Posts Tagged 'South Atlantic'

Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins

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.

Continue reading ‘Environmental factors influencing benthic communities in the oxygen minimum zones on the Angolan and Namibian margins’

Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)

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.

Continue reading ‘Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)’

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

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.

Continue reading ‘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’

Ecotoxicological responses of a reef calcifier exposed to copper, acidification and warming: a multiple biomarker approach

Highlights

• Copper increased bleaching, respiration and inhibited calcification-related enzymes.

• Thermal stress was the main driver of mortality.

• Relative tolerance to climate change scenario (ocean warming + acidification).

• Integrated biomarker response related more to co-exposures than isolated biomarkers.

• Integrated analysis showed higher stress under climate change + copper condition.

Abstract

Multiple global and local stressors threat coral reefs worldwide, and symbiont-bearing foraminifera are bioindicators of reef health. The aim of this study was to investigate single and combined effects of copper (Cu) and climate change related stressors (ocean acidification and warming) on a symbiont-bearing foraminifer by means of an integrated biomarker analysis. Using a mesocosm approach, Amphistegina gibbosa were exposed for 25 days to acidification, warming and/or Cu contamination on a full orthogonal design (two levels each factor). Cu was the main factor increasing bleaching and respiration rates. Warming was the main cause of mortality and reduced growth. Calcification related enzymes were inhibited in response to Cu exposure and, in general, the inhibition was stronger under climate change. Multiple biological endpoints responded to realistic exposure scenarios in different ways, but evidenced general stress posed by climate change combined with Cu. These biological responses drove the high values found for the ‘stress index’ IBR (Integrated Biomarker Response) – indicating general organismal health impairment under the multiple stressor scenario. Our results provide insights for coral reef management by detecting potential monitoring tools. The ecotoxicological responses indicated that Cu reduces the tolerance of foraminifera to climate change (acidification + warming). Once the endpoints analysed have a high ecological relevance, and that responses were evaluated on a classical reef bioindicator species, these results highlight the high risk of climate change and metal pollution co-exposure to coral reefs. Integrated responses allowed a better effects comprehension and are pointed as a promising tool to monitor pollution effects on a changing ocean.

Continue reading ‘Ecotoxicological responses of a reef calcifier exposed to copper, acidification and warming: a multiple biomarker approach’

Control of CaCO3 dissolution at the deep seafloor and its consequences

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

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

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.

Continue reading ‘Water acidification causes death of marine ornamental fish (Perciformes: Pomacentridae) during transport: contributing to the conservation of wild populations’


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Ocean acidification in the IPCC AR5 WG II

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