The potential impacts of climate change on marine habitats were assessed using RCP4.5 and RCP8.5 projections of environmental parameters that included sea surface temperature (SST), pH, salinity, planktonic productivity (PP) and current strength (CS). The analysis was conducted separately for three distinct oceanographic regions of the Portuguese coastline (North, Centre and South) up to the middle of the century. Temporal trends in environmental variables were assessed using time series analyses. Overall, changes expected up to the middle of the century include increasing SST and PP, decreasing pH and salinity, and slight increases in CS. Spatial–temporal analyses revealed high present–future environmental overlay for most environmental variables. However, changes in individual environmental variables cumulatively resulted in statistically significant changes in environmental similarity. Still, the projected changes are not expected to exceed ecological thresholds, above which they would be likely to alter species’ habitat suitability or to result in species distribution shifts. Anomaly analyses suggest that present–future shifts do not surpass 1/5 (pH, PP, CS) or 2/3 (salinity) of the unit, regardless of projection and area, while SST anomalies ranged from −1.1 °C to 1.1 °C. Compared to IPCC large-scale predictions for Atlantic/Mediterranean regions, the intensity of shifts on the Portuguese coast may be lower.
Continue reading ‘Impact of climate change on Portuguese marine coastal environments’Posts Tagged 'chemistry'
Impact of climate change on Portuguese marine coastal environments
Published 9 July 2026 Science ClosedTags: chemistry, modeling, regionalmodeling, review
Climate assessment report for the Central Arctic Ocean (CAO) [Suppl. to ICES Scientific Reports 8(25)]
Published 9 July 2026 Science ClosedTags: Arctic, chemistry, community composition, fish, mammals, zooplankton
Climate change is transforming the Central Arctic Ocean (CAO) at an unprecedented pace. Sea ice is rapidly declining in extent, thickness, and age, with projections indicating an ice-free summer Arctic by mid-century, possibly earlier. This loss of ice amplifies warming, alters stratification and circulation, and accelerates ocean acidification—occurring up to four times faster than the global average—threatening calcifying organisms and ecosystem stability.
Biological impacts are profound: shifts in microbial and primary producer communities, reduced ice-associated biodiversity, and boreal species moving northward disrupt food webs. Benthic ecosystems show signs of long-term decline in biodiversity and organic carbon supply, while fish, seabirds, and marine mammals face habitat loss, changing prey availability, and new stressors such as increased predation and contaminants. Some species may benefit from enhanced productivity, but cumulative effects of warming, acidification, and ice loss remain uncertain. These changes interact with other pressures—pollution, invasive species, and human activities—creating complex, compounding stress on the CAO ecosystem. Knowledge gaps on tipping points and resilience underscore the urgent need for research on circulation, carbon dynamics, and species adaptation to inform conservation and management strategies.
Continue reading ‘Climate assessment report for the Central Arctic Ocean (CAO) [Suppl. to ICES Scientific Reports 8(25)]’Study on the mechanical characteristics of the stress relaxation in the carbonate rock after high-temperature acidification
Published 3 July 2026 Science ClosedTags: chemistry, laboratory, modeling, paleo
To elucidate the mechanism by which acidification influences wellbore stability in deep reservoir formations, this study investigates the rheological and mechanical behaviors of the carbonate rock subjected to high-temperature acid etching. A novel experimental system was developed to characterize the stress relaxation behavior of the acid-etched carbonate rock, and the characteristics of the stress relaxation curves under various acid etching conditions and strain levels were systematically analyzed. Combined with Burgers model and the Levenberg–Marquardt algorithm, the evolution of rheological parameters of the carbonate rock under different acid etching regimes was quantitatively evaluated. The results indicate that the acid-etched carbonate rock exhibit significant rheological mechanical properties due to the presence of developed microcracks and complex pore structures. Under the identical acid etching duration and temperature, the initial stress, residual stress, and time required for stress relaxation stabilization all increase with increasing the strain level. Overall, the stress relaxation magnitude prior to the core fracture ranges from 15 to 25 MPa, and the stabilization time for the core stress relaxation falls between 5 and 7 h. The stress relaxation behavior of the acid-etched carbonate core is well described by the Burgers model. At fixed strain levels and temperatures, the instantaneous shear modulus decreases linearly with extended acid etching time, whereas the instantaneous shear modulus and the viscosity coefficients and exhibit exponential degradation. The final variation ranges of the key rheological parameters are determined as follows: instantaneous shear modulus ranges from 5 × 103 to 2 × 104 MPa, instantaneous shear modulus ranges from 6 × 105 to 2 × 106 MPa, viscosity coefficient ranges from 2 × 107 to 8 × 107 MPa h, and viscosity coefficient ranges from 1 × 105 to 1.2 × 106 MPa h. Furthermore, the evolutionary equations correlating the global model fitting parameters with the porosity of acid-etched samples are established, using acid etching time as an intermediate variable. The results of this study provide a theoretical basis for the analysis of wellbore stability after acidification and the selection of acid fracturing completion methods of deep reservoirs.
Continue reading ‘Study on the mechanical characteristics of the stress relaxation in the carbonate rock after high-temperature acidification’Entering the era of directly supporting society with observation-based ocean acidification data
Published 2 July 2026 Science ClosedTags: chemistry, methods
Ocean acidification is a growing concern for many nations around the world. However, our capacity to monitor changes in carbonate chemistry with sufficient spatial and temporal resolution, has until now, been limited, which has impeded effective action and decision-making at international, national, and regional levels. Recent advancements in machine learning have enabled the integration of Earth observation data with in situ measurements, enhancing data coverage and improving our ability to monitor ocean acidification globally. Here, we highlight how space agencies, particularly the European Space Agency, have supported the development of such products and explore their utility for a broad spectrum of end users, ranging from scientists to resource managers to policy makers and the general public. Spatial and temporal resolution of these products is now on the order of 0.25 × 0.25° and 8-daily, respectively; with similar or slightly enhanced accuracy compared to other methods (e.g., fCO2 in open and coastal ocean are 13 and 25 μatm, respectively). We provide five use cases that demonstrate how the data can be used to: (a) communicate ocean acidification; (b) aid marine planning activities; (c) set up national monitoring and understand baseline conditions; (d) assess impacts of aquaculture; and (e) assess impacts to coral habitats. While these developments represent significant progress, further efforts will enhance the efficacy of observational-data in coastal waters, and could develop complementary biological or water quality indicators. These activities will be accelerated by further building global capacity to ensure equitable access and application of these tools.
Plain Language Summary
Ocean acidification, a change in ocean chemistry caused by the long-term increase in atmospheric carbon dioxide, is a growing global concern. However, it is hard to track these changes accurately across the entire ocean, making it difficult for governments and communities to understand the threat and respond effectively. New advances in machine learning now make it possible to combine satellite data with ocean measurements which have improved our ability to monitor ocean acidification. Here, we highlight how projects funded by the European Space Agency have helped to develop tools that make this information accessible and useful for multiple groups, including scientists, resource managers, policy makers, and the general public. We present five examples for using the data: raising awareness about ocean acidification, supporting marine planning, creating national monitoring systems, understanding the effects on aquaculture like shellfish farming, and evaluating risks to coral reefs. This progress has been long needed, and efforts are beginning to focus on further improving our abilities to observe coastal areas, where conditions can change quickly. Future efforts can now focus on exploring new ways to track changes, and making sure people around the world have the tools and training needed to use these new resources effectively.
Continue reading ‘Entering the era of directly supporting society with observation-based ocean acidification data’Aragonite saturation state in the East China Sea during fall 2022: roles of temperature, biology, and mixing
Published 30 June 2026 Science ClosedTags: chemistry, field, North Pacific
This work presents a comprehensive spatial distribution of aragonite saturation state (Ωara) during fall 2022 across the entire shelf of the East China Sea (ECS), a marginal sea of the North Pacific. Our observations revealed pronounced spatial heterogeneity in Ωara. Specifically, surface Ωara was higher in the southeastern ECS in (3.22−3.41), which is influenced by the Taiwan Warm Current and the Kuroshio, than the northern ECS (2.23−2.60), which is affected by the Yellow Sea and the Changjiang River. The lowest Ωara values (1.73−2.20) occurred beneath the mixed layer on the southeastern ECS shelf. Correlation analyses and a one-dimensional diagnostic model identified biological activity and temperature as primary controls on the spatial variability of Ωara. For example, on the southeastern ECS shelf, within the mixed layer, both biological activities and temperature increased Ωara, accounting for ~45% and ~33% of the total absolute contribution of each process. While below the mixed layer, these two processes decreased Ωara, accounting for approximately -38% and -24% of the total absolute contribution. Additionally, water mass mixing substantially influenced Ωara within interaction zones, such as in the intrusion areas of the Yellow Sea and Changjiang River waters. Projections indicate that under future elevated atmospheric carbon dioxide conditions (RCP6.0 and RCP8.5), sea surface Ωara will continue to decline, but the magnitude of decline will be smaller in the northern ECS than in the southeastern ECS, reflecting the carbonate system’s intrinsic buffering effect.
Continue reading ‘Aragonite saturation state in the East China Sea during fall 2022: roles of temperature, biology, and mixing’Skeletal porosity of a cold-water coral increases with decreasing aragonite saturation state along a depth gradient in the Mediterranean Sea
Published 29 June 2026 Science ClosedTags: biogeochemistry, biological response, BRcommunity, chemistry, corals, laboratory, Mediterranean, physiology
Background
Cold-water corals (CWCs) are key ecosystem engineers that create complex three-dimensional habitats much like tropical reefs, but in deep, cold seas. However, like other reef-building systems, they are increasingly threatened by climate change and ocean acidification. CWC communities in the Mediterranean Sea may be especially vulnerable because these waters absorb more atmospheric CO2 than the global ocean, making it a mesocosm that mirrors broader global trends affecting marine life. Since calcification is energetically costly and likely becomes even more demanding as pH and carbonate ion availability decline, understanding how the decrease in aragonite saturation state (Ωarag) affects biomineralization is essential for predicting the future of these corals.
Results
Here, we investigated skeletal structural and compositional changes of the scleractinian CWC Desmophyllum dianthus along an Ωarag gradient in the Mediterranean Sea using specimens collected between 400 and 1200 m depth. Our findings indicate that skeletal porosity increases at the macro-scale with decreasing Ωarag, while micro- and nano-scale structural and compositional features remained unaffected.
Conclusions
The persistence of micro- and nano-scale skeletal features across an 800 m depth gradient suggests that D. dianthus maintains tight biological control over mineralization at these scales, even as Ωarag declines. This control does not extend to the macro-scale, where increasing porosity alters the skeleton’s overall architecture under lower Ωarag. D. dianthus thus appears to preserve the fundamental “building blocks” of its skeleton while changing its larger-scale structure, a decoupling that may make macro-scale porosity an early marker of acidification stress in CWCs.
Continue reading ‘Skeletal porosity of a cold-water coral increases with decreasing aragonite saturation state along a depth gradient in the Mediterranean Sea’Identification of the source of carbonaceous aerosols using stable carbon and nitrogen isotopes and the implications of its deposition on the coastal ocean
Published 24 June 2026 Science ClosedTags: chemistry, Indian
Highlights
- Aerosols and their major sources are seasonally variable at Visakhapatnam.
- Total suspended matter was higher during winter than during summer.
- Biomass burning is a dominant source of aerosols during winter.
- Fossil fuel and coal combustion are the major sources during summer.
Abstract
The continuous rise in anthropogenic aerosol emissions degrades ambient air quality, and their deposition onto the surface ocean alters chemical and biological characteristics. Identifying the sources of aerosols is crucial for taking appropriate measures to minimize their impacts. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) are promising tools for identifying sources of carbonaceous aerosols. The objective of this study is to identify the dominant sources of carbonaceous aerosols over an urban region using stable carbon (δ13C) and nitrogen (δ15N) isotope ratios, and to evaluate their potential influence on surface ocean acidification in the coastal Bay of Bengal. Aerosol samples were collected between March 2016 and February 2017 at a fortnightly interval, over an urban region, to examine the sources of carbonaceous aerosols and to evaluate the possible impacts on surface ocean acidification. Significantly high concentrations of total suspended particulates (TSP) during winter (112 ± 26 μg m−3) compared to summer (58.8 ± 8 μg m−3), associated with an insignificant seasonality in δ13CTC (−26.9‰ to −22.9‰), indicating ageing of organic aerosol through oxidation. In contrast, higher δ15NTN during winter (2.2‰ to 12.1‰; 5.4 ± 2.9‰) than summer (−12.9‰ to −1.8‰; −4.7 ± 3.3‰) indicate different sources. Based on source characteristics of δ13CTC, δ15NTN and the isotope mixing model, biomass burning and coal combustion are the major sources of carbonaceous aerosols during winter, whereas coal and fossil fuel burning contributed during summer. Since biomass burning contains higher concentrations of acidic aerosols, such as sulfates, and its deposition over the surface ocean results in higher level of pH levels compared to coal ashes. A higher decline in pH of the coastal waters during winter than summer was reported in the coastal Bay of Bengal. This study confirms that the deposition of higher sulphate and nitrates due to biomass burning in the Indo-Gangetic Plain (IGP) region is responsible for a greater decline in pH of the surface ocean during winter than summer. Taking appropriate measures to reduce biomass burning in the IGP region would decrease ocean acidification and allow the atmospheric CO2 sink into the coastal Bay of Bengal to achieve net zero carbon emissions in the future.
Continue reading ‘Identification of the source of carbonaceous aerosols using stable carbon and nitrogen isotopes and the implications of its deposition on the coastal ocean’Recalculating the Surface Ocean CO2 Atlas (SOCAT) to a sea surface temperature climate data record
Published 24 June 2026 Science ClosedTags: chemistry
The Surface Ocean CO2 Atlas (SOCAT) is a global scientific community effort to collate and provide additional quality control and standardisation for surface ocean carbon dioxide (CO2) data. Each year the international marine carbon community submit any new measurements collected on research vessels, ships of opportunity, moorings, uncrewed surface vehicles and sailing yachts for inclusion in the annual update of the SOCAT database. The data synthesis effort, which published its first data product in 2011, includes a variety of systems, sampling strategies, maintenance cycles and instrument calibrations. Each in-water CO2 gas measurement is paired, and linked, with a sea surface temperature (SST) measurement. However, the differences in measurement systems means that data pairs from different platforms are representative of differing depths in the ocean, whilst SST measurements can suffer from warming within the observation platform. These complexities can limit the accuracy and precision of any atmosphere-ocean CO2 assessments that use the SOCAT products. Here the SOCATv2025 database with an estimated uncertainty in the fugacity of CO2 in seawater (fCO2 (sw)) of less than 5 µatm is recalculated to a reference temperature at a consistent depth of 0.2 m using the European Space Agency (ESA) Climate Change Initiative (CCI) SST climate data record. This recalculation process of the fCO2 values does not assume isochemical conditions and so temperature driven carbonate speciation is captured. The data pairing is maintained so the resulting dataset is well suited for the analysis of atmosphere-ocean CO2 exchange. The synthesis cruise data and gridded data products, that include both the original and recalculated data, are provided and consistency with the original SOCAT data products and format is confirmed. The importance of robustly accounting for the observed warm bias is demonstrated as removing this signal by recalculation to a climate data record temperature shows a ~0.4 Pg C yr−1 (~12%) increase in the 2024 ocean CO2 sink (3.4 Pg C yr−1). These recalculated data products are needed for annual carbon assessments therefore these will be routinely provided each year following each annual SOCAT dataset release.
Continue reading ‘Recalculating the Surface Ocean CO2 Atlas (SOCAT) to a sea surface temperature climate data record’High-precision performance of a full-ocean-depth pH sensor: calibration and assessment under simulated hadal pressure conditions
Published 23 June 2026 Science ClosedTags: chemistry, methods, sensor
Real-time in situ pH monitoring in the hadal zone is essential for resolving deep-sea carbon dynamics but is severely challenged by extreme hydrostatic pressures and complex biochemical environments. Current sensors often lack the necessary robustness and calibration protocols for full-ocean-depth applications. To address these challenges, we developed a solid-state electrochemical pH sensor system comprising a fouling-resistant sulfonated poly(ether ether ketone)/ionic liquid composite IrOx (SP/IL-IrOx) working electrode and a pressure-tolerant silica-stabilized ionic liquid (Si-StabIL) reference electrode. Using Tris-artificial seawater (Tris-AS) buffers, we established a standardized high-pressure calibration protocol and systematically evaluated sensor performance over the full-ocean-depth pressure range (0.1−120 MPa) under simulated hadal pressure conditions. The sensor exhibited near-Nernstian sensitivity with high reversibility and repeatability, with potential deviations of no more than 1.6 mV, corresponding to less than 0.03 pH units across the investigated pressure range. Long-term reliability was demonstrated by a minimal drift of only 0.01 pH units during continuous operation in the Tris-AS buffer at 120 MPa for 65 h. Crucially, the sensor captured the nonlinear, pressure-driven acidification of simulated hadal-zone seawater during a 7 day pressurization experiment while maintaining stable response in calibration buffers. These results demonstrate the robustness of the sensor system and provide an experimental basis for calibration and pH assessment under simulated full-ocean-depth pressure conditions.
Continue reading ‘High-precision performance of a full-ocean-depth pH sensor: calibration and assessment under simulated hadal pressure conditions’Long term strengthening of the CO2 sink and spatiotemporal pCO2 dynamics in the northern Gulf of Mexico: insights from a 22 year satellite based machine learning reconstruction
Published 23 June 2026 Science ClosedTags: chemistry, North Atlantic
The northern Gulf of Mexico (nGOM) is a river‑dominated marginal sea with strong physical‑biogeochemical variability. We reconstruct sea surface partial pressure of CO2 (pCO2) at 4‑km, 8-day resolution from 2003 to 2024 using a satellite‑based, season‑specific random forest model (independent validation R² = 0.82, RMSE = 27.6 μatm). The climatological pCO2 distribution exhibits a sharp coastal‑to‑offshore gradient: river‑influenced coastal waters (SSS < 33) have persistently low pCO2 with high spatial variability, while offshore waters (SSS > 33) have higher pCO2 with weaker heterogeneity and lower seasonal amplitude. The nGOM acts as a net CO2 sink for atmospheric, largely concentrated in the river‑influenced plume region due to riverine nutrient‑stimulated biological uptake. Seasonal pCO2 variation is dominantly controlled by temperature but counteracted by spring‑summer biological drawdown (reducing pCO2) and autumn‑winter vertical mixing with CO2‑rich deeper water (raising pCO2). Interannual pCO2 variability is dominantly affected by year-to-year changes in river discharge and nutrient loading, with higher discharge leading to lower pCO2 via enhanced biological uptake. On a decadal timescale, sea surface pCO2 increased at a rate of 0.50 ± 0.20 μatm yr-1, much slower than atmospheric pCO2 (2.13 ± 0.04 μatm yr-1), leading to a strengthening oceanic CO2 sink with the sea-to-air flux becoming more negative at −0.41 ± 0.06 mmol C m-2 d-1 yr-1. Furthermore, a decreasing frequency of easterly winds has reduced the westward transport of the Mississippi River plume, causing a higher pCO2 increasing rate on the western Texas‑Louisiana shelf.
Continue reading ‘Long term strengthening of the CO2 sink and spatiotemporal pCO2 dynamics in the northern Gulf of Mexico: insights from a 22 year satellite based machine learning reconstruction’Marine radionuclides in climate change studies: Pacific Ocean and marginal seas
Published 22 June 2026 Science ClosedTags: chemistry, methods
Highlights
- Marine radionuclides with well-constrained input histories have proven to be sensitive tracers.
- Radionuclides in oceanic compartments enable to study transport and biogeochemical processes.
- A decline in vertical mixing of upper waters in the North Pacific over recent decades was identified.
- Radionuclides were used in climate change studies in marginal seas of the NW Pacific.
Abstract
Observed global warming has profoundly affected the world’s oceans, which are experiencing increasingly frequent marine heatwaves and a slowdown of the Global Meridional Overturning Circulation. These changes disrupt ocean circulation patterns, alter biogeochemical cycles, enhance surface ocean acidification, and drive poleward migration of marine organisms. Marine radionuclides (e.g., 3H, 14C, 90Sr, 129I, 134Cs, 137Cs, and Pu isotopes), released from nuclear activities since the 1940s, provide time-resolved tracers of oceanic processes owing to their well-documented input functions and distinct chemical behaviors. Their distributions in seawater, bottom sediments, and marine biota have recorded climate-driven modifications in ocean circulation and stratification. The Pacific Ocean, the largest ocean basin on Earth, has undergone changes in recent decades under ongoing climate forcing. Long-term radionuclide observations indicate a decline in vertical mixing in the upper North Pacific Ocean, likely associated with enhanced stratification. Variability linked to Asian monsoon systems and El Niño–Southern Oscillation (ENSO) events is also clearly reflected in radionuclide records from the marginal seas of the Northwest Pacific. Radionuclide datasets provide essential reference benchmarks for calibrating and validating Ocean General Circulation Models and Earth System Models under future climate scenarios. To strengthen predictive capability, coordinated international, high-resolution sampling programs covering the entire world ocean are required, together with measurement campaigns employing newly developed ultra-sensitive analytical techniques. Particular attention should be given to the Southern, Arctic, and Subarctic Oceans because of their critical role in the global climate system and the current scarcity of comprehensive radionuclide data.
Continue reading ‘Marine radionuclides in climate change studies: Pacific Ocean and marginal seas’A basin-wide assessment of pH changes in the Mediterranean Sea based on reanalysis products
Published 19 June 2026 Science ClosedTags: biogeochemistry, chemistry, Mediterranean, modeling, regionalmodeling
Ocean acidification, driven by increasing atmospheric CO2 concentrations, poses a growing threat to marine ecosystems and biogeochemical processes. The Mediterranean Sea, characterized by complex circulation patterns and distinct hydrographic sub-basins, represents a sensitive region for assessing basin-scale pH variability. However, long-term in situ pH observations remain spatially sparse and unevenly distributed, limiting the assessment of coherent spatiotemporal trends across the basin. Here, we present a basin-wide spatiotemporal assessment of pH trends in the Mediterranean using an 18-year biogeochemical reanalysis dataset from the Copernicus Marine Environment Monitoring Service. Our analysis reveals a consistent vertical structuring of pH trends, with negative trends in surface waters and contrasting, often neutral to weakly positive tendencies at depth. The magnitude and vertical extent of these trends vary regionally and are closely linked to local circulation regimes, water-mass formation processes, and remineralization dynamics. In deep-water formation regions such as the Adriatic, Ionian, and Aegean Seas, negative pH trends extend throughout much of the water column, whereas in the Levantine Basin, mesoscale circulation structures confine pH changes primarily to a relatively thin surface layer. These results demonstrate that basin-scale analyses based on high-quality, publicly accessible biogeochemical reanalysis products, such as CMEMS, can provide a spatially integrated perspective on long-term pH variability, complementing existing observational records by bridging spatial and temporal gaps. The framework presented here offers a reproducible approach for systematically assessing depth and region resolved pH trends.
Continue reading ‘A basin-wide assessment of pH changes in the Mediterranean Sea based on reanalysis products’Physical-chemical gradients, CO2 venting dynamics and microbial community composition in a shallow Mediterranean CO2-rich hydrothermal system
Published 19 June 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, Mediterranean, otherprocess, physiology, prokaryotes, vents
Shallow-water CO2-rich hydrothermal systems provide natural laboratories for studying localized ocean acidification under realistic environmental conditions. Here, we present a multidisciplinary characterization of the Calent mound CO2-rich system (Columbretes Islands, Western Mediterranean), based on oceanographic surveys conducted in 2020 and 2021. Localized pH anomalies were detected directly above active vents, reaching maximum reductions of 1.12 pH units, whereas water-column temperature anomalies were minimal and subsurface sediment temperatures exceeded ambient seawater by 5.67 °C. Gas analyses indicated high CO2 concentrations (0.094 ± 0.008 mol L− 1), with heterogeneous degassing regimes, ranging from sporadic to continuous emissions and an average flux of 189.4 ± 15.4 kg CO2 m− 2 yr− 1 at the active vent field. Vent fluids were significantly enriched in dissolved inorganic nutrients, particularly silicate, phosphate, nitrate+nitrite, and ammonium. Benthic microbial mats hosted metabolically diverse prokaryotic and eukaryotic communities, including hydrothermal-associated taxa such as Zetaproteobacteria, Campylobacterota, and Nitrosophaeria, consistent with iron, sulfur, and ammonia oxididation metabolisms. Several microbial core taxa persisted across years despite shifts in relative abundance. These findings demonstrate that Calent mound sustains an intense yet highly localized biogeochemical environment within the photic zone, where CO2 venting and nutrient inputs jointly influence carbonate chemistry and microbial community structure.
Continue reading ‘Physical-chemical gradients, CO2 venting dynamics and microbial community composition in a shallow Mediterranean CO2-rich hydrothermal system’A systematic bias in float pH leads to overestimation of derived pCO2 and underestimation of carbon uptake by the Southern Ocean
Published 17 June 2026 Science ClosedTags: Antarctic, chemistry
The carbon flux estimated from biogeochemical Argo float data indicates a lower annual carbon uptake by the Southern Ocean compared to fluxes derived from other observations (e.g., ship and aircraft measurements). The root cause of this discrepancy remains controversial, with growing evidence suggesting that potential biases in float-derived pCO2 may be a plausible explanation. Here, we perform a multi-variable comparison of vertical profiles between float- and ship based-data and reveal consistent discrepancies in pH, pCO2 and dissolved inorganic carbon, which are not found in other variables such as dissolved oxygen, nitrate and total alkalinity. Our findings are consistent with a previously unrecognized negative bias in float pH driving a positive offset in float-derived pCO2. The float-derived surface pCO2 is, on average, biased high by 15 ± 3 µatm compared to ship data, representing a larger magnitude of bias than previously recognized. Biases exist in both surface and deep waters, including old deep waters containing minimal anthropogenic carbon. A more sophisticated adjustment for float pH, involving multiple cross-reference depths, may be required for accurate estimation of air-sea CO2 exchange in the Southern Ocean.
Continue reading ‘A systematic bias in float pH leads to overestimation of derived pCO2 and underestimation of carbon uptake by the Southern Ocean’Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island
Published 16 June 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, cnidaria, community composition, corals, field, Indian, otherprocess, vents
Gas hydrates modulate methane and carbon dioxide benthic fluxes into the ocean and usually occur embedded in the sediment. Here we use acoustic surveys alongside optical and geochemical observations from remotely operated vehicles to show that CO2 hydrate mounds are forming directly on the seafloor atop a large liquid CO2 vent field offshore Mayotte Island. The venting, which initiated following volcanic activity in 2018, deleteriously impacts surrounding coral communities due to local acidification.
Continue reading ‘Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island’Cross-seasonal influence of China Coastal Current water on spring carbonate system in the northern South China Sea
Published 15 June 2026 Science ClosedTags: chemistry, North Pacific
This study investigates the carbonate system in the northern South China Sea shelf off the Pearl River estuary during the spring of 2023. Contrary to the typical distribution pattern observed in river-dominated coast where dissolved inorganic carbon (DIC) increases offshore, field observations revealed higher DIC in inshore waters (> 1980 µmol kg− 1) than in offshore seawaters (< 1970 µmol kg− 1), with DIC in the coastal zone being 20.9±8.8 µmol kg− 1 higher than that offshore. An end-member mixing model indicated that the high DIC coastal water was primarily attributed to mixing with the remnant high-DIC southward winter China Coastal Current water. In addition, biological processes and air-sea CO2 exchange also played important roles. Two representative regions were examined: the inshore high-DIC region and the offshore low-DIC region. In the inshore high-DIC region, biological processes and air-sea CO₂ exchange increased DIC by 11.6 ± 3.0 (relative to air-sea CO2 equilibrium) and 1.1 ± 7.0 µmol kg− 1 (relative to conservative mixing), respectively. In the offshore low-DIC region, biological processes decreased DIC by 5.1 ± 3.5 µmol kg− 1, whereas air-sea CO2 exchange increased DIC by 9.9 ± 2.8 µmol kg− 1. Overall, this study highlights the dominant role of the cross-seasonal influence of the remnant water of the coastal current, as well as the secondary but significant contributions of biological activity and air-sea CO2 exchange to the DIC distribution in coastal regions.
Continue reading ‘Cross-seasonal influence of China Coastal Current water on spring carbonate system in the northern South China Sea’High-resolution reconstruction of the pH-upregulation and its seasonal drivers in the temperate coral Cladocora caespitosa
Published 12 June 2026 Science ClosedTags: biological response, chemistry, corals, laboratory, Mediterranean
Ocean acidification (OA) and associated changes in seawater carbonate chemistry, combined with thermal stress, hampers coral calcification. By upregulating pH and dissolved inorganic carbon, corals can optimize their calcification, giving them some resilience to OA. Little is known about the seasonal- and interannual‑scale impacts of thermal stress and OA on pH upregulation and calcification in the temperate coral Cladocora caespitosa, despite it being the only zooxanthellate reef builder in the Mediterranean Sea. δ¹¹B and B/Ca were determined seasonally in C. caespitosa skeletons from two NW Mediterranean sites to reconstruct the effect of seawater temperature and pH on the carbonate chemistry of the coral calcifying fluid (CF), at a bimonthly resolution from June 2013 to August 2017 (Columbretes Islands, Spain), and June 2016 to February 2022 (Villefranche-sur-Mer, France). Cladocora caespitosa displayed a similar pH upregulation strategy to most tropical corals, albeit with an apparently lower sensitivity to seasonal environmental change. Temperature was the main driver of seasonal variability in the CF composition and coral calcification, with seawater pH having a comparatively lower seasonal variability, and acting on longer timescales. While longer coral records and investigations into inter-population variability would still be beneficial in order to fully understand the response of C. caespitosa to environmental change, our records constitute an important first step in understanding the biomineralization strategy of this ecologically important coral species.
Continue reading ‘High-resolution reconstruction of the pH-upregulation and its seasonal drivers in the temperate coral Cladocora caespitosa’Optimization of UV-Vis spectrophotometer (OCaPI) parameters for measuring the pH and pCO2 of the ocean carbonate system in seawater to assess ocean acidification (Mediterranean Sea)
Published 9 June 2026 Science ClosedTags: chemistry, Mediterranean
Automating the measurement of carbonate system parameters is essential for improving our understanding of biogeochemical processes in marine regions. The portable OCaPI (Ocean Carbon Parameters Instrument) is designed to perform simultaneous and accurate measurements of hydrogen ion concentration (pH) and partial pressure of carbon dioxide (pCO2)1 in the ocean environment. Optimizing the parameters of the UV-Vis spectrophotometer (integration time, scan-to-average, boxcar) facilitates the quantification of ocean acidification, with significantly improved measurement accuracy and reliability. The results obtained are consistent with existing techniques and offer a simplified approach to data collection, even under challenging conditions. This work, based on design principles, performance, and preliminary results obtained in the Mediterranean Sea, paves the way for the integration of these optimized techniques into long-term monitoring programs. This will contribute to a better understanding of the impacts of climate change on marine ecosystems and to improved management in the face of ocean acidification.
Continue reading ‘Optimization of UV-Vis spectrophotometer (OCaPI) parameters for measuring the pH and pCO2 of the ocean carbonate system in seawater to assess ocean acidification (Mediterranean Sea)’Ocean acidification alters hypoxia sensitivity and oxyregulation in reef-building corals
Published 9 June 2026 Science ClosedTags: biological response, BRcommunity, chemistry, corals, laboratory, North Atlantic, physiology
Coastal marine ecosystems are increasingly threatened by multiple stressors such as ocean acidification and deoxygenation, but how these co-occurring stressors interact is often poorly understood. This is especially true for tropical coral reefs where deoxygenation is an emerging yet understudied threat. Using hypoxia response curves combined with rigorous pH control, we show that acidification alters hypoxia sensitivity and oxyregulation of reef-building corals in a species-specific manner: three species exhibited increased sensitivity to various degrees, while the fourth showed enhanced tolerance. Consequently, acidification pushes critical hypoxia thresholds into oxygen regimes already prevalent on reefs today, potentially driving shifts in community composition and accelerating risks to reef resilience as these stressors intensify in the future. Our findings challenge assumptions of uniform coral vulnerability under multi-faceted climate change, emphasizing the need for trait-based approaches and to account for stressor interactions in predictive models to better anticipate coral reef futures under rapid climate change.
Continue reading ‘Ocean acidification alters hypoxia sensitivity and oxyregulation in reef-building corals’Systematic review of chemistry educational strategies and curriculum integration in ocean acidification
Published 8 June 2026 Science ClosedTags: chemistry, education, review
This systematic literature review examines the trends and developments in ocean acidification education research from 2011 to 2025. Using the PRISMA methodology, 30 articles from the Scopus database were analyzed to identify key themes, research gaps, and future directions in teaching and learning about ocean acidification. The findings reveal a growing interest in integrating ocean acidification into science education curricula, with a significant emphasis on inquiry-based learning, technology-enhanced instruction, and interdisciplinary approaches. The United States leads research production (51 authors), followed by Spain, Sweden, and Greece. Key educational innovations include virtual reality applications, computational modelling, hands-on laboratory experiments, and collaborative learning strategies. With an average of 23.37 citations per document, this field has a substantial academic impact. However, challenges persist in terms of public awareness, teacher preparation, and curriculum integration. The review identifies the critical need for enhanced pedagogical resources, professional development programs, and assessment tools to effectively teach ocean acidification as a climate change issue. These findings provide valuable insights for educators, curriculum developers, and policymakers seeking to strengthen ocean and climate change education in formal and informal settings.
Continue reading ‘Systematic review of chemistry educational strategies and curriculum integration in ocean acidification’
