The increasing emission of carbon dioxide (CO2) is altering seawater chemistry, lowering ocean pH and threatening marine biodiversity. Predicting how marine biota will be adversely affected by ocean acidification (OA) remains a key challenge. Here, we document that functional morphological traits offer a more robust metric of calcifier sensitivity to OA than taxonomic diversity alone. Using benthic foraminifera from a Mediterranean CO2 vent system, we identify an empirically derived pH threshold beyond which community structure and function shift markedly. Applying this threshold to end-of-century projections under Shared Socioeconomic Pathway SSP5-8.5 reveals that most western Mediterranean coastal zones will exceed critical acidification levels by 2090–2100. These results highlight the susceptibility of the Mediterranean coastal ecosystems to OA under high-emission scenarios, underscoring the risk of widespread biodiversity loss and impaired ecosystem functioning. Our approach provides a trait-based framework for forecasting ecosystem responses to OA and informing adaptation strategies in climate-sensitive marine regions.
Continue reading ‘Ocean acidification pushes Mediterranean marine calcifiers toward a tipping point’Posts Tagged 'regionalmodeling'
Ocean acidification pushes Mediterranean marine calcifiers toward a tipping point
Published 10 November 2026 Science Leave a CommentTags: biological response, community composition, dissolution, field, Mediterranean, modeling, molecular biology, morphology, otherprocess, protists, regionalmodeling, vents
Contrasting catchment characteristics and carbonate buffering capacity shape acidification susceptibility and CO2 source-sink dynamics in tropical lagoons
Published 6 November 2026 Science Leave a CommentTags: biogeochemistry, chemistry, field, Indian, mitigation, modeling, regionalmodeling
Coastal ecosystems face increasing anthropogenic pressure, driving acidification and shifting them from carbon sinks to sources, yet comparative assessments across contrasting catchment types remain limited, particularly in the Indian Ocean region. We investigated carbonate chemistry in two contrasting tropical Sri Lankan lagoons, Negombo Lagoon, impacted by intensive anthropogenic and marsh-derived inputs, and minimally disturbed Rekawa Lagoon. In Negombo, low-pH, low total alkalinity (TA), and high-CO2 river water and acid-sulfate marsh inputs, combined with weaker carbonate buffering, intensified acidification (pH = 7.66 ± 0.45) and sustained CO2 outgassing (9.1 ± 10.2 mmol m-2 d-1). The lowest pH and weakest buffering occurred in the inner lagoon, and increased toward the seawater inlet through river-sea mixing. In contrast, catchment-derived higher-pH, higher-TA, lower-CO2 river water and strong buffering in Rekawa supported higher pH (8.31 ± 0.52) and net CO2 uptake (−1.8 ± 0.9 mmol m-2 d-1). Our simulations showed that riverine alkalinity enhancement (292–526 µmol kg-1 TA addition) mitigated acidification and CO2 outgassing in Negombo within 40–50 days. Our regional data synthesis showed that pH increased significantly with increasing TA/DIC ratio across estuaries and lagoons. These findings highlight carbonate buffering and catchment management as key strategies for mitigating coastal acidification and CO2 emissions.
Continue reading ‘Contrasting catchment characteristics and carbonate buffering capacity shape acidification susceptibility and CO2 source-sink dynamics in tropical lagoons’Time-variant bioeconomic risks on a gastropod fishery affected by uncertain ocean acidification trajectories
Published 3 November 2026 Science Leave a CommentTags: abundance, biological response, chemistry, field, fisheries, growth, modeling, mollusks, mortality, North Pacific, otherprocess, regionalmodeling, socio-economy
Introduction: In the north-eastern Pacific, high-value abalone fisheries, which are sensitive to pH variations, require in situ pH data to properly assess the bioeconomic effects of their possible dynamic trajectories under alternative fishing mortalities.
Methods: In situ pH data were collected every 15 min using a HOBO® MX2501 sensor in the La Bocana pink abalone fishing grounds and compared them with Argo float and Copernicus Marine Service observations. The observed pH distribution was fitted to the Extreme Value Minimum distribution based on the Anderson–Darling goodness-of-fit statistic. Stochastic pH trajectories were generated through 10,000 Monte Carlo replications under three IPCC ocean acidification scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5) and three fishing mortalities (FD = 0.02, 0.04, and 0.06). These trajectories were incorporated into a dynamic age-structured bioeconomic model by making individual growth and age-specific natural mortality functions dependent on pH. Biomass and resource rent per boat were projected from 2025 to 2100, and linear mixed-effects models, sensitivity analyses, and 95% confidence intervals were used to evaluate temporal responses and parameter uncertainty. Dynamic risks were estimated as the probability that biomass and resource rent fell below their respective limit reference points (LRPs: 190 t and USD 15,000 yr-1) across scenarios and fishing mortalities.
Results: The results indicate considerable variability in pH measurements between remote and in situ sources, which may introduce a proportional bias into the bioeconomic modeling if local observations are absent. Also, the effects of ocean acidification on H. corrugata biomass, survival, and fishery resource rent increase with time, IPCC pH scenario, and alternative exploitation intensity. Under the current exploitation rate (FMSY = 0.06), effects were negligible in the short term under SSP1-2.6, whereas by 2100 pH-related growth effects decreased by 4%, 13%, and 26% under SSP1-2.6, SSP2-4.5, and SSP5-8.5, respectively. Over the same period, pH effects on survival rates resulted in a slight increase of 2.14% under SSP1-2.6, but reductions of 6.48% and 22% under SSP2-4.5 and SSP5-8.5, respectively, while age-specific biomass peaks declined by up to 20% and 44% under SSP2-4.5 and SSP5-8.5. Mixed-effects models confirmed significant effects of pH scenario, exploitation rate, and time on biomass and resource rent, including significant interactions (all p < 0.001). By 2100, annual resource rent per small-scale boat was significantly higher under SSP1-2.6 than under SSP2-4.5 and SSP5-8.5 by USD 3,083 and USD 7,482, respectively (p < 0.0001). Under FMSY, the risk of biomass falling below its LRP was <25% during 2025–2040 but increased to 34% and 54% under SSP2-4.5 and SSP5-8.5, respectively, by 2100; corresponding risks for resource rent increased to 27% and 48%.
Discussion: These results indicate that ocean acidification may substantially increase the long-term bioeconomic vulnerability of the fishery, particularly under high-emission scenarios. Management actions to mitigate the undesired bioeconomic effects of OA will likely depend on the fishery authority’s risk attitude (i.e., degree of risk aversion) and corresponding exploitation-rate strategy selection.
Continue reading ‘Time-variant bioeconomic risks on a gastropod fishery affected by uncertain ocean acidification trajectories’Climate-driven habitat loss of Chinese sturgeon in the Northwestern Pacific and implications for marine protected area design
Published 3 November 2026 Science Leave a CommentTags: abundance, biological response, fish, methods, modeling, multiple factors, North Pacific, nutrients, otherprocess, oxygen, regionalmodeling, salinity, temperature
Highlights
- Ensemble modeling integrates eleven algorithms to predict sturgeon habitat suitability.
- Temperature is the dominant driver, followed by pH and total suspended matter.
- Suitable habitats are projected to disappear completely by 2100 under SSP5–8.5.
- Static protected areas must transition to climate-adaptive zoning strategies.
Abstract
The conservation of endangered anadromous fishes depends on understanding their full-lifecycle habitat requirements, yet the marine phase of Chinese sturgeon (Acipenser sinensis) remains a critical knowledge gap despite over 90% of its lifespan occurring at sea. We integrated multi-source occurrence data (satellite tagging, bycatch records, environmental DNA, and online databases) and applied an ensemble modeling framework (Biomod2 with eleven algorithms) to predict habitat suitability across the Northwestern Pacific Ocean (100°E–150°E, 10°N–55°N). After collinearity filtering, seven key environmental drivers were retained, among which mean temperature contributed most, followed by maximum pH, total suspended matter and mean silicate. The ensemble model achieved high predictive performance (median TSS = 0.944) and identified the Changjiang Estuary and coastal waters of Zhejiang and Jiangsu provinces as current distribution hotspots. Under the high-emission scenario (SSP5–8.5), suitable habitats are projected to disappear completely by 2100, accompanied by a significant northward contraction. These projections should be regarded as a potential worst-case scenario under high-emission conditions rather than a deterministic forecast. These findings demonstrate that business-as-usual emissions would eliminate viable marine habitat for this critically endangered species. Conservation priorities should therefore focus on (1) protecting benthic prey resources in the Changjiang Estuary and Zhoushan Archipelago as core refugia, and (2) transitioning from static marine protected areas to dynamic, climate-adaptive zoning informed by real-time habitat predictions. The ensemble modeling approach developed here is transferable to other data-limited, endangered marine species facing similar climate threats.
Continue reading ‘Climate-driven habitat loss of Chinese sturgeon in the Northwestern Pacific and implications for marine protected area design’Does the evolution of Indian Ocean acidification follow CMIP6 projections under a high-emission scenario?
Published 2 November 2026 Science Leave a CommentTags: chemistry, Indian, modeling, regionalmodeling
The Indian Ocean (IO) surface acidification is governed by pronounced regional variability that is inadequately resolved in coarse-resolution CMIP6 models. Here, we employ eddy-resolving, dynamically downscaled outputs from three CMIP6 Earth System Models under the high-emissions SSP5-8.5 scenario to project future changes in IO acidification, with the model ensemble selected to account for uncertainty in future projections. Eddy-resolving simulations improve representation of mesoscale-driven surface acidification variability by ∼5%–10% relative to CMIP6 models, particularly in coastal regions, while reducing inter-model spatio-temporal heterogeneity. The analysis indicates a relatively weaker mean increase in [H+] compared with CMIP6 projections. The downscaled models yield a dynamically consistent, improved representation of the seasonal cycle of [H+] compared to CMIP6 models, particularly in the northern IO. This facilitates a more robust assessment of future anthropogenically driven changes in [H+] amplitude, with the monthly composite amplitude projected to increase by ∼63%–83% during the far-future period (FF; 2071–2100) across the IO. However, in the Arabian Sea, the increase is ∼37% smaller than in CMIP6, whereas other regions exhibit largely comparable changes. This amplification is primarily driven by enhanced sensitivity of [H+] to surface temperature and dissolved inorganic carbon under warming and increased CO2 uptake. Consistent with these changes, acidification extremes intensify (∼26%–45%) and become more frequent (∼3–5 times higher) in FF. Notably, in coastal regions after 2070, anthropogenic acidification signals emerge later in the downscaled projections than in CMIP6. These results highlight the need for high-resolution projections to improve estimates of future IO acidification and its associated risks.
Plain Language Summary
In the Indian Ocean (IO), acidification is driven by processes that vary widely in space and time. Global climate models are too coarse to fully represent these regional processes. To address this limitation, this study uses a high-resolution model to downscale three CMIP6 models and assess future ocean acidification under a high-emission scenario. Changes are assessed for the future period (2015–2100) relative to the historical baseline (1980–2014). Results indicate that ocean acidity will increase across the IO by 2100, although less intensely than CMIP6 projections suggest. The downscaling results in inter-model agreement of the seasonal cycle, especially in the northern IO. This enables a more robust assessment of anthropogenic changes in acidification amplitude, whose seasonal cycle closely follows CMIP6 across the IO but shows ∼37% less increase in the Arabian Sea. This intensification is mainly due to increased sensitivity to sea-surface temperature and dissolved inorganic carbon as the ocean’s natural buffering capacity weakens. Additionally, extreme acidification events are expected to become more frequent and intense in the future. After 2070, downscaling shows that human-induced acidification changes will emerge later than anticipated by CMIP6 models. This study underscores the importance of capturing regional processes to improve acidification projections.
Continue reading ‘Does the evolution of Indian Ocean acidification follow CMIP6 projections under a high-emission scenario?’Putting a time scale on emerging climate change stressors: a vulnerability index for Atlantic Ocean marine ecosystem services
Published 2 November 2026 Science Leave a CommentTags: chemistry, modeling, multiple factors, North Atlantic, oxygen, policy, regionalmodeling, socio-economy, South Atlantic, temperature
Highlights
- Climate stressor emergence is highly heterogeneous across the Atlantic.
- Multi-stressor emergence before 2100 is projected for all Atlantic EEZs.
- Vulnerability is driven by emerging climate stressors, amplified by a high sensitivity of habitats and communities, and a low adaptive capacity.
- Lower vulnerability is partly driven by robust governance and infrastructure.
- Adaptive responses must address socio-economic differences and variable exposure to stressors.
Abstract
Marine ecosystem services underpin human wellbeing and support resilient socio-ecological systems, yet existing vulnerability assessments remain fragmented, often focusing on isolated industries and overlooking the whole-system socio-ecological context. To bridge this gap, we develop a comprehensive Vulnerability Index to assess marine ecosystem service vulnerability to emerging climate stressors in the Atlantic. Using high-resolution ocean simulations and moving beyond traditional long-term projections, we employ the Time of Emergence metric to address actionable decision-making timescales (2–3 decades). We found that all Atlantic marine ecosystem services are projected to be exposed to multiple emerging stressors before 2100, though the sequence and the timing of emergence are highly heterogenous. Overall vulnerability is highest in tropical West Africa due to the early emergence of hypoxia and sea level rise extremes compound by low adaptive capacity. Additional hotspots are found in subpolar and polar regions driven by rapid sea ice retreat and the sensitivities of region-specific habitats alongside a high dependence on marine ecosystems. Coupled with socio-ecological data, we determined which services (provisioning, regulatory and cultural) are most sensitive to potential impacts in each EEZ. We anticipate this index to be a starting point to develop targeted vulnerability indices for specific ecosystem services and regions. Mitigative and adaptive efforts must be multi-scale and tailored to national and local contexts, addressing not only socio-economic differences but also variable climate stressors and their impacts. Uncertainties associated with time series data gaps and indicator aggregation, particularly for island and remote territories, highlight the need for targeted national adaptation.
Continue reading ‘Putting a time scale on emerging climate change stressors: a vulnerability index for Atlantic Ocean marine ecosystem services’Navigating uncertainty in the Pacific Arctic region: toward adaptive fisheries management under climate change and ocean acidification impacts
Published 30 October 2026 Science Leave a CommentTags: abundance, Arctic, biological response, fish, fisheries, modeling, mortality, otherprocess, policy, regionalmodeling
Fisheries management under climate change in the Pacific Arctic Region faces profound uncertainties, particularly concerning the trajectory of environmental drivers and the biological responses of fish species to ocean acidification (OA), which affect both stock productivity and spatial distributions. Here, we employed the Dynamic Bioclimate Envelope Model to project century-scale changes in abundance, maximum catch potential, and species distributions for key commercial fish under two climate scenarios (SSP1-2.6 and SSP5-8.5) and two alternative assumptions about OA responses, namely without OA effect and with OA effect parameterized as increases in basal metabolic rate and elevated larval mortality. Fishing mortality was treated as a management control variable, and the minimax regret criterion was applied to select the fishing mortality strategy that minimizes the worst-case loss in landed value relative to the scenario-specific optimal strategy across all climate and OA response scenarios. Results indicate strong regional heterogeneity: southern LMEs (East Bering Sea, West Bering Sea, and Aleutians) experienced persistent declines in abundance and maximum catch potential, with negative responses to OA further amplifying reductions, whereas the northern LME (Northern Bering–Chukchi Seas) exhibited substantial gains. These poleward shifts were accompanied by increased spatial aggregation, highlighting that species are not only shifting northward but also becoming more spatially concentrated within suitable habitats. Assessments that ignore OA effects risk overestimating long-term yields and exposing fisheries to productivity and revenue losses. Precautionary reductions in fishing mortality consistently minimized long-term regret across most species and LMEs. These findings highlight the critical interplay between climate change, OA effects, and management decisions, providing a scientific basis for adaptive fisheries management in the rapidly changing Pacific Arctic Region.
Continue reading ‘Navigating uncertainty in the Pacific Arctic region: toward adaptive fisheries management under climate change and ocean acidification impacts’Assessing the skill of a biogeochemical model tailored to a global coupled forecasting system: a case study for the Bay of Bengal carbon cycle
Published 22 October 2026 Science ClosedTags: biogeochemistry, chemistry, Indian, modeling, regionalmodeling
To achieve real-time prediction of surface ocean carbonaceous variables in the Indian Ocean, we integrate an extended-range coupled forecast system with a global ocean biogeochemistry model incorporating an explicit carbon cycle. The physical ocean state is provided by the Indian Institute of Tropical Meteorology Extended Range Prediction for Applications to Society (IITM-ERPAS) coupled model, which drives the Ocean Tracer Transport Model (OTTM) with phosphate-dependent biology and OCMIP-II-type carbonate chemistry (hereafter referred to as OTTM-ERPAS-BGC). Daily mean outputs from IITM-ERPAS are used to drive the biogeochemical simulations. Model skill is evaluated against in situ observations of surface partial pressure of CO₂ (pCO₂) and pH from the Bay of Bengal Ocean Acidification (BOBOA) mooring (90°E, 15°N) over the period 2013-2018. The model successfully reproduces observed variability, with strong and statistically significant correlations (r = 0.65 for pCO₂ and r = 0.80 for pH; p < 0.001). Based on this performance, a coherent region of influence (87.5°E-92.5°E, 12.5°N-17.5°N) is identified to further assess model skill against BOBOA time-series observations, climatological products and other derived datasets of pCO₂ and pH in terms of seasonal cycle, subseasonal variability and long-term trends. Seasonal cycle analysis reveals that the updated Takahashi climatological pCO₂ product is systematically underestimated by ∼18 ± 3 μatm compared to BOBOA observations, OTTM-ERPAS-BGC simulations and other derived products. Subseasonal variability exhibits pronounced intraseasonal signals, with significant spectral peaks at 13-41 days for pCO₂ and 17-41 days for pH, reflecting dominant intraseasonal modulation of the Bay of Bengal carbon cycle. Long-term trends indicate a robust increase in pCO₂ (2.02 μatm yr⁻¹) and a concomitant decline in pH (-0.00253 yr⁻¹), consistent with progressive acidification of the basin. The decomposition analysis demonstrates that dissolved inorganic carbon (DIC) and total alkalinity (ALK) exert dominant and complementary controls on pCO₂ and pH variability, respectively, while sea surface temperature (SST) plays a secondary role. Overall, this study demonstrates that coupling extended-range physical forecasts with ocean biogeochemical models provides a viable pathway for the operational prediction of carbon variables. Such capability is critical for the early detection of ocean acidification and hypercapnia hotspots, with significant implications for marine ecosystem management and climate services in the Indian Ocean.
Continue reading ‘Assessing the skill of a biogeochemical model tailored to a global coupled forecasting system: a case study for the Bay of Bengal carbon cycle’Seasonal prediction of ocean biogeochemistry in the northeast U.S. large marine ecosystem using a regional ocean-biogeochemistry model
Published 20 October 2026 Science ClosedTags: biogeochemistry, chemistry, modeling, North Atlantic, regionalmodeling
We couple an ocean biogeochemical model to a regional ocean model of the Northwest Atlantic and assess the potential skill of bottom dissolved oxygen, aragonite saturation state, and pH forecasts along the Northeast U.S. Continental Shelf using a reanalysis-forced model run as the true biogeochemical state. Across 30 years of retrospective forecasts initialized four times per year, the model has substantial potential skill for all three variables, with skill generally highest in the deep Gulf of Maine and lowest in the shallower Mid-Atlantic Bight and Georges Bank. Forecasts initialized in January and April benefit from the insulation of the bottom from the unpredictable atmosphere by stratification and tend to have greater skill at longer lead times. Using two case studies, we show how predictable variations in ocean temperature, salinity, and currents are associated with predictable variability in bottom biogeochemistry in both the Mid-Atlantic Bight and Gulf of Maine. The forecast model evaluated in this study has been developed as an operational prototype for NOAA’s Changing Ecosystems and Fisheries Initiative, with the goal of applying the forecasts to improve the yield and sustainability of living marine resources.
Continue reading ‘Seasonal prediction of ocean biogeochemistry in the northeast U.S. large marine ecosystem using a regional ocean-biogeochemistry model’Ocean acidification in the Northwestern gulf of America
Published 19 October 2026 Science ClosedTags: chemistry, field, modeling, North Atlantic, regionalmodeling
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’Assessing the projected impacts of climate change on underwater cultural heritage in the Nuevo Gulf, Argentina
Published 19 October 2026 Science ClosedTags: chemistry, communityMF, modeling, multiple factors, oxygen, regionalmodeling, salinity, South Atlantic, temperature
Highlights
- CMIP6 models can quantify future climate threats to UHC sites in Northern Patagonia.
- Projected ∼2.1 °C warming by 2100 will accelerate corrosion and wood-boring activity.
- Ocean pH drop (4.5%) will accelerate corrosion and destabilise calcareous concretions.
- Salinity changes remain negligible across all projected climate change scenarios.
- UHC managers profit locally by integrating in situ data with climate model outputs.
Abstract
Climate change presents a significant and increasing threat to Underwater Cultural Heritage (UCH) worldwide. To better understand the risks that this entails, this study examines the archaeological wreck site of the schooner Emma in the Nuevo Gulf, Northern Patagonia, Argentina. It addresses a geographic research gap and the complex interaction of multiple environmental stressors. Using the information from state-of-the-art climate models, we assess the potential impacts in the near and far future of specific environmental parameters including temperature, salinity, dissolved oxygen, and pH, all relevant at the wreck site’s location, and identified to play a driving role in its conservation.
Results consistently demonstrate a clear trend toward a warmer and more acidic marine environment, with the greatest changes projected under the highest-emission scenario. In that case, sea temperature at the wreck site’s depth increases by approximately 14.5% (∼2.1 °C) by the end of this century, which would accelerate corrosion rates of metals and intensify the activity of wood-boring organisms. In parallel, acidification is projected to increase with pH decreasing by approximately 4.5% (∼0.36 units), contributing to the destabilisation of protective concretions and the intensification of metal corrosion. While dissolved oxygen is projected to decrease (∼3.92%) and salinity remains nearly unchanged, the synergy of warming and acidification suggests the wreck of the Emma will face a more aggressive environment by 2100. The methodology integrates a characterisation of the site’s materials, the main deterioration processes involved and the surrounding environmental context. This study also provides UCH managers with a climate-projection-based assessment of future slow-onset climate-related marine environmental pressures and the likely conservation implications that will inform the development of conservation and monitoring strategies for the Emma and other shipwrecks in the Nuevo Gulf and adjacent coastal areas.
Continue reading ‘Assessing the projected impacts of climate change on underwater cultural heritage in the Nuevo Gulf, Argentina’Reducing nitrate loads to the St. Lawrence river could mitigate hypoxia and acidification in its deep estuary and gulf
Published 15 October 2026 Science ClosedTags: 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’Spatiotemporal water quality dynamics in Southern U.S. coastal reserves: a long-term perspective
Published 14 October 2026 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling
Water quality monitoring in estuarine ecosystems is essential for assessing the health and sustainability of these dynamic coastal habitats, which are increasingly vulnerable to environmental change and human impacts. This study aims to characterize long-term trends and seasonal drivers of seven key water quality parameters: temperature, salinity, dissolved oxygen (DO), pH, chlorophyll-a (Chla), nitrate + nitrite (NOx), and phosphate (PO4) across four southern U.S. National Estuarine Research Reserves (Apalachicola Bay, Grand Bay, Mission-Aransas, and Weeks Bay) to identify which reserves and processes are most vulnerable to climate and anthropogenic change. Using two decades of data (1995–2020) and applying Generalized Additive Models (GAMs), we identified significant spatial and temporal patterns linked to environmental and anthropogenic factors. Results revealed a warming trend in Weeks Bay (+0.1035 °C/year, P = 0.0013), a salinity decline in Grand Bay (−0.1699 PSU/year, P = 0.033), and a salinity increase in Apalachicola Bay (+0.2055 PSU/year, P = 0.003). DO concentrations peaked in spring and dropped in summer, reflecting seasonal nutrient inputs. Grand Bay exhibited the highest Chla variability (CV=131.48%). NOx concentrations declined in Grand Bay (−0.0003 mg/L/year, P = 0.0162), while PO4 levels remained relatively stable. pH trends suggested localized acidification, particularly in Mission-Aransas (−0.0071/year, P = 0.0016). GAM results emphasized the combined effects of long-term and seasonal changes, with site-specific differences. These findings provide critical insights into estuarine functioning and highlight the need for regionally tailored management strategies to enhance resilience and biodiversity conservation in U.S. coastal reserves.
Continue reading ‘Spatiotemporal water quality dynamics in Southern U.S. coastal reserves: a long-term perspective’Variability in nitrogen uptake rates related to anthropogenic nutrient sources and carbonate system dynamics in the tropical coastal ocean
Published 12 October 2026 Science ClosedTags: 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’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’Seasonal forecasts of pH and aragonite saturation for the Bering Sea shelf
Published 28 August 2026 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling
The number of numerical model forecasts of ocean environmental conditions has greatly expanded in recent years, including biogeochemical variables. Forecasts can provide marine resource managers with advance warning of extreme events such as heatwaves and hypoxia, though forecast products are scarcer in high-latitude environments. The Bering Sea shelf is a large marine ecosystem that supports critical commercial, cultural, and subsistence ecosystem services that are vulnerable to extreme events and anthropogenic stressors such as ocean acidification (OA). Here, we use a regional oceanographic model of the Bering Sea to assess model forecast skill in predicting bottom water pH and aragonite saturation state (Ωarag) on lead times from 1 to 9 months. We simulate 28 years (1982–2010) of 3-member ensemble retrospective forecasts, initialized both in April and May following the retreat of winter sea ice and several months in advance of early fall when the most acidic bottom water conditions occur. The results suggest that the model is skillful (anomaly correlation coefficients > 0.5) in forecasting shelf-wide anomalies in bottom water pH and Ωarag, on lead times up to 9 months owing primarily to strong persistence. However, predictive skill for finer scale spatial anomalies is more limited and variable. Model forecast skill is also strong in Bristol Bay, home to the red king crab fishery that has faced recent closures and is threatened by OA. The model forecasts presented here can provide several months advanced notice for acidified water conditions and bolster a suite of products used to support evidence-based fisheries management.
Plain Language Summary
Similar to weather forecasts for the atmosphere, numerical models can also be used to forecast ocean conditions. The skill of these forecasts can be high up to several months in advance because the ocean has a relatively long memory and changes occur more slowly, particularly below the surface. The Bering Sea sustains substantial marine fisheries, which are threatened by changing ocean conditions such as increasing water acidity. Here we used an ocean model to test how well the model can forecast acidified bottom water conditions several months in advance. We did this by running a suite of reforecasts (i.e., we retroactively forecast years that have already occurred) and comparing to the model simulation of the conditions that did occur. Our results suggest that the model can generate skillful forecasts with lead times of up to 9 months, mainly because the conditions that occur at the start of our forecast tend to persist through the summer and into the fall. These forecasts can provide Bering Sea resource managers with advance warnings of water conditions that are harmful to marine species, such as Bristol Bay red king crab.
Continue reading ‘Seasonal forecasts of pH and aragonite saturation for the Bering Sea shelf’Variation and influencing factors of water alkalinity in estuary-bay waters of Zhanjiang Bay, China
Published 27 July 2026 Science ClosedTags: chemistry, field, modeling, North Pacific, regionalmodeling
This study investigated the spatial distribution, seasonal variation, and drivers of surface seawater alkalinity (Alk) in Zhanjiang Bay (ZJB) using high-frequency seasonal sampling in the summers and winters of 2023. Surface Alk ranged from 525.3 to 2213.3 μmol·L−1, with mean values of 1373.1 ± 420.9 μmol·L−1 (summer, n = 28) and 1612.3 ± 343.7 μmol·L−1 (winter, n = 20). Spatially, Alk increased progressively from the estuary to the inner bay and further to the bay mouth, reflecting a typical dilution gradient. Correlation analyses showed that summer Alk was positively correlated with salinity (ρ = 0.706, p < 0.001), indicating that salinity changes associated with conservative mixing were a dominant control, whereas the weaker winter correlation (ρ = 0.473, p < 0.001) suggested that biological processes may play a more important role. Tidal forcing was significantly associated with diurnal Alk variations, particularly in the estuary and inner bay. In the estuary, high Alk occurred during high tide, consistent with tidal mixing; in the inner bay, elevated Alk was observed during low tide, suggesting a possible tidal pumping effect. These findings provide baseline data on Alk dynamics in a subtropical estuarine bay and contribute to understanding the carbonate system and buffering capacity in similar coastal systems. However, because measurements of dissolved inorganic carbon and pCO2 were unavailable, a quantitative assessment of carbon sink capacity requires further investigation.
Continue reading ‘Variation and influencing factors of water alkalinity in estuary-bay waters of Zhanjiang Bay, China’Seawater acidification and bubble plume dispersion from accidental subsea CO₂ pipeline rupture: a multiphase CFD study
Published 24 July 2026 Science ClosedTags: modeling, regionalmodeling
The ecology and maritime traffic safety would be at risk if a CO₂ reservoir or transmission pipeline were to leak. To address this need, multiphase Computational Fluid Dynamics (CFD) models were developed using ANSYS Fluent to predict these coupled processes. The 3D Eulerian-Eulerian CFD model has been developed for validation and the 2D model for predicting the 50m case. The physical and chemical processes involved, such as buoyancy, turbulence, and gas dissolution kinetics, are all considered. The mass transfer coefficient is estimated using the Hughmark correlation. Seawater temperature and salinity are used for estimating dissociation and Henry’s Law constant. The 3D model is validated with the QICS and Hauser Tank Experiments. Hypothetical CO2 release from High Island 10L was simulated and compared to prior work. Findings indicate that the water column can fully mitigate a CO2 release of 35 kg/s in 50 m of water due to CO2 absorption in seawater during ascent. The CFD simulations offer understanding of environmental impact including bubble plume behavior, dissolution into the water column, and consequent changes in seawater pH and pCO₂ and a framework for evaluating CO2 leak impacts on marine environments in the Gulf of Mexico.
Continue reading ‘Seawater acidification and bubble plume dispersion from accidental subsea CO₂ pipeline rupture: a multiphase CFD study’Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait
Published 23 July 2026 Science ClosedTags: Arctic, biological response, community composition, field, laboratory, modeling, multiple factors, otherprocess, oxygen, photosynthesis, primary production, prokaryotes, regionalmodeling, respiration
Highlights
- Remote sensing indicates declining bloom in cold and developing bloom in warm water
- Primary production peaks in polar and arctic surface water masses
- Bacterial production is coupled to primary production despite thermal sensitivity
- Oxygen-based community respiration is highest in warmer water masses
- Oxygen-based and INT-based respiration estimates differ by an order of magnitude
Abstract
The Fram Strait is the primary oceanic gateway to the Arctic Ocean and has highly dynamic oceanographic conditions. Oceanographic conditions can shape community compositions, which is increasingly shown using molecular studies, but rate measurements remain scarce, especially for respiration in the Arctic Ocean. Here, we assessed primary production (PP), bacterial production (BP), bacterial abundances (BA), and community respiration (CR) using Winkler titrations and in vivo Iodo-Nitro-Tetrazolium (INT) reduction within the upper 50 m across water masses of the Fram Strait that had varying bloom conditions in spring 2021. We complemented in situ observations with remote sensing of sea surface temperature (SST) and chlorophyll-a (SSC) to infer bloom phenology in warm (θ>2°C), intermediate (2>θ>0°C), and cold (θ<0°C) waters using remote sensing machine-learning. In the cold, nutrient-rich surface waters, a subsiding spring bloom was associated with elevated PP, BP, and BA alongside a high temperature sensitivity (Q10) that indicates active microbial turnover. In contrast, the warm Atlantic-influenced waters exhibit a relatively lower PP but moderate cell-specific BP, suggesting bacterial maintenance metabolism under pre-bloom conditions. Notably, bacterial respiration (BR) estimates differed by 5- to 80-fold between the Winkler and in vivo INT methods. Although the true BR likely lies between these estimates, our results highlight the substantial microbial activity and underscore the need for more accurate BR measurements in Arctic studies.
Continue reading ‘Water mass-driven variations in primary production and bacterial respiration during the spring bloom in the Fram Strait’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’
