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’Posts Tagged 'regionalmodeling'
Variation and influencing factors of water alkalinity in estuary-bay waters of Zhanjiang Bay, China
Published 27 July 2026 Science Leave a CommentTags: chemistry, field, modeling, North Pacific, regionalmodeling
Seawater acidification and bubble plume dispersion from accidental subsea CO₂ pipeline rupture: a multiphase CFD study
Published 24 July 2026 Science Leave a CommentTags: 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 Leave a CommentTags: 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 Leave a CommentTags: 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’Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)
Published 29 April 2026 Science ClosedTags: Antarctic, chemistry, field, modeling, regionalmodeling, sensor
Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO2, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO2 sink and was most pronounced since 2006. The CO2 sink leads to a positive increase of surface water total CO2 concentrations (CT) (+0.44 ± 0.01 µmol.kg-1.yr-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the CT concentrations in the future, based on observed anthropogenic CO2 concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.
Continue reading ‘Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)’Future projections of compound events around the Main Hawaiian Islands
Published 15 April 2026 Science ClosedTags: modeling, North Pacific, regionalmodeling
The consequences of overlapping environmental stressors — referred to as compound events — may be more harmful to marine ecosystems than as individual stressors. Using recently conducted submesoscale-permitting future projections for the Main Hawaiian Islands, we present the first assessment of future compound events for Hawaiian waters. Our analysis focuses on surface and sub-surface heat-stress, ocean acidification, and low-oxygen events and is based on three different greenhouse gas emission scenarios. We show that a large fraction of ocean around Hawai‘i will be subject to compound events in the near future. However, the projected event characteristics such as duration and intensity vary substantially across the region suggesting that potential ecosystem impacts may differ over short distances. Our results reveal that these spatial differences are mainly driven by considerably different magnitudes of natural variability in ocean physics and chemistry across the domain driven by mesoscale processes, while anthropogenic trends exhibit only minor spatial differences. Our analysis demonstrates that small-scale tidal variability can significantly mitigate compound events in near-shore regions including some designated Marine Protected Areas. Overall, our findings highlight the need for high-resolution numerical models as well as for an extended observation network for robust future projections of local extreme events.
Continue reading ‘Future projections of compound events around the Main Hawaiian Islands’An interpretable machine learning approach for alkalinity reconstruction in the Mediterranean Sea
Published 9 April 2026 Science ClosedTags: chemistry, Mediterranean, modeling, regionalmodeling
Highlights
- Genetic Programming provides interpretable alkalinity models for Mediterranean Sea.
- Genetic Programming models capture typical alkalinity patterns and its finer-scale variability.
- Genetic Programming matches or exceeds linear models while remaining interpretable.
- Neural networks yield lowest errors but lack model transparency.
Abstract
Ocean acidification has significant impacts on marine ecosystems and human activities, and its understanding relies on an accurate characterization of the marine carbonate system, in which alkalinity plays a central role.
We propose a Machine Learning (ML) approach based on Genetic Programming (GP) to model alkalinity and apply this framework to the surface layers of the Mediterranean Sea. Our framework produces interpretable equations that capture alkalinity typical patterns and its finer-scale variability by inferring its relation with key physical and biogeochemical variables.
Results, supported by quantitative metrics and visual analyses, demonstrate that our method reliably reproduces the spatio-temporal variability of alkalinity with a high level of predictive accuracy when compared with in situ observations. Moreover, we use the derived alkalinity equations to produce gap-free 2D surface alkalinity maps using satellite data. The maps correctly capture spatial gradients, seasonal patterns, and riverine contributions, reinforcing the robustness of the proposed approach.
Continue reading ‘An interpretable machine learning approach for alkalinity reconstruction in the Mediterranean Sea’Analysing the distribution and variability of dissolved inorganic carbon and alkalinity over the Bay of Bengal region using the coupled ocean biogeochemical modeling
Published 25 March 2026 Science ClosedTags: chemistry, Indian, modeling, regionalmodeling
Highlights
- High-resolution regional coupled ocean biogeochemical modeling in the Bay of Bengal.
- Spatio-temporal variability of Dissolved Inorganic Carbon and Alkalinity is studied.
- Aragonite (calcite) saturation depth in the Bay of Bengal is estimated.
- ENSO and IOD events significantly influence surface DIC of the BoB region.
Abstract
A prototype high-resolution regional coupled ocean biogeochemical modeling experiment is carried out in the Bay of Bengal (BoB) region to study the distribution and spatio-temporal variability of Dissolved Inorganic Carbon (DIC) and Alkalinity (Alk) during the period 2000-2021. It is found that in the eastern as well as head BoB, the DIC concentration remains less (1.6-1.7 mol/m3) as compared to the south-west and west-central BoB, where the DIC concentration remains particularly high (>1.9 mol/m3). The highest (lowest) DIC concentration in the BoB remains in the Mar-April (Oct) months. The seasonal variability of the DIC and Alk is studied vis-à-vis seasonal changes in the currents and freshwater flux. The depth profiles of DIC, Alk, and DIC/Alk ratio are also investigated across different sections in the BoB. The DIC remains stratified in the BoB, and the stratification becomes much more pronounced on moving from south to north (and west to east) part of the model domain. The aragonite (calcite) saturation depth ranges between approx. 100-400 m (500-4000 m) in the BoB. The particularly high (>8.1) and low (∼8) pH values are found in the head BoB and southwest BoB, respectively. It is shown that the influence of El Nino – Southern Oscillation (ENSO) event on the surface DIC concentration over the BoB region is much stronger as compared to the Indian Ocean Dipole (IOD) event.
Continue reading ‘Analysing the distribution and variability of dissolved inorganic carbon and alkalinity over the Bay of Bengal region using the coupled ocean biogeochemical modeling’Contrasting effects of river and erosion-derived inputs on Arctic Ocean acidification
Published 18 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, modeling, regionalmodeling
Although the Arctic Ocean is relatively small in volume, its extensive coastline delivers large quantities of terrigenous material from rivers and coastal erosion. As a result, the Arctic Ocean is impacted more strongly by terrigenous material than most other parts of the global ocean. Yet the effect of this material on carbon cycling and ocean acidification remains poorly quantified. In this study, we use an ocean biogeochemical model driven by observation-based estimates of terrigenous carbon, alkalinity, and nutrients to evaluate their contribution to the mean state, depth pattern, and seasonal cycle of ocean acidification, as measured by the aragonite saturation state. Riverine alkalinity generally mitigates acidification, whereas organic carbon from coastal erosion intensifies it. Nutrients from both sources mitigate ocean acidification at the surface by stimulating primary production, but intensify it at depth through subsequent remineralisation. Together, riverine and erosion-derived inputs account for about 20–40 % of the seasonal variability in the saturation state of the surface ocean. This amplification of the natural seasonal cycle is primarily caused by an increase in the summertime maximum of the saturation state. Terrigenous inputs also reduce the Arctic Ocean’s capacity to absorb atmospheric CO2 by 17–25 %. Accurately representing carbon and nutrient inputs from rivers and coastal erosion in biogeochemical models is therefore important for reliable assessments of ocean acidification, ecosystem health, and carbon budgets in the Arctic Ocean.
Continue reading ‘Contrasting effects of river and erosion-derived inputs on Arctic Ocean acidification’Modelling seawater pCO2 and pH in the Canary Islands region based on satellite measurements and machine learning techniques
Published 4 March 2026 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling
Recent advancements in remote sensing systems, combined with new machine-learning model-fitting algorithms, have enabled the estimation of seawater carbon dioxide partial pressure (pCO2,sw) and pH (pHT,is) in the waters around the Canary Islands (13–19° W; 27–30° N). Continuous time-series data collected from moored buoys and Voluntary Observing Ships (VOS) between 2019 and 2024 were used to train and validate the models, providing a robust observational basis for satellite-derived estimates.
Among all models tested, bootstrap aggregation (bagging) performed best, achieving an RMSE of 2.0 µatm (R2>0.99) for pCO2,sw and 0.002 for pHT,is. Multilinear regression (MLR), neural networks (NN) and categorical boosting (CatBoost) also showed good predictive skill, with RMSE values between 5.4 and 10 µatm for pCO2,sw (360–481 µatm) and 0.004–0.008 for pHT,is (7.97–8.07). Using the most reliable model, we identified an increasing trend in pCO2,sw of 3.51±0.31 µatm yr−1, exceeding the atmospheric CO2 growth rate (2.3 µatm yr−1), alongside an acidification trend of −0.003 ± 0.001 yr−1.
Over the 2019–2024 period, rising atmospheric CO2 and increasing sea surface temperatures (reaching up to 0.2 °C yr−1 during the unprecedented 2023 marine heatwave) likely contributed to these trends. The Canary Islands region shifted from a weak CO2 source (0.90 Tg CO2 yr−1) in 2019 to 4.5 Tg CO2 yr−1 in 2024. After 2022, eastern sites that previously acted as annual CO2 sinks became net sources.
Continue reading ‘Modelling seawater pCO2 and pH in the Canary Islands region based on satellite measurements and machine learning techniques’Physics-guided machine-learning forecasting and analysis of carbonate changes in the surface Western Mediterranean
Published 3 March 2026 Science ClosedTags: chemistry, Mediterranean, modeling, regionalmodeling
Highlights
- Physics-guided ML forecasts surface pCO2 and pH along a Western Mediterranean VOS line.
- Day-ahead pCO2 is predicted with μatm-level RMSE; pH behaves nearly deterministically.
- Boosted trees and sequence models retain skill under strict, deployable forecast conditions.
- Explainable AI recovers dominant thermal control and air–sea CO2 gradient drivers.
- Improved pCO2 forecasts directly reduce uncertainty in air–sea CO2 flux estimates.
Abstract
We introduce a hybrid, physics-guided machine-learning system for forecasting and explaining surface marine carbonate changes along a fixed Volunteer Observing Ship route between Gibraltar and Barcelona from 2019 to 2024. The dataset includes more than 90 high-frequency transects collected under ICOS/SOOP standards, containing underway pCO2/fCO2, pH (measured and derived), sea-surface temperature, and salinity. After applying consistent quality control and harmonizing the data in time and space, we combine physics-based carbonate diagnostics—such as the thermal/non-thermal decomposition (FASS) and first-order Taylor attribution of temperature, salinity, total alkalinity, and dissolved inorganic carbon sensitivities—with time-aware models including linear regressions, boosted trees, and sequence networks (1-D CNNs and LSTMs) trained on historical windows. We evaluate generalization and uncertainty through chronological splits, leave-one-year-out tests, and year-wise bootstrap sampling. With all current predictors available, day-ahead pH and pCO2 predictions reach near-optimal skill; pH behaves almost deterministically, while pCO2 achieves RMSE on the order of a few μatm. Even under stricter forecast conditions without real-time carbonate chemistry, boosted trees and sequence models maintain strong performance by exploiting persistence and seasonal timing. Model-explanation tools (SHAP, partial dependence) recover the expected carbonate drivers, highlighting dominant thermal effects and key roles of seawater CO2 state and air–sea gradients. Spatial–temporal diagnostics reveal amplified summer pCO2 peaks in the Alboran/northern Morocco region and out-of-phase pH patterns. Predicted fields are converted to air–sea CO2 flux using standard solubility and gas-transfer formulations, and propagated uncertainties show that improving pCO2 accuracy directly reduces flux uncertainty. The resulting air–sea CO2 fluxes exhibit a pronounced seasonal cycle, with summer outgassing reaching several mmol m-2 d-1 and winter uptake of comparable magnitude along the transect, while interannual variability dominates over 2019–2024 and no statistically robust long-term trend is detected; typical flux uncertainties are on the order of 0.1–0.2 mmol m-2 d-1. Altogether, this delivers an explainable, uncertainty-aware system ready for deployment, linking forecast skill to process understanding and CO2 exchange in a climate-sensitive corridor.
Continue reading ‘Physics-guided machine-learning forecasting and analysis of carbonate changes in the surface Western Mediterranean’Decadal biogeochemical predictions for the bottom marine environment of the Northeast U.S. Continental Shelf
Published 27 February 2026 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling
The Gulf of Maine and the surrounding Northeast U.S. Continental Shelf are experiencing rapid marine environmental change arising from complex regional dynamics that challenge near-term (1–10 years) predictive capabilities for valuable living marine resources. Here, using a high-resolution regional ocean model, we demonstrate skilful decadal forecasts of ocean bottom habitat characteristics including bottom temperature, dissolved oxygen (O2), pH and aragonite saturation state (Ωar). Bottom temperature and pH predictions show substantial skill driven primarily by radiatively forced warming and carbon uptake trends, while bottom O2 and Ωar predictions benefit more from initialization due to stronger internal variability. Retrospective forecasts successfully predicted observed historical changes in water masses and environmental properties, including recent cooling/freshening transitions driven by replacement of Warm Slope Water with Labrador Slope Water. This water mass variability also modulates biogeochemical conditions and ocean acidification buffering capacity, with our recent forecasts indicating that benefits from the expected respite from rapid warming might be tempered by challenges posed by rapid acidification. The demonstrated predictability of coupled physical-biogeochemical processes supports developing integrated prediction systems for climate-informed marine resource management.
Continue reading ‘Decadal biogeochemical predictions for the bottom marine environment of the Northeast U.S. Continental Shelf’Understanding the resilient carbon cycle response to the 2014–2015 Blob event in the Gulf of Alaska using a regional ocean biogeochemical model
Published 24 February 2026 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling
Marine heatwaves (MHWs), characterized by anomalously high sea surface temperatures, are occurring with increasing frequency and intensity, profoundly impacting ocean circulation, biogeochemistry, and marine ecosystems. The MHW known as the Blob, which persisted in the subarctic NE Pacific from 2014 to 2015, significantly affected surrounding ecosystems. Warming-induced solubility reduction is expected to raise the partial pressure of carbon dioxide (pCO2) in the surface water, causing outgassing of CO2 to the atmosphere. Outgassing of CO2 is another source of atmospheric CO2 in addition to anthropogenic fossil fuel burning. However, moored observations at Ocean Station Papa (OSP; 145° W, 50° N) shows a moderate decrease in oceanic pCO2 during the Blob, resisting the warming-induced outgassing of CO2. This response is opposite of what is expected from warming alone, and instead has been attributed to reductions in dissolved inorganic carbon (DIC), although the mechanisms driving this reduction have remained unclear. We employed a regional model that accurately reproduces the temporal variability of oceanic pCO2 at OSP to investigate the cause of decrease pCO2 during the Blob. The analysis of model outputs indicates that the observed oceanic pCO2 decline resulted from the offset between warming-induced solubility reduction (increasing pCO2) and weakened physical transport of DIC (decreasing pCO2), with the latter dominating. Both horizontal and vertical transports played important roles. The near-surface carbon budget over the broad region was primarily driven by changes in the vertical transport. The decrease in DIC during the Blob resulted from the suppression of upwelling of DIC-rich subsurface waters in the winter of 2013. In this period, the horizontal transport also contributed substantially to DIC reduction. In particular, at OSP, the effect of the horizontal transport was comparable to that of the vertical transport, reflecting the northward advection of low-DIC water masses. These findings indicate that changes in physical circulation were the primary driver of the moderately enhanced CO2 uptake observed during the Blob. This study provides a critical insight into the complexity of biogeochemical response to extreme warming events and underscores the importance of resolving physical transport processes in assessing oceanic carbon uptake during MHWs.
Continue reading ‘Understanding the resilient carbon cycle response to the 2014–2015 Blob event in the Gulf of Alaska using a regional ocean biogeochemical model’
