The composition of Earth’s atmosphere and oceans have varied over the Phanerozoic and is tightly coupled with the planet’s climate and the extinction and evolution of life. Central to Earth’s climate and habitability is the concentration of CO2 in the atmosphere-ocean system, where rapid perturbations of CO2 correspond with hyperthermal and mass extinction events. These intervals of environmental catastrophes coincide with several periods of large-scale volcanic eruptions (million km3 of lava) called Large Igneous Provinces (LIPs), capable of releasing massive quantities of CO2. Among these events, the end-Triassic extinction (ETE; 201.564 Ma) represents one of the most severe biotic crises of the Phanerozoic and is temporally associated with the emplacement of the Central Atlantic Magmatic Province (CAMP). As one of the most voluminous large igneous provinces, CAMP is characterized by repeated disruptions to the global carbon cycle and intense ocean acidification events. However, understanding the relationship between the massive release of CO2, ocean chemistry, and extinction dynamics requires robust constraints on ancient CO2 concentrations. For time intervals prior to the ice core record, CO2 reconstructions rely on geochemical proxies derived from fossils and minerals. While these proxies often reproduce similar long-term trends, they commonly diverge in absolute CO2 estimates, limiting confidence in quantitative reconstructions of ancient atmospheric and oceanic carbon reservoirs. Direct constraints on CO2 in deep time can overcome this limitation, which can be achieved by using fluid inclusions hosted in minerals that precipitated in equilibrium with the environment. These fluid inclusions trap and preserve aliquots of ancient air and brine at the time of mineral formation in which the bulk gas compositions can be directly quantified using mass spectrometry and Raman spectroscopy. Fluid inclusions have increasingly been recognized to be excellent archives of past environmental conditions, including temperature, salinity, and atmospheric composition, though uncertainties remain about carbon speciation, the fidelity of preserved gas and brine compositions, and the broader applicability of using fluid inclusions to reconstruct major carbon cycle perturbations. This dissertation applies direct and quantitative methods to extract CO2 concentrations from fluid inclusions trapped in sedimentary minerals. Confocal Raman spectroscopy is used to quantify carbonate system parameters using fluid inclusions hosted in calcite, enabling reconstruction of pH and pCO2 conditions during mineral formation. Subsequently, fluid inclusions in halite are assessed for their reliability to trap gases during mineral precipitation and validate their use for ancient CO2 reconstructions. Fluid inclusion analyses were applied to deep ocean bedded cherts, showing repeated pulses of elevated CO2 and associated decreases in ocean pH and aragonite saturation state across the ETE and the Triassic-Jurassic transition. Integration of these records with carbon cycle modeling constrains the magnitude and pacing of the carbon release associated with CAMP volcanism and shows that large, repeated CO2 injections are sufficient to reproduce observed perturbations in ocean chemistry. By combining fluid inclusion analyses with carbon cycle modeling and independent geological and paleontological constraints, link large igneous province volcanism, repeated disruptions to the global carbon cycle, mass extinctions, and widespread ocean acidification during the end-Triassic.
Continue reading ‘Ocean acidification and mass extinctions: reconstructing CO2 from fluid inclusions’Posts Tagged 'methods'
Ocean acidification and mass extinctions: reconstructing CO2 from fluid inclusions
Published 10 November 2026 Science Leave a CommentTags: chemistry, globalmodeling, methods, modeling, paleo
Quantifying coastal ocean anthropogenic carbon changes and their uncertainties
Published 10 November 2026 Science Leave a CommentTags: biogeochemistry, chemistry, methods
Despite recent progress in quantifying anthropogenic carbon (Canth) in global oceans, coastal regions remain understudied due to methodological and observational challenges. Here, we develop and generalize a Regional rEgression–based Coastal Anthropogenic carbon estimation algorithm (RECA) designed specifically for coastal environments. Regional rEgression–based Coastal Anthropogenic carbon estimation algorithm builds upon the extended multiple linear regression framework, incorporating adaptations such as improved regression construction strategies, optimized data selection, and reduced subjectivity in decision-making, creating a unified approach across diverse coastal settings. Using synthetic datasets with known ∆Canth from global ocean biogeochemical model simulations across multiple North American coastal regions, we estimate that the uncertainty of RECA is about 3.25 μmol kg−1. We also compare RECA with two other regression-based algorithms, originally developed for the open ocean, to evaluate their performance in coastal environments after some adaptations. All three approaches have similar biases but different strengths, underscoring the importance of using a consistent method. An ensemble approach combining these three algorithms modestly improves reconstruction fidelity, but at the cost of increased complexity. We also evaluate the contributions of non-steady-state variations of both natural and Canth components because uncertainty about these components has long challenged the interpretation of regression-based ∆Canth results. We find that the algorithms indeed remove most, but not all, of the natural variations and appear to capture some, but not all, of the non-steady-state Canth. This methodological framework provides a robust, broadly applicable, and easy-to-implement tool for estimating coastal ∆Canth with uncertainty quantification, allowing us to more confidently track Canth accumulation in a changing dynamic coastal ocean.
Continue reading ‘Quantifying coastal ocean anthropogenic carbon changes and their uncertainties’Spectroscopic transduction in miniaturized lab-on-a-chip devices: functional nanomaterials and edge AI integration for real-time in situ environmental monitoring of heavy metals, pesticides, and marine pollutants
Published 9 November 2026 Science Leave a CommentTags: chemistry, methods, review
The rising demand for real-time, in situ monitoring of heavy metals, pesticides, marine pollutants, and ocean acidification proxies has exposed the limitations of conventional laboratory-based spectroscopic methods, which suffer from slow turnaround, high costs, and poor adaptability to remote environments. This critical review surveys advances from 2023–2026 in microfluidic lab-on-a-chip (LOC) platforms that integrate functional nanomaterials with spectroscopic transduction (primarily fluorescence, absorbance, surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), and quantum dot-based optical detection) and edge-deployable AI. Emphasis is placed on how nanomaterials enhance spectroscopic signals within microfluidic channels while addressing laminar flow control, passive mixing, antifouling, and stability in high-salinity and high-pressure marine matrices. The convergence with lightweight, hardware-aware AI/ML for on-chip denoising, drift compensation, multiplexing, and anomaly detection is examined under strict power and memory constraints. Ocean acidification monitoring requiring high-precision spectrophotometric pH and total alkalinity (TA) measurements serves as a rigorous benchmark for Arctic, open-ocean, and buoy deployments. Performance metrics, matrix interferences, autonomy limitations, and scalability barriers of these spectroscopic LOC systems are critically evaluated, with a forward-looking roadmap toward autonomous, IoT-enabled, and biodegradable spectroscopic microfluidic platforms for sustainable environmental monitoring.
Continue reading ‘Spectroscopic transduction in miniaturized lab-on-a-chip devices: functional nanomaterials and edge AI integration for real-time in situ environmental monitoring of heavy metals, pesticides, and marine pollutants’Metabolic dynamics of an offshore coral reef in the central Red Sea: observations from autonomous sensors
Published 9 November 2026 Science Leave a CommentTags: abundance, algae, biogeochemistry, biological response, calcification, chemistry, community composition, corals, dissolution, field, methods, otherprocess, photosynthesis, physiology, porifera, primary production, Red Sea, respiration
Abstract
Coral reefs are increasingly threatened by local and global stressors. Traditional visual reef monitoring methods are time-intensive and provide only a snapshot of reef condition. Recent efforts aim to measure reef metabolism, or the balance of net community production (NCP) and net community calcification (NCC), as coral reef carbonate budgets shift globally toward declining NCC and greater NCP influence. Resolving these metabolic changes requires comprehensive, high-resolution biogeochemical measurements unattainable by traditional sampling alone. This work reports the novel multi-month deployment of a high-resolution, autonomous total alkalinity (TA) sensor alongside pH, partial pressure of CO2, and dissolved oxygen (DO) sensors at Cement Wreck, a central Red Sea offshore reef. Observations from the back reef and fore reef revealed strong diel variability and distinct reef-zone biogeochemical dynamics linked to contrasting benthic compositions. On the back reef, pH and DO were tightly coupled and closely matched a Redfield-based model (𝑅2=0.943), while the fore reef relationship was weaker (𝑅2=0.145). TA observations allowed characterization of the back reef carbonate system, with TA–DIC stoichiometry yielding a slope of 0.26, indicating NCP accounted for approximately 87% of observed carbonate system variability. Compared to global reefs, Cement Wreck exhibits high % NCP contribution. However, the observed 2023 TA–DIC slope closely matches those from Red Sea observations from 1997 to 2013, suggesting that while reefs around the world shift, Red Sea reefs like Cement Wreck represent a persistent metabolic state. Scaled-up autonomous deployments, like the one presented here, will better enable predictions of global reef health in future conditions.
Plain Language Summary
Globally, coral reefs are threatened by rising temperatures, changes in seawater chemistry, pollution, and overfishing. The health of coral reefs is traditionally monitored by reef community composition through visual analysis, however changes in surrounding seawater chemistry can provide insight into reef processes and holistically monitor reef health. Here, we deploy a newly developed total alkalinity (TA) sensor, alongside commercially available pH and oxygen sensors on a coral reef in the Red Sea. Autonomous sensors allow the collection of high-resolution data on reef seawater chemistry, including daily cycles and changes over time, with a cost per data point much lower than traditional discrete samples. Furthermore, the TA sensor allows us to evaluate the relative balance between the reef-building processes and reef-eroding processes occurring, which are important parameters when evaluating a reef’s present and future health. We found that the reef studied here was strongly influenced by organic production, and that this signal closely matched Red Sea observations from the last 25 years. This suggests that some Red Sea reefs may represent a persistent metabolic state rather than a recent shift. The Red Sea lacks high-resolution carbonate-system observations, and this deployment contributes to baseline understanding of Red Sea reef metabolism and carbonate budgets.
Continue reading ‘Metabolic dynamics of an offshore coral reef in the central Red Sea: observations from autonomous sensors’Overlooked contribution of organic alkalinity in Arctic Ocean margins biases ocean acidification estimates
Published 5 November 2026 Science Leave a CommentTags: Arctic, chemistry, field, methods
Organic alkalinity has been recognized as a potentially substantial fraction of total alkalinity in coastal waters. However, conventional assessments of ocean acidification typically neglect its contribution when calculating pH and aragonite saturation state, potentially biasing the derived values. Here, we present elevated organic alkalinity in Arctic margins, and show that failure to account for it introduces substantial biases in calculated [H+] (1% – 51%) and aragonite saturation state (1% – 117%) in the Svalbard fjords, Tanafjorden, and the Barents Sea Opening, with potential implications for the broader Atlantic sector of the Arctic margins. Regional projections based on Earth system model outputs further indicate that accounting for organic alkalinity leads to a larger and faster pH decline. These results indicate non-negligible biases in conventional ocean acidification assessments for Arctic margins and highlight the need to account for organic alkalinity in coastal waters and beyond.
Continue reading ‘Overlooked contribution of organic alkalinity in Arctic Ocean margins biases ocean acidification estimates’Africa’s first permanent Ocean Observatory: powering science, defending nature, and shaping policy for ocean governance and the blue economy
Published 5 November 2026 Science Leave a CommentTags: biogeochemistry, chemistry, field, Indian, methods
Sustained, high-resolution ocean observation is essential for understanding how marine ecosystems respond to climate variability, human pressure, and conservation action. Yet long-term observing platforms remain scarce across the Global South, limiting the capacity to detect environmental change, evaluate management interventions, and support evidence-based ocean governance. To help address this gap, we established Africa’s first permanent, multi-ecosystem Ocean Observatory in Mozambique’s Bazaruto Archipelago, operated by the Bazaruto Center for Scientific Studies (BCSS) and Kisawa Sanctuary through a novel Resort-to-Research (R2R) funding and operational model. The observatory spans ~6,850 km² of ocean habitats in the Western Indian Ocean (WIO) region, a domain nearly six times larger than Bazaruto Archipelago National Park-BANP (1,430 km²) and more than fourteen times the San Sebastian Sanctuary (472 km²). It extends ecosystem-scale monitoring beyond protected-area boundaries across coral reefs, seagrass meadows, mangroves, sandy habitats, seamounts, coastal waters, and open-ocean environments. Between 2017 and 2026, the observatory generated more than 22 million high-frequency measurements across more than 30 ocean, weather, and biodiversity variables from 14 long-term stations distributed across six ecosystem types. These records are complemented by more than 250,000 minutes of underwater soundscape recordings, more than 120,000 georeferenced species records, and over 14,000 kg of marine debris recovered through monitoring and clean-up operations. Together, these datasets constitute one of the most comprehensive long-term environmental and biodiversity time-series currently available for the WIO region. The observatory is organized around four thematic programs: ecosystem dynamics, habitat mapping, migratory populations, and marine plastics, integrating physical, chemical, biological, and anthropogenic dimensions of environmental change. This publication forms part of a paired contribution on the BCSS Ocean Observatory. The companion technical/data paper published in Frontiers in Marine Science, “Africa’s first long-term ocean observatory in the Bazaruto Archipelago for multi-ecosystem and biodiversity data,” describes the observatory architecture, sensor systems, measured variables, QA/QC procedures, metadata structure, DOI-linked repositories, FAIR data-access pathways, and reuse potential. Building on this technical foundation, the present publication examines the observatory’s broader scientific, institutional, conservation, governance, and blue-economy significance. Embedded within the R2R model, the BCSS Ocean Observatory links eco-tourism, science, education, and community stewardship to support long-term operational continuity. Its open-access, DOI-linked datasets provide a foundation for environmental reporting and future monitoring, reporting, and verification applications related to climate, weather, ocean physics and chemistry, biodiversity, and pollution. More broadly, the observatory shows how locally anchored and community-engaged science can produce actionable knowledge for conservation planning, policy support, and selected blue-economy applications, including the future development of blue bonds, biodiversity credits, or plastic credits where appropriate validation and governance frameworks exist. The BCSS Ocean Observatory and R2R model therefore provide a transferable Africa-based example of how sustained ocean observation can support environmental accountability and strengthen long-term ocean governance.
Continue reading ‘Africa’s first permanent Ocean Observatory: powering science, defending nature, and shaping policy for ocean governance and the blue economy’Climate-driven habitat loss of Chinese sturgeon in the Northwestern Pacific and implications for marine protected area design
Published 3 November 2026 Science Leave a CommentTags: abundance, biological response, fish, methods, modeling, multiple factors, North Pacific, nutrients, otherprocess, oxygen, regionalmodeling, salinity, temperature
Highlights
- Ensemble modeling integrates eleven algorithms to predict sturgeon habitat suitability.
- Temperature is the dominant driver, followed by pH and total suspended matter.
- Suitable habitats are projected to disappear completely by 2100 under SSP5–8.5.
- Static protected areas must transition to climate-adaptive zoning strategies.
Abstract
The conservation of endangered anadromous fishes depends on understanding their full-lifecycle habitat requirements, yet the marine phase of Chinese sturgeon (Acipenser sinensis) remains a critical knowledge gap despite over 90% of its lifespan occurring at sea. We integrated multi-source occurrence data (satellite tagging, bycatch records, environmental DNA, and online databases) and applied an ensemble modeling framework (Biomod2 with eleven algorithms) to predict habitat suitability across the Northwestern Pacific Ocean (100°E–150°E, 10°N–55°N). After collinearity filtering, seven key environmental drivers were retained, among which mean temperature contributed most, followed by maximum pH, total suspended matter and mean silicate. The ensemble model achieved high predictive performance (median TSS = 0.944) and identified the Changjiang Estuary and coastal waters of Zhejiang and Jiangsu provinces as current distribution hotspots. Under the high-emission scenario (SSP5–8.5), suitable habitats are projected to disappear completely by 2100, accompanied by a significant northward contraction. These projections should be regarded as a potential worst-case scenario under high-emission conditions rather than a deterministic forecast. These findings demonstrate that business-as-usual emissions would eliminate viable marine habitat for this critically endangered species. Conservation priorities should therefore focus on (1) protecting benthic prey resources in the Changjiang Estuary and Zhoushan Archipelago as core refugia, and (2) transitioning from static marine protected areas to dynamic, climate-adaptive zoning informed by real-time habitat predictions. The ensemble modeling approach developed here is transferable to other data-limited, endangered marine species facing similar climate threats.
Continue reading ‘Climate-driven habitat loss of Chinese sturgeon in the Northwestern Pacific and implications for marine protected area design’Critical swimming speed in fish: measurement, determinants, and applications in aquaculture and fisheries management
Published 2 November 2026 Science Leave a CommentTags: biological response, fish, fisheries, methods, performance, physiology, review
Critical swimming speed (Ucrit) is widely used as a non-invasive and practical metric for quantifying swimming performance in fish. This review summarizes current advances in Ucrit research, focusing on measurement methods, environmental and biological determinants, and the underlying genetic and molecular mechanisms. We highlight key methodological developments, including step and ramp protocols, while addressing ongoing challenges such as the lack of standardized procedures and the limited comparability across studies. Environmental factors, including temperature, dissolved oxygen, salinity, and ocean acidification, strongly influence Ucrit, while intrinsic traits such as body size, sex, and physiological capacity further shape its variation. Recent studies have begun to uncover the genetic architecture of Ucrit, with evidence from heritability estimates, genome-wide association studies, and transcriptomic analyses pointing to a polygenic basis and a central role of energy metabolism and mitochondrial function. We further discuss the applications of Ucrit in aquaculture and fisheries management, including selective breeding, exercise training, fish passage design, and stock enhancement. Finally, we outline future research directions, emphasizing the need to establish standardized measurement frameworks, develop high-throughput phenotyping technologies integrated with artificial intelligence, and achieve multi-omics integration. Advancing these approaches will deepen our understanding of swimming performance and facilitate the development of more efficient and sustainable aquaculture, while promoting continued innovation in fisheries science.
Continue reading ‘Critical swimming speed in fish: measurement, determinants, and applications in aquaculture and fisheries management’On the future strategy for dissolution kinetics of CaCO3 in seawater by the solution-oriented approach
Published 2 November 2026 Science Leave a CommentTags: chemistry, laboratory, methods
Highlights
- A new strategy for the laboratory study of CaCO3 dissolution in seawater using the Solution oriented approach is proposed based on the mixed kinetics model.
- A check-list is provided against which any new design of experiment choosing to adopt this new strategy, can be tested before implementation.
Abstract
While the distribution of undersaturation of CaCO3 in the oceans is broadly known by applying chemical equilibrium theory, there is an increasing need, especially with advancing Climate Change and acidification of the oceans, to know about CaCO3-dissolution kinetics in more mobile systems. Experiments conducted in the laboratory to mimic conditions in the oceans in these faster circumstances often operate at even higher overall velocities, and matching laboratory simulations to field conditions is once again, problematic. Added to this, it has been shown in the last few years that when heterogeneous chemical kinetics developed out of its homogeneous counterpart, essential kinetics rigor was not carried forward. The Solution-oriented approach has been developed to recover the lost rigor, and the mathematical modelling of an in-line sequence of, molecular and diffusion components, which rely upon rigorous chemical kinetics, accompanies these developments. This paper supports workers adopting this new approach by describing 9 major practical issues that should be built into future experiments intending to prove the modelling.
Continue reading ‘On the future strategy for dissolution kinetics of CaCO3 in seawater by the solution-oriented approach’Standard Operating Procedure – Calibration of measurement systems for total dissolved inorganic carbon in seawater
Published 2 November 2026 Science Leave a CommentTags: chemistry, methods
Total dissolved inorganic carbon (DIC) is a fundamental variable for characterizing the marine carbonate system and quantifying key biogeochemical processes, including ocean acidification, carbon storage, air-sea CO2 fluxes, and monitoring, reporting, and verification for marine carbon dioxide removal. Although standardized guidelines exist (e.g., IOCCP Report No. 8, SOP 2), routine oceanographic practice frequently relies on single-point calibrations using seawater reference materials (RMs) near ~2000 µmol/kg. While this practice has significantly improved inter-laboratory comparability, it often lacks formal metrological traceability to the International System of Units (SI), fails to verify system response linearity across the full working range, and leaves major components of the measurement uncertainty budget unconstrained.
To address these metrological limitations, the International Association for the Physical Sciences of the Oceans Best Practice Study Group (IAPSO-BP-SG) on ‘Calibrating Measurements of Total Dissolved Inorganic Carbon in Seawater’ was established in late 2023. This IAPSO-BP-SG presents a updated Standard Operating Procedure (SOP) based on recent inter-laboratory comparison results. This SOP unifies calibration guidelines across diverse analytical architectures. The recommended framework is structured around four primary operational pillars:
- Daily single-point calibration and adjustment: Using a characterized seawater RM to adjust for daily slope drift and verify operational stability.
- Periodic linearity verification: Assessing system linearity over the entire working range (0–2500 µmol/kg) using a minimum of six sodium carbonate standard solutions or calibrated gas loops to evaluate baseline intercepts and prevent scaling errors.
- Repeatability quantification: Regularly determining system and method precision through replicate measurements under repeatable laboratory conditions.
- Metrological uncertainty evaluation: Constructing a robust uncertainty budget following the Guide to the Expression of Uncertainty in Measurement (GUM), propagating contributions from standard materials, repeatability, density conversions, and potential instrumental drift.
Additionally, the SOP outlines detailed procedures for volumetric and gravimetric preparation of primary standard solutions under CO2-free conditions, along with guidelines for density corrections and uncertainty propagation. Implementing this SOP ensures SI-traceable, high-precision DIC data suitable for long-term oceanographic monitoring and global data repositories.
Integrated study of ocean warming, CO₂ uptake, and acidification under anthropogenic emissions
Published 30 October 2026 Science Leave a CommentTags: chemistry, globalmodeling, methods, mitigation, modeling, multiple factors, phytoplankton, temperature
The study examines the influence of greenhouse gas pollutants on ocean waters. A key parameter describing ocean properties is pH, whose decrease negatively affects marine flora and fauna. Ocean surface temperatures rise over time due to the absorption of anthropogenic heat, with the most significant processes occurring within the upper 10 m layer. Phytoplankton, increasingly important for addressing ecological issues, is also affected by decreasing pH levels. To quantitatively describe ocean conditions, a thermodynamic calorimetric method is proposed. Validation is performed through a comparison of calculated and observed temperature variations, as well as the estimated specific heat capacity of ocean water. Measured pH variations are also compared with calculated values. The resulting expression incorporates temperature change, absorbed heat, and CO₂ content. Phytoplankton photosynthetic activity is further assessed in relation to potential cultivation areas on the ocean surface.
Continue reading ‘Integrated study of ocean warming, CO₂ uptake, and acidification under anthropogenic emissions’Unlocking spatial ecological assessment for tropical seagrass habitats using a new rapid assessment method (SEARAM)
Published 29 October 2026 Science Leave a CommentTags: biological response, community composition, field, Indian, methods, otherprocess, phanerogams
Highlights
- Rapid and standardized assessment of tropical seagrass ecological state.
- Multimetric index combining structure and vitality indicators.
- Spatial mapping of seagrass fragmentation and degradation.
- Links between habitat condition, environment, and megafauna.
- A practical tool for coastal monitoring and impact mitigation.
Abstract
Seagrass meadows are key coastal ecosystems supporting biodiversity, carbon storage, and essential trophic functions, yet they are increasingly threatened by anthropogenic and climatic pressures. Based on the Seagrass Meadows Rapid Assessment Method (SEARAM), a standardized protocol grounded in seagrass biodiversity indicators (SBIs), we developed a reliable and operational index to assess seagrass ecological state at high spatial resolution. Using 536 circular plots and 144 faunal stations across three intertidal reef habitats in Mayotte (Western Indian Ocean), SEARAM integrates structural and vitality sub-indices into a composite seagrass ecological state index (SESI), spatialized by geostatistical interpolation and analyzed using ANOVA, PCA, and multiple regression models. Results revealed highly fragmented meadows dominated by Halodule uninervis and Halophila ovalis, with low canopy height (5 ± 2 cm) and substantial epiphyte loads (37 ± 17%). The inner fringing reef flat showed the poorest ecological state (SESI = 4.8 ± 0.7/10), whereas the barrier reef (5.4 ± 0.8/10) and exposed fringing reef flat (5.6 ± 0.8/10) exhibited moderate scores. Key environmental drivers (turbidity, grain size, pH), significantly explained spatial patterns of seagrass structure and vitality, confirming the influence of sediment and light regimes. Functional relationships were also demonstrated between seagrass condition and associated fauna, particularly green turtle density and dugong feeding traces. SEARAM proved to be a rapid and robust tool for diagnosing tropical seagrass states. Its multimetric framework connects benthic condition to habitat suitability for megafauna, offering an operational foundation for ecological monitoring, management, and impact mitigation within the Avoid–Reduce–Offset (ARO) doctrine.
Graphical abstract
The climate observing system – ocean acidification
Published 28 October 2026 Science Leave a CommentTags: chemistry, methods, policy
The ocean has absorbed approximately one-quarter of anthropogenic carbon dioxide (CO2) emissions since the industrial era, moderating atmospheric warming while driving significant changes in marine carbonate chemistry. Collectively referred to as ocean acidification (OA), these changes include declining seawater pH, reduced carbonate ion availability, and decreasing calcium carbonate saturation states, with consequences for marine ecosystems, biogeochemical cycles, and ocean services. Detecting and quantifying OA is challenging because anthropogenic trends are superimposed on substantial natural variability across a wide range of spatial and temporal scales. Consequently, no single variable, platform, or observing approach can adequately characterize OA.
This chapter reviews the principal components of the contemporary OA observing system and the methodologies used to quantify changes in marine carbonate chemistry. It introduces the marine carbonate system and the analytical methods used to measure key OA variables, including pH, dissolved inorganic carbon (DIC), total alkalinity (TA), and partial pressure of CO2 (pCO2). The chapter examines the role of sustained time-series stations in detecting long-term trends and distinguishing anthropogenic change from natural variability, highlighting evidence for widespread acidification across open-ocean, coastal, polar, and marginal seas. The complementary contributions of surface underway observations, repeat hydrography programs, and autonomous observing platforms are reviewed, including major international initiatives such as SOCONET, SOCAT, GO-SHIP, GLODAP, and Biogeochemical-Argo (BGC-Argo). Particular emphasis is placed on how these observing elements provide complementary information across spatial and temporal scales and together form an integrated OA observing system.
Finally, the chapter discusses uncertainty assessment, trend attribution, data integration, and the role of international coordination mechanisms, including GOOS, GCOS, IOCCP, and GOA-ON. It further examines how OA observations support climate assessments, model evaluation, ecosystem-risk assessments, Sustainable Development Goal (SDG) 14.3.1 reporting, and emerging monitoring, reporting, and verification needs associated with marine carbon dioxide removal.
Continue reading ‘The climate observing system – ocean acidification’Extreme compound events in the Agulhas Leakage
Published 21 October 2026 Science ClosedTags: chemistry, Indian, methods, South Atlantic
Marine heatwaves (MHWs) and ocean acidity extremes (OAXs) are intensifying under anthropogenic climate change, and their compound co-occurrence can amplify ecological impacts. Yet the Agulhas Leakage, a key gateway transferring warm, saline Indian Ocean water into the Atlantic, remains understudied. Here we characterise MHWs over 1982–2024 and OAXs, and their compound events in this region over 1982–2021, comparing analyses of original and linearly detrended data. Under a fixed baseline, MHW cumulative intensity rose from approximately 29.95 to 109.51 °C-year in the original data and 49.4 to 66.7 °C-year after detrending between the first and fourth decades. OAX intensity increased from approximately 0.24 to 4.10 nmol kg–¹-year in the original data and from 0.35 to 0.46 nmol kg–¹-year after detrending. Compound events emerge only after the 2000s. Detrending reveals that most of this increase reflects the long-term warming and acidification trends, while residual variability remains in the dynamically active Agulhas Retroflexion, where anticyclonic eddies trap warm, high [H+] Indian Ocean waters. A likelihood multiplication factor confirms statistically significant positive MHW–OAX dependence that persists after detrending, indicating statistically significant positive co-occurrence between MHW and OAX on interannual timescales, consistent with physical coupling through carbonate chemistry. Baseline choice critically shapes compound-extreme risk assessment.
Continue reading ‘Extreme compound events in the Agulhas Leakage’Single-larva transcriptomics resolve phenotype-anchored Na+ K+ ATPase expression during first shell formation in Pacific oyster larvae under ocean acidification conditions
Published 5 October 2026 Science ClosedTags: biological response, laboratory, methods, molecular biology, mollusks, physiology
Bivalve larvae are highly sensitive to ocean acidification (OA) conditions, a global climate shift that applies selective pressure on calcareous marine organisms. Although a growing body of work exists on the effects of OA on bivalve larvae, most studies rely on pooled-larval sampling, which may obscure gene expression patterns by including larvae with severely underdeveloped or deformed phenotypes, which are common in OA conditions but are unlikely to survive to metamorphosis. Here, we tested a combination of single-larva transcriptomic techniques to investigate the expression of a candidate gene previously shown to be upregulated in OA conditions, Na+ K+ ATPase (NKA), in Pacific oyster larvae of known phenotypes. We found that upregulation of the NKA gene is detected primarily in larvae with a developed first shell (prodissoconch I), and was not pronounced in underdeveloped or deformed larvae, suggesting its expression reflects active shell formation under OA conditions, rather than a generalized stress response. Further, NKA mRNA was primarily localized along the dorsal shell hinge, the site of CaCO3 deposition, substantiating its role in early shell development. This study provides a methodological framework for phenotype-anchored sampling to investigate the expressional signatures underpinning successful shell development in OA conditions.
Continue reading ‘Single-larva transcriptomics resolve phenotype-anchored Na+ K+ ATPase expression during first shell formation in Pacific oyster larvae under ocean acidification conditions’The divergence between chronic offshore acidification and volatile estuarine pH dynamics: a 60-year East China sea record
Published 2 October 2026 Science ClosedTags: biogeochemistry, chemistry, field, methods, North Pacific
Coastal ocean acidification in river-dominated marginal seas exhibits distinct evolutionary trajectories from the open ocean. However, quantitatively decoupling its multi-stressor drivers remains challenging due to historical data scarcity and the confounding effects of shifting hydrology and localized human activities. We established a robust calibration framework using sedimentary 3‑hydroxy fatty acids to reconstruct a 60-year pH history in the Changjiang Estuary and the adjacent East China Sea shelf. Our reconstruction reveals that the shelf water pH declined at a rate of −0.00093 units yr-1 over the past six decades, closely tracking the invasion of atmospheric CO2, whereas the estuarine zone was governed by regional biogeochemical processes. Variation partitioning analysis and generalized additive models quantify that hydrological forcing, anthropogenic forcing and hydro-biological fluctuations accounted for independent variance contributions of 41.3%, 24.8% and 16.3% of the pH variability in the estuary. These findings suggest that the sensitivity of coastal carbonate chemistry to climate-related environmental change depends not merely on atmospheric CO2 forcing, but also on the balance between regional hydrological regimes and ecosystem state. Scenario-based perturbation analyses further suggest that variations in freshwater discharge, warming, and oxygen dynamics will either amplify or partially buffer coastal acidification signals, depending on the dynamic competition between physical dilution and biologically mediated carbonate processes. This underscores the critical necessity of conducting integrated, multi-stressor assessments to guide adaptive watershed coastal management, rather than treating river-dominated marginal seas as a single homogeneous domain.
Continue reading ‘The divergence between chronic offshore acidification and volatile estuarine pH dynamics: a 60-year East China sea record’Novel approaches for bridging chemical and biological time series observations to reveal underlying impacts of ocean acidification on marine organisms and ecosystems
Published 23 September 2026 Science ClosedTags: biological response, chemistry, methods
There is increasing demand to compare long-term biological observations with derived or measured carbonate chemistry data to characterize the biological consequences of ocean acidification (OA) in natural environments. Meeting this need calls for a standardized methodology by which to quantify and directly compare biological and carbonate chemistry change. Widdicombe et al. (2023) proposed a conceptual framework based on biological traits and paired biological-chemical rate comparisons, but its practical implementation has remained unresolved.
Here we operationalize that conceptual framework through a standardized analytical workflow that integrates heterogeneous biological observations with established OA time-series methodology. The workflow addresses five analytical challenges that hinder comparison of long-term biological and OA records: 1) fundamentally different temporal structures of biological and OA time series, 2) heterogeneity of biological observations, 3) sparse and irregular biological sampling, 4) nonlinear biological trajectories, and 5) appearance–disappearance events that invalidate conventional relative change metrics. The workflow addresses these challenges through standardized biological grouping, annual aggregation, piecewise linear segmentation, normalization by ecological boundaries, and direct pairing of biological and chemical rates of change.
We evaluated workflow performance using 36 synthetic biological time series generated by applying predefined temperature-pH-driven biological performance functions to a 108-year hydrodynamic-biogeochemical model simulation under the SSP3-7.0 emissions scenario. Biological rates estimated by the workflow closely agreed with the corresponding reference rates. Rate estimates remained similar across the two annual representations, and their relative ordering was largely preserved across contrasting site-specific temperature-pH transitions. These results demonstrate the robustness of the workflow under the tested patterns of abiotic forcing.
The analytical workflow developed here operationalizes the conceptual approach of Widdicombe et al. (2023) by standardizing the estimation and comparison of rates of change in biological and carbonate chemistry time series. It supports comparisons among compatible biological indicators while retaining the ecological context of each time series. The workflow does not establish causality; instead, it assesses the temporal coherence between long-term changes in candidate biological indicators of OA and concurrent changes in carbonate chemistry. It therefore provides a practical foundation for regional and global syntheses of biological responses to OA and other long-term abiotic stressors.
Continue reading ‘Novel approaches for bridging chemical and biological time series observations to reveal underlying impacts of ocean acidification on marine organisms and ecosystems’Coastal marine carbon and air-sea fluxes quantified from pH sensors on an extended AUV deployment
Published 16 September 2026 Science ClosedTags: chemistry, field, methods, North Atlantic
For the first time, the Autosub Long Range (ALR) completed a fully autonomous, long-distance (2,000 km) scientific mission, delivering new insight into coastal carbonate dynamics and air-sea CO2 fluxes. Equipped with a suite of oceanographic sensors, including a Lab-on-Chip (LOC) pH sensor and a Sea-Bird SeaFET pH sensor, the mission generated nearly 50,000 high-resolution pH measurements, providing one of the most detailed continuous coastal carbonate data sets collected to date in the region. We evaluated the adjustment of the SeaFET reference potential (k0), testing both the co-deployed LOC sensor and neural network estimates as reference pH. Before correction, the LOC and SeaFET sensors showed close agreement (ΔpHT = 0.013 ± 0.009), which improved to ΔpHT = 0.00004 ± 0.007 after LOC-based k0 adjustment. Both sensors diverged from model estimates, indicating reduced ability of models to resolve fine-scale coastal variability and reinforcing the need for direct in situ observations. Total alkalinity (TA) was derived from salinity-based relationships and model predictions, and paired with pH (SeaFET, LOC, and modeled) to estimate the partial pressure of CO2 (pCO2), which ranged 263–598 ± 27 μatm. Resulting air-sea CO2 fluxes ranged −17.0 to 7.1 ± 1.09 mmol m−2 d−1, with the Celtic Margin acting as a net CO2 sink in May–June of 2022. pCO2 and CO2 flux proved sensitive to subtle pH differences, but less so to TA estimates. Our findings demonstrate the critical role of high-resolution autonomous observations in quantifying coastal carbonate dynamics and CO2 fluxes, capturing processes and variability that are largely unresolved by ship-based surveys or global models.
Plain Language Summary
For the first time, the Autosub Long Range (ALR), a robotic underwater vehicle, completed a long-distance (2,000 km) scientific mission without ship support. During the mission, the ALR collected ocean data using sensors that measured water temperature, oxygen, and seawater acidity (pH). The mission generated nearly 50,000 high-resolution pH measurements, providing one of the most detailed continuous coastal carbonate data sets collected in this region. We evaluated how well two onboard pH sensors agreed with each other and with model-based estimates, and tested an applied correction method. Before and after correction, the sensors closely agreed, showing that autonomous platforms can gather high-quality chemical measurements that resolve coastal marine carbon dynamics better than model estimates alone. We used the pH data, along with estimates of TA, to calculate carbon dioxide (CO2) exchange between the ocean and atmosphere, finding that the region operates primarily as a carbon sink in May–June. Our calculations were strongly influenced by pH input but much less by alkalinity, highlighting the importance of accurate pH observations. This study shows that autonomous sensors can improve monitoring of carbon cycling in dynamic, understudied coastal waters that play a key role in the global carbon system.
Continue reading ‘Coastal marine carbon and air-sea fluxes quantified from pH sensors on an extended AUV deployment’Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform
Published 25 August 2026 Science ClosedTags: biological response, corals, field, methods, mitigation, mortality, physiology
Scleractinian (stony) corals can build highly ordered aragonite (CaCO3) exoskeletons, which are vital for marine ecosystems, coastal stability, and of cultural and economic importance through supporting fisheries and tourism. However, they face multiple challenges through global climate change, unsustainable human activity, and coral-specific diseases. In the latter category, Stony Coral Tissue Loss Disease (SCTLD) has recently emerged as one of the most destructive coral diseases, spreading rapidly and causing widespread tissue mortality across many marine species [1]. We have recently started exploring remnant effects of this disease on Montastraea cavernosa exoskeletons, abundant throughout the Caribbean Sea, Gulf of Mexico, and Atlantic Ocean. Indeed, through use of multi-scale electron diffraction characterization techniques, we find that their skeletogenisis is impacted by this disease from the micro- through atomic scale [2]. Notably, at the nanoscale we observe pockets of more soluble amorphous calcium carbonate (ACC) within centers of calcification (CoCs; i.e. the center of the three-dimensional fans containing arranged elongated aragonite crystals) for healthy corals, which appear absent in STCLD-afflicted corals. At the atomic level, we reveal planar defects in diseased coral, which are much lower in density in healthy corals, presumably inflicted through dysregulation processes after tissue death.
Yet, the most severe threat to global coral reefs and their exoskeletons is climate change. As oceans increase the uptake of anthropogenic CO2 primarily from burning fossil fuels, ocean acidity has increased. The reduction in pH because of this Ocean Acidification (OA) not only reduces the rate of net ecosystem calcification, but also increases net dissolution of skeletons. At current trends, most coral exoskeletons are expected to dissolve starting in 2050 [3]. Currently, it is unclear how exactly (the onset of) dissolution proceeds and affects their aragonitic framework. Given our expertise in characterization of coral skeletons, herein we discuss a developed in-situ platform to investigate OA effects at the nanoscale.
As proof of concept, we sandwiched crushed geological aragonite nanoparticles between own fabricated SiNx-based chips, compatible with a Protochips Atmosphere gas cell holder [4]. Thereafter, we introduced water vapor at 14 Torr at room temperature (∼60% relative humidity) for 10 minutes to create a hydrated environment for the particles (Fig. 1b). In a third step, we introduced gaseous CO2 at a pressure of 1 atm (Fig. 1c). The formed unstable carbonic acid produces HCO3– and H+, which increases acidity (i.e. lowers pH). Indeed, we observe rapid dissolution of aragonite particles after CO2. While we expect roughly a pH ∼4 in this system, this experimental observation matches theoretical expectations that aragonite would dissolve under these conditions (Fig 1c-f). We further observe nucleation and growth of new particles in a dendritic fashion in the vicinity of the dissolved particles (Fig 1c-f). Likely, this is crystallization of calcite, the most stable crystalline polymorph of CaCO3, induced by local dissolution of aragonite [5]. Although pCO2 in the oceans is expected to be much lower (∼400 – 500 µatm) and thus dissolution timescales are expected to shift, this illustrates our platform can capture aragonite dissolution.
To expand our platform methodology, using conventional Ga+ FIB-methods, we prepared a lamella of geological aragonite with a thinned region (∼100 nm), which was then transferred on top of a SiNx-based chip, and attached this in one of the corners between the Si support and the SiNx layer (Fig. 2a). We were able to sandwich the lamella between both chips when observing the cell in the TEM (Fig 2b,c). Next, we will target healthy and STCLD-afflicted coral sections to investigate how nanoscale dissolution proceeds at/near more soluble areas including defects due to the devastating OA process. This understanding may allow for more accurate forecasting of marine ecosystem collapse, enabling targeted mitigation strategies, protecting food supplies, and predicting climate feedback loops [6].
Fig. 1. In-situ OA platform experiment showing TEM snapshots of: a) Initial geological aragonite nanoparticles. Inset: selected area diffraction pattern indicating aragonite spots. b) Introduction of water vapor (14 Torr) after 10 min. The white arrow indicates an apparent hydration layer surrounding the large particle. c) Introduction of CO2 at 1 atm pressure after 10 s. d) 60s e) 90s and f) 150s. White arrows in c-f) mark the outer layer of the large particle dissolving in time, red arrows illustrate growth of new crystals.
Fig. 2. a) SEM image of geological aragonite lamella attached to SiNx chip. b) TEM image of lamella after cell assembly (top and bottom chip). c) In-situ selected area diffraction pattern of the lamella.
Continue reading ‘Elucidating impact of ocean acidification on coral exoskeletons using an in-situ (S)TEM platform’Recent history of surface ocean acidification extremes that compound marine heatwaves
Published 25 August 2026 Science ClosedTags: field, methods, modeling
Compound extremes are of concern for ocean health, such as when ocean acidification extremes (OAX) and marine heatwaves (MHW) co-occur. These compound events (OAX∩MHW) may amplify stress beyond the impact of each driver alone, yet their historical distribution remains poorly quantified. We used an observation-based product (OceanSODA-ETHZ) to investigate surface ocean OAX∩MHW from 1982 to 2024. OAX and MHW are defined when detrended surface hydrogen ion concentration and sea surface temperature exceed their 95th percentiles. Events show distinct spatial and temporal patterns: they occur roughly four times more often than by chance in the low- to mid-latitudes, but are rare in the eastern tropical Pacific and the high latitudes. They occur primarily in summer and show strong variability associated with the El Niño-Southern Oscillation. Most events are small ( <106 km2) and brief (1 month), but several are exceptional, including: the Blob (2015) in the northeastern Pacific (12.6 ×106 km2), the North Atlantic marine heatwave lasting nearly a year (2023–2024), and the most intense event off the Western Australian coast (2011). Mechanistically, OAX∩MHW occur when warming-induced increases in [H+] are not offset by a reduction in dissolved inorganic carbon that typically accompanies MHW. This is typical of the permanently stratified low-to-mid latitude oceans, where the seasonal cycle of [H+] is controlled by temperature. By characterizing past compound extremes and improving our understanding of individual events, we highlight conditions that may lead to future ecosystems being at risk.
Plain Language Summary
This study examines the recent history of “compound extremes” in the ocean, where marine heatwaves and ocean acidification extremes occur simultaneously. Using observational data from 1982 to 2024, we find that these compound events are happening more frequently than would be expected by chance, particularly in the low- to mid-latitudes. Conversely, they are rare in the eastern equatorial Pacific and polar regions. These compound events are most prevalent during summer and are influenced primarily by the El Niño/Southern Oscillation. While most of these events are relatively small and short-lived, there have been a few exceptionally large, long, and intense occurrences. Some of the most notable events include: “The Blob,” in the northeastern Pacific in 2015; the longest-lasting event that occurred in the Atlantic Ocean from 2023 to 2024; and the most intense event that occurred off Western Australia in 2011. These compound extremes happen in areas where the warming from a marine heatwave also leads to an increase in ocean acidity. This phenomenon is most common in regions of the ocean that are permanently stratified, meaning they have distinct layers of water that do not mix well.
Continue reading ‘Recent history of surface ocean acidification extremes that compound marine heatwaves’
