Volcanism-driven ocean acidification has repeatedly disrupted Earth’s carbon cycle and ecosystems. Calcium isotopes (δ44/40Ca) provide a potential means of tracking these perturbations, since both the weathering and burial of CaCO3 and the isotopic compositions associated with these fluxes are sensitive to changes in seawater pH. However, the use of δ44/40Ca to reconstruct acidification and infer biocalcification stress is often complicated from overprinting by diagenetic processes. In this paper, we investigate stable Ca (δ44/40Ca) and Sr (δ88/86Sr) isotope responses to ocean acidification during Oceanic Anoxic Event 2 (OAE 2) in a pelagic marine carbonate succession from the Western Interior Seaway. The records are reconstructed using the Iona-1 core in Texas, which fully captures Os isotope evidence for the onset of LIP volcanism that is missing from a previously published Ca isotope record in the Western Interior Seaway in Colorado. Here we show that a negative Ca isotope excursion occupies the missing part of the previously published Western Interior Seaway record, and that it the begins with the onset of large igneous province volcanism as represented by the abrupt shift to lower initial 187Os/188Os isotopic ratios in the core. Box-model simulations show that the negative Ca isotope excursion could be produced through reduced Ca isotope fractionation affecting pelagic carbonate production under conditions of transient acidification stress, followed by rapid recovery through carbonate alkalinity feedback. δ88/86Sr values broadly covary with δ44/40Ca values but deviate from the expected kinetic slope, instead defining a mixing array consistent with seawater-buffered recrystallization. Together, the coupled stable Ca-Sr isotope systematics distinguishes primary acidification-driven signals from diagenetic modification and demonstrate the utility of dual-isotope approaches for tracing volcanism-induced perturbations to the marine carbon cycle.
Continue reading ‘Stable Ca and Sr isotope responses to ocean acidification during Oceanic Anoxic Event 2’Posts Tagged 'chemistry'
Stable Ca and Sr isotope responses to ocean acidification during Oceanic Anoxic Event 2
Published 20 May 2026 Science ClosedTags: chemistry, paleo
Changes in salinity impact nitrogen removal and carbon preservation in coastal wetlands sediment
Published 18 May 2026 Science ClosedTags: biological response, chemistry, laboratory, multiple factors, North Pacific, salinity, sediment
Highlights
- Coastal freshening suppressed N removal via denitrification while accelerating net organic carbon mineralization.
- Salinity shaped N removal vs. N retention and carbonate vs. alkalinity balance through sulfate availability.
- Salinity changes had concurrent implications for coastal eutrophication and ocean acidification.
Abstract
Coastal wetlands naturally remediate nitrogen (N) pollution through microbial pathways that either remove reactive N via denitrification and anammox, or retain it via dissimilatory nitrate reduction to ammonium (DNRA). The balance among three processes is closely linked to the carbon (C) cycle, as both heterotrophic denitrification and DNRA consume organic C and release alkalinity. While salinity fluctuations can disrupt these processes through direct ionic stress or sulfur (S) cycling, their net impact on N removal and C preservation services remains unclear. Here, we deployed microcosm experiments using mangrove sediments under a large salinity gradient (0-30 psu). We quantified N transformation rates using 15N isotope tracing technique, combined with geochemical analysis, and functional genes quantification. Freshening from ambient 30 psu to 10 psμ decreased N removal efficiency by ∼20%. This decline was caused by reduced denitrification, whereas anammox and DNRA were unaffected. Meanwhile, lower salinity appears to have stimulated C decomposition via reduced ionic stress. The reduced sulfate input diminished total alkalinity (TA) generation relative to dissolved inorganic carbon (DIC). The stoichiometric shift of TA:DIC ratio could further contribute to acidification in adjacent coastal waters. Additionally, the S-mediated regulation of N partitioning appears to be nitrate-dependent: under nitrate limitation, higher sulfate favored N retention; conversely, with enriched nitrate, it potentially favored N removal. Integrating the coupling effect of salinity on interaction between N, C and S cycles, our study demonstrates that coastal water freshening may weaken wetlands’ ability to remove N and preserve C.
Continue reading ‘Changes in salinity impact nitrogen removal and carbon preservation in coastal wetlands sediment’High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning
Published 14 May 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, corals, field, laboratory, North Pacific, otherprocess, phanerogams, physiology, reproduction
Highlights
- Seagrass-coral habitats act as CO2 sources driven by intense nighttime respiration
- High-resolution data enable predictive modeling of DIC, DOC, and POC dynamics
- Metabolic cues govern DIC, while temperature and alkalinity regulate POC and DOC
- Episodic coral spawning and rainfall trigger rapid ocean acidification
- Short-term disturbances dramatically shift organic and inorganic nutrient loads
Abstract
Seagrass meadows and coral reefs are global hotspots for productivity, yet they are often studied in isolation despite their intense biogeochemical connectivity. Significant gaps remain in understanding how coupled inorganic and organic processes within the water column drive blue carbon services in such mixed habitats, particularly during rapid environmental disturbances. Here, we investigated a unique, intertwined ecosystem in the Dongsha Atoll, where massive Porites corals are distributed on seagrass meadows, creating a natural laboratory for studying water column carbon biogeochemistry. During a 10-day sampling period, we collected continuous hydrological and discrete biogeochemical data at two- to four-hour intervals. Our results reveal that the dissolved inorganic carbon (DIC) covaried with dissolved oxygen and pH in strong diurnal patterns, which were governed by photosynthesis and respiration. As an outcome, variable but mostly high pCO2 values (141–2070 μatm) indicate the seagrass meadow was a source of CO2 to the atmosphere due to strong night-time respiration. Particulate organic carbon (POC) increased with temperature but showed no diurnal pattern. Dissolved organic carbon (DOC) showed a weak diurnal pattern and was linked to variations in POC and total alkalinity, highlighting the tight coupling between the organic production of the meadow and the inorganic chemistry of the calcification framework. Additionally, coral spawning led to a surge in organic content and changed inorganic nutrient levels. Rainfall events significantly acidified the ocean and enhanced submarine groundwater discharge to the seagrass-coral habitat. The distinctive contributions of this study are the extremely high temporal resolution of discrete samples, allowing the simultaneous tracking of multiple organic and inorganic pools during natural disturbances. The high-resolution data provide fundamental information for parametrizing models that explain DIC, POC, and DOC, which yield insights into organic carbon cycling in seagrass meadow-coral habitats.
Continue reading ‘High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning’Anti-predatory responses of Mytilus coruscus to the combined effects of ocean acidification and microplastics
Published 13 May 2026 Science ClosedTags: biological response, chemistry, crustaceans, laboratory, mollusks, multiple factors, North Pacific, performance, physiology, plastics
Highlights
1.Predator cues can significantly induce byssal secretion in Mytilus coruscus.
2.Ocean acidification inhibits the anti-predatory responses of Mytilus coruscus.
3.Microplastics exerts sublethal effects on the byssus of Mytilus coruscus.
4.The presence of predators amplifies the mild disturbances caused by ocean acidification and microplastics.
5.The combined stress shows a synergistic inhibitory trend on the anti-predatory capability of Mytilus coruscus.
Abstract
Ocean acidification (OA) and microplastics (MPs) pollution are major abiotic stressors in coastal ecosystems. Byssus is the core structural trait for Mytilus coruscus to defend against predators, and it is vulnerable to environmental stress, which in turn impairs its anti-predator function. However, the anti-predator response characteristics of M. coruscus byssus and the interaction mechanisms among OA, MPs and predation pressure from Charybdis japonica remain unclear under their combined stress. The study conducted acute exposure experiments, measuring five key byssus indicators: secretion frequency, quantity, diameter, volume and tensile strength, to explore the variation characteristics of the byssus-based anti-predator function of M. coruscus under multi-stressor conditions. Results showed that predators served as a key biological signal to trigger the anti-predator responses and significantly promoted byssus secretion; OA had the most prominent inhibitory effect on byssus function; MPs exposure only induced sublethal disturbances with no significant effects on core anti-predator indicators. Furthermore, the combined stress of ocean acidification and microplastics exhibited a synergistic trend, impairing the byssus-centered anti-predatory defense capacity of M. coruscus. This study provides experimental evidence for analyzing the variation patterns of mussel byssus under multiple stressors and suggests that future marine ecological risk assessments should focus on the interactions between biotic and abiotic stressors to more accurately predict the dynamic changes of coastal ecosystems.
Continue reading ‘Anti-predatory responses of Mytilus coruscus to the combined effects of ocean acidification and microplastics’Leveraging AI-driven predictors of enzyme pH optima to unravel microbial adaptation to environmental pH
Published 12 May 2026 Science ClosedTags: chemistry, modeling
It is well-known that pH (potential of hydrogen) influences enzyme catalytic activity (Schomburg and Salzmann, 1991; Nelson et al., 2021). The pH optimum (pHopt), at which an enzyme displays maximal catalytic activity, is therefore critical for enzyme design and applications (Zhang et al., 2025). To identify suitable enzymes for target pH environments or optimize enzymatic performance in biotechnology, enzyme engineering requires efficient characterization of kinetic properties across large numbers of amino acid sequences. However, experimental determination of pHopt for numerous sequences is time-consuming, labor-intensive, and costly. To address these limitations, computational approaches based on machine learning have been developed for rapid prediction of enzyme pHopt, supporting applications in protein engineering.
Recent advances, exemplified by EpHod (enzyme pH optimum prediction with deep learning) (Gado et al., 2025), enable prediction of the enzyme pHopt directly from protein sequences. The EpHod model leverages embeddings from the protein language model (PLM) ESM-1v and achieves a root mean squared error (RMSE) of 1.25 pH units on the held-out test data (Gado et al., 2025). To further improve predictive performance, an increasing number of AI-driven tools have been developed. For instance, (Zhang et al. 2025) introduced the model VENUS-DREAM, which employs the PLM ESM-2 and reduces the RMSE to 0.809. These AI-powered tools are revolutionizing enzyme discovery and design by enabling high-throughput prediction of pHopt.
Similarly, studies of microbial adaptation to environmental pH frequently require knowledge of enzyme pHopt. This information can be used to investigate the underlying adaptive mechanisms. However, experimental determination of pHopt for large-scale enzyme sequences remains impractical due to high costs and low throughput. Fortunately, the high-throughput predictive capacity of these AI-driven tools offers a powerful alternative for obtaining enzyme pHopt values, which can facilitate investigations into the mechanisms by which microorganisms adapt to environmental pH. The potential applications are illustrated with examples below.
Continue reading ‘Leveraging AI-driven predictors of enzyme pH optima to unravel microbial adaptation to environmental pH’Aragonite saturation state and coral reefs health assessment in Sri Lanka
Published 11 May 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, Indian
Ocean acidification (OA) and nutrient enrichment can separately or together threaten coral reefs by reducing calcification efficiency and increasing physiological stress, ultimately weakening reef resilience. Therefore, the study evaluates the prevailing OA level over the Sri Lankan coral reef areas using the aragonite saturation state (ΩAr) and assesses the nitrate (NO3−), and phosphate (PO43−) concentrations over the coral sites. The study was conducted on coral reefs on the eastern coast (EC), southern coast (SC), northern coast (NC), and west coast (WC) of Sri Lanka from April to June 2024. A total of 63 seawater samples were collected around each coastal site for analysis. The ΩAr were supersaturated (ΩAr > 1) and ranged from 2.98 ± 0.04 to 4.92 ± 0.12. Throughout the study period, the study sites had ΩAr values exceeding 2.92 ± 0.16, indicating that the nation’s corals were resilient to deterioration, and the comparative analysis demonstrates that these sites were not vulnerable to OA. However, the NC exhibited significantly (P < 0.05) the lowest ΩAr values (3.2 ± 0.64), positioning the regions near the lower bound of optimal calcification conditions. While ΩAr values indicate low OA stress during sampling, elevated NO3− concentrations (2 – 5 μmol L−1) in SC (2.19 ± 1.28 µmol L−1) and WC (3.52 ± 1.48 µmol L−1) may exacerbate coral bleaching during thermal stress events, representing a co-stressor rather than OA effect. Coral bleaching HotSpot (HS) identification emphasizes how spatially distributed HS are from January to June. The OA risk assessment confirmed that climate change will bring high risk to the coral calcification, reproduction, and damage to the breeding ground, which impact on the ecology and economy of Sri Lanka.
Continue reading ‘Aragonite saturation state and coral reefs health assessment in Sri Lanka’Controls on boron isotope ratios in marine bivalve shells: insights from a controlled experiment across pH and temperature gradients
Published 8 May 2026 Science ClosedTags: biological response, BRcommunity, calcification, chemistry, growth, mollusks, multiple factors, reproduction, temperature
Documenting spatial and temporal patterns of ocean acidification and understanding the way marine organisms build carbonate skeletons is critical to assessing their potential vulnerability to present and future stressors. The boron isotopic composition (δ11Bc) of many marine carbonates provides insight into the pH at the site of calcification within biocalcifiers and, by extension, the pH of ambient seawater when the carbonate formed. The modification of seawater carbonate chemistry at the site of calcification by marine calcifiers and the utility of different taxa as paleo-pH proxy archives remains an area of active research. Despite the significance of marine bivalves to ecosystem function, high-resolution paleoclimatic studies, and the shellfish industry, their biocalcification mechanisms, controls on internal pH, and potential for reconstructing records of past seawater pH remain unclear. To address these gaps, a 20.5-week flowthrough tank experiment was conducted in which four species of commercially important bivalves from the northwest Atlantic Ocean were grown in tanks with controlled pHT (pH 7.4 to 8.0) and temperature conditions (6 to 12 °C). A total of 106 shell samples from 99 individuals of adult and juvenile Arctica islandica (ocean quahog), juvenile Mercenaria mercenaria (northern quahog or hard clam), juvenile Mya arenaria (soft-shell clam) and juvenile Placopecten magellanicus (Atlantic sea scallop) were analyzed from this controlled experiment to assess the seawater pH, temperature, and growth rate controls on shell δ11Bc.These four bivalve species, grown under identical, controlled conditions, showed differential responses to the same seawater temperature and pH, likely due to differences in how they regulate the pH of their internal fluids. Juvenile P. magellanicus and juvenile M. mercenaria demonstrated significant relationships (R≥0.60; p-value <0.006) between tank pHT and δ11Bc, suggesting potential utility as proxies for past ambient seawater pH. Conversely, the δ11Bc of juvenile A. islandica and juvenile M. arenaria did not yield a strong relationship with seawater pHT but instead yielded significant relationships with shell growth rate (linear extension), with a positive relationship for M. arenaria and a negative relationship for juvenile A. islandica. The δ11B results from the few (n=9) adult A. islandica shells measured show the most variability across the range of pH and temperatures (range of 16‰) and no significant relationship was found with seawater pH or growth rate. Despite rigorous oxidative cleaning of samples, the data suggest that adult A. islandica shells contain boron-rich organic phases resistant to traditional cleaning techniques. This suggests that the next step in the development of boron-based pH proxies in A. islandica requires additional research into robust cleaning and sampling methods of periostracum and other organics. Despite the need for further investigations to constrain growth rate effects and cleaning techniques in A. islandica and M. arenaria, there is potential for developing paleo-pH proxies from P. magellanicus and M. mercenaria to better understand spatial and temporal patterns of past, present and future ocean acidification.
Continue reading ‘Controls on boron isotope ratios in marine bivalve shells: insights from a controlled experiment across pH and temperature gradients’Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)
Published 29 April 2026 Science ClosedTags: Antarctic, chemistry, field, modeling, regionalmodeling, sensor
Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO2, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter. Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO2 sink and was most pronounced since 2006. The CO2 sink leads to a positive increase of surface water total CO2 concentrations (CT) (+0.44 ± 0.01 µmol.kg-1.yr-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the CT concentrations in the future, based on observed anthropogenic CO2 concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.
Continue reading ‘Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)’Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters
Published 27 April 2026 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, field, molecular biology, morphology, North Pacific, phytoplankton
Coccolithophores, as calcifying phytoplankton, play a critical role in the global carbon cycle by producing calcium carbonate (CaCO3) in the ocean through their calcitic coccoliths. Here we examine Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related species abundance and genetic diversity along the West Coast of North America from samples taken on the 2021 NOAA West Coast Ocean Acidification (WCOA21) cruise, along the margin from British Columbia, Canada, to San Diego, California, USA. Significant carbonate chemistry gradients were observed across 17 transects, mostly in the onshore-offshore and north-to-south direction. Abundance and morphometrics of Gephyrocapsa spp. was evaluated using real-time PCR of mitochondrial cytochrome c oxidase subunit 3 ( cox3 ) gene and by microscopy. Variation in PIC concentrations, G. huxleyi and related species abundance, and coccosphere thickness were found to be associated with the gradients in carbonate chemistry and nutrient concentrations (phosphate, nitrate, nitrite, ammonium) across stations sampled during the cruise. We identified 5 unique amplicon sequence variants (ASVs) of Gephyrocapsa spp. cox3 that systematically varied in relative abundance across the California Current System. Southern California locations had greater diversity in cox3 sequences than northerly locations. These analyses represent baselines for evaluation of the impacts of future environmental changes in coastal waters along this productive upwelling regime.
Continue reading ‘Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters’Real-time acidification monitoring through Sofar buoy and SAMI-pH integration
Published 23 April 2026 Science ClosedTags: chemistry, field, methods
Ocean acidification (OA) impairs the ability of corals to build and maintain reef structures by reducing calcium carbonate deposition and accelerating the dissolution of existing frameworks. OA conditions can result from both natural pH fluctuations, driven by diel and seasonal variability in biological activity and water quality, and long-term increases in atmospheric CO2 absorption. Accurate characterization of OA requires precise, high-frequency time-series data, particularly in nearshore ecosystems where benthic community metabolism can cause rapid, localized shifts in carbonate chemistry. However, continuous, high-resolution pH monitoring remains challenging, and most existing technologies lack real-time feedback capabilities. Here, we present a real-time acidification monitoring system that integrates a Sofar Spotter buoy with a Sunburst SAMI-pH sensor. The system delivers continuous environmental data (benthic pH and temperature, surface temperature, wind, wave height, and barometric pressure) and sensor health diagnostics (battery levels and cellular connectivity status) to a public-facing dashboard. This system enables real-time access to high-frequency pH data and provides a modular and cost-effective alternative to larger, more complex platforms such as MAPCO2 buoys. Increased accessibility supports broader and more scalable monitoring efforts, supporting scientists, resource managers, and policymakers in tracking diel, seasonal, and long-term OA dynamics.
Continue reading ‘Real-time acidification monitoring through Sofar buoy and SAMI-pH integration’Decadal shifts in hypoxia and acidification reveal changing anthropogenic pressures on bottom waters of a coastal shelf
Published 20 April 2026 Science ClosedTags: chemistry, field, North Atlantic
Coastal systems provide habitat that sustains valuable shellfisheries but are subject to dissolved oxygen (DO) and/or carbonate chemistry impairment from anthropogenic pressures such as eutrophication and increasingly, climate change. Although extreme events can have disproportional negative ecological impacts, their ephemeral nature and a lack of baseline monitoring data make them challenging to characterize. Through assessments of historical records and a series of modern-day cruises, this study documented the magnitude and extent of summer hypoxia and acidification in the coastal shelf bottom waters of an urban shelf ecosystem, the New York Bight, before and during a devastating hypoxic event in 1976 and at present. In 1974, the most severe DO (2.39 mg L−1) and carbonate chemistry [pHN: 7.47; aragonite saturation state (ΩAr): 0.45] conditions occurred as a halo around a now derelict sewage disposal site, while averaging 4.43 mg L−1 (DO), 7.84 (pH), and 1.25 (ΩAr) across the region that August. During the mass mortality event of 1976, extremely low DO (< 1 mg L−1), pHN (< 7.5), and ΩAr (< 0.5) levels were observed across bottom waters during summer. Comparisons of modern subsurface chemistry to that of 1974—a year with ocean dumping but no mass mortality—indicated increases in bottom water DO, with evidence to suggest that ocean acidification has dampened the concomitant increases in ΩAr over the intervening half-century. This study highlights the impacts of ocean dumping and the threat of ocean acidification to systems that are experiencing or recovering from coastal hypoxia.
Continue reading ‘Decadal shifts in hypoxia and acidification reveal changing anthropogenic pressures on bottom waters of a coastal shelf’Quantifying the role of land-based inputs on coastal ocean acidification from a tropical semi-arid region
Published 15 April 2026 Science ClosedTags: biogeochemistry, chemistry, Indian
The land-based inputs in the form of river discharge, wastewater runoff, and submarine groundwater discharge (SGD) are among the major land-based natural pathways for the Coastal Ocean Acidification (COA). This study evaluates the direct influence of these land-based drivers, along with the aerosol deposition, and in-situ biogeochemical processes on COA along a highly populated tropical coastal area. The results suggest that spatially, aerosol deposition and in-situ biogeochemical processes in Kutch region are the major (72%) contributors to COA. In contrast, cumulative land runoff significantly (70%) contributes to COA in South Gujarat. Among these drivers, river water mixing causes the most significant pH decrease (0.093), while wastewater input results in the minimum pH drop (0.016) along the Gujarat coast. The seasonal nature of river water discharge, compared to continuous seepage of both fresh and recirculated (saline) SGD, highlights the role of SGD in COA. These findings align with the global studies represented SGD as one of the prominent land-based drivers for COA. Additionally, the low annual average pH (~ 7.954) along the Gujarat coast is attributed to the region’s macrotidal characteristics, which facilitate the release of sediment bound CO2, leading to a reduction in pH levels. The findings from the current study emphasis the need for comprehensive data collection on physicochemical and biogeochemical parameters to accurately assess COA dynamics and quantification of spatial and seasonal impacts of each driver along the India’s west coast.
Continue reading ‘Quantifying the role of land-based inputs on coastal ocean acidification from a tropical semi-arid region’NOAA PMEL scientists provide analysis and expertise for 2026 California Coast and Ocean Assessment report
Published 14 April 2026 Web sites and blogs ClosedTags: chemistry, North Pacific
California’s 2026 Coast and Ocean Assessment was released in March by the California Ocean Protection Council (OPC), in partnership with the California Ocean Science Trust. This coast and ocean assessment is the result of the work of more than 120 scientific experts from academic institutions, state and federal agencies including NOAA, NGOs, and Tribes.
The report features the OA (ocean acidification) indicators analysis from NOAA PMEL Carbon Program scientists Adrienne Sutton and Simone Alin (starting on page 85). NOAA OAP (Ocean Acidification Program) funded coastal time-series moorings provided the foundation for the annual “trend” analysis and indicator development, led by Adrienne Sutton. Simone Alin, a long-time co-lead of WCOA cruises, served as West Coast OA subject matter expert.
NOAA teams were key to the development of the assessment report. OAP provided long-term coastal monitoring and data management, with significant partnership and synergy from the Global Ocean Monitoring and Observing (GOMO) Program-funded observation and data analysis efforts throughout the global ocean. Pacific Marine Environmental Laboratory (PMEL) supports lead researchers/primary investigators to engage with diverse coastal ocean interest holders, including fishery and water quality managers like the consortium of West Coast managers who requested the assessments in this report.
The 2026 report was initiated three years ago to codevelop ocean health indicators that could be used by the multiple California State agencies, non-governmental organizations, and tribal groups. These indicators provide the state with unified, comparable status and trend information, enabling better cross-organization collaboration.
Continue reading ‘NOAA PMEL scientists provide analysis and expertise for 2026 California Coast and Ocean Assessment report’Acidification in the Earthʼs oceans: trends and persistence
Published 13 April 2026 Newsletters and reports ClosedTags: chemistry, globalmodeling, modeling
This paper applies fractional integration methods to obtain evidence on ocean acidification, namely the decrease in the pH level in the Earth’s oceans, using the annual Hawaii Ocean Time-series Station ALOHA series as well as the logged one for the period 1985-2024. The chosen modelling framework is more general than standard ones based on the I(0) versus I(1) dichotomy and sheds light on the long memory and persistence properties, as well as on the possible presence of trends, in the pH Level in the Earth’s oceans. The results indicate that the series exhibit a negative and significant time trend; however, whether or not the null hypothesis of a unit root is rejected depends on the assumption made about the errors. The key finding (when the errors are not incorrectly specified as I(0) processes) is the presence of long memory, which implies that the effects of shocks are long-lived, regardless of whether or not mean reversion occurs. Moreover, the recursive analysis indicates that both the degree of persistence and the downward trend in the pH level have increased over time. This evidence points to the urgent need for decisive policies to address the issue of ocean acidification and protect marine life and biodiversity.
Continue reading ‘Acidification in the Earthʼs oceans: trends and persistence’Responses of reef fish populations to similar environmental changes across distant oceanic islands
Published 9 April 2026 Science ClosedTags: abundance, adaptation, biological response, chemistry, field, fish, otherprocess, South Atlantic
Oceanic islands are among the most remote and understudied regions of the planet, yet they harbour unique reef fish communities that are increasingly vulnerable to global environmental change. Because these islands are geographically isolated, their populations are often assumed to respond mainly to local environmental conditions. However, by analysing temporal patterns in oceanographic variables across two distant systems (3204 km apart) in the South Mid-Atlantic Ridge (both encompassed by marine protected areas—MPAs), we found that temporal alignment in environmental conditions was associated with coordinated shifts in counts of nine reef fish populations in each study area. Among the evaluated variables, pH emerged as the most influential factor. Despite the divergent responses among reef fishes, possibly reflecting differences in physiological plasticity, shared temporal patterns in pH appeared central to parallel population patterns observed across assemblages. Increases in sea surface height and chlorophyll-a played secondary roles, potentially benefiting some populations, although such effects may be transient. These results suggest that climate-driven convergence in environmental conditions can override geographic isolation, promoting similar biological responses that may reduce resilience and increase extinction risk. Given that both islands are legally protected, our findings highlight that even MPAs are not insulated from large-scale oceanographic stressors, underscoring the need for long-term monitoring and adaptative conservation strategies for remote reef systems.
Continue reading ‘Responses of reef fish populations to similar environmental changes across distant oceanic islands’An interpretable machine learning approach for alkalinity reconstruction in the Mediterranean Sea
Published 9 April 2026 Science ClosedTags: chemistry, Mediterranean, modeling, regionalmodeling
Highlights
- Genetic Programming provides interpretable alkalinity models for Mediterranean Sea.
- Genetic Programming models capture typical alkalinity patterns and its finer-scale variability.
- Genetic Programming matches or exceeds linear models while remaining interpretable.
- Neural networks yield lowest errors but lack model transparency.
Abstract
Ocean acidification has significant impacts on marine ecosystems and human activities, and its understanding relies on an accurate characterization of the marine carbonate system, in which alkalinity plays a central role.
We propose a Machine Learning (ML) approach based on Genetic Programming (GP) to model alkalinity and apply this framework to the surface layers of the Mediterranean Sea. Our framework produces interpretable equations that capture alkalinity typical patterns and its finer-scale variability by inferring its relation with key physical and biogeochemical variables.
Results, supported by quantitative metrics and visual analyses, demonstrate that our method reliably reproduces the spatio-temporal variability of alkalinity with a high level of predictive accuracy when compared with in situ observations. Moreover, we use the derived alkalinity equations to produce gap-free 2D surface alkalinity maps using satellite data. The maps correctly capture spatial gradients, seasonal patterns, and riverine contributions, reinforcing the robustness of the proposed approach.
Continue reading ‘An interpretable machine learning approach for alkalinity reconstruction in the Mediterranean Sea’Climate change influence on salinity, temperature, dissolved oxygen and pH in Biscayne Bay (Florida): two decades of observations (2001–2021)
Published 8 April 2026 Science ClosedTags: chemistry, field, North Atlantic
Highlights
- Research Highlight 1: Biscayne Bay is transitioning from an estuarine to a more marine regime due to sea level rise.
- Research Highlight 2: Salinity is increasing at canal mouths, with saltwater intrusion detected in bottom layers.
- Research Highlight 3: Global warming has raised Bay water temperature, and the past decade has been the warmest on record.
- Research Highlight 4: Ocean acidification is influencing the Bay.
Abstract
An evaluation of 20 years (2001-2021) of monthly data from a long-term monitoring program was performed to determine the temporal, seasonal and spatial changes in the distribution of salinity, temperature, dissolved oxygen, and pH, to identify the potential impacts of climate change on Biscayne Bay, the largest estuary on the Atlantic coast of Florida. Data were evaluated by decade, season, and zone. Decade 2 showed higher salinity in four of eight zones, along with saltwater intrusion in the bottom layer of some canals. The zones most influenced by the Atlantic Ocean did not show decadal salinity changes. In decade 2, the overall median temperature in-creased (+0.5◦C), with North Bay exhibiting the highest increase (+0.8◦C). In decade 2, dissolved oxygen was higher in four zones, while pH decreased in six zones, suggesting that ocean acidification is also influencing the Bay. Temperature, dissolved oxygen, and pH displayed pronounced seasonal patterns across zones. Collectively, these results suggest that sea level rise and climate change are gradually transforming Biscayne Bay from an estuarine system to one that is more marine in nature.
Continue reading ‘Climate change influence on salinity, temperature, dissolved oxygen and pH in Biscayne Bay (Florida): two decades of observations (2001–2021)’Effects of upwelling-driven acidification and deoxygenation on the dissolved inorganic carbon system over the southeastern Arabian Sea shelf
Published 8 April 2026 Science ClosedTags: chemistry, field, Indian
Highlights
- Summer monsoon upwelling drives strong acidification and deoxygenation over the EAS shelf.
- Non-upwelling DIC and TAlk variability is largely governed by conservative water-mass mixing.
- Elevated nDIC35 during upwelling confirms DIC enrichment beyond salinity stratification alone.
- AOU-nDIC35 coupling indicates respiratory amplification of upwelled CO2-rich source waters.
- Reduced buffering and lower ΩCa–ΩAr increase seasonal chemical stress on shelf ecosystems.
Abstract
Repeated measurements of inorganic carbon system parameters over one year along two coastal transects (Kochi in the southern EAS and Mangalore in the central EAS) in the eastern Arabian Sea (EAS) reveal strong seasonal coupling between upwelling, deoxygenation, acidification, and inorganic carbon accumulation on the shelf. During the non-upwelling (oxic) period, the variability of dissolved inorganic carbon (DIC) concentrations and total alkalinity (TAlk) was governed predominantly by conservative water-mass mixing, particularly between low-salinity Bay of Bengal-derived waters and more saline Arabian Sea shelf waters, as demonstrated by the marked reduction in salinity normalised DIC (nDIC35) and TAlk (nTAlk35). In contrast, during the summer monsoon (June–September), coastal upwelling transported oxygen-poor, DIC-rich subsurface waters onto the shelf, leading to pronounced subsurface inorganic carbon enrichment, hypoxia, and acidification. Vertical profiles of nDIC35 showed that elevated inorganic carbon concentrations persisted even after removing salinity effects, increasing from ∼1950–2000 μmol kg−1 at the surface to >2100–2200 μmol kg−1 below ∼40 m. Nearshore surface waters during peak upwelling exhibited a strong offset between measured DIC and nDIC35, indicating localized freshwater dilution, but salinity-normalised values confirmed that the underlying carbon inventory remained high. Apparent oxygen utilisation (AOU) and nDIC35 were positively correlated, indicating that a substantial fraction of the residual DIC enrichment was associated with oxygen consumption, although this relationship reflects the combined imprint of DIC-rich upwelled source waters and subsequent microbial remineralisation within the stratified shelf system. Thus, carbon accumulation during the summer monsoon is best explained by a two-stage mechanism: (i) physical advection of CO2-rich, oxygen-deficient upwelled waters, followed by (ii) secondary amplification through local respiration. In contrast, TAlk exhibited much weaker non-conservative modification, and the elevated alkalinity generated under low-oxygen conditions was insufficient to counteract the strong DIC-driven reduction in carbonate-system buffering capacity, thereby increasing the system’s vulnerability to pCO2 build-up and acidification. Consequently, calcite and aragonite saturation states declined sharply during upwelling, with ΩCa and ΩAr falling to ∼2.5 and ∼ 1.5, respectively, when pCO2 exceeded 1000 μatm under severe oxygen depletion. The co-occurrence of hypoxia, acidification, and weakened carbonate buffering characterises the eastern Arabian Sea shelf as a highly dynamic natural laboratory for understanding multi-stressor impacts on coastal biogeochemistry and ecosystem vulnerability.
Continue reading ‘Effects of upwelling-driven acidification and deoxygenation on the dissolved inorganic carbon system over the southeastern Arabian Sea shelf’Millennial-scale changes in marine lithofacies during the Paleocene-Eocene Thermal Maximum: a deep-time analog for Anthropocene hydrologic and acidification impacts
Published 30 March 2026 Science ClosedTags: chemistry, field, paleo
Highlights
- Global marine sediment changes during the PETM were quantitatively reconstructed.
- Sediment changes controlled by sea level and latitudinal hydrology.
- Acidification influenced pelagic sediment composition, especially in the Atlantic.
- Carbonate “overshoot” occurred during the PETM recovery.
Abstract
Extreme climatic events can significantly alter marine lithofacies. However, global oceanic sediment patterns during deep-time hyperthermal events, which are potential analogues for the hydrologic and climatic impacts of modern anthropogenic warming, remain poorly constrained. Here, we compile 162 marine stratigraphic records to track millennial-scale sediment dynamics during the Paleocene–Eocene Thermal Maximum (PETM). We find that sedimentation was primarily controlled by hydrologic intensification (resulting in ∼36% carbonate platform demise), eustatic fluctuations (resulting in ∼52% siliciclastic shelf retrogradation), and ocean acidification (resulting in ∼41% deep-sea calcareous sediment replacement). Lithofacies changes along continental margins show distinct latitudinal zonation, reflecting variations in hydrologic intensity and carbonate productivity. The impact of eustatic sea-level change is strongest in region where hydrologic effects are muted. Deep-sea acidification was widespread, with the strongest expression in the Atlantic, and weaker effects in the Pacific and Indian oceans. Widespread carbonate “overshoot” following PETM recovery suggests enhanced continental weathering. This study implies that ongoing anthropogenic warming could rapidly reorganize marine sedimentation through intensified hydrological cycle, accelerated sea-level rise, and ocean acidification on centennial timescales, much faster than during the PETM and potentially with greater magnitude.
Continue reading ‘Millennial-scale changes in marine lithofacies during the Paleocene-Eocene Thermal Maximum: a deep-time analog for Anthropocene hydrologic and acidification impacts’State of the global climate 2025
Published 30 March 2026 Newsletters and reports ClosedTags: chemistry, policy, review
The temperature of the Earth changes in response to the rate at which energy enters and leaves the Earth system. Increasing concentrations of greenhouse gases in the atmosphere such as carbon dioxide, methane and nitrous oxide, all of which reached their highest level in 800 000 years in 2024 (the last year for which we have consolidated global figures), reduce the rate at which energy leaves the Earth system. This imbalance – the Earth’s energy imbalance, a new indicator in this year’s report – leads to an accumulation of excess energy.
One of the longest observational records of climate change is that of global mean near-surface temperature. The past three years are the three warmest years in the 176-year combined land and ocean observational record. The year 2025 is the second or third warmest year, depending on the dataset used, slightly cooler than the record warmth of 2024, due in part to the transition from El Niño at the start of 2024 to La Niña in 2025. The warming seen at the surface and throughout the troposphere represents just 1% of the excess energy trapped by greenhouse gases.
The vast majority of the excess energy – around 91% – has been absorbed by the ocean in the form of heat. Ocean heat content reached a new record high in 2025, reflecting the continued increase in energy.
Another 3% of the excess energy warms and melts ice. In a global set of reference glaciers with long-term measurements, eight of the ten most negative annual glacier mass balances since 1950 have occurred since 2016. The ice sheets on Antarctica and Greenland have both lost significant mass since satellite records began.
The extent of sea ice in the Arctic has decreased in all seasons since satellite measurements began in 1979, and the annual maximum extent in 2025 was the lowest or second lowest in the observed records. Sea-ice extent around Antarctica showed a small long-term increase until 2015, but since then, extents throughout the annual cycle have dropped considerably, and the past four years have seen the four lowest Antarctic sea-ice minima on record.
The warming ocean and melting of ice on land from glaciers and ice sheets have both contributed to the long-term rise in global mean sea level. The rate of global sea-level rise has increased since satellite measurements began in 1993.
The remaining ~5% of the excess energy is stored in the continents, increasing the temperature of the land mass and thereby affecting terrestrial processes.
As well as absorbing the majority of the energy trapped by increasing concentrations of greenhouse gases, the ocean has also absorbed around 29% of the anthropogenic emissions of carbon dioxide in the past decade. While this helps to buffer the effects of climate change, it also alters the chemical composition of the ocean water, reducing the pH in a process known as ocean acidification.
These rapid large-scale changes in the Earth system have cascading impacts on human and natural systems, contributing to food insecurity and displacement where hazards intersect with high vulnerability and limited adaptive capacity.
Continue reading ‘State of the global climate 2025’
