Total alkalinity (AT) and total dissolved inorganic carbon (CT) in the oceans are important properties to understand the ocean carbon cycle and its link with climate change (ocean carbon sinks and sources) or global change (ocean acidification). We present a data-base of more than 44 400 AT and CT observations in various ocean regions obtained since 1993 mainly in the frame of French projects. This includes both surface and water columns data acquired in open oceans, coastal zones and in the Mediterranean Sea and either from time-series or punctual 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. Given the lack of observations in the Indian and Southern Oceans, we added sea surface underway AT and CT data obtained in 1998–2018 in the frame of OISO cruises and in 2019 during the CLIM-EPARSES cruise measured onboard using the same technique. Separate datasets for the global ocean, and for the Mediterranean Sea are provided in a single format (https://doi.org/10.17882/95414, Metzl et al., 2023) that offers a direct use for regional or global purposes, e.g. AT/Salinity relationships, long-term CT estimates, constraint and validation of diagnostics CT–AT reconstructed fields or ocean carbon and coupled climate/carbon models simulations, as well as data derived from BG-ARGO floats. When associated with other properties, these data can also be used to calculate pH, fugacity of CO2 (fCO2) and other carbon systems properties to derive ocean acidification rates or air-sea CO2 fluxes.
Continue reading ‘A synthesis of SNAPO-CO2 ocean total alkalinity and total dissolved inorganic carbon measurements from 1993 to 2022’Posts Tagged 'South Atlantic'
A synthesis of SNAPO-CO2 ocean total alkalinity and total dissolved inorganic carbon measurements from 1993 to 2022
Published 23 August 2023 Science ClosedTags: Antarctic, chemistry, field, Indian, Mediterranean, North Atlantic, North Pacific, South Atlantic, South Pacific
Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth
Published 22 August 2023 Science ClosedTags: Antarctic, Arctic, chemistry, Indian, modeling, North Atlantic, North Pacific, regionalmodeling, review, South Atlantic, South Pacific
Highlights
- Ocean acidification has caused the carbonate compensation depth (CCD) to rise by ~98 m.
- Seafloor area below the CCD has increased by 3.6% in the last 200 years.
- Risk of impact of rising CCD is greatest in the western equatorial Atlantic Ocean.
- Different geomorphic features impacted by rising CCD in different ocean areas.
Abstract
Due to burning of fossil fuels, carbon dioxide is being absorbed by the ocean where its chemical conversion to carbonic acid has already caused the surface ocean to become more acidic than it has been for at least the last 2 million years. Global ocean modeling suggests that the carbonate compensation depth (CCD) has already risen by nearly 100 m on average since pre-industrial times and will likely rise further by several hundred meters more this century. Potentially millions of square kilometres of ocean floor will undergo a rapid transition in terms of the overlying water chemistry whereby calcareous sediment will become unstable causing the carbonate “snow line” to rise.We carried out a spatial analysis of seafloor geomorphology to assess the area newly submerged below the rising CCD. We found that shoaling of the CCD since the industrial revolution has submerged 12,432,096 km2 of ocean floor (3.60% of total ocean area) below the CCD. Further hypothetical shoaling of the CCD by 100 m increments illustrated that the surface area of seafloor submerged below the CCD has risen by 14% with 300 m of shoaling, such that 51% of the ocean area will be below the CCD. All categories of geomorphic feature mapped in one global database intersect the lysocline and will be (or already are) submerged below the CCD with much regional variation since the rise in CCD depth during the last 150 years varies significantly between different ocean regions. For seamounts, the highest percentages of increase in area submerged below the CCD occurred in the Southern Indian Ocean and the South West Atlantic regions (6.3% and 5.9%, respectively). For submarine canyons we found the South West Atlantic increased from 3.9% in pre-industrial times to 8.0% at the present time, the highest percentage of canyons found below the CCD in any ocean region.We also carried out a relative risk assessment for future submergence of ocean floor below the CCD in 17 ocean regions. In our assessment we assumed that the change in CCD from pre-industrial times to the present is an indicator of the likelihood and the change in percentage of seafloor submerged below the CCD due to a hypothetical 300 m rise in the CCD is an indicator of the consequences. We found that the western equatorial Atlantic is at high risk and 9 other Ocean Regions are at moderate risk. Overall, geomorphic features in the Atlantic Ocean and southern Indian Ocean are at greater risk of impact from a rising CCD than Pacific and other Indian Ocean regions.A separate analysis of the Arctic Ocean points to the possible submergence of glacial troughs incised on the continental shelf within a mid-depth (400–800 m) acidified water mass. We also found that the area of national Exclusive Economic Zones submerged below the rising CCD exhibits extreme variability; with 300 m of CCD shoaling we found a > 12% increase in area submerged below the CCD for 23 national EEZs, whereas there was virtually no change for other countries.
Continue reading ‘Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth’Benthic foraminiferal response to the Aptian−Albian carbon cycle perturbation in the Atlantic Ocean
Published 13 July 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, field, North Atlantic, otherprocess, paleo, protists, South Atlantic
A planktic foraminiferal mass extinction, coeval with the major carbon cycle perturbation of Oceanic Anoxic Event (OAE) 1b, occurred at the Aptian−Albian boundary interval (AABI). However, the scarcity of high-resolution records across the AABI hampers an assessment of the impacts of OAE 1b on deep-water benthic foraminiferal assemblages. Here we present high-resolution benthic foraminiferal census counts at Deep Sea Drilling Project (DSDP) Site 511 (southern South Atlantic Ocean) and Ocean Drilling Program (ODP) Site 1049 (western subtropical North Atlantic Ocean) over the AABI. Our records at these bathyal sites provide conclusive evidence that there was no benthic foraminiferal extinction at the Aptian−Albian boundary, although marked reorganizations of relative abundances occurred. During the latest Aptian, cyclic increases in the abundance of infaunal species at both sites point to repeated pulses of reduced bottom water oxygenation and increased organic carbon flux to the ocean floor. Additionally, agglutinated and weakly calcified benthic foraminiferal species were relatively abundant during the latest Aptian, suggesting deep-water carbonate ion depletion in the Atlantic Ocean, although we did not identify signs of carbonate dissolution at these relatively shallow sites. At Site 511, abundances of infaunal foraminifera increased in tandem with the negative carbonate carbon isotope (δ13Ccarb) excursion of the Kilian sub-event within OAE 1b, suggesting decreased bottom water ventilation and increased organic carbon flux to the ocean floor during the sub-event. Bottom water ventilation and carbonate ion saturation improved during the earliest Albian in the Atlantic Ocean, followed by high-amplitude oscillations, as suggested by abundance trends of heavily calcified epifaunal foraminifera at Sites 511 and 1049.
Continue reading ‘Benthic foraminiferal response to the Aptian−Albian carbon cycle perturbation in the Atlantic Ocean’The meridional and seasonal variability of the carbonate system in the Southeast Atlantic sector of the Southern Ocean: SCALE 2019 Experiment
Published 10 July 2023 Science ClosedTags: chemistry, field, South Atlantic
Unlike well-characterized regions that have emerging pH and carbonate data, distant areas like polar oceans remain seasonally undersampled. Consequently, there may be a significant gap in our understanding of biological implications of future ocean acidification (OA). This study seeks to examine the seawater state conditions of the carbonate system that are currently experienced by marine organisms that depend on pH and Aragonite saturation (ΩAr) for calcification. The main focus was on how the physical and carbonate characteristics are sensitive to seasonal variability in the S.E Atlantic sector of the Southern Ocean. We analyzed the temperature, salinity, Dissolved Inorganic Carbon (CT), alkalinity data (AT), pH and Omega (ΩAr) at the surface and in the upper 1000m. We then compared the seasonal meridional gradients in the surface layer and in the upper 1000m water column. The CT and AT were measured using a VINDTA instrument while pH and ΩAr were derived using the CO2SYS program. The initial hypothesis was that the southernmost part of the Southern Ocean would acidify more in winter than in spring. This was based on the idea that colder waters hold more CO2. However, we found remarkable results showing that the surface CT was consistently higher in spring than in winter, with mean seasonal differences ranging from 5.86-21.90µmol/kg although SST was consistently higher in spring than winter, with mean seasonal differences ranging from 0.67-2.12˚C within the ocean front boundaries. It was then hypothesized that the temperature, biological production and CO2 flux seasonal cycles may have been out of phase. Consistent with the CT gradient, the surface pH and ΩAr were ±0.05 units lower in the warmer waters of spring and comparatively higher in winter. The seasonal lag was seen even within the interior layers of the column. There were three main findings in this study: Firstly, since the biogeochemically controlled seasonal CO2 seasonal transition variability lagged the heat flux influence on SST, the expected winter and spring seasonal conditions for carbonate were not reflected in the timing of the winter and spring cruises. Secondly, we observed an uncoupling of pH and ΩAr surface meridional gradients. While pH had no significant meridional gradient trend apart from frontal variability, ΩAr followed the meridional trend that was driven by CT. This was due to the impact of the meridional temperature gradient on K2 that compensated for the impact of the CT gradient on the pH. Lastly, we found that the impact of the seasonal cycle of carbonate stretched down to 1000 m and it was attributed to physical processes. Our findings led us to infer that from a carbonate perspective, the winter cruise was in fact the tail end of autumn while the spring cruise was the tail end of winter.
Continue reading ‘The meridional and seasonal variability of the carbonate system in the Southeast Atlantic sector of the Southern Ocean: SCALE 2019 Experiment’A glimpse into the climate, seasonality, hydrological cycle, carbonate chemistry and marine ecosystem shift of the pre-Petm and the Petm using Ncar Cesm1.2
Published 22 June 2023 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, modeling, North Atlantic, paleo, phytoplankton, regionalmodeling, South Atlantic
The Paleocene-Eocene Thermal Maximum (PETM, ~56 my ago, 170,000y event) is characterized by a negative δ13C excursion into the atmosphere. This event caused global temperature to increase by about 5-6 °C, followed by climate responses such as marine acidification, ocean stratification, shoaling of calcite compensation depth (CCD), stronger hydrological cycle, and significant changes in marine ecosystems. It is one of the very few analogies of today’s global warming climate and thus is valuable to study. It still holds much potential for research, including using the state-of-the-art model CESM1.2. Proxy records are limited due to the nature of geological preservation and tectonic evolution. Modeling and simulations can provide insights to supplement the limited proxy records research. Here, we explore the seasonality, hydrological cycles, and controlling factors of their changes from pre-PETM to the PETM in the first paper; the ability of CESM1.2 to simulate carbonate chemistry, changes in lysocline and CCD in the Atlantic Ocean in the second paper; and the shift of phytoplankton functional groups, using the same preferendum to capture first-hand reactions to environmental changes, from pre-industrial pCO2 to pre-PETM in the third paper. All papers use CESM1.2 simulation results with or without BEC. Our results show that from pre-PETM to PETM, seasonality increases in mid-latitude continental interiors and decreases in high and low latitudes, along with globally enhanced moisture transfer in hydrological cycles. The main controlling factors of these areas are snow-albedo effect, soil moisture, and precipitation. CESM1.2 and ocean Biogeochemical (BGC) Elemental Cycling (BEC) can simulate the changes of carbonate chemistry of the Atlantic Ocean, with certain modifications in the code base and without the need of extra models. There are noticeable and significant changes in chlorophyll, nutrient and NPP from PETM in pre-industrial pCO2 and pre-PETM, but distinct variations from pre-industrial and PETM in pre-industrial pCO2 simulations. Proxy record scarcity is the main limitation of the studies on PETM and should be used with care. In the meantime, machine learning is encouraged for multi-disciplinary research of complicated topics such as carbon chemistry and phytoplankton functional group preferendum and ecosystem dynamics.
Continue reading ‘A glimpse into the climate, seasonality, hydrological cycle, carbonate chemistry and marine ecosystem shift of the pre-Petm and the Petm using Ncar Cesm1.2’Influence of changes in pH and temperature on the distribution of apparent iron solubility in the oceans
Published 21 June 2023 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic, South Atlantic, South Pacific
Abstract
An insufficient supply of the micronutrient iron (Fe) limits phytoplankton growth across large parts of the ocean. Ambient Fe speciation and solubility are largely dependent on seawater physico-chemical properties. We calculated the apparent Fe solubility (SFe(III)app) at equilibrium for ambient conditions, where SFe(III)app is defined as the sum of aqueous inorganic Fe(III) species and Fe(III) bound to organic matter formed at a free Fe3+ concentration equal to the solubility of Fe hydroxide. We compared the SFe(III)app to measured dissolved Fe (dFe) in the Atlantic and Pacific Oceans. The SFe(III)app was overall ∼2–4-fold higher than observed dFe at depths less than 1,000 m, ∼2-fold higher than the dFe between 1,000 and 4,000 m and ∼3-fold higher than dFe below 4,000 m. Within the range of used parameters, our results showed that there was a similar trend in the vertical distributions of horizontally averaged SFe(III)app and dFe. Our results suggest that vertical dFe distributions are underpinned by changes in SFe(III)app, which are driven by relative changes in ambient pH and temperature. Since both pH and temperature are essential parameters controlling ambient Fe speciation, these should be accounted for in investigations of changing Fe dynamics, particularly in the context of ocean acidification and warming.
Key Points
- Apparent iron solubility is driven by ambient pH, temperature (T) and dissolved organic carbon (DOC) and showed a 6-fold variation between surface (pH = 8.05 on the total scale, DOC = 71.8 μmol L−1, T = 20.4°C) and deep oceanic waters (pH = 7.82, DOC = 38.6 μmol L−1, T = 1.1°C)
- Higher values of apparent iron solubility were determined for deep Atlantic and Pacific waters, with lower values in subtropical gyres
- Calculated apparent iron solubility showed a similar trend in vertical distribution to dissolved iron, highlighting the importance of considering the impact of changes in ambient physico-chemical conditions on seawater iron chemistry
Ocean warming and CO2-driven acidification can alter the toxicity of metal-contaminated sediments to the meiofauna community
Published 8 May 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, crustaceans, laboratory, mesocosms, metals, multiple factors, nematodes, otherprocess, South Atlantic, temperature, toxicants, zooplankton
Highlights
- Contamination interacted with warming but the effect on density was taxon dependent.
- Warming increased metal effects in nematods and copepods, and decreased in acoelomorphs.
- Copepod densities were lower, and acoelomorphs higher, in the high CO2/low pH scenario.
- Global change studies should consider multispecies exposures in multi-stressor scenarios.
Abstract
Interactive effects of trace metal contamination, ocean warming, and CO2-driven acidification on the structure of a meiofaunal benthic community was assessed. Meiofauna microcosm bioassays were carried out in controlled conditions in a full factorial experimental design which included three fixed factors: metal contamination in the sediment (3 levels of a mixture of Cu, Pb, Zn, and Hg), temperature (26 and 28 °C) and pH (7.6 and 8.1). Metal contamination caused a sharp decrease in the densities of the most abundant meiobenthic groups and interacted with temperature rise, exacerbating deleterious effects for Nematoda and Copepoda, but mitigating effects for Acoelomorpha. CO2-driven acidification resulted in increased acoelomorphs density, but only in sediments with lower levels of metals. Copepod densities, in turn, were lower in the CO2-driven acidification scenario regardless of contamination or temperature. The results obtained in the present study showed that temperature rise and CO2-driven acidification of coastal ocean waters, at environmentally relevant levels, interacts with trace metals in marine sediments, differently affecting the major groups of benthic biota.
Continue reading ‘Ocean warming and CO2-driven acidification can alter the toxicity of metal-contaminated sediments to the meiofauna community’Calcareous sponges can synthesize their skeleton under short-term ocean acidification
Published 28 April 2023 Science ClosedTags: biological response, laboratory, morphology, porifera, South Atlantic
Calcifying organisms are considered as threatened by ocean acidification, because of their calcium carbonate skeleton. This study investigated if a calcareous sponge could synthesize its skeleton (i.e. spicules) under ocean-acidification conditions. Sponge cell aggregates that have the potential to develop into a functional sponge, called primmorphs, were submitted to a 5-day experiment, with two treatments: control (pH 8.1) and acidified conditions (pH 7.6). Primmorphs of the calcareous sponge Paraleucilla magna were able to synthesize a skeleton, even under low pH, and to develop into functional sponges. The spicules had the same shape in both conditions, although the spicules synthesized in low pH were slightly thinner than those in the control. These results suggest that P. magna may be able to survive near-future ocean-acidification conditions.
Continue reading ‘Calcareous sponges can synthesize their skeleton under short-term ocean acidification’Short-term responses of Corallina officinalis (rhodophyta) to global-change drivers in a stressful environment of Patagonia, Argentina
Published 28 April 2023 Science ClosedTags: biological response, corals, laboratory, light, multiple factors, nutrients, physiology, primary production, South Atlantic
Over the last two decades, an increasing interest has arisen in the responses of primary producers to global-change drivers and, more recently, in the need to consider how those various drivers may interact. To understand how Corallina officinalis (hereafter Corallina) can be affected by future changing conditions, we investigated the short-term direct effects of co-occurring increased nutrient loads, solar radiation, and lower pH, assessing how these clustered drivers affected Corallina‘s overall physiological performance in a harsh Patagonian coastal environment. To describe the seasonal trend of the physiological parameters in the field, we sampled subtidal Corallina to determine their net oxygen production (NOP), pigments, and carbonate content (CC). Furthermore, we conducted seasonal 10-days experiments, simulating the conditions predicted for the year 2100 by the IPCC (RCP 8.5) —manipulating pH, nutrients, and irradiance—along with the current conditions. The pigments and carotenoids/chlorophyll-a ratio were, in general, constant in the field over the seasons; but the NOP and CC dropped in spring, when the carotenoids peaked. After the experiment, the highest carotenoid/chlorophyll-a ratio was registered in summer under both the currentand the predictedconditions and in winter under the predictedcondition. This lower physiological status was also reflected in almost all other variables. Thus, Corallina may display an acclimatation strategy to cope with high ultraviolet-radiation levels by adjusting its pigment composition to avoid photoinhibition. An understanding of how Corallina, as a habitat-forming species, will respond to future global-change may provide clues about the extent of effects on the ecosystem functions and services.
Continue reading ‘Short-term responses of Corallina officinalis (rhodophyta) to global-change drivers in a stressful environment of Patagonia, Argentina’Benthic foraminiferal turnover and trait changes across the Palaeocene–Eocene Thermal Maximum (PETM) at ODP site 1265A, Walvis Ridge, SE Atlantic Ocean
Published 26 April 2023 Science ClosedTags: abundance, biological response, BRcommunity, community composition, field, morphology, otherprocess, paleo, protists, sediment, South Atlantic
Benthic foraminiferal turnover during the Palaeocene–Eocene Thermal Maximum (PETM) has been extensively studied but numerous questions remained unresolved, question such as why some foraminiferal species went into extinction at a particular location but survive in another or why some species survive in extremely low oxygen environment. Because foraminiferal community interaction with the environment is driven by biological traits instead of taxonomic composition, this study has adopted trait-based approach to provide insight into the life strategies of foraminifera that enables them to survive in extreme environmental conditions. The result from this study shows that traits such as test composition, perforation, ornamentation and living habits play an important role in the ecological functioning and adaptability of foraminifera in the environment. The faunal assemblage in the studied site is dominantly cosmopolitan taxa suggesting the environment was perturbed during the PETM. Foraminiferal composition is characterised by faunal turnover indicated in extensive mortalities and extinction of both planktonic and benthic fauna. The ordination (non-metric dimensional scaling) of faunal composition also indicated ecological disturbance. The planktonic community was relatively stable before and after PETM but experienced a high level of ecological perturbation during the carbon isotopic excursion (CIE). The benthic community showed higher evidence of perturbation as the fauna assemblage ordination indicated that ecological stress started before the PETM with the disarray of samples in the ordination diagram. Only the recovery interval experienced some level of ecological stability. The environmental disturbance noticed in the fauna composition reflected on the trait. Benthic foraminiferal traits indicated instability throughout the studied section. The evidence of environmental disturbance in the benthic community suggests that the source of the light carbon that caused the PETM may have originated beneath sea floor in the Atlantic Ocean.
Continue reading ‘Benthic foraminiferal turnover and trait changes across the Palaeocene–Eocene Thermal Maximum (PETM) at ODP site 1265A, Walvis Ridge, SE Atlantic Ocean’Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean
Published 24 March 2023 Science ClosedTags: biological response, fish, fisheries, individualmodeling, modeling, multiple factors, oxygen, South Atlantic, temperature
Climate change impacts on fishery resources have been widely reported worldwide. Nevertheless, a knowledge gap remains for the warm-temperate Southwest Atlantic Ocean—a global warming hotspot that sustains important industrial and small-scale fisheries. By combining a trait-based framework and long-term landing records, we assessed species’ sensitivity to climate change and potential changes in the distribution of important fishery resources (n = 28; i.e., bony fishes, chondrichthyans, crustaceans, and mollusks) in Southern Brazil, Uruguay, and the northern shelf of Argentina. Most species showed moderate or high sensitivity, with mollusks (e.g., sedentary bivalves and snails) being the group with the highest sensitivity, followed by chondrichthyans. Bony fishes showed low and moderate sensitivities, while crustacean sensitivities were species-specific. The stock and/or conservation status overall contributed the most to higher sensitivity. Between 1989 and 2019, species with low and moderate sensitivity dominated regional landings, regardless of the jurisdiction analyzed. A considerable fraction of these landings consisted of species scoring high or very high on an indicator for potential to change their current distribution. These results suggest that although the bulk of past landings were from relatively climate-resilient species, future catches and even entire benthic fisheries may be jeopardized because (1) some exploited species showed high or very high sensitivities and (2) the increase in the relative representation of landings in species whose distribution may change. This paper provides novel results and insights relevant for fisheries management from a region where the effects of climate change have been overlooked, and which lacks a coordinated governance system for climate-resilient fisheries.
Continue reading ‘Sensitivity of fishery resources to climate change in the warm-temperate Southwest Atlantic Ocean’High-resolution marine osmium and carbon isotopic record across the Aptian–Albian boundary in the southern South Atlantic: evidence for enhanced continental weathering and ocean acidification
Published 22 February 2023 Science ClosedTags: field, paleo, South Atlantic
The Early Cretaceous Aptian–Albian boundary (AAB) interval (∼113 Ma) was marked by severe environmental perturbations, including Oceanic Anoxic Event (OAE) 1b, global warming, and a major species turnover of planktonic foraminifera. Most paleoenvironmental studies across the AAB have focused on Tethyan sedimentary sequences deposited at low latitudes, but, because of the scarcity of well-dated sedimentary sequences across the AAB at high latitudes, the global extent of these environmental perturbations remains uncertain. Deep Sea Drilling Project (DSDP) Site 511 was drilled on the Falkland Plateau, southern South Atlantic, and is one of the few sedimentary sequences at southern high latitudes to record an almost continuous AAB interval. Previous studies documented the planktonic foraminiferal changes across the AAB at DSDP Site 511, but chemostratigraphic information has been limited. We reconstructed an osmium and carbon isotopic stratigraphy to further constrain the position of the AAB. We also inferred the paleo-marine redox conditions at southern high latitudes by combining chemical and lithological information. We found an abrupt negative δ13Ccarb shift coincident with the first occurrence of Microhedbergella renilaevis, an event that marks the base of the Albian Stage. This negative δ13Ccarb shift has also been observed across the AAB interval in the Tethyan and Atlantic regions. The fact that the osmium isotopic ratios show a pronounced radiogenic shift after the AAB is consistent with osmium isotopic variations detected in the Tethys and Pacific regions. Because the Os shift corresponded to a warming event during OAE1b in the low-latitude Atlantic and Tethyan regions, we interpret this radiogenic osmium isotopic shift as a response to increased continental weathering caused by global warming. A large marcasite crystal in the AAB interval at DSDP Site 511 suggests that the southern Atlantic Ocean may have been oxygen-depleted with a low pH caused by contemporaneous global environmental perturbations.
Continue reading ‘High-resolution marine osmium and carbon isotopic record across the Aptian–Albian boundary in the southern South Atlantic: evidence for enhanced continental weathering and ocean acidification’Ocean acidification and long-rerm changes in the carbonate system properties of the South Atlantic Ocean
Published 4 October 2022 Science ClosedTags: chemistry, field, South Atlantic
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
Effects of the ocean acidification on the functional structure of coral reef nematodes
Published 15 September 2022 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, corals, field, laboratory, mesocosms, nematodes, otherprocess, physiology, South Atlantic
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.
Continue reading ‘Effects of the ocean acidification on the functional structure of coral reef nematodes’The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin
Published 9 September 2022 Science ClosedTags: corals, methods, paleo, South Atlantic
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.
Continue reading ‘The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin’Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling
Published 1 September 2022 Science ClosedTags: field, methods, North Atlantic, protists, sediment, South Atlantic
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.
Continue reading ‘Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling’Seasonal variability of carbonate chemistry and its controls in a subtropical estuary
Published 29 August 2022 Science ClosedTags: chemistry, field, multiple factors, South Atlantic, temperature
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.
Continue reading ‘Seasonal variability of carbonate chemistry and its controls in a subtropical estuary’Climate resilience and adaptation in West African oyster fisheries: an expert-based assessment of the vulnerability of the oyster Crassostrea tulipa to climate change
Published 26 August 2022 Science ClosedTags: adaptation, biological response, fisheries, mollusks, otherprocess, South Atlantic
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.
Continue reading ‘Climate resilience and adaptation in West African oyster fisheries: an expert-based assessment of the vulnerability of the oyster Crassostrea tulipa to climate change’Stylasterid corals build aragonite skeletons in undersaturated water despite low pH at the site of calcification
Published 11 August 2022 Science ClosedTags: Antarctic, biological response, chemistry, corals, laboratory, North Atlantic, physiology, South Atlantic
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.
Continue reading ‘Stylasterid corals build aragonite skeletons in undersaturated water despite low pH at the site of calcification’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
Published 11 August 2022 Science ClosedTags: biological response, chemistry, field, multiple factors, oxygen, photosynthesis, phytoplankton, South Atlantic
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’
