Posts Tagged 'South Atlantic'

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The sea-air CO2 net fluxes in the South Atlantic Ocean and the role played by Agulhas eddies

Published 7 February 2019 Science Closed
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Highlights

• A mean FCO2 of −3.76 mmol m−2 d−1 was obtained in the FORSA cruise track.
• An Agulhas eddy can uptake up to −3.16 kg CO2 d−1, leading to −2.5 t CO2 lifetime−1.
• The seawater temperature is the main driver of the CO2 variability in the SAO.

Abstract

The South Atlantic Ocean is vitally important to the global overturning circulation, which is influenced by heat, salt and other properties carried by Agulhas eddies. However, this influence is not yet fully understood, mainly in the context of the biogeochemistry changes on the CO2 system. This study uses in situ data obtained during the Following Ocean Rings in the South Atlantic cruise, which occurred between Cape Town, South Africa and Arraial do Cabo, Brazil in July 2015 when six eddies and the surrounding waters were sampled. The seawater and atmospheric CO2 molar fraction, surface temperature and salinity were continuously measured to calculate the oceanic and atmospheric CO2 partial pressures (pCO2sw and pCO2atm, respectively). This study investigated the role played by the Agulhas eddies in the sea-air CO2 net flux (FCO2) and modeled the seawater CO2 as a function of environmental parameters. The mean pCO2sw and pCO2atm for the entire region were 351.5 and 390.6 μatm, respectively. The mean difference (ΔpCO2) was −39.1 μatm. The CO2 uptake was dominated by temperature (r = 0.88) during the period analyzed. The mean FCO2 was −3.76 and −3.62 mmol m−2 d−1 using two different KT-models. We show that an Agulhas eddy can contribute to an ocean uptake of −3.16 kg CO2 d−1, leading to the capture of approximately 2.52 t CO2 lifetime−1. Thus, providing evidence that the Agulhas eddies propagation can likely play a key role on the rapid seawater acidification of the South Atlantic Central Water. A multiple linear regression model was developed that could reliably reconstruct the cruise survey with better results than previously published.

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Vulnerability of juvenile hermit crabs to reduced seawater pH and shading

Published 9 October 2018 Science Closed
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Highlights

• Local impacts may potentially increase effects of global environmental changes.
• We assessed combined effects of reduced pH and shading caused by harbor structures.
• Reduced seawater pH and shading affected behavioral responses of hermit crabs.
• Multiple stressors induced high mortality and reduced growth.
• Maintenance of local populations may be impaired by the impact of both stressors.

Abstract

Multiple simultaneous stressors induced by anthropogenic activities may amplify their impacts on marine organisms. The effects of ocean acidification, in combination with other anthropogenic impacts (apart from temperature) are poorly understood, especially in coastal regions. In these areas, shading caused by infrastructure development, such as harbor construction, may potentially interact with CO2-induced pH reduction and affect invertebrate populations. Here, we evaluated the effects of reduced pH (7.6) and shading (24h in darkness) on mortality, growth, calcification and displacement behavior to live predator (danger signal) and dead gastropod (resource availability signal) odors using juveniles of the hermit crab Pagurus criniticornis collected in Araçá Bay (São Paulo state, Southeastern Brazil). After a 98 day experimental period, both stressors had a significant interaction effect on mortality, and an additive effect on total growth. No difference in calcification was recorded among treatments, indicating that individuals were able to maintain calcification under reduced pH conditions. When exposed to odor of live predators, crab responses were only affected by shading. However, an interactive effect between both stressors was observed in response to gastropod odor, leading to reduced displacement behavior. This study shows how local disturbance impacts may enhance the effects of global environmental change on intertidal crustacean populations.

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Physiological and biochemical responses of a coralline alga and a sea urchin to climate change: Implications for herbivory

Published 2 October 2018 Science Closed
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Highlights

• Algal metabolism and phenolic content were unaffected by CO2 and temperature treatments.
• CaCO3 content of algae decreased in high CO2 treatments.
• Total sugar content of algae was affected by both CO2 and temperature.
• Sea urchin respiration and feeding increased under high CO2, low temperature.
• Direct effects to sea urchin metabolism drove feeding more than algal palatability.

Abstract

Direct responses to rising temperatures and ocean acidification are increasingly well known for many single species, yet recent reviews have highlighted the need for climate change research to consider a broader range of species, how stressors may interact, and how stressors may affect species interactions. The latter point is important in the context of plant-herbivore interactions, as increasing evidence shows that increasing seawater temperature and/or acidification can alter algal traits that dictate their susceptibility to herbivores, and subsequently, community and ecosystem properties. To better understand how marine rocky shore environments will be affected by a changing ocean, in the present study we investigated the direct effects of short-term, co-occurring increased temperature and ocean acidification on a coralline alga (Jania rubens) and a sea urchin herbivore (Echinometra lucunter) and assessed the indirect effects of these factors on the algal-herbivore interaction. A 21-day mesocosm experiment was conducted with both algae and sea urchins exposed to ambient (24 °C, Low CO2), high-temperature (28 °C, Low CO2), acidified (24 °C, High CO2), or high-temperature plus acidified (28 °C, High CO2) conditions. Algal photosynthesis, respiration, and phenolic content were unaffected by increased temperature and CO2, but calcium carbonate content was reduced under high CO2 treatments in both temperatures, while total sugar content of the algae was reduced under acidified, lower temperature conditions. Metabolic rates of the sea urchin were elevated in the lower temperature, high CO2 treatment, and feeding assays showed that consumption rates also increased in this treatment. Despite some changes to algal chemical composition, it appears that at least under short-term exposure to climate change conditions, direct effects on herbivore metabolism dictated herbivory rates, while indirect effects caused by changes in algal palatability seemed to be of minor importance.

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Ocean acidification studies and the uncertainties relevance on measurements of marine carbonate system properties

Published 6 August 2018 Science Closed
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The global ocean has a key role on the Earth’s climate system. It possesses a direct connection with the atmospheric gases, including the greenhouses, allowing exchanges between those compartments and oceanic storage of carbon. Through the years, this exchange of gases occurred based on gas equilibrium between ocean and atmosphere. After the Industrial Revolution, human activities have increased the emissions of greenhouse gases, mainly carbon dioxide (CO2), which changed the atmospheric concentration from ~280 ppm of CO2 to values as high as 391 ppm between c.a. 1750 and 2011 (Ciais et al., 2013). Recently, the measured CO2 atmospheric values are ranging near or above 400 ppm, as recorded by the Mauna Loa observatory, in Hawaii (daily CO2 measurements information available on www.scripps.ucsd.edu). A regional study in the south-southeast Brazilian continental shelf agrees with this value, which has measured an average of 396.7±2.5 ppm in the atmosphere during the spring of October 2014 (Kerr et al., 2016). This enhancement is reflected in the ocean, which has absorbed about 25% to 30% of the anthropogenic atmospheric CO2 emissions (Sabine and Tanhua, 2010); Le Quére et al., 2016). The CO2 uptake by the oceans directly affects the seawater chemistry and marine biogeochemical processes, impacting both the ecosystems and their respective biota (Doney et al., 2009).

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Analysis of Na+/K+ -ATPase gene expression and physiological parameters in the crab Callinectes danae submitted to future scenarios of ocean acidification in the laboratory (in Portuguese)

Published 31 July 2018 Science Closed
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Oceanic acidification, a process resulting from the emission of carbon dioxide (CO2) in the atmosphere by activities of anthropic nature, has been causing in recent decades a change in the chemical balance of the bicarbonate / carbonate system and consequently a decrease in the pH of the oceans. Estimates indicate that this decrease can be 0.7 units per year of 2300, which can affect the growth, reproduction and even survival of the species. In this sense, studies are needed to evaluate the impact of oceanic acidification on physiological and molecular levels in different marine species. The Callinectes danae crab is an important ecological and economic resource of the Region of the Baixada Santista and inhabitant of different ranges of salinity. The present study evaluated the effects of ocean acidification on C. danae crab on a set of physiological parameters (oxygen consumption, ammonia excretion, O: N ratio, hepatosomatic index and osmo-and ionoregulatory capacity of hemolymph), and gene expression of Na + / K + – ATPase, an important enzyme in the process of osmoregulation and acid base balance. The animals were kept at different salinities (20, 25, 30, 35 and 40) and at pHs 8.0 (control) and 7.3 (acidified) for a period of three and thirty days. It was observed an increase in the oxygen consumption in salinities 25 (3 days), 20 and 40 (30 days) probably due to a greater energy requirement for the maintenance of systems related to acid-base regulation. Metabolic depression was also observed at the salinity of 30 (30 days). Ammonia excretion decreased in salinities 30 (3 days), 25, 30 and 35 (30 days) possibly due to competition between Na + / H + and Na + / NH + 4 transporters. The hepatosomatic index had an increase in salinities of 30 (3 days) and 40 (30 days) due to a possible accumulation of reserves in stressful situations. The energy substrate and the osmoregulatory pattern remained unchanged in all treatments. However, the Cl- and Na + concentrations were reduced at the salinity of 25 and 35 (30 days), probably due to some changes in their transporters. Molecularly, a regulation of Na + / K + ATPase expression was observed, with a decrease in salinities of 35 and 40 (3 days), and a subsequent increase in the period of 30 days. The work was the first to evaluate the physiological and molecular parameters of C.danae in different salinities. Animals that remained longer on exposure to high pCO2 are more negatively affected than animals that were exposed in 3 days. The observed changes may indicate that although C. danae is an eurialan animal and inhabits different environments, ocean acidification can alter its physiological and molecular patterns, taking organisms out of their homeostasis, having consequences on the growth, development and distribution of the species.

Continue reading ‘Analysis of Na+/K+ -ATPase gene expression and physiological parameters in the crab Callinectes danae submitted to future scenarios of ocean acidification in the laboratory (in Portuguese)’

Seawater acidification and anthropogenic carbon distribution on the continental shelf and slope of the western South Atlantic Ocean

Published 4 July 2018 Science Closed
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Highlights

• We have measured hydrographic and carbonate system parameters in the western South Atlantic Ocean (WSAO).
• AT and CT are governed by calcification/dissolution and dilution/evaporation processes in the WSAO.
• Cant has already invaded the central and intermediate layers in the WSAO.
• The acidification of SACW and AAIW resulted in long-term pH changes of −0.17 ± 0.07 and −0.10 ± 0.06, respectively

Abstract

Increases in atmospheric carbon dioxide (CO2) concentrations since the beginning of the Industrial Revolution have led to increases in the flux of CO2 into the oceans. A large fraction of this increased flux occurs due to anthropogenic carbon (Cant), i.e., the excess carbon released by human activities. The oceans take up large amounts of Cant, and this process likely affects calcifying organisms and the formation and dissolution of calcium carbonate (CaCO3). In this study, we measured hydrographic and carbonate system parameters in the western South Atlantic Ocean (WSAO). This region is key for understanding climate issues; however, it remains understudied, especially regarding the drivers of ocean acidification and its effects on marine organisms and ecosystems. Using novel data collected in this undersampled area of the global ocean, we (i) determined values of the marine carbonate system parameters and (ii) characterized the seawater acidification state along the western boundary current off the southeastern and southern coasts of Brazil. Specifically, we measured total alkalinity (AT) and pH and applied the TrOCA approach (to derive the Cant storage in the water masses) in the study area. Our results show that (i) AT and the dissolved inorganic carbon distribution in the study region are governed by calcification/dissolution and dilution/evaporation processes and that (ii) Cant is present in the central and intermediate water masses at an average concentration (± method precision) of 75.0 ± 6.6 μmol kg−1 and at depths of up to ~1000 m. The highest concentrations are observed in the lower levels of the Tropical Water (TW), although we cannot exclude an overestimated Cant concentration in this layer, and the South Atlantic Central Water (SACW). These findings suggest that cross-shelf processes likely contribute to increased Cant along western boundary current systems. The storage of Cant in the SACW and the Antarctic Intermediate Water (AAIW) has led to long-term pH decreases of −0.17 ± 0.07 and −0.10 ± 0.06 pH units, respectively.

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Oxidative stress in the hydrocoral Millepora alcicornis exposed to CO2-driven seawater acidification

Published 18 June 2018 Science Closed
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Global impacts are affecting negatively coral reefs’ health worldwide. Ocean acidification associated with the increasing CO2 partial pressure in the atmosphere can potentially induce oxidative stress with consequent cellular damage in corals and hydrocorals. In the present study, parameters related to oxidative status were evaluated in the hydrocoral Millepora alcicornis exposed to three different levels of seawater acidification using a mesocosm system. CO2-driven acidification of seawater was performed until reaching 0.3, 0.6 and 0.9 pH units below the current pH of seawater pumped from the coral reef adjacent to the mesocosm. Therefore, treatments corresponded to control (pH 8.1), mild (pH 7.8), intermediate (pH 7.5) and severe (pH 7.2) seawater acidification. After 0, 16 and 30 d of exposure, hydrocorals were collected and the following parameters were analyzed in the holobiont: antioxidant capacity against peroxyl radicals (ACAP), total glutathione (GSHt) concentration, reduced (GSH) and oxidized (GSSG) glutathione ratio (GSH/GSSG), lipid peroxidation (LPO) and protein carbonyl group (PC) levels. ACAP was increased in hydrocorals after 16 d of exposure to intermediate levels of seawater acidification. GSHt and GSH/GSSG did not change over the experimental period. LPO was increased at any level of seawater acidification, while PC content was increased in hydrocorals exposed to intermediate and severe seawater acidification for 30 d. These findings indicate that the antioxidant defense system of M. alcicornis is capable of coping with acidic conditions for a short period of time (16 d). Additionally, they clearly show that a long-term (30 d) exposure to seawater acidification induces oxidative stress with consequent oxidative damage to lipids and proteins, which could compromise hydrocoral health.

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Alkalinity, inorganic carbon and CO2 flux variability during extreme rainfall years (2010-2011) in two polluted tropical estuaries NE Brazil

Published 18 June 2018 Science Closed
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The susceptibility of coastal environments to shifts in the biogeochemical cycles of carbon and nutrients driven by anthropogenic pressure and climate change is a real challenge for the scientific community. This paper evaluated the effects of an extreme rainfall event over the nutrients and carbonate parameters in two polluted tropical estuaries. Surface water samples were taken seasonally along a salinity gradient in the Capibaribe and Barra de Jangadas estuaries in order to investigate the spatial and seasonal variability of dissolved nutrients, chlorophyll-a, dissolved oxygen, total alkalinity, inorganic carbon, partial pressure of CO2 (pCO2) and CO2 fluxes. The increased riverine influence caused by the fluvial flooding during the extremely rainy season augmented the nitrogen concentrations in the plumes, which also presented reduced salinity, alkalinity and dissolved oxygen values. In the Capibaribe plume it has also shifted the mean CO2 flux value of – 4.01 mmolC m-2 d-1 during the dry season, to a positive mean flux of + 5.7 mmolC m-2 d-1 during the rainy season. Within the estuaries the BOD5,20 and dissolved phosphorus values were higher during the dry season (p<0.0001), they showed positive correlation with the phytoplanktonic blooms that reached a chl-a value of 85 mg m-3 in the Capibaribe. The high alkalinity found in both estuaries, with mean values between dry and wet seasons respectively from 1808 to 1373 µmol kg-1 in the Capibaribe estuary and 1616 to 1058 µmol kg-1 in Barra de Jangadas estuary, may act as a buffer to the process of coastal acidification due to eutrophication. The increased rivers discharge lead to a greater transport of organic matter and nutrients to the coast, decreasing the oxygen availability and shifting the metabolic status of the estuarine plume to heterotrophic, whereas increased the water quality within the estuaries due the flushing promoted by the extreme rainfall event.

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Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean

Published 25 April 2018 Science Closed
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Highlights

• In a future scenario, attenuation by DOM outcompetes its physico-chemical role.
• Global change conditions will favor growth and photosynthesis of nanoplankton.
• Global change favors growth and photosynthesis of nano- as compared to microplankton.

Abstract

We evaluated the dual role of DOM (i.e., as a source of inorganic nutrients and as an absorber of solar radiation) on a phytoplankton community of the western South Atlantic Ocean. Using a combination of microcosms and a cluster approach, we simulated the future conditions of some variables that are highly influenced by global change in the region. We increased nutrients (i.e., anthropogenic input) and dissolved organic matter (DOM), and we decreased the pH, to assess their combined impact on growth rates (μ), species composition/abundance and size structure, and photosynthesis (considering in this later also the effects of light quality i.e., with and without ultraviolet radiation). We simulated two Future conditions (Fut) where nutrients and pH were similarly manipulated, but in one the physical role of DOM (Futout) was assessed whereas in the other (Futin) the physico-chemical role was evaluated; these conditions were compared with a control (Present condition, Pres). The μ significantly increased in both Fut conditions as compared to the Pres, probably due to the nutrient addition and acidification in the former. The highest μ were observed in the Futout, due to the growth of nanoplanktonic flagellates and diatoms. Cells in the Futin were photosynthetically less efficient as compared to those of the Futout and Pres, but these physiological differences, also between samples with or without solar UVR observed at the beginning of the experiment, decreased with time hinting for an acclimation process. The knowledge of the relative importance of both roles of DOM is especially important for coastal areas that are expected to receive higher inputs and will be more acidified in the future.

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Influence of ocean acidification on elemental mass balances and particulate organic matter stoichiometry in natural plankton communities  

Published 26 March 2018 Science Closed
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The oceanic uptake of anthropogenic CO2 leads to a gradual acidification of the ocean. Ocean acidification (OA) is known to affect marine biota from the organism to the ecosystem level but with largely unknown consequences for the cycling of key elements such as carbon, nitrogen, and phosphorus. However, the ocean’s ability to absorb anthropogenic carbon or to provide sufficient food for humankind depends on these oceanic material cycles. This doctoral dissertation thus aimed to assess the influence of OA on biogeochemical cycles of elements in natural pelagic food webs of several trophic levels (up to fish larvae) over extended time scales of weeks to months. Large-scale pelagic mesocosms (up to 75 m3 per unit) were deployed in different marine ecosystems and new methods were developed to quantify the downward flux of particulate organic matter under simulated OA. This thesis reports on the potential influence of OA on element pool partitioning and particulate organic matter stoichiometry with consequences for biogeochemical cycling of elements in the ocean. Furthermore the potential and limitations of biogeochemical measurements inside pelagic mesocosms that host entire plankton communities are elucidated.

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Population biology of the sea star Anasterias minuta (Forcipulatida: Asteriidae) threatened by anthropogenic activities in rocky intertidal shores of San Matías Gulf, Patagonia, Argentina

Published 15 December 2017 Science Closed
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 In Patagonian coastal areas, intertidal benthic communities are exposed to extreme physical conditions. The interaction between harsh environment and anthropogenic pressure can generate changes in population biology of marine invertebrates, like density and reproduction. The oral brooding sea star Anasterias minuta is a key organism in food chains of Atlantic Patagonian rocky intertidals, hence changes on its population structure can negatively affect shore communities. We studied the population biology of A. minuta and assess the effect of environmental parameters and anthropogenic activities on its population on rocky intertidal shores of San Matías Gulf, Patagonia, Argentina. Seasonal sea surface temperature, pH, salinity, water velocity, desiccation rate, boulders density, and anthropogenic influence (tourists and octopus fishermen) were recorded. In sites with less tourist influence and high refuge, an increase in density was recorded, especially during the summer. Brooding individuals were found in fall and winter, while feeding individuals were observed in all seasons (12 different prey, mainly the molluscs Tegula patagonica and Perumytilus purpuratus). Environmental variables such as boulders density and water velocity were the most important predictor of variation in population structure. Tourism and pH were the most important variables negatively correlated with density.

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Native and exotic oysters in Brazil: comparative tolerance to hypercapnia

Published 21 November 2017 Science Closed
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Highlights

• C. gigas and C. brasiliana showed differentiated biochemical response to hypercapnia.
• Juveniles presented a more pronounced stress response than adults in both species.
• Contrasting metabolic shifts were observed between both species to endure hypercapnia.
• Antioxidant and metabolic responses were sufficient to prevent excessive LPO.
Abstract

Environmental hypercapnia in shallow coastal marine ecosystems can be exacerbated by increasing levels of atmospheric CO2. In these ecosystems organisms are expected to become increasingly subjected to pCO2 levels several times higher than those inhabiting ocean waters (e.g.: 10,000 µatm), but still our current understanding on different species capacity to respond to such levels of hypercapnia is limited. Oysters are among the most important foundation species inhabiting these coastal ecosystems, although natural oyster banks are increasingly threatened worldwide. In the present study we studied the effects of hypercapnia on two important oyster species, the pacific oyster C. gigas and the mangrove oyster C. brasiliana, to bring new insights on different species response mechanisms towards three hypercapnic levels (ca. 1,000; 4,000; 10,000 µatm), by study of a set of biomarkers related to metabolic potential (electron transport system – ETS), antioxidant capacity (SOD, CAT, GSH), cellular damage (LPO) and energetic fitness (GLY), in two life stages (juvenile and adult) after 28 days of exposure.

Results showed marked differences between each species tolerance capacity to hypercapnia, with contrasting metabolic readjustment strategies (ETS), different antioxidant response capacities (SOD, CAT, GSH), which generally allowed to prevent increased cellular damage (LPO) and energetic impairment (GLY) in both species. Juveniles were more responsive to hypercapnia stress in both congeners, and are likely to be most sensitive to extreme hypercapnia in the environment. Juvenile C. gigas presented more pronounced biochemical alterations at intermediate hypercapnia (4,000 µatm) than C. brasiliana. Adult C. gigas showed biochemical alterations mostly in response to high hypercapnia (10,000 µatm), while adult C. brasiliana were less responsive to this environmental stressor, despite presenting decreased metabolic potential.

Our data bring new insights on the biochemical performance of two important oyster species, and suggest that the duration of extreme hypercapnia events in the ecosystem may pose increased challenges for these organisms as their tolerance capacity may be time limited.

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Aragonite saturation state in a tropical coastal embayment dominated by phytoplankton blooms (Guanabara Bay – Brazil)

Published 16 November 2017 Science Closed
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Highlights

  • The spatio-temporal variations of Ωarag were studied in a highly polluted coastal embayment.
  • High values of Ωarag were prevalent in surface waters dominated by phytoplankton blooms.
  • Lowest values of Ωarag were restricted to poorly buffered waters that receive direct effluent discharges.
  • Variations of Ωarag related to biological processes override those related to the atmospheric CO2.

Abstract

The dynamics of the aragonite saturation state (Ωarag) were investigated in the eutrophic coastal waters of Guanabara Bay (RJ-Brazil). Large phytoplankton blooms stimulated by a high nutrient enrichment promoted the production of organic matter with strong uptake of dissolved inorganic carbon (DIC) in surface waters, lowering the concentrations of dissolved carbon dioxide (CO2aq), and increasing the pH, Ωarag and carbonate ion (CO32 −), especially during summer. The increase of Ωarag related to biological activity was also evident comparing the negative relationship between the Ωarag and the apparent utilization of oxygen (AOU), with a very close behavior between the slopes of the linear regression and the Redfield ratio. The lowest values of Ωarag were found at low-buffered waters in regions that receive direct discharges from domestic effluents and polluted rivers, with episodic evidences of corrosive waters (Ωarag < 1). This study showed that the eutrophication controlled the variations of Ωarag in Guanabara Bay.

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How fast is the Patagonian shelf-break acidifying?

Published 13 November 2017 Science Closed
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Highlights

• Carbonate system has been driven by dilution/evaporation and sea–air CO2 exchanges.
• The Patagonian shelf is a key area of anthropogenic carbon uptake.
• SACW is acidifying faster in the Patagonian shelf-break than in the South Atlantic.
• AAIW is under risk for aragonite undersaturation near the Patagonian shelf-break.

Abstract

Anthropogenic carbon (Cant) concentration is determined according to the TrOCA method, from carbonate system data and hydrographic parameters collected during two consecutive spring cruises (2007 and 2008) in the Argentinean Patagonian shelf-break zone between 36°S and 50°S. Cant has intruded the water column until intermediate depths, with no Cant below 1000 m, in the deeper waters (i.e., North Atlantic Deep Water and Antarctic Bottom Water) of the Northern sector of the study area (i.e., North of 38°S). The higher Cant concentration is observed in Subantarctic Shelf Water in the Southern region, whereas in the Northern sector both Tropical Water and South Atlantic Central Water are equally affected by Cant intrusion. The Antarctic Intermediate Water represents the depth-limit achieved by Cant penetration, reinforcing the role that this water mass plays as an important vehicle to transport Cant to the oceans interior. The estimated Cant average (± method precision) is 46.6 ± 5.3 μmol kg− 1, considering the full depth of the water column. The ocean acidification state (ΔpH) shows an average (± standard deviation) of − 0.11 ± 0.05, thus, indicating an annual pH reduction of − 0.0010 yr− 1 since the Industrial Revolution (c.a. 1750). The degree of aragonite saturation is lowered towards undersaturation levels of calcite. The Patagonian shelf and shelf-break zones—a strong CO2 sink region in the global ocean—are likely a key area for Cant intrusion in the southwestern South Atlantic Ocean.

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The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt (update)

Published 10 November 2017 Science Closed
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The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Samples for phytoplankton enumeration were collected from the upper mixed layer (30 m) during two cruises, the first to the South Atlantic sector (January–February 2011; 60° W–15° E and 36–60° S) and the second in the South Indian sector (February–March 2012; 40–120° E and 36–60° S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Subtropical, Polar, and Subantarctic fronts. The influence of environmental parameters, such as sea surface temperature (SST), salinity, carbonate chemistry (pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macronutrients (nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB was assessed statistically. Nanophytoplankton (cells 2–20 µm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, with the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, F. pseudonana, and Pseudo-nitzschia spp. as the most numerically dominant and widely distributed. A combination of SST, macronutrient concentrations, and pCO2 provided the best statistical descriptors of the biogeographic variability in biomineralizing species composition between stations. Emiliania huxleyi occurred in silicic acid-depleted waters between the Subantarctic Front and the Polar Front, a favorable environment for this species after spring diatom blooms remove silicic acid. Multivariate statistics identified a combination of carbonate chemistry and macronutrients, covarying with temperature, as the dominant drivers of biomineralizing nanoplankton in the GCB sector of the Southern Ocean.

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Seasonal pH and carbondioxide level as indicator of vulnerability of fresh and marine aquatic systems to climate change in Nigeria

Published 28 August 2017 Science Closed
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Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans; raising concern over the current and future effects it may have on world climates. Certain changes are already evident but the impact of these changes on marine and coastal living resources is only poorly understood at this stage, particularly in sub-Saharan Africa. This study assessed seasonal dissolved carbon dioxide and pH of fresh and marine aquatic systems in Nigeria. Dissolved CO2 was non-significantly (p=0.07) higher in freshwater during the wet season (20±7ppm) compared to dry season (15 ± 1ppm), while in the marine system, dissolved CO2 level was significantly (p=0.02) higher (42±6ppm) during the dry season compared to the rainy season (31±5ppm). Mean pH values was significantly higher (p=0.003 and 0.05) in freshwater (6.8±0.8 and 6.9±0.2ppm) relative to marine (6.2±0.2 and 6.5±0.3ppm) during wet and dry seasons, respectively. The pH values were generally at the borderline of the acidic limit of the recommended pH values for aquaculture (6.5-9) during the two seasons. Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to a greater CO2 uptake by the oceans, acidification and consequently, saturation, thereby affecting the ocean’s continued ability to store CO2. This study therefore provides preliminary information on seasonal changes in CO2 and pH of fresh and marine systems in Nigeria; and their potential impacts on global climate and aquatic ecosystems.

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Assessment of the environmental impacts of ocean acidification (OA) and carbon capture and storage (CCS) leaks using the amphipod Hyale youngi

Published 16 August 2017 Science Closed
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This study aims to ascertain the effects of CO2 induced water acidification and leaks from Carbon Capture and Storage activities on the South American amphipod Hyale youngi. A 10-day acute toxicity test was performed using sediments from two sites located inside the Santos Estuarine System. They were subjected to five pH treatments (8.1, 7.6, 7.0, 6.5, and 6.0). Metals (Cd, Cu, Cr, Pb, Ni and Zn) and the metalloid As were analyzed to determine the influence of their acidification-related mobility on the amphipods mortality. The results showed that mortality becomes significant when compared to control in pH 6.5 in the Canal de Piaçaguerasediment (contaminated) and at pH 6.0 in Ilha das Palmas sediment (reference).

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Time series pCO2 at a coastal mooring: internal consistency, seasonal cycles, and interannual variability

Published 6 July 2017 Science Closed
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Marine carbonate system monitoring programs often consist of multiple observational methods that include underway cruise data, moored autonomous time series, and discrete water bottle samples. Monitored parameters include all, or some of the following: partial pressure of CO2 of the water (pCO2w) and air, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH. Any combination of at least two of the aforementioned parameters can be used to calculate the others. In this study at the Gray’s Reef (GR) mooring in the South Atlantic Bight (SAB) we: examine the internal consistency of pCO2wfrom underway cruise, moored autonomous time series, and calculated from bottle samples (DIC-TA pairing); describe the seasonal to interannual pCO2w time series variability and air-sea flux (FCO2), as well as describe the potential sources of pCO2wvariability; and determine the source/sink for atmospheric pCO2. Over the ~8.5 years of GR mooring time series, mooring-underway and mooring-bottle calculated-pCO2wstrongly correlate with r-values > 0.90. pCO2w and FCO2 time series follow seasonal thermal patterns; however, seasonal non-thermal processes, such as terrestrial export, net biological production, and air-sea exchange also influence variability. The linear slope of time series pCO2w increases by 5.2±1.4 µatm y−1 with FCO2 increasing 51 to 70 mmol m−2 y−1. The net FCO2 sign can switch interannually with the magnitude varying greatly. Non-thermal pCO2w is also increasing over the time series, likely indicating that terrestrial export and net biological processes drive the long term pCO2w increase.

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Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification

Published 28 June 2017 Science Closed
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The effects of ultraviolet radiation (UVR) under future expected conditions of acidification and increase in nutrient inputs were studied on a post-bloom phytoplankton and bacterioplankton community of Patagonian coastal waters. We performed an experiment using microcosms where two environmental conditions were mimicked using a cluster approach: present (ambient nutrients and pH) and future (increased nutrients and acidification), and acclimating the samples for five days to two radiation treatments (full solar radiation [+UVR] and exclusion of UVR [–UVR]). We evaluated the short-term (hours) sensitivity of the community to solar UVR through chlorophyll afluorescence parameters (e.g. the effective photochemical quantum yield of PSII [ΦPSII]) at the beginning, at the mid-point and at the end of the acclimation period. Primary production and heterotrophic bacterial production (HBP) were determined, and biological weighting functions were calculated, at the beginning and at the end of the acclimation period. Mid-term effects (days) were evaluated as changes in taxonomic composition, growth rates and size structure of the community. Although the UVR-induced inhibition on ΦPSII decreased in both clusters, samples remained sensitive to UVR after the 5 days of acclimation. Also, under the future conditions, there was, in general, an increase in the phytoplankton carbon incorporation rates along the experiment as compared to the present conditions. Bacterioplankton sensitivity to UVR changed along the experiment from inhibition to enhancement of HBP, and future environmental conditions stimulated bacterial growth, probably due to indirect effects caused by phytoplankton. Those changes in the microbial loop functioning and structure under future global change conditions might have important consequences for the carbon pump and thus for the carbon sequestration and trophodynamics of Patagonian coastal waters.

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Combined effects of sea water acidification and copper exposure on the symbiont-bearing foraminifer Amphistegina gibbosa

Published 22 June 2017 Science Closed
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Coral reefs are threatened by global and local stressors such as ocean acidification and trace metal contamination. Reliable early warning monitoring tools are needed to assess and monitor coral reef health. Symbiont-bearing foraminifers (Amphistegina gibbosa) were kept under ambient conditions (no sea water acidification and no copper addition) or exposed to combinations of different levels of sea water pH (8.1, 7.8, 7.5 and 7.2) and environmentally relevant concentrations of dissolved copper (measured: 1.0, 1.6, 2.3 and 3.2 µg L−1) in a mesocosm system. After 10- and 25-d exposure, foraminifers were analyzed for holobiont Ca2+-ATPase activity, bleaching, growth and mortality. Enzyme activity was inhibited in foraminifers exposed to pH 7.2 and 3.2 µg L−1 Cu for 25 d. Bleaching frequency was also higher at pH 7.2 combined with copper addition. There was no significant effect of sea water acidification and copper addition on mortality. However, test size was smaller in foraminifers exposed to copper, with a positive interactive effect of sea water acidification. These findings can be explained by the higher availability of free copper ions at lower water pH. This condition would increase Cu competition with Ca2+ for the binding sites on the organism, thus inhibiting Ca2+-ATPase activity and affecting the organism’s overall fitness. Findings reported here suggest that key processes in A. gibbosa, such as calcification and photosynthesis, are affected by the combined effect of global (sea water acidification) and local (copper contamination) stressors. Considering the experimental conditions employed (mesocosm system, possible ocean acidification scenarios, low copper concentrations, biomarkers of ecological relevance and chronic exposure), our findings support the use of foraminifera and biomarkers analyzed in the present study as reliable tools to detect and monitor the ecological impacts of multiple stressors in coral reef environments.

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