (r2=0.93 , p<0.01). In the northern part of our study region, divergence from atmospheric CO 2 is enhanced by increased local wind stress curl, enhancing upwelling and entrainment of naturally CO 2 -rich subsurface waters, leading to decade-long intervals of strong winter outgassing. During recent Pacific marine heat waves from 2013 on, we find enhanced atmospheric CO 2 uptake (by as much as 45 %) due to limited wintertime entrainment. Our product estimates long-term surface ocean p CO 2 increase at a rate below the atmospheric trend (1.4 ± 0.1 µ atm yr -1) with the slowest increase in the center of the subpolar gyre where there is strong interaction with subsurface waters. This mismatch suggests the northeast Pacific Ocean sink for atmospheric CO 2 may be increasing. [ABSTRACT FROM AUTHOR]

Ocean acidification reduces seawater pH and calcium carbonate saturation states (Ω), which can have detrimental effects on calcifying organisms such as shellfish. Nearshore areas, where shellfish aquaculture typically operates, have limited data available to characterize variability in key ocean acidification parameters pH and Ω, as samples are costly to analyse and difficult to collect. This study collected samples from four nearshore locations at shellfish aquaculture sites on the Canadian Pacific coast from 2015–2018 and analysed them for dissolved inorganic carbon (DIC) and total alkalinity (TA), enabling the calculation of pH and Ω for all seasons. The study evaluated the diel and seasonal variability in carbonate chemistry conditions at each location and estimated the contribution of drivers to seasonal and diel changes in pH and Ω. Nearshore locations experience a greater range of variability and seasonal and daily changes in pH and Ω than open waters. Biological uptake of DIC by phytoplankton is the major driver of seasonal and diel changes in pH and Ω at our nearshore sites. The study found that freshwater is not a key driver of diel variability, despite large changes over the day in some locations. Shellfish mortality events coincide with highly favourable pH and Ω conditions during summer and are most likely linked to high surface temperatures and disease rather than ocean acidification. To reduce shellfish mortality, shellfish could be hung lower in the water column (5–20 m) to avoid high temperatures and disease, while still experiencing favourable pH and Ω conditions for shellfish. [ABSTRACT FROM AUTHOR]

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]

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]

The balance between ocean mixing and stratification influences primary productivity through light limitation and nutrient supply in the euphotic ocean. Here, we apply a hierarchical clustering algorithm (Ward's method) to four factors relating to stratification (wind energy, freshwater index, water-column-averaged vertical eddy diffusivity, and halocline depth), as well as to depth-integrated phytoplankton biomass, extracted from a biophysical ocean model of the Salish Sea. Running the clustering algorithm on 4 years of model output, we identify distinct regions of the model domain that exhibit contrasting wind and freshwater input dynamics, as well as regions of varying water-column-averaged vertical eddy diffusivity and halocline depth regimes. The spatial regionalizations in physical variables are similar in all 4 analyzed years. We also find distinct interannually consistent biological zones. In the northern Strait of Georgia and Juan de Fuca Strait, a deeper winter halocline and episodic summer mixing coincide with higher summer diatom abundance, while in the Fraser River stratified central Strait of Georgia, shallower haloclines and stronger summer stratification coincide with summer flagellate abundance. Cluster-based model results and evaluation suggest that the Juan de Fuca Strait supports more biomass than previously thought. Our approach elucidates probable physical mechanisms controlling phytoplankton abundance and composition. It also demonstrates a simple, powerful technique for finding structure in large datasets and determining boundaries of biophysical provinces. [ABSTRACT FROM AUTHOR]

Estuarine systems host a rich diversity of marine life that is vulnerable to changes in ocean chemistry due to addition of anthropogenic carbon. However, the detection and impact of secular carbon trends in these systems is complicated by heightened natural variability as compared to open‐ocean regimes. We investigate biogeochemical changes between the pre‐industrial (PI) and modern periods using a high‐resolution, three‐dimensional, biophysical model of the Salish Sea, a representative Northeast Pacific coastal system. While the seasonal amplitude of the air‐sea difference in pCO2 has increased on average since pre‐industrial times, the net CO2 source has changed little. Our simulations show that inorganic carbon has increased throughout the model domain by 29–39 mmol m−3 (28–38 µmol kg−1) from the pre‐industrial to present. While this increase is modest in a global context, the region's naturally high inorganic carbon content and the low buffering capacity of the local carbonate system amplify the resultant effects. Notably, this increased carbon drives the estuary toward system‐wide undersaturation of aragonite, negatively impacting shell‐forming organisms. Undersaturation events were rare during the pre‐industrial experiment, with 10%–25% of the domain undersaturated by volume throughout the year, while under present‐day conditions, the majority (55%–75%) of the system experiences corrosive, undersaturated conditions year‐round. These results are extended using recent global coastal observations to show that estuaries throughout the Pacific Rim have already undergone a similar saturation state regime shift. Plain Language Summary: The coastal ocean hosts rich ecosystems which are critical to marine organisms and people and sensitive to human‐caused climate change. We used a detailed computer simulation to understand the carbon cycle in a complex, productive North Pacific coastal system that is fed by a large un‐dammed river, has connecting fjords, and narrows that have strong tides. We determine how much extra carbon has entered the system since the beginning of the industrial revolution. This increase is important because extra carbon in the ocean makes it harder for animals to build shells and structures. We find that large chemical changes have occurred. In fact, we are surprised to find that an important threshold under which shells dissolve has already been crossed in most of the region. We consider observations from other global coastal oceans and find that this same threshold may have been crossed throughout coastal oceans in much of the Pacific, and that this shift will likely become prominent in the Atlantic Ocean by 2080. Key Points: On average, dissolved inorganic carbon has increased by 29–39 mmol m−3 in the Salish Sea, causing a shift to majority aragonite undersaturation by volumeModern aragonite saturation conditions, though variable, are typically outside of the range of pre‐industrial values throughout the domainMuch of the coastal Pacific Rim has similar carbonate chemistry conditions, and comparable shifts in aragonite saturation may have occurred [ABSTRACT FROM AUTHOR]

The different mechanisms is reviewed and formulate equations describing changes in particle size distributions throughout the water column as a result of particle sinking, coagulation, disaggregation, and bacterial and zooplankton consumption. The model developed can be used to predict vertical and temporal changes in particle size spectra in a one-dimensional system, given surface forcing and a prescribed zooplankton community and microbial activity.

We measured the carbonate system (between 2015 and 2018) in an isolated and a well‐connected temperate estuary, both known for shellfish growth. We evaluated end‐member model estimates of inorganic carbon, alkalinity, pH, mineral saturation states (Ωa), and pH sensitivity (βDIC). We find winter conditions are estimated within observational uncertainty. Spring‐summer primary productivity elevates observed pH and Ωa above theoretical lines, beyond uncertainty. Both estuaries are sensitive in winter and likely to experience rapid pH changes with increased inorganic carbon inputs. Summer pH sensitivity is reduced by productivity and is least sensitive in the midsalinity region. We estimate carbon increased by up to 49 μmol kg−1, since the pre‐industrial period resulting in significant decreases in pH (0.2) and Ωa (0.5). The largest pH decrease occurred outside the minimum buffer zone, at higher salinities where carbon increase was greatest. The largest pH decrease occurred in winter, but the largest Ωa decrease occured in summer. Plain Language Summary: The ocean has absorbed about a third of human carbon dioxide emissions, increasing its acidity. Increasing acidity negatively affects marine organisms such as shellfish and fish that build calcium carbonate structures because they must spend more energy building and maintaining these structures. Most farmed and wild shellfish live in estuarine environments where acidification has not been widely studied. We made complete carbon system measurements over several years and across all seasons, in two distinct estuaries with significant aquaculture, where no previous carbon data existed. We estimated key acidification parameters and evaluated our ability to predict these parameters using only salinity, once properties in the freshest and saltiest water in the systems were well defined in all seasons. Our simple "mixing model" estimates winter conditions well, but during summer, phytoplankton blooms take up carbon and make conditions more favorable than predicted. We found that both estuaries are sensitive to future increases in carbon and are likely to experience rapid changes in chemistry. We estimate that human activity has already caused significant increases in inorganic carbon and associated acidification. The largest change critical to shell‐building organisms has occurred during the summer, and at higher salinities that are typical of grow sites. Key Points: End‐member mixing estimates winter pH and mineral saturation states in temperate estuaries within measurement uncertaintySeasonal productivity keeps pH and mineral saturation states above theoretical mixing curves by up to ∼1 pH and ∼2.5 Ωa, respectivelySince the preindustrial period nearshore estuarine pH declined by 0.05–0.2 with largest decline outside the minimum buffer zone [ABSTRACT FROM AUTHOR]

The balance between ocean mixing and stratification influences primary productivity through light limitation and nutrient supply in the euphotic ocean. Here, we apply a hierarchical clustering algorithm (Ward's method) to four factors relating to stratification and depth-integrated phytoplankton biomass extracted from a biophysical regional ocean model of the Salish Sea to assess spatial co-occurrence. Running the clustering algorithm on four years of model output, we identify distinct regions of the model domain that exhibit contrasting wind and freshwater input dynamics, as well as regions of varying watercolumn-averaged vertical eddy diffusivity and halocline depth regimes. The spatial regionalizations in physical variables are similar in all four analyzed years. We also find distinct interannually consistent biological zones. In the Northern Strait of Georgia and Juan de Fuca Strait, a deeper winter halocline and episodic summer mixing coincide with higher summer diatom abundance, while in the Fraser River stratified Central Strait of Georgia, shallower haloclines and stronger summer stratification coincide with summer flagellate abundance. Cluster based model results and evaluation suggest that the Juan de Fuca Strait supports more biomass than previously thought. Our approach elucidates probable physical mechanisms controlling phytoplankton abundance and composition. It also demonstrates a simple, powerful technique for finding structure in large datasets and determining boundaries of biophysical provinces. [ABSTRACT FROM AUTHOR]

The ocean absorbs anthropogenic carbon, slowing atmospheric CO2 increase but driving ocean acidification. Long‐term changes in the carbon system are typically assessed from single‐point time series or from hydrographic sections spaced by decades. Using higher resolution observations (1–3 year−1) from the Line P time series, we investigate processes modulating trends in the carbon system of the northeast subarctic Pacific. Dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) from 1990 to 2019 reveal substantial trends over most of the upper water column along the 1,500 km coastal to open ocean transect. At the surface, an increasing trend in salinity‐normalized DIC (sDIC33) (+0.5 ± 0.4 μmol kg−1 yr−1) is associated with a decrease in pH (0.01–0.02 decade−1) and a decrease in aragonite saturation state (0.04–0.08 decade−1). These observed trends are driven by anthropogenic CO2 uptake, partially offset by trends in surface salinity or temperature. Stratification associated with recent marine heat waves appears to have caused anomalously low surface pCO2. sDIC33 trends of similar magnitude were found below the seasonal thermocline on the 26.7–26.8 isopycnals (150–300 m), which are ventilated in the western Pacific. Roughly, a third (20%–50%) of the subsurface sDIC33 trend is driven by increased remineralization, likely caused by long‐term decreases in ventilation in the western Pacific. Bidecadal oscillations in the ventilation of the 26.7–26.8 isopycnals arising from the Lunar Nodal Cycle cause oscillations in sDIC33 and AOU at the offshore end of our transect. We trace the oscillations to alternating periods of higher anthropogenic carbon uptake or higher carbon remineralization. Plain Language Summary: The ocean takes up anthropogenic carbon and slows the rate at which atmospheric carbon dioxide is increasing. Using 30 years of data from the NE Pacific, we show that the surface ocean is indeed absorbing anthropogenic carbon and undergoing ocean acidification in this region. We find that carbon is also increasing in the subsurface waters. This excess carbon was absorbed in the western Pacific, where dense waters sink from the surface to the subsurface and transport anthropogenic carbon and oxygen eastward. This western Pacific breathing process appears to be weakening in time. If this trend continues, less anthropogenic carbon will be taken up and stored in subsurface waters in the future. Despite this reduction, some carbon will still naturally accumulate as the available oxygen is consumed and natural carbon dioxide is produced. Using data from three decades, we demonstrate the impact of climatic events and natural variability on the carbon system. At the surface, recent marine heat waves have reduced the amount of carbon absorbed by the ocean. In the subsurface waters, we observed that anthropogenic carbon increased in decades with stronger ventilation, while natural carbon generated by respiration of organic matter increased during periods of weaker ventilation. Key Points: Local uptake of anthropogenic CO2 decreases surface pH in the NE Pacific but the trend appears modulated by recent temporal variabilityDeclining ventilation in the NW Pacific appears responsible for 20%–50% of the inorganic carbon increase in NE Pacific intermediate waterThe signature of tidally driven bidecadal oscillations propagates east to Line P producing fluctuations in intermediate water preformed DIC [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is causing our oceans to lose oxygen and become more acidic at an unprecedented rate, threatening marine ecosystems and their associated animals. In deep‐sea environments, where conditions have typically changed over geological timescales, the associated animals, adapted to these stable conditions, are expected to be highly vulnerable to any change or direct human impact. Our study coalesces one of the longest deep‐sea observational oceanographic time series, reaching back to the 1960s, with a modern visual survey that characterizes almost two vertical kilometers of benthic seamount ecosystems. Based on our new and rigorous analysis of the Line P oceanographic monitoring data, the upper 3,000 m of the Northeast Pacific (NEP) has lost 15% of its oxygen in the last 60 years. Over that time, the oxygen minimum zone (OMZ), ranging between approximately 480 and 1,700 m, has expanded at a rate of 3.0 ± 0.7 m/year (due to deepening at the bottom). Additionally, carbonate saturation horizons above the OMZ have been shoaling at a rate of 1–2 m/year since the 1980s. Based on our visual surveys of four NEP seamounts, these deep‐sea features support ecologically important taxa typified by long life spans, slow growth rates, and limited mobility, including habitat‐forming cold water corals and sponges, echinoderms, and fish. By examining the changing conditions within the narrow realized bathymetric niches for a subset of vulnerable populations, we resolve chemical trends that are rapid in comparison to the life span of the taxa and detrimental to their survival. If these trends continue as they have over the last three to six decades, they threaten to diminish regional seamount ecosystem diversity and cause local extinctions. This study highlights the importance of mitigating direct human impacts as species continue to suffer environmental changes beyond our immediate control. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: A three‐dimensional coupled physical‐biological model has been developed that simulates currents, nutrients, and phytoplankton in the Salish Sea. Comparisons with observations show that the model successfully represents key aspects of the nitrogen cycle in the Strait of Georgia, including the seasonal cycle and regional differences. The model is used to investigate mechanisms through which tidal currents lead to nutrient supply to the surface layer, where phytoplankton have enough light to grow, in the northern Strait of Georgia. Strong tidal flow through the narrow Discovery Passage leads to turbulence that mixes deep nutrients to the surface. Tidal currents then advect the surface nutrient plume further into the Strait of Georgia. Additional mixing and vertical motion also occur downstream, increasing the amount of nutrients supplied to the surface. Key Points: A physical‐biological model of the Salish Sea represents spring blooming and seasonal and spatial patterns in nutrients and chlorophyllA tidal jet drives mixing and transport, producing a surface nitrate plume, fueling significant summertime primary productionA wave associated with the jet propagates southward along the Vancouver Island coast and makes a smaller contribution to mixing and transport of nitrate [ABSTRACT FROM AUTHOR]

Wastewater disposal often has deleterious impacts on the receiving environment. Low dissolved oxygen levels are particularly concerning. Here, we investigate the impacts on dissolved oxygen and carbon chemistry of screened municipal wastewater in the marine waters off Victoria, Canada. We analyzed data from undersea moorings, ship-based monitoring, and remotely-operated vehicle video. We used these observations to construct a two-layer model of the nearfield receiving environment. Despite the lack of advanced treatment, dissolved oxygen levels near the outfalls were well above a 62 μmol kg −1 hypoxic threshold. Furthermore, the impact on water column oxygen at the outfall is likely <2 μmol kg −1 . Dissolved inorganic carbon is not elevated and pH not depressed compared to the surrounding region. Strong tidal currents and cold, well-ventilated waters give Victoria's marine environment a high assimilative capacity for organic waste. However, declining oxygen levels offshore put water near the outfall at risk of future hypoxia. [ABSTRACT FROM AUTHOR]

Under physically isolated conditions, net community production (NCP) can be accurately estimated from the rate of oxygen evasion to the atmosphere derived from local mixed layer oxygen/argon measurements. We use a simple box model to demonstrate that, when physical inputs are negligible, the sea‐to‐air flux of biological oxygen (bioflux) represents the average NCP exponentially weighted over the past several residence times of oxygen in the mixed layer. This new weighting scheme shows that there is no apparent lag between bioflux and exponentially weighted time‐averaged NCP. Furthermore, a strict steady state assumption is unnecessary to this relationship. However, this widely used O2/Ar method is not effective in dynamic coastal zones where low oxygen water upwells to the surface. Yet these zones are highly productive and their episodic productivity needs to be quantified. We use a quasi‐2‐D version of the Regional Ocean Modeling System, including oxygen and argon as prognostic variables, to explore the application of this method and the relationship between NCP and bioflux in a coastal upwelling system. We show that bioflux is an accurate measure of NCP over large regions of time and space. Bioflux is most biased near the shore following upwelling favorable winds, where bioflux is sometimes negative (flux from the atmosphere to the ocean) and even positive bioflux values can severely underestimate NCP. Assessing a range of model variables that are easily observed in the field, we show that sea surface temperature is the most effective at identifying bioflux measurements that are likely to be biased. [ABSTRACT FROM AUTHOR]

Ocean acidification threatens to reduce pH and aragonite saturation state (ΩA) in estuaries, potentially damaging their ecosystems. However, the impact of highly variable river total alkalinity (TA) and dissolved inorganic carbon (DIC) on pH and ΩA in these estuaries is unknown. We assess the sensitivity of estuarine surface pH and ΩA to river TA and DIC using a coupled biogeochemical model of the Strait of Georgia on the Canadian Pacific coast and place the results in the context of global rivers. The productive Strait of Georgia estuary has a large, seasonally variable freshwater input from the glacially fed, undammed Fraser River. Analyzing TA observations from this river plume and pH from the river mouth, we find that the Fraser is moderately alkaline (TA 500-1000μmolkg-1) but relatively DIC-rich. Model results show that estuarine pH and ΩA are sensitive to freshwater DIC and TA, but do not vary in synchrony except at high DIC:TA. The asynchrony occurs because increased freshwater TA is associated with increased DIC, which contributes to an increased estuarine DIC:TA and reduces pH, while the resulting higher carbonate ion concentration causes an increase in estuarine ΩA. When freshwater DIC:TA increases (beyond ~1.1), the shifting chemistry causes a paucity of the carbonate ion that overwhelms the simple dilution/enhancement effect. At this high DIC:TA ratio, estuarine sensitivity to river chemistry increases overall. Furthermore, this increased sensitivity extends to reduced flow regimes that are expected in future. Modulating these negative impacts is the seasonal productivity in the estuary which draws down DIC and reduces the sensitivity of estuarine pH to increasing DIC during the summer season. [ABSTRACT FROM AUTHOR]

Ocean acidification threatens to reduce pH and aragonite saturation state (ΩA) in estuaries, potentially damaging their ecosystems. However, the impact of highly variable river total alkalinity (TA) and dissolved inorganic carbon (DIC) on pH and ΩA in these estuaries is unknown. We assess the sensitivity of estuarine surface pH and ΩA to river chemistry using a 1-dimensional, biogeochemical-coupled model of the Strait of Georgia on the Canadian Pacific coast and generalize the results in the context of global rivers. The productive Strait of Georgia estuary has a large, seasonally variable freshwater input from the glacially fed, undammed Fraser River. Analyzing TA and pH observations from this river and its estuary, we find that the Fraser is moderately alkaline (TA 500-1350 μmol kg-1) but relatively DIC-rich, especially during winter (low flow). Model results show that estuarine pH and ΩA, while sensitive to freshwater DIC and TA, do not vary in synchrony. Instead, rivers with high DIC and TA produce lower estuarine pH due to an increased estuarine DIC : TA ratio, but higher estuarine ΩA because of DIC contributions to the carbonate ion. This estuarine pH sensitivity decreases with increasing mean river TA, but the zone of maximum pH sensitivity also moves to higher salinity which could impact a larger areal extent of the estuary. Many temperate rivers, such as the Fraser, are expected to experience weaker freshets and stronger winter flows under climate change, reducing the extent of the river plume and the impact of river chemistry in much of the estuary. However, increasing carbon in rivers will move the highest sensitivity zone to higher salinities that cover larger areas under present-day flow regimes. [ABSTRACT FROM AUTHOR]

As the oceans absorb anthropogenic CO2 they become more acidic, a problem termed ocean acidification (OA). Since this increase in CO2 is occurring rapidly, OA may have profound implications for marine ecosystems. In the temperate northeast Pacific, fisheries play key economic and cultural roles and provide significant employment, especially in rural areas. In British Columbia (BC), sport (recreational) fishing generates more income than commercial fishing (including the expanding aquaculture industry). Salmon (fished recreationally and farmed) and Pacific Halibut are responsible for the majority of fishery-related income. This region naturally has relatively acidic (low pH) waters due to ocean circulation, and so may be particularly vulnerable to OA. We have analyzed available data to provide a current description of the marine ecosystem, focusing on vertical distributions of commercially harvested groups in BC in the context of local carbon and pH conditions. We then evaluated the potential impact of OA on this temperate marine system using currently available studies. Our results highlight significant knowledge gaps. Above trophic levels 2–3 (where most local fishery-income is generated), little is known about the direct impact of OA, and more importantly about the combined impact of multi-stressors, like temperature, that are also changing as our climate changes. There is evidence that OA may have indirect negative impacts on finfish through changes at lower trophic levels and in habitats. In particular, OA may lead to increased fish-killing algal blooms that can affect the lucrative salmon aquaculture industry. On the other hand, some species of locally farmed shellfish have been well-studied and exhibit significant negative direct impacts associated with OA, especially at the larval stage. We summarize the direct and indirect impacts of OA on all groups of marine organisms in this region and provide conclusions, ordered by immediacy and certainty. [ABSTRACT FROM AUTHOR]

The distribution of dissolved (<0.4 μm) iron (Fe) across the continental shelf and slope of Queen Charlotte Sound on the west coast of Canada was examined to estimate the potential of these waters as a source of Fe to the Fe-limited waters of the subarctic northeast Pacific. Iron profiles obtained in shelf, slope, and offshore waters demonstrate decreasing concentrations of Fe with distance from the continent. Within 50 m of the shelf sediments dissolved Fe concentrations were 5.3 ± 0.3 nM. This signal was detected, although attenuated by 80%, along the isopycnal surface at offshore stations 40-50 km seaward of the shelf break, strongly suggesting cross-shelf transport of an Fe-rich plume originating in low dissolved oxygen (<3 ml L-1, <130 μmol kg-1) waters in subsurface water over the continental shelf. Several physical mechanisms that may cause these Fe-enriched waters to advect offshore in this region (i.e., tidal currents and Ekman transport in the bottom boundary layer, coastal downwelling/relaxation from upwelling, and the formation of anticyclonic, westward-propagating, coastal eddies) are discussed. We suggest that strong tidal currents over broad continental shelves may play a key role in Fe supply to ocean basins. [ABSTRACT FROM AUTHOR]

The influence of the coastal ocean on global net annual air-sea CO2 fluxes remains uncertain. However, it is well known that air-sea pCO2 disequilibria can be large (ocean pCO2 ranging from ∼400 µatm above atmospheric saturation to ∼250 µatm below) in eastern boundary currents, and it has been hypothesized that these regions may be an appreciable net carbon sink. In addition it has been shown that the high productivity in these regions (responsible for the exceptionally low surface pCO2) can cause nutrients and inorganic carbon to become more concentrated in the lower layer of the water column over the shelf relative to adjacent open ocean waters of the same density. This paper explores the potential role of the winter season in determining the net annual CO2 flux in temperate zone eastern boundary currents, using the results from a box model. The model is parameterized and forced to represent the northernmost part of the upwelling region on the North American Pacific coast. Model results are compared to the few summer data that exist in that region. The model is also used to determine the effect that upwelling and downwelling strength have on the net annual CO2 flux. Results show that downwelling may play an important role in limiting the amount of CO2 outgassing that occurs during winter. Finally data from three distinct regions on the Pacific coast are compared to highlight the importance of upwelling and downwelling strength in determining carbon fluxes in eastern boundary currents and to suggest that other features, such as shelf width, are likely to be important. [ABSTRACT FROM AUTHOR]

The mixed layer depth (MLD) at Ocean Station Papa (OSP) in the northeast Pacific Ocean has been shoaling for the past 50 years, with the shallowest maximum MLDs ever recorded occurring in the winters of 2002-03 and 2003-04. We use the General Ocean Turbulence Model (GOTM) to estimate the MLD and to determine how various atmospheric forcings from 2001-05 at four stations in the northeast Pacific affect the MLD. Three of the stations are in the Alaskan Gyre: OSP (50°N, 145°W) in the south; S16 (49°17'N, 134°40'W) at the southeastern edge; CAG (55°N, 145°W) in the centre; and one, NSG (40°N, 145°W), is south of the Alaskan Gyre. Interpolated Argo temperature and salinity, for both initial conditions and restoring, and atmospheric inputs (heat fluxes and wind stress) from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis were used. Experiments showed that in the winter, the MLD was most sensitive to increased winds at all stations and also to decreased heat fluxes everywhere except at OSP. In summer, MLD was most sensitive to changes in the shortwave radiation. A combination of effects from the 2002-03 El Niño (i.e., decreased outgoing heat fluxes, cloud cover and wind speeds) and a strong stratification created by a subsurface cold water anomaly caused the MLD to be shallow in the Gulf of Alaska during the winter of 2002-03. Finally, our results show that for the modelled period (2001-05), the MLD at OSP behaved differently than at other stations in the Gulf of Alaska and therefore OSP may not be the best location to represent the region.[Traduit par la rédaction] L'épaisseur de la couche de mélange (ECM) à la station océanique Papa (OSP) dans le nord-est de l'océan Pacifique s'est amincie au cours des 50 dernières années, les ECM maximales les plus faibles à avoir été observées s'étant produites au cours des hivers 2002-2003 et 2003-2004. Nous utilisons le modèle général de turbulence océanique (MGTO) pour estimer l'ECM et pour déterminer comment divers forçages atmosphériques entre 2001 et 2005 à quatre stations dans le nord-est du Pacifique influencent la couche de mélange. Trois de ces stations sont situées dans la gyre de l'Alaska : OSP (50°N, 145°O) au sud; S16 (49°17'N, 134°40'O) près du bord sud-est; CAG (55°N, 145°O) au centre; et une, NSG (40°N, 145°O), est au sud de la gyre de l'Alaska. Nous avons utilisé les données Argo interpolées de température et salinité, à la fois pour les conditions initiales et la restauration, et les apports atmosphériques (flux de chaleur et tension du vent) de la réanalyse de NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research). Des expériences ont montré qu'au cours de l'hiver, l'ECM était très sensible aux vents plus forts à toutes les stations et aussi aux flux de chaleur plus faibles partout sauf à OSP. En été, l'ECM était très sensible aux variations du rayonnement de courtes longueurs d'onde. Une combinaison d'effets du El Niño (c.-à-d. les flux de chaleur sortant, la couverture nuageuse et les vitesses de vent plus faibles) et une forte stratification créée par une anomalie d'eau froide subsuperficielle ont eu pour conséquence une faible ECM dans le golfe de l'Alaska durant l'hiver 2002-2003. Finalement, nos résultats montrent qu'au cours de la période modélisée (2001-2005), l'ECM s'est comportée différemment à OSP qu'aux autres stations dans le golfe d'Alaska, et par conséquent OSP n'est peut-être pas le meilleur endroit pour représenter la région. [ABSTRACT FROM AUTHOR]

We present continuous, high-resolution measurements of surface dimethylsulfide (DMS), pCO2, and O2/Ar obtained in coastal waters off British Columbia, Canada, using membrane inlet mass spectrometry (MIMS). Sampled underway at a frequency of twice per minute (every ~160 m at 10 knots cruising speed), our data reveal fine-scale structure in gas variability and its covariance with a number of hydrographic parameters. All parameters exhibited large ranges (pCO2, 200-747 ppm; DMS, <1-29 nM; chl a, <0.1-33 µg L-1), highlighting the dynamic nature of the study area. A strong anticorrelation between pCO2 and O2/Ar was observed across the survey region, with the distributions of these gases influenced by biology and its interplay with physical processes. In contrast, DMS levels, which varied dramatically over short distances, showed no significant correlations with any single variable for the full, high-resolution data set. However, when measurements were binned to a much coarser spatial resolution, we found a linear relationship between surface DMS and the chlorophyll/mixed layer depth ratio. The slope of this relationship differed significantly from that previously derived from open ocean data. We used several statistical techniques to estimate the spatial variability of gases and hydrographic parameters and the inherent sampling errors associated with low-frequency sampling approaches. These analyses emphasize the importance of high-resolution sampling in coastal areas, particularly for DMS. [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]