The physical and chemical oceanographic properties of the Gulf of Mexico (GOM, recognized by the United States as the Gulf of America) remain incompletely characterized. Evidence suggests that GOM carbonate chemistry is mainly influenced by physical mixing, changes in atmospheric CO2 levels, and localized processes including eutrophication, hypoxia, and upwelling. The purpose of this dissertation is to increase sampling coverage in the northwestern Gulf (nwGOM), analyze decadal trends using both new and existing data, explore two cross-shelf transects from surface to bottom over 16+ years, and develop statistical models to estimate pH and ΩAragonite from hydrographic measurements. The research incorporates both laboratory and computational analyses across all chapters, including data collected from sensors (moored and shipboard). Samples for carbonate chemistry parameters were analyzed in the lab following standard practices. Computational work was conducted using RStudio, Python, and MATLAB. The statistical models can estimate water column pH and ΩAragonite with R2 values over 0.93 with small mean square errors (<0.0005 and <0.04 for pH and ΩAragonite, respectively), demonstrating their effectiveness. Key findings include seasonal patterns and long-term temperature trends in the nwGOM, as well as spatial variability and upward shoaling of the aragonite saturation horizons (ΩAragonite) from full water-column transects. These results reveal that subsurface waters are experiencing both declining dissolved oxygen (DO) and a shoaling saturation horizon. At the same time, surface waters also show progressive acidification, marked by decreasing pH and rising CO2 partial pressure (pCO2), despite significant seasonal fluctuations and an overall warming trend. The collected data provide essential spatial and temporal coverage of carbonate chemistry. The numerous changes occurring in the Gulf highlight the importance of quantifying these variations to guide resource management and conservation efforts.
Continue reading ‘Ocean acidification in the Northwestern gulf of America’Posts Tagged 'field'
Ocean acidification in the Northwestern gulf of America
Published 19 October 2026 Science Leave a CommentTags: chemistry, field, modeling, North Atlantic, regionalmodeling
Hydroclimatic controls on nearshore pollution and ecosystem stress along a tropical urban coastline
Published 19 October 2026 Science Leave a CommentTags: biogeochemistry, chemistry, field, Indian
Highlights
- Integrated indices revealed nutrient, microbial, and organic pollution patterns.
- Urbanization and monsoon hydroclimate jointly intensified coastal degradation.
- Seasonal eutrophication and oxygen depletion were strongly temperature driven.
- Microbial contamination increased during post-monsoon runoff and tourism.
- Multi-index approach clarified pollution processes in tropical coastal waters.
Abstract
Urbanizing coasts face escalating pollution from anthropogenic sources and climate change. This study provides an integrated seasonal assessment of coastal water quality along the Visakhapatnam coast, India, using a multi-index framework combining the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), Trophic State Index (TSI), and Pollution Index (PI). Surface water samples were collected from eleven representative locations including fishing settlements, recreational beaches, leisure beaches, and industrial-port zones. Physicochemical factors, nutrients, chlorophyll-a, and microbial indicators were assessed using multivariate statistical analysis to determine significant environmental stressors. Results revealed clear spatial and seasonal differences driven by monsoon runoff interacting with localized urban pollution sources. Jalaripeta exhibited the lowest water quality, with low WQI scores (<40), eutrophic to hypereutrophic status (TSI >56), and elevated microbial contamination associated with untreated sewage and inadequate flushing. In comparison, RK Beach and the Harbour area showed moderate degradation, characterized by intermittent nutrient influx, spikes in microbes, localized hypoxia associated with tourism pressure and port activities. Principal Component Analysis also revealed that nutrient-microbe enrichment, thermal-biological productivity, and organic matter breakdown are major environmental gradients influencing water quality variability. The findings indicate that the interplay between urbanization and seasonal hydroclimate intensifies environmental stress along the Visakhapatnam coast. This integrated multi-index framework provides as a valuable decision-support tool for identification pollution hotspot and adaptive management of tropical urban coasts under increasing climate and anthropogenic pressures.
Reducing nitrate loads to the St. Lawrence river could mitigate hypoxia and acidification in its deep estuary and gulf
Published 15 October 2026 Science Leave a CommentTags: biogeochemistry, chemistry, field, modeling, North Atlantic, regionalmodeling
Hypoxia in marine systems is expanding worldwide due to anthropogenic activities. Deep waters of the St. Lawrence Estuary and Gulf are rapidly deoxygenating (∼1 mmol O2 m−3 y−1), driven by changes in Atlantic water-mass intrusion and nutrient‐fueled remineralization, and are simultaneously acidifying (∼0.004 pH unit y−1). These changes alter biogeochemical cycles and degrade habitats, causing biotic and economic consequences. Using a coupled physical-biogeochemical model, we tested whether watershed-scale nitrate reductions could mitigate deep‐water deoxygenation and carbonate-system degradation. Three nitrate‐reduction scenarios reduced riverine St. Lawrence River nitrate loads by about 11%, 30%, and 50% (−2.8, −7.5, and −11.7 mmol N m−3, respectively). Relative to the baseline simulation, these scenarios increased dissolved oxygen concentrations (DO) (+1.6, +4.3, and +6.7 mmol O2 m−3), pH (+0.004, +0.010, and +0.016), and aragonite saturation state (Ωarag) (+0.003, +0.009, and +0.015) in the deep Laurentian Channel (⩾175 m). The volume of deep waters with DO saturation <30% decreased by 3%, 8%, and 13% (−27, −75, −122 km3), while volumes with pH <7.65 declined by 1.0%, 2.8%, and 4.5% (−22, −60, −96 km3). Severely corrosive waters (Ωarag <0.6) dropped by 1.4%, 3.7%, and 5.9% (−26, −71, −112 km3). Over 2014–2024, modelled improvements exceeded small interannual variability but remained within seasonal amplitudes of deep DO concentrations (∼11 mmol O2 m−3) and pH (∼0.015 units), nevertheless pointing to a detectable management signal. Although nutrient‐driven improvements remained smaller than climate‐forced trends, modelled nitrate load reductions could offset ∼56% and 80% of recent observed oxygen and pH declines, respectively, while reducing hypoxic and acidified (pH and Ωarag) water volumes. These findings provide quantitative evidence that watershed‐scale nitrogen mitigation, through improved agricultural practices and wastewater nitrogen removal, which necessitates cooperation across jurisdictions, can alleviate hypoxia and acidification in deep coastal ecosystems, making nutrient management an essential complement to climate adaptation strategies.
Continue reading ‘Reducing nitrate loads to the St. Lawrence river could mitigate hypoxia and acidification in its deep estuary and gulf’Variability in nitrogen uptake rates related to anthropogenic nutrient sources and carbonate system dynamics in the tropical coastal ocean
Published 12 October 2026 Science Leave a CommentTags: biogeochemistry, chemistry, field, Indian, modeling, regionalmodeling
Highlights
- Elevated CO2 and diverse nitrogen inputs interactively modulate nitrogen uptake rates.
- Ammonium-induced suppression of nitrate and subsequent co-dominance maximize nitrogen uptake.
- Efficient biological pump as the regenerated and new production coexist.
- West coast of India serves as a model system for rapidly developing tropical basins.
Abstract
The interaction between CO2 enrichment and nitrogen uptake under anthropogenic nitrogen inputs in the tropical coastal seas remains poorly understood. In this experimental study, we investigate the effects of elevated CO2 and impacts of various nitrogen sources such as river runoff, submarine groundwater discharge, industrial effluents, and atmospheric deposition, adding on NH4+ and NO3−uptake in tropical coastal waters. Using microcosm experiments along the west coast of India, a representative model system for tropical coastal ecosystems experiencing rapid anthropogenic development, we show that CO2 enrichment enhances nitrogen uptake, under intense anthropogenic nutrient enrichment. Our observations revealed a distinct uptake pattern of initial preference for NH4+ actively suppressed NO3− assimilation, subsequently leading to the co-dominance of NO3− and NH4+ uptake rates. The correlation between regenerated and new production acts as an efficient coastal biological pump in the coastal waters. These findings suggest that rising anthropogenic CO2, alongside nutrient inputs, may intensify nitrogen cycling in tropical coastal oceans, with implications for primary production and ecosystem dynamics under changing environmental conditions.
Continue reading ‘Variability in nitrogen uptake rates related to anthropogenic nutrient sources and carbonate system dynamics in the tropical coastal ocean’Coupling and decoupling of DIC, TA and O2 benthic fluxes along the Rhône River-dominated ocean margin
Published 9 October 2026 Science Leave a CommentTags: biogeochemistry, chemistry, field, Mediterranean
River-dominated ocean margins (RiOMar) and their benthic compartments play a key role in coastal carbon cycling due to the combined effect of high inputs of particulate organic carbon (POC), benthic mineralization and burial processes. This study quantified benthic fluxes of DIC, TA, and oxygen along a transect influenced by riverine POC inputs, providing new insights in diagenetic processes when switching from anaerobic to aerobic dominated sediment form the river mouth to the adjacent shelf. Fluxes at the sediment-water interface were measured ex-situ with sediment cores incubation during two cruises at the end of spring 2018 and 2022. Stations closest to the river mouth exhibit high benthic fluxes averaging 54 ± 20, 30 ± 21 and −27 ± 14 mmol m−2 d−1 for DICflux, TAflux and TOU, respectively, reflecting intense anaerobic remineralization and a strong decoupling between oxygen consumption and DIC production (DICflux:TOU ratio of 1.5 to 3.5). These large TA fluxes further support that FeS burial limits the reoxidation of reduced compounds in these sediments, allowing the upward diffusion of TA produced at depth towards bottom waters. Offshore, In contrast, shelf stations show lower flux intensities, 8 ± 3 mmol m−2 d−1 for DICflux, −1 ± 2 mmol m−2 d−1 for TAflux and −9 ± 2 mmol m−2 d−1 for TOU, suggesting a greater influence of aerobic mineralization, reoxidation processes and nitrification. Stations located in the Rhône prodelta show intermediate benthic fluxes of 24 ± 11, 6 ± 4 and −17 ± 7 mmol m−2 d−1 for DICflux, TAflux and TOU, respectively. By substantially expanding the spatial and temporal resolution of benthic DICflux, TAflux and TOU in this system, this study provides a robust quantitative framework for assessing the contribution of RiOMar sediments to coastal alkalinity budgets and emphasizes the important role of TA fluxes released from the sediment in increasing the buffering capacity bottom waters.
Continue reading ‘Coupling and decoupling of DIC, TA and O2 benthic fluxes along the Rhône River-dominated ocean margin’Diversity and dynamics of sponge microbiomes under ocean acidification: insights from natural CO₂ vents and reciprocal transplant experiments
Published 8 October 2026 Science Leave a CommentTags: adaptation, biological response, BRcommunity, field, molecular biology, otherprocess, physiology, porifera, prokaryotes, vents
Marine sponges are key benthic organisms whose ecological success is closely linked to their associated microbial communities. This thesis investigated the microbiome responses of three Mediterranean HMA demosponges, Chondrosia reniformis, Petrosia ficiformis, and Chondrilla nucula, inhabiting natural CO₂ vents off Ischia Island. By comparing wild populations under ambient and reduced pH with in situ transplants, this work explored long-term acclimatization and short-term responses. Species-specific transplantation protocols were optimized to ensure survival of the three sponges and experimental reliability. Then, 16S rRNA gene metabarcoding was used to characterize sponge-associated and seawater microbial communities. Results showed that sponge microbiomes were distinct from seawater and structured by host identity but each species displayed different degrees of stability and plasticity under acidified conditions. Chondrosia reniformis exhibited a highly stable microbiome, with acidification inducing only fine-scale shifts within a conserved core. Petrosia ficiformis showed greater flexibility, but short-term responses were strongly constrained by donor identity and source-associated signatures. In C. nucula, light availability emerged as the main driver of microbiome reorganization, while low pH modulated this response, promoting shifts from photosymbiosis-related taxa toward lineages potentially linked to nitrification and chemoautotrophy. Overall, sponge holobiont resilience appears to rely not on extensive microbial replacement, but on species-specific rearrangements of resident symbionts within persistent host-associated frameworks.
Continue reading ‘Diversity and dynamics of sponge microbiomes under ocean acidification: insights from natural CO₂ vents and reciprocal transplant experiments’The divergence between chronic offshore acidification and volatile estuarine pH dynamics: a 60-year East China sea record
Published 2 October 2026 Science ClosedTags: biogeochemistry, chemistry, field, methods, North Pacific
Coastal ocean acidification in river-dominated marginal seas exhibits distinct evolutionary trajectories from the open ocean. However, quantitatively decoupling its multi-stressor drivers remains challenging due to historical data scarcity and the confounding effects of shifting hydrology and localized human activities. We established a robust calibration framework using sedimentary 3‑hydroxy fatty acids to reconstruct a 60-year pH history in the Changjiang Estuary and the adjacent East China Sea shelf. Our reconstruction reveals that the shelf water pH declined at a rate of −0.00093 units yr-1 over the past six decades, closely tracking the invasion of atmospheric CO2, whereas the estuarine zone was governed by regional biogeochemical processes. Variation partitioning analysis and generalized additive models quantify that hydrological forcing, anthropogenic forcing and hydro-biological fluctuations accounted for independent variance contributions of 41.3%, 24.8% and 16.3% of the pH variability in the estuary. These findings suggest that the sensitivity of coastal carbonate chemistry to climate-related environmental change depends not merely on atmospheric CO2 forcing, but also on the balance between regional hydrological regimes and ecosystem state. Scenario-based perturbation analyses further suggest that variations in freshwater discharge, warming, and oxygen dynamics will either amplify or partially buffer coastal acidification signals, depending on the dynamic competition between physical dilution and biologically mediated carbonate processes. This underscores the critical necessity of conducting integrated, multi-stressor assessments to guide adaptive watershed coastal management, rather than treating river-dominated marginal seas as a single homogeneous domain.
Continue reading ‘The divergence between chronic offshore acidification and volatile estuarine pH dynamics: a 60-year East China sea record’Environmental impact on calcifying organisms: focus on the effects of river runoff and ocean acidification on health status and pollutant bioaccumulation
Published 29 September 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, growth, Mediterranean, multiple factors, physiology, temperature, toxicants, vents
This doctoral thesis presents a multi-scale and interdisciplinary investigation into the impacts of climate change and anthropogenic pressures on coastal marine ecosystems, integrating the regional dynamics of the Adriatic Sea and the broader context of the Mediterranean Sea. This research combines long-term environmental data analysis with physiological and biochemical studies on key indicator species to elucidate the complex, and often synergistic, nature of the major threats facing these vulnerable environments. The first part of the work highlights a shift in the Adriatic Sea’s physical and biogeochemical regime, from historical eutrophication toward contemporary oligotrophic conditions. The combined effects of reduced Po River runoff and climate-driven warming, particularly during summer, modify the hydrography of the entire basin. These changes have cascading effects, clearly visible in the clam Chamelea gallina. Northern populations, while showing short-term resilience (e.g., higher survival in air), exhibit a lower condition index and higher bioaccumulation of trace metals, which activate costly metabolic defense mechanisms. This energetic stress makes the populations more vulnerable to additional pressures, possibly aligning with the recurrent mass mortality events. The second part of this work was conducted at the Panarea CO2 vents, which constitute a natural laboratory for assessing future global change impacts. Through the study of the coral Balanophyllia europaea, it is found that ocean acidification (OA), especially when combined with ocean warming, significantly impairs coral tissue regeneration, with species-specific responses. A crucial finding was that OA appears to stimulate a response mediated by the coral’s microbiome, enhancing its bacterial degradation capacity and reducing the presence of PAHs in coral tissues. Collectively, this work demonstrates that synergistic stressor interactions pose the greatest threat to marine ecosystems. While evidence of resilience emerges through physiological and microbial adaptations, the findings emphasize the urgent need for integrated management strategies that address cumulative impacts across scales.
Continue reading ‘Environmental impact on calcifying organisms: focus on the effects of river runoff and ocean acidification on health status and pollutant bioaccumulation’Submarine groundwater discharge drives massive carbon outwelling and impacts ocean acidification buffering in a mangrove-dominated bay of the Beibu Gulf, China
Published 28 September 2026 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Mangrove ecosystems are critical blue carbon sinks, yet the role of submarine groundwater discharge (SGD) in carbon outwelling and coastal acidification buffering remains a major knowledge gap. This study integrates radium isotopes (224Ra and 228Ra) and carbonate system parameters to quantify SGD-driven carbon fluxes and their impacts on ocean acidification buffering in Tieshan Bay, a mangrove-fringed semi-enclosed bay in Beibu Gulf, China. Field measurements revealed SGD fluxes of (3.93 ± 1.52) × 107 m3/d (11.6 ± 4.5 cm/d), delivering 31-fold more dissolved inorganic carbon [DIC, (1.06 ± 0.13) × 108 mol/d] and 21-fold more total alkalinity [TA, (7.25 ± 0.89) × 107 mol/d] than local rivers. Notably, SGD exhibited a low TA/DIC ratio (0.68 ± 0.14), which mechanistically weakens the bay’s buffering capacity against acidification by reducing the efficiency of the carbonate system to neutralize atmospheric CO2. Furthermore, bicarbonate dominated SGD-derived DIC (84.7% ± 14.3%), enhancing long-term carbon sequestration potential but concurrently suppressing carbonate saturation states via dilution of carbonate ions [SGD: (27.4 ± 28.1) µmol/L vs. bay: (80.3 ± 22.4) µmol/L]. These findings demonstrate SGD’s dual role as a major carbon outwelling vector and a driver of coastal acidification, redefining blue carbon budgets in mangrove ecosystems.
Continue reading ‘Submarine groundwater discharge drives massive carbon outwelling and impacts ocean acidification buffering in a mangrove-dominated bay of the Beibu Gulf, China’The spatial and temporal variability physicochemical seawater parameter in Dangli Island of Langkawi, Malaysia
Published 28 September 2026 Science ClosedTags: chemistry, field, Indian
Marine environments that are subjected to seasonal changes are increasingly exposed to various factors, such as water pollution, climate change, coastal development, and human impacts. Therefore, this study examined seasonal changes in the main physicochemical parameters of seawater around Dangli Island, Langkawi, Malaysia to better understand the environmental conditions that affect the local marine ecosystem. This study examined seasonal variations in the main physicochemical parameters of seawater such as salinity, temperature, conductivity, pH, dissolved oxygen (DO), Total Ammoniacal Nitrogen (TAN), and Orthophosphate (PO₄³⁻) between twelve monitoring stations D1–D12 around Dangli Island during the Southwest and Northwest Monsoons. The results showed a significant difference between the Southwest Monsoon (SWM) season, which exhibited higher salinity up to 31.16 ppt, temperature up to 30.62°C, and conductivity, while the Northwest Monsoon (NEM) was recorded with cooler temperatures as low as 28.73°C and a slight increase in dissolved oxygen in some areas. This phenomenon causes the ocean to absorb CO₂ and control ocean acidification. Warmer waters during NEM can reduce CO₂ solubility, while cooler, oxygen-rich SWM conditions increase CO₂ uptake, potentially increasing acidification. By studying and understanding how these seasonal conditions affect ocean chemistry, it can help assess the long-term impacts of climate change on the marine environment of Dangli Island and allow us to prepare early conservation strategies for the future. These factors can be influenced by seasonal variations and upwelling phenomena. Two-way ANOVA results demonstrated that all physicochemical parameters have no significant difference between sampling stations (p > 0.05). In addition, there have high significant differences between monsoon seasons (p < 0.05) except for conductivity and DO level. The variations in the physicochemical properties of seawater around Dangli Island reveal the influences of rainfall, river discharges, and upwelling phenomenon on stratification shifts that show the differences in the distribution of seawater physicochemical parameters. These findings also provide valuable insights and help to conserve the marine environment, offering a basis for future research and environmental management strategies around Dangli Island.
Continue reading ‘The spatial and temporal variability physicochemical seawater parameter in Dangli Island of Langkawi, Malaysia’Thermal history and behavioural plasticity shape reef fish tolerance to marine heatwaves
Published 25 September 2026 Science ClosedTags: adaptation, biological response, field, fish, laboratory, morphology, multiple factors, North Pacific, performance, physiology, temperature
Marine heatwaves are becoming more frequent and intense, driving mass fish mortalities and reshaping marine ecosystems, yet the capacity of fishes to tolerate heatwaves remains unclear. We quantified physiological condition and behavioural responses of juvenile warm-water (Abudefduf vaigiensis) and cool-water (Microcanthus strigatus) fishes from three natural climate analogues—an ambient temperate reef, an ocean warming analogue, and a combined warming and extreme acidification analogue—before and during the 2023 global marine heatwave, and under a + 3 °C simulated heatwave in the laboratory. In the laboratory, warm-water fish from the warm reef began the experiment in leaner condition than cool reef fish but increased their bite rates under heatwave conditions, compensating for elevated metabolic demand and maintaining body condition. Cool-water fish showed no behavioural adjustment to the heatwave, and body condition diverged by reef origin: cool reef fish lost weight across all treatments while warm- and extreme-origin fish maintained condition, suggesting tolerance was conferred by prior thermal history rather than acute behavioural responses. In the field, warm-water fish were leaner and had lower protein content during the 2023 heatwave than before it, while cool-water fish from the extreme reef had lower body condition than those from the cool reef prior to the heatwave. Our findings suggest that behavioural plasticity can facilitate warm-water fish tolerance to heatwaves at their cold leading edges, while thermal history supports heatwave tolerance in cool-water fish within their core ranges. Populations inhabiting naturally extreme climate analogues may therefore harbour pre-adapted, climate-resilient fish in a future ocean.
Continue reading ‘Thermal history and behavioural plasticity shape reef fish tolerance to marine heatwaves’Substrate stability drives zoobenthic recruitment in sessile polychaetes in interstitial marine habitats
Published 25 September 2026 Science ClosedTags: annelids, biological response, BRcommunity, field, Mediterranean, multiple factors, reproduction, substrate
Early life stages play a key role in structuring marine benthic communities, yet the mechanisms controlling recruitment in confined habitats remain poorly understood. In particular, the relative importance of substrate stability and visual cues under low-exchange, low-light conditions is unresolved. We investigated zoobenthic recruitment on 8 natural rock types differing in mineral composition, grain size, and surface reflectance, in simulated interstitial sub-boulder conditions in the Ligurian Sea (NW Mediterranean). After 90 d immersion, recruitment was dominated by spirorbid and serpulid polychaetes. Settlement intensity differed markedly among lithotypes, decreasing from granitoids (239.4 ± 37.7 spirorbids and 23.9 ± 3.4 serpulids) to marbles (128.7 ± 45.5 and 13.6 ± 4.8, respectively) and highly porous travertines (55.4 ± 18.5 and 8.4 ± 2.8), in agreement with their estimated dissolution rates. These results suggest that substrate stability is a primary driver of recruitment under confined conditions, likely mediated by localized acidification and enhanced dissolution of calcareous substrates. Within lithotypes, differences in recruitment were also associated with surface reflectance: specifically, a clear preference for darker surfaces emerged within marbles, whereas the colour effect was overridden by structural or mineralogical traits within the heterogeneous matrix of granitoids. These findings indicate that both chemical stability and optical properties contribute to recruitment patterns, although their relative importance varies with environmental context. The modulation of the early colonization in these restricted sub-boulder environments provide a valuable hypothetical framework to investigate the effects of large-scale environmental stressors like future ocean acidification scenario.
Continue reading ‘Substrate stability drives zoobenthic recruitment in sessile polychaetes in interstitial marine habitats’Aragonite saturation state indicates emerging ocean acidification hotspots in the Gulf of Mannar and Palk Bay along the southeast coast of India
Published 23 September 2026 Science ClosedTags: biogeochemistry, chemistry, field, Indian
The impact of ocean acidification (OA) on seawater carbonate chemistry, particularly on the aragonite saturation state (Ωarag), is inadequately understood in the Gulf of Mannar (GoM) and Palk Bay (PB). In this study, we analyzed the spatial and temporal variability of Ωarag to pinpoint potential ocean acidification hotspots within these two ecologically critical coastal habitats along the southeastern coast of India. A pilot study was conducted over 24 locations during 2023–2024. The findings reveal that PB had a higher mean pH (8.33 ± 0.06) than GoM (8.08 ± 0.02). In GoM, Ωarag values were lower, at 2.82 ± 0.20, indicating that calcification conditions were not adequate. In PB, it reached 3.22 ± 0.57, which means that conditions for calcifying organisms were favourable. Seasonal variability in Ωarag was primarily controlled by pH, carbonate ion concentration, pCO2, and monsoonal hydrographic processes Seasonal patterns corroborated that these conditions were modulated by both anthropogenic activities and natural processes. During the Northeast and Southwest monsoons, there were significant drops in Ωarag that matched changes in important biogeochemical indices. Overall, these results reveal that PB experiences greater variability in Seawater carbonate chemistry, while GoM exhibits relatively stable but slightly lower carbonate saturation. Pearson correlation and Structural Equation Modelling further demonstrated that pH and carbonate ion concentration positively influenced Ωarag, whereas pCO2 and Revelle factor showed negative relationships. The findings enunciate that GoM is more vulnerable to ocean acidification than PB and emphasize the value of Ωarag as a sensitive indicator for detecting emerging acidification hotspots in coastal waters. It also emphasizes the importance of regular monitoring of OA parameters in these regions to protect these critical ecosystems and their associated services.
Continue reading ‘Aragonite saturation state indicates emerging ocean acidification hotspots in the Gulf of Mannar and Palk Bay along the southeast coast of India’Ocean acidification drives grazer niche convergence and trophic homogenization in benthic communities
Published 22 September 2026 Science ClosedTags: algae, annelids, biological response, BRcommunity, community composition, crustaceans, echinoderms, field, North Atlantic, otherprocess, performance, porifera, vents
Highlights
- Acidification compresses benthic community isotopic space via carbon homogenization.
- Functional groups show differential isotopic responses consistent with bottom-up trophic reorganization.
- Arbacia lixula shifts from a sponge-dominated diet to herbivory under low pH.
- Paracentrotus lividus maintains stable trophic niche despite acidification.
- Asymmetric grazer responses drive site-specific increases in isotopic niche overlap under acidification.
Abstract
Ocean acidification is expected to alter marine food webs, yet community-level evidence from long-term, naturally acidified systems remains limited. We used stable isotope ratios (δ13C and δ15N) to investigate how natural acidification restructures benthic trophic interactions, from basal resources to consumer niche dynamics, a naturally acidified system (pH gradient: 8.1 to ~7.4; pHT scale) spanning present-day to end-of-century projected conditions (SSP2–4.5 to SSP5–8.5). After accounting for local differences in the isotopic baseline, we found that: (1) community isotopic space contracted under acidification, with the carbon range decreasing as primary producers converged toward 13C-depleted values, while the nitrogen range expanded, indicating species-specific trophic adjustments; (2) functional groups responded asymmetrically, with primary producers showing the strongest δ13C shifts, filter-feeders remaining relatively stable, and omnivorous consumers showing reduced δ13C and δ15N values; (3) the two dominant sea urchin grazers responded in opposite directions — the macrophyte-based omnivore Paracentrotus lividus maintained stable isotopic values across the pH gradient, whereas the invertebrate-based omnivore Arbacia lixula exhibited pronounced isotopic shifts — resulting in markedly increased, though site-dependent, niche overlap at the most acidified sites (up to 27%); (4) Bayesian mixing models revealed that this convergence was driven by dietary shifts in A. lixula, which transitioned from a predominantly invertebrate-based diet (70–79% animal prey) toward algal-based feeding under acidification (19–24% animal prey), while P. lividus maintained relatively consistent dietary composition (50–70% algae). Together, these results indicate that acidification-driven homogenization of primary producers, combined with asymmetric consumer responses, compresses trophic niche space, with broad implications for the resilience and functioning of benthic ecosystems under future ocean change.
Graphical abstract
Along a natural CO2 gradient in the Canary Islands (pH 8.1–7.4, pHT scale; spanning present-day to end-of-century projected conditions, SSP2-4.5–SSP5-8.5), ocean acidification compresses community isotopic space through homogenization of primary producers. The two dominant sea urchin grazers respond asymmetrically: Paracentrotus lividus maintains a stable trophic niche, while Arbacia lixula shifts toward algal-based feeding, increasing niche overlap up to 27% at the most acidified sites.
Physiological responses of coralline algae to climate change
Published 18 September 2026 Science ClosedTags: adaptation, algae, biological response, calcification, community composition, field, laboratory, molecular biology, morphology, mortality, multiple factors, North Pacific, otherprocess, photosynthesis, reproduction, South Pacific, temperature, vents
Ocean acidification and ocean warming are among the most pressing threats to marine ecosystems, with significant implications for calcifying organisms such as crustose coralline algae (CCA). These habitat-forming species play critical ecological roles in reef systems, yet they are particularly vulnerable to ocean acidification and ocean warming. While laboratory studies have documented declines in coralline algal growth and calcification under elevated CO₂ and temperature, less is known about their responses in natural settings where environmental variability and potential acclimatization may modulate stress impacts. Furthermore, the interactive effects of multiple stressors across generations remain poorly understood, limiting our ability to predict ecosystem-level consequences of climate change. This thesis explores the physiological responses of coralline algae to ocean acidification, ocean warming, and marine heatwaves through complementary field and laboratory approaches. Using natural climate analogues, I investigated how CCA communities respond to chronic exposure to low pH and elevated temperatures in situ (Chapters 2 and 3). These natural systems provide unique opportunities to assess long-term acclimatization and identify potentially resilient populations. To disentangle the mechanisms underlying stress responses and examine multi-generational effects, I conducted a multigenerational, multi-stressor laboratory experiment exposing coralline algae to factorial combinations of elevated pCO₂ and temperature over successive generations (Chapter 4). Together, these approaches enabled assessment of single-driver impacts, stressor interactions, and the capacity for phenotypic plasticity and acclimatization under both fluctuating natural conditions and controlled experimental regimes. Results from natural analogues revealed species-specific variation in stress tolerance, with some CCA populations maintaining growth and calcification despite chronic exposure to conditions projected for year 2100. The laboratory experiment revealed that growth significantly declined when exposed to ocean acidification and the combined effect of ocean acidification and ocean warming over multiple generations. This research advances our understanding of how marine calcifiers respond to climate change across ecological and temporal scales. The findings have important implications for predicting ecosystem trajectories and identifying potential climate refugia in an increasingly acidic and warming ocean.
Continue reading ‘Physiological responses of coralline algae to climate change’Coral acclimatization to novel, co-varying stressors is associated with fitness trade-offs
Published 18 September 2026 Science ClosedTags: adaptation, biological response, calcification, corals, field, morphology, mortality, multiple factors, North Atlantic, oxygen, photosynthesis, physiology, respiration, temperature
Reef-building corals are under pressure to acclimatize and/or adapt to multiple co-occurring stressors, including climate change and declines in water quality. However, their capacity to do so is largely unknown. Yet, some corals naturally persist in habitats with multi-stressor conditions which can provide crucial insight into coral adaptive capacity under future ocean conditions. To assess the role of phenotypic plasticity and local adaptation in coral acclimatory responses to novel conditions, we reciprocally transplanted two coral species (Siderastrea siderea, branching Porites) between an inland bay characterized by multiple, co-varying stressors, including warmer seawater temperatures, higher pollution and more variable temperatures, pH and dissolved oxygen concentrations, and an environmentally less extreme, more stable fringing reef. We measured key phenotypic traits (e.g., calcification, tissue biomass, metabolic rates, chlorophyll concentrations) of all transplant groups after 0, 4 and 12 months. Reef-origin corals demonstrated high plasticity when transplanted to the bay, as both species maintained high survival and calcification, and matched bay natives’ other phenotypic traits. Yet, reef-to-bay transplants of both species had reduced photosynthesis-to-respiration ratios in the bay, highlighting the risk of metabolic trade-offs unless compensated for through increased heterotrophy. Conversely, bay-origin corals had enhanced photosynthetic performance but lower calcification on the reef. Reaction norms provided stronger evidence for environmental specialization in bay-origin than reef-origin corals, which could limit their use as stress-tolerant source corals for reef restoration. Overall, our findings suggest multi-stressor variability may promote specialized genotypes, rather than increased phenotypic plasticity, though this may also depend on predictability of environmental variability.
Continue reading ‘Coral acclimatization to novel, co-varying stressors is associated with fitness trade-offs’Surficial acidic and CO2 plumes in marine shallow hydrothermal vents of Deception Island active volcano, Antarctica
Published 17 September 2026 Science ClosedTags: Antarctic, chemistry, field, vents
We characterize surficial seawater physico-chemical conditions and dissolved CO2 dynamics at the active volcanic system of Deception Island (Antarctica), with emphasis on identifying hydrochemical plumes associated with shallow sea hydrothermal vents (SHV). During the austral summers of 2024 and 2025, spatial surveys of pH, temperature, salinity, and total alkalinity were conducted along the inner coast of Port Foster. Acidification plumes (down to pH ~ 6.1), carbonate undersaturation, and elevated total alkalinity (2,400–7,000 μmol kg⁻1) were identified in areas affected by volcanic–hydrothermal emissions. Dissolved CO2 reached up to 90,000 μatm, with extreme values approaching 160,000 μatm, far exceeding atmospheric equilibrium. The results reveal a strong tidal control on CO2 dynamics in Port Foster, with low tide conditions enhancing nearshore accumulation and potential outgassing. Fluid compositions suggest mixed contributions from hydrothermal inputs, seawater, and meteoric components. These findings highlight the value of carbonate system parameters for detecting and monitoring SHV activity, and position Deception Island as a natural laboratory to investigate volcanic impacts on coastal ocean acidification under polar conditions.
Continue reading ‘Surficial acidic and CO2 plumes in marine shallow hydrothermal vents of Deception Island active volcano, Antarctica’Coastal marine carbon and air-sea fluxes quantified from pH sensors on an extended AUV deployment
Published 16 September 2026 Science ClosedTags: chemistry, field, methods, North Atlantic
For the first time, the Autosub Long Range (ALR) completed a fully autonomous, long-distance (2,000 km) scientific mission, delivering new insight into coastal carbonate dynamics and air-sea CO2 fluxes. Equipped with a suite of oceanographic sensors, including a Lab-on-Chip (LOC) pH sensor and a Sea-Bird SeaFET pH sensor, the mission generated nearly 50,000 high-resolution pH measurements, providing one of the most detailed continuous coastal carbonate data sets collected to date in the region. We evaluated the adjustment of the SeaFET reference potential (k0), testing both the co-deployed LOC sensor and neural network estimates as reference pH. Before correction, the LOC and SeaFET sensors showed close agreement (ΔpHT = 0.013 ± 0.009), which improved to ΔpHT = 0.00004 ± 0.007 after LOC-based k0 adjustment. Both sensors diverged from model estimates, indicating reduced ability of models to resolve fine-scale coastal variability and reinforcing the need for direct in situ observations. Total alkalinity (TA) was derived from salinity-based relationships and model predictions, and paired with pH (SeaFET, LOC, and modeled) to estimate the partial pressure of CO2 (pCO2), which ranged 263–598 ± 27 μatm. Resulting air-sea CO2 fluxes ranged −17.0 to 7.1 ± 1.09 mmol m−2 d−1, with the Celtic Margin acting as a net CO2 sink in May–June of 2022. pCO2 and CO2 flux proved sensitive to subtle pH differences, but less so to TA estimates. Our findings demonstrate the critical role of high-resolution autonomous observations in quantifying coastal carbonate dynamics and CO2 fluxes, capturing processes and variability that are largely unresolved by ship-based surveys or global models.
Plain Language Summary
For the first time, the Autosub Long Range (ALR), a robotic underwater vehicle, completed a long-distance (2,000 km) scientific mission without ship support. During the mission, the ALR collected ocean data using sensors that measured water temperature, oxygen, and seawater acidity (pH). The mission generated nearly 50,000 high-resolution pH measurements, providing one of the most detailed continuous coastal carbonate data sets collected in this region. We evaluated how well two onboard pH sensors agreed with each other and with model-based estimates, and tested an applied correction method. Before and after correction, the sensors closely agreed, showing that autonomous platforms can gather high-quality chemical measurements that resolve coastal marine carbon dynamics better than model estimates alone. We used the pH data, along with estimates of TA, to calculate carbon dioxide (CO2) exchange between the ocean and atmosphere, finding that the region operates primarily as a carbon sink in May–June. Our calculations were strongly influenced by pH input but much less by alkalinity, highlighting the importance of accurate pH observations. This study shows that autonomous sensors can improve monitoring of carbon cycling in dynamic, understudied coastal waters that play a key role in the global carbon system.
Continue reading ‘Coastal marine carbon and air-sea fluxes quantified from pH sensors on an extended AUV deployment’Variability of carbon chemistry at the marine protected area of Savaia Village, Upolu Island, Samoa
Published 10 September 2026 Science ClosedTags: chemistry, field, sensor, South Pacific
The Pacific Small Island Developing States (Pacific SIDS) are at the forefront of climate change impacts, yet these effects remain understudied and therefore poorly understood. Ocean acidification (OA) research in Samoa is in its infancy, with a new OA project established to monitor seawater carbon chemistry in coastal ecosystems. The study measured seawater carbon chemistry—including pH, dissolved carbon dioxide and total alkalinity—within the marine protected area (MPA) of Savaia, Lefaga, on Upolu Island, Samoa. Sampling was conducted over twelve months at four locations within the MPA (Site 1, Site 2, Site 3, Site 4), focusing on spatio-temporal variability in pH, temperature and total alkalinity. Measurements were obtained using water samples and an iSAMI pH sensor. The mean pH recorded was 8.06 ± 0.07, while the mean total alkalinity was 1955.1 ± 25 µmol∙kg−1, which is lower than the typical value of 2305 µmol∙kg−1 observed in tropical environments. This decline in total alkalinity and the corresponding low pH could be a potential source of acidification to downstream coastal ecosystems with potential implications for coral reefs, biodiversity and fishery livelihoods.
Continue reading ‘Variability of carbon chemistry at the marine protected area of Savaia Village, Upolu Island, Samoa’High-resolution mapping of carbonate system parameters over coastal waters using integrated uncrewed aircraft systems (UAS) and Autonomous Surface Vessel (ASV) observations
Published 7 September 2026 Science ClosedTags: chemistry, field, modeling, North Atlantic, regionalmodeling
Coastal acidification, distinct from ocean acidification, is influenced by localized factors such as nutrient runoff, freshwater input, and decomposition. This study estimates carbonate system parameters in the Western Mississippi Sound (WMS) using integrated uncrewed aircraft systems (UAS) and autonomous surface vessel (ASV) observations. During 2018 to 2022, high-ressolution UAS imagery and in 2021 in situ ASV data including pH, pCO2, SST, SSS, CDOM, and Chl-a were collected. Machine learning algorithms were developed to estimate pCO2 and total alkalinity (TA), with random forest models achieving high accuracy (R2 > 0.91). A CDOM-based model was developed to derive SSS, which, along with Chl-a, fed into time-series mapping of TA and pCO2. Results highlight the effectiveness of combining UAS and ASV data to produce fine-scale carbonate system maps. This approach supports improved monitoring of coastal acidification and can be extended to estimate additional parameters such as calcite and aragonite saturation states and DIC.
Continue reading ‘High-resolution mapping of carbonate system parameters over coastal waters using integrated uncrewed aircraft systems (UAS) and Autonomous Surface Vessel (ASV) observations’
