Posts Tagged 'sediment'

Fermentative iron reduction buffers acidification and promotes microbial metabolism in marine sediments

Microbial iron reduction is a crucial process in natural ecosystems, contributing to the cycling of elements and supporting the biological activities of organisms. However, the significance of fermentative iron reduction in marine environments and microbial metabolism remains understudied compared with iron reduction coupled with respiration. The main objective of our study was to investigate the influence of fermentative iron reduction on microbial populations and marine sediment. Our findings revealed a robust iron-reducing activity in the enriched marine sediment, demonstrating a maximum ferrihydrite-reducing rate of 0.063 mmol/h. Remarkably, ferrihydrite reduction exhibited an intriguing pH-buffering effect through the release of OH+ and Fe2+ ions, distinct from fermentation alone. This effect resulted in substantial improvements in glucose consumption (71.4%), bacterial growth (48.1%), and metabolite production (80.8%). To further validate the acidification-buffering and metabolism-promoting effects of ferrihydrite reduction, we conducted iron-reducing experiments using a pure strain, Clostridium pasteurianum DMS525. The observed pH-buffering effect resulted from microbial iron reduction in marine sediment and has potential environmental implications by reducing CO2 emissions, mitigating acidification, and preserving the delicate balance of marine ecosystems.

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The estuarine environment and pH variation: natural limits and experimental observation of the acidification effect on phosphorus bioavailability (in Portuguese)

This study shows the variation of pH in the Cananéia-Iguape Estuarine-Lagoon Complex (CIELC). Data from 3 years (2019, 2021, 2022) were obtained in 17 points presenting the following ranges: temperature (14.88-27.05 ºC), pH (7.16-8.40) and DIP (0.20-11.28 µmol L-1) along a saline gradient (0.05-32.09) under different hydrodynamics, biogeochemical processes and anthropogenic influence. The pH buffering capacity due to the presence of weak acid salts in saline water (S ≥ 30) was associated to the lowest DIP, decreasing with low salinity values, confirming the direct correlation among salinity and pH. The highest temperatures in the winter of 2021, corroborated with the abnormal climate event in that year. An in vitro experiment showed results of the interaction of PID and sediments with different textures, with and without the presence of the benthic microbiota under a considerable decreasing of the pH (acidification) in relation to the natural condition of this environment. The P sediment flux characterized Iguape sector as a P sink with or without biota, Ararapira sector as a P source with biota and Cananéia, as P source without biota. The salt water buffered the pH and sediment buffered DIP both associated to the biogeochemical and hydrodynamic processes contribute to the homeostasis in the system.

Continue reading ‘The estuarine environment and pH variation: natural limits and experimental observation of the acidification effect on phosphorus bioavailability (in Portuguese)’

Microbial communities inhabiting shallow hydrothermal vents as sentinels of acidification processes

Introduction: Shallow hydrothermal vents are considered natural laboratories to study the effects of acidification on biota, due to the consistent CO2 emissions with a consequent decrease in the local pH.

Methods: Here the microbial communities of water and sediment samples from Levante Bay (Vulcano Island) with different pH and redox conditions were explored by Next Generation Sequencing techniques. The taxonomic structure was elucidated and compared with previous studies from the same area in the last decades.

Results and discussion: The results revealed substantial shifts in the taxonomic structure of both bacterial and archaeal communities, with special relevance in the sediment samples, where the effects of external parameters probably act for a long time. The study demonstrates that microbial communities could be used as indicators of acidification processes, by shaping the entire biogeochemical balance of the ecosystem in response to stress factors. The study contributes to understanding how much these communities can tell us about future changes in marine ecosystems.

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Constraining oceanic carbonate chemistry evolution during the Cretaceous-Paleogene transition: combined benthic and planktonic calcium isotope records from the equatorial Pacific Ocean

The Mesozoic-Cenozoic transition is a period of biogeochemical cycle perturbations. The strongest of them is the Cretaceous-Paleogene boundary (K-Pg) crisis, characterized by one of the most important extinctions of planktonic marine calcifiers in Earth’s history. One of the primary drivers of this biocalcification crisis is thought to be the increase in atmospheric CO2 concentration and ocean acidification triggered by the Chicxulub Impact, and/or Deccan volcanism. Because it reflects changes of the calcium cycle and/or depends on parameters of the carbonate system, the Ca isotope composition of carbonate minerals precipitated from seawater (44/40Ca) offers the potential to reconstruct some of the environmental changes that occurred. Here we present new high-resolution planktonic and benthic foraminiferal 44/40Ca, 18O, 13C, and Sr/Ca records across the K-Pg transition from Shatsky rise (Leg 198; ODP Site 1209, Hole C). The 44/40Ca record displays a succession of rapid shifts of ca. ‰−0.4‰ across the K-Pg transition. They are similar though not identical between the planktonic and benthic records. These shifts took place on a timescale significantly shorter than the residence time of Ca in the oceans and are therefore unlikely to result from global disequilibrium in the oceanic Ca budget. Instead, changes in the fractionation factor between carbonate minerals and seawater in response to changes in precipitation rates may explain the observed 44/40Ca and Sr/Ca record. The benthic and planktonic 44/40Ca records show a late Maastrichtian and an early Danian negative excursions best explained by a succession of episodes of ocean alkalinity increase related to increased continental weathering caused by CO2 emissions from Deccan volcanism and the aftermath of the K-Pg biocalcification crisis. Carbonate compensation via carbonate sediment dissolution, biological carbonate compensation via reduction of biocalcification, and/or an increase in continental weathering must have occurred to offset the excess CO2, ultimately resulting in rapid changes in ocean carbonate chemistry, in combination with reduced surface alkalinity export in response to the early Paleogene planktonic biomineralization crisis.

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Did changes in terrigenous components of deep-sea cherts across the end-Triassic extinction relate to the Central Atlantic magmatic province volcanism?

The end-Triassic mass extinction event (ETE) is considered to be linked with the emplacement of the Central Atlantic magmatic province (CAMP), yet their temporal relation and underlying nature of global environmental and biotic changes remain controversial. A drastic radiolarian faunal turnover was associated with deep-sea acidification and changes in the chemical composition of pelagic terrigenous components, which were interpreted as the results of increased CAMP-derived material, such as Fe2O3/Al2O3, MgO/Al2O3, and SiO2/Al2O3, without statistical tests. Here we re-examined these CAMP-like signatures in terms of changes in the chemical composition of the Triassic-Jurassic pelagic deep-sea chert succession in Japan. Our newly compiled dataset suggests that changes in Fe2O3/Al2O3 and MgO/Al2O3 across the ETE were not significant, and thus they may not be appropriate proxies for CAMP-derived material potentially due to the dissolution of iron by ocean acidification and the formation of chlorite during the diagenesis, respectively. Decreased SiO2/Al2O3 was also considered to have been reflected in increased CAMP-related dust flux and/or decreased biosiliceous productivity, but a slight increase in Al2O3/TiO2 ratio (a biosiliceous productivity proxy) and an increase in shale bed thickness (dust flux proxy) across the radiolarian ETE implies the increased eolian dust flux rather than decreased productivity. Besides, statistically significant Na-enrichment at the radiolarian ETE level might be related to the CAMP volcanism and/or associated changes in the source areas of eolian dust.

Continue reading ‘Did changes in terrigenous components of deep-sea cherts across the end-Triassic extinction relate to the Central Atlantic magmatic province volcanism?’

Effects of sediment and water column acidification on growth, survival, burrowing behaviour, and GABAA receptor function of benthic invertebrates

In coastal regions, sediment-dwelling animals are exposed to a high degree of variability in seawater and sediment pH and pH is expected to decline due to anthropogenic effects. The impacts of 6-week exposure to reduced-pH seawater on length, weight, and survival of two species of molluscs that inhabit mudflats, juvenile soft-shell clams (Mya arenaria) and adult mud snails (Tritia obsoleta), were examined in two laboratory trials (2017 and 2018). The interactive effects of this prior exposure to water column acidification and subsequent sediment acidification on burrowing behaviour were then investigated for these mollusc species and adults of the amphipod Corophium volutator. In a separate experiment, the potential involvement of GABAA receptors in changes in burrowing behaviour in reduced-pH conditions was tested by exposing three species: C. volutatorT. obsoleta, and the Baltic clam Limecola balthica to sediment acidification and the neuroinhibitor gabazine. Reduced-pH water conditions only decreased the shell length of T. obsoleta in 2017 while all other morphometric metrics were not significantly impacted for this species in either year or for M. arenaria. The burrowing of T. obsoleta was reduced by 13% in acidified sediments in one of the two years but not by prior exposure to water column acidification. The burrowing of M. arenaria was not affected by either factor. The burrowing of C. volutator was impacted by the interaction of water column exposure and sediment acidification in 2017 with the acidified water, control sediment treatment having 14% higher burrowing then the remaining treatment combinations. In 2018, C. volutator burrowing was reduced in acidified sediment by 30%. The presence of gabazine only had an interactive effect on the burrowing of one species, C. volutator. The presence of gabazine increased the proportion of C. volutator individuals burrowed in the acidified water treatment by almost 30%, suggesting that GABAA neuroreceptors are involved in the mechanism for the impact of sediment acidification on burrowing in this species. The results of our experiments indicate that there is taxonomic variation in species’ responses of benthic invertebrates to ocean and sediment acidification with respect to growth, survival, and burrowing behaviour.

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Variations in the Southern Ocean carbonate production, preservation, and hydrography for the past 41, 500 years: evidence from coccolith and CaCO3 records

Changes in ocean alkalinity affect atmospheric pCO2 (i.e., higher alkalinity lowers atmospheric pCO2). Ocean alkalinity is partly determined by sedimentary burial of carbonates, which is primarily controlled by carbonate flux and the degree of deep ocean carbonate saturation. In this study, we investigate the factors determining the coccolith burial in subantarctic sediments and the surface ocean changes in the subtropical South Indian Ocean. The downcore coccolith records from the subantarctic region (SK200/22a) of the Indian sector of the Southern Ocean display low coccolith concentration during the glacial period. A possible explanation for this is, 1) the low glacial production of coccolithophores due to the competition from diatoms and 2) dilution by biogenic silica in the glacial sediments. Additionally, reduced carbonate burial owing to the low carbonate saturation of the deep-water accounts for the decline in glacial coccolith concentration. This also explains the low coccolith dissolution index and enrichment of the large dissolution-resistant coccolith species, Coccolithus pelagicus subsp. braarudii in the glacial sediments. The low carbonate saturation is attributed to, 1) the replacement of carbonate saturated, North Atlantic Deep Waters by the undersaturated southern sourced water masses and 2) increased storage of dissolved CO2 in the deep glacial Southern Ocean. Our study suggests that changes in coccolith production and the deep ocean carbonate saturation determine their burial in subantarctic sediments for the last 41,500 years. Other than these changes, the study region also records the changes in the Agulhas Return Current via variation in the proportion of tropical-subtropical coccolith assemblage.

Continue reading ‘Variations in the Southern Ocean carbonate production, preservation, and hydrography for the past 41, 500 years: evidence from coccolith and CaCO3 records’

Risk assessment of a coastal ecosystem from SW Spain exposed to CO2 enrichment conditions

The Weight-of-Evidence (WOE) approach uses multiple lines of evidence to analyze the adverse effects associated with CO2 enrichment in two stations from the Gulf of Cádiz (Spain) with different contamination degrees. Sediment contamination and metal (loid) mobility, toxicity, ecological integrity, and bioaccumulation from the samples exposed to different acidification scenarios (pH gradient from 8.0 to 6.0) were used in the WOE. The experiments were conducted under laboratory conditions using a CO2-bubbling system. Different integration approaches such as multivariate analyses were used to evaluate the results. The results indicated that the adverse biological effects under pH 6.5 were related to the mobility of dissolved elements (As, Fe, Cu, Ni, and Zn). Furthermore, the pH reduction was correlated to the increase of bioaccumulation of As, Cr, Cu, Fe, and Ni in the tissues of mussels at pH 7.0. The noncontaminated sediment showed environmental degradation related to the acidification at pH values of 7.0; whereas the sediment moderately contaminated showed both environmental risks, caused by acidification and the presence and the increase of the bioavailability of contaminants. The WOE approach supposes an effective tool to identify and distinguish the causes of adverse effects related to the enrichment of CO2 in marine environments.

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Strong variation in sedimental antibiotic resistomes among urban rivers, estuaries and coastal oceans: evidence from a river-connected coastal water ecosystem in northern China

Sediment is thought to be a vital reservoir to spread antibiotic resistance genes (ARGs) among various natural environments. However, the spatial distribution patterns of the sedimental antibiotic resistomes around the Bohai Bay region, a river-connected coastal water ecosystem, are still poorly understood. The present study conducted a comprehensive investigation of ARGs among urban rivers (UR), estuaries (ES) and Bohai Bay (BHB) by metagenomic sequencing. Overall, a total of 169 unique ARGs conferring resistance to 15 antimicrobial classes were detected across all sediment samples. The Kruskal-Wallis test showed that the diversity and abundance of ARGs in the UR were all significantly higher than those in the ES and BHB (p < 0.05 and p < 0.01), revealing the distance dilution of the sedimental resistomes from the river to the ocean. Multidrug resistance genes contained most of the ARG subtypes, whereas rifamycin resistance genes were the most abundant ARGs in this region. Our study demonstrated that most antimicrobial resistomes were highly accumulated in urban river sediments, whereas beta-lactamase resistance genes (mainly PNGM-1) dramatically increased away from the estuary to the open ocean. The relative abundance of mobile genetic elements (MGEs) also gradually decreased from rivers to the coastal ocean, whereas the difference in pathogenic bacteria was not significant in the three classifications. Among MGEs, plasmids were recognized as the most important carriers to support the horizontal gene transfer of ARGs within and between species. According to co-occurrence networks, pathogenic Proteobacteria, Actinobacteria, and Bacteroidetes were recognized as potential and important hosts of ARGs. Heavy metals, pH and moisture content were all recognized as the vital environmental factors influencing the distribution of ARGs in sediment samples. Overall, the present study may help to understand the distribution patterns of ARGs at a watershed scale, and help to make effective policies to control the emergence, spread and evolution of different ARG subtypes in different habitats.

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Reduction in size of the calcifying phytoplankton Calcidiscus leptoporus to environmental changes between the Holocene and modern Subantarctic Southern Ocean

The Subantarctic Zone of the Southern Ocean plays a disproportionally large role on the Earth system. Model projections predict rapid environmental change in the coming decades, including ocean acidification, warming, and changes in nutrient supply which pose a serious risk for marine ecosystems. Yet despite the importance of the Subantarctic Zone, annual and inter-annual time series are extremely rare, leading to important uncertainties about the current state of its ecosystems and hindering predictions of future response to climate change. Moreover, as the longest observational time series available are only a few decades long, it remains unknown whether marine pelagic ecosystems have already responded to ongoing environmental change during the industrial era. Here, we take advantage of multiple sampling efforts – monitoring of surface layer water properties together with sediment trap, seafloor surface sediment and sediment core sampling – to reconstruct the modern and pre-industrial state of the keystone calcifying phytoplankton Calcidiscus leptoporus, central to the global marine carbonate cycle. Morphometric measurements reveal that modern C. leptoporus coccoliths are 15% lighter and 25% smaller than those preserved in the underlying Holocene-aged sediments. The cumulative effect of multiple environmental drivers appears responsible for the coccolith size variations since the Last Deglaciation, with warming and ocean acidification most likely playing a predominant role during the industrial era. Notably, extrapolation of our results suggests a future reduction in cell and coccolith size which will have a negative impact on the efficiency of the biological pump in the Southern Ocean through a reduction of carbonate ballasting. Lastly, our results tentatively suggest that C. leptoporus coccolith size could be used as a palaeo-proxy for growth rate. Future culture experiments will be needed to test this hypothesis.

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Explosive volcanism periodicity past cycles record within the last 0.8 Mya evidenced by tephra and benthic foraminifera of IODP Hole U1485AA (Exp. 363 WPWP)

Volcanic eruptions with increase in the amount of carbon dioxide (CO2) and other gases are responsible for the extinction of many species because of decreased pH and carbonate availability which creates ocean acidification. Here we show how benthic foraminifera have evolved, by studying sediments from U1485A (1145 m water depth) core in the Papua New Guinea (PNG) collected during IODP Expedition 363 in the Western Pacific Warm Pool (WPWP), one of the warmest marine waters of the world. High-stressed environments dominated by low diversity of opportunistic species after volcanic activity was detected by the presence of tephra and volcanic ashes within the last 0.8 Mya. The decrease in the diversity patterns show an inverse correlation to the presence of tephra and ash right after Pleistocene volcanic eruptions in the past. Deep-water fauna is dominated by Cibicidoides pachiderma, from the early Oligocene through the Pleistocene, Uvigerina hispida from early Miocene through Pleistocene, U. prosbocidae from late Oligocene through Pleistocene, and an outer neritic upper bathyal Uvigerina mediterranea from high salinities, warm waters, low dissolved oxygen, and high organic matter. Bolivinita quadrilatera characteristic of 200-500m depth, Bolivina robusta from 3 to 900m, and the Rotalinoides compressiusculus, a shallow warm water species, from 2-37m depth show higher diversity peaks in interglacial cycles. High-stress conditions with mass extinction after volcanic eruptions leads to enhanced weathering, global warming and cooling afterwards, and ocean acidification, resulting in a crisis in the marine environment in terms of carbonate. Diversity gradients suggested that foraminiferal species responded to the cyclic pulses of volcanic eruptions, and its unstable ecological conditions created by the increase in the temperature and CO2. Here we show that tephra layers and ash record a periodicity of explosive volcanism within the last 0.8 Myr maintaining a strong 100 kyr periodicity, and that earth’s orbital cycles might trigger peaks of volcanic eruptions 41,000-year cycle.

Continue reading ‘Explosive volcanism periodicity past cycles record within the last 0.8 Mya evidenced by tephra and benthic foraminifera of IODP Hole U1485AA (Exp. 363 WPWP)’

Coastal acidification alters estuarine sediment nitrous oxide and methane fluxes


The impact of coastal acidification on sediment nitrous oxide (N2O) and methane (CH4) fluxes is largely unknown. We exposed temperate estuarine sediments to moderate (pH 7.3) and extreme (pH 6.3) acidification. Sediments were collected from two sites—one exposed to high and the other to low nitrogen loading. We demonstrate that low pH has a strong effect on greenhouse gas fluxes. The response, in terms of both magnitude and direction, was site specific. Sediments from the high nitrogen loading site exhibited increased N2O fluxes and decreased CH4 fluxes under moderate and extreme acidification. In contrast, sediments from the low nitrogen loading site exhibited decreased N2O fluxes under moderate and extreme acidification while CH4 fluxes both decreased (moderate) and increased (extreme). This study highlights the dynamic response of sediment N2O and CH4 fluxes to low pH and emphasizes the need for deeper understanding of ofcoastal acidification impacts on sediment biogeochemistry.

Scientific Significance Statement

Estuaries are increasingly exposed to low pH conditions (i.e., coastal acidification) largely driven by rising temperatures, increased precipitation, and excess nutrient loading. The impact of coastal acidification on sediment biogeochemical processes, including those responsible for the production or consumption of greenhouse gases (GHGs) are largely unknown. Here, we show that sediment fluxes of two powerful GHGs (nitrous oxide: N2O and methane: CH4) respond rapidly to low pH conditions. In addition, the magnitude and direction of this response varies within an estuary, even at sites with similar pH exposure histories. Overall, this study highlights the need to incorporate current and future pH conditions in forecasting models and in the development of coastal GHG budgets.

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The Paleocene-Eocene transition in the Gulf of Guinea: evidence of the Petm in the Douala Basin, Cameroon

The Paleocene-Eocene Thermal Maximum (PETM) was identified for the first time in two sections (Bongue and Dibamba) from the Douala sub-basin located in the Gulf of Guinea, Cameroon. This discovery was based on a multi-disciplinary approach including benthic and planktic foraminifera, ostracods, major and trace elements, mercury, carbon stable isotope (δ13C values), total organic carbon (TOC), whole-rock and clay mineralogy. A combination of lithology, microfossil assemblage, and carbon isotope data indicate zone P5 and the top of the Paleocene enabling the definition of the Paleocene-Eocene boundary (PEB). A negative carbon-isotope excursion (CIE) spanning from the uppermost Paleocene deposits to the earliest Eocene sediments (PETM interval) shows a shift in δ13Corg values of 1.5 ‰ in Bongue and 3.0 ‰ in Dibamba. In both sections, this interval is affected by widespread acidification, as revealed by carbonate dissolution and microfossil preservation (i.e., species are dwarfed, broken, thin shelled, and with holes). The very low carbonate content and the scarcity of microfauna indicate the severity of acidification during the PETM, especially in the early Eocene where only one species was identified (Igorina broedermanni). Mercury anomalies, TOC contents, and trace element concentration ratios, point to volcanic activity linked to the Cameroon Volcanic Line (CVL) intrusive magma, and a decrease in productivity prior to the PETM. In addition to climate change, our geochemical and mineralogical data support the hypothesis that other environmental perturbations such as an increase in productivity and detrital input, as well as a decrease in bottom water oxygenation occurred during the PETM in the Douala sub-basin.

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Foraminiferal assemblages and test characteristics associated with natural low pH waters at Puerto Morelos reef lagoon springs, QR Mexico

Ocean acidification is expected to negatively affect many ecologically important organisms. Here we explored the response of Caribbean benthic foraminiferal assemblages to naturally discharging low-pH waters similar to expected future projections for the end of the 21st century. At low pH (~7.7 pH units) and low calcite saturation, agglutinated and symbiont-bearing species were relatively more abundant, indicating higher resistance to potential carbonate chemistry changes. Diversity and other taxonomical metrics declined steeply with decreasing pH, despite exposure of this ecosystem for millennia to low pH conditions, suggesting that tropical foraminifera communities will be negatively impacted under acidification scenarios SSP3-7.0 and SSP5-8.5. The species Archaias angulatus, a major contributor to sediment production in the Caribbean, was able to calcify at conditions more extreme than those projected for the late 21st century (7.1 pH units), but the calcified tests were of lower density than those exposed to higher-pH ambient conditions (7.96 pH units), indicating that reef foraminiferal carbonate budget might decrease. Smaller foraminifera were highly sensitive to decreasing pH and our results demonstrate their potential as indicators to monitor increasing OA conditions.

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Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry

Understanding the variations in past ocean carbonate chemistry is critical to elucidating the role of the oceans in balancing the global carbon cycle. The fossil shells from marine calcifiers present in the sedimentary record are widely applied as past ocean carbon cycle proxies. However, the interpretation of these records can be challenging due to the complex physiological and ecological response to the carbonate system during an organisms’ life cycle and the potential for preservation at the seafloor. Here we present a new dissolution proxy based on the morphological attributes of coccolithophores from the Noëlaerhabdaceae family (Emiliania huxleyi > 2 µm, and small Gephyrocapsa spp.). To evaluate the influences of coccolithophore calcification and coccolith preservation on fossil morphology, we measured morphological attributes, mass, length, thickness, and shape factor (ks) of coccoliths in a laboratory dissolution experiment and surface sediment samples from the South China Sea. The coccolith morphological data in surface sediments were also analyzed with environment settings, namely surface temperature, nutrients, pH, chlorophyll a concentration, and carbonate saturation of bottom water by a redundancy analysis. Statistical analysis indicates that carbonate saturation of the deep ocean explains the highest proportion of variation in the morphological data instead of the environmental variables of the surface ocean. Moreover, the dissolution trajectory in the ks vs. length of coccoliths is comparable between natural samples and laboratory dissolution experiments, emphasizing the importance of carbonate saturation on fossil coccolith morphology. However, the mean ks alone cannot fully explain the main variations observed in our work. We propose that the normalized ks variation (), which is the ratio between the standard deviation of ks (σ) and the mean ks, could reflect different degrees of dissolution and size-selective dissolution, influenced by the assemblage composition. Applied together with the  ratio, the ks factor of fossil coccoliths in deep ocean sediments could be a potential proxy for a quantitative reconstruction of past carbonate dissolution dynamics.

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The impact of potential leakage from the sub-seabed CO2 storage site on the phosphorus transformation in marine sediments – an experimental study


  • The goal was to study the effect of CO2 leakage from a sub-seabed storage on P pools.
  • We conducted series of experiments exposing sediments to CO2-enriched seawater.
  • Acidification can reduce the efficiency of the burial of P in marine sediments.
  • Under acidic pH, apatite P is transformed into organic and non-apatite inorganic P.


Carbon Capture and Storage (CCS) in the sub-seabed geological formations is a method of mitigation of carbon dioxide (CO2) emissions to avoid anthropogenic climate change. While CCS can be one of the most promising technologies to reduce atmospheric CO2 in the short and medium term, it raises serious concerns about the potential leakage of gas from storage sites. In the present study, the impact of acidification induced by CO2 leakage from a sub-seabed storage site on geochemical pools, and thus the mobility, of phosphorus (P) in sediment was investigated during laboratory experiments. The experiments were conducted in a hyperbaric chamber at a hydrostatic pressure of 900 kPa, which simulates pressure conditions at a potential sub-seabed CO2 storage site in the southern Baltic Sea. We performed three separate experiments in which the partial pressure of CO2 was: 352 μatm (corresponding pH = 7.7); 1815 μatm (corresponding pH = 7.0), and 9150 μatm (corresponding pH = 6.3). Under pH 7.0 and 6.3, apatite P is transformed into organic and non-apatite inorganic forms, which are less stable than Casingle bondP bonds and can be more easily released into the water column. At pH 7.7, P released during mineralization of organic matter and microbial reduction of Fesingle bondP phases is bound with Ca, and the concentration of this form increases. The obtained results indicate that acidification of bottom water can reduce the efficiency of P burial in marine sediments, which contributes to an increase in P concentration in the water column and promote eutrophication especially in shallow areas.

Continue reading ‘The impact of potential leakage from the sub-seabed CO2 storage site on the phosphorus transformation in marine sediments – an experimental study’

Acidification alters sediment nitrogen source-sink dynamics in eelgrass (Zostera marina (L.)) beds

Dissolved carbon dioxide (CO2) in seawater lowers water pH and can disrupt microbial nutrient cycles. It is unclear how acidification impacts hot spots of nutrient cycling in marine ecosystems such as eelgrass (Zostera marina) beds. We measured nutrient and gas fluxes in sediment cores from Z. marina beds and unvegetated-sediment habitats in Shinnecock Bay, New York, USA in a continuous-flow system with acidified and ambient pH treatments. Under ambient conditions, uptake of N2 by nitrogen (N) fixation was greater than production of N2 by denitrification. Denitrification, however, was dominant under acidified conditions. We then enriched flowing seawater with 15NO3 to test the impact of a nutrient pulse with ambient pH or acidified conditions in the eelgrass and unvegetated cores. Sediment N2 efflux was higher in eelgrass than unvegetated sediments under acidified pH with N-enriched treatments. Results suggest that eelgrass beds may serve as sinks rather than sources of N under the combined stressors of acidification and N-loading. Documenting changes to N pathways under acidification can inform efforts to manage marine ecosystems and conserve benthic habitats.

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Calcification response of planktic foraminifera to environmental change in the western Mediterranean Sea during the industrial era (update)

The Mediterranean Sea sustains a rich and fragile ecosystem currently threatened by multiple anthropogenic impacts that include, among others, warming, pollution, and changes in seawater carbonate speciation associated to increasing uptake of atmospheric CO2. This environmental change represents a major risk for marine calcifiers such as planktonic foraminifera, key components of pelagic Mediterranean ecosystems and major exporters of calcium carbonate to the sea floor, thereby playing a major role in the marine carbon cycle. In this study, we investigate the response of planktic foraminifera calcification in the northwestern Mediterranean Sea on different timescales across the industrial era. This study is based on data from a 12-year-long sediment trap record retrieved in the in the Gulf of Lions and seabed sediment samples from the Gulf of Lions and the promontory of Menorca. Three different planktic foraminifera species were selected based on their different ecology and abundance: Globigerina bulloidesNeogloboquadrina incompta, and Globorotalia truncatulinoides. A total of 273 samples were weighted in both sediment trap and seabed samples.

The results of our study suggest substantial different seasonal calcification patterns across species: G. bulloides shows a slight calcification increase during the high productivity period, while both N. incompta and G. truncatulinoides display a higher calcification during the low productivity period. The comparison of these patterns with environmental parameters indicate that controls on seasonal calcification are species-specific. Interannual analysis suggests that both G. bulloides and N. incompta did not significantly reduce their calcification between 1994 and 2005, while G. truncatulinoides exhibited a constant and pronounced increase in its calcification that translated in an increase of 20 % of its shell weight. The comparison of these patterns with environmental data reveals that optimum growth conditions affect positively and negatively G. bulloides and G. truncatulinoides calcification, respectively. Sea surface temperatures (SSTs) have a positive influence on N. incompta and G. truncatulinoides calcification, while carbonate system parameters appear to affect positively the calcification of three species in the Gulf of Lions throughout the 12-year time series.

Finally, comparison between sediment trap data and seabed sediments allowed us to assess the changes of planktic foraminifera calcification during the late Holocene, including the pre-industrial era. Several lines of evidence indicate that selective dissolution did not bias the results in any of our data sets. Our results showed a weight reduction between pre-industrial and post-industrial Holocene and recent data, with G. truncatulinoides experiencing the largest weight loss (32 %–40 %) followed by G. bulloides (18 %–24 %) and N. incompta (9 %–18 %). Overall, our results provide evidence of a decrease in planktic foraminifera calcification in the western Mediterranean, most likely associated with ongoing ocean acidification and regional SST trends, a feature consistent with previous observations in other settings of the world’s oceans.

Continue reading ‘Calcification response of planktic foraminifera to environmental change in the western Mediterranean Sea during the industrial era (update)’

A rapid onset of ocean acidification associated with the end-Permian mass extinction

The end-Permian mass extinction (EPME) resulted in the most severe biodiversity loss in Earth’s history, the cause(s) of which are still heavily debated. Recent studies have emphasized the role of ocean acidification on marine ecosystem collapse during the EPME, but the timing of the onset of ocean acidification and its relationship to contemporaneous large igneous province (LIP) magmatism remain ambiguous. Here, we present the first in-situ secondary ion mass spectrometry (SIMS) sulfur isotope data for pyrite and marcasite from the Meishan section, which hosts the Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary (PTB). We found a sharp increase in marcasite abundance and a concurrent decrease in marcasite δ34S to highly negative values (ca. –50‰) within the EPME interval (i.e., Beds 25–28). Combined with the morphology of marcasite, we infer that the formation of 34S-depleted anhedral marcasite occurred in a sulfate-unlimited porewater environment that was likely well connected to the overlying water column. A similar negative shift in δ34Smarcasite was observed in the EPME interval of the Penglaitan section. Given that marcasite forms only in acidic conditions and low δ34Smarcasite values suggest an open porewater system, the sharp negative shift in the δ34S of syndepositional marcasite records a sudden acidification of Late Permian seawater. This conclusion is broadly consistent with previously reported boron isotope data of brachiopod-shell which witnessed a negative shift at the same stratigraphic horizons. While the ocean acidification event started after the starting point (base of Bed 25) of EPME, it occurred broadly within the extinction interval (Beds 25 to 28), supporting the hypothesis that ocean acidification may have been a major environmental factor contributing to the end-Permian marine ecosystem collapse.

Continue reading ‘A rapid onset of ocean acidification associated with the end-Permian mass extinction’

Benthic foraminiferal turnover and trait changes across the Palaeocene–Eocene Thermal Maximum (PETM) at ODP site 1265A, Walvis Ridge, SE Atlantic Ocean

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’

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