Posts Tagged 'field'

The potential of kelp Saccharina japonica in shielding Pacific oyster Crassostrea gigas from elevated seawater pCO2 stress

Ocean acidification (OA) caused by elevated atmospheric CO2 concentration is predicted to have negative impacts on marine bivalves in aquaculture. However, to date, most of our knowledge is derived from short-term laboratory-based experiments, which are difficult to scale to real-world production. Therefore, field experiments, such as this study, are critical for improving ecological relevance. Due to the ability of seaweed to absorb dissolved carbon dioxide from the surrounding seawater through photosynthesis, seaweed has gained theoretical attention as a potential partner of bivalves in integrated aquaculture to help mitigate the adverse effects of OA. Consequently, this study investigates the impact of elevated pCO2 on the physiological responses of the Pacific oyster Crassostrea gigas in the presence and absence of kelp (Saccharina japonica) using in situ mesocosms. For 30 days, mesocosms were exposed to six treatments, consisting of two pCO2 treatments (500 and 900 μatm) combined with three biotic treatments (oyster alone, kelp alone, and integrated kelp and oyster aquaculture). Results showed that the clearance rate (CR) and scope for growth (SfG) of C. gigas were significantly reduced by elevated pCO2, whereas respiration rates (MO2) and ammonium excretion rates (ER) were significantly increased. However, food absorption efficiency (AE) was not significantly affected by elevated pCO2. The presence of S. japonica changed the daytime pHNBS of experimental units by ~0.16 units in the elevated pCO2 treatment. As a consequence, CR and SfG significantly increased and MO2 and ER decreased compared to C. gigas exposed to elevated pCO2 without S. japonica. These findings indicate that the presence of S. japonica in integrated aquaculture may help shield C. gigas from the negative effects of elevated seawater pCO2.

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Understanding the impacts of environment and parasitism on Eastern oyster (Crassostrea virginica) vulnerability to ocean acidification

The global process of ocean acidification caused by the absorption of increased atmospheric carbon dioxide decreases the concentration of carbonate ions and reduces the associated seawater saturation state (ΩCaCO3) – making it more energetically costly for marine calcifying organisms to build their shells or skeletons. Bivalves are particularly vulnerable to the adverse effects of ocean acidification on calcification, and they inhabit estuaries and coastal zones – regions most susceptible to ocean acidification. However, the response of an individual to elevated pCO2 can depend on the carbonate chemistry dynamics of its current environment and the environment of its parents. Additionally, an organism’s response to ocean acidification can depend on its ability to control the chemistry at the site of calcification. Biotic and abiotic stressors can modify bivalves’ control of calcifying fluid chemistry – known as extrapallial fluid (EPF). Understanding the responses of bivalves – which are foundation species – to ocean acidification is essential for predicting the impacts of oceanic change on marine communities. This dissertation uses a culturally, ecologically, and economically important bivalve in the northwest Atlantic – the Eastern oyster (Crassostrea virginica) – to explore the effects of environment and species interactions on responses to elevated pCO2.

Chapter 2 describes a field study that characterized diurnal and seasonal carbonate chemistry dynamics of two estuaries in the Gulf of Maine that support Eastern oyster populations. The estuaries were monitored at high temporal resolution (half-hourly) over four years (2018-2021) using pH and conductivity loggers. Measured pH, salinity, and temperature were used to calculate carbonate chemistry parameters. Both estuaries exhibited strong seasonal and diurnal fluctuations in carbonate chemistry. They also experienced pCO2 values that greatly exceeded current atmospheric carbon dioxide levels and those projected for the year 2100.

Chapter 3 describes a laboratory experiment that examined the capacity of intergenerational exposure to mitigate the adverse effects of ocean acidification on larval growth, shell morphology, and survival. Adult oysters were cultured in control or elevated pCO2 conditions for 30 days then crossed using a North Carolina II cross design. Larvae were grown for three days under control and elevated pCO2 conditions. Intergenerational exposure to elevated pCO2 conditions benefited early larval growth and shell morphology, but not survival. However, parental exposure was insufficient to completely counteract the adverse effects of the elevated pCO2 treatment on shell formation and survival.

Chapter 4 describes a laboratory experiment that examined the interplay between ocean acidification and parasite-host dynamics. Eastern oysters infested and not infested with bioeroding sponge (Cliona sp.) were cultured under three pCO2 conditions (539, 1040, 3294 ppm) and two temperatures (23, 27˚C) for 70 days to assess oyster control of EPF chemistry, growth, and survival. Bioeroding sponge infestation and elevated pCO2 reduced oyster net calcification and EPF pH but did not affect condition or survival. Infested oyster EPF pH was consistently lower than seawater pH, while EPF dissolved inorganic carbon was consistently elevated relative to seawater. These findings suggested that infested oysters effectively precipitated repair shell to prevent seawater intrusion into extrapallial fluid through bore holes across all treatments.

Chapter 5 characterizes the concentration of a suite of 56 elements normalized to calcium in EPF and shell of Crassostrea virginica grown under three pCO2 conditions (570, 990, 2912 ppm) and sampled at four timepoints (days 2, 9, 79, 101) to assess effects of pCO2 on organismal control of EPF and shell elemental composition and EPF-to-shell elemental partitioning. Elevated pCO2 significantly influenced the relative abundance of elements in the EPF (29) and shell (13) and altered EPF-to-shell elemental partitioning for 45 elements. Importantly, elevated pCO2 significantly influenced the concentration of several elements in C. virginica shell that are used in other biogenic carbonates as paleo-proxies for other environmental parameters. This result suggests that elevated pCO2 could influence the accuracy of paleo reconstructions.

Overall, this dissertation provides insights that can help improve our understanding of past, present, and future ocean environments. Understanding current local carbonate chemistry dynamics and the capacity for C. virginica to acclimate intergenerationally to elevated pCO2 can inform site and stock selection for aquaculture and restoration efforts. Studying parasite-host environment interactions provides critical insights into the potential for parasitism to alter responses to future ocean acidification. Finally, exploring the impact of elevated pCO2 on elemental composition of EPF and shell allowed us to understand better biomineralization processes, identify potential proxies for seawater pCO2 in bivalves, and offer insights that could help improve the accuracy of paleo reconstructions.

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Influence of climate on seawater quality and green mussel production

This study aimed to investigate the relationships between atmospheric parameters, seawater quality and green mussel production which were cultured in pond, estuary and coastal areas. Seawater and mussel samples were collected from mussel farms in the inner Gulf of Thailand from January to December 2019. Climate data were obtained from the Thai Meteorological Department. The correlations between selected atmospheric and seawater parameters were developed using linear and non-linear models. The influence of seawater quality on mussel production was evaluated using principal component analysis and stepwise multiple linear regression. The effects of atmospheric variation on green mussel productivity were simulated. The results showed that high air temperature and rainfall caused an increase in seawater temperature and a decrease in salinity, respectively. It was observed that the most influential factors affecting mussel production were nutrients and dissolved oxygen in ponds, temperature and salinity in estuaries, and nutrients and pH in coastal areas. The simulation indicated that mussel production can deteriorate when air temperature reaches 34°C and rainfall is higher than 200 mm per month. Our results suggest that under climate change events, locations with less riverine influence can provide higher mussel productivity. These results can be used as a guideline for farmers during a climate change event.

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Seasonal quantification of carbonate dissolution and CO2 emission dynamics in the Indian Sundarbans estuaries

Shifts in carbonate dissolution can help understand the exchange of carbon dioxide between the air and water of estuarine systems. Adequate spatial coverage is required to understand these emission dynamics. Hence, the distribution of carbonate parameters in three estuaries covering a vast expanse of the Indian Sundarbans is described from total alkalinity (TA), dissolved inorganic carbon (DIC) and pH data collected between 2016 and 2020. The seasonal impacts on inorganic carbon parameters were also studied by comparing pre-monsoon, monsoon, and post-monsoon data compiled from the study period. The estuaries showed the highest TA (up to 2506μmol kg −1) and DIC (up to 2203μmol kg −1) in the pre-monsoon. Both the parameters overall were positively associated with salinity. TA and DIC decreased by 369 and 208μmol kg −1, respectively, in the monsoon compared to pre-monsoon. From the monsoon to the post-monsoon, TA and DIC increased by 121 and 85μmol kg −1, respectively. Both showed strong positive associations with high chlorophyll- a and high dissolved oxygen in the post-monsoon suggesting an important role of primary production in the estuaries in raising the concentrations of inorganic carbon parameters. The carbonate mineral saturation states (ΩCa and ΩAr) followed the same pattern as that of TA and DIC. The pair was always supersaturated although freshwater influence caused the values to drop to close to saturation. While pCO2 was mostly supersaturated in the system relative to atmospheric concentration, it became minimal in the post-monsoon corresponding to heightened primary production. Despite high organic carbon recycling in mangroves, the system showed less expression in terms of CO2 emission in a seasonal cycle. Overall, the Indian Sundarbans estuarine system emitted low amounts of CO2 with its estimated water-to-air flux densities varying from 0.40 ± 0.61 (pre-monsoon) to 1.62 ± 1.74 mmol m−2h−1(monsoon).

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Author correction: contrasting drivers and trends of ocean acidification in the subarctic Atlantic

The Original Article was published on 07 July 2021

Correction to: Scientific Reports, published online 07 July 2021

The original version of this Article contained errors.

In Table 2 legend, the symbol of “picomol” was incorrectly given as “nanomol”.

“Average trends obtained with the seasonally detrended data the in situ temperature (T in °C yr−1), salinity (S in yr−1), Total Alkalinity (TA in µmol kg−1 yr−1), salinity-normalized alkalinity (nTA in µmol kg−1 yr−1), total dissolved inorganic carbon (DIC in µmol kg−1 yr−1), salinity-normalized dissolved inorganic carbon (nDIC in µmol kg−1 yr−1), in situ pH in total scale (pHT yr−1), total hydrogen ion concentrations ([H+]T in nanomol kg−1 yr−1), ion carbonate concentration excess over aragonite saturation (exCO3 = in µmol kg−1 yr−1), and anthropogenic CO2.”

now reads:

“Average trends obtained with the seasonally detrended data the in situ temperature (T in °C yr−1), salinity (S in yr−1), Total Alkalinity (TA in µmol kg−1 yr−1), salinity-normalized alkalinity (nTA in µmol kg−1 yr−1), total dissolved inorganic carbon (DIC in µmol kg−1 yr−1), salinity-normalized dissolved inorganic carbon (nDIC in µmol kg−1 yr−1), in situ pH in total scale (pHT yr−1), total hydrogen ion concentrations ([H+]T in picomol kg−1 yr−1), ion carbonate concentration excess over aragonite saturation (exCO3 = in µmol kg−1 yr−1), and anthropogenic CO2.”

Additionally, the article contains a repeated error where the symbol for “pmol” was incorrectly given as “nmol” in the Results section, under the subheading ‘Acidifcation drivers’, in Figure 6 legend, and in the Conclusions.

Furthermore, in Figure 6A and Supplementary Figure S5A “pmol” was incorrectly given as “nmol” in the y-axis. The original Figure 6 and accompanying legend, and Supplementary Information file appear below.

Acidification trends and drivers decomposition (T,S, nDIC and nTA) for the seasonally detrended average time series of total hydrogen ions concentration in pmol/kg/yr (Δ[H+]TA) and for excess of [CO3= ] over the [CO3= ] at aragonite saturation in µmol/kg/yr (Δex[CO3=]B). The nDIC driver trends is split in natural (nCnat) and anthropogenic components (nCanth). The colour code is shown on both panels.

The original Article and accompanying Supplementary Information file have been corrected.

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Ichnodiversity in the eastern Canadian Arctic in the context of polar microbioerosion patterns

Studies of marine microbioerosion in polar environments are scarce. They include our recent investigations of bioerosion traces preserved in sessile balanid skeletons from the Arctic Svalbard archipelago and the Antarctic Ross Sea. Here, we present results from a third study site, Frobisher Bay, in the eastern Canadian Arctic, together with a synthesis of our current knowledge of polar bioerosion in both hemispheres. Barnacles from 62 to 94 m water depth in Frobisher Bay were prepared using the cast-embedding technique to enable visualization of microboring traces by scanning electron microscopy. In total, six ichnotaxa of traces produced by organotrophic bioeroders were found. All recorded ichnotaxa were also present in Mosselbukta, Svalbard, and most in the Ross Sea. Frobisher Bay contrasts with Mosselbukta in that it is a siliciclastic-dominated environment and shows a lower ichnodiversity, which may be accounted for by the limited bathymetrical range and a high turbidity and sedimentation rate. We evaluate potential key ichnotaxa for the cold-temperate and polar regions, of which the most suitable are Flagrichnus baiulus and Saccomorpha guttulata, and propose adapted index ichnocoenoses for the interpretation of palaeobathymetry accordingly. Together, the three studies allow us to make provisional considerations about the biogeographical distribution of polar microbioerosion traces reflecting the ecophysiological limits of their makers.

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The diel and seasonal heterogeneity of carbonate chemistry and dissolved oxygen in three types of macroalgal habitats

As concerns about ocean acidification continue to grow, the importance of macroalgal communities in buffering coastal seawater biogeochemistry through their metabolisms is gaining more attention. However, studies on diel and seasonal fluctuations in seawater chemistry within these communities are still rare. Here, we characterized the spatial and temporal heterogeneity in diel and seasonal dynamics of seawater carbonate chemistry and dissolved oxygen (DO) in three types of macroalgal habitats (UAM: ulvoid algal mat dominated, TAM: turf algal mat dominated, and SC: Sargassum horneri and coralline algae dominated). Our results show that diel fluctuations in carbonate parameters and DO varied significantly among habitat types and seasons due to differences in their biological metabolisms (photosynthesis and calcification) and each site’s hydrological characteristics. Specifically, carbonate parameters were most affected by biological metabolisms at the SC site, and by environmental variables at the UAM site. Also, we demonstrate that macroalgal communities reduced ocean acidification conditions when ocean temperatures supported photosynthesis and thereby the absorption of dissolved inorganic carbon. However, once temperatures exceeded the optimum ranges for macroalgae, respiration within these communities exceeded photosynthesis and increased CO2 concentrations, thereby exacerbating ocean acidification conditions. We conclude that the seawater carbonate chemistry is strongly influenced by the metabolisms of the dominant macroalgae within these different habitat types, which may, in turn, alter their buffering capacity against ocean acidification.

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Quasi-synchronous accumulation of apparent oxygen utilization and inorganic carbon in the South Yellow Sea cold water mass from spring to autumn: the acidification effect and roles of community metabolic processes, water mixing, and spring thermal state

To better understand seasonal acidification in the South Yellow Sea (SYS), four field surveys conducted in 2019 and the historical data obtained in 2018 were incorporated in this study. The lowest aragonite saturation state (Ωarag) value of 1.15 was observed in the central SYS in late autumn. Despite interannual variations in the rate of net community respiration, the quasi-synchronous accumulation of apparent oxygen utilization and excess dissolved inorganic carbon (DIC) relative to the air equilibrium were revealed in the SYS cold water mass (SYSCWM) from late spring to autumn. Correspondingly, the two acidification indexes (Ωarag and pH) decreased in logarithmic forms in the SYSCWM in warm seasons. To examine the potential influences of hydrological dynamics on seasonal acidification in the SYSCWM, a three-endmember water-mixing model was applied. The results showed that the cumulative effect of various non-conservative processes on DIC was comparable with the excess DIC relative to the air equilibrium. This implied that the summer and autumn carbonate dynamics and the acidification status of the cold water mass were almost free from the potential impacts of the weak water mixing and internal circulation in summer and autumn in a given year. The Yellow Sea Warm Current carries oceanic DIC into the SYS only in winter and early spring. This study also showed that the re-equilibrium with atmospheric CO2 at given temperature in early spring determined the initial Ωarag of the SYS before Ωarag declining in late spring, summer, and autumn. The sensitivity of coastal Ωarag changes to DIC addition is subject to both spatial and temporal variations.

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Effects of shellfish and macro-algae IMTA in North China on the environment, inorganic carbon system, organic carbon system, and sea–air CO2 fluxes

Shellfish and macro-algae integrated multi-trophic aquaculture (IMTA) contribute greatly to the sustainability of aquaculture. However, the effects of large-scale shellfish and macro-algae aquaculture on the functions of the ocean carbon sink are not clear. To clarify these effects, we studied the spatial and temporal changes of inorganic and organic carbon systems in seawater under different aquaculture modes (monoculture or polyculture of shellfish and macro-algae) in Sanggou Bay, together with the variation of other environmental factors. The results show that the summertime dissolved oxygen (DO) concentration in the shellfish culture zone was significantly lower than other zones (p < 0.05), with a minimum value of 7.07 ± 0.25 mg/L. The variation of pH and total alkalinity (TA) were large across different culture modes, and the seawater in the shellfish culture zone had the lowest pH and TA than the other zones. Seasonal environment and aquaculture modes significantly affected the variation of dissolved inorganic carbon (DIC), CO2 partial pressure (pCO2), dissolved organic carbon (DOC), and particulate organic carbon (POC) concentrations. The highest values of DIC, pCO2, and POC appeared in summer, and the lowest appeared in winter. For DOC concentration, the lowest value appeared in autumn. Spatially, DIC and pCO2 were highest in the shellfish culture zone and lowest in the macro-algae culture zone, DOC was highest in the macro-algae culture zone and lowest in the shellfish culture zone, and POC was lower in the shellfish culture zone and macro-algae culture zone and higher in the remaining zones. The results of sea–air CO2 fluxes showed that except for the shellfish culture zone during summertime, which released CO2 to the atmosphere, all culture zones were the sinks of atmospheric CO2 during the culture period, with the whole bay being a strong CO2 sink during autumn and winter. In summary, large-scale shellfish–macro-algae IMTA plays an important role in the local carbon cycle and contributes to mitigating ocean acidification and hypoxia.

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Ocean biogeochemical signatures of the North Pacific Blob


The Blob was the early manifestation of the Northeast Pacific marine heat wave from 2013 to 2016. While the upper ocean temperature in the Blob has been well described, the impacts on marine biogeochemistry have not been fully studied. Here, we characterize and develop understanding of Eastern North Pacific upper ocean biogeochemical properties during the Winter of 2013-14 using in situ observations, an observation-based product, and reconstructions from a collection of ocean models. We find that the Blob is associated with significant upper ocean biogeochemical anomalies: a 5% increase in aragonite saturation state (temporary reprieve of ocean acidification) and a 3% decrease in oxygen concentration (enhanced deoxygenation). Anomalous advection and mixing drive the aragonite saturation anomaly, while anomalous heating and air-sea gas exchange drive the oxygen anomaly. Marine heatwaves do not necessarily serve as an analog for future change as they may enhance or mitigate long-term trends.

Plain Language Summary

The global ocean is experiencing major changes due to human-made carbon emissions and climate change, leading to a warming ocean with increasing acidity and declining oxygen. On top of these long-term changes in the ocean are short-term extreme events, such as marine heatwaves. These extreme events quickly change the ocean state and can stress marine ecosystems in multiple ways. The Northeast Pacific marine heat wave (2013-2016) was one such marine heatwave. Here we focus on the early portion of this marine heatwave, called the Blob. While the ocean temperature changes during the event are well understood, the effects on ocean biogeochemistry have not been fully examined. In this study, we use an earth system model that accurately simulates the Blob to examine short-term changes in oxygen and acidity. We find that the warming signal leads to a decline in the effects of ocean acidification, mainly due to changes in the movement of carbon, and lowers the amount of oxygen, due primarily to temperature-driven effects. These results suggest that some effects of climate change may be exacerbated (warming) or mitigated (ocean acidification) by marine heatwaves.

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Potential resilience to ocean acidification of benthic foraminifers living in Posidonia oceanica meadows: the case of the shallow venting site of Panarea

This research shows the results regarding the response to acidic condition of the sediment and Posidonia foraminiferal assemblages collected around the Panarea Island. The Aeolian Archipelago represents a natural laboratory and a much-promising study site for multidisciplinary marine research (carbon capture and storage, geochemistry of hydrothermal fluids and ocean acidification vs. benthic and pelagic organisms). The variability and the complexity of the interaction of the ecological factors characterizing extreme environments such as shallow hydrothermal vents did not allow us to carry out a real pattern of biota responses in situ, differently from those observed under controlled laboratory conditions. However, the study provides new insights into foraminiferal response to increasing ocean acidification (OA) in terms of biodiversity, faunal density, specific composition of the assemblages and morphological variations of the shells. The study highlights how the foraminiferal response to different pH conditions can change depending on different environmental conditions and microhabitats (sediments, Posidonia leaves and rhizomes). Indeed, mineral sediments were more impacted by acidification, whereas Posidonia microhabitats, thanks to their buffer effect, can offer “refugia” and more mitigated acidic environment. At species level, rosalinids and agglutinated group represent the most abundant taxa showing the most specific resilience and capability to face acidic conditions.

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Tracking the space-time evolution of ocean acidification extremes in the California Current System and Northeast Pacific


Ocean acidification is punctuated by episodic extremes of low pH and saturation state with regard to aragonite (ΩA). Here, we use a hindcast simulation from 1984 to 2019 with a high-resolution regional ocean model (ROMS-BEC) to identify and track ocean acidification extremes (OAX) in the Northeast Pacific and the California Current System (CCS). In the first step, we identify all grid cells whose pH and ΩA are simultaneously below their first percentile over the analysis period (1984-2019). In the second step, we aggregate all neighboring cells with extreme conditions into three-dimensional time evolving events, permitting us to track them in a Lagrangian manner over their lifetime. We detect more than twenty-two thousand events that occur at least once in the upper 100 m during their lifetime, with broad distributions in terms of size, duration, volume and intensity, and with 26% of them harboring corrosive conditions (ΩA < 1). By clustering the OAXs, we find three types of extremes in the CCS. Near the coast, intense, shallow, and short-lasting OAXs dominate, caused by strong upwelling. A second type consists of large and long-lasting OAX events that are associated with westward propagating cyclonic eddies. They account for only 3% of all extremes, but are the most severe events. The third type are small extremes at depth arising from pycnocline heave. OAX potentially have deleterious effects on marine life. Marine calcifiers, such as pteropods, might be especially impacted by the long-lasting events with corrosive conditions.

Plain Language Summary

The emission of carbon dioxide by human activities causes ocean acidification, i.e., the decrease of the pH and saturation level of seawater with respect to the carbonate mineral aragonite. Episodic events of unusually low pH and aragonite saturation level punctuate these long-term declines, potentially intensifying stress on marine plankton. Particularly prone to extremes is the California Current System off the U.S. West coast due to its naturally low pH-aragonite waters and its strong variability. We use a high-resolution numerical model to identify and characterize extreme events associated with ocean acidification in this region, and understand their drivers. We find extremes to have a broad range of volumes, durations and strengths, with a quarter of them carrying corrosive conditions for shelled organisms, i.e., aragonite saturation levels below 1. The largest and longest-lived events are associated with cyclonic eddies (whirls of approximately 50 to 100 km in diameter) that trap upwelled low pH-aragonite waters near the coast. Although representing only 3% of the events, they cause most of the total excess of acidity induced by all identified extremes. The vertical extent and duration of extremes with corrosive mean conditions are expected to impact calcifying organisms, such as pteropods.

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Comprehending the role of different mechanisms and drivers affecting the sea-surface pCO2 and the air-sea CO2 fluxes in the Bay of Bengal: a modeling study

We apply a coupled physical and biogeochemical (ROMS+PISCES) to understand the influence of distinct drivers and mechanisms on the sea-surface pCO2 and the air-sea CO2 flux of the Bay of Bengal (BoB). The model evaluation suggests that the model simulated sea-surface pCO2 is in accord with the observations. The north of BoB is found to be a sink for the atmospheric CO2, whereas the rest of the region acts as a source. The effect of dissolved inorganic carbon (DIC) and the total alkalinity (TALK) is found to be predominant but is contrasting in nature. Mixing-induced changes in DIC and TALK results in high pCO2 (+570μatm) and, consequently, the positive CO2 flux. The biological activity does draw down the surface pCO2 (−120μatm) but is insufficient in completely opposing the effect of mixing. The uptake of CO2 in the north is due to the CO2 solubility, which is a function of salinity and temperature. The northern rivers, having a high discharge rate, reduce the salinity and temperatures in the north, which possibly aids in this region to be a sink. In the northeast monsoon season, the impact of temperature and DIC is high and opposing. The TALK reduces the pCO2 in the northeast monsoon, but the magnitude is low. The pCO2 in the southwest monsoon is influenced primarily by temperature, whereas in the postmonsoon monsoon, the freshwater dominates. The pre-monsoon season experiences the TALK, temperature, and freshwater increase the pCO2 anomalies, and only the DIC reduces pCO2 anomalies.

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Controls on buffering and coastal acidification in a temperate estuary

Estuaries may be uniquely susceptible to the combined acidification pressures of atmospherically driven ocean acidification (OA), biologically driven CO2 inputs from the estuary itself, and terrestrially derived freshwater inputs. This study utilized continuous measurements of total alkalinity (TA) and the partial pressure of carbon dioxide (pCO2) from the mouth of Great Bay, a temperate northeastern U.S. estuary, to examine the potential influences of endmember mixing and biogeochemical transformation upon estuary buffering capacity (βH). Observations were collected hourly over 28 months representing all seasons between May 2016 and December 2019. Results indicated that endmember mixing explained most of the observed variability in TA and dissolved inorganic carbon (DIC), concentrations of which varied strongly with season. For much of the year, mixing dictated the relative proportions of salinity-normalized TA and DIC as well, but a fall season shift in these proportions indicated that aerobic respiration was observed, which would decrease βH by decreasing TA and increasing DIC. However, fall was also the season of weakest statistical correspondence between salinity and both TA and DIC, as well as the overall highest salinity, TA and βH. Potential biogeochemically driven βH decreases were overshadowed by increased buffering capacity supplied by coastal ocean water. A simple modeling exercise showed that mixing processes controlled most monthly changes in TA and DIC, obscuring impacts from air–sea exchange or metabolic processes. Advective mixing contributions may be as important as biogeochemically driven changes to observe when evaluating local estuarine and coastal OA.

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Understanding the seasonality, trends and controlling factors of Indian ocean acidification over distinctive bio-provinces

The Indian Ocean (IO) is witnessing acidification as a direct consequence of the continuous rising of atmospheric CO2 concentration and indirectly due to the rapid ocean warming, which disrupts the pH of the surface waters. This study investigates the pH seasonality and trends over various bio-provinces of the IO and regionally assesses the contribution of each of its controlling factors. Simulations from a global and a regional ocean model coupled with biogeochemical modules were validated with pH measurements over the basin, and used to discern the regional response of pH seasonality (1990-2010) and trend (1961-2010) in response to changes in Sea Surface Temperature (SST), Dissolved Inorganic Carbon (DIC), Total Alkalinity (ALK) and Salinity (S). DIC and SST are significant contributors to the seasonal variability of pH in almost all bio-provinces. Total acidification in the IO basin was 0.0675 units from 1961 to 2010, with 69.3% contribution from DIC followed by 13.8% contribution from SST. For most of the bio-provinces, DIC remains a dominant contributor to changing trends in pH except for the Northern Bay of Bengal and Around India (NBoB-AI) region, wherein the pH trend is dominated by ALK (55.6%) and SST (16.8%). Interdependence of SST and S over ALK is significant in modifying the carbonate chemistry and biogeochemical dynamics of NBoB-AI and a part of tropical, subtropical IO bio-provinces. A strong correlation between SST and pH trends infers an increasing risk of acidification in the bio-provinces with rising SST and points out the need for sustained monitoring of IO pH in such hotspots.

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Kelp (Saccharina latissima) mitigates coastal ocean acidification and increases the growth of North Atlantic bivalves in lab experiments and on an oyster farm

Coastal zones can be focal points of acidification where the influx of atmospheric CO2 can be compounded by additional sources of acidity that may collectively impair calcifying organisms. While the photosynthetic action of macrophytes may buffer against coastal ocean acidification, such activity has not been well-studied, particularly among aquacultured seaweeds. Here, we report on field and laboratory experiments performed with North Atlantic populations of juvenile hard clams (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), and blue mussels (Mytilus edulis) grown with and without increased CO2 and with and without North Atlantic kelp (Saccharina latissima) over a range of aquaculture densities (0.3 – 2 g L-1). In all laboratory experiments, exposure to elevated pCO2 (>1,800 µatm) resulted in significantly reduced shell- and/or tissue-based growth rates of bivalves relative to control conditions. This impairment was fully mitigated when bivalves were exposed to the same acidification source but also co-cultured with kelp. Saturation states of aragonite were transformed from undersaturated to saturated in the acidification treatments with kelp present, while the acidification treatments remained undersaturated. In a field experiment, oysters grown near aquacultured kelp were exposed to higher pH waters and experienced significantly faster shell and tissue based growth rates compared to individuals grown at sites away from kelp. Collectively, these results suggest that photosynthesis by S. latissima grown at densities associated with aquaculture increased pH and decreased pCO2, fostering a carbonate chemistry regime that maximized the growth of juvenile bivalves. As S. latissima has been shown to benefit from increased CO2, growing bivalves and kelp together under current or future acidification scenarios may be a synergistically beneficial integrated, multi-trophic aquaculture approach.

Continue reading ‘Kelp (Saccharina latissima) mitigates coastal ocean acidification and increases the growth of North Atlantic bivalves in lab experiments and on an oyster farm’

The role of epiphytes in seagrass productivity under ocean acidification

Ocean Acidification (OA), due to rising atmospheric CO2, can affect the seagrass holobiont by changing the plant’s ecophysiology and the composition and functioning of its epiphytic community. However, our knowledge of the role of epiphytes in the productivity of the seagrass holobiont in response to environmental changes is still very limited. CO2 vents off Ischia Island (Italy) naturally reduce seawater pH, allowing to investigate the adaptation of the seagrass Posidonia oceanica L. (Delile) to OA. Here, we analyzed the percent cover of different epiphytic groups and the epiphytic biomass of P. oceanica leaves, collected inside (pH 6.9–7.9) and outside (pH 8.1–8.2) the CO2 vents. We estimated the contribution of epiphytes to net primary production (NPP) and respiration (R) of leaf sections collected from the vent and ambient pH sites in laboratory incubations. Additionally, we quantified net community production (NCP) and community respiration (CR) of seagrass communities in situ at vent and ambient pH sites using benthic chambers. Leaves at ambient pH sites had a 25% higher total epiphytic cover with encrusting red algae (32%) dominating the community, while leaves at vent pH sites were dominated by hydrozoans (21%). Leaf sections with and without epiphytes from the vent pH site produced and respired significantly more oxygen than leaf sections from the ambient pH site, showing an average increase of 47 ± 21% (mean ± SE) in NPP and 50 ± 4% in R, respectively. Epiphytes contributed little to the increase in R; however, their contribution to NPP was important (56 ± 6% of the total flux). The increase in productivity of seagrass leaves adapted to OA was only marginally reflected by the results from the in situ benthic chambers, underlining the complexity of the seagrass community response to naturally occurring OA conditions.

Continue reading ‘The role of epiphytes in seagrass productivity under ocean acidification’

Regional sensitivity patterns of Arctic Ocean acidification revealed with machine learning

Ocean acidification is a consequence of the absorption of anthropogenic carbon emissions and it profoundly impacts marine life. Arctic regions are particularly vulnerable to rapid pH changes due to low ocean buffering capacities and high stratification. Here, an unsupervised machine learning methodology is applied to simulations of surface Arctic acidification from two state-of-the-art coupled climate models. We identify four sub-regions whose boundaries are influenced by present-day and projected sea ice patterns. The regional boundaries are consistent between the models and across lower (SSP2-4.5) and higher (SSP5-8.5) carbon emissions scenarios. Stronger trends toward corrosive surface waters in the central Arctic Ocean are driven by early summer warming in regions of annual ice cover and late summer freshening in regions of perennial ice cover. Sea surface salinity and total alkalinity reductions dominate the Arctic pH changes, highlighting the importance of objective sub-regional identification and subsequent analysis of surface water mass properties.

Continue reading ‘Regional sensitivity patterns of Arctic Ocean acidification revealed with machine learning’

Monsoon-driven biogeochemical dynamics in an equatorial shelf sea: time-series observations in the Singapore Strait


  • Multi-year time-series data show strong monsoonal seasonality.
  • River input from regional peatlands is a major driver of seasonal variation.
  • Light limitation likely modulates phytoplankton response to nutrient input.
  • Lower buffer capacity from peatland carbon remineralisation raises diel pH variation.


Coastal tropical waters are experiencing rapid increases in anthropogenic pressures, yet coastal biogeochemical dynamics in the tropics are poorly studied. We present a multi-year biogeochemical time series from the Singapore Strait in Southeast Asia’s Sunda Shelf Sea. Despite being highly urbanised and a major shipping port, the strait harbours numerous biologically diverse habitats and is a valuable system for understanding how tropical marine ecosystems respond to anthropogenic pressures. We observed strong seasonality driven by the semi-annual reversal of ocean currents: dissolved inorganic nitrogen (DIN) and phosphorus varied from ≤0.05 μmol l−1 during the intermonsoons to ≥4 μmol l−1 and ≥0.25 μmol l−1, respectively, during the southwest monsoon. Si(OH)4 exceeded DIN year-round. Based on nutrient concentrations, their relationships to salinity and coloured dissolved organic matter, and the isotopic composition of NOx, we infer that terrestrial input from peatlands is the main nutrient source. This input delivered dissolved organic carbon (DOC) and nitrogen, but was notably depleted in dissolved organic phosphorus. In contrast, particulate organic matter showed little seasonality, and the δ13C of particulate organic carbon (−21.0 ± 1.5‰) is consistent with a primarily autochthonous origin. The seasonal pattern of the diel changes in dissolved O2 suggests that light availability controls primary productivity more than nutrient concentrations. However, diel changes in pH were greater during the southwest monsoon, when remineralisation of terrestrial DOC lowers the seawater buffer capacity. We conclude that terrestrial input results in mesotrophic conditions, and that the strait might undergo further eutrophication if nutrient inputs increase during seasons when light availability is high. Moreover, the remineralisation of terrestrial DOC within the Sunda Shelf may enhance future ocean acidification.

Continue reading ‘Monsoon-driven biogeochemical dynamics in an equatorial shelf sea: time-series observations in the Singapore Strait’

Eelgrass beds can mitigate local acidification and reduce oyster malformation risk in a subarctic lagoon, Japan: a three-dimensional ecosystem model study


  • An ecosystem model representing carbonate systems in a lagoon was developed.
  • The effect of ocean acidification on oyster malformation was evaluated.
  • Simulation under the absence of eelgrass bed was also performed.
  • The model could reproduce the spatiotemporal variations of the observed values.
  • Eelgrass beds mitigate the adverse effects of acidification on oyster growth.


It is well known that ocean acidification (OA) inhibits growth of marine calcifying organisms. Therefore, the adverse effects of acidification on marine ecosystems and aquaculture, such as oyster farming, are of concern. Since eelgrass beds in neritic areas have a high potential for carbon assimilation, this study focuses on local scale mitigation of OA effects. Using a three-dimensional lower-trophic system ecosystem model, we modeled nitrogen and carbon cycles, and the dynamics of carbonate parameters in a subarctic shallow lagoon and bay, where nitrogen availability limits the photosynthesis of primary producers. Simulation of the present conditions allowed reproduction of spatiotemporal variations in water quality and, by assuming future environmental changes quantitatively, revealed that the progress of OA significantly elevated the probability of shell malformation in juvenile oysters. The results represent the spatiotemporal variations in carbonate parameters inside and outside eelgrass beds and enable the evaluation of the alleviation effect on local acidification by the presence of a dense eelgrass bed. Our study shows that in the absence of the eelgrass bed scenario, the effect of OA on oysters became more remarkable. The simulations revealed that maintaining eelgrass beds is essential to mitigate the effects of acidification on oysters.

Continue reading ‘Eelgrass beds can mitigate local acidification and reduce oyster malformation risk in a subarctic lagoon, Japan: a three-dimensional ecosystem model study’

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