Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of δ11B of calcite tests to seawater pH. However, our knowledge of the relationship between δ11B and pH remains incomplete for many taxa. Thus, to expand the potential scope of application of this proxy, we report δ11B data for seven different species of planktonic foraminifera from sediment core tops. We utilize a method for the measurement of small samples of foraminifera and calculate the δ11B-calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or without sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia menardii, and Globorotalia tumida, including for unstudied core tops and species. These taxa have diverse ecological preferences and are from sites that span a range of oceanographic regimes, including some that are in regions of air–sea equilibrium and others that are out of equilibrium with the atmosphere. The sensitivity of δ11Bcarbonate to δ11Bborate (e.g., Δδ11Bcarbonate∕Δδ11Bborate) in core tops is consistent with previous studies for T. sacculifer and G. ruber and close to unity for N. dutertrei, O. universa, and combined deep-dwelling species. Deep-dwelling species closely follow the core-top calibration for O. universa, which is attributed to respiration-driven microenvironments likely caused by light limitation and/or symbiont–host interactions. Our data support the premise that utilizing boron isotope measurements of multiple species within a sediment core can be utilized to constrain vertical profiles of pH and pCO2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pumps.
Posts Tagged 'South Atlantic'
Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients (update)
Published 13 July 2020 Science ClosedTags: biogeochemistry, biological response, field, Indian, North Atlantic, North Pacific, paleo, protists, South Atlantic, South Pacific
Air-sea CO2 flux in an equatorial continental shelf dominated by coral reefs (Southwestern Atlantic Ocean)
Published 29 June 2020 Science ClosedTags: biological response, calcification, chemistry, corals, South Atlantic
Highlights
•Air-sea CO2 fluxes and carbonate chemistry were investigated in coral reef-dominated waters (SW Atlantic).
•The relationship between nTA and nDIC evidenced occurrence of CaCO3 calcification in coral reefs.
•CaCO3 calcification increased the values of fCO2sw, and lowered the pHT and Ωara.
•Aquatic emissions of CO2 in coral reefs were higher than nearshore and offshore locations.
•The results have implications considering the carbon budget at the SW Atlantic Ocean.
Abstract
Coral reefs are ecosystems highly vulnerable to changes in seawater carbonate chemistry, including those related to the ocean acidification and global warming. Brazilian coral reefs contains the major area of reefs coverage in the Southwestern (SW) Atlantic Ocean, however, studies aimed at investigating the controls of seawater carbonate chemistry in coral reefs are still overlooked in Brazil. This study comprehends the first investigation of complete seawater carbonate chemistry parameters in a section of the equatorial continental shelf dominated by coral reefs in the SW Atlantic Ocean. The sampling included spatial continuous underway measurements of sea surface CO2 fugacity (fCO2sw), temperature (SST), salinity (SSS), and discrete investigations of total alkalinity (TA), dissolved inorganic carbon (DIC), bicarbonate (HCO3–), carbonate (CO32−), and saturation state of aragonite (Ωara). The study was conducted during a dry period (July-2019) in the Marine State Park of Pedra da Risca do Meio (PRM), a marine protected area dominated by coral reef communities. Overall, the coral-reef dominated waters presented higher values of fCO2sw (475 ± 28 μatm), and lower values of pHT (7.98 ± 0.008), CO32− (217 ± 5 μmol kg-1) and Ωara (3.49 ± 0.07), compared to nearshore regions without the influence of coral reef waters, where the averages of fCO2sw, pHT, CO32−, and Ωarawere, respectively, 458 ± 21 μatm, 8.00 ± 0.007, 224 ± 4 μmol kg-1, and 3.58 ± 0.05. The relationship between salinity-normalized TA (nTA) and salinity-normalized DIC (nDIC) showed a slope higher than 1 (1.26) in the coral reef, evidencing the occurrence of calcium carbonate (CaCO3) precipitation and prevalence of inorganic carbon metabolism. The CaCO3 precipitation involves the consumption of TA and DIC in a ratio 2:1, with production of CO2. This mechanism explains the higher values of fCO2sw in the coral reef-dominated waters. The values of fCO2sw were always higher than the atmospheric values (fCO2air), indicating a permanent source of CO2 in the study area during the sampled period. The calculated fluxes of CO2 at the air-sea interface averaged 8.4 ± 6.5 mmolC m-2 d-1 in the coral reef-dominated waters, and these data are higher than those verified in nearshore and offshore locations. These higher emissions of CO2 in coral reef-dominated waters evidence that the carbon budgets calculated for North and Northeastern continental shelf of Brazil must include these environments taking into account the widespread coral reef coverage in the region. This study also confirms that biogeochemical processes occurring in coral reefs are modifying the seawater carbonate chemistry, with implication in the context of the current process of ocean acidification.
Continue reading ‘Air-sea CO2 flux in an equatorial continental shelf dominated by coral reefs (Southwestern Atlantic Ocean)’Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa
Published 26 June 2020 Science ClosedTags: biological response, dissolution, growth, laboratory, mollusks, morphology, multiple factors, South Atlantic, temperature
Global warming and ocean acidification influence marine calcifying organisms, particularly those with external shells. Among these, mussels may compensate for environmental changes by phenotypic plasticity, but this may entail trade-offs between shell deposition, growth and reproduction. We assessed main and interactive effects of pH and temperature on four mussel species on the west coast of South Africa (33°48′ S, 18°27′ E) in October 2012 by comparing shell dissolution, shell growth, shell breaking force and condition index of two native species, the ribbed mussel Aulacomya atra and the black mussel Choromytilus meridionalis, and two aliens, the Mediterranean mussel Mytilus galloprovincialis and the bisexual mussel Semimytilus algosus. Live mussels and dead shells were exposed for 42 days to seawater of pH 7.5 or 8.0, at 14 °C or 20 °C. Low pH, high temperature and their combination increased shell dissolution of the two aliens but their growth rates and condition indices remained unchanged. Aulacomya atra also experienced greater shell dissolution at a low pH and high temperature, but grew faster in low-pH treatments. For C. meridionalis, shell dissolution was unaffected by pH or temperature; it also grew faster in low-pH treatments, but had a lower condition index in the higher temperature treatment. Shell strength was not determined by thickness alone. In most respects, all four species proved to be robust to short-term reduction of pH and elevation of temperature, but the native species compensated for greater shell dissolution at low pH by increasing growth rate, whereas the aliens did not, so their invasive success cannot be ascribed to benefits accruing from climate change.
Continue reading ‘Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa’Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO2, CH4 and O2 from field deployments in contrasting environments
Published 12 May 2020 Science ClosedTags: Baltic, biogeochemistry, chemistry, field, methods, South Atlantic
Comparatively the ocean and inland waters are two separate worlds, with concentrations in greenhouse gases having orders of magnitude in difference between the two. Together they create the Land-Ocean Aquatic Continuum (LOAC), which comprises itself largely of areas with little to no data in regards to understanding the global carbon system. Reasons for this include remote and inaccessible sample locations, often tedious methods that require collection of water samples and subsequent analysis in the lab, as well as the complex interplay of biological, physical and chemical processes. This has led to large inconsistencies, increasing errors and inevitably leading to potentially false upscaling. Here we demonstrate successful deployment in oceanic to remote inland regions, over extreme concentration ranges with multiple pre-existing oceanographic sensors combined set-up, allowing for highly detailed and accurate measurements. The set-up consists of sensors measuring pCO2, pCH4 (both flow-through, membrane-based NDIR or TDLAS sensors), O2, and a thermosalinograph at high-resolution from the same water source simultaneously. The flexibility of the system allowed deployment from freshwater to open ocean conditions on varying vessel sizes, where we managed to capture day-night cycles, repeat transects and also delineate small scale variability. Our work demonstrates the need for increased spatiotemporal monitoring, and shows a way to homogenize methods and data streams in the ocean and limnic realms.
Continue reading ‘Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO2, CH4 and O2 from field deployments in contrasting environments’The effects of mining tailings in the physiology of benthic algae: understanding the relation between mud’s inductive acidification and the heavy metal’s toxicity
Published 6 April 2020 Science ClosedTags: algae, biological response, growth, laboratory, physiology, South Atlantic
Highlights
• Mariana’s mud was evaluated for toxic effects of heavy metals and acidification.
• Sargassum cymosum and Hypnea musciformis were evaluated for physiological responses.
• The presence of mud and acidic conditions caused lethality and metabolic damages.
• The acidified condition had the greatest impact over physiology of both species.
• The toxicity effects of mining tailings are intensified by abiotic changes.
Abstract
The direct and indirect effects of mining tailing on macroalgae were evaluated in vitro to determine the relationship between heavy metals toxicity and pH alterations caused by the presence of pollutants. The marine brown seaweed Sargassum cymosum (C. Hagard 1820) and its main epiphytic alga, the red seaweed Hypnea pseudomusciformis (Nauer, Cassano, Oliveira, 2015), were exposed to Mariana’s mud in cross treatments, including presence or absence of mud, and normal (˜8.0) or acidic (˜7.0) pH conditions. The effects of different biological conditions were also evaluated in two treatments, with seaweed in isolated or associative conditions, for a seven-day period. The measured variables were growth rates and metabolic descriptors, such as chlorophyll a, phenolic compounds, total proteins, and the analysis of enzymatic activity, e.g. catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD). Kruskal-Wallis and post-hoc Dunn’s test were performed to evaluate the significant differences among treatments and biological conditions. Decreased growth rates in treatments with presence of mud or in acidic conditions were detected and probably related to deviations of metabolic energy towards the synthesis of defensive metabolites. Especially in the acidified culture medium, both algae species presented significant declines in pigments concentration, antioxidant compounds and an accentuated inhibition of enzymatic activity. The algal association was not beneficial for either species and H. pseudomusciformis was responsible for reducing the defensive ability of Sargassum against stressors. Considering the results, we infer that the physiological ability of both algae to resist metals and/or acidified conditions was affected not only by their mutual interference in each other, but also by the interaction between the abiotic parameters evaluated in this study.
Acid-base adjustments and first evidence of denticle corrosion caused by ocean acidification conditions in a demersal shark species
Published 23 December 2019 Science ClosedTags: biological response, fish, laboratory, morphology, physiology, South Atlantic
Global ocean acidification is expected to chronically lower the pH to 7.3 (>2200 µatm seawater pCO2) by the year 2300. Acute hypercapnia already occurs along the South African west and south coasts due to upwelling- and low-oxygen events, with increasing frequency. In the present project we investigated the impact of hypercapnia on the endemic demersal shark species Haploblepharus edwardsii. Specifically, we experimentally analysed acid-base regulation during acute and chronic hypercapnia, the effects of chronic hypercapnia on growth rates and on denticle structure- and composition. While H. edwardsii are physiologically well adapted to acute and chronic hypercapnia, we observed, for the first time, denticle corrosion as a result of chronic exposure. We conclude that denticle corrosion could increase denticle turnover and compromise hydrodynamics and skin protection.
Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins
Published 18 November 2019 Science ClosedTags: chemistry, field, South Atlantic
Thriving benthic communities were observed in the oxygen minimum zones along the southwestern African margin. On the Namibian margin, fossil cold-water coral mounds were overgrown by sponges and bryozoans, while the Angolan margin was characterized by cold-water coral mounds covered by a living coral reef. To explore why benthic communities differ in both areas, present-day environmental conditions were assessed, using conductivity–temperature–depth (CTD) transects and bottom landers to investigate spatial and temporal variations of environmental properties. Near-bottom measurements recorded low dissolved oxygen concentrations on the Namibian margin of 0–0.15 mL L−1 (≜0 %–9 % saturation) and on the Angolan margin of 0.5–1.5 mL L−1 (≜7 %–18 % saturation), which were associated with relatively high temperatures (11.8–13.2 ∘C and 6.4–12.6 ∘C, respectively). Semidiurnal barotropic tides were found to interact with the margin topography producing internal waves. These tidal movements deliver water with more suitable characteristics to the benthic communities from below and above the zone of low oxygen. Concurrently, the delivery of a high quantity and quality of organic matter was observed, being an important food source for the benthic fauna. On the Namibian margin, organic matter originated directly from the surface productive zone, whereas on the Angolan margin the geochemical signature of organic matter suggested an additional mechanism of food supply. A nepheloid layer observed above the cold-water corals may constitute a reservoir of organic matter, facilitating a constant supply of food particles by tidal mixing. Our data suggest that the benthic fauna on the Namibian margin, as well as the cold-water coral communities on the Angolan margin, may compensate for unfavorable conditions of low oxygen levels and high temperatures with enhanced availability of food, while anoxic conditions on the Namibian margin are at present a limiting factor for cold-water coral growth. This study provides an example of how benthic ecosystems cope with such extreme environmental conditions since it is expected that oxygen minimum zones will expand in the future due to anthropogenic activities.
Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)
Published 14 November 2019 Science ClosedTags: biological response, crustaceans, laboratory, mortality, multiple factors, physiology, salinity, South Atlantic
Minuca mordax is a model for studies on ocean acidification and sea-level rise because lives in mangroves and riverbanks with low pH. We investigated the physiology of the crabs exposed to differents pH (6.5 and 5.8) and salinity (25, 30, 35, 40 45S). There was not mortality or alterations in the hypo-osmoregulation, suggesting that the factors did not affect salt absorption/secretion. Reduced pH changed metabolism, ammonia excretion, and hepatosomatic index in relation to the animals kept in control pH. At elevated salinities, metabolism increased when animals were kept in control pH, but it decreased when they were exposed to acidified pH. energy substrate, varied between proteins to a mixture of proteins and lipids. Important physiological parameters, related to the catabolism of amino acids and to the energy demand are changed and the consequences might include alterations in growth and reproduction due to the energy channeling to limiting processes of homeostasis.
Optimum satellite remote sensing of the marine carbonate system using empirical algorithms in the global ocean, the Greater Caribbean, the Amazon Plume and the Bay of Bengal
Published 12 November 2019 Science ClosedTags: globalmodeling, Indian, modeling, North Atlantic, regionalmodeling, South Atlantic
Highlights
• Satellite salinity measurements enable estimation of surface carbonate parameters.
• Uncertainties within these observation-based estimates are well characterized.
• Monthly satellite salinity and temperature allows synoptic monitoring.
• Satellite observations allow study of seasonal, interannual and episodic variations.
Abstract
Improving our ability to monitor ocean carbonate chemistry has become a priority as the ocean continues to absorb carbon dioxide from the atmosphere. This long-term uptake is reducing the ocean pH; a process commonly known as ocean acidification. The use of satellite Earth Observation has not yet been thoroughly explored as an option for routinely observing surface ocean carbonate chemistry, although its potential has been highlighted. We demonstrate the suitability of using empirical algorithms to calculate total alkalinity (AT) and total dissolved inorganic carbon (CT), assessing the relative performance of satellite, interpolated in situ, and climatology datasets in reproducing the wider spatial patterns of these two variables. Both AT and CT in situ data are reproducible, both regionally and globally, using salinity and temperature datasets, with satellite observed salinity from Aquarius and SMOS providing performance comparable to other datasets for the majority of case studies. Global root mean squared difference (RMSD) between in situ validation data and satellite estimates is 17 μmol kg−1 with bias < 5 μmol kg−1 for AT and 30 μmol kg−1 with bias < 10 μmol kg−1 for CT. This analysis demonstrates that satellite sensors provide a credible solution for monitoring surface synoptic scale AT and CT. It also enables the first demonstration of observation-based synoptic scale AT and CT temporal mixing in the Amazon plume for 2010–2016, complete with a robust estimation of their uncertainty.
Control of CaCO3 dissolution at the deep seafloor and its consequences
Published 15 October 2019 Science ClosedTags: biogeochemistry, dissolution, Indian, modeling, North Atlantic, North Pacific, South Atlantic, South Pacific
Prediction of the neutralization of anthropogenic CO2 in the oceans and the interpretation of the calcite record preserved in deep-sea sediments requires the use of the correct kinetics for calcite dissolution. Dissolution rate information from suspended calcite-grain experiments consistently indicates a high-order nonlinear dependence on undersaturation, with a well-defined rate constant. Conversely, stirred-chamber and rotating-disc dissolution experiments consistently indicate linear kinetics of dissolution and a strong dependence on the fluid flow velocity. Here, we resolve these seeming incongruities and establish reliably the kinetic controls on deep-sea calcite dissolution. By equating the carbonate-ion flux from a dissolving calcite bed, governed by laboratory-based nonlinear kinetics, to the flux across typical diffusive boundary layers (DBL) at the seafloor, we show that the net flux is influenced both by boundary layer and bed processes, but that flux is strongly dominated by the rate of diffusion through the DBL. Furthermore, coupling that calculation to an equation for the calcite content of the seafloor, we show that a DBL-transport dominated model adeptly lysoclines adeptly, i.e., CaCO3 vs ocean depth profiles, observed across the oceans. Conversely, a model with only sediment-side processes fails to predict lysoclines in all tested regions. Consequently, the past practice of arbitrarily altering the calcite-dissolution rate constant to allow sediment-only models to fit calcite profiles constitutes confirmation bias. From these results, we hypothesize that the reason suspended-grain experiments and bed experiments yield different reaction orders is that dissolution rates of individual grains in a bed are fast enough to maintain porewaters at or close to saturation, so that the exact reaction order cannot be measured and dissolution appears to be linear. Finally, we provide a further test of DBL-transport dominated calcite dissolution by successfully predicting, not fitting, the in-situ pH profiles observed at four stations reported in the literature.
Continue reading ‘Control of CaCO3 dissolution at the deep seafloor and its consequences’
Carbon chemistry variability around a tropical archipelago
Published 1 October 2019 Science ClosedTags: biogeochemistry, chemistry, field, South Atlantic
Oceanic islands affect the surrounding oceanic circulation by producing upwelling or vortices, resulting in the rising of a richer and colder subsurface water mass. This process increases primary production and can change some biogeochemical processes, such as carbon chemistry and the biological pump. The aim of this study was to describe the vertical variability of carbon chemistry around Fernando de Noronha Archipelago (FNA) and to verify how the island mass effect (IME) can affect carbon distribution. Two transects on opposite sides of the FNA were established according to the direction of the central South Equatorial Current, and samples were collected in July 2010, September 2012 and July 2014 from the surface down to a depth of 500 m. The results showed strong stratification, with an uplift of the thermohaline structure, which resulted in an increase of chlorophyll-a concentration downstream of the island during the 2010 and 2014 cruises. Carbon chemistry parameters were strongly correlated with temperature, salinity and dissolved oxygen along the water column and did not change between sides of the island in the periods studied. We conclude that the IME did not significantly affect carbon chemistry, which was more correlated with thermohaline gradient.
Continue reading ‘Carbon chemistry variability around a tropical archipelago’
Water acidification causes death of marine ornamental fish (Perciformes: Pomacentridae) during transport: contributing to the conservation of wild populations
Published 13 August 2019 Science ClosedTags: biological response, fish, laboratory, mortality, physiology, South Atlantic
Pomacentridae is a common family in the aquarium fish trade. Most species are harvested from nature. Here we evaluate the following water parameters in the pomacentrid sergeant major, Abudefduf saxatilis (Linnaeus, 1758), to assess their stress level during a 24, 48, and 72 hours transport: dissolved oxygen (DO), total ammonia, and pH. In addition, we evaluated the following physiological parameters: plasma osmolality, muscle water content, blood glucose, and the enzyme activities of the branchial carbonic anhydrase (CA), the hepatic glutathione S-transferase (GST), catalase (CAT), and superoxide dismutase (SOD). The mortality of fish measuring >6 cm total length was 22%, while no mortality was observed for fish measuring <6 cm. The pH of the water was significantly correlated with fish mortality, especially for the initial 24 hours of transport. Hypoxia after 24–48 hours also led to fish mortality, but build up ammonia was not a problem even after 72 hours. We suggest that a minimum water volume of 125 ml/g fish is necessary for safe and cost-effective transport of the sergeant major, preferably with <6 cm in total length.
Seawater pH reconstruction using boron isotopes in multiple planktonic foraminifera species with different depth habitats and their potential to constrain pH and pCO2 gradients
Published 9 August 2019 Science ClosedTags: biogeochemistry, biological response, field, Indian, North Atlantic, North Pacific, paleo, protists, South Atlantic, South Pacific
Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of δ11B of their calcite tests to seawater pH. However, our knowledge of the relationship between δ11B and pH remains incomplete for several taxa. Thus, to expand the potential scope of application of this proxy, we report data for 7 different species of planktonic foraminifera from sediment core-tops. We utilize a method for the measurement of small samples of foraminifera and calculate the δ11B-calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or w/o sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia menardii and Globorotalia tumida, including for unstudied coretops and species. The sensitivity of δ11Bcarbonate to δ11Bborate (eg. Δδ11Bcarbonate/Δδ11Bborate) in core-tops is close to unity. Deep-dwelling species closely follow the core-top calibration for O. universa, which is attributed to respiration-driven microenvironments, likely caused by light limitation for symbiont-bearing foraminifera. These taxa have diverse ecological preferences and are from sites that span a range of oceanographic regimes, including some that are in regions of air-sea equilibrium and others that are out of equilibrium with the atmosphere. Our data support the premise that utilizing boron isotope measurements of multiple species within a sediment core can be utilized to constrain vertical profiles of pH and pCO2 at sites spanning different oceanic regimes, thereby constraining changes in vertical pH gradients and yielding insights into the past behavior of the oceanic carbon pump.
Harmful effects of cocaine byproduct in the reproduction of sea urchin in different ocean acidification scenarios
Published 4 July 2019 Science ClosedTags: biological response, echinoderms, laboratory, multiple factors, reproduction, South Atlantic, toxicants
Highlights
• Impact of different acidification scenarios by enrichment of CO2 on contaminants of emerging concern.
• Toxicity of a cocaine byproduct in different scenarios of ocean acidification.
• Combined effects of crack cocaine and low pH on reproduction of sea urchin.
• Hazards and risks of illicit drugs pose to public health and the environment.
Abstract
This study has as main objective assessing the toxicity of crack-cocaine combined with different scenarios of ocean acidification on fertilization rate and embryo-larval development of Echinometra lucunter sea urchin. Effects on early life stages were assessed at five different concentrations (6,25 mg.L-1; 12,5 mg.L-1; 25 mg.L-1; 50 mg.L-1 and 100 mg.L-1) of crack-cocaine at four different pH values (8.5; 8.0; 7.5; 7.0). The pH values were achieved using two different methodologies: adding hydrochloric acid (HCl) and injecting carbon dioxide (CO2). The fertilization test did not show significant differences (p≤0.05) compared with control sample at pH values 8.5; 8.0 and 7.5. Results of embryo-larval assays showed a half maximal effective concentration (EC50) of crack-cocaine at pH values tested (8.5, 8.0, 7.5) as 58.83, 10.67 and 11.58 mg/L-1 for HCl acidification and 58.83, 23.28 and 12.57 mg/L-1 for CO2 enrichment. At pH 7.0 the effects observed in fertilization rate and embryo development were associated with the acidification. This study is the first ecotoxicological assessment of illicit drug toxicity in aquatic ecosystems at different ocean acidification scenarios.
The effect of Agulhas eddies on absorption and transport of anthropogenic carbon in the South Atlantic Ocean
Published 24 June 2019 Science ClosedTags: biogeochemistry, chemistry, field, modeling, regionalmodeling, South Atlantic
The South Atlantic Ocean is currently undergoing significant alterations due to climate change. This region is important to the global carbon cycle, but marine carbon data are scarce in this basin. Additionally, this region is influenced by Agulhas eddies. However, their effects on ocean biogeochemistry are not yet fully understood. Thus, we aimed to model the carbonate parameters in this region and investigate the anthropogenic carbon (Cant) content in 13 eddies shed by the Agulhas retroflection. We used in situ data from the CLIVAR/WOCE/A10 section to elaborate total dissolved inorganic carbon (CT) and total alkalinity (AT) models and reconstruct those parameters using in situ data from two other Brazilian initiatives. Furthermore, we applied the Tracer combining Oxygen, inorganic Carbon, and total Alkalinity (TrOCA) method to calculate the Cant, focusing on the 13 identified Agulhas eddies. The CT and AT models presented root mean square errors less than 1.66 and 2.19 μmol kg−1, indicating Global Ocean Acidification Observing Network climate precision. The Cant content in the Agulhas eddies was 23% higher than that at the same depths of the surrounding waters. We observed that Agulhas eddies can play a role in the faster acidification of the South Atlantic Central Water.
Effects of chronic hypercapnia and elevated temperature on the immune response of the spiny lobster, Jasus lalandii
Published 14 June 2019 Science ClosedTags: biological response, crustaceans, laboratory, multiple factors, performance, physiology, South Atlantic, temperature
Highlights
• Lobsters are very efficient at rendering an injected dose of bacteria non-culturable.
• There is an interactive effects of temperature and pH on lobster immunity.
• Haemocyte numbers are reduced following chronic exposure to hypercapnia/high temperature.
• Chronic exposure to hypercapnia/high temperature does not affect the ability of J. lalandii to defend itself against bacterial infection.
Abstract
The West Coast rock lobster (WCRL), Jasus lalandii, inhabits highly variable environments frequented by upwelling events, episodes of hypercapnia and large temperature variations. Coupled with the predicted threat of ocean acidification and temperature change for the coming centuries, the immune response in this crustacean will most likely be affected. We therefore tested the hypothesis that chronic exposure to hypercapnia and elevated seawater temperature will alter immune function of the WCRL. The chronic effects of four combinations of two stressors (seawater pCO2 and temperature) on the total number of circulating haemocytes (THC) as well as on the lobsters’ ability to clear (inactivate) an injected dose of Vibrio anguillarum from haemolymph circulation were assessed. Juvenile lobsters were held in normocapnic (pH 8.01) or hypercapnic (pH 7.34) conditions at two temperatures (15.6 and 18.9 °C) for 48 weeks (n = 30 lobster per treatment), after which a subsample of lobsters (n = 8/treatment), all at a similar moult stage, were selected from each treatment for the immune challenge. Baseline levels of haemocytes (THC ml−1) and bacteria (CFU ml−1) in their haemolymph were quantified 24 h prior to bacterial challenge. Lobsters were then challenged by injecting 4 × 104 V. anguillarum per g body weight directly into the cardiac region of each lobster and circulating haemocyte and culturable bacteria were measured at 20 min post challenge. No significant differences in THC ml−1 (p < 0.05) were observed between any of the treatment groups prior to the bacterial challenge. However lobsters chronically exposed to a combination of hypercapnia and low temperature had significantly higher (p < 0.05) THCs post-challenge in comparison with lobsters chronically exposed to hypercapnia and high temperature. A significant interactive effect was recorded between temperature and pH for the post-challenge THC data (two-way ANOVA, p = 0.0025). Lobster were very efficient at rendering an injected dose of bacteria non-culturable, with more than 83% of the theoretical challenge dose (∼1.7 × 105 Vibrio ml−1 haemolymph) inactivated within the first 10 min following injection. Although differences in the inactivation of V. anguillarum were observed between treatment groups, none of these differences were significant. Clearance efficiency was in the following order: Hypercapnia/low temperature > normocapnia/high temperature > normocapnia/low temperature > hypercapnia/high temperature. This study demonstrated that despite chronic exposure to combinations of reduced seawater pH and high temperature, the WCRL was still capable of rapidly rendering an injected dose of bacteria non-culturable.
Isotopic fractionation of carbon during uptake by phytoplankton across the South Atlantic subtropical convergence
Published 24 May 2019 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, field, phytoplankton, South Atlantic
The stable isotopic composition of particulate organic carbon (δ13CPOC) in the surface waters of the global ocean can vary with the aqueous CO2 concentration ([CO2(aq)]) and affects the trophic transfer of carbon isotopes in the marine food web. Other factors such as cell size, growth rate and carbon concentrating mechanisms decouple this observed correlation. Here, the variability in δ13CPOC is investigated in surface waters across the south subtropical convergence (SSTC) in the Atlantic Ocean, to determine carbon isotope fractionation (εp) by phytoplankton and the contrasting mechanisms of carbon uptake in the subantarctic and subtropical water masses. Our results indicate that cell size is the primary determinant of δ13CPOC across the Atlantic SSTC in summer. Combining cell size estimates with CO2 concentrations, we can accurately estimate εp within the varying surface water masses in this region. We further utilize these results to investigate future changes in εp with increased anthropogenic carbon availability. Our results suggest that smaller cells, which are prevalent in the subtropical ocean, will respond less to increased [CO2(aq)] than the larger cells found south of the SSTC and in the wider Southern Ocean. In the subantarctic water masses, isotopic fractionation during carbon uptake will likely increase, both with increasing CO2 availability to the cell, but also if increased stratification leads to decreases in average community cell size. Coupled with decreasing δ13C of [CO2(aq)] due to anthropogenic CO2 emissions, this change in isotopic fractionation and lowering of δ13CPOC may propagate through the marine food web, with implications for the use of δ13CPOC as a tracer of dietary sources in the marine environment.
Seagrass can mitigate negative ocean acidification effects on calcifying algae
Published 20 February 2019 Science ClosedTags: algae, biological response, calcification, chemistry, field, laboratory, mesocosms, physiology, South Atlantic
The ultimate effect that ocean acidification (OA) and warming will have on the physiology of calcifying algae is still largely uncertain. Responses depend on the complex interactions between seawater chemistry, global/local stressors and species-specific physiologies. There is a significant gap regarding the effect that metabolic interactions between coexisting species may have on local seawater chemistry and the concurrent effect of OA. Here, we manipulated CO2 and temperature to evaluate the physiological responses of two common photoautotrophs from shallow tropical marine coastal ecosystems in Brazil: the calcifying alga Halimeda cuneata, and the seagrass Halodule wrightii. We tested whether or not seagrass presence can influence the calcification rate of a widespread and abundant species of Halimeda under OA and warming. Our results demonstrate that under elevated CO2, the high photosynthetic rates of H. wrightii contribute to raise H. cuneata calcification more than two-fold and thus we suggest that H. cuneata populations coexisting with H. wrightii may have a higher resilience to OA conditions. This conclusion supports the more general hypothesis that, in coastal and shallow reef environments, the metabolic interactions between calcifying and non-calcifying organisms are instrumental in providing refuge against OA effects and increasing the resilience of the more OA-susceptible species.
Continue reading ‘Seagrass can mitigate negative ocean acidification effects on calcifying algae’
Implicações fisiológicas e ecológicas de interações interespecíficas nos bentos marinho-subsídio para o entendimento de cenários atuais e futuros (in Portuguese)
Published 18 February 2019 Science ClosedTags: algae, BRcommunity, echinoderms, laboratory, mesocosms, multiple factors, photosynthesis, physiology, South Atlantic, temperature
Biotic interactions are increasingly known to shape ecosystem community structure. Recently, there has been a renewed focus on species interactions in light of global change, especially ocean warming (OW) and ocean acidification (OA) in marine ecosystems. In coastal environments, macroalgae are among the most important taxa as they are often the most abundant primary producers and form the base of food webs. However, due to their sedentary nature, they are also vulnerable to the effects of climate change. In order to better understand how species interactions will be affected by climate change stressors, a solid understanding of how interspecies interactions operate under present-day conditions is needed. The first chapter of this thesis attempts to characterize seasonal variation in macroalgal physiology and biochemistry, and how interspecific interactions might affect algal fitness and palatability to a sea urchin herbivore (Echinometra lucunter). Specimens of Jania rubens, Sargassum cymosum, and Ulva lactuca were collected from monospecific patches or from associations , where individuals were in physical contact with another species, in both summer and winter. Net photosynthesis, nitrogen reductase activity, and pigment, phenolic and carbonate content of algae were evaluated among different associations across the two seasons. The results indicate that in addition to seasonal variation in most parameters measured, interactions between algae could change in both magnitude and sign (positive, negative or neutral) in different seasons. The no-choice herbivory assay (conducted in winter) revealed that both Jania and Ulva were consumed at higher rates when they were associated with each other, whereas Sargassum was not affected. These results suggest that macroalgae may influence the physiology and biochemical composition of neighboring species and subsequently affect their palatability, which may influence local community structure. To further evaluate effects of species interactions under climate change stressors, an experiment was performed to assess algal-herbivore interactions under OW and OA conditions. The most preferentially consumed algae from the first experiment (Jania rubens) and the sea urchin E. lucunter were evaluated in a 21-day mesocosm study with treatments of control, OW, OA, and OW+OA. Algal physiology was unaffected by increased temperature (+4°C) and pCO2 (1,000 ppm), but changes in the biochemical composition of the algal tissue were found. Metabolic rates of the sea urchin E. lucunter were higher in the ambient temperature, high pCO2 treatment, and feeding assays showed that this influenced consumption, with increased feeding rates in this treatment. The results here show that although algal biochemical composition was affected by future pCO2, at least in the short term, direct effects to sea urchin metabolism were more important for impacting this algae-herbivore interaction.
