Identifying the causes and consequences of natural variations in ocean acidification and atmospheric CO2 due to complex earth processes has been a major challenge for climate scientists in the past few decades. Recent developments in the boron isotope (δ11B) based seawater pH and pCO2 (or pCO2sw) proxy have been pivotal in understanding the various oceanic processes involved in air-sea CO2 exchange. Here we present the first foraminifera-based δ11B record from the north-eastern Arabian Sea (NEAS) covering the mid-late Holocene (~ 8–1 ka). Our record suggests that the region was overall a moderate to strong CO2 sink during the last 7.7 kyr. The region behaved as a significant CO2 source during two short intervals around 5.5–4 ka and 2.8–2.5 ka. The decreased pH and increased CO2 outgassing during those abrupt episodes are associated with the increased upwelling in the area. The upwelled waters may have increased the nutrient content of the surface water through either increased supply or weaker export production. This new dataset from the coastal NEAS suggests that, as a potential result of changes in the strength of the El-Nino Southern Oscillation, the region experienced short episodes of high CO2 outgassing and pre-industrial ocean acidification comparable to or even greater than that experienced during the last ~ 200 years.
Continue reading ‘Abrupt upwelling and CO2 outgassing episodes in the north-eastern Arabian Sea since mid-Holocene’Posts Tagged 'sediment'
Abrupt upwelling and CO2 outgassing episodes in the north-eastern Arabian Sea since mid-Holocene
Published 21 March 2022 Science ClosedTags: Indian, laboratory, phytoplankton, sediment
Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: developing a new paleo-CO2 probe
Published 18 March 2022 Science ClosedTags: biological response, laboratory, North Atlantic, physiology, phytoplankton, sediment
Beyond the pCO2 records provided by ice core measurements, the quantification of atmospheric CO2 concentrations and changes thereof relies on proxy data, the development of which represents a foremost challenge in paleoceanography. In the paleoceanographic toolbox, the coccolithophores occupy a notable place, as the magnitude of the carbon isotopic fractionation between ambient CO2 and a type of organic compounds that these photosynthetic microalgae synthesize (the alkenones) represents a relatively robust proxy to reconstruct past atmospheric CO2 concentrations during the Cenozoic. The isotopic composition of coeval calcite biominerals found in the sediments and also produced by the coccolithophores (the coccoliths) have been found to record an ambient CO2 signal through culture and sediment analyses. These studies have, however, not yet formalized a transfer function that quantitatively ties the isotopic composition of coccolith calcite to the concentrations of aqueous CO2 and, ultimately, to atmospheric CO2 levels. Here, we make use of a microseparation protocol to compare the isotopic response of two size-restricted coccolith assemblages from the North Atlantic to changes in surface ocean CO2 during Termination II (ca. 130–140 ka). Performing paired measurements of the isotopic composition (δ13C and δ18O) of relatively large and small coccoliths provides an isotopic offset that can be designated as a “differential vital effect”. We find that the evolution of this offset follows that of aqueous CO2 concentrations computed from the ice core CO2 curve and an independent temperature signal. We interpret this biogeochemical feature to be the result of converging carbon fixation strategies between large and small cells as the degree of carbon limitation for cellular growth decreases across the deglaciation. We are therefore able to outline a first-order trend between the coccolith differential vital effects and aqueous CO2 in the range of Quaternary CO2 concentrations. Although this study would benefit from further constraints on the other controls at play on coccolith geochemistry (growth rate, air–sea gas exchange, etc.), this test of the drivers of coccolith Δδ13C and Δδ18O in natural conditions is a new step in the development of a coccolith paleo-CO2 probe.
Continue reading ‘Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: developing a new paleo-CO2 probe’Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum
Published 17 March 2022 Science ClosedTags: laboratory, North Atlantic, paleo, phytoplankton, protists, sediment
The Paleocene-Eocene Thermal Maximum (PETM) is recognized by a major negative carbon isotope (δ13C) excursion (CIE) signifying an injection of isotopically light carbon into exogenic reservoirs, the mass, source, and tempo of which continue to be debated. Evidence of a transient precursor carbon release(s) has been identified in a few localities, although it remains equivocal whether there is a global signal. Here, we present foraminiferal δ13C records from a marine continental margin section, which reveal a 1.0 to 1.5‰ negative pre-onset excursion (POE), and concomitant rise in sea surface temperature of at least 2°C and a decline in ocean pH. The recovery of both δ13C and pH before the CIE onset and apparent absence of a POE in deep-sea records suggests a rapid (< ocean mixing time scales) carbon release, followed by recovery driven by deep-sea mixing. Carbon released during the POE is therefore likely more similar to ongoing anthropogenic emissions in mass and rate than the main CIE.
Continue reading ‘Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum’Effects of local acidification on benthic communities at shallow hydrothermal vents of the Aeolian Islands (Southern Tyrrhenian, Mediterranean Sea)
Published 10 March 2022 Science ClosedTags: field, laboratory, Mediterranean, sediment, vents, zooplankton
Simple Summary
Ocean acidification is causing major changes in marine ecosystems, with varying levels of impact depending on the region and habitat investigated. Here, we report noticeable changes in both meio- and macrobenthic assemblages at shallow hydrothermal vents located in the Mediterranean Sea. In general, the areas impacted by the vent fluids showed decrease in the abundance of several taxa and a shift in community composition, but with a clear biomass reduction evident only for macrofauna. CO2 emissions at shallow hydrothermal vents cause a progressive simplification of community structure and a general biodiversity decline due to the loss of the most sensitive meio- and macrofaunal taxa, which were replaced by the more tolerant groups, such as oligochaetes, or highly mobile species, able to escape from extreme conditions. Our results provide new insight on the tolerance of marine meio- and macrofaunal taxa to the extreme conditions generated by hydrothermal vent emissions in shallow-water ecosystems.
Abstract
The Aeolian Islands (Mediterranean Sea) host a unique hydrothermal system called the “Smoking Land” due to the presence of over 200 volcanic CO2-vents, resulting in water acidification phenomena and the creation of an acidified benthic environment. Here, we report the results of a study conducted at three sites located at ca. 16, 40, and 80 m of depth, and characterized by CO2 emissions to assess the effects of acidification on meio- and macrobenthic assemblages. Acidification caused significant changes in both meio- and macrofaunal assemblages, with a clear decrease in terms of abundance and a shift in community composition. A noticeable reduction in biomass was observed only for macrofauna. The most sensitive meiofaunal taxa were kinorhynchs and turbellarians that disappeared at the CO2 sites, while the abundance of halacarids and ostracods increased, possibly as a result of the larger food availability and the lower predatory pressures by the sensitive meiofaunal and macrofaunal taxa. Sediment acidification also causes the disappearance of more sensitive macrofaunal taxa, such as gastropods, and the increase in tolerant taxa such as oligochaetes. We conclude that the effects of shallow CO2-vents result in the progressive simplification of community structure and biodiversity loss due to the disappearance of the most sensitive meio- and macrofaunal taxa.
Continue reading ‘Effects of local acidification on benthic communities at shallow hydrothermal vents of the Aeolian Islands (Southern Tyrrhenian, Mediterranean Sea)’Isotopic filtering reveals high sensitivity of planktic calcifiers to Paleocene–Eocene thermal maximum warming and acidification
Published 9 March 2022 Science ClosedTags: chemistry, field, methods, mitigation, North Pacific, paleo, sediment
Significance
Human-induced carbon emissions are causing global temperatures to rise and oceans to acidify. To understand how these rapid perturbations affect marine calcifying communities, we investigate a similar event in Earth’s geologic past, the Paleocene–Eocene thermal maximum (PETM). We introduce a method, isotopic filtering, to mitigate the time-averaging effects of sediment mixing on deep-sea microfossil records. Contrary to previous studies, we find that tropical planktic foraminifers in the central Pacific ocean were adversely affected by PETM conditions, as evidenced by a decrease in local diversity, extratropical migration, and impaired calcification. While these species survived the PETM through migration to cooler waters, it is unclear whether marine calcifiers can withstand the rapid changes our oceans are experiencing today.
Abstract
Ocean warming and acidification driven by anthropogenic carbon emissions pose an existential threat to marine calcifying communities. A similar perturbation to global carbon cycling and ocean chemistry occurred ∼56 Ma during the Paleocene–Eocene thermal maximum (PETM), but microfossil records of the marine biotic response are distorted by sediment mixing. Here, we use the carbon isotope excursion marking the PETM to distinguish planktic foraminifer shells calcified during the PETM from those calcified prior to the event and then isotopically filter anachronous specimens from the PETM microfossil assemblages. We find that nearly one-half of foraminifer shells in a deep-sea PETM record from the central Pacific (Ocean Drilling Program Site 865) are reworked contaminants. Contrary to previous interpretations, corrected assemblages reveal a transient but significant decrease in tropical planktic foraminifer diversity at this open-ocean site during the PETM. The decrease in local diversity was caused by extirpation of shallow- and deep-dwelling taxa as they underwent extratropical migrations in response to heat stress, with one prominent lineage showing signs of impaired calcification possibly due to ocean acidification. An absence of subbotinids in the corrected assemblages suggests that ocean deoxygenation may have rendered thermocline depths uninhabitable for some deeper-dwelling taxa. Latitudinal range shifts provided a rapid-response survival mechanism for tropical planktic foraminifers during the PETM, but the rapidity of ocean warming and acidification projected for the coming centuries will likely strain the adaptability of these resilient calcifiers.
Continue reading ‘Isotopic filtering reveals high sensitivity of planktic calcifiers to Paleocene–Eocene thermal maximum warming and acidification’Aragonite dissolution protects calcite at the seafloor
Published 3 March 2022 Science ClosedTags: chemistry, methods, sediment
In the open ocean, calcium carbonates are mainly found in two mineral forms. Calcite, the least soluble, is widespread at the seafloor, while aragonite, the more soluble, is rarely preserved in marine sediments. Despite its greater solubility, research has shown that aragonite, whose contribution to global pelagic calcification could be at par with that of calcite, is able to reach the deep-ocean. If large quantities of aragonite settle and dissolve at the seafloor, this represents a large source of alkalinity that buffers the deep ocean and favours the preservation of less soluble calcite, acting as a deep-sea, carbonate version of galvanization. Here, we investigate the role of aragonite dissolution on the early diagenesis of calcite-rich sediments using a novel 3D, micrometric-scale reactive-transport model combined with 3D, X-ray tomography structures of natural aragonite and calcite shells. Results highlight the important role of diffusive transport in benthic calcium carbonate dissolution, in agreement with recent work. We show that, locally, aragonite fluxes to the seafloor could be sufficient to suppress calcite dissolution in the top layer of the seabed, possibly causing calcite recrystallization. As aragonite producers are particularly vulnerable to ocean acidification, the proposed galvanizing effect of aragonite could be weakened in the future, and calcite dissolution at the sediment-water interface will have to cover a greater share of CO2 neutralization.
Continue reading ‘Aragonite dissolution protects calcite at the seafloor’Methane hydrate dissociation across the Oligocene–Miocene boundary
Published 28 February 2022 Science ClosedTags: Antarctic, field, modeling, paleo, regionalmodeling, sediment, toxicants
Methane hydrate dissociation has long been considered as a mechanism for global carbon cycle perturbations, climate change and even mass extinctions in Earth’s history. However, direct evidence of hydrate destabilization and methane release coinciding with such events is scarce. Here we report the presence of diagnostic lipid biomarkers with depleted carbon isotopes from three sites in the Southern Ocean that are directly linked to methane release and subsequent oxidation across the Oligocene–Miocene boundary (23 million years ago). The biomarker evidence indicates that the hydrate destabilization was initiated during the peak of the Oligocene–Miocene boundary glaciation and sea-level low stand, consistent with our model results suggesting the decrease in hydrostatic pressure eroded the base of global methane hydrate stability zones. Aerobic oxidation of methane in seawater consumes oxygen and acidifies the ocean, acting as a negative feedback that perhaps facilitated the rapid and mysterious termination of glaciation in the early Miocene.
Continue reading ‘Methane hydrate dissociation across the Oligocene–Miocene boundary’Ocean acidification modifies the impact of warming on sediment nitrogen recycling and assimilation by enhancing the benthic microbial loop
Published 22 February 2022 Science ClosedTags: biological response, BRcommunity, laboratory, multiple factors, sediment, temperature
Nitrogen that has been recycled in the benthos supports high rates of primary and secondary production in estuaries. However, little is known about the effect of future climate on benthic nitrogen recycling and assimilation. An ex situ core incubation was used to assess the impact of combinations of warming (8°C range) and ocean acidification (OA) (i.e. increased pCO2 and decreased pH) on ammonium (NH4+) and nitrate/nitrite (NOx) fluxes and 15N-nitrate assimilation in shallow unvegetated estuarine sediments. Dissolved inorganic nitrogen (DIN = NH4+ + NOx) fluxes were significantly affected by the interaction of warming and OA, highlighting the importance of considering combined stressor treatments when investigating ecosystem responses to future climates. Warming alone increased DIN efflux from the sediments. At current mean ambient temperatures (23°C) and below (Δ-3°C), OA significantly increased DIN effluxes, but there was little to no effect of OA on DIN fluxes at warmer temperatures (Δ+3°C and Δ+5°C). OA reduced the 15N assimilation/retention of the sediments across all temperatures, suggesting that nitrogen retention in bacterial biomass was reduced, despite OA also increasing primary productivity. As such, under the projected future climate of ~3°C warming and doubling of pCO2 (~1000 µatm), unvegetated estuarine sediments are likely to have a more rapid turnover of DIN driven by greater microphytobenthos production and recycling.
Continue reading ‘Ocean acidification modifies the impact of warming on sediment nitrogen recycling and assimilation by enhancing the benthic microbial loop’Seasonal carbonate system vis-a-vis pH and salinity in selected tropical estuaries: implications on polychaete diversity and composition towards predicting ecological health
Published 16 February 2022 Science ClosedTags: annelids, biogeochemistry, biological response, Indian, laboratory, multiple factors, salinity, sediment
Highlights
- The role of salinity-pH gradient coupled with carbonate species on the polychaete community distribution was studied.
- Salinity-pH was positively correlated with carbonate and DOC.
- pCO2 was positively correlated with POC, DIC and CO2.
- High levels of carbonate species and low pH have a greater impact on polychaete diversity and richness.
Abstract
Salinity and pH play a fundamental role in structuring spatial patterns of physical properties, biota, and biogeochemical processes in the estuarine ecosystem. In this study, the influence of salinity-pH gradient and carbonate system on polychaete diversity in Ennore, Uppanar, Vellar, and Kaduvaiyar estuaries was investigated. Water and sediment samples were collected from September 2017 to August 2018. Univariate and multivariate statistical analyses were employed to define ecological status. Temperature, Salinity, pH, and partial pressure of carbon-di-oxide varied between 21 and 30°C; 29 and 39 ppt; 7.4 and 8.3; and 89.216 and 1702.558 µatm, respectively. PCA and CCA results revealed that DO, chlorophyll, carbonate species, and sediment TOC have a higher influence on polychaete community structure. Forty-two species such as Ancistrosyllis parva, Cossura coasta, Eunice pennata, Euclymene annandalei, Lumbrineris albidentata, Capitella capitata, Prionospio cirrifera, P. pinnata, P. cirrobranchiata, and Notomastus sp. were found dominantly in all estuaries. Shannon index values ranged between 1.619 (UE-1) and 3.376 (VE-2). Based on these findings, high levels of carbonate species and low pH have a greater impact on polychaete diversity and richness values. The results of the AMBI Index revealed that stations UE-1, UE-2, UE-3 in Uppanar, EC-1, EC-2 in Ennore indicate “moderately disturbed”, while other stations are under the “slightly disturbed” category. This trend was quite evident in M-AMBI as well.
Continue reading ‘Seasonal carbonate system vis-a-vis pH and salinity in selected tropical estuaries: implications on polychaete diversity and composition towards predicting ecological health’Does pH variation influence the toxicity of organic contaminants in estuarine sediments? Effects of Irgarol on nematode assemblages
Published 2 February 2022 Science ClosedTags: biological response, community composition, laboratory, multiple factors, nematodes, otherprocess, physiology, sediment, South Atlantic, toxicants
Highlights
- Effects of acidification on the Irgarol toxicity to a benthic community was assessed.
- Lower nematode diversity was observed at the highest Irgarol concentration.
- Estuarine nematode assemblage was impacted by continuous exposure to low pHs.
- Toxicity of Irgarol was independent of pH variation.
Abstract
Natural pH values in coastal waters vary largely among locations, ecosystems, and time periods; still, there is an ongoing acidification trend. In this scenario, more acidic pH values can alter bioavailability of organic contaminants, to organisms. Despite this, interactive effects between pH and chemical substances are not usually considered in Ecological Risk Assessment protocols. This study investigated the effects of pH on the toxicity of a hydrophobic organic compound on a benthic community using a microcosm experiment setup to assess the response of nematode assemblages exposed to environmentally relevant concentrations of Irgarol at two natural pH conditions. Estuarine nematode assemblages were exposed to two concentrations of Irgarol at pH 7.0 and 8.0 for periods of 7 and 35 days. Lower diversity of nematode genera was observed at the highest tested Irgarol concentration (1281 ± 65 ng.g−1). The results showed that the effects of Irgarol contamination were independent of pH variation, indicating no influence of acidification within this range on the toxicity of Irgarol to benthic meiofauna. However, the results showed that estuarine nematode assemblages are impacted by long-term exposure to low (but naturally occurring) pHs. This indicates that estuarine organisms may be under naturally high physiological pressure and that permanent changes in the ecosystem’s environmental factors, such as future coastal ocean acidification, may drive organisms closer to the edges of their tolerance windows.
Continue reading ‘Does pH variation influence the toxicity of organic contaminants in estuarine sediments? Effects of Irgarol on nematode assemblages’Microbial alkalinity production and silicate alteration in methane charged marine sediments: implications for porewater chemistry and diagenetic carbonate formation
Published 26 January 2022 Science ClosedTags: biogeochemistry, methods, sediment, South Pacific
A numerical reaction-transport model was developed to simulate the effects of microbial activity and mineral reactions on the composition of porewater in a 230-m-thick Pleistocene interval drilled in the Peru-Chile Trench (Ocean Drilling Program, Site 1230). This site has porewater profiles similar to those along many continental margins, where intense methanogenesis occurs and alkalinity surpasses 100 mmol/L. Simulations show that microbial sulphate reduction, anaerobic oxidation of methane, and ammonium release from organic matter degradation only account for parts of total alkalinity, and excess CO2 produced during methanogenesis leads to acidification of porewater. Additional alkalinity is produced by slow alteration of primary aluminosilicate minerals to kaolinite and SiO2. Overall, alkalinity production in the methanogenic zone is sufficient to prevent dissolution of carbonate minerals; indeed, it contributes to the formation of cemented carbonate layers at a supersaturation front near the sulphate-methane transition zone. Within the methanogenic zone, carbonate formation is largely inhibited by cation diffusion but occurs rapidly if cations are transported into the zone via fluid conduits, such as faults. The simulation presented here provides fundamental insight into the diagenetic effects of the deep biosphere and may also be applicable for the long-term prediction of the stability and safety of deep CO2 storage reservoirs.
Continue reading ‘Microbial alkalinity production and silicate alteration in methane charged marine sediments: implications for porewater chemistry and diagenetic carbonate formation’Acidity, electric conductivity, dissolved oxygen total dissolved solid and salinity profiles of marine water in Gaza: influence of wastewater discharge
Published 15 December 2021 Science ClosedTags: chemistry, Mediterranean, sediment
Effects of wastewater discharge on the coastal area in Gaza strip Palestine are not fully investigated. This study investigated the effect wastewater discharge of the physical and chemical properties of marine water in the coastal area over a period of 2 year. Sea water and sediment samples were collected from about 20 different sites. The water and the sediments were collected wastewater/sea water mixing zone at depth 0, 2.5 and 5 m water column depth at a direct wastewater discharging pipe line from different location and similarly from other locations. Water temperature T, electric conductivity (EC), dissolved oxygen (DO), pH, total dissolved solid (TDS) and salinity were determined for water samples using field equipment such as pH-meter, DO meter, TDS-/ and EC-meter. On the other hand, NO3–, SO42-, PO43- were determined in the laboratory using chemical methods, details are described in materials and method section. Results showed average and standard deviation of T, EC, DO, pH, TDS and salinity were 22.02°C ± 4.1°C, EC: 58.41 ± 4.8 ms/cm; DO: 6.96 ± 1.8 mg/L; pH: 7.69 ± 0.37; TDS: 30.51 ± 3.29 and salinity 4.39 ± 0.12 (%); whereas, average and standard deviation of NO3–: were 299.8 ± 204.1 mg/L; SO42-, 5736.9 ± 817.1; and PO43-: 164.35 ± 120.7 mg/L. The measured values indicate significant differences due to high value of standard deviation of some measured parameters. This indicates the influence of wastewater discharge in sea water as shown inside the manuscript in the appropriate section. The study recommends efficient treatment of wastewater and reuses it for agricultural purposes instead of discharging it in sea.
Continue reading ‘Acidity, electric conductivity, dissolved oxygen total dissolved solid and salinity profiles of marine water in Gaza: influence of wastewater discharge’Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment
Published 10 December 2021 Science ClosedTags: laboratory, methods, sediment, South Pacific
Ecosystem feedbacks in response to ocean acidification can amplify or diminish diel pH oscillations in productive coastal waters. Benthic microalgae generate such oscillations in sediment porewater and here we ask how CO2 enrichment (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. We placed a 1-mm layer of ground oyster shells, mimicking the arrival of dead calcifying biota (+Calcite), or sand (Control) onto intact silt sediment cores, and then gradually increased the pCO2 in the seawater above half of +Calcite and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO2:HCO3− from 4.8 to 9.6 × 10−4). Porewater [O2] and [H+] microprofiles measured 16 d later showed that this enrichment had decreased the O2 penetration depth (O2-pd) in +Calcite and Control, indicating a metabolic response. In CO2-enriched seawater: (1) sediment biogeochemical processes respectively added and removed more H+ to and from the sediment porewater in darkness and light, than in ambient seawater increasing the amplitude of the diel porewater [H+] oscillations, and (2) in darkness, calcite dissolution in +Calcite sediment decreased the porewater [H+] below that in overlying seawater, reversing the sediment–seawater H+ flux and decreasing the amplitude of diel [H+] oscillations. This dissolution did not, however, counter the negative effect of CO2 enrichment on O2-pd. We now hypothesise that feedback to CO2 enrichment—an increase in the microbial reoxidation of reduced solutes with O2—decreased the sediment O2-pd and contributed to the enhanced porewater acidification.
Continue reading ‘Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment’A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: the enhancement of metabolic carbonate dissolution in a semienclosed lagoon
Published 15 November 2021 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific, phanerogams, sediment, tracheophyta
In contrast to other seagrass meadows where seawater carbonate chemistry generally shows strong diel variations with higher pH but lower partial pressure of CO2 (pCO2) during the daytime and lower pH but higher pCO2 during nighttime due to the alternation in photosynthesis and respiration, the seagrass meadows of the inner lagoon (IL) on Dongsha Island had a unique diel pattern with extremely high pH and low pCO2 across a diel cycle. We suggest that this distinct diel pattern in pH and pCO2 could be associated with the enhancement of total alkalinity (TA) production coupled to carbonate sediment dissolution in a semienclosed lagoon. The confinement of the IL may hamper water exchange and seagrass detritus export to the adjacent open ocean, which may result in higher organic matter loading to the sediments, and longer residence time of the water in the IL, accompanied by microbial respiration (both aerobic and anaerobic) that may reduce carbonate saturation level to drive carbonate dissolution and thus TA elevation, thereby forming such a unique diel pattern in carbonate chemistry. This finding further highlights the importance of considering TA production through metabolic carbonate dissolution when evaluating the potential of coastal blue carbon ecosystems to buffer ocean acidification and to absorb atmospheric CO2, in particular in a semienclosed setting.
Continue reading ‘A unique diel pattern in carbonate chemistry in the seagrass meadows of Dongsha island: the enhancement of metabolic carbonate dissolution in a semienclosed lagoon’Carbon dynamics driven by seawater recirculation and groundwater discharge along a forest-dune-beach continuum of a high-energy meso-macro-tidal sandy coast
Published 4 November 2021 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic, sediment
High-energy tidal beaches are exposed to strong physical forcings. The submarine groundwater discharge (SGD) that occurs in intertidal sandy sediments includes both terrestrial, fresh groundwater flow and seawater recirculation, and plays a significant role in regulating biogeochemical cycles in some coastal zones. In this transition zone between land and sea, complex biogeochemical reactions alter the chemical composition of pore waters that discharge to the coastal ocean. Recent studies highlight that SGD can be a significant source of carbon to the coastal ocean but very few have investigated SGD in high-energy environments. We have characterized the dissolved carbon dynamics in such a high-energy environment (Truc Vert Beach, SW France) through pore-water sampling in key compartments of the SGD system. Dissolved organic carbon (DOC), pH, total alkalinity (TA), and the isotopic composition of dissolved inorganic carbon (δ13C-DIC) were measured in pore waters sampled at regular intervals between 2011 and 2014 in the intertidal zone of the beach, the mixing zone of the subterranean estuary (STE), and the freshwater aquifer upstream from the beach. Results reveal that SGD exports dissolved carbon mostly as DIC to the Aquitaine coast, some of which originates from the aerobic respiration of marine organic matter within the beach aquifer. This is highlighted by the reverse spatial trend of DOC, which is consumed, and DIC, which is produced. Saline pore waters expelled from the beach through tidally-driven recirculation of seawater provide about 4400 tons of carbon per year to the coastal zone of the 240-kmlong Aquitaine sandy coast. Terrestrial groundwater, characterized by high pCO2 values, is also a significant contributor to the DIC flux to the coastal ocean (16,200 tons per year). This flux is abated by CO2 evasion in the upper beach, at the onset of the salinity gradient in the STE, and within the surficial freshwater aquifer along the forest-beach transect below the coastal foredune. Accordingly, the DIC:TA ratio evolves to below 1, suggesting that this SGD increases the buffer capacity of coastal seawater against acidification. This study demonstrates that high-energy beaches are active vectors of DIC from the land to the coastal ocean as well as significant sources of CO2 to the atmosphere, and must therefore be taken into consideration in SGD carbon budgets.
Continue reading ‘Carbon dynamics driven by seawater recirculation and groundwater discharge along a forest-dune-beach continuum of a high-energy meso-macro-tidal sandy coast’Pliocene decoupling of equatorial Pacific temperature and pH gradients
Published 25 October 2021 Science ClosedTags: biological response, chemistry, laboratory, modeling, North Pacific, paleo, protists, regionalmodeling, sediment
Ocean dynamics in the equatorial Pacific drive tropical climate patterns that affect marine and terrestrial ecosystems worldwide. How this region will respond to global warming has profound implications for global climate, economic stability and ecosystem health. As a result, numerous studies have investigated equatorial Pacific dynamics during the Pliocene (5.3–2.6 million years ago) and late Miocene (around 6 million years ago) as an analogue for the future behaviour of the region under global warming1,2,3,4,5,6,7,8,9,10,11,12. Palaeoceanographic records from this time present an apparent paradox with proxy evidence of a reduced east–west sea surface temperature gradient along the equatorial Pacific1,3,7,8indicative of reduced wind-driven upwelling—conflicting with evidence of enhanced biological productivity in the east Pacific13,14,15 that typically results from stronger upwelling. Here we reconcile these observations by providing new evidence for a radically different-from-modern circulation regime in the early Pliocene/late Miocene16 that results in older, more acidic and more nutrient-rich water reaching the equatorial Pacific. These results provide a mechanism for enhanced productivity in the early Pliocene/late Miocene east Pacific even in the presence of weaker wind-driven upwelling. Our findings shed new light on equatorial Pacific dynamics and help to constrain the potential changes they will undergo in the near future, given that the Earth is expected to reach Pliocene-like levels of warming in the next century.
Continue reading ‘Pliocene decoupling of equatorial Pacific temperature and pH gradients’Biological effects of the antihypertensive losartan under different ocean acidification scenarios
Published 11 October 2021 Science ClosedTags: biological response, BRcommunity, echinoderms, laboratory, mollusks, multiple factors, physiology, reproduction, sediment, South Atlantic, toxicants
Highlights
- Losartan was quantified in samples of marine water (up to 7.63 ng/L) and sediment (up to 3.10 ng/g).
- Sediment spiked with an environmental concentration of losartan affected lysosomal stability.
- Losartan effects were pH dependent and pH effects were dependent on the concentration of losartan.
- Ocean acidification exacerbates the negative effects of losartan in waterborne exposure.
Abstract
Since the last decade, several studies have reported the presence and effects of pharmaceutical residues in the marine environment, especially those of the antihypertensive class, such as losartan. However, there is little knowledge about the physiological effects of losartan in marine invertebrates regarding its behavior under possible coastal ocean acidification scenarios. The objective of this study was to evaluate biological effects on marine organisms at different levels of the biological organization caused by the compound losartan in water and sediment under coastal ocean acidification scenarios. Water and sediment samples were collected at five sites around the Santos Submarine Sewage outfall (SSO) and two sites around the Guarujá Submarine Sewage Outfall (GSO). Losartan was found in concentrations ranging from <LOD to 7.63 ng/L in water and from <LOQ to 3.10 ng/g in sediments. Statistical analysis showed interactive effects pH and losartan on the toxicity results. The water toxicity test with Echinometra lucunter embryos/larvae showed LOECs 50–100 mg/L, with values decreasing as the pH decreased. In the sediment assays, LOEC value for sea urchin embryo-larval development was 1.0 μg/g for all tested pHs. Regarding the lysosomal membrane stability assays with adult bivalves, a LOEC of 3000 ng/L was found for Perna perna in water exposure (both at pH 8.0 and 7.6). Effects for Mytella guyanensis were observed at environmentally relevant concentrations in sediment (LOEC = 3 ng/g at pH 8.0 and 7.6). This study demonstrated that coastal ocean acidification by itself causes effects on marine invertebrates, but can also increase the negative effects of losartan in waterborne exposure. There is a need to deepen the studies on the ecotoxicity of pharmaceutical residues and acidification of the marine environment.
Continue reading ‘Biological effects of the antihypertensive losartan under different ocean acidification scenarios’First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)
Published 10 September 2021 Science ClosedTags: chemistry, field, laboratory, Mediterranean, mollusks, morphology, photosynthesis, sediment, zooplankton
Pteropods are marine pelagic calcifier mollusks sensitive to chemical changes in seawater due to their highly soluble aragonite shells. Increased acidity (reduced pH) of seawater causes difficulties in precipitating their shells and/or results in their dissolution, which is related to increased atmospheric CO2 concentrations and warming of seawater. They are therefore indicators of environmental changes. In this paper, we present the first record of the straight-needle pteropod Creseis acicula Rang, 1828 bloom in the surface waters of the Ҫanakkale Strait, Turkey (NE Aegean Sea), encountered in July 2020, when the highest sea surface temperatures and pH levels since 2007 were recorded. In coastal zones, such as the Ҫanakkale Strait, anthropogenic activity contributes significantly to environmental changes. Consequently, the increase in pH at elevated temperatures indicates an auxiliary factor (i.e. anthropogenic activity) that triggered the C. acicula bloom, rather than global atmospheric CO2 levels.
Continue reading ‘First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)’
