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’Posts Tagged 'regionalmodeling'
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 Leave a CommentTags: biogeochemistry, chemistry, Indian, modeling, regionalmodeling
Seasonal prediction of ocean biogeochemistry in the northeast U.S. large marine ecosystem using a regional ocean-biogeochemistry model
Published 20 October 2026 Science Leave a CommentTags: 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 Leave a CommentTags: 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 Leave a CommentTags: 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 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’Spatiotemporal water quality dynamics in Southern U.S. coastal reserves: a long-term perspective
Published 14 October 2026 Science Leave a CommentTags: 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 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’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’Impact of climate change on Portuguese marine coastal environments
Published 9 July 2026 Science ClosedTags: chemistry, modeling, regionalmodeling, review
The potential impacts of climate change on marine habitats were assessed using RCP4.5 and RCP8.5 projections of environmental parameters that included sea surface temperature (SST), pH, salinity, planktonic productivity (PP) and current strength (CS). The analysis was conducted separately for three distinct oceanographic regions of the Portuguese coastline (North, Centre and South) up to the middle of the century. Temporal trends in environmental variables were assessed using time series analyses. Overall, changes expected up to the middle of the century include increasing SST and PP, decreasing pH and salinity, and slight increases in CS. Spatial–temporal analyses revealed high present–future environmental overlay for most environmental variables. However, changes in individual environmental variables cumulatively resulted in statistically significant changes in environmental similarity. Still, the projected changes are not expected to exceed ecological thresholds, above which they would be likely to alter species’ habitat suitability or to result in species distribution shifts. Anomaly analyses suggest that present–future shifts do not surpass 1/5 (pH, PP, CS) or 2/3 (salinity) of the unit, regardless of projection and area, while SST anomalies ranged from −1.1 °C to 1.1 °C. Compared to IPCC large-scale predictions for Atlantic/Mediterranean regions, the intensity of shifts on the Portuguese coast may be lower.
Continue reading ‘Impact of climate change on Portuguese marine coastal environments’Erosion-driven delayed warming and marine stress prior to the end-Permian mass extinction
Published 30 June 2026 Science ClosedTags: modeling, paleo, regionalmodeling
The end-Permian mass extinction (EPME) presents an anomaly: intense global warming lags the onset of the carbon isotope excursion (CIE) by ~50,000 years, challenging the presumed link between carbon cycle perturbations and climate warming. Using biogeochemical modeling, Bayesian inversion, and multiple proxies, here we show that incorporating continental erosion as a forcing term into the hyperthermal models can resolve this decoupling. Enhanced erosion, likely resulting from the terrestrial die-off of vegetation, accelerates continental weathering, which buffers early carbon release and delays global warming. This process also increases riverine phosphorus export to the oceans, fostering gradual marine anoxia and preconditioning the oceans for the extinction event. With these findings, we present a coherent unifying scenario for the EPME environmental dynamics. Furthermore, our study refines the hyperthermal paradigm, offering implications for future climate scenarios.
Continue reading ‘Erosion-driven delayed warming and marine stress prior to the end-Permian mass extinction’A basin-wide assessment of pH changes in the Mediterranean Sea based on reanalysis products
Published 19 June 2026 Science ClosedTags: biogeochemistry, chemistry, Mediterranean, modeling, regionalmodeling
Ocean acidification, driven by increasing atmospheric CO2 concentrations, poses a growing threat to marine ecosystems and biogeochemical processes. The Mediterranean Sea, characterized by complex circulation patterns and distinct hydrographic sub-basins, represents a sensitive region for assessing basin-scale pH variability. However, long-term in situ pH observations remain spatially sparse and unevenly distributed, limiting the assessment of coherent spatiotemporal trends across the basin. Here, we present a basin-wide spatiotemporal assessment of pH trends in the Mediterranean using an 18-year biogeochemical reanalysis dataset from the Copernicus Marine Environment Monitoring Service. Our analysis reveals a consistent vertical structuring of pH trends, with negative trends in surface waters and contrasting, often neutral to weakly positive tendencies at depth. The magnitude and vertical extent of these trends vary regionally and are closely linked to local circulation regimes, water-mass formation processes, and remineralization dynamics. In deep-water formation regions such as the Adriatic, Ionian, and Aegean Seas, negative pH trends extend throughout much of the water column, whereas in the Levantine Basin, mesoscale circulation structures confine pH changes primarily to a relatively thin surface layer. These results demonstrate that basin-scale analyses based on high-quality, publicly accessible biogeochemical reanalysis products, such as CMEMS, can provide a spatially integrated perspective on long-term pH variability, complementing existing observational records by bridging spatial and temporal gaps. The framework presented here offers a reproducible approach for systematically assessing depth and region resolved pH trends.
Continue reading ‘A basin-wide assessment of pH changes in the Mediterranean Sea based on reanalysis products’Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica
Published 3 June 2026 Science ClosedTags: algae, biological response, community composition, corals, echinoderms, field, modeling, North Pacific, otherprocess, photosynthesis, physiology, regionalmodeling
Reef-building corals form the calcium-carbonate frameworks that underpin tropical coral reefs, yet global coral cover has declined by ~50% in recent decades, due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that buffer stress, promote recovery, and enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photo-physiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and richer in chlorophyll a. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin cover, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp.. When significant, photophysiological measurements showed 9.7 – 44.5% higher photosynthetic efficiency (Fv’/Fm’) in Papagayo corals and 19.94 – 42.75 % higher maximum photosynthetic rates (Pmax) in Sámara corals. These results highlight how contrasting environmental regimes within a relatively small geographic area can shape distinct coral community compositions and photophysiological strategies, with implications for identifying areas of reef persistence or refugia.
Continue reading ‘Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica’Upper-ocean variability of the marine carbonate system in the Northeast Pacific
Published 2 June 2026 Science ClosedTags: chemistry, field, globalmodeling, modeling, North Pacific, regionalmodeling
In the Northeast Pacific, the marine carbonate system’s variability across timescales is not well constrained. Here, we quantify observed seasonal and non-seasonal variability in Dissolved Inorganic Carbon (DIC), partial pressure of carbon dioxide () and aragonite saturation state and discuss potential drivers. We used three decades of observations from four Line P time series stations, the longest marine carbonate system time series in the Northeast Pacific (1990–2019). To gauge the spatial extent of the variability patterns, we used output from a global ocean model representing the observed period. In the Northeast Pacific, seasonal and non-seasonal variability at 10 m was minimal, mostly damped by the opposing influence of DIC and temperature changes at both seasonal and interannual timescales. For DIC and , the seasonal cycle dominated total variability in the top 60–70 m, with mean-transect 10 m seasonal amplitudes of 35 3 μmol and 0.31 0.04, respectively. In the upper 60–70 m, the magnitude of non-seasonal variability was at least half that of the seasonal variability for most variables. From five climate indices examined, we focused on the basin-scale Pacific Decadal Oscillation index (PDO) to investigate potential drivers of non-seasonal variability, with 20%–40% of the non-seasonal variability in DIC and associated to this index. In the Northeast Pacific, positive PDO periods were linked to a mean reduction in 10 m DIC of 5 μmol and an increase in 10 m of 0.04 for each PDO unit increase, which could potentially reduce the occurrence and severity of ocean acidification events. The opposite could be expected during negative PDO periods.
Plain Language Summary
Using 30 years of observations from the Northeast Pacific, we characterized sources of variability for three marine carbonate system variables: , dissolved inorganic carbon (DIC) and the saturation state of aragonite (an common indicator of ocean acidification). The seasonal and non-seasonal variability was minimal in the top 10 m. The seasonal cycle of DIC and aragonite saturation state was the major contributor to total variability in the top 60–70 m, and not detectable below. Also, in the top 70 m of the water column, up to 20%–40% of the DIC and aragonite saturation state non-seasonal variability was associated to the Pacific Decadal Oscillation index (PDO). The PDO is a statistics-derived index that captures variability patterns influencing the whole Pacific basin and has a positive and negative phase. We found that a warmer than usual upper water column in the Northeast Pacific during a positive PDO phase, potentially driven by reduced mixing, was linked to a lower DIC and higher values of aragonite saturation state. The opposite could be expected during negative PDO periods. Knowing the magnitude of natural variability in the marine carbonate system is important to identify the emergence of ocean acidification and other human-driven changes in the ocean.
Continue reading ‘Upper-ocean variability of the marine carbonate system in the Northeast Pacific’Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective
Published 28 May 2026 Science ClosedTags: field, Indian, modeling, regionalmodeling, salinity
This study comprehensively assesses the long-term variability of temperature, ocean acidity changes, and their implications on sound absorption and acoustic propagation in the Bay of Bengal. The analysis reveals a persistent warming trend in the Indian Ocean over the past 50 years, with a significant increase in temperature observed during the Sagar Maitri cruise in 2019. Thermal structure analysis using HadleySST EN4 data indicates warming in the upper 50m but a cooling trend in the 100-200m depth range. Oceanic Heat Content analysis highlights an increasing tendency of heat storage in the upper 50m, indicative of global warming.
In the context of surface ducted propagation, Sonic Layer Depth (SLD) and gradients in the Sound Speed Profile (SSP) were crucial factors influencing acoustic energy behavior. The study revealed a decreasing trend in in-layer gradient (Gr_SL) since 1990, intensifying after that period. The below-layer gradient (Gr_BL) also exhibited a decreasing trend, implying complex dynamics in the sonic layer with potential implications for sound propagation in the surface duct.
The investigation into pH changes spanning 65 years demonstrates a declining trend, particularly since the 1990s, attributed to increased atmospheric CO2 dissolution. The study linked this decrease to anthropogenic activities, aligning with global trends. The analysis of sound absorption illustrated a nonlinear relationship between absorption, frequency, and pH, emphasizing a significant impact of ocean acidification on sound absorption in the Bay of Bengal. The acoustic propagation modeling further highlighted a decrease in transmission loss with reducing pH, leading to increased sound travel and potentially noisier oceans. Salinity variations play a more significant role than temperature in influencing sound absorption.
Continue reading ‘Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective’Projected future of African marine ecosystems under climate change and stratospheric aerosol injection
Published 8 May 2026 Science ClosedTags: biological response, modeling, multiple factors, North Atlantic, phytoplankton, regionalmodeling, salinity, temperature
Stratospheric Aerosol Injection (SAI) has been proposed as a potential strategy to cool the planet. The ARISE-SAI-1.5 approach, which employes a moderate emission scenario, is simulated to limit future global warming to 1.5°C by injecting aerosols into the stratosphere in the year 2035. However, the climate response to this SAI scenario, particularly along the African coast, remains unclear. In this study, we investigate the potential impacts of climate change under the SSP2-4.5 scenario and ARISE-SAI-1.5 on regional African marine ecosystems through key biological (chlorophyll), physical (salinity, temperature), and chemical (nitrate, acidification, and dissolved oxygen) parameters. Our results indicate that climate change may reduce productivity in African coastal ecosystems, with chlorophyll concentrations decreasing between 10% and 62%. Sea surface temperatures are projected to rise by 1.5°C along the entire coast by 2069, while surface salinity increases up to 0.3 g/kg, except for a slight decrease of up to 0.1 g/kg along the Congolese-Angolan coast. This salinity dipole in the Gulf of Guinea results from enhanced precipitation and river discharge, reinforced by stratification that traps freshwater at the surface. Additionally, climate change drives ocean acidification and may expand the oxygen minimum zone in the Gulf of Guinea, with oxygen levels decreasing by 10%–30% at depths of 100–200 m. Although ARISE-SAI-1.5 may help reduce surface oxygen depletion, it may not significantly mitigate subsurface oxygen loss or continued acidification. Nevertheless, it may reduce some negative climate change impacts on marine ecosystems by stabilizing chlorophyll levels, sea surface temperatures, and salinity.
Plain Language Summary
Stratospheric Aerosol Injection is being explored as a way to cool the planet and limit future global warming, for instance, to 1.5°C in the scenario we explore here (ARISE-SAI-1.5). However, its effects on the ocean, especially along the African coast, are not fully understood. This study examines key factors such as chlorophyll, water temperature, salinity, and oxygen levels to assess changes in marine ecosystems. Our findings show that climate change could reduce productivity, with chlorophyll levels dropping by 10%–62%. Sea surface temperatures are expected to rise by 1.5°C by 2069, and salinity will increase along most coastal areas. The low-oxygen zone in the Gulf of Guinea may expand, making deep waters less habitable for marine life. While the SAI we study here helps slow oxygen loss near the surface, it does not prevent deeper waters from losing oxygen or the ocean from becoming more acidic. However, it can still reduce some harmful effects of climate change by stabilizing chlorophyll levels, temperatures, and salinity.
Continue reading ‘Projected future of African marine ecosystems under climate change and stratospheric aerosol injection’
