Search

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 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]

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.

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]

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]