Organic carbon mineralization is generally recognized as the primary source of dissolved inorganic carbon (DIC) released from sediments in coastal seas. The CO2 accumulation or the formation of corrosive microenvironment induced by organic carbon degradation can promote the dissolution of calcium carbonate (CaCO3) in sediments, complicating the efficiency of carbon burial and total alkalinity (TA) inputs to aquatic environments. However, quantitative assessments of sediment CaCO3 dissolution and its impacts on the seawater carbonate remain poorly constrained. In this study, we selected typical high-productivity regions, mariculture farms, and applied the 224Ra–228Th disequilibrium approach to quantify the effluxes of DIC and TA across the sediment-water interface. Stable carbon isotopes of DIC (δ13CDIC) were employed to trace DIC sources in porewater. The results showed that CaCO3 dissolution in sediments accounted for 27–56 % of the benthic DIC efflux. Notably, a high contribution of CaCO3 dissolution did not coincide with strong organic carbon degradation across sites, suggesting that dynamic disturbance on sediments, which weakened the metabolic CO2 accumulation in porewater, was also a crucial factor affecting carbonate dissolution. According to the evaluation of the influence that benthic DIC and TA efflux exerted on the seawater CO2 content, the TA supplied by the CaCO3 dissolution was identified to enhance the carbonate buffering capacity of seawater and counteracted the acidification driven by organic matter remineralization. This indicates that CaCO3 dissolution in sediments should be involved in coastal carbon cycling and assessments on coastal ecosystem resilience under the risk of CO2 elevation.
Continue reading ‘Unveiling carbonate dissolution in coastal sediments and its influence on seawater buffering capacity with δ13CDIC and 224Ra–228Th disequilibria’Posts Tagged 'field'
Unveiling carbonate dissolution in coastal sediments and its influence on seawater buffering capacity with δ13CDIC and 224Ra–228Th disequilibria
Published 21 July 2026 Science ClosedTags: algae, chemistry, field, North Pacific, sediment
Carbonate chemistry in groundwater and rivers draining to the Baltic Sea: implications for coastal ocean acidification
Published 21 July 2026 Science ClosedTags: Baltic, chemistry, field
Terrestrial inputs can alter total alkalinity (TA) and dissolved inorganic carbon (DIC) of the coastal ocean and modify seawater pH. Here, we first characterize the carbonate system in river and groundwater draining to the Baltic Sea using observations of TA, DIC, δ13C-DIC, and major ions across 6 countries and 17 beaches. We then assess whether submarine groundwater discharge (SGD) may impact coastal acidification. TA and DIC concentrations were about 2 times greater in groundwater than river water. 84% of the groundwater and 72% of river samples showed potential to acidify receiving Baltic Sea waters and degas CO2 due to low TA/DIC ratios. Mixing plots revealed non-conservative production of TA and DIC in subterranean estuaries. δ13C-DIC values imply that organic matter respiration was a main source of DIC to northern catchments, while calcium carbonate (CaCO3) dissolution was more important along the southeastern coast. Fresh SGD contributed only < 2% of TA and DIC, and 5–7% of Ca, Mg, and SO4 fluxes compared to river discharge when extrapolated to the entire Baltic Sea. However, unquantified total SGD (fresh groundwater plus recirculated seawater) water and chemical fluxes are likely higher. Overall, SGD can locally acidify the Baltic Sea and should be considered in regional carbon budgets.
Continue reading ‘Carbonate chemistry in groundwater and rivers draining to the Baltic Sea: implications for coastal ocean acidification’Distinct polar carbon regimes reveal hemispheric asymmetry in surface ocean pCO₂ regulation
Published 17 July 2026 Science ClosedTags: chemistry, field, modeling, regionalmodeling
Polar oceans play a major role in the global carbon cycle, absorbing a substantial fraction of human-emitted carbon dioxide and helping regulate Earth’s climate. Extreme conditions and seasonal sea-ice limit in situ observations, leaving major uncertainties in how carbon exchange varies across these regions. Consequently, the processes controlling surface ocean carbon at high latitudes remain poorly understood. Here we demonstrate that polar oceans exhibit a pronounced hemispheric asymmetry in the drivers of surface carbon variability. By combining machine learning with a data-driven regionalization of biogeochemical provinces, we reconstruct surface carbon patterns across both polar oceans over the period 1998-2022 and identify their dominant controls. Variability in the Southern Ocean is primarily governed by non-thermal processes linked to biological activity and wind-driven mixing, whereas in the Arctic Ocean thermodynamic forcing dominates in open waters and freshwater-driven stratification shapes the central basin. Polar oceans therefore do not operate as a single carbon regime. Instead, distinct mechanisms governing carbon cycling in each hemisphere are associated with opposing long-term pCO₂ trajectories, with weak or negative trends across much of the Southern Ocean but widespread increases throughout the Arctic.
Continue reading ‘Distinct polar carbon regimes reveal hemispheric asymmetry in surface ocean pCO₂ regulation’Climate change and ocean acidification outweigh local stressors in Mediterranean mussels: a multi-method convergence analysis
Published 15 July 2026 Science ClosedTags: biological response, BRcommunity, field, laboratory, Mediterranean, metals, mollusks, multiple factors, physiology
Highlights
- Climate change explains ∼40% of biological stress variance in Mediterranean mussels.
- Ocean acidification drives 67% of metal bioavailability changes via pH-metal speciation.
- 64% of climate effects on biomarkers operate indirectly through metal bioaccumulation.
- Multi-method convergence (LMG, GAM, SEM, Bayesian Networks) confirms stressor ranking.
- Only SSP1-2.6 keeps biological stress below the chronic-stress threshold through 2050.
Abstract
Marine coastal ecosystems face concurrent pressure from climate change and anthropogenic contamination, yet their relative contributions to biological stress remain poorly quantified. Here we present a decade-long (2014–2023) biomonitoring study on Mytilus galloprovincialis in the Ligurian Sea (NW Mediterranean), integrating quarterly biomarker measurements, heavy metal bioaccumulation data (12 metals), and high-resolution oceanographic records at a control site (Gorgona Island Marine Protected Area) and an offshore regasification terminal.
Biological stress variance was partitioned using five complementary analytical frameworks — Lindeman–Merenda–Gold (LMG) variance decomposition, Hierarchical and Generalised Additive Models (HGAM/GAM), Structural Equation Modelling (SEM), and Bayesian Networks — applied to four biomarkers: DNA damage, lysosomal membrane stability, gill tissue integrity, and immune response. A campaign-specific T0 baseline normalisation isolated environmental signals from initial population variability.
Climate change emerged as the dominant driver, consistently explaining ∼40% of variance across all methods, significantly exceeding metal bioaccumulation (∼30%), terminal influence (∼13%), and seasonal effects (∼2%). Ocean acidification was the primary climate mechanism, influencing 67% of analysed metals. Causal mediation analysis revealed that 64% of the climate effect operates indirectly through enhanced metal bioaccumulation (Climate→Metals→Biomarkers), while 36% acts directly. Climate and biological stress indices co-varied strongly (ρ = 0.78, p < 0.001), with marine heatwaves coinciding with peak biomarker responses.
Under IPCC Shared Socioeconomic Pathway (SSP) scenarios, the Biological Stress Index is projected to cross chronic-stress thresholds by 2035–2040 under the high-emission scenario (SSP5-8.5) and the intermediate-emission scenario (SSP2-4.5), with only the low-emission scenario (SSP1-2.6) maintaining stress below critical levels through 2050.
These findings challenge pollution-centric monitoring paradigms and demonstrate that CO2 mitigation now constitutes the highest-leverage intervention for marine invertebrate health in the Mediterranean.
Graphical abstract
This graphical abstract illustrates the main findings of a decade-long field study (2014–2023) on the effects of climate change and metal contamination on Mytilus galloprovincialis in the Ligurian Sea (NW Mediterranean). Three panels summarise the causal chain from environmental drivers to biological outcomes. The first panel depicts the key oceanographic trends recorded at the study site: ocean warming (+0.41°C/decade), acidification (−0.020 pH units/decade), deoxygenation, and a doubling of marine heatwave frequency after 2018. The second panel shows how pH decline enhances the bioavailability of 67% of the metals analysed, driving a predominantly indirect pathway (64%) from climate stressors to biological stress, mediated by metal bioaccumulation, as revealed by structural equation modelling and Bayesian network analysis. The final panel presents the four biomarkers used to compute the Biological Stress Index (BSI), its strong temporal correlation with the Climate Change Index (ρ = 0.78), and BSI projections to 2050 under three IPCC emission scenarios, showing that only SSP1-2.6 keeps BSI below the chronic-stress threshold throughout the projection period.
Development of hypoxia and acidification during harmful algal blooms: dynamic multi-stressor conditions in NY, USA, estuaries
Published 14 July 2026 Science ClosedTags: algae, biological response, chemistry, field, multiple factors, North Atlantic, sensor, toxicants
Highlights
- Alexandrium blooms occurred with normoxic conditions and moderate pH (7.5-8.0).
- Alexandrium blooms occurred with moderate pCO2 (400 – 1,000 µatm) and saturating conditions for aragonite.
- Dinophysis blooms co-occurred nocturnal acidification (8.71 to 13.6 hr d−1) and hypoxia (0.52 to 3.88 hr d−1).
- Dinophysis blooms co-occurred with high pCO2 (1,000 – 3,500 µatm) and undersaturated aragonite (Ωar < 1).
- The co-occurrence of nocturnal hypoxia, acidification, Ωar undersaturation, and HABs coupled is a significant threat for marine life.
Abstract
While harmful algal blooms (HABs), hypoxia, and ocean acidification are common occurrences in coastal zones, research investigating the co-occurrence and interactions between these processes has been lacking. Here, we documented the initiation, peak, and demise of eight distinct HAB events caused by Alexandrium catenella and Dinophysis acuminata over a two-year period in two estuaries (Northport Harbor and Cold Spring Harbor, NY, USA). We concurrently characterized the dynamics of carbonate chemistry, including pCO2 and the saturation state of aragonite (Ωar), pH, dissolved oxygen (DO), and general environmental conditions in space and time. HABs occurred in succession and reached high densities with A. catenella blooms exceeding 104 cells L−1 being succeeded by D. acuminata blooms exceeding 106 cells L−1. A. catenella blooms occurred during spring months under generally normoxic conditions with moderate levels of pCO2 (400 – 1,000 µatm), only brief periods of acidification (pH < 7.5), mostly saturating conditions for aragonite, and an absence of hypoxia. In contrast, D. acuminata blooms, which occurred in summer, consistently co-occurred with bouts of extended nocturnal acidification (8.71 to 13.6 hr d−1) and hypoxia (0.52 to 3.88 hr d−1) coupled with higher levels of pCO2 (1,000 – 3,500 µatm), and undersaturating conditions for aragonite (Ωar < 1). During both blooms, nearshore locations hosted higher cell densities, lower pH and DO, and higher pCO2 compared to open water regions. The co-occurrence of multiple stressors including nocturnal hypoxia, acidification, Ωar undersaturation, and HABs, coupled with strong diel cycling of DO, pH, and pCO2, especially during D. acuminata blooms, represents a significant and previously unrecognized threat for marine life.
Continue reading ‘Development of hypoxia and acidification during harmful algal blooms: dynamic multi-stressor conditions in NY, USA, estuaries’Brown algae as winners: divergent resilience to high light under acidified conditions shapes macroalgal communities around a carbon dioxide vent
Published 14 July 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, field, laboratory, light, multiple factors, North Pacific, otherprocess, physiology, vents
To investigate the effects of ocean acidification (OA) on macroalgae, we conducted in situ surveys along a natural CO2 vent gradient in Shikine Island, Japan, together with complementary laboratory culture experiments. The in-situ surveys revealed that near the CO2 vent (where pH dropped by 0.37), macroalgal diversity and species-richness were less than half those at the reference sites under ambient pH conditions. Nevertheless, the rates of CO2 assimilation of several common macroalgae increased from the reference site to the areas near the CO2 vent. This enhancement coincided with decreased photosynthetic CO2 affinity, reflecting that the acidified area down-regulated CO2-concentrating mechanisms in the algae. Measured photosystem II activity revealed that macroalgae at reference sites had lower electron transport rate and light utilization efficiency. The laboratory culture experiments, in which the dominant species (Gelidium elegans and Dictyopteris undulata), were cross-exposed to ambient and elevated CO2 conditions, further demonstrated that the stress near the CO2 vent significantly exacerbated photoinhibition under high light stress. Our results demonstrate that reduced pH and high sunlight act synergistically to impair macroalgal photosynthesis through exacerbated photoinhibition. This effect was more pronounced in red algae (e.g., G. elegans) than in brown algae (e.g., D. undulata). These different physiological responses provide a mechanistic explanation for an observed community shift, from red algal dominance in ambient pCO2 areas to brown algal dominance near the vent. Our findings imply that future OA, when combined with high-light stress, may selectively disadvantage high-light-sensitive species, thereby altering macroalgal community structure in coastal waters.
Continue reading ‘Brown algae as winners: divergent resilience to high light under acidified conditions shapes macroalgal communities around a carbon dioxide vent’Strong effects of sun exposure on oyster shell corrosion and compensatory calcification: a factor confounding coastal acidification responses
Published 13 July 2026 Science ClosedTags: biological response, calcification, field, laboratory, molecular biology, mollusks, North Pacific, physiology
The dynamics of calcium carbonate structures in marine organisms (skeletons and shells) has become increasingly important due to heightened interest in marine environmental acidification. Research into molluscan shell corrosion and calcification in response to acidification is typically carried out in laboratory-controlled settings, which often overlooks the intricate interactions found in natural environments. Mollusks inhabiting intertidal zones are especially susceptible to intense shell weathering caused by tidal cycles of heating, cooling, wetting, and drying, exacerbated by solar radiation during periods of air exposure. We investigated the effect of sun exposure (solar radiative heating) on both outer shell corrosion and inner shell compensatory calcification in the tropical oyster, Saccostrea scyphophilla. Shell properties were compared between oysters from neighboring populations in sun-exposed and shaded habitats. Habitat temperatures were measured using iButtons, and right shell valve corrosion was quantified. Compensatory calcification was assessed through measurements of shell thickness, shell density, shell compression strength, and mineralogical properties. Our results revealed that oysters in the sun that experience global irradiance, higher temperature peaks and broader daily temperature ranges (averaging an increase of 10 °C) show considerably greater outer shell surface corrosion (87%) compared to shaded oysters (31%) that experience only diffuse irradiance. Sun-exposed shells also become thickened in the midsection and around the adductor muscle, and they are slightly stronger, indicating compensation for the outer shell loss. These findings highlight the need for caution when interpreting molluscan shell dynamics based on laboratory marine acidification protocols that fail to account for the many natural environmental factors influencing shell formation and dissolution.
Continue reading ‘Strong effects of sun exposure on oyster shell corrosion and compensatory calcification: a factor confounding coastal acidification responses’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’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’Ocean acidification, more than warming or heatwaves, constrains shoaling behaviour in a range-extending fish through habitat simplification
Published 8 June 2026 Science ClosedTags: biological response, BRcommunity, field, fish, North Pacific, performance
- Social context is a critical yet underexplored determinant of behavioural resilience to climate change. Group living can buffer individuals against environmental stress through enhanced vigilance, reduced predation risk and improved foraging efficiency.
- However, whether these behavioural expressions persist under chronic (warming, acidification) and acute (marine heatwaves) climate stressors remains unclear. Using natural climate analogues spanning present-day, ocean warming and combined warming–acidification reefs, we quantified how shoal size influences behavioural expression in a range-extending reef fish (Pomacentrus coelestis).
- Across all climate conditions, fish in larger shoals consistently exhibited higher foraging and activity levels and reduced risk-avoidance behaviours, whereas direct effects of warming, acidification and heatwaves on behaviour were negligible.
- In contrast, ocean acidification most likely constrained collective behaviour indirectly by simplifying benthic habitats, where fish densities were 84% lower than at the warming reef, resulting in shoals that were up to 79% smaller than the Warming and Control reefs.
- Combined, our data suggest that shoal size mediates behavioural expression between foraging and predator avoidance and that acidification-driven habitat simplification can alter behavioural expression indirectly by reducing fish densities and the formation of large shoals.
- We conclude that climate change can indirectly modify behavioural expression in shoal-forming fishes through habitat-driven erosion of social structure.
Assessing recent anthropogenic carbon dioxide and acidification in the Ross Sea, Antarctica
Published 5 June 2026 Science ClosedTags: Antarctic, chemistry, field
Over the past decade, the East Ross Sea has experienced a significant decline in sea ice, enabling direct observational studies of regional carbon dynamics. The accumulation rate of anthropogenic CO2 in the East Ross Sea is up to six times higher than the long-term Industrial Era mean due to the inflow of seawater from the Amundsen Sea by accelerated glacial melting. In contrast, the West Ross Sea exhibited comparatively smaller changes. Measurements of dissolved inorganic carbon and stable carbon isotope indicate that, over the period 2011–2020, changes in δ13C (Suess effect) and anthropogenic CO2 were 0.20 ± 0.06‰ and −5 ± 2 μmol kg−1 in the West Ross Sea, and −0.15 ± 0.01‰ and 9 ± 1 μmol kg−1 in the East Ross Sea. These findings suggest rapid acidification in the East Ross Sea, with aragonite undersaturation likely to occur by the mid-2030s, accompanied by an expected pH decrease of ∼0.2 units by the end of the century.
Continue reading ‘Assessing recent anthropogenic carbon dioxide and acidification in the Ross Sea, Antarctica’Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica
Published 3 June 2026 Science ClosedTags: algae, biological response, community composition, corals, echinoderms, field, modeling, North Pacific, otherprocess, photosynthesis, physiology, regionalmodeling
Reef-building corals form the calcium-carbonate frameworks that underpin tropical coral reefs, yet global coral cover has declined by ~50% in recent decades, due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that buffer stress, promote recovery, and enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photo-physiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and richer in chlorophyll a. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin cover, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp.. When significant, photophysiological measurements showed 9.7 – 44.5% higher photosynthetic efficiency (Fv’/Fm’) in Papagayo corals and 19.94 – 42.75 % higher maximum photosynthetic rates (Pmax) in Sámara corals. These results highlight how contrasting environmental regimes within a relatively small geographic area can shape distinct coral community compositions and photophysiological strategies, with implications for identifying areas of reef persistence or refugia.
Continue reading ‘Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica’Upper-ocean variability of the marine carbonate system in the Northeast Pacific
Published 2 June 2026 Science ClosedTags: chemistry, field, globalmodeling, modeling, North Pacific, regionalmodeling
In the Northeast Pacific, the marine carbonate system’s variability across timescales is not well constrained. Here, we quantify observed seasonal and non-seasonal variability in Dissolved Inorganic Carbon (DIC), partial pressure of carbon dioxide () and aragonite saturation state and discuss potential drivers. We used three decades of observations from four Line P time series stations, the longest marine carbonate system time series in the Northeast Pacific (1990–2019). To gauge the spatial extent of the variability patterns, we used output from a global ocean model representing the observed period. In the Northeast Pacific, seasonal and non-seasonal variability at 10 m was minimal, mostly damped by the opposing influence of DIC and temperature changes at both seasonal and interannual timescales. For DIC and , the seasonal cycle dominated total variability in the top 60–70 m, with mean-transect 10 m seasonal amplitudes of 35 3 μmol and 0.31 0.04, respectively. In the upper 60–70 m, the magnitude of non-seasonal variability was at least half that of the seasonal variability for most variables. From five climate indices examined, we focused on the basin-scale Pacific Decadal Oscillation index (PDO) to investigate potential drivers of non-seasonal variability, with 20%–40% of the non-seasonal variability in DIC and associated to this index. In the Northeast Pacific, positive PDO periods were linked to a mean reduction in 10 m DIC of 5 μmol and an increase in 10 m of 0.04 for each PDO unit increase, which could potentially reduce the occurrence and severity of ocean acidification events. The opposite could be expected during negative PDO periods.
Plain Language Summary
Using 30 years of observations from the Northeast Pacific, we characterized sources of variability for three marine carbonate system variables: , dissolved inorganic carbon (DIC) and the saturation state of aragonite (an common indicator of ocean acidification). The seasonal and non-seasonal variability was minimal in the top 10 m. The seasonal cycle of DIC and aragonite saturation state was the major contributor to total variability in the top 60–70 m, and not detectable below. Also, in the top 70 m of the water column, up to 20%–40% of the DIC and aragonite saturation state non-seasonal variability was associated to the Pacific Decadal Oscillation index (PDO). The PDO is a statistics-derived index that captures variability patterns influencing the whole Pacific basin and has a positive and negative phase. We found that a warmer than usual upper water column in the Northeast Pacific during a positive PDO phase, potentially driven by reduced mixing, was linked to a lower DIC and higher values of aragonite saturation state. The opposite could be expected during negative PDO periods. Knowing the magnitude of natural variability in the marine carbonate system is important to identify the emergence of ocean acidification and other human-driven changes in the ocean.
Continue reading ‘Upper-ocean variability of the marine carbonate system in the Northeast Pacific’Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective
Published 28 May 2026 Science ClosedTags: field, Indian, modeling, regionalmodeling, salinity
This study comprehensively assesses the long-term variability of temperature, ocean acidity changes, and their implications on sound absorption and acoustic propagation in the Bay of Bengal. The analysis reveals a persistent warming trend in the Indian Ocean over the past 50 years, with a significant increase in temperature observed during the Sagar Maitri cruise in 2019. Thermal structure analysis using HadleySST EN4 data indicates warming in the upper 50m but a cooling trend in the 100-200m depth range. Oceanic Heat Content analysis highlights an increasing tendency of heat storage in the upper 50m, indicative of global warming.
In the context of surface ducted propagation, Sonic Layer Depth (SLD) and gradients in the Sound Speed Profile (SSP) were crucial factors influencing acoustic energy behavior. The study revealed a decreasing trend in in-layer gradient (Gr_SL) since 1990, intensifying after that period. The below-layer gradient (Gr_BL) also exhibited a decreasing trend, implying complex dynamics in the sonic layer with potential implications for sound propagation in the surface duct.
The investigation into pH changes spanning 65 years demonstrates a declining trend, particularly since the 1990s, attributed to increased atmospheric CO2 dissolution. The study linked this decrease to anthropogenic activities, aligning with global trends. The analysis of sound absorption illustrated a nonlinear relationship between absorption, frequency, and pH, emphasizing a significant impact of ocean acidification on sound absorption in the Bay of Bengal. The acoustic propagation modeling further highlighted a decrease in transmission loss with reducing pH, leading to increased sound travel and potentially noisier oceans. Salinity variations play a more significant role than temperature in influencing sound absorption.
Continue reading ‘Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective’Present and future seawater CO2 chemistry across multiple coral reef habitats and scales at Dongsha Atoll and Taiping Island in the South China Sea
Published 22 May 2026 Science ClosedTags: biogeochemistry, chemistry, corals, field, laboratory, North Pacific, sensor
Coral reefs consist of diverse benthic habitats that influence seawater CO2 chemistry variability on multiple spatial and temporal scales. Understanding the present-day seawater CO2 chemistry variability across both habitat-specific and reef-wide scales is critical to accurately predict the effects of future environmental change. Here, we utilize autonomous sensors and discrete seawater samples across diverse habitats at multiple scales ranging from habitat-specific (inner lagoon, patch reefs and seagrass beds; 0.02–0.72km2) to reef-wide scales at Dongsha Atoll (250km2) and Taiping Island (20km2) to characterize seawater chemistry. Across all habitats, daily mean pH ranged from 7.79–8.60 with mean diel variability ranging from 0.19–0.91. Spatially, pH variability ranged from 0.08 (patch reef) to 1.29 (inner lagoon). Biogeochemical modification of seawater chemistry was dominated by organic carbon cycling at individual habitat scales, whereas inorganic carbon cycling dominated at the scale of Dongsha Atoll. The largest alkalinity depletion (net calcification) was associated with patch reef habitats, whereas the highest alkalinity repletion was associated with a semi-enclosed lagoon. Under two climate change scenarios (linear dissolved inorganic carbon increase derived from historical observations and the CMIP6 SSP5-8.5 pathway), pH and/or aragonite saturation state (ΩAr) observations across all habitats in this study are projected to be below proposed thresholds for net reef accretion (pH < 7.7: inner lagoon ~ 10–13%; seagrass beds ~ 21–44%; patch reefs ~ 0–100%; atoll-wide ~ 4–98% of observations) or net dissolution (ΩAr < 2.92: inner lagoon ~ 10–18%; seagrass beds ~ 44–75%; patch reefs ~ 77–100%; atoll-wide ~ 94–100% of observations) by the year 2100. The results highlight the importance of habitat-specific and scale-conscious assessments of future coral reef environmental conditions.
Continue reading ‘Present and future seawater CO2 chemistry across multiple coral reef habitats and scales at Dongsha Atoll and Taiping Island in the South China Sea’Ocean acidification, more than warming or heatwaves, constrains shoaling behaviour in a range-extending fish through habitat simplification
Published 18 May 2026 Science ClosedTags: biological response, corals, field, fish, North Pacific, performance
- Social context is a critical yet underexplored determinant of behavioural resilience to climate change. Group living can buffer individuals against environmental stress through enhanced vigilance, reduced predation risk and improved foraging efficiency.
- However, whether these behavioural expressions persist under chronic (warming, acidification) and acute (marine heatwaves) climate stressors remains unclear. Using natural climate analogues spanning present-day, ocean warming and combined warming–acidification reefs, we quantified how shoal size influences behavioural expression in a range-extending reef fish (Pomacentrus coelestis).
- Across all climate conditions, fish in larger shoals consistently exhibited higher foraging and activity levels and reduced risk-avoidance behaviours, whereas direct effects of warming, acidification and heatwaves on behaviour were negligible.
- In contrast, ocean acidification most likely constrained collective behaviour indirectly by simplifying benthic habitats, where fish densities were 84% lower than at the warming reef, resulting in shoals that were up to 79% smaller than the Warming and Control reefs.
- Combined, our data suggest that shoal size mediates behavioural expression between foraging and predator avoidance and that acidification-driven habitat simplification can alter behavioural expression indirectly by reducing fish densities and the formation of large shoals.
- We conclude that climate change can indirectly modify behavioural expression in shoal-forming fishes through habitat-driven erosion of social structure.
Impacts of ocean acidification and warming (OAW) on abalone growth and reproduction: a dynamic energy budget model approach across SSP scenarios
Published 18 May 2026 Science ClosedTags: biological response, field, individualmodeling, laboratory, modeling, mollusks, morphology, performance, physiology, reproduction
Ocean acidification and warming (OAW) are expected to alter physiology, growth and reproduction of marine ectotherms, yet their combined effects on life-history traits remain unresolved, particularly under poorly defined future food conditions. Using a Dynamic Energy Budget (DEB) model, we investigated how interacting changes in temperature, seawater pH, and food quality may shape somatic growth and reproductive phenology of the European abalone Haliotis tuberculata across four contrasting coastal environments and three Shared Socioeconomic Pathway (SSP) climate scenarios. OAW effects were modeled as increased metabolic maintenance costs, while reduced food quality, driven by OAW, lowered assimilation efficiency, aligning with experimentally-supported limited compensatory feeding.,Our results reveal that warming and food quality strongly drive somatic growth, whit ocean acidification playing a minor role within the modeled range. Food quality remained the primary determinant of maximum body size, while warming amplified growth across all locations, with the largest proportional increases in cooler northern bays. Individuals in the warmest areas remained the largest across scenarios within the model framework. Reproductive timing also shifted consistently, with first spawning occurring markedly earlier under end-of-century conditions, advancing consistently with scenario intensity. Food quality modulated reproductive investment but had weaker effects on the timing of first spawning., These findings highlight that food quality critically mediates organismal responses to OAW and can offset temperature-driven gains in growth and reproduction. By combining expected nutritional constraints with SSP scenarios, our DEB-based approach provide mechanistic insights into the future responses of benthic marine invertebrates to climate change, highlighting the value of these scenario-based projections for better management strategies.
Continue reading ‘Impacts of ocean acidification and warming (OAW) on abalone growth and reproduction: a dynamic energy budget model approach across SSP scenarios’High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning
Published 14 May 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, corals, field, laboratory, North Pacific, otherprocess, phanerogams, physiology, reproduction
Highlights
- Seagrass-coral habitats act as CO2 sources driven by intense nighttime respiration
- High-resolution data enable predictive modeling of DIC, DOC, and POC dynamics
- Metabolic cues govern DIC, while temperature and alkalinity regulate POC and DOC
- Episodic coral spawning and rainfall trigger rapid ocean acidification
- Short-term disturbances dramatically shift organic and inorganic nutrient loads
Abstract
Seagrass meadows and coral reefs are global hotspots for productivity, yet they are often studied in isolation despite their intense biogeochemical connectivity. Significant gaps remain in understanding how coupled inorganic and organic processes within the water column drive blue carbon services in such mixed habitats, particularly during rapid environmental disturbances. Here, we investigated a unique, intertwined ecosystem in the Dongsha Atoll, where massive Porites corals are distributed on seagrass meadows, creating a natural laboratory for studying water column carbon biogeochemistry. During a 10-day sampling period, we collected continuous hydrological and discrete biogeochemical data at two- to four-hour intervals. Our results reveal that the dissolved inorganic carbon (DIC) covaried with dissolved oxygen and pH in strong diurnal patterns, which were governed by photosynthesis and respiration. As an outcome, variable but mostly high pCO2 values (141–2070 μatm) indicate the seagrass meadow was a source of CO2 to the atmosphere due to strong night-time respiration. Particulate organic carbon (POC) increased with temperature but showed no diurnal pattern. Dissolved organic carbon (DOC) showed a weak diurnal pattern and was linked to variations in POC and total alkalinity, highlighting the tight coupling between the organic production of the meadow and the inorganic chemistry of the calcification framework. Additionally, coral spawning led to a surge in organic content and changed inorganic nutrient levels. Rainfall events significantly acidified the ocean and enhanced submarine groundwater discharge to the seagrass-coral habitat. The distinctive contributions of this study are the extremely high temporal resolution of discrete samples, allowing the simultaneous tracking of multiple organic and inorganic pools during natural disturbances. The high-resolution data provide fundamental information for parametrizing models that explain DIC, POC, and DOC, which yield insights into organic carbon cycling in seagrass meadow-coral habitats.
Continue reading ‘High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning’Aragonite saturation state and coral reefs health assessment in Sri Lanka
Published 11 May 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, Indian
Ocean acidification (OA) and nutrient enrichment can separately or together threaten coral reefs by reducing calcification efficiency and increasing physiological stress, ultimately weakening reef resilience. Therefore, the study evaluates the prevailing OA level over the Sri Lankan coral reef areas using the aragonite saturation state (ΩAr) and assesses the nitrate (NO3−), and phosphate (PO43−) concentrations over the coral sites. The study was conducted on coral reefs on the eastern coast (EC), southern coast (SC), northern coast (NC), and west coast (WC) of Sri Lanka from April to June 2024. A total of 63 seawater samples were collected around each coastal site for analysis. The ΩAr were supersaturated (ΩAr > 1) and ranged from 2.98 ± 0.04 to 4.92 ± 0.12. Throughout the study period, the study sites had ΩAr values exceeding 2.92 ± 0.16, indicating that the nation’s corals were resilient to deterioration, and the comparative analysis demonstrates that these sites were not vulnerable to OA. However, the NC exhibited significantly (P < 0.05) the lowest ΩAr values (3.2 ± 0.64), positioning the regions near the lower bound of optimal calcification conditions. While ΩAr values indicate low OA stress during sampling, elevated NO3− concentrations (2 – 5 μmol L−1) in SC (2.19 ± 1.28 µmol L−1) and WC (3.52 ± 1.48 µmol L−1) may exacerbate coral bleaching during thermal stress events, representing a co-stressor rather than OA effect. Coral bleaching HotSpot (HS) identification emphasizes how spatially distributed HS are from January to June. The OA risk assessment confirmed that climate change will bring high risk to the coral calcification, reproduction, and damage to the breeding ground, which impact on the ecology and economy of Sri Lanka.
Continue reading ‘Aragonite saturation state and coral reefs health assessment in Sri Lanka’Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations
Published 5 May 2026 Science ClosedTags: algae, biological response, field, mitigation, North Atlantic, phytoplankton
The oceanic uptake of anthropogenic CO2 has resulted in ocean acidification (OA). Macroalgae farming has the potential to mitigate OA by removing CO2 from the surface water via photosynthesis. However, continuous in-situ observations of marine carbonate chemistry related to macroalgae farming remain limited, leaving its effectiveness in addressing OA uncertain. To address these knowledge gaps, this study examined a 2-acre Saccharina latissima, sugar kelp, farm located at Point Judith, Rhode Island, as a case study to assess the potential of sugar kelp aquaculture in mitigating local OA. Over the full growing season from December 2022 to May 2023, high-temporal-resolution (every 30–60 minutes) measurements of surface temperature, salinity, dissolved oxygen and pH were taken inside and outside the kelp farm. The results demonstrate that sugar kelp farming does not significantly impact the carbonate system, thus providing negligible OA mitigation locally. Specifically, a temporary, local-scale CO2 reduction and higher pH occurred during very early kelp growth in early February, but was reversed by a higher surface CO2, exaggerating OA, starting in mid-February. Over the entire observation period, kelp growth resulted in a 5.1 ± 11.6 μatm increase of pCO2 per week compared to the control site in the surface, a signal which is small compared to the substantial natural variability. However, the minimal pCO2 difference at the kelp farm may be reflective of the relatively small cultivation area (2 acres) or depressed growth of phytoplankton, resulting from nutrient competition between the kelp and in-situ phytoplankton. This study underscores the need for future sustained observations to evaluate the impact of seaweed cultivation on OA mitigation and the carbon cycle at the ecosystem scale.
Continue reading ‘Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations’
