Posts Tagged 'field'

Toward citizen science-based ocean acidification observations using smartphone devices

pH is a key parameter in many chemical, biological, and biogeochemical processes, making it a fundamental aspect of environmental monitoring. Rapid and accurate seawater pH measurements are essential for effective ocean observation and acidification investigations, resulting in the need for novel solutions that allow robust, precise, and affordable pH monitoring. In this study, a versatile smartphone-based environmental analyzer (vSEA) was used for the rapid measurement of seawater pH in a field study. The feasibility of the use of the vSEA algorithm for pH quantification was explored and verified. When used in conjunction with a three-dimensional (3D)-printed light-proof shell, the quality of captured images is guaranteed. The quantitative accuracy of vSEA pH measurements reached 0.018 units with an uncertainty of <0.01, meeting the requirements of the Global Ocean Acidification Observing Network (GOA-ON) for “weather” goals (permitting a maximum pH uncertainty of 0.02). The vSEA–pH system was successfully applied for on-site pH measurements in coastal seawater and coral systems. The performance of the vSEA–pH system was validated using different real-world samples, and t-test results showed that the vSEA–pH system was consistent with pH measurements obtained using a state-of-the-art benchtop spectrophotometer (t = 1.986, p = 0.7949). The vSEA–pH system is applicable to different types of smartphone devices, making it possible for vSEA–pH to be widely promoted for public citizen use. The vSEA–pH system offers a simple, accurate, and applicable method for the on-site measurement of seawater pH, assisting the large-scale monitoring of ocean acidification by allowing the contribution of citizen science-based data collection.

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Investigating the effect of silicate and calcium based ocean alkalinity enhancement on diatom silicification

Gigatonne-scale atmospheric carbon dioxide removal (CDR) will almost certainly be needed to supplement the emission reductions required to keep global warming between 1.5–2 °C. Ocean alkalinity enhancement (OAE) is an emerging marine CDR method with the addition of pulverized minerals to the surface ocean being one widely considered approach. A concern of this approach is the potential for dissolution products released from minerals to impact phytoplankton communities. We conducted an experiment with 10 pelagic mesocosms (M1–M10) in Raunefjorden, Bergen, Norway to assess the implications of simulated silicate- and calcium-based mineral OAE on a coastal plankton community. Five mesocosms (M1, M3, M5, M7 and M9) were enriched with silicate (~75 µmol L-1 Na2SiO3), alkalinity along a gradient from 0 to ~600 µmol kg-1, and magnesium in proportion to alkalinity additions. The other five mesocosms (M2, M4, M6, M8, M10) were enriched with alkalinity along the same gradient and calcium in proportion to alkalinity additions. The experiment explored many components of the plankton community, from microbes to fish larvae, and here we report on the influence of mineral based OAE on diatom silicification. Macronutrients (nitrate and phosphate) limited silicification at the onset of the experiment until nutrient additions on day 26. Silicification was significantly greater in the silicate-based mineral treatments, with silicate concentrations limiting silicification in the calcium-based treatment. The degree of silicification varied significantly between genera, and genera specific silicification also varied significantly between alkalinity mineral sources, with the exception of CylindrothecaPseudo-nitzschia was the only genus affected by alkalinity, whereby silicification increased with increasing alkalinity during some periods of the experiment. No other genera displayed significant changes in silicification as a result of alkalinity increases between 0 and 600 µmol kg-1 above natural levels. Nor did we observe any indication of interactive effects between simulated mineral dissolution products and changes in carbonate chemistry. Previous experiments have provided evidence of alkalinity effects on diatoms underscoring the necessity for further studies under a range of boundary/environmental conditions to extract a more robust pattern of diatom responses to OAE. In summary, our findings suggest limited genus-specific impacts of alkalinity on diatoms, while also highlighting the importance of understanding the full breadth of different OAE approaches, their risks, co-benefits, and potential for interactive effects.

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More than marine heatwaves: a new regime of heat, acidity, and low oxygen compound extreme events in the Gulf of Alaska

Recent marine heatwaves in the Gulf of Alaska have had devastating and lasting impacts on species from various trophic levels. As a result of climate change, total heat exposure in the upper ocean has become longer, more intense, more frequent, and more likely to happen at the same time as other environmental extremes. The combination of multiple environmental extremes can exacerbate the response of sensitive marine organisms. Our hindcast simulation provides the first indication that more than 20 % of the bottom water of the Gulf of Alaska continental shelf was exposed to quadruple heat, positive [H+], negative Ωarag, and negative [O2] compound extreme events during the 2018-2020 marine heat wave. Natural intrusion of deep and acidified water combined with the marine heat wave triggered the first occurrence of these events in 2019. During the 2013-2016 marine heat wave, surface waters were already exposed to widespread marine heat and positive [H+] compound extreme events due to the temperature effect on the [H+]. We introduce a new Gulf of Alaska Downwelling Index (GOADI) with short-term predictive skill, which can serve as indicator of past and near-future positive [H+], negative Ωarag, and negative [O2] compound extreme events on the shelf. Our results suggest that the marine heat waves may have not been the sole environmental stressor that led to the observed ecosystem impacts and warrant a closer look at existing in situ inorganic carbon and other environmental data in combination with biological observations and model output.

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Mississippi river chemistry impacts on the interannual variability of aragonite saturation state in the Northern Gulf of Mexico

In the northern Gulf of Mexico shelf, the Mississippi-Atchafalaya River System (MARS) impacts the carbonate system by delivering freshwater with a distinct seasonal pattern in both total alkalinity (Alk) and dissolved inorganic carbon (DIC), and promoting biologically-driven changes in DIC through nutrient inputs. However, how and to what degree these processes modulate the interannual variability in calcium carbonate solubility have been poorly documented. Here, we use an ocean-biogeochemical model to investigate the impact of MARS’s discharge and chemistry on interannual anomalies of aragonite saturation state (ΩAr). Based on model results, we show that the enhanced mixing of riverine waters with a low buffer capacity (low Alk-to-DIC ratio) during high-discharge winters promotes a significant ΩAr decline over the inner-shelf. We also show that increased nutrient runoff and vertical stratification during high-discharge summers promotes strong negative anomalies in bottom ΩAr, and less intense but significant positive anomalies in surface ΩAr. Therefore, increased MARS discharge promotes an increased frequency of suboptimal ΩAr levels for nearshore coastal calcifying species. Additional sensitivity experiments further show that reductions in the Alk-to-DIC ratio and nitrate concentration from the MARS significantly modify the simulated ΩAr spatial patterns, weakening the positive surface ΩAr anomalies during high-discharge summers or even producing negative surface ΩAr anomalies. Our findings suggest that riverine water carbonate chemistry is a main driver of interannual variability in ΩAr over river dominated ocean margins.

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Influence of seagrass on juvenile Pacific oyster growth in two US west coast estuaries with different environmental gradients

Ocean acidification threatens many marine organisms, including oysters. Seagrass habitat has been suggested as a potential refuge for oysters because it may ameliorate stressful carbonate chemistry and augment food availability. We conducted an in situ study to investigate whether eelgrass Zostera marina habitat affects the growth of juvenile Pacific oysters Crassostrea gigas and influences local carbonate chemistry or food quantity at sites where we expected contrasting conditions in two US west coast estuaries. Juvenile oysters were out-planted in typical intertidal on-bottom (just above sediment) and off-bottom (45 cm above sediment) culture positions and in adjacent eelgrass and unvegetated habitats from June to September 2019. Water quality was measured with sondes for 24 h periods each month, and discrete water samples were collected in conjuncture. Results show that eelgrass habitat did not alter average local carbonate chemistry (pH, pCO2, Ωcalcite), but consistently reduced available food (relative chlorophyll a). Eelgrass habitat had little to no effect on the shell or tissue growth of juvenile oysters but may have influenced their energy allocation; oysters displayed a 16% higher ratio of shell to tissue growth in eelgrass compared to unvegetated habitat when cultured on-bottom. At the seascape scale, average site-level pH was negatively correlated with shell to tissue growth but not with shell growth alone. Overall, these findings suggest that juvenile oysters may display a compensatory response and allocate more energy to shell than tissue growth under stressful conditions like acidic water and/or altered food supply due to reduced immersion or eelgrass presence.

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Seasonality of marine calcifiers in the northern Barents Sea: spatiotemporal distribution of planktonic foraminifers and shelled pteropods and their contribution to carbon dynamics


  • In the northern Barents Sea there is a seasonal pattern of production and size distribution of planktonic foraminifers and pteropods, increasing from winter (March) to summer (July–August) and late autumn (December).
  • In general, pteropods dominate over planktonic foraminifera in the Arctic influenced stations.
  • In the study area, pteropods contribute the most (>80%) to carbon standing stocks and export production.
  • The highest values of carbon standing stocks and export production were found in the seasonal ice zone during all seasons.


The Barents Sea is presently undergoing rapid warming and the sea-ice edge and the productive zones are retreating northward at accelerating rates. Planktonic foraminifers and shelled pteropods are ubiquitous marine calcifiers that play an important role in the carbon budget and being particularly sensitive to ocean biogeochemical changes and ocean acidification. Their distribution at high latitudes have rarely been studied, and usually only for the summer season. Here we present results of their distribution patterns in the upper 300 m in the water column (individuals m−3), protein content and size distribution on a seasonal basis to estimate their inorganic and organic carbon standing stocks (µg m−3) and export production (mg m−2 d−1). The study area constitutes a latitudinal transect in the northern Barents Sea from 76˚ N to 82˚ N including seven stations through both Atlantic, Arctic, and Polar surface water regimes and the marginal and seasonal sea-ice zones. The transect was sampled in 2019 (August and December) and 2021 (March, May, and July). The highest carbon standing stocks and export production were found at the Polar seasonally sea-ice covered shelf stations with the contribution from shelled pteropods being significantly higher than planktonic foraminifers during all seasons. We recorded the highest production of foraminifers and pteropods in summer (August 2019 and July 2021) and autumn (December 2019) followed by spring (May 2021), and the lowest in winter (March 2021).

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Spatial distribution, source apportionment, and assessment of marine water quality parameters in the Bohai Sea, China


  • Terrestrial inputs are the main sources of organic matter and nutrients.
  • Port activities and offshore oilfield exploration cause petroleum pollution.
  • Seawater in the Bohai Sea did not exhibit acidification.
  • Phosphorus -limiting conditions are present in the Bohai Sea.


A two–year (2020−2021) survey dataset of six water quality parameters (pH, dissolved oxygen (DO), chemical oxygen demand (COD), dissolved inorganic nitrogen (DIN), soluble reactive phosphate (SRP), and petroleum pollutants) was used to investigate their spatial distribution in the Bohai Sea and quantify their potential sources. There were significant differences in spatial distribution of the parameters. High concentrations of COD, DIN and SRP were found in three bays, with terrestrial input being the main pollution source. Phosphorus–limiting conditions were present in the Bohai Sea. High petroleum pollutant concentrations were identified in port areas, offshore oilfields, and adjacent areas. The pH was above the global oceanic average and there were no signs of acidification. The contribution of the mixed terrestrial inputs, maritime transportation, and offshore oil exploitation sources, oceanic and associated biotic sources, and seawater–atmosphere exchange and atmospheric deposition sources to water quality were 63.4 %, 8.0 %, and 28.6 %, respectively.

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Carbonate Chemistry and the Potential for Acidification in Georgia Coastal Marshes and the South Atlantic Bight, USA

In coastal regions and marginal bodies of water, the increase in partial pressure of carbon dioxide (pCO2) in many instances is greater than that of the open ocean due to terrestrial (river, estuarine, and wetland) influences, decreasing buffering capacity and/or increasing water temperatures. Coastal oceans receive freshwater from rivers and groundwater as well as terrestrial-derived organic matter, both of which have a direct influence on coastal carbonate chemistry. The objective of this research is to determine if coastal marshes in Georgia, USA, may be “hot-spots” for acidification due to enhanced inorganic carbon sources and if there is terrestrial influence on offshore acidification in the South Atlantic Bight (SAB). The results of this study show that dissolved inorganic carbon (DIC) and total alkalinity (TA) are elevated in the marshes compared to predictions from conservative mixing of the freshwater and oceanic end-members, with accompanying pH around 7.2 to 7.6 within the marshes and aragonite saturation states (ΩAr) <1. In the marshes, there is a strong relationship between the terrestrial/estuarine-derived organic and inorganic carbon and acidification. Comparisons of pH, TA, and DIC to terrestrial organic material markers, however, show that there is little influence of terrestrial-derived organic matter on shelf acidification during this period in 2014. In addition, ΩAr increases rapidly offshore, especially in drier months (July). River stream flow during 2014 was anomalously low compared to climatological means; therefore, offshore influences from terrestrial carbon could also be decreased. The SAB shelf may not be strongly influenced by terrestrial inputs to acidification during drier than normal periods; conversely, shelf waters that are well-buffered against acidification may not play a significant role in mitigating acidification within the Georgia marshes.

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A decade of marine inorganic carbon chemistry observations in the northern Gulf of Alaska – insights to an environment in transition

As elsewhere in the global ocean, the Gulf of Alaska is experiencing the rapid onset of ocean acidification (OA) driven by oceanic absorption of anthropogenic emissions of carbon dioxide from the atmosphere. In support of OA research and monitoring, we present here a data product of marine inorganic carbon chemistry parameters measured from seawater samples taken during biannual cruises between 2008 and 2017 in the northern Gulf of Alaska. Samples were collected each May and September over the 10–year period using a conductivity, temperature, depth (CTD) profiler coupled with a Niskin bottle rosette at stations including a long–term hydrographic survey transect known as the Gulf of Alaska (GAK) Line. This dataset includes discrete seawater measurements such as dissolved inorganic carbon and total alkalinity, which allows the calculation of other marine carbon parameters, including carbonate mineral saturation states, carbon dioxide (CO2), and pH. Cumulative daily Bakun upwelling indices illustrate the pattern of downwelling in the northern Gulf of Alaska, with a period of relaxation spanning between the May and September cruises. The observed time and space variability impart challenges for disentangling the OA signal despite this dataset spanning a decade. However, this data product greatly enhances our understanding of seasonal and interannual variability on the marine inorganic carbon system parameters. The product can also aid in the ground truthing of biogeochemical models, refining estimates of sea–air CO2 exchange, and determining appropriate CO2 parameter ranges for experiments targeting potentially vulnerable species. Data are available at (Monacci et al., 2023).

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The benthic-pelagic coupling affects the surface water carbonate system above groundwater-charged coastal sediments

Submarine groundwater discharge (SGD) can be a significant source of dissolved nutrients, inorganic and organic carbon, and trace metals in the ocean and therefore can be a driver for the benthic-pelagic coupling. However, the influence of hypoxic or anoxic SGD on the carbonate system of coastal seawater is still poorly understood. In the present study, the production of dissolved inorganic carbon (DIC) and alkalinity (AT) in coastal sediments has been investigated under the impact of oxygen-deficient SGD and was estimated based on the offset between the measured data and the conservative mixing of the end members. Production of AT and DIC was primarily caused by denitrification and sulphate reduction. The AT and DIC concentrations in SGD decreased by approximately 32% and 37% mainly due to mixing with seawater counterbalanced by reoxidation and CO2 release into the atmosphere. Total SGD-AT and SGD-DIC fluxes ranged from 0.1 to 0.2mol m-2 d-1 and from 0.2 to 0.3mol m-2 d-1, respectively. These fluxes are probably the reason why the seawater in the Bay of Puck is enriched in AT and DIC compared to the open waters of the Baltic Sea. Additionally, SGD had low pH and was undersaturated with respect to the forms of the aragonite and calcite minerals of CaCO3. The seawater of the Bay of Puck also turned out to be undersaturated in summer (Inner Bay) and fall (Outer Bay). We hypoth​e​size that SGD can potentially contribute to ocean acidification and affect the functioning of the calcifying invertebrates.

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The estuarine environment and pH variation: natural limits and experimental observation of the acidification effect on phosphorus bioavailability (in Portuguese)

This study shows the variation of pH in the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC). Data from 3 years (2019, 2021, 2022) were obtained in 17 points presenting the following ranges: temperature (14.88-27.05 ºC), pH (7.16-8.40) and DIP (0.20-11.28 µmol L-1) along a saline gradient (0.05-32.09) under different hydrodynamics, biogeochemical processes and anthropogenic influence. The pH buffering capacity due to the presence of weak acid salts in saline water (S ≥ 30) was associated to the lowest DIP, decreasing with low salinity values, confirming the direct correlation among salinity and pH. The highest temperatures in the winter of 2021, corroborated with the abnormal climate event in that year. An in vitro experiment showed results of the interaction of PID and sediments with different textures, with and without the presence of the benthic microbiota under a considerable decreasing of the pH (acidification) in relation to the natural condition of this environment. The P sediment flux characterized Iguape sector as a P sink with or without biota, Ararapira sector as a P source with biota and Cananéia, as P source without biota. The salt water buffered the pH and sediment buffered DIP both associated to the biogeochemical and hydrodynamic processes contribute to the homeostasis in the system.

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Prolonged deep-ocean carbonate chemistry recovery after the Paleocene-Eocene Thermal Maximum


  • N. truempyi B/Ca can be used to reconstruct the Early Cenozoic deep-water Ω.
  • PETM deep-water Ω recovery is slower than suggested by sedimentary %CaCO3.
  • PETM Ω recovery implies sustained carbon injection into the ocean-atmosphere system.


The Paleocene-Eocene Thermal Maximum (PETM) is a hyperthermal event at ∼56 Ma ago, caused by rapid and massive carbon releases into the ocean-atmosphere system. Currently, the PETM ocean acidification is mainly quantified in the surface ocean. By contrast, PETM carbonate chemistry changes of the deep ocean, a larger carbon reservoir, are largely qualitatively constrained by sedimentary calcium carbonate contents (%CaCO3). Here, we revisit a previously proposed method for quantifying Early Cenozoic deep-water carbonate chemistry, using boron to calcium ratios (B/Ca) in extinct benthic foraminifera Nuttallides truempyi (Brown et al., 2011). We show that calibrating core-top B/Ca in the extant relative of N. truempyi against deep-water calcite saturation degree (Ω, Ω = [CO32−] /[CO32−]saturated), rather than calcite saturation state (Δ[CO32−], Δ[CO32−] = [CO32−] – [CO32−]saturated) as originally proposed better reflects Early Cenozoic carbonate chemistry changes. Furthermore, we provide multiple deep-water Ω reconstructions paired with benthic foraminiferal carbon isotopes during the PETM. At two sites, deep-water Ω recovered synchronously with carbon isotopes but lagged the sedimentary %CaCO3 rebound, indicating a slower post-PETM deep-water Ω recovery than previously thought. This may imply that during the PETM recovery phase, carbon could have been injected into the ocean-atmosphere system, despite net carbon loss, over a prolonged period after the initial release. If so, during this period, carbon removal from the ocean via calcite burial on the seafloor in response to enhanced silicate weathering may be weakened, suggesting that more carbon was sequestered via other processes such as those related to organic carbon burial.

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Anthropogenic carbon estimation in the surface ocean from atmospheric CO2 fugacity at the BATS (Bermuda Atlantic time-series study) station

In surface seawater, it is usually very difficult to quantify anthropogenic carbon concentrations. Many processes (such as air-sea exchanges of gases and heat, biological activity, and mixing of water masses), are at play and often on different timescales. Thus, various hypotheses are used to estimate the anthropogenic concentrations in surface waters. Here, using the relatively long (1980s to present) time series data sets from the Bermuda Atlantic Time-series Study site (BATS; 31°40′N, 64°10′W) in the North Atlantic Ocean, we evaluate results based upon two different hypotheses. The results clearly confirm that it is very difficult to assess anthropogenic carbon concentrations in surface waters from sole oceanic properties. However, this study further indicates that at this ocean site, they can be appropriately determined from low-frequency variations of atmospheric CO2 concentrations. Consequently, the impact of anthropogenic carbon penetration in surface waters on their acidification could be predicted.

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Microbial communities inhabiting shallow hydrothermal vents as sentinels of acidification processes

Introduction: Shallow hydrothermal vents are considered natural laboratories to study the effects of acidification on biota, due to the consistent CO2 emissions with a consequent decrease in the local pH.

Methods: Here the microbial communities of water and sediment samples from Levante Bay (Vulcano Island) with different pH and redox conditions were explored by Next Generation Sequencing techniques. The taxonomic structure was elucidated and compared with previous studies from the same area in the last decades.

Results and discussion: The results revealed substantial shifts in the taxonomic structure of both bacterial and archaeal communities, with special relevance in the sediment samples, where the effects of external parameters probably act for a long time. The study demonstrates that microbial communities could be used as indicators of acidification processes, by shaping the entire biogeochemical balance of the ecosystem in response to stress factors. The study contributes to understanding how much these communities can tell us about future changes in marine ecosystems.

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Anthropogenic acidification of surface waters drives decreased biogenic calcification in the Mediterranean Sea

Anthropogenic carbon dioxide emissions directly or indirectly drive ocean acidification, warming and enhanced stratification. The combined effects of these processes on marine planktic calcifiers at decadal to centennial timescales are poorly understood. Here, we analyze size normalized planktic foraminiferal shell weight, shell geochemistry, and supporting proxies from 3 sediment cores in the Mediterranean Sea spanning several centuries. Our results allow us to investigate the response of surface-dwelling planktic foraminifera to increases in atmospheric carbon dioxide. We find that increased anthropogenic carbon dioxide levels led to basin wide reductions in size normalized weights by modulating foraminiferal calcification. Carbon (δ13C) and boron (δ11B) isotopic compositions also indicate the increasing influence of fossil fuel derived carbon dioxide and decreasing pH, respectively. Alkenone concentrations and test accumulation rates indicate that warming and changes in biological productivity are insufficient to offset acidification effects. We suggest that further increases in atmospheric carbon dioxide will drive ongoing reductions in marine biogenic calcification in the Mediterranean Sea.

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Assessing drivers of estuarine pH: a comparative analysis of the continental U.S.A.’s two largest estuaries

In estuaries, local processes such as changing material loads from the watershed and complex circulation create dynamic environments with respect to ecosystem metabolism and carbonate chemistry that can strongly modulate impacts of global atmospheric CO2 increases on estuarine pH. Long-term (> 20 yr) surface water pH records from the USA’s two largest estuaries, Chesapeake Bay (CB) and Neuse River Estuary-Pamlico Sound (NRE-PS) were examined to understand the relative importance of atmospheric forcing vs. local processes in controlling pH. At the estuaries’ heads, pH increases in CB and decreases in NRE-PS were driven primarily by changing ratios of river alkalinity to dissolved inorganic carbon concentrations. In upper reaches of CB and middle reaches of the NRE-PS, pH increases were associated with increases in phytoplankton biomass. There was no significant pH change in the lower NRE-PS and only the polyhaline CB showed a pH decline consistent with ocean acidification. In both estuaries, interannual pH variability showed robust, positive correlations with chlorophyll a (Chl a) during the spring in mid to lower estuarine regions indicative of strong control by net phytoplankton production. During summer and fall, Chl a and pH negatively correlated in lower regions of both estuaries, given a shift toward heterotrophy driven by changes in phytoplankton community structure and increases in the load ratio of dissolved inorganic nitrogen to organic carbon. Tropical cyclones episodically depressed pH due to vertical mixing of CO2 rich bottom waters and post-storm terrestrial organic matter loading. Local processes we highlight represent a significant challenge for predicting future estuarine pH.

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Spatiotemporal variability of pH in coastal waters of New Brunswick (Canada) and potential consequences for oyster aquaculture

There is a void in the knowledge of the acidification status of Eastern Canada’s coastal waters. This knowledge is crucial to evaluating the threats posed to marine life, particularly oyster farming, a flagship of New Brunswick seafood production. In this study, we measured the temporal variability of pH and related environmental parameters in three bays of Northeastern New Brunswick. We also evaluated the potential impact of the observed pH levels on the Eastern oyster (Crassostrea virginica Gmelin, 1791), based on the available literature on this species’ sensitivity to acidification. We investigated the presence of inherent cycles of pH with the Fourier transform and the spectral filtering technique. Our results show that pH is highly variable in the studied area, with values ranging from 7.31 to 8.90. A seasonal effect was apparent, as the pH fluctuations were set at the lowest level in winter when the cover of ice and snow on the bay was present. The spectral analysis revealed a clear semidiurnal tidal pattern of pH, this variable being inversely related to the water level in summer and directly related to it in winter. The spectral subtraction of all the tidal components allowed the detection of a circadian rhythm that was not in pace with the alternation between day and night but rather slowly drifted so that the pH troughs occurred at night during the full moon period. Short periodicities of circa 8 and 6 h also existed in two of the three bays. Based on current knowledge of C. virginica’s sensitivity to acidification, this species’ recruitment, growth, and survival are unlikely to be impacted by the present pH levels in the studied area. However, further acidification might overcome the resilience of C. virginica, especially that of the larvae that are produced during the winter in commercial hatcheries.

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Variability and controls of the ocean acidification metrics pH and pCO2 in a large embayment of an Eastern Boundary Upwelling System (EBUS)


  • Deoxygenation and acidification extrema observed in St Helena Bay.
  • Mean surface pCO2 385 μatm indicative of system serving as a CO2 sink.
  • PCO2 shown to be a function of both Chl a and PAR through water column.
  • Winter mixing causes seasonal reversal of the air-sea pCO2 gradient.
  • Mean surface pCO2 also elevated above atmospheric levels in nearshore.


An assessment was undertaken of the spatial and temporal variability of pCO2 and pH in St Helena Bay, a highly productive, wide-open bay located in the Benguela, a major eastern boundary upwelling system (EBUS). Mechanisms controlling their patterns of variability and their linkage to the distribution of oxygen are explored. The mean surface pCO2 was 385 μatm, below the mean atmospheric concentration of 410 μatm, indicative of a system serving as a CO2 sink. The corresponding mean pH of bay surface waters was 8.3. The greatest variation from these means was driven by deep winter mixing causing a seasonal reversal of the air-sea pCO2 gradient. Mean surface pCO2 was also elevated above mean atmospheric levels in the nearshore (<15 m depth), a likely consequence of higher microbial respiration in the upper water column due to regular resuspension of detrital material. The nearshore of the bay is also sometimes subject to high biomass dinoflagellate blooms referred to as red tides, and their decay leads to exceptional pCO2 concentrations. Discharge from the Berg River and the associated degradation of terrestrially derived organic matter also contributes to higher pCO2 in the nearshore particularly during winter when rainfall is highest. Through the water column the important role of photosynthesis in determining the vertical distribution of pCO2 is evident in that pCO2 is shown to be a function of both Chl a and PAR. In St Helena Bay nearly 50% of water column biomass is located below the community compensation depth (i.e. where respiration carbon loss exceeds gross community production) leading to rapidly declining O2 and increasing pCO2 concentrations with depth. Resulting conditions of bottom water hypoxia/anoxia are therefore accompanied by more corrosive waters (pH declining to ∼7.4) and conditions of severe hypercapnia (pCO2 exceeding 2000 μatm) subjecting marine life to multiple stressors. St Helena Bay and similar bays in EBUS are likely to provide extrema in the deoxygenation and acidification of coastal waters.

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Physiological responses of scallops and mussels to environmental variability: implications for future shellfish aquaculture


  • High acclimatization capability in mussels and scallops
  • Growth rates, δ13C, δ15N, and shell strength differed between seasons and depths.
  • Mussels and scallops had higher growth rates at 5 m than 30 m.
  • Shell strength changed with depth in mussels but not in the scallops.
  • Differences in nutritional sources between depths are higher in winter than spring.


Puget Sound (Washington, USA) is a large estuary, known for its profitable shellfish aquaculture industry. However, in the past decade, scientists have observed strong acidification, hypoxia, and temperature anomalies in Puget Sound. These co-occurring environmental stressors are a threat to marine ecosystems and shellfish aquaculture. Our research assesses how environmental variability in Puget Sound impacts two ecologically and economically important bivalves, the purple-hinge rock scallop (Crassodoma gigantea) and Mediterranean mussel (Mytilus galloprovincialis). Our study examines the effect of depth and seasonality on the physiology of these two important bivalves to gain insight into ideal grow-out conditions in an aquaculture setting, improving the yield and quality of this sustainable protein source. To do this, we used Hood Canal (located in Puget Sound) as a natural multiple-stressor laboratory, which allowed us to study acclimatization capacity of shellfish in their natural habitat and provide the aquaculture industry information about differences in growth rate, shell strength, and nutritional sources across depths and seasons. Bivalves were outplanted at two depths (5 and 30 m) and collected after 3.5 and 7.5 months. To maximize mussel and scallop growth potential in an aquaculture setting, our results suggest outplanting at 5 m depth, with more favorable oxygen and pH levels. Mussel shell integrity can be improved by placing out at 5 m, regardless of season, however, there were no notable differences in shell strength between depths in scallops. For both species, δ13C values were lowest at 5 m in the winter and δ15N was highest at 30 m regardless of season. Puget Sound’s combination of naturally and anthropogenically acidified conditions is already proving to be a challenge for shellfish farmers. Our study provides crucial information to farmers to optimize aquaculture grow-out as we begin to navigate the impacts of climate change.

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From individual to ecosystem: multi-stressor effects of acidification and warming on the physiological responses of coastal marine invertebrates

Climate change is directly impacting the services humans derive from the sea at an accelerated rate. Ocean warming and acidification (i.e., a decrease in ocean pH) are leading to modifications in population sizes and ecosystem functioning. The observed shifts in these higher order processes are a direct result of individuals’ responses (i.e., physiology, including metabolism, growth, calcification, and survival) occurring within communities. Natural variation in past environmental exposure experienced by individuals may lead to greater population resilience, or it may push individuals past physiological thresholds leading to increased sensitivity and vulnerability to climate change. Thus, we need to determine how individual-level physiological responses to climate change scale up to influence marine ecosystems. Rocky intertidal habitats are an ideal study system for evaluating the relationships between individual physiological responses, ecosystem functioning, and climate change. Tide pools possess unique thermal and pH environments and can be monitored under natural conditions or manipulated with field-experiments over daily and seasonal time scales, creating natural “experimental mesocosms”. In addition, many species within rocky intertidal habitats are exposed to environmental conditions close to their tolerance limits, increasing their potential vulnerability to climate change. In Chapter 1, by utilizing the unique thermal environments of tide pools, I showed that across small spatial scales (pools), thermal history influences thermal sensitivity of marine invertebrates for short-term time intervals (1-week and 1-day) and that this relationship differs seasonally and between species with differing traits, including mobility. This suggests that variability in thermal responses among individuals may allow for a natural buffer at a population level in response to climate change. Multiple stressors may affect individuals independently or interactively, amplifying or mitigating effects. Thus, to determine the impacts of climate change, in Chapter 2, I used a 6-month long field manipulation of ocean warming and acidification in tide pools. I examined the combined effects of warming and acidification on the shell structure (shell thickness and corrosion) and functional properties (shell strength) of the ecologically critical species, the Pacific blue mussel (Mytilus trossulus). Acidification led to thinner, weaker, and more corroded shells whereas combined warming and acidification resulted in an increase in shell strength. My results suggest that to some degree, warming may mitigate the negative impacts of acidification on this mollusk species. Lastly, in Chapter 3, I characterize how warming and acidification, individually and interactively, impact net ecosystem calcification and the individual and population-level mechanisms driving impacts on net ecosystem calcification. Net ecosystem calcification tended to increase during the day and decrease at night; however, addition of CO2 during the hottest months led to decreased net ecosystem calcification and increased dissolution during both day and night. I found that individual mussel metabolic rates increased significantly in the presence of elevated CO2 and increased daily maximum of pool temperatures. Through this individual-level pathway, pH and temperature had a strong impact on the metabolic rates of individuals ultimately resulting in changes in net ecosystem calcification. On the other hand, greater mussel abundance was associated with increased net ecosystem calcification. Yet, with the addition of CO2, calcification decreased even in pools with the highest abundance of mussels, indicating that there are other pathways by which changes in pH can drive alterations in net ecosystem calcification. My dissertation reveals how species’ traits and natural thermal variation from short-term to seasonal time scales influence metabolic sensitivity to future warming among individuals (Ch. 1), independent climate stressors can negatively impact shellfish in situ, whereas the combined interactive effects between multiple stressors can lead to mitigation of the negative impacts of a single stressor alone (Ch. 2), and that ecosystem-level consequences of climate change are mediated by the abundance of dominant calcifiers and that this effect is dependent on the magnitude of acidification and warming (Ch. 3).

Continue reading ‘From individual to ecosystem: multi-stressor effects of acidification and warming on the physiological responses of coastal marine invertebrates’

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