Posts Tagged 'South Atlantic'

Ocean acidification and long-rerm changes in the carbonate system properties of the South Atlantic Ocean

Abstract

The wind-driven part of the South Atlantic Ocean is primarily ventilated through central and intermediate water formation. Through the water mass formation processes, anthropogenic carbon (Cant) is introduced into the ocean’s interior which in turn makes the South Atlantic region vulnerable to ocean acidification. Cant and the accompanying acidification effects have been estimated for individual sections in the region since the 1980s but a comprehensive synthesis for the entire basin is still lacking. Here, we quantified the Cant accumulation rates and examined the changes in the carbonate system properties for the South Atlantic using a modified extended multiple linear regression method applied to five hydrographic sections and data from the GLODAPv2.2021 product. From 1989 to 2019, a mean Cant column inventory change of 0.94 ± 0.39 mol C m−2 yr−1 was found. Cant accumulation rates of 0.89 ± 0.33 μmol kg−1 yr−1 and 0.30 ± 0.29 μmol kg−1 yr−1 were observed in central and intermediate waters, accompanied by acidification rates of −0.0020 ± 0.0007 pH units yr−1 and −0.0009 ± 0.0009 pH units yr−1, respectively. Furthermore, increased remineralization was observed in intermediate waters, amplifying the acidification of this water mass, especially at the African coast along 25°S. This increase in remineralization is likely related to circulation changes and increased biological activity nearshore. Assuming no changes in the observed trends, South Atlantic intermediate waters will become unsaturated with respect to aragonite in ∼30 years, while the central water of the eastern margins will become unsaturated in ∼10 years.

Key Points

  • The western margin and southern limit of the South Atlantic Ocean are more impacted by anthropogenic carbon (Cant) uptake
  • A Cant column inventory change of 0.94 ± 0.39 mol C m−2 yr−1 was found in the region, higher than the global mean storage rate
  • Aragonite unsaturation is expected in the next two decades along the eastern margin if the anthropogenic changes maintain the present trend
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Effects of the ocean acidification on the functional structure of coral reef nematodes

A mesocosm experiment was designed to study the effects of acidification on the phytal nematofauna of a coral reef. We hypothesized that phytal nematodes are responsive to different seawater acidification levels and that their assemblage structure and functional indicators (combination of maturity index and trophic diversity index) are useful to evaluate the effects of acidification. Artificial substrate units (ASU) were first colonized in a coral reef zone (Recife de Fora Municipal Marine Park, Porto Seguro, Bahia, Brazil) to obtain standardized assemblage samples. ASUs were transferred to laboratory and exposed to control and three levels of seawater acidification (pH reduced by 0.3, 0.6 and 0.9 units below field levels) and collected after 15 and 30 d. Contrary to our expectations that acidification may change the taxonomic structure of nematodes, while the functional structure may deviate from the expected under high levels of acidification, we found that univariate functional indicators of the community (index of trophic diversity and maturity index) did not show significant differences between the control and experimental treatments throughout the exposure period. It is probably because the frequent exposure of shallow-water nematodes to rather large environmental variations leads the faunal response to acidification to be complex and subtle. On the other hand, the density of the life-history strategy groups 3 and 4 and the structure of nematode assemblages were significantly affected by different pH levels throughout the exposure period. Both history strategy groups include all kinds of feeding groups. These results suggest that the impact of pH changes predicted by the years 2100 and 2300 may be strong enough to provide different traits or life-history strategies of nematodes to take advantage under changing conditions.

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The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin

Recent oceanographic observations have identified significant changes of intermediate water masses characterized by increased temperatures, lowered pH and deoxygenation. In order to improve our understanding as to how these changes may impact deep-sea ecosystems one important strategy is to reconstruct past oceanic conditions. Here we examine the applicability of the scleractinian cold-water coral Solenosmilia variabilis as a marine archive for the reconstructions of past intermediate water mass temperatures by using Lithium (Li)/Magnesium (Mg) ratios. In particular, our study addresses 1) the calibration of Li/Mg ratios against in-situ temperature data, 2) the reconstruction of past intermediate water mass temperatures using scleractinian coral fossil samples from the Brazilian continental margin and 3) the identification of intraspecies variability within the coral microstructure. Results showed that Li/Mg ratios measured in the skeletons of S. variabilis fit into existing Li/Mg-T calibrations of other cold-water scleractinian. Furthermore, the coral microstructure exhibits interspecies variability of Li/Ca and Mg/Ca ratios were also similar to what has been observed in other cold-water scleractinian corals, suggesting a similar biomineralization control on the incorporation of Li and Mg into the skeleton. However, the Li/Mg based temperature reconstruction using fossil samples resulted in unexpectedly high variations >10°C, which might not be solely related to temperature variations of the intermediate water mass over the last 160 ka on the Brazilian continental margin. We speculate that such temperature variability may be caused by vertical movements of the aragonite saturation horizon and the associated seawater pH changes, which in turn influence the incorporation of Li and Mg into the coral skeleton. Based on these results it is recommended that future studies investigating past oceanic conditions need to consider the carbonate system parameters and how they might impact the mechanisms of Li and Mg being incorporated into skeletons of cold-water coral species such as S. variabilis.

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Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling

The carbon cycle is a key regulator of Earth’s climate. On geological time-scales, our understanding of particulate organic matter (POM), an important upper ocean carbon pool that fuels ecosystems and an integrated part of the carbon cycle, is limited. Here we investigate the relationship of planktonic foraminifera-bound organic carbon isotopes (δ13Corg-pforam) with δ13Corg of POM (δ13Corg-POM). We compare δ13Corg-pforam of several planktonic foraminifera species from plankton nets and recent sediment cores with δ13Corg-POM on a N-S Atlantic Ocean transect. Our results indicate that δ13Corg-pforam of planktonic foraminifera are remarkably similar to δ13Corg-POM. Application of our method on a glacial sample furthermore provided a δ13Corg-pforam value similar to glacial δ13Corg-POM predictions. We thus show that δ13Corg-pforam is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ13Corg-POM and better understanding of the evolution of the carbon cycle over geological time-scales.

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Seasonal variability of carbonate chemistry and its controls in a subtropical estuary

Graphical abstract

Highlights

  • The seasonal variability in CO2 system was evaluated in the Patos Lagoon Estuary (PLE) between 2017 and 2021.
  • Mixing between riverine freshwater and seawater drives the changes in the CO2 system in the PLE.
  • The nonthermal effects on seasonal changes in the pCO2 prevail over thermal effects.
  • The waters of PLE are susceptible to CaCO3 undersaturation conditions during winter and spring.
  • The CO2 system in the PLE swings between an ocean-dominated and riverine-dominated estuarine behavior.

Abstract

We performed an unprecedented investigation of the seasonal variability in carbonate system parameters (total alkalinity – AT, total dissolved inorganic carbon – CT, pH, and partial pressure of carbon dioxide – pCO2) in the lower zone of the Patos Lagoon Estuary (PLE), the largest choked lagoon in the world. Sampling was conducted monthly from May 2017 to June 2021. AT and pH were measured during the study period, while other carbonate system parameters were estimated using CO2Sys software. The pH distribution reflected the average natural alkaline conditions throughout the year, with an average of 8.0 pH units. The surface waters in the lower zone of the PLE are generally characterized by a supersaturated calcium carbonate environment. However, a susceptibility to undersaturation conditions was observed during winter (calcite and aragonite) and spring (aragonite). Furthermore, the average surface water pCO2 was 394 μatm during the analyzed period, with the highest values recorded in winter and early spring. The predominant estuarine processes governing changes in the carbonate system in the PLE were the dilution and concentration of salts. These processes depend on the complex balance between freshwater outflows and oceanic inflows that change the surface salinity and produce favorable conditions for primary producer development and the input of continental carbon. However, the remineralization of organic matter and CO2 ingassing likely contribute to the deviations in the theoretical mixing line, causing the increased CT in the region. In addition, the nonthermal effects on seasonal changes in the pCO2 prevail over thermal effects, and the region presents an ocean-dominated (riverine-dominated) condition during summer and autumn (winter and spring). The novel results described here reveal the complexity and challenges that still exist to a better comprehension of how carbonate system parameters evolve temporally and spatially in the PLE, especially considering the climate- and anthropogenic-driven stressors. Finally, this study contributes to the understanding of carbonate system variability in coastal ecosystems and highlights the need for more intense and continuous biogeochemical monitoring of Southern Hemisphere estuaries.

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Climate resilience and adaptation in West African oyster fisheries: an expert-based assessment of the vulnerability of the oyster Crassostrea tulipa to climate change

Graphical abstract

Globally, over 85% of oyster reefs have been lost, and the combined effects of climate change, ocean acidification, and environmental degradation, including pollution and mangrove overharvesting, could further reduce global oyster fisheries in the coming decades. To understand the level of impact of climate change on the oyster fishery in West Africa, an expert-based vulnerability assessment to climate change was conducted for the West African mangrove oyster (Crassostrea tulipa, Lamarck 1819). Using a combination of the exposure of the oyster to climatic stressors (estuarine temperature, salinity, river flow, surface run-off, sea level rise, and estuarine circulation) together with an assessment of sensitivity to these stressors, we estimate the overall vulnerability of C. tulipa to climate change. A very high overall climate vulnerability score of 12 on a scale of 16 was calculated for C. tulipa. While the overall climate exposure score in the West African coastal region remained high, the high sensitivity of C. tulipa to hydrographic conditions of its habitat, in particular salinity, coupled with its sessile and habitat-specific nature, pushed the overall vulnerability to very high. Early life history settlement requirements, adult mobility, and sensitivity to salinity were the three most important biological and sensitivity attributes that determined the vulnerability score. By leaving each of these three sensitivity attributes out of the analysis, the overall vulnerability score was reduced to 9 (i.e., from very high to high). A negative directional effect of climate change, coupled with a low potential for change in distribution, threatens the C. tulipa fishery in a long-term adverse climate scenario. We recommend management efforts that incorporate climate resilience and adaptation practices to prioritize recruitment success, as well as the development of breeding lines with climate-resilient traits.

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Stylasterid corals build aragonite skeletons in undersaturated water despite low pH at the site of calcification

Anthropogenic carbon emissions are causing seawater pH to decline, yet the impact on marine calcifiers is uncertain. Scleractinian corals and coralline algae strongly elevate the pH of their calcifying fluid (CF) to promote calcification. Other organisms adopt less energetically demanding calcification approaches but restrict their habitat. Stylasterid corals occur widely (extending well below the carbonate saturation horizon) and precipitate both aragonite and high-Mg calcite, however, their mode of biocalcification and resilience to ocean acidification are unknown. Here we measure skeletal boron isotopes (δ11B), B/Ca, and U/Ca to provide the first assessment of pH and rate of seawater flushing of stylasterid CF. Remarkably, both aragonitic and high-Mg calcitic stylasterids have low δ11B values implying little modification of internal pH. Collectively, our results suggest stylasterids have low seawater exchange rates into the calcifying space or rely on organic molecule templating to facilitate calcification. Thus, despite occupying similar niches to Scleractinia, Stylasteridae exhibit highly contrasting biocalcification, calling into question their resilience to ocean acidification.

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Physical-chemical factors influencing the vertical distribution of phototrophic pico-nanoplankton in the Oxygen Minimum Zone (OMZ) off Northern Chile: the relative influence of low pH/low O2 conditions

Highlights

  • Pico-nano eukaryotes and phototrophic nanoflagellates showed high abundances in the upper layer decreasing in abundance down to the upper oxycline.
  • Temperature, oxygen, and carbonate chemistry parameters (pH and dissolved inorganic carbon, DIC) influenced significantly the vertical distribution of phototrophic pico-nanoplankton.
  • The phototrophic nanoflagellate Imantonia sp. upon an experimental treatment mimicking OMZ conditions, declined dramatically, suggesting this nanoflagellate did not survive upon such conditions.

Abstract

The vertical distribution of phytoplankton is of fundamental importance in the structure, dynamic, and biogeochemical pathways in marine ecosystems. Nevertheless, what are the main factors determining this distribution remains as an open question. Here, we evaluated the relative influence of environmental factors that might control the coexistence and vertical distribution of pico-nanoplankton associated with the OMZ off northern Chile. Our results showed that in the upper layer Synechococcus-like cells were numerically important at all sampling stations. Pico-nano eukaryotes and phototrophic nanoflagellates (PNF) also showed high abundances in the upper layer decreasing in abundance down to the upper oxycline, while only Prochlorococcus showed high abundances under oxycline and within the oxygen-depleted layer. Statistical analyses evidenced that temperature, oxygen, and carbonate chemistry parameters (pH and dissolved inorganic carbon, DIC) influenced significantly the vertical distribution of phototrophic pico-nanoplankton. Additionally, we experimentally-evaluated the combined effect of low pH/low O2 conditions on a nanophytoplankton species, the haptophyte Imantonia sp. Under control conditions (pH = 8.1; O2 = 287.5 μM, light = 169.6 μEm−2s−1), Imantonia sp. in vivo fluorescence increased over fifty times, inducing supersaturated O2 conditions (900 μM) and an increasing pH (8.5), whereas upon an experimental treatment mimicking OMZ conditions (pH = 7.5; O2 = 55.6 μM; light = 169.6 μEm−2s−1), in vivo fluorescence declined dramatically, suggesting that Imantonia sp. did not survive. Although preliminary, our study provides evidence about the role of low pH/low O2 conditions on the vertical distribution of nanophytoplankton, which deserve future attention through both fieldwork and more extended experimental experiences.

Continue reading ‘Physical-chemical factors influencing the vertical distribution of phototrophic pico-nanoplankton in the Oxygen Minimum Zone (OMZ) off Northern Chile: the relative influence of low pH/low O2 conditions’

Inventory of water masses and carbonate system from Brazilian’s northeast coast: monitoring ocean acidification

This manuscript presents an inventory of the carbonate system from the main water masses comprising the marine current system on Brazil’s northeast coast (South Atlantic Ocean). For this purpose, four transects were conducted with an approximate length of 357 km (each one) through the platform and continental slope of the Sergipe–Alagoas sedimentary basin. Water samples were then collected in vertical profiles measuring from 5 to 1,799 meters depth, totaling 34 stations. Total alkalinity, calcium, and total boron were obtained analytically from these samples and by relationships with salinity. Speciation and concentration of the carbonate system were obtained by means of thermodynamic modeling. The results revealed that the empirical models used to calculate the concentrations of TA, calcium and total boron showed relevant variation when compared to the analytical values (TA: 5.0–6.5%; Ca: 0.4–4.8%; BT: 7.0–18.9%). However, the speciation and concentration of the carbonate system (CA, DIC, CO32-, CO2(aq), ΩCalc, and ΩArag) obtained from the empirical values of TA, calcium and total boron did not differ significantly from those obtained analytically (0.0–6.1%). On the other hand, the parameters of pH, HCO3 , CO32-(aq), CO2(aq), ρCO2, ΩCalc, and ΩArag varied significantly within the different water masses (p < 0.05). This study supports and encourages acidification monitoring projects in the South Atlantic Ocean, based on modeling the carbonate system parameters generated in real-time.

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Gaining insights into the seawater carbonate system using discrete fCO2 measurements

Understanding the ocean carbon sink and its future acidification-derived changes requires accurate and precise measurements with good spatiotemporal coverage. In addition, a deep knowledge of the thermodynamics of the seawater carbonate system is key to interconverting between measured and calculated variables. To gain insights into the remaining inconsistencies in the seawater carbonate system, we assess discrete water column measurements of carbon dioxide fugacity (fCO2), dissolved inorganic carbon (DIC), total alkalinity (TA), and pH measured with unpurified indicators, from hydrographic cruises in the Atlantic, Pacific, and Southern Oceans included in GLODAPv2.2020 (19,013 samples). An agreement of better than ± 3% between fCO2 measured and calculated from DIC and pH is obtained for 94% of the compiled dataset, while when considering fCO2 measured and calculated from DIC and TA, the agreement is better than ± 4% for 88% of the compiled dataset, with a poorer internal consistency for high-CO2 waters. Inspecting all likely sources of uncertainty from measured and calculated variables, we conclude that the seawater carbonate system community needs to (i) further refine the thermodynamic model of the seawater carbonate system, especially K2, including the impact of organic compounds and other acid-base systems on TA; (ii) update the standard operating procedures for the seawater carbonate system measurements following current technological and analytical advances, paying particular attention to the pH methodology that is the one that evolved the most; (iii) encourage measuring discrete water column fCO2 to further check the internal consistency of the seawater carbonate system, especially given the new era of sensor-based seawater measurements; and (iv) develop seawater Certified Reference Materials (CRMs) for fCO2 and pH together with seawater CRMs for TA and DIC over the range of values encountered in the global ocean. Our conclusions also suggest the need for a re-evaluation of the adjustments applied by GLODAPv2 to pH, which were based on DIC and TA consistency checks but not supported by fCO2 and DIC consistency.

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Eutrophication amplifies the diel variability of carbonate chemistry in an equatorial, semi-arid, and negative estuary

This study presents high-resolution data on diel variations of carbonate chemistry in a semi-arid estuary (Jaguaribe River) in NE Brazil, which has witnessed decreasing annual rainfall and freshwater inputs due to climate change and river damming. In addition, the estuary has been suffering with increasing discharges from shrimp farm and urban effluents. We monitored surface water and atmospheric CO2 partial pressure (pCO2), temperature, salinity, and wind speed with continuous real-time measurements during two eulerian surveys in October 2017 (33 h) and September 2018 (44 h), during spring tides in the dry season. Additionally, pH, total alkalinity (TA), dissolved inorganic carbon (DIC), carbonate (CO32–), and saturation state of calcite (Ωcal) and aragonite (Ωara) were monitored hourly. Higher salinity (>38) during ebb tides confirmed the hypersalinity and negative estuarine circulation. TA and DIC concentrations in the estuary were higher than in the adjacent coastal ocean due to evaporation, showing positive correlation with salinity and negative correlation with tidal height. Measured TA and DIC concentrations were slightly higher than those calculated by the conservative evaporation model, suggesting their production in the estuary by aerobic and anaerobic processes. CO32–, Ωcal, and Ωara showed a clear semi-diurnal (tidal-driven) and diel (24 h; biological-driven) patterns: lowest values occurred at flood tide during night-time (respectively, 185 μmol kg–1, 4.3 and 2.8), whereas highest occurred during ebb tide and daytime (respectively, 251 μmol kg–1, 5.7 and 3.8). DIC/TA ratios were higher at night-time supporting a diel control (linked to solar irradiance) of the carbonate buffering capacity. pCO2 was oversaturated comparing to the atmosphere (512–860 μatm) and the estuary was a source of CO2, with fluxes ranging from 2.2 to 200.0 mmol C m–2 d–1 (51.9 ± 26.7 mmol C m–2 d–1), which are higher than emissions normally found in low-inflow, marine-dominated estuaries. The diel variability of DIC indicated a net heterotrophic metabolism averaging −5.17 ± 7.39 mmol C m–2 h–1. Eutrophication amplifies the diel variability of the CO2 system generating large differences between daytime and night-time. The results highlight the importance of considering diel variability when estimating CO2 fluxes and carbonate chemistry in eutrophic, semi-arid, and tidally dominated estuaries under rapid environmental changes, and may represent future conditions in estuaries worldwide experiencing warming, increasing aridity and eutrophication.

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Calcification accretion units (CAUs): a standardized approach for quantifying recruitment and calcium carbonate accretion in marine habitats

  1. Standardized metrics that quantify a component of ecosystem functioning are essential for evaluating the current status of coastal marine habitats and for monitoring how ecologically important ecosystems are changing in response to global and local environmental change. Calcification accretion units (CAUs) are a standardized tool for quantifying net calcium carbonate accretion, early successional community structure, recruitment of algae and sessile invertebrates and other response metrics that can be determined from image analyses in coastal marine habitats.
  2. CAUs are comprised of paired-settlement tiles that are separated by a spacer. This design mimics the presence of different representative habitats that are common in most marine systems such as exposed benthic surfaces, cryptic spaces inaccessible to grazers and shaded overhangings. The protected space between the tiles facilitates recruitment and inclusion of cryptic taxa in community assemblage estimates. After a period of deployment, CAUs are photographed for image analysis and then decalcified to quantify calcium carbonate accretion rates.
  3. The CAU methodology provides a cost-effective, standardized protocol for evaluating structure and function in marine benthic habitats. We illustrate how CAU data can be used to compare accretion rates and the relative proportion of carbonate polymorphs in ecosystems across the globe.
  4. Here we provide a comprehensive standard operating procedure for building, deploying and processing CAUs, to ensure that a consistent protocol is used for accurate data collection and cross-system comparative studies.
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Global assessment of coralline algae mineralogy points to high vulnerability of Southwestern Atlantic reefs and rhodolith beds to ocean acidification

Coralline algae constitute one of the main groups of highly vulnerable calcified benthic organisms to ocean acidification. Although damaging effects of seawater acidification on the coralline algae skeleton have been widely demonstrated, the susceptibility to dissolution varies according to the Mg2+ in the calcite lattice. Even though the Southwest Atlantic Ocean exhibits the world’s largest rhodolith beds, which occupies 20,902 km2, there is no information regarding the coralline algae species mineralogy in this area. Here, we provide mineralogical data of twenty-four coralline algae species, examine the similarity in taxonomic groups, spatial occurrence and the vulnerability of these algae to seawater acidification. Mineralogy revealed that coralline algae skeletons were mainly composed of high-Mg calcite (> 70%) with minor presence of aragonite (< 30%) and dolomite (< 3%). There were no similarities between the skeletal mineralogy of taxonomic groups and sampling regions. Remarkably, the mean Mg-substitution of encrusting coralline algae from the Brazilian Shelf was 46.3% higher than global average. Because of the higher mean Mg-substitution in calcite compared with worldwide coralline algae, these algae from Southwest Atlantic Ocean would be highly susceptible to dissolution caused by the expected near-future ocean acidification and will compromise CaCO3 net production across the Brazilian Shelf.

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Calcification, dissolution and test properties of modern planktonic foraminifera from the central Atlantic Ocean

The mass of well-preserved calcite in planktonic foraminifera shells provides an indication of the calcification potential of the surface ocean. Here we report the shell weight of 8 different abundant planktonic foraminifera species from a set of core-to sediments along the Mid-Atlantic Ridge. The analyses showed that near the equator, foraminifera shells of equivalent size weigh on average 1/3 less than those from the middle latitudes. The carbonate preservation state of the samples was assessed by high resolution X-ray microcomputed tomographic analyses of Globigerinoides ruber and Globorotalia truncatulinoides specimens. The specimen preservation was deemed good and does not overall explain the observed shell mass variations. However, G. ruber shell weights might be to some extent compromised by residual fine debris internal contamination. Deep dwelling species possess heavier tests than their surface-dwelling counterparts, suggesting that the weight of the foraminifera shells changes as a function of the depth habitat. Ambient seawater carbonate chemistry of declining carbonate ion concentration with depth cannot account for this interspecies difference. The results suggest a depth regulating function for plankton calcification, which is not dictated by water column acidity.

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Transcriptomic responses of adult versus juvenile Atlantids to ocean acidification

Shelled holoplanktonic gastropods are among the most vulnerable calcifiers to ocean acidification. They inhabit the pelagic environment and build thin and transparent shells of aragonite, a metastable form of calcium carbonate. While shelled pteropods have received considerable attention and are widely regarded as bioindicators of ocean acidification, atlantids have been much less studied. In the open ocean, atlantids are uniquely positioned to address the effects of ocean acidification at distinct trophic levels. From juvenile to adult, they undergo dramatic metamorphosis. As adults they are predatory, feeding primarily on shelled pteropods, copepods and other zooplankton, while as juveniles they feed on algae. Here we investigated the transcriptome and the impact of a three-day CO2 exposure on the gene expression of adults of the atlantid Atlanta ariejansseni and compared these to results previously obtained from juveniles. Individuals were sampled in the Southern Subtropical Convergence Zone (Atlantic Ocean) and exposed to ocean chemistry simulating past (~mid-1960s), present (ambient) and future (2050) conditions. In adults we found that the changes in seawater chemistry had significantly affected the expression of genes involved in biomineralization and the immune response, although there were no significant differences in shell growth between the three conditions. In contrast, juveniles experienced substantial changes in shell growth and a broader transcriptomic response. In adults, 1170 genes had the same direction of expression in the past and future treatments when compared to the ambient. Overall, this type of response was more common in adults (8.6% of all the genes) than in juveniles (3.9%), whereas a linear response with decreasing pH was more common in juveniles (7.7%) than in adults (4.5%). Taken together, these results suggest that juveniles are more sensitive to increased acidification than adults. However, experimental limitations including short incubation times, one carboy used for each treatment and two replicates for transcriptome analysis, require us to be cautious about these conclusions. We show that distinct transcriptome profiles characterize the two life stages, with less than 50% of shared transcripts. This study provides an initial framework to understand how ocean acidification may affect the molecular and calcification responses of adult and juvenile atlantids.

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Predicted changes in temperature, more than acidification, affect the shell morphology and survival of the girdled dogwhelk, Trochia cingulata (Linnaeus, 1771)

Despite the existing body of research that considers altered ocean temperature and acidification as co-occurring stressors, our understanding of the consequences of such shifts remains limited. This is particularly problematic in relation to predators such as whelks, as they can exert strong top-down control of communities yet, as calcifying ectotherms, they are likely to be vulnerable to climate change. This study assessed the effects of simultaneous changes in water temperature and pH on the South African girdled dogwhelk Trochia cingulata. For 12 weeks, whelks were exposed to three temperatures, 9 °C (cooling), 13 °C (current) and 17 °C (warming), each at three target pH levels, 8.0 (current), 7.7 (intermediate) and 7.5 (extreme). For each treatment shell thickness, strength and shape were measured after 6 and 12 weeks, while mortality was recorded daily. Survival was not affected by pH and was highest at 9 °C. Almost all whelks exposed to warming died within 2 weeks. After 6 weeks, shell strength declined significantly as acidity increased, regardless of temperature, and shells of whelks held at 9 °C were thinner. By 12 weeks, whelks exposed to cooling and extreme pH had the weakest shells. Notably, temperature no longer influenced shell thickness, but whelks held at 9 °C became globular in shape. These changes in shell morphology likely resulted from the increased cost of shell maintenance in cool, acidic conditions. The differences observed at 6 and 12 weeks demonstrate how responses can change over time, a point that should be kept in mind when assessing species sensitivities to changing environments. The dominant effect of temperature highlights that T. cingulata is particularly vulnerable to warming, while regional cooling may pose a challenge with respect to shell morphology.

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Mangrove macroalgae increase their growth under ocean acidification: a study with Bostrychia (Rhodophyta) haplotypes from different biogeographic provinces

Increasing oceanic CO2 has caused a decrease in oceanic pH, a process termed ocean acidification (OA). OA may benefit fleshy macroalgae due to the increased availability of inorganic carbon sources for photosynthesis since they are tolerant of decreases in pH. In this study, we analyzed multiple physiological responses of Bostrychia montagnei and Bostrychia calliptera from two biogeographic provinces of Brazil (Tropical Southwestern Atlantic [TSA] and Warm Temperate Southwestern Atlantic [WTSA]) after culturing them at a set of bioreactors in three pH levels (7.2, 7.6, and 8.0). Two pH were decreased by CO2 enrichment into the culture medium. Molecular analyses using plastidial (rbcL-3P) and mitochondrial (COI-5P) DNA markers were also performed to identify genetic divergences between macroalgae from TSA and WTSA. Molecular evidence of COI-5P marker demonstrated that the specimens of both B. montagnei and B. calliptera from TSA and WTSA constitute different haplotypes, with a strong segregation between them. Macroalgae from both localities increased their growth in treatments of decreased pH with increased CO2 availability. Overall, physiological responses of the algae were not negatively affected by decreased pH. B. montagnei from TSA increased its polysaccharide and allophycocyanin content at pH 7.2, and B. montagnei from WTSA increased its low molecular weight carbohydrate content at pH 7.2 as well. Antioxidant activity — a proxy for physiological stress — was not affected by decreased pH. Our study indicates that haplotypes of B. montagnei and B. calliptera from TSA and WTSA can be relevant to CO2 sequestration in mangroves once they are tolerant of decreased pH and increase their growth under increased CO2 availability.

Continue reading ‘Mangrove macroalgae increase their growth under ocean acidification: a study with Bostrychia (Rhodophyta) haplotypes from different biogeographic provinces’

Coastal ocean acidification in Brazil: a brief overview and perspectives

This perspective paper aims at presenting the current knowledge on the processes of ocean acidification (OA) and coastal acidification (CA) in the Brazilian coastal ocean. We define and differentiate the processes of OA and CA: the first driven by the actual global increase of atmospheric carbon dioxide (CO2); the second driven by a combination of ocean uptake of atmospheric CO2 and other local/regional chemical additions or subtractions in aquatic ecosystems at the land-ocean interface. Regarding OA, we have centered our analysis on the data available for the main water masses along the Brazilian coast: South Atlantic Central Water (SACW), Tropical Water (TW), and Coastal Water (CW). The few data available for the shallow coastal waters (< 200 m depth) of the continental shelf reveal an increase in the anthropogenic component of the total dissolved inorganic carbon (DIC) pool in the SACW, with a decline in the ocean pH (over two decades; 1993-2013), and in the saturation state of calcium carbonate (CaCO3) minerals. We could not find OA trends for TW and CW because no data was available. Overall, the colder water masses (SACW, Plata Plume) have lower buffering capacity and simulations show that will potentially experience earlier negative OA impacts than the warmer waters masses (TW, Amazon Plume). Regarding CA, we have identified some local/regional studies investigating the carbonate chemistry in nearshore/estuarine ecosystems, particularly on the quantification of sources and sinks of CO2 , and determining short-term variabilities. Apparently, spreading coastal eutrophication in Brazil can enhances or reduces the process of OA, depending on the net ecosystem metabolism in combination with other chemical alterations. However, we could not find medium-long term acidification trends due to the limited data. There is a limited capacity to produce long time-series of carbonate chemistry parameters in key ecosystems and regions along the Brazilian coast. This lack of past information hinders and impairs the scientific community for identifying potential patterns of acidification along the Brazilian coast. We call for an urgent action in Brazil, with emphasis on the establishment of moored buoys/stations and/or scientific programs in the long term with continuous, real-time measurements of the main carbonate chemistry parameters.

Continue reading ‘Coastal ocean acidification in Brazil: a brief overview and perspectives’

The contribution of nutrients and water properties to the carbonate system in three particular areas of the tropical Atlantic (NE-Brazil)

Tropical waters show different regional aspects due to specificities in their nutrient biogeochemical cycles, which can affect the carbon system and influence their regional role as sinks or sources of CO2. This study was performed on particular tropical areas that present a different seasonal behaviour related to the carbon cycle observed in the late rainy season (July 2013). Understanding the CO2 drawdown and outgassing potential in these areas is needed to call attention to more long-term monitoring efforts and protect understudied tropical coastal systems more efficiently. This study is focused on nutrient values, hydrological data, biogeochemical carbon behaviour linked to the carbonate system and includes estimates of CO2 fluxes in three contrasting areas off the northeastern Brazilian shelf: 1) an urbanised estuary (Recife-REC), 2) a coastal Island (Itamaracá-ITA) and 3) an oceanic archipelago (Fernando de Noronha-FN). In general, REC acted as a source, while ITA and FN as carbon sinks. In ITA, despite the high DIC and Total Alkalinity observed (mean ~2360 μmol·kg-1), the sink is associated with an effective cascading of atmospheric CO2 associated with turbulent shallow waters coupled with biogenic removal of and precipitation of CaCO3 by coralline algae. FN acted as a sink, linked to minor decreases in Total Alkalinity (mean~2295 μmol·kg-1) influenced by ammonium-based primary production, nitrogen fixation and sporadic entrainment of nutrient rich waters in the upper thermocline. More studies in different western tropical Atlantic coastal systems can improve the knowledge of tropical shelf seas and their contribution to the ocean carbon budget under specific regional trophic regimes.

Continue reading ‘The contribution of nutrients and water properties to the carbonate system in three particular areas of the tropical Atlantic (NE-Brazil)’

A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceans

We have estimated global air–sea CO2 fluxes (fgCO2) from the open ocean to coastal seas. Fluxes and associated uncertainty are computed from an ensemble-based reconstruction of CO2 sea surface partial pressure (pCO2) maps trained with gridded data from the Surface Ocean CO2 Atlas v2020 database. The ensemble mean (which is the best estimate provided by the approach) fits independent data well, and a broad agreement between the spatial distribution of model–data differences and the ensemble standard deviation (which is our model uncertainty estimate) is seen. Ensemble-based uncertainty estimates are denoted by ±1σ. The space–time-varying uncertainty fields identify oceanic regions where improvements in data reconstruction and extensions of the observational network are needed. Poor reconstructions of pCO2 are primarily found over the coasts and/or in regions with sparse observations, while fgCO2 estimates with the largest uncertainty are observed over the open Southern Ocean (44 S southward), the subpolar regions, the Indian Ocean gyre, and upwelling systems.

Our estimate of the global net sink for the period 1985–2019 is 1.643±0.125 PgC yr−1 including 0.150±0.010 PgC yr−1 for the coastal net sink. Among the ocean basins, the Subtropical Pacific (18–49 N) and the Subpolar Atlantic (49–76 N) appear to be the strongest CO2 sinks for the open ocean and the coastal ocean, respectively. Based on mean flux density per unit area, the most intense CO2 drawdown is, however, observed over the Arctic (76 N poleward) followed by the Subpolar Atlantic and Subtropical Pacific for both open-ocean and coastal sectors. Reconstruction results also show significant changes in the global annual integral of all open- and coastal-ocean CO2 fluxes with a growth rate of  PgC yr−2 and a temporal standard deviation of 0.526±0.022 PgC yr−1 over the 35-year period. The link between the large interannual to multi-year variations of the global net sink and the El Niño–Southern Oscillation climate variability is reconfirmed.

Continue reading ‘A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceans’

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