This study examined the carbon cycling dynamics in the tropical Atlantic Ocean from 1985 to 2023, focusing on factors influencing the surface partial pressure of CO2 (pCO2), freshwater input, total alkalinity (ALK), total dissolved carbon (TCO2), and pH levels. The time series data revealed significant trends, with average pCO2 concentrations rising from approximately 350 μatm in the early 1990s to over 400 μatm by 2023. The TCO2 levels increased from about 2000 μmol/kg to 2200 μmol/kg, while ALK rose from approximately 2300 μmol/kg to 2500 μmol/kg. This increase highlights the ocean’s role as a carbon sink, particularly in areas with high biological productivity and upwelling where TCO2 also rose. This study employed Empirical Orthogonal Functions (EOFs) to identify variability modes and understand spatial patterns of pCO2. Freshwater dynamics significantly affect TCO2 concentrations, particularly in coastal regions, where pH can shift from 8.2 to 7.9, exacerbating acidification. Rising sea surface temperatures have been linked to elevated pCO2 values. These findings support the need for ongoing monitoring and effective management strategies to mitigate the impacts of climate change and ensure the sustainability of marine resources. This study documented the long-term trends in tropical Atlantic CO2 parameters linked to the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO).
Continue reading ‘Interannual and seasonal variability of CO2 parameters in the tropical Atlantic Ocean’Posts Tagged 'South Atlantic'
Interannual and seasonal variability of CO2 parameters in the tropical Atlantic Ocean
Published 11 December 2024 Science ClosedTags: chemistry, field, South Atlantic
Major threats to rhodolith beds: ocean acidification, global warming, and local stressors
Published 6 December 2024 Science ClosedTags: algae, biological response, BRcommunity, physiology, review, South Atlantic
Since the industrial revolution, the human population has accelerated its magnitude of impact on the world’s oceans. The observed consequences of our rising population and globalization have expanded substantially and are expected to affect even the deepest ecosystems. The extensive rhodolith beds along the Brazilian coastline that are present from the shallows down to 133 m are predicted and already observed to suffer from the consequences of human interference. Rhodolith beds are predicted to experience a daunting diversity of anthropogenic threats, which act at different scales. Global stressors such as ocean acidification and global climate change are shown to affect fundamental metabolic processes, which over time are expected to jeopardize the integrity of these ecosystems. Local stressors such as nutrient runoff, pollution, oil/gas exploitation, predatory fishing as bottom trawling, and direct coralline mining are expected to interact with global stressors and, in multiple cases, exacerbate already negative prognosis.
Continue reading ‘Major threats to rhodolith beds: ocean acidification, global warming, and local stressors’Sea-air CO2 exchanges, pCO2 drivers and phytoplankton communities in the southwestern South Atlantic Ocean during spring
Published 3 December 2024 Science ClosedTags: biological response, chemistry, community composition, field, otherprocess, phytoplankton, respiration, South Atlantic
Highlights
- The southwestern Brazilian margin behaved as a weak CO2 outgassing zone in austral spring of 2014.
- Haptophytes were conspicuous along the entire study area, while Trichodesmium was prominent at SBB and diatoms at SBS.
- CaCO3 production was observed at SBB, whereas seawater dilution dominated the changes of sea surface pCO2 at SBS.
- Nitrification by Trichodesmium likely allowed increased contribution of haptophytes seen at open ocean oligotrophic waters.
- Net respiration was the main biogeochemical process regulating sea-air CO2 exchanges in the study area.
Abstract
Hydrographic properties and carbon dioxide partial pressure (pCO2) were measured through underway survey of surface waters during spring 2014, mainly along the Surface Haline Front in the continental shelf-break domain in the southwestern South Atlantic Ocean margin. Additionally, discrete seawater surface samples were collected along the ship track to identify the phytoplankton community and measure seawater chemical properties. This study aims to identify the drivers of the marine CO2‑carbonate chemistry and the role played by the phytoplankton composition on changes in the surface marine carbonate properties and the sea-air CO2 exchanges in two biogeochemical provinces (i.e., South Brazil Bight – SBB, and Southern Brazilian Shelf – SBS) governed by the dynamics of the Brazil Current system in the South Atlantic Ocean. The water masses identified on the surface of the region were Tropical Water (mostly present at offshore regions), Subtropical Shelf Water (mostly present over the continental shelf and slope), and Plata Plume Water (present in the south coastal domain of the SBS). On average, the study area behaved as a weak net CO2 outgassing zone of 1.2 ± 2.3 mmol m−2 d−1 during the spring, despite some subregions behaving as CO2 ingassing zones. The CO2 uptake verified in the SBB was related with mesoscale activity bringing cold waters in the region while CO2 uptake in the continental shelf domain of SBS was associated with the presence of cooler and fresher Plata Plume Water. Changes in total alkalinity and dissolved inorganic carbon at surface were mainly governed by CaCO3 production in SBB and seawater dilution in SBS, although other processes may also have influenced on their spatial variability. The dominant phytoplankton groups were haptophytes (31 %), Trichodesmium (21 %), and picocyanobateria (28 %), corresponding to Synechococcus (17 %) and Prochlorococcus (11 %). The dominance of the diatom group was associated with a decrease in sea surface pCO2 (mainly at coastal zones at southern areas), although the sea-air CO2 exchanges were regulated by cooling process due the presence of Plata Plume Water in that region. Changes in surface pH were related to high concentration of Trichodesmium slicks at offshore zones with the highest microalgae concentration, leading to pH drops of up to 0.4. Trichodesmium slicks likely allowed the development of haptophytes in offshore oligotrophic waters due to its role on N2 fixation. An increase of ∼20 % in the dominance of haptophytes contribution was verified in that situation, which was likely in a post-bloom development stage, since an increased dissolved inorganic carbon content was observed, associated with a prevalence of net respiration processes.
Continue reading ‘Sea-air CO2 exchanges, pCO2 drivers and phytoplankton communities in the southwestern South Atlantic Ocean during spring’Ecophenotypic variation in a cosmopolitan reef-building coral suggests reduced deep-sea reef growth under ocean change
Published 7 November 2024 Science ClosedTags: biological response, communitymodeling, corals, field, Mediterranean, modeling, morphology, North Atlantic, South Atlantic
Sensitivity of reef-building corals to environmental factors has far-reaching ecosystem implications, especially in the limited number of cold-water coral (CWC) species that form reefs in the deep sea. Understanding CWC responses to large-scale oceanographic variation in their natural habitat can elucidate their sensitivity to global anthropogenic stressors. Here, we use skeletal samples to analyse fine-scale phenotypic variation in the widespread reef-building CWC Desmophyllum pertusum (Lophelia pertusa) in relation to broad physicochemical gradients in different sites across the Atlantic Ocean and Mediterranean Sea. We find evidence, amidst local and regional differentiation, of species-wide growth responses to physicochemical factors, mainly affecting corallite length, width and their ratio (slenderness). Our results suggest that higher temperature and lower oxygen levels negatively affect skeletal linear extension and budding rate of polyps. As also hinted by the reduced corallite length and slenderness in less developed reefs, these widespread responses may lead to a general decline in CWC reef growth rates as a long-term consequence of ocean warming and deoxygenation. Given this relevance, such responses can be used to model reef growth in a changing ocean.
Continue reading ‘Ecophenotypic variation in a cosmopolitan reef-building coral suggests reduced deep-sea reef growth under ocean change’“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle
Published 7 October 2024 Science ClosedTags: algae, biological response, calcification, primary production, South Atlantic
Current evidence suggests that macroalgal-dominated habitats are important contributors to the oceanic carbon cycle, though the role of those formed by calcifiers remains controversial. Globally distributed coralline algal beds, built by pink coloured rhodoliths and maerl, cover extensive coastal shelf areas of the planet, but scarce information on their productivity, net carbon flux dynamics and carbonate deposits hampers assessing their contribution to the overall oceanic carbon cycle. Here, our data, covering large bathymetrical (2–51 m) and geographical ranges (53°N–27°S), show that coralline algal beds are highly productive habitats that can express substantial carbon uptake rates (28–1347 g C m−2 day−1), which vary in function of light availability and species composition and exceed reported estimates for other major macroalgal habitats. This high productivity, together with their substantial carbonate deposits (0.4–38 kilotons), renders coralline algal beds as highly relevant contributors to the present and future oceanic carbon cycle.
Continue reading ‘“Pink power”—the importance of coralline algal beds in the oceanic carbon cycle’pH distributions and determining processes along the U.S. East Coast
Published 16 September 2024 Science ClosedTags: chemistry, field, North Atlantic, South Atlantic
pH is a key index in ocean biogeochemical and acidification research. However, there remains a limited understanding of the spatial patterns and drivers of pH across different coastal oceans. In this study, we present the distribution of spectrophotometric pHT (in total proton scale) from a synoptic summer cruise in 2018. We examine the processes controlling pHT along the U.S. East Coast, covering the South Atlantic Bight (SAB), Mid-Atlantic Bight (MAB), and Gulf of Maine (GoM). Our findings reveal a continuous low pHT band associated with the oxygen minimum and CO2 maximum zone along the slope of the entire east coast, extending from the bottom layer (∼1,000 m) in the SAB to the middle layer (300–500 m) in the MAB and GoM. We also identified unique low pHT features in each subregion, including an onshore upwelling of the low pHT slope water in the SAB, a seasonal low pHT feature on the bottom of the MAB shelf associated with the Cold Pool water, and an inflow of low pHT slope water to the bottom of the GoM. Our findings suggest that net biological production plays a prominent role in regulating sea-surface pHT, driving it away from the air-sea equilibrated pHT and mitigating the pHT decrease caused by the anthropogenic carbon dioxide (CO2) uptake. Furthermore, net biological respiration dominates the interior pHT distributions. Our analysis provides new insights and establishes a foundation for interpreting future pH changes in response to processes such as water masses shifting, ocean warming, and anthropogenic carbon uptake in coastal oceans.
Key Points
- The subsurface pH minimum layer extends from the slope bottom in the south to the middle layer of the slope in the north
- Each subregion has a distinct low-pH feature, including onshore upwelling, Cold Pool water, and Gulf bottom water
- Surface pH deviates from air-sea gas equilibrium due to net biological production, while interior ocean pH is dominated by respiration
Plain Language Summary
Given that pH is a crucial index for assessing ocean acidification, understanding pH distribution patterns and its controlling factors in coastal oceans is essential. This study investigates pH from a summer 2018 cruise along the entire U.S. East Coast. We found that the surface-water pH deviates from the atmospheric equilibrium, primarily due to net biological production. Subsurface pH patterns are also mainly controlled by biological factors. Along the slope, a continuous low pH band is associated with the oxygen minimum zone, extending from the bottom in the SAB to the middle depth in the MAB and GoM. On the shelf, each subregion has unique subsurface low pH features, including a shoreward upwelling of the low pH slope water in the SAB, a seasonal low pH feature in the MAB Cold Pool, and an inflow of low pH slope water in the bottom of GoM. This research provides new insights into the processes controlling pH distribution and lays a foundation for interpreting current and future pH decadal trends in the context of climate change.
Continue reading ‘pH distributions and determining processes along the U.S. East Coast’Organic matter decay and bacterial community succession in mangroves under simulated climate change scenarios
Published 24 July 2024 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, laboratory, molecular biology, morphology, otherprocess, physiology, prokaryotes, sediment, South Atlantic
Mangroves are coastal environments that provide resources for adjacent ecosystems due to their high productivity, organic matter decomposition, and carbon cycling by microbial communities in sediments. Since the industrial revolution, the increase of Greenhouse Gases (GHG) released due to fossil fuel burning led to many environmental abnormalities such as an increase in average temperature and ocean acidification. Based on the hypothesis that climate change modifies the microbial diversity associated with decaying organic matter in mangrove sediments, this study aimed to evaluate the microbial diversity under simulated climate change conditions during the litter decomposition process and the emission of GHG. Thus, microcosms containing organic matter from the three main plant species found in mangroves throughout the State of São Paulo, Brazil (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) were incubated simulating climate changes (increase in temperature and pH). The decay rate was higher in the first seven days of incubation, but the differences between the simulated treatments were minor. GHG fluxes were higher in the first ten days and higher in samples under increased temperature. The variation in time resulted in substantial impacts on α-diversity and community composition, initially with a greater abundance of Gammaproteobacteria for all plant species despite the climate conditions variations. The PCoA analysis reveals the chronological sequence in β-diversity, indicating the increase of Deltaproteobacteria at the end of the process. The GHG emission varied in function of the organic matter source with an increase due to the elevated temperature, concurrent with the rise in the Deltaproteobacteria population. Thus, these results indicate that under the expected climate change scenario for the end of the century, the decomposition rate and GHG emissions will be potentially higher, leading to a harmful feedback loop of GHG production. This process can happen independently of an impact on the bacterial community structure due to these changes.
Continue reading ‘Organic matter decay and bacterial community succession in mangroves under simulated climate change scenarios’Trends and drivers of CO2 parameters, from 2006 to 2021, at a time-series station in the Eastern Tropical Atlantic (6°S, 10°W)
Published 27 March 2024 Science ClosedTags: chemistry, methods, modeling, regionalmodeling, South Atlantic
The seawater fugacity of CO2 (fCO2) has been monitored hourly at an instrumented mooring at 6°S, 10°W since 2006. The mooring is located in the South Equatorial Current and is affected by the equatorial Atlantic cold tongue. This site is characterized by large seasonal sea surface temperature variations (>4°C). The fCO2 is measured by a spectrophotometric sensor deployed at about 1.5 meters deep. Measurements of seawater fCO2, sea surface temperature (SST) and sea surface salinity (SSS) are used to calculate total dissolved inorganic carbon (TCO2) and pH. Total alkalinity (TA) is calculated using an empirical relationship with SSS determined for this region. Satellite chlorophyll-a concentrations at 6°S, 10°W are low (<0.2 mg m-3) but some peaks over 0.8 mg m-3 are sometimes detected in August. Nevertheless, the site is a permanent source of CO2 to the atmosphere, averaging 4.7 ± 2.4 mmol m-2d-1 over 2006-2021. Despite the weakening of the wind, the CO2 flux increases significantly by 0.20 ± 0.05 mmol m-2d-1 yr-1. This suggests that the source of CO2 is increasing in this region. This is explained by seawater fCO2 increasing faster than the atmospheric increase during 2006-2021. Most of the seawater fCO2 increase is driven by the increase of TCO2, followed by SST. The fCO2 increase leads to a pH decrease of -0.0030 ± 0.0004 yr-1. The SST anomalies (SSTA) at 6°S, 10°W are correlated to the Tropical Southern Atlantic (TSA) index and to the Atlantic 3 region (ATL3) index with a correlation coefficient higher than 0.75. The strong positive phase of both ATL3 and TSA, observed towards the end of the time-series, is likely contributing to the strong increase of seawater fCO2.
Continue reading ‘Trends and drivers of CO2 parameters, from 2006 to 2021, at a time-series station in the Eastern Tropical Atlantic (6°S, 10°W)’Fouling communities from the South African west coast are vulnerable to cooling and ocean acidification
Published 15 March 2024 Science ClosedTags: abundance, annelids, biological response, BRcommunity, bryozoa, chordata, community composition, crustaceans, fish, mollusks, multiple factors, otherprocess, prokaryotes, South Atlantic, temperature
Changing temperature and ocean acidification are well-recognised consequences of climate change in marine systems. In contrast to global trends, the South African west coast is experiencing cooling due to increased frequency and intensity of upwelling. The implications of concurrent cooling and acidification for marine biota are poorly understood, particularly at the community level. This laboratory study assessed how cooling and acidification might affect fouling communities along the South African west coast. Communities were experimentally exposed to two temperatures, 13℃ (current) and 9℃ (cooling), and three pH treatments, 7.9 (current), 7.6 and 7.4, for 18 days. Cooling and acidification altered community structure. Species diversity declined in response to acidification but was not affected by cooling. This was driven by greatest loss of species at 7.4 pH. Notably, acidification reduced the abundance of both calcifying and soft-bodied taxa, highlighting the vulnerability of taxa like ascidians to acidification. Overall, these results highlight the dominant threat posed by acidification, even for alien taxa that are often perceived as resilient to climate change. Additionally, in regions experiencing cooling, acidification may pose a greater threat to fouling communities than thermal changes.
Continue reading ‘Fouling communities from the South African west coast are vulnerable to cooling and ocean acidification’The impact of extreme weather events exceeds those due to global-change drivers on coastal phytoplankton assemblages
Published 1 March 2024 Science ClosedTags: abundance, biological response, BRcommunity, community composition, flow, laboratory, light, multiple factors, nutrients, otherprocess, photosynthesis, phytoplankton, South Atlantic, temperature
Highlights
- Extreme wind and rainfall events have become frequent phenomena in coastal ecosystems.
- We simulated these events under global change for five phytoplankton assemblages.
- Extreme events were responsible for the bulk of variability on photosynthesis efficiency.
- The impact of extreme events is low in assemblages with high diversity and evenness
- Extreme events should be considered in global change studies.
Abstract
Extreme wind and rainfall events have become more frequent phenomena, impacting coastal ecosystems by inducing increased mixing regimes in the upper mixed layers (UML) and reduced transparency (i.e. browning), hence affecting phytoplankton photosynthesis. In this study, five plankton assemblages from the South Atlantic Ocean, from a gradient of environmental variability and anthropogenic exposure, were subjected to simulated extreme weather events under a global change scenario (GCS) of increased temperature and nutrients and decreased pH, and compared to ambient conditions (Control). Using multiple linear regression (MLR) analysis we determined that evenness and the ratio of diatoms/ (flagellates + dinoflagellates) significantly explained the variations (81–91 %) of the photosynthesis efficiency (i.e. Pchla/ETRchla ratio) for each site under static conditions. Mixing speed and the optical depth (i.e. attenuation coefficient * depth, kdz), as single drivers, explained 40–76 % of the variability in the Pchla/ETRchla ratio, while GCS drivers <9 %. Overall, assemblages with high diversity and evenness were less vulnerable to extreme weather events under a GCS. Extreme weather events should be considered in global change studies and conservation/management plans as even at local/regional scales, they can exceed the predicted impacts of mean global climate change on coastal primary productivity.
Continue reading ‘The impact of extreme weather events exceeds those due to global-change drivers on coastal phytoplankton assemblages’Habitat sensitivity in the West African coastal area: inferences and implications for regional adaptations to climate change and ocean acidification
Published 1 February 2024 Science ClosedTags: chemistry, field, North Atlantic, South Atlantic
This study focuses on assessing coastal vulnerability and habitat sensitivity along the West African coast by delineating hotspots based on surface temperature, pH, chlorophyll-a, particulate organic carbon, and carbonate concentrations between 2018 and 2023 depending on data availability. Initial exploration of these variables revealed two distinct focal points i.e., the Togo-Nigerian coastal stretch and the stretch from Sierra Leone to Mauritania. Lower pH trends (acidification) in surface waters were observed off the West African coast, particularly in areas around the south-south Niger Delta in Nigeria and the coastal regions of Guinea and Guinea Bissau. Sea surface temperature analysis revealed highest temperatures (27–30°C) within Nigeria to Guinea coastal stretch, intermediate temperatures (24–27°C) within the Guinea Bissau and Senegal coastal stretch, and the lowest temperatures off the coast of Mauritania. Furthermore, correlation analysis between sea surface temperature and calcite concentration in the Mauritania-Senegal hotspot, as well as between overland runoff and particulate organic carbon in the Togo-Nigeria hotspot, revealed strong positive associations (r>0.60) and considerable predictive variability (R2 ≈ 0.40). From the habitat sensitivity analysis, certain regions, including Cape Verde, Côte d’Ivoire, Nigeria, Senegal, and Sierra Leone, exhibited high sensitivity due to environmental challenges and strong human dependence on coastal resources. Conversely, Gambia, Guinea, Guinea-Bissau, Liberia, and Togo displayed lower sensitivity, influenced by geographical-related factors (e.g. coastal layout, topography, etc.) and current levels of economic development (relatively lower industrialization levels). Regional pH variations in West African coastal waters have profound implications for ecosystems, fisheries, and communities. Addressing these challenges requires collaborative regional policies to safeguard shared marine resources. These findings underscore the link between ecosystem health, socioeconomics, and the need for integrated coastal management and ongoing research to support effective conservation.
Continue reading ‘Habitat sensitivity in the West African coastal area: inferences and implications for regional adaptations to climate change and ocean acidification’A synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2022: the SNAPO-CO2-v1 dataset (update)
Published 31 January 2024 Science ClosedTags: Antarctic, chemistry, field, Indian, Mediterranean, North Atlantic, North Pacific, South Atlantic, South Pacific
Total alkalinity (AT) and dissolved inorganic carbon (CT) in the oceans are important properties with respect to understanding the ocean carbon cycle and its link to global change (ocean carbon sinks and sources, ocean acidification) and ultimately finding carbon-based solutions or mitigation procedures (marine carbon removal). We present a database of more than 44 400 AT and CT observations along with basic ancillary data (spatiotemporal location, depth, temperature and salinity) from various ocean regions obtained, mainly in the framework of French projects, since 1993. This includes both surface and water column data acquired in the open ocean, coastal zones and in the Mediterranean Sea and either from time series or dedicated one-off cruises. Most AT and CT data in this synthesis were measured from discrete samples using the same closed-cell potentiometric titration calibrated with Certified Reference Material, with an overall accuracy of ±4 µmol kg−1 for both AT and CT. The data are provided in two separate datasets – for the Global Ocean and the Mediterranean Sea (https://doi.org/10.17882/95414, Metzl et al., 2023), respectively – that offer a direct use for regional or global purposes, e.g., AT–salinity relationships, long-term CT estimates, and constraint and validation of diagnostic CT and AT reconstructed fields or ocean carbon and coupled climate–carbon models simulations as well as data derived from Biogeochemical-Argo (BGC-Argo) floats. When associated with other properties, these data can also be used to calculate pH, the fugacity of CO2 (fCO2) and other carbon system properties to derive ocean acidification rates or air–sea CO2 fluxes.
Continue reading ‘A synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2022: the SNAPO-CO2-v1 dataset (update)’Low molecular weight carbohydrate patterns of mangrove macroalgae from different climatic niches under ocean acidification, warming and salinity variation
Published 12 January 2024 Science ClosedTags: biological response, laboratory, performance, physiology, phytoplankton, South Atlantic
Ocean acidification has increased due to the enhanced solubility of CO2 in seawater. Mangrove macroalgae in tropical and subtropical coastal regions can benefit from the higher availability of CO2 for photosynthesis and primary production. However, they can be negatively affected by the simultaneously occurring warming and increased salinity in estuaries. Thus, we analyzed the isolated effects of ocean acidification and the interactive effects of increased temperature and salinity on the low molecular weight carbohydrate (LMWC) contents of the mangrove red macroalgae Bostrychia montagnei and Bostrychia calliptera from Brazilian tropical and subtropical populations. Specimens from both climatic niches were tolerant to pH decreased by CO2 enrichment and enhanced their LMWC contents under increased availability of CO2. Specimens from both climatic niches also accumulated their dulcitol and sorbitol contents to cope with warming and salt stress. Nevertheless, temperature of 34 °C was lethal for tropical macroalgae, while 29 °C and 31 °C were lethal for subtropical B. calliptera under salinity of 35. Tropical and subtropical B. montagnei synthesized dulcitol (5–110 mmol kg−1 dry weight) and sorbitol (5–100 mmol kg−1 dry weight) as osmoregulatory, energy and thermal protection compounds, whereas tropical and subtropical B. calliptera synthesized mainly dulcitol (10–210 mmol kg−1 dry weight). Although digeneaside has an energy function in Bostrychia spp., it is not an osmolyte or thermal protection compound. Our data demonstrated that both tropical and subtropical Bostrychia spp. benefit from ocean acidification by CO2 enrichment, increasing their LMWC contents. However, warming and increased salinity in estuaries will be detrimental to them, even they producing protective metabolites. Multifactorial approaches are recommended to investigate whether negative effects of increased temperature and salinity nullify positive effects of ocean acidification on these Bostrychia species/populations.
Continue reading ‘Low molecular weight carbohydrate patterns of mangrove macroalgae from different climatic niches under ocean acidification, warming and salinity variation’Effect of low pH on embryonic and larval traits in the estuarine semi-terrestrial crab Neohelice granulata
Published 11 January 2024 Science ClosedTags: biological response, crustaceans, laboratory, morphology, mortality, physiology, reproduction, South Atlantic
Introduction
The life cycle of marine invertebrates alternates between development phases which exhibit different physiological and ecological characteristics. The larvae (and sometimes the eggs) of most crustaceans, echinoderms, and mollusks, for example, are small and conventionally mobile, and they constitute the dispersive stages. In addition, larvae and embryos are considered in some traits less “complex” than adults, often lacking certain physiological mechanisms that allow advanced stages to cope with slight or even higher changes in the environment. However, early life stages are as important as subsequent instars; either population renewal, dispersion as connectivity, rely on the ability of these stages to overcome the adverse environmental conditions (Levin, 2006; DiBacco et al., 2006). As any impact observed in those early life phases will be deleterious to the whole population, functioning as a “bottleneck”, it is fundamental to understand the effect and capacity of response to the different stressors.
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Continue reading ‘Effect of low pH on embryonic and larval traits in the estuarine semi-terrestrial crab Neohelice granulata’Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes
Published 2 January 2024 Science ClosedTags: Arctic, chemistry, field, Indian, North Atlantic, North Pacific, South Atlantic, South Pacific
Mangroves and saltmarshes are biogeochemical hotspots storing carbon in sediments and in the ocean following lateral carbon export (outwelling). Coastal seawater pH is modified by both uptake of anthropogenic carbon dioxide and natural biogeochemical processes, e.g., wetland inputs. Here, we investigate how mangroves and saltmarshes influence coastal carbonate chemistry and quantify the contribution of alkalinity and dissolved inorganic carbon (DIC) outwelling to blue carbon budgets. Observations from 45 mangroves and 16 saltmarshes worldwide revealed that >70% of intertidal wetlands export more DIC than alkalinity, potentially decreasing the pH of coastal waters. Porewater-derived DIC outwelling (81 ± 47 mmol m−2 d−1 in mangroves and 57 ± 104 mmol m−2 d−1 in saltmarshes) was the major term in blue carbon budgets. However, substantial amounts of fixed carbon remain unaccounted for. Concurrently, alkalinity outwelling was similar or higher than sediment carbon burial and is therefore a significant but often overlooked carbon sequestration mechanism.
Continue reading ‘Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes’Emergent properties of free-living nematode assemblages exposed to multiple stresses
Published 7 December 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, laboratory, mesocosms, metals, multiple factors, nematodes, otherprocess, sediment, South Atlantic, temperature
Highlights
- Co-occurring stressors have significant interactive effects on nematode assemblages.
- Metal contamination surpasses the effects of temperature rise and acidification.
- Temperature rise intensified contamination effects on nematodes.
- Acidification acted as a buffer to the contamination effects on nematodes.
- Nematode genera showed variable responses to contamination.
Abstract
Biological communities are currently facing multi-stressor scenarios whose ecological impacts are challenging to estimate. In that respect, considering the complex nature of ecosystems and types and interaction among stressors is mandatory. Microcosm approaches using free-living nematode assemblages can effectively be used to assess complexity since they preserve the interactions inherent to complex systems when testing for multiple stress effects. In this study, we investigated the interaction effects of three stress factors, namely i-metallic mixture of Cu, Pb, Zn, and Hg (control [L0], low, [L1] and high [L2]), ii- CO2-driven acidification (pH 7.6 and 8.0), and iii- temperature rise (26 and 28 °C), on estuarine free-living nematode assemblages. Metal contamination had the greatest influence on free-living nematode assemblages, irrespective of pH and temperature scenarios. Interestingly, whilst the most abundant free-living nematode genera showed significant decreases in their densities when exposed to contamination, other, less abundant, genera were apparently favored and showed significantly higher densities in contaminated treatments. The augmented densities of tolerant genera may be attributed to indirect effects resulting from the impacts of toxicity on other components of the system, indicating the potential for emergent effects in response to stress. Temperature and pH interacted significantly with contamination. Whilst temperature rise had potentialized contamination effects, acidification showed the opposite trend, acting as a buffer to the effects of contamination. Such results show that temperature rise and CO2-driven acidification interact with contamination on coastal waters, highlighting the importance of considering the intricate interplay of these co-occurring stressors when assessing the ecological impacts on coastal ecosystems.
Continue reading ‘Emergent properties of free-living nematode assemblages exposed to multiple stresses’Warming, acidification, and calcification feedback during the first hyperthermal of the Cenozoic—The Latest Danian Event
Published 21 November 2023 Science ClosedTags: field, paleo, protists, South Atlantic
The Latest Danian Event (LDE; ca. 62.15 Ma) is a major double-spiked eccentricity-driven transient warming event and carbon cycle perturbation (hyperthermal) in the early Paleocene, which has received significantly less attention compared to the larger events of the late Paleocene−early Eocene. A better understanding of the nature of the LDE may broaden our understanding of hyperthermals more generally and improve our knowledge of Earth system responses to extreme climate states. We present planktic and benthic foraminiferal Mg/Ca and B/Ca records that shed new light on changes in South Atlantic temperature and carbonate chemistry during the LDE. Our planktic Mg/Ca record reveals a pulsed increase in sea-surface temperature of at least ∼1.5 °C during the older carbon isotope excursion, and ∼0.5 °C during the younger isotope excursion. We observe drops in planktic and benthic B/Ca, synchronous with pronounced negative excursions in benthic δ13C, which suggest a shift in the carbonate system toward more acidic, dissolved inorganic carbon−rich conditions, in both the surface and deep ocean. Conditions remained more acidic following the LDE, which we suggest may be linked to an enhanced ocean alkalinity sink due to changes in the makeup of planktic calcifiers, hinting at a novel feedback between calcifier ecology and ocean-atmosphere CO2.
Continue reading ‘Warming, acidification, and calcification feedback during the first hyperthermal of the Cenozoic—The Latest Danian Event’Daily variability of pH and temperature in seawater from a near-pristine oceanic atoll, Southwest Atlantic
Published 3 November 2023 Science ClosedTags: chemistry, field, South Atlantic
Highlights
- Daily variability of pH, T and [H+] were influenced by daily light cycle and tides.
- High variability of the carbonate system is observed in the Rocas Atoll.
- High daily variability of pH on the reef was explained mainly by metabolic processes.
- Temperature and pH showed a significant correlation due to solar irradiation.
Abstract
The study of pH and temperature variability in reef environments, and the underlying processes that control this variability, is of great importance for ocean acidification research. Therefore, in the reef environment of Rocas Atoll, we conducted continuous monitoring of pH and temperature and periodic sampling of carbonate chemistry, and we hypothesize that seawater temperature is not the determining factor in the daily variability of pH at this atoll. Our results showed that the seawater of the atoll presented a high daily variability in pH, [H+], and temperature. The cycles of variations occurred primarily with a periodicity of ∼24 h, related to the daily light cycle, and secondarily with a periodicity of ∼12 h, associated with the semi-diurnal tidal cycles of the atoll. The results indicate that the relative balance of net organic carbon metabolism is the main process modulating carbonate chemistry on the atoll throughout the day.
Continue reading ‘Daily variability of pH and temperature in seawater from a near-pristine oceanic atoll, Southwest Atlantic’Prolonged deep-ocean carbonate chemistry recovery after the Paleocene-Eocene Thermal Maximum
Published 5 September 2023 Science ClosedTags: chemistry, field, Indian, North Atlantic, paleo, South Atlantic
Highlights
- N. truempyi B/Ca can be used to reconstruct the Early Cenozoic deep-water Ω.
- PETM deep-water Ω recovery is slower than suggested by sedimentary %CaCO3.
- PETM Ω recovery implies sustained carbon injection into the ocean-atmosphere system.
Abstract
The Paleocene-Eocene Thermal Maximum (PETM) is a hyperthermal event at ∼56 Ma ago, caused by rapid and massive carbon releases into the ocean-atmosphere system. Currently, the PETM ocean acidification is mainly quantified in the surface ocean. By contrast, PETM carbonate chemistry changes of the deep ocean, a larger carbon reservoir, are largely qualitatively constrained by sedimentary calcium carbonate contents (%CaCO3). Here, we revisit a previously proposed method for quantifying Early Cenozoic deep-water carbonate chemistry, using boron to calcium ratios (B/Ca) in extinct benthic foraminifera Nuttallides truempyi (Brown et al., 2011). We show that calibrating core-top B/Ca in the extant relative of N. truempyi against deep-water calcite saturation degree (Ω, Ω = [CO32−] /[CO32−]saturated), rather than calcite saturation state (Δ[CO32−], Δ[CO32−] = [CO32−] – [CO32−]saturated) as originally proposed better reflects Early Cenozoic carbonate chemistry changes. Furthermore, we provide multiple deep-water Ω reconstructions paired with benthic foraminiferal carbon isotopes during the PETM. At two sites, deep-water Ω recovered synchronously with carbon isotopes but lagged the sedimentary %CaCO3 rebound, indicating a slower post-PETM deep-water Ω recovery than previously thought. This may imply that during the PETM recovery phase, carbon could have been injected into the ocean-atmosphere system, despite net carbon loss, over a prolonged period after the initial release. If so, during this period, carbon removal from the ocean via calcite burial on the seafloor in response to enhanced silicate weathering may be weakened, suggesting that more carbon was sequestered via other processes such as those related to organic carbon burial.
Continue reading ‘Prolonged deep-ocean carbonate chemistry recovery after the Paleocene-Eocene Thermal Maximum’Variability and controls of the ocean acidification metrics pH and pCO2 in a large embayment of an Eastern Boundary Upwelling System (EBUS)
Published 29 August 2023 Science ClosedTags: chemistry, field, South Atlantic
Highlights
- Deoxygenation and acidification extrema observed in St Helena Bay.
- Mean surface pCO2 385 μatm indicative of system serving as a CO2 sink.
- PCO2 shown to be a function of both Chl a and PAR through water column.
- Winter mixing causes seasonal reversal of the air-sea pCO2 gradient.
- Mean surface pCO2 also elevated above atmospheric levels in nearshore.
Abstract
An assessment was undertaken of the spatial and temporal variability of pCO2 and pH in St Helena Bay, a highly productive, wide-open bay located in the Benguela, a major eastern boundary upwelling system (EBUS). Mechanisms controlling their patterns of variability and their linkage to the distribution of oxygen are explored. The mean surface pCO2 was 385 μatm, below the mean atmospheric concentration of 410 μatm, indicative of a system serving as a CO2 sink. The corresponding mean pH of bay surface waters was 8.3. The greatest variation from these means was driven by deep winter mixing causing a seasonal reversal of the air-sea pCO2 gradient. Mean surface pCO2 was also elevated above mean atmospheric levels in the nearshore (<15 m depth), a likely consequence of higher microbial respiration in the upper water column due to regular resuspension of detrital material. The nearshore of the bay is also sometimes subject to high biomass dinoflagellate blooms referred to as red tides, and their decay leads to exceptional pCO2 concentrations. Discharge from the Berg River and the associated degradation of terrestrially derived organic matter also contributes to higher pCO2 in the nearshore particularly during winter when rainfall is highest. Through the water column the important role of photosynthesis in determining the vertical distribution of pCO2 is evident in that pCO2 is shown to be a function of both Chl a and PAR. In St Helena Bay nearly 50% of water column biomass is located below the community compensation depth (i.e. where respiration carbon loss exceeds gross community production) leading to rapidly declining O2 and increasing pCO2 concentrations with depth. Resulting conditions of bottom water hypoxia/anoxia are therefore accompanied by more corrosive waters (pH declining to ∼7.4) and conditions of severe hypercapnia (pCO2 exceeding 2000 μatm) subjecting marine life to multiple stressors. St Helena Bay and similar bays in EBUS are likely to provide extrema in the deoxygenation and acidification of coastal waters.
Continue reading ‘Variability and controls of the ocean acidification metrics pH and pCO2 in a large embayment of an Eastern Boundary Upwelling System (EBUS)’
