Corals demonstrate vulnerability to environmental changes, exhibiting the capacity to substantially modify coral calcification. In this study, we estimated declines in the density of Pocillopora coral species in the Mexican Pacific. The samples utilized in this study encompass both recently collected corals and those stored in Mexican repositories collected in the northeastern and southern Mexican Pacific regions. Density estimates indicate a 28.6% decline in coral density over the past 23 years (−0.0227 g CaCO3 cm-3 y-1) in the southern Mexican Pacific, while at the entrance to the Gulf of California, density has decreased by 15.4% over the past 20 years (−0.017 g CaCO3 cm-3 y-1). A comprehensive evaluation of environmental data reveals that the observed decline in Pocillopora skeletal density in Mexican Pacific reefs is concomitant with decreases in Ωar and pH, and an increase in ocean temperature on a substantial regional scale. When considered in conjunction with the previously documented reductions in coral growth of Pocillopora spp. skeletons in the eastern Tropical Pacific, our findings indicate a potential decline in CaCO3 production within the region’s reef systems. The results of this study underscore the significance of generating long-term series of coral growth parameters for relevant reef-building species and the carbonate system in key and representative coastal areas, particularly those that are already challenging for coral survival and reef maintenance.
Continue reading ‘Two decades of skeletal density decline in Pocillopora spp. corals in the Mexican Pacific Ocean: insight into a tropical eastern Pacific acidification scenario?’Two decades of skeletal density decline in Pocillopora spp. corals in the Mexican Pacific Ocean: insight into a tropical eastern Pacific acidification scenario?
Published 10 March 2026 Science Leave a CommentTags: biological response, chemistry, corals, field, morphology, North Pacific
Consequences of rising atmospheric CO₂ on ocean acidification and dissolved carbon cycling: a systematic review
Published 10 March 2026 Science Leave a CommentTags: chemistry, review
Increasing atmospheric CO2 and temperature diminish ocean pH and raise the amounts of dissolved inorganic and organic carbons, causing wide-ranging shifts in marine water carbon chemistry and predicting the impacts on long-term ecosystems. This review aimed to determine the ocean chemistry and spatial variation of CO2 at a global scale, as well as to predict the influences of anthropogenic and natural changes on marine ecosystems. The literature has demonstrated that the southern polar oceans, Antarctica, and any coastal zone are predominantly susceptible to marine acidification and the dissolved carbon cycle. Based on 355 studies conducted over the last 30 years, this investigation found that marine acidification and the dissolved cycle are complex and poorly understood phenomena. These two facts and climate change are very interrelated, and the potential of these threats is very spatial, seasonal, stratified, and complex also. It was found that the atmospheric CO2 has increased by about 50% since preindustrial times and excess CO2 raise the seawater acidity through some equilibrium reactions in aqueous medium. The study observed that over the past half-century, the marine surface water acidity has risen by 30%, and predicted that by 2100, it will increase to 150. Moreover, this study critically reviewed the actual rules of marine dissolved organic and inorganic carbon on the global carbon cycle and marine acidification and vice versa. Such a major change in ocean chemistry will already have wide consequences for marine life and ocean ecosystems.
Continue reading ‘Consequences of rising atmospheric CO₂ on ocean acidification and dissolved carbon cycling: a systematic review’Sex-specific physiological-biochemical and multi-omics responses of Sargassum thunbergii to ocean acidification
Published 10 March 2026 Science Leave a CommentTags: algae, biological response, laboratory, molecular biology, North Pacific, photosynthesis, physiology
Highlights
- A multi-omics study on sexual dimorphism of macroalgae under OA.
- Male S. thunbergii adopted a growth-oriented strategy under OA.
- Female S. thunbergii showed a defense-oriented survival strategy under OA.
- Fundamental trade-off between growth and defense underlay sex-specific responses.
Abstract
Ocean acidification (OA), driven by increasing atmospheric CO2 concentrations, poses significant threats to the ecologically important intertidal macroalgae. Multiple previous studies have indicated species-specific responses to OA, the sex-specific physiological-biochemical responses and underlying molecular mechanisms in dioecious macroalgae remain poorly understood. In this study, we investigated the responses of male and female Sargassum thunbergii to acidification treatment (2000 ppm CO2) by integrating physiological-biochemical, transcriptomic, and metabolomic analyses. Both sexes maintained photosynthetic performance, with increased maximum relative electron transport rates (rETRmax). Males exhibited a growth-oriented strategy, characterized by higher accumulation of storage compounds like triglycerides and up-regulation of genes related to the photosynthesis and biosynthesis pathways. In contrast, females displayed a survival-oriented strategy, with reduced carbon storage, increased soluble protein and phenolic substance contents, and up-regulation of genes related to defense- and stress-response pathways. These findings provided physiological-biochemical and molecular evidence for a growth and defense trade-off between male and female S. thunbergii under acidification treatment. Our study provided the mechanistic insights into the sex-specific responses of marine macroalgae to global climate change and highlighted the importance of accounting for sexual dimorphism in predicting the ecological resilience of intertidal macroalgae populations under future ocean conditions.
Continue reading ‘Sex-specific physiological-biochemical and multi-omics responses of Sargassum thunbergii to ocean acidification’Carbon dioxide released into the atmosphere and absorbed by water lowers its pH level, making the ocean more acidic and less able to sustain life. In 2009 a group of scientists included this ocean acidification (OA) as one of nine planetary boundaries that must remain within safe bounds if the earth is to remain stable and resilient. That study recognised that ocean health is integral to the overall health of the planet. A more recent study concluded that by 2020 the planetary boundary for OA had already been crossed. It is the seventh of the boundaries to have been breached.
For over two decades, governments and international organisations have recognised the danger that OA poses to marine life, and by extension to economies and societies. Supported by a large volume of scientific research detailing the threat, measures to combat OA have been incorporated into numerous national policies and international agreements, including the United Nations Sustainable Development Goals (SDGs). But the crossing of the planetary boundary is a clear indicator that those efforts have failed.
Policy fragmentation, at both international and national levels, is a major reason for the lack of progress on OA. Seen in conflicting objectives, duplication and weak accountability for results, such fragmentation is, an issue across ocean management as a whole. Many experts believe that a more holistic, systems-based approach to ocean management can integrate OA action more effectively alongside parallel efforts to address other stressors of ocean and planetary health. In this article, they discuss why such an approach has potential to eventually turn the tide.
Continue reading ‘The ocean as system’Acidification stimulates N2O production by oceanic nitrifying bacteria
Published 9 March 2026 Science Leave a CommentTags: biological response, laboratory, multiple factors, otherprocess, oxygen, physiology, prokaryotes
Recent studies have shown changes in the production rates of nitrous oxide (N2O) in aerobic seawater in response to ocean acidification (OA). Understanding how N2O production responds to OA is crucial because N2O is a strong greenhouse gas and stratospheric ozone‐depleting substance emitted from the ocean. The pH dependence of N2O production rates on marine bacteria Nitrosococcus oceani strain NS58, one of the ammonia oxidizing bacteria that are relevant to nitrification occurring in eutrophic seawater, was investigated under several dissolved oxygen (DO) conditions. We also measured abundance ratios of N2O molecules substituted with rare stable isotopes (isotopocules) to distinguish the two major pathways of N2O production by nitrifiers: NH2OH oxidation and NO2⁻ reduction. The ammonium oxidation rate (VNO2 ) and N2O production rate (VN2O ) calculated respectively from the temporal change of the product concentrations were 4–34 × 10⁻¹⁵ mol h⁻¹ cell⁻¹ and 1–15 × 10⁻¹⁷ mol h⁻¹ cell⁻¹. When compared in the stable phase (t = 44–76 hr), VNO2 decreased concomitantly with decreasing DO, also exhibiting a slight increase in acidified water. In contrast, VN2O was highest at 35% DO (air saturation), showing a 5%–60% increase by acidification (pH 7.7 vs. 8.0) depending on DO. Isotopocule ratios showed an increased contribution from NO2⁻ reduction over NH2OH oxidation under 35% and 3% DO, but its pH dependence was negligible except under 3% DO. These results suggest that OA increases N2O emission in particular from eutrophic seawater and that both N2O production pathways can be stimulated to the same degree.
Continue reading ‘Acidification stimulates N2O production by oceanic nitrifying bacteria’IAEA trains early-career scientists to assess the impacts of multiple ocean stressors
Published 9 March 2026 Web sites and blogs Leave a Comment
Winter School lecturer Sam Dupont, from the University of Gothenburg, demonstrates a technique for an experiment on sea urchin fertilization. (Photo: IAEA)
The IAEA is training early-career scientists to assess the impacts of ocean acidification and pollution, helping countries respond to environmental changes.
Marine biodiversity faces growing pressure from environmental changes and pollution. To help countries understand and respond to these combined threats, the IAEA is equipping young scientists with advanced skills to study the ocean’s most pressing challenges.
The Ocean Acidification International Coordination Centre (OA-ICC) trained 14 early-career scientists from around the world in key concepts and cutting-edge techniques to assess the impacts of environmental changes from multiple stressors on the ocean. The third edition of the OA-ICC Winter School on Ocean Acidification and Multiple Stressors was held at the IAEA Marine Environment Laboratories in Monaco from 24 November to 5 December 2025.
Threats to Ocean Health
The ocean faces multiple pressures, including from acidification, warming and pollution. These stressors threaten biodiversity and food security in many regions. Understanding their combined effects is essential to develop effective mitigation and adaptation strategies.
“Ocean acidification is not occurring in isolation, but expertise in studying multiple stressors is often lacking. The OA-ICC capacity building programme plays a key role in expanding this knowledge base,” said Lina Hansson, Associate Project Officer at the IAEA.
During the two-week course, participants learned best practices in experimental design and applied them in a hands-on laboratory study. They investigated the combined effects of ocean acidification, warming and lithium pollution on the reproductive success of a common Mediterranean Sea urchin.
Participants also visited the Laboratoire d’Oceanographie de Villefranche (LOV) in France for practical training in seawater chemistry monitoring and connected with researchers at the Centre Scientifique de Monaco. The Winter School emphasized science communication and community engagement. Through a series of guest lectures, participants explored principles for co-designing research, including integrating traditional knowledge from local communities.
“The Mediterranean Sea is heavily affected by multiple stressors. Record-breaking marine heatwaves, pollution, combined with acidification, have led to mass mortality of key species,” said Steeve Comeau, Research Scientist at LOV and Winter School lecturer. “Training this new generation in multifaceted experimental approaches is critical for predicting future impacts.”
Continue reading ‘IAEA trains early-career scientists to assess the impacts of multiple ocean stressors’Introducing the first ocean carbonate chemistry products hub
Published 6 March 2026 Press releases Leave a CommentTags: chemistry, review
The ocean plays a critical role in stabilizing Earth’s climate. As the planet’s largest active carbon sink, it absorbs about 25% of global carbon dioxide emissions and roughly 90% of the excess heat generated by those emissions. This critical role helps regulate the planet’s climate, but comes at a cost.
“As carbon dioxide enters the ocean, some of it reacts with water to form a weak acid that increases the acidity of the ocean and alters the natural chemical balance of seawater,” said Liqing Jiang, a research scientist at Earth System Science Interdisciplinary Center and NOAA’s National Centers for Environmental Information (NCEI), “As more carbon dioxide enters the ocean, seawater becomes increasingly acidic. In fact, ocean acidity has risen by about 30% since the beginning of the Industrial Revolution.”
A more acidic ocean reduces carbonate ions, which alongside calcium, is a building block for ocean creatures that form skeletons and shells like coral reefs and oysters. Higher acidity reduces coral larval survival, weakens reef structures, and increases ecosystem vulnerability to storms and bleaching. These creatures function as key marine health indicators, and their decline threatens the entire marine ecosystem.
However, the ocean is vast, and the interconnected physical, chemical, and biological processes require scientists like Jiang to integrate many different types of data to piece together the full picture of how ocean chemistry is changing.
To support researchers navigating this complexity, Jiang led a team of international researchers to publish a comprehensive review of over 60 major ocean carbonate chemistry data products. The catalog brings together a wide range of global datasets, including historical time series, model outputs, and aggregated products spanning multiple time periods, making it one of the most comprehensive compilations of ocean carbonate chemistry data products to date.
Jiang’s goal is to present all available ocean carbonate chemistry products. He continues to collect datasets through the catalog to widen the library of data.
“My hope is that researchers will use these products to better understand changes in ocean carbonate chemistry, to improve model inputs for more accurate projections of future ocean conditions, and to support more robust assessments of marine ecosystem vulnerability,” said Jiang.
The paper detailing this work, “Synthesis of data products for ocean carbonate chemistry”, has been published in Earth System Science Data. The full data product catalog is publicly accessible at the following link.
Continue reading ‘Introducing the first ocean carbonate chemistry products hub’Glacial meltwater impacts marine carbonate chemistry on Iceland’s continental shelf
Published 6 March 2026 Science Leave a CommentTags: chemistry, field, North Atlantic
Increased meltwater runoff from glaciers may drive localized ocean acidification and impact carbon dioxide (CO2) uptake in the coastal ocean. However, the paucity of carbonate system observations from continental shelves receiving inputs from glaciers limits our understanding of cryosphere‐ocean connectivity. Here, we contrast meltwater impacts on seawater carbonate chemistry and stable isotopes (δ13C‐DIC) off marine‐ and land‐terminating glacier outflows off Iceland. On the shelf outside a marine‐terminating glacier, glacial meltwater reduced the seawater buffer capacity of receiving surface waters through dilution of total alkalinity, and increased CO2 uptake through salinity‐driven drawdown of pCO2. Primary production acted as a counterbalance to the lowered [TA‐DIC]. On the shelf area receiving meltwater from large glacial river deltas, CO2 uptake was almost halved and the saturation state of aragonite was 0.2 units lower than on the marine‐terminating glacier shelf. Reduced net autotrophy due to higher turbidity and upwelling of low‐pH deep waters off the delta‐dominated shelf likely explain those differences. The diverging carbonate dynamics on the two shelves build on previous observations that land‐terminating glaciers can reduce the buffer capacity as well as CO2 uptake potential of nearshore surface waters in comparison to marine‐terminating glaciers. The future retreat of many marine‐terminating glaciers onto land is likely to modify how meltwater will impact coastal seawater carbonate chemistry.
Continue reading ‘Glacial meltwater impacts marine carbonate chemistry on Iceland’s continental shelf’Applying omics techniques to examine microscopic life fueling Gulf region ecosystems
Published 6 March 2026 Press releases Leave a CommentTags: biological response, chemistry, field, North Atlantic
Scientists at NOAA’s Atlantic Oceanographic & Meteorological Lab and the Northern Gulf Institute applied omics techniques to provide the first basin-scale assessment of the microbial communities at the base of marine ecosystems across the Gulf region. The new study from Dr. Luke Thompson’s group, conducted by Dr. Sean Anderson and co-authors, is the largest environmental DNA (eDNA) or microbiome survey of the Gulf of America ever performed.
Scientists collected environmental DNA (eDNA) – genetic material from whole microbes or shed by marine life into the environment – during the 2021 Gulf and Ocean Monitoring Ecosystems and Carbon Cruise (GOMECC). These samples unlock crucial new insights into the microscopic life across an entire basin – from nearshore coastal ecosystems out to the open Gulf. By analyzing the microbial communities throughout the water column, we can better understand how they are being impacted by changing environmental conditions.
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Changes in the composition of these microbial communities in any given region has cascading effects, influencing the biodiversity and feasibility of commercially viable species to survive and flourish in a specific region. Understanding how microbial diversity throughout the water column varies with changing conditions – changes in salinity, temperature, nutrient levels – could unlock key insights and provide early indicators of how entire ecosystems will be impacted by exacerbated environmental stressors, including ocean acidification.
Continue reading ‘Applying omics techniques to examine microscopic life fueling Gulf region ecosystems ‘Call for abstracts: The Ocean in a High CO2 World Symposium
Published 5 March 2026 Events Leave a Comment
The Call for Abstracts is now open. Please submit your abstract no later than 1 April 2026 (any time zone). Full submission guidelines are provided below.
A limited number of early acceptances are available for applicants with time‑sensitive funding requirements. To request early consideration, please email highco2@confer.co.nz with your abstract submitted through the online form and a brief explanation of why early approval is needed.
Abstracts are invited that align with the themes and special sessions listed below. Details of confirmed special sessions are available here.
During submission, authors should select the theme or special session that best matches their abstract.
Colony formation sustains the global competitiveness of nitrogen-fixing Trichodesmium under ocean acidification
Published 5 March 2026 Science Leave a CommentTags: biological response, growth, individualmodeling, modeling, nitrogen fixation, photosynthesis, physiology, prokaryotes
Anthropogenic carbon dioxide emissions drive ocean acidification. Trichodesmium, a key marine nitrogen-fixing cyanobacterium, displays contrasting growth responses to ocean acidification across morphotypes: negative in filamentous free trichomes but neutral or positive in colonies. However, lacking mechanistic understanding for these discrepancies has impaired our ability to predict Trichodesmium’s ecophysiological response. Here, we develop ecophysiological models to underpin mechanisms behind these divergent responses. For free trichomes, ocean acidification reduces nitrogen-fixing enzyme activity and photosynthetic energy production. In colonies, however, it alleviates copper and ammonia toxicity within the microenvironment—likely synergizing with enhanced iron acquisition—thereby outweighing minor benefit from relieved inorganic carbon limitation in the colony center. Projections suggest that globally, ocean acidification will reduce nitrogen fixation of trichomes by 16 ± 6% but increase that of colonies by 19 ± 24% within this century. By resolving morphotype-specific mechanisms, our study clarifies Trichodesmium’s adaptive strategies for sustaining its competitiveness and biogeochemical impacts in the changing ocean.
Continue reading ‘Colony formation sustains the global competitiveness of nitrogen-fixing Trichodesmium under ocean acidification’Synthesis of data products for ocean carbonate chemistry
Published 5 March 2026 Science Leave a CommentTags: chemistry, field, globalmodeling, modeling, review
As the largest active carbon reservoir on Earth, the ocean is a cornerstone of the global carbon cycle,
playing a pivotal role in modulating ocean health and the Earth’s climate system. Understanding these crucial
roles requires access to a broad array of data products documenting the changing chemistry of the global ocean
as a vast and interconnected system. This review article provides an overview of 68 existing ocean carbonate
chemistry data products and data product sets, encompassing compilations of cruise datasets, derived gap-filled
data products, model simulations, and compilations thereof. It is intended to help researchers identify and access
data products that best align with their research objectives, thereby advancing our understanding of the ocean’s
evolving carbonate chemistry. The list will be updated periodically to incorporate new data products. The most
up-to-date list is available at https://oceanco2.github.io/co2-products/ (Gregor and Jiang, 2026).
Guest column: the world’s largest bank faces liquidation
Published 5 March 2026 Media coverage Leave a CommentOcean protection is too often treated as a moral issue, yet this conceals a harder truth: our oceans are vital economic systems under mounting pressure. In fact, if they knew what was good for them, every mercenary across the planet would want to protect our great blue expanse.
In many ways, the ocean operates like the world’s largest bank. Storing capital by preserving marine biodiversity, upholding food systems, and generating returns through fisheries, eco-tourism and coastal protection. Perhaps most importantly, it absorbs 30% of carbon dioxide (CO₂) emissions annually, protecting us and the global economy, at least in part, from our own polluting activities.
As the ocean’s investors, however, we are not making smart financial decisions.
Overfishing, bottom trawling, and pollution reflect a familiar pattern: prioritising short-term extraction over long-term economic resilience. We are running down natural capital while congratulating ourselves on marginal gains. Yet the greatest financial threat to the ocean economy is still widely misunderstood and dangerously undervalued.
That threat is ocean acidification.
The short-term, short-sighted mindset
For years, we have hugely overstated the capacity of blue carbon habitats such as seagrasses, mangroves and saltmarshes, to solve our emissions problem. These ecosystems are rightly celebrated for their ability to lock away carbon and support biodiversity, but they are too often framed as quick wins – assets that can be restored or offset on short timelines.
In reality, while their capacity to store carbon is exceptional, the rate at which they absorb it is slow. The habitats that hold the greatest carbon stocks – and provide the strongest protection – are typically ancient, intact systems that have accumulated value over centuries. In economic terms, these ecosystems function less like high-yield savings accounts and more like environmental pensions. They deliver steady, compounding returns, but only if they are safeguarded and invested in over decades.
The lesson is clear. Even when we act in the ocean’s favour, we often do so through a short-term lens – one that favours visible, measurable gains over long-term stability.
Ocean acidification exposes the flaw in this thinking.
Continue reading ‘Guest column: the world’s largest bank faces liquidation’High vertical resolution measurements of pH, pCO2, total alkalinity, and dissolved inorganic carbon using a new approach: the carbonate profiler
Published 4 March 2026 Science Leave a CommentTags: Arctic, Baltic, chemistry, field, methods
The equilibrium between the different parameters of the marine carbonate system–dissolved inorganic carbon (DIC), total alkalinity (TA), partial pressure of CO2, and pH–is the core of ocean acidification studies, evaluation of inorganic carbon inventory, and air-sea CO2 fluxes. To date, it has been challenging to simultaneously measure all those components in the water column due to different sampling methodologies, and especially in stratified waters, where sharp vertical biogeochemical gradients may occur. In this study, we designed a low-cost and easy-to-assemble pumping system, which, combined with a CTD profiler, makes a PUMP-CTD system that can efficiently serve as a precise water column sampler, allowing for simultaneous measurements and sampling of dissolved inorganic carbon, total alkalinity, partial pressure of CO2, and pH with high vertical resolution. Importantly, this water sampler (denoted as the carbonate profiler) can be easily integrated with equilibrator-based continuous pCO2 measurement systems, which are routinely used for underway data acquisition, making them suitable for water column sampling as well. We tested the carbonate profiler in the open ocean water column, where we obtained excellent consistency between measured pCO2 and calculated values based on pH and DIC. Afterwards, we tested the operability of the system by measuring the vertical variability of all the components of the marine carbonate system in the Vistula River estuarine waters (southern Baltic Sea) and within the Arctic fjords affected by continental freshwater runoff. Overall, this system performed outstandingly, with a vertical resolution of half a meter, proving its utility in accurately measuring steep biogeochemical changes in the water column regardless of the analytical method used.
Continue reading ‘High vertical resolution measurements of pH, pCO2, total alkalinity, and dissolved inorganic carbon using a new approach: the carbonate profiler’Modelling seawater pCO2 and pH in the Canary Islands region based on satellite measurements and machine learning techniques
Published 4 March 2026 Science Leave a CommentTags: 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’Integrated ocean carbon research: a vision primed for implementation
Published 4 March 2026 Newsletters and reports Leave a CommentTags: policy
Executive Summary
The mission of the ‘Integrated Ocean Carbon Research’ (IOC-R) programme is to enhance our understanding of the ocean as a changing sink for human-produced CO2 and its climate change mitigation capacity, as well as the vulnerability of ocean ecosystems to increasing CO2 levels. The IOC-R programme aims to provide an actionable foundation for addressing the challenges of ocean carbon research. In doing so, it is contributing to the objectives of the United Nations (UN) Decade of Ocean Science for Sustainable Development by integrating the latest scientific findings and observational data for ocean carbon.
Supported by interdisciplinary research, the understanding of the ocean carbon cycle has advanced significantly since the last release of a report from the IOC-R community (IOC of UNESCO, 2021; Sabine et al., 2024). However, major knowledge and observational gaps remain, leading to considerable uncertainties in model projections. These hamper the development of climate change adaptation and mitigation strategies, including those involving ocean based solutions.
The IOC-R programme itself is co-sponsored by five international research and coordination programmes which have a strong involvement and focus on ocean carbon (Global Carbon Project1, SOLAS2, IMBeR3, CLIVAR4and IOCCP5) and the Intergovernmental Oceanographic Commission of UNESCO (IOC)6.
This IOC-R report is a global community effort with 72 authors and 13 reviewers from 23 countries. The report aims to guide the scientific focus of these programmes, as well as GOOS7, and to highlight new global cross-cutting priorities of ocean carbon research that help national and international ocean science funding entities determine future areas of investment. It will accomplish this by identifying knowledge gaps and coordinated research approaches to increase understanding about the ocean carbon cycle in a changing world.
The IOC-R community has defined five focus areas for ocean carbon research (Figure ES1), which will be further developed and explained in the report (Section 3):
- Evolution of the ocean carbon sink under a changing climate,
- The changing role of biology in the ocean carbon cycle,
- Carbon exchanges across the land-ocean-ice continuum,
- The impact of ocean industrial processes on the ocean bio logical carbon cycle,
- Future changes in the carbon cycle from deliberate ocean-based climate interventions.
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5.b Capacity development
Among the organizations supporting integrated ocean carbon research, nine programmes and organizations, including science networks and programmes, Ocean Decade activities and UN organizations were identified as having a specific mandate in capacity development (Table 1). Many of these focus on human and technical capacity development, as well as awareness raising. However, only a few organizations put emphasis on research policies.
Physics-guided machine-learning forecasting and analysis of carbonate changes in the surface Western Mediterranean
Published 3 March 2026 Science Leave a CommentTags: 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’Interactive effects of ocean acidification and settlement biofilm on the early development of the European abalone Haliotis tuberculata
Published 3 March 2026 Science Leave a CommentTags: biological response, communityMF, laboratory, mollusks, morphology, multiple factors, North Atlantic, performance, phytoplankton, reproduction, respiration
Highlights
- Interactive effects of OA and settlement biofilm were investigated on juvenile abalone.
- Post-larval density and total length decreased significantly under lower pH.
- Biofilm composition induced indirect effects through changes in diatom biomass.
- (pH × Ulvella) interaction affected abalone shell resistance and colouration.
Abstract
Ocean acidification (OA) and associated shifts in carbonate chemistry represent major threats to marine organisms, particularly calcifiers. OA effects can be influenced by other environmental variables, including the biotic environment. This study investigated the effects of OA and algal density, acting through an Ulvella-conditioned settlement biofilm, on post-larval and juvenile abalone (Haliotis tuberculata). In a three-month full factorial experiment, abalone were exposed from metamorphosis onward to two pH conditions (ambient 8.0 and reduced 7.7) and two initial densities of the green alga Ulvella lens on settlement plates. Biofilm biomass and composition were characterised using spectral reflectance and HPLC pigment analysis. Biological (density, length), physiological (respiration rate), behavioural (hiding response) and shell parameters (colour, surface corrosion, strength) of abalone were measured. Biofilm biomass and composition assessed with pigment proxies remained relatively stable under both pH conditions, though greater variability in algal biomass occurred at low initial Ulvella density. Post-larval density and total length decreased significantly under low pH, while high Ulvella density reduced juvenile length at 80 days, likely due to competition between algal groups. A pH × Ulvella interaction affected shell fracture resistance and colouration, but not metabolism or behaviour, indicating that juvenile abalone maintained vital functions. Overall, the results confirm the sensitivity of early H. tuberculata stages to moderate OA (−0.3 pH unit) and highlight indirect macroalgal effects through changes in diatom cover. In natural environment, the capacity of abalone to cope with future OA will depend on complex trade-offs between direct acidification effects and food-related biotic interactions.
Continue reading ‘Interactive effects of ocean acidification and settlement biofilm on the early development of the European abalone Haliotis tuberculata’Neglecting organic alkalinity introduces greater error than assuming boron to salinity ratios in Arctic sea ice brine carbonate system calculations
Published 3 March 2026 Science Leave a CommentTags: Arctic, biogeochemistry, chemistry, field, methods
While total alkalinity (AT) is traditionally attributed to dissolved inorganic constituents, dissolved organic matter (DOM) can significantly contribute to AT as organic alkalinity (OrgAlk), introducing errors in calculated carbonate parameters, such as the CaCO3 saturation state (Ω) and partial pressure of CO2 (pCO2). This study presents measurements of OrgAlk in the Arctic Ocean sea ice system and assesses its influence on carbonate speciation, with OrgAlk contributing 0.1–1.0% to AT. Sea ice brine exhibited elevated DOM and OrgAlk, with an OrgAlk/DOC ratio of 0.13 ± 0.06 µmol kg− 1 µM− 1, consistent with global ocean values. Correcting AT for OrgAlk increased computed pCO2 up to 84 µatm and decreased Ω ≤ 0.2 for aragonite and ≤ 0.3 for calcite compared to un-adjusted values. Elevated brine pCO2 suggests that conventional estimates of Arctic sea ice CO2 uptake may be overestimated when AT is used as an input parameter, particularly in spring as OrgAlk is released. The omission of OrgAlk contributed greater errors to calculated carbonate parameters than the differences in boron from using direct measurements versus salinity based ratios, highlighting the necessity of accounting for even minor OrgAlk to refine predictions of surface pCO2, net air-sea CO2 flux, and the fate of CaCO3 minerals.
Continue reading ‘Neglecting organic alkalinity introduces greater error than assuming boron to salinity ratios in Arctic sea ice brine carbonate system calculations’Persistence of coral reef structures into the twenty-first century
Published 2 March 2026 Science Leave a CommentTags: biological response, BRcommunity, corals, review
Coral reefs provide important socioecological services but are vulnerable to climate change, which shifts the balance between the production and erosion of calcium carbonate (CaCO3). In this Review, we summarize understanding of reef accretion, describe the mechanisms of carbonate production and erosion, and consider the effects of future ocean warming and acidification on key reef-building and eroding taxa. The combined stressors of climate change substantially reduce net carbonate production, with a more pronounced effect on calcifying algae than corals. However, declining coral cover driven by marine heatwaves and mass bleaching will probably be the dominant determinant of future reef carbonate budgets, and thus only reefs with thermally adapted populations are predicted to maintain the ability to sustain positive CaCO3 production under climate change, even if calcareous algal cover increases. As carbonate budgets become net negative in the future, the longevity of pre-existing reef frameworks remains unknown and understudied owing to the timescales required to meaningfully assess framework removal rates. Improving estimates of the rates of biologically driven framework loss and chemical dissolution will also be important in better predicting future reef persistence. Key knowledge gaps exist in understanding the effects of deoxygenation on coral reefs, as well as the influence of climate change on understudied sediment-producing taxa such as foraminifera and tropical molluscs.
Continue reading ‘Persistence of coral reef structures into the twenty-first century’
