Submarine groundwater discharge (SGD) and its influence on coastal acidification and trace-metal enrichment have not been studied in Borneo. This study characterizes SGD from northwest Borneo into the South China Sea, focusing on iron (Fe) and aluminum (Al) inputs, hydrogeochemical controls on their mobility, and SGD’s role in coastal acidification. Samples were collected along transects at Tungku and Empire beaches, spanning the peritidal to subtidal zones, as well as from streams, pools, and beach sand. SGD contained elevated Fe and Al (Tungku: 4.07 mg/L Fe, 1.31 mg/L Al; Empire: 2.12 mg/L Fe, 0.38 mg/L Al), identifying these as key SGD-derived trace metals. pH was near-neutral in many samples (minimum 6.6), rising from 7.72 (Tungku) and 7.48 (Empire) in SGD to 8.11 and 8.01 in adjacent seawater, creating steep pH gradients favoring Al and Fe precipitation. Acid sulfate soils and high dissolved organic matter enhance groundwater acidity and trace-metal mobility. Major-ion chemistry indicates dominance of non-carbonate alkalis (SO₄²⁻ + Cl⁻ >CO₃²⁻ + HCO₃⁻; Na⁺ + K⁺ >Ca²⁺ + Mg²⁺) and low phosphate and nitrate, with mixed freshwater–saline contributions. The combination of low pH, elevated Fe and Al, and anthropogenic disturbance may degrade coastal and groundwater quality, affecting marine biogeochemical cycles, biodiversity, and ecosystem functioning. Overall, SGDs in Brunei deliver acidic, Fe- and Al-enriched water, contributing to coastal acidification and contamination, with implications for regional climate resilience.
Continue reading ‘Hydrogeochemistry of submarine groundwater discharge along a Bruneian coastline: iron and aluminum enrichment along with coastal acidification’Posts Tagged 'chemistry'
Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries
Published 29 December 2025 Science ClosedTags: algae, biological response, BRcommunity, chemistry, field, fisheries, mitigation, mollusks, morphology, North Atlantic
The co-cultivation of seaweeds with bivalve shellfish is a potential strategy for protecting bivalve crops against anthropogenic coastal acidification and hypoxia. We co-cultivated seaweeds and bivalves using a succession of seaweed species according to season (winter, Saccharina latissima → spring, Ulva spp. → summer, Gracilaria spp.) together with eastern oysters (Crassostrea virginica) and blue mussels (Mytilus edulis). Bivalves and seaweeds were deployed in two estuaries that contrasted in trophic state, one mesotrophic and one eutrophic. In all five experiments in the mesotrophic system, cocultivation with seaweeds significantly increased weight- and/or shell-based growth of bivalves (p < 0.05). Growth rate increases for C. virginica were modest, with weight-based growth improving by 17–21% and shell-based growth improving by 3–27% with seaweed co-culture of all macroalgal species. For M. edulis, the effect was large; co-culture with S. latissima caused 47% and 114% increases in shell- and weight-based growth rates, respectively. In the four experiments in the eutrophic estuary, co-culture with seaweeds did not significantly improve bivalve growth. Seaweed cultivation significantly improved water quality metrics (increased pH and dissolved oxygen (DO); p < 0.05 in all cases) in and around the seaweed sites at both locations, although increases in pH and DO were modest, and even in control treatments, there were no prolonged periods of harmful pH or DO levels. An abundance of macroalgal detritus may have bolstered the diets of co-cultivated bivalves in the mesotrophic estuary, a hypothesis supported by lower chlorophyll a concentration, and therefore lower planktonic food levels, at that site. Given that seaweeds display species-specific allelopathic effects against phytoplankton, it is also possible that the presence of seaweeds altered the phytoplankton community to the benefit of the bivalves. Regardless, the findings here demonstrate that co-cultivation with seaweeds can accelerate the growth of bivalves.
Continue reading ‘Aquaculture of seaweeds (Saccharina latissima, Ulva spp., Gracilaria spp.) significantly improves the growth of co-cultivated bivalves in mesotrophic, but not eutrophic, estuaries’An autonomous pH sensor for real-time high-frequency monitoring of ocean acidification in estuarine and coastal areas
Published 26 December 2025 Science ClosedTags: chemistry, field, methods, North Pacific
In situ pH sensing is crucial for the real-time monitoring of ocean acidification and investigations into the marine carbon cycle. Although ion sensitive field-effect transistor (ISFET) has been proven suitable for marine pH monitoring, its supply and implementation remain challenging. An underwater pH sensor for environmental analysis (uSEA-pH) based on ISFET was developed herein, incorporating a modified commercial laboratory pH probe through engineering design. Laboratory characterization demonstrated that uSEA-pH exhibited a Nernstian response (slope −57.60 ± 1.05 mV/pH, R2 > 0.999), rapid response time (∼7 s), and low measurement uncertainty (<0.01 pH). The sensor supports a sampling frequency of 1 Hz with an average power consumption of only 0.72 W. Its compact design (self-contained with battery: Φ15 × 45 cm; miniaturized version: Φ6.4 × 21 cm) facilitates deployment on various observational platforms. During high-frequency underway monitoring in the Pearl River Estuary and Dongshan Bay, uSEA-pH successfully detected subtle pH variations (<0.05 pH). In extended in situ deployments, buoy-mounted uSEA-pH reliably recorded tidal-driven pH fluctuations in Dapeng Bay (27 days) and Xiamen Bay (7 days), generating over 2.3 million field measurements. This study presents a viable, robust, and high-resolution approach for continuous pH monitoring in estuarine and coastal areas.
Continue reading ‘An autonomous pH sensor for real-time high-frequency monitoring of ocean acidification in estuarine and coastal areas’Chapter 4 – Insights into the role of micronanoplastics in accelerating ocean acidification
Published 18 December 2025 Science ClosedTags: chemistry, review
While micronanoplastic pollution is among the most severe anthropogenic threats, ocean acidification is an equally concerning ecological issue. Several studies have highlighted the toxicological effects, interactions, and behavior of micronanoplastics across different environmental domains. However, their role in accelerating ocean acidification remains poorly understood. Ocean acidification refers to the decrease in seawater pH due to increased dissolution of atmospheric carbon dioxide into the ocean. This phenomenon poses a serious threat to marine life and ecosystem functioning. Based on current evidence regarding the behavior and interactions of micronanoplastics in marine systems, it can be proposed that these polymer particles may play a significant role in accelerating seawater acidification. This chapter focuses on exploring the evidence linking micronanoplastic pollution to ocean acidification and aims to comprehensively examine its causes, mechanisms, and consequences.
Continue reading ‘Chapter 4 – Insights into the role of micronanoplastics in accelerating ocean acidification’Symmetrical pH electrochemical cell coupled to constant potential coulometry for improved sensitivity and precision: part 2. Submersible probe for in situ measurements
Published 17 December 2025 Science ClosedTags: chemistry, field, methods
Seawater pH is a critical parameter influencing many processes in the ocean. Today it is mainly measured by indicator- based spectrophotometry to allow for high precision. This, however, is at the expense of traceability and systematic errors originating from changes in temperature, salinity and other matrix effects. Moreover, in routine practice this approach is not performed in situ and requires sampling and manual manipulations, which is prone to introduce additional errors including gas exchange with the atmosphere. Unfortunately, in the last few decades the electrochemical sensing community has failed to make efforts to improve the performance of the gold standard method, which is potentiometric detection with pH glass electrodes. To address this, we aim here to improve the sensitivity and precision of submersible pH probes on the basis of pH glass electrodes by minimizing systematic errors from temperature changes and by implementing a recently described coulometric method. The electrodes are mounted in a symmet- rical cell reported in part 1 of this work to reduce sensor drift and minimize inaccuracies due to liquid junction potential variations and pH changes of the inner solution from temperature fluctuations. The development and construction of the probe is explained. The circuit is evaluated and the sensors are calibrated over a range of temperatures, approaching ideal behavior. The submersible probe was deployed in situ in April 2025 in the vertically stratified Krka River Estuary in Croatia. The precision of the probe were evaluated in situ by stability experiments in the seawater layer. The determined precision is 0.001 pH unit, which is significantly better than reported earlier for routine pH probes. A recalibration procedure with synthetic seawater is also evaluated for minimizing drift. A depth profile with changing salinity was performed and compared with CTD probes.
Continue reading ‘Symmetrical pH electrochemical cell coupled to constant potential coulometry for improved sensitivity and precision: part 2. Submersible probe for in situ measurements’Aragonite lithium/magnesium as an indicator of calcification media saturation state in marine calcifiers
Published 16 December 2025 Science ClosedTags: chemistry, laboratory
Marine calcifiers support ecosystem services, including shell fisheries and coral reefs. Constraining the saturation state of the calcification media of these organisms is essential to understand the response of biomineralisation to environmental change. Here we synthesise aragonite over variable pH, saturation state, temperature, and in the presence of simple biomolecules. We show that the lithium/magnesium distribution coefficient, relating aragonite and precipitation fluid compositions, is significantly affected by precipitation rate but not by temperature or pH. Precipitation rate reflects saturation state and temperature, so lithium/magnesium of biogenic aragonite can be used to calculate mineral precipitation rate and, if the precipitation temperature is known, to reconstruct calcification medium saturation state. Applying the distribution coefficients to a published calcifier dataset indicates that calcification media saturation state is ca. 9 to 13 at 18–30 °C and ca. 6 to 10 at 10–18 °C. Coral calcification media saturation state varies between ocean sites, species, and reef zones.
Continue reading ‘Aragonite lithium/magnesium as an indicator of calcification media saturation state in marine calcifiers’Water property variability into a semi-enclosed sea dominated by dynamics, modulated by properties
Published 15 December 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, regionalmodeling
The biogeochemistry of the Salish Sea is strongly connected to its Pacific Ocean inflow through Juan de Fuca Strait (JdF), which varies seasonally and interannually in both volume and property flux. Long-term trends in warming, acidification, and deoxygenation are a concern in the region, and inflow variability influences the flux of tracers potentially contributing to these threats in the Salish Sea. Using ten years (2014–2023, inclusive) of Lagrangian particle tracking from JdF, we quantified the contributions of distinct Pacific source waters to interannual variability in JdF inflow and its biogeochemical properties. We decompose variability in salinity, temperature, dissolved oxygen, nitrate, and carbonate system tracers into components arising from changes in water source transport (dynamical variability) and changes in source properties (property variability). Observations in the region provide insight into source water processes not resolvable in the Lagrangian simulations, including denitrification and trace metal supply. Deep source waters dominate total inflow volume and drive variability in nitrate flux through changes in transport. Shallow source waters, particularly south shelf water, exhibit greater interannual variability and disproportionately affect temperature, oxygen, and [TA–DIC], driving change through both dynamical and property variability. This study highlights the combined roles of circulation and source water properties in shaping biogeochemical variability in a semi-enclosed sea, and how these roles differ between biogeochemical tracers. It provides a framework for attributing flux changes to specific source waters and physical and biogeochemical drivers, with implications for forecasting coastal ocean change under future climate scenarios.
Continue reading ‘Water property variability into a semi-enclosed sea dominated by dynamics, modulated by properties’Symmetrical pH electrochemical cell coupled to constant potential coulometry for improved sensitivity and precision: part 1. fundamental considerations
Published 12 December 2025 Science ClosedTags: chemistry, methods
pH is a major variable in complex aquatic ecosystems, influencing biological activity, metal speciation and more. The gold standard method to routinely measure pH is potentiometric measurements with a glass electrode connected to a reference Ag/AgCl element in contact with the sample through a liquid junction. However, it has been largely replaced by optical pH assays in the field of seawater pH measurements because much better precisions could be achieved. Glass electrodes also suffer from bias such as liquid junction potential changes and temperature influence on the inner solution pH that generate inaccuracies. Moreover, the Nernstian relationship between observed potential and pH results in limited sensitivity. To overcome these limitations, an alternative readout called constant potential coulometry is implemented in the measurement system for increased sensitivity. A symmetrical pH cell is proposed in which two identical glass electrodes, separated by an open 3 M KCl channel, are measured against each other. One of them is kept in a NIST buffer while the other is used to measure the pH of the sample or the calibrant solution. Glass electrodes are evaluated at different temperatures in NIST buffers versus a classical reference electrode and versus each other in a symmetrical flow cell. The latter features open junctions that should improve the repeatability of the liquid junction potential. The determined measurement repeatability is as low as 0.3 mpH with a precision of 0.001 pH, which is drastically improved over routinely available pH probes.
Continue reading ‘Symmetrical pH electrochemical cell coupled to constant potential coulometry for improved sensitivity and precision: part 1. fundamental considerations’Seasonal variations of physico-chemical variables interaction and their influence on phytoplankton and pCO2 dynamics in the Southwest Bay of Bengal
Published 12 December 2025 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, community composition, field, Indian, otherprocess, phytoplankton
The carbonate system and nutrient dynamics play a crucial role in regulating phytoplankton productivity and carbon cycling in tropical coastal ecosystems, which are highly sensitive to climate change and anthropogenic activities. The present study investigates the spatio-temporal variability of physico-chemical parameters, nutrient dynamics and their influence on phytoplankton community structure along the southwest coast of Bay of Bengal (SWBoB), with particular focus on their relationship with partial pressure of carbon di-oxide (pCO₂). Seasonal sampling was carried out entirely with onboard cruise programs, with each cruise representing different season such as pre-monsoon, monsoon, post-monsoon and summer. The study covered SWBoB among six stations namely Tuticorin, Nagapattinam, Poombuhar, Pondicherry, Mahabalipuram and Chennai during 2022–2023. A total of 77 phytoplankton species representing five taxonomic classes were identified and quantified, where minimum and maximum phytoplankton density were observed during summer (7.498 × 103 cells. L-1) and pre-monsoon (7.0014 × 104 cells. L-1) respectively. A pronounced spatio-temporal variations were observed in physico-chemical parameters and nutrients with peak phytoplankton density and pCO₂ value (487.47 µatm) during pre-monsoon period were attributed to enhanced microbial respiration, riverine input and upwelling of CO₂-rich subsurface waters. In contrast, reduced pCO₂ level (274.27 µatm) observed during summer coincided with water column stratification, nutrient limitation and elevated photosynthetic uptake by phytoplankton. Canonical Correspondence Analysis (CCA) indicated a strong association were attributed nutrient availability and phytoplankton assemblages, with diatoms prevailing under nutrient-rich and moderate pCO₂ conditions, simultaneously dinoflagellate dominated at high pCO₂ conditions. A significant positive relationship between pCO₂ and phytoplankton species with canonical score (0.91) of Noctiluca scintillans highlights the sensitivity of SwBoB productivity to carbon system variability. During pre-monsoon, high pCO₂ (487.47 µatm), chlorophyll-a (3.10 µg L-1) and phytoplankton density (7.0014 × 104 cells. L-1) at station T2, co-dominated by both diatom (46 %) and dinoflagellates (40 %), specifically Noctiluca scintillans (6.32 %). This indicated that nutrient enrichment and CO₂-rich upwelling enhanced phytoplankton productivity and carbon dynamics. These findings imply that pCO₂ variations, determined by temperature, salinity and nutrient inputs which influence the phytoplankton structure and productivity, impacts carbon cycling and ecosystem dynamics in the SWBoB region. This study provides valuable insights into carbon cycling and ecosystem functioning, crucial for sustaining regional fisheries and anticipating monsoon-driven changes in coastal productivity.
Continue reading ‘Seasonal variations of physico-chemical variables interaction and their influence on phytoplankton and pCO2 dynamics in the Southwest Bay of Bengal’Observed large-scale and deep-reaching compound ocean state changes over the past 60 years
Published 9 December 2025 Science ClosedTags: chemistry, review
Multiple climate-related stressors affect the ocean, including warming, acidification, deoxygenation and variations in salinity, with profound effects on Earth system cycles, marine ecosystems and human well-being. Nevertheless, a global perspective on the combined impacts of these changes on both surface and subsurface ocean conditions remains unclear. Here, applying a time-of-emergence methodology to observed physical and biogeochemical variables, collectively referred to as compound climatic impact-drivers, we show individual and compound ocean state changes have become increasingly prominent globally over the past 60 years. In particular, observations show the simultaneous emergence of compound climatic impact-drivers in regions spanning the subtropical and tropical Atlantic, the subtropical Pacific, the Arabian Sea and the Mediterranean Sea. We highlight extensive exposure of different ocean layers to compound emergence, characterized by significant intensity, duration and magnitude. These results provide a comprehensive framework and perspective to illustrate the ocean’s vulnerability to pervasive and interconnected changes in a warming climate.
Continue reading ‘Observed large-scale and deep-reaching compound ocean state changes over the past 60 years’Progressive changes in coral reef communities with increasing ocean acidification
Published 8 December 2025 Science ClosedTags: algae, BRcommunity, chemistry, community composition, corals, field, otherprocess, vents
Ocean acidification from increasing atmospheric CO2 is progressively affecting seawater chemistry, but predicting ongoing and near-future consequences for marine ecosystems is challenging without empirical field data. Here we quantify tropical coral reef benthic communities at 37 stations with varying exposure to submarine volcanic CO2 seeping, and determine the aragonite saturation state (ΩAr) where significant changes occur in situ. With declining ΩAr, reef communities displayed progressive retractions of most reef-building taxa and a proliferation in the biomass and cover of non-calcareous brown and red algae, without clear tipping points. The percent cover of all complex habitat-forming corals, crustose coralline algae (CCA) and articulate coralline Rhodophyta declined by over 50% as ΩAr levels declined from present-day to 2, and importantly, the cover of some of these groups was already significantly altered at an ΩAr of 3.2. The diversity of adult and juvenile coral also rapidly declined. We further quantitatively predict coral reef community metrics for the year 2100 for a range of emissions scenarios, especially shared socio-economic pathways SSP2-4.5 and SSP3-7.0. The response curves show that due to ocean acidification alone, reef states will directly depend on CO2 emissions, with higher emissions causing larger deviations from the reefs of today.
Continue reading ‘Progressive changes in coral reef communities with increasing ocean acidification’Resilience of pH to seasonal change in a large subtropical lagoonal estuary
Published 5 December 2025 Science ClosedTags: biogeochemistry, chemistry, field, South Atlantic
Highlights
- The lower Patos Lagoon Estuary displays a broad range of alkalinity and pH values, with riverine inputs marked by low buffering capacity.
- A critical period of corrosive conditions occurs from winter to mid-spring, likely driven by enhanced respiration and/or external CO₂ inputs.
- The estuary operates as a moderate to weakly buffered system, exhibiting aragonite undersaturation even under medium to high salinity conditions.
- pH sensitivity to environmental drivers is highest in summer and winter, whereas autumn presents the most uniform seasonal response.
Abstract
Coastal ecosystems exhibit a wide range of pH trends, from −0.023 to 0.023 pH units yr−1, making them particularly susceptible to acidification or basification. These variations are primarily driven by ecosystem metabolism and the influence of oceanic and riverine endmembers, as observed in the subtropical system of the Patos Lagoon Estuary (PLE, southern Brazil), where biogeochemical variability is largely governed by mixing of water masses with different properties. This study provides the first quantification of the seasonal variability of pH buffering capacity in the inner and outer zones of PLE. From May 2017 to September 2023, we assessed temporal variability using multiple approaches: (i) carbonate system parameters, (ii) sensitivity factors, (iii) buffering capacity of pH to fractional change of dissolved inorganic carbon (βDIC), (iv) metabolic effects on pH, and (v) environmental drivers of pH. The results revealed a distinct seasonal pH pattern, especially between summer with winter and spring, with consistently higher values at the outer station compared to the inner station, though spatial differences were not statistically significant. In winter and particularly in early spring, calcium carbonate (CaCO3) dissolution prevailed due to riverine input characterized by low buffering capacity. Along the salinity gradient, pH exhibited a pronounced difference, particularly between low and high salinity conditions. However, the persistent negative deviation of the metabolic effect on pH throughout the year and in salinity ranges, even under seawater conditions, supports the characterization of this coastal ecosystem as a net CO2 source, with especially high variability at mid-salinity conditions. Although the salinity gradient was comparable between stations, they exhibited differences in the magnitude of pH sensitivity to seasonal biogeochemical changes. These findings indicate that PLE functions as a system with moderate to low buffering capacity, with the outer zone showing greater resilience to pH fluctuations.
Continue reading ‘Resilience of pH to seasonal change in a large subtropical lagoonal estuary’A global perspective on river alkalinity: drivers and implications for coastal ocean carbonate chemistry
Published 4 December 2025 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, modeling
Abstract
The chemical nature of river water significantly influences the coastal carbonate system, contributing to coastal acidification and creating suboptimal conditions for marine calcifiers. While several regional efforts have assessed observationally based riverine concentrations and fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC), these values in global ocean biogeochemical models have generally been simplified, often set to zero or balanced against global sediment calcium carbonate burial. To enhance our understanding of rivers’ role in the coastal carbonate system, we applied multiple linear regression (MLR) to develop global empirical relationships for estimating river TA and DIC from watershed properties. We find that river TA values are primarily controlled by forest, carbonate rock coverage, and annual mean precipitation, explaining 74% of the spatial variability in TA. The variability explained improves to 77% with the inclusion of permafrost and glacial coverage, especially in high latitude and altitude regions. Additionally, nearly 30% of the spatial variability in the river DIC-to-TA ratio can be explained by terrestrial gross primary production and carbonate rock coverage. Applying these MLR-derived TA and DIC concentrations to a 1/4° resolution global ocean model reduces the high bias in model estimates of global coastal CO2 uptake by 69% (equivalent to 0.11 Pg C yr−1 less CO2 uptake) compared to the case with zero river TA and DIC. This study elucidates key drivers of the river carbonate system and underscores the importance of accurately representing riverine inputs to improve predictions of global coastal carbon dynamics and ecosystem responses to environmental changes.
Plain Language Summary
Rivers play a critical role in shaping the chemistry of coastal waters, influencing how much carbon dioxide (CO2) the ocean absorbs and creating conditions that affect marine life, such as shellfish and corals. Global models are essential for predicting carbon dynamics at large scales, offering insights into the interactions between rivers, coastal systems, and the global ocean. However, global models often simplify or partially overlook key chemical contributions from rivers, leading to biases in predictions. In this study, we analyzed how river chemistry, particularly river carbon inputs, is influenced by factors such as forest cover, carbonate rocks, rainfall, permafrost, and glaciers on land. We developed statistical models to estimate two key properties: total alkalinity and dissolved inorganic carbon. Incorporating these improved river chemistry estimates into a global ocean model markedly reduced the overestimation of coastal CO2 absorption. This research underscores the importance of accurately including riverine inputs in global models to enhance predictions of coastal carbon dynamics and ecosystem responses to climate change.
Key Points
- Global empirical relationships are developed using multiple linear regression (MLR) to estimate river TA and DIC concentrations from watershed properties
- Forest and carbonate rock coverage, and annual mean precipitation explain 74% of the spatial variability in global river TA values
- Applying MLR-derived river TA and DIC concentrations to a global ocean model substantially reduces biases in coastal CO2 uptake estimates
Ocean acidification in Southeast Asia: a multiannual time series of carbonate system variability in the central Sunda shelf sea
Published 2 December 2025 Science ClosedTags: chemistry, field, North Pacific
Ocean acidification due to anthropogenic carbon dioxide (CO2) uptake threatens marine ecosystems, but coastal waters have complex and highly variable carbonate system dynamics. More coastal time series are therefore needed to better constrain coastal pH dynamics, but especially in the tropics such time series are rare. Southeast Asia’s Sunda Shelf Sea has exceptionally high marine biodiversity and rapidly increasing anthropogenic pressures, but we have little knowledge of coastal carbonate system dynamics in the region. We analyzed 7-years of monthly carbonate system data from the Singapore Strait in the central Sunda Shelf. Our results show consistently low seawater pH (total scale; pHT; < 8.0) and aragonite saturation state (ΩAr, usually < 3.0), but with a clear seasonal pHT variation by 0.11–0.19 units. The observed seasonality reflects the monsoon-driven advection of water masses that have been shaped by different biogeochemical processes. Specifically, during the southwest monsoon, remineralization of terrestrial dissolved organic carbon originating from regional peatlands lowers pHT, while calcium carbonate (CaCO3) formation and dissolution are more important during other seasons. Comparing our data to predicted values for purely conservative mixing of river water and seawater shows that these non-conservative biogeochemical processes are dominant drivers. Our time series shows a significant decreasing trend in pHT of –0.043 units per decade, exceeding the theoretical trend detection time (TDT) of 5.0 ± 1.3 years. However, the seasonal pHT variability itself shows interannual variability, and pHT is also correlated with the El Niño Southern Oscillation. This longer-term climatic control may complicate trend quantification. Our study highlights how terrestrial dissolved organic carbon remineralization may enhance future ocean acidification in Sunda Shelf region, emphasizing the importance of continuing the time series to better quantify climatic drivers and long-term trends.
Continue reading ‘Ocean acidification in Southeast Asia: a multiannual time series of carbonate system variability in the central Sunda shelf sea’Diverging relationships between acidification and hypoxia off the Changjiang Estuary
Published 2 December 2025 Science ClosedTags: chemistry, field, North Pacific
Abstract
Acidification and hypoxia present significant ecological and environmental challenges for coastal oceans, particularly estuarine systems with high nutrient inputs such as the Changjiang Estuary (CJE). We conducted three replicate cruises from July to September in 2020 along the same transects off the CJE to investigate dynamic changes of coastal acidification and hypoxia. Bottom hypoxia expanded and intensified from July to August and alleviated in September. Changes in pHT generally followed those of dissolved oxygen (DO), although the spatial and temporal patterns did not entirely align. In August, the tight connection between hypoxia and acidification differed between the northern and southern regions. The northern region experienced widespread hypoxia and acidification with DO and pHT as low as 39 μmol kg−1 and 7.66, whereas the southern region maintained similar pHT values despite higher DO (>94 μmol kg−1). By September, hypoxia was alleviated, and pHT showed a more pronounced rise, with pHT increasing by ∼0.02 at the same DO level. Aerobic remineralization emerged as the primary driver of bottom acidification and hypoxia off the CJE during summer, peaking in August and diminishing by September. In August, the northern region experienced synchronous and severe hypoxia and acidification, whereas intermittent localized mixing in the south alleviated hypoxia. By September, enhanced mixing in the CJE increased the buffering capacity of subsurface waters, mitigating pH decline despite ongoing hypoxia. These findings improve our understanding of short-term dynamics in estuarine carbon cycling, acidification and hypoxia.
Plain Language Summary
Coastal areas, such as the Changjiang Estuary, are facing significant environmental challenges due to acidification and low oxygen levels. In 2020, we conducted three cruises from July to September to understand these changes better. We found that oxygen conditions worsened from July to August but improved by September. Interestingly, changes in acidity (pH levels) did not always match changes in oxygen levels. In August, the northern part of the estuary experienced both low oxygen and acidity, whereas the southern part had stable acidity despite higher oxygen levels. By September, enhanced water mixing by wind in the region helped improve oxygen levels and increased the resistance to acidification. Our research shows that remineralization of organic matter and wind stress are the main factors controlling pH and oxygen during summer. Understanding the drivers of acidification and deoxygenation is essential to predict future environmental changes and their potential consequences for coastal ecosystems.
Key Points
- Aerobic remineralization is the dominant driver of bottom hypoxia and acidification of the CJE, with peak intensity observed in August
- During August, intermittent localized mixing replenished bottom water oxygen, reducing hypoxia yet leaving acidification unchanged
- By September, enhanced mixing in the CJE increased buffering capacity, limiting pH decline where hypoxia persisted
Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value
Published 1 December 2025 Science ClosedTags: algae, Antarctic, biological response, chemistry, field, physiology, vents
Highlights
- Chlorophyll a content in some seaweed species increased with latitude along the Antarctic Peninsula.
- Seaweeds from fumarole vent sites revealed variations in fatty acids and pigments.
- Lower nutritional value in Antarctic seaweeds from fumarole sites suggests potential responses to ocean warming and acidification.
- Species-specific biochemical shifts in Antarctic seaweeds are anticipated under global change scenarios.
Abstract
Global change is driving ocean warming (OW) and acidification (OA), impacting marine ecosystems worldwide, including polar regions. Seaweeds, as key primary producers in coastal ecosystems, synthesize a wide range of biochemical compounds that support higher trophic levels. Their biochemical composition is conditioned by local environmental factors, including seawater temperature, pH, and nutrient availability. However, how polar seaweeds respond to ongoing global change remains poorly understood. In this study, we examined the influence of local environmental changes on the biochemical composition – including fatty acids (FA), pigments, carbon, and nitrogen – of nine Antarctic brown and red seaweed species. Specifically, we considered a latitudinal gradient from the South Shetland Islands (⁓62°S) to Yalour Island (⁓65°S), and the presence of active fumarole vents at Deception Island. Our results reveal species-specific and location-dependent biochemical shifts in most species. While chlorophyll a concentrations tended to increase with latitude, specimens collected from fumarole vents exhibited a reduction in total FA content, PUFA:SFA (polyunsaturated to saturated fatty acid) ratios, PUFA omega-3, and pigment concentrations. These shifts under hydrothermal influence are likely driven by elevated seawater temperatures and acidic conditions, suggesting a potential decline in nutritional value under future global change scenarios. Additionally, higher magnesium content was found in the skeletons of crustose coralline algae from shallow waters than in those at 22 m depth. Our results highlight the species-specific nature of biochemical responses to environmental stressors, underlining the complexity of predicting the impacts of global change on seaweed physiology and the potential cascading effects on Antarctic food webs.
Continue reading ‘Distinct biochemical profiles in Antarctic seaweeds reflect acclimation to polar and hydrothermal environments with implications for biomass nutritional value’Typhoon-induced cascade effects on hydrological and biogeochemical dynamics in estuary-coast continuum: insights from multidisciplinary observations and model forecasting in Zhanjiang Bay, China
Published 28 November 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Highlights
- Typhoon-induced nutrient surge triggered cascade effects in Zhanjiang Bay.
- Skeletonema costatum proliferated and decayed rapidly in eutrophic waters.
- Bloom collapse caused water acidification and oxygen depletion.
- A CNN-LSTM model achieved 73% relative accuracy in 6 h Chl-a rolling forecast.
Abstract
Typhoons can trigger biogeochemical cascade effects, including eutrophication, algal blooms, acidification, and dissolved oxygen (DO) depletion in the estuary-coast continuum, yet the underlying mechanisms remain poorly understood. This study employed a multidisciplinary observation approach, combining high-frequency in situ monitoring with field surveys, to capture the dynamics of the cascade during Typhoon “Yagi” (Sep 2024) in Zhanjiang Bay (ZJB). The analysis incorporated multivariate hydrological, meteorological, and physicochemical parameters, stable isotopes (δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δD-H2O), and phytoplankton community characterization. Results showed that during the pre-algal bloom period, freshwater discharge, fluxes of dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP) increased by factors of 8.7, 43.4, and 3.0, respectively, relative to the pre-typhoon stage, while salinity decreased by 9.7%. This nutrient surge exacerbated eutrophication, leading to a serious algal bloom eight days after the typhoon. Subsequent bloom decay triggered acidification and DO decline. Field investigations confirmed typhoon-driven freshwater input and algal blooms. Moreover, a deep learning model was developed for Chlorophyll-a forecasts, achieving 73% relative accuracy (RA) in rolling 6-hour forecasting. Typhoon-driven nutrient surge triggered the cascade: Skeletonema costatum bloomed under extreme thermohaline perturbation and decayed rapidly, leading to acidification and DO depletion. This study advances mechanistic understanding of typhoon-driven cascading effects in tropical coastal ecosystems, providing a scientific basis for the assessment of their ecological consequences and predictive coastal management strategies.
Continue reading ‘Typhoon-induced cascade effects on hydrological and biogeochemical dynamics in estuary-coast continuum: insights from multidisciplinary observations and model forecasting in Zhanjiang Bay, China’Surface pCO2 and hydrography in the dense water formation area of the southern Adriatic
Published 27 November 2025 Science ClosedTags: chemistry, field, Mediterranean
The rising CO2 concentration in the atmosphere leads to an increase in CO2 uptake in the ocean and to significant changes in seawater chemistry. These changes, in turn, exert profound effects on marine ecosystems across multiple trophic levels. The Mediterranean Sea is considered a hotspot for climate change. Despite such relevance, observations and studies on its carbonate system remain limited, especially in regions that play a crucial role in regulating air-sea CO2 exchange like intermediate and dense water formation areas. The southern Adriatic Sea, a key site for dense water formation in the eastern Mediterranean, hosts the EMSO ERIC and ICOS ERIC South Adriatic observatory (EMSO-E2M3A), operated by the Italian National Institute of Oceanography and Applied Geophysics (OGS). This facility allows the study of physical and biogeochemical dynamics in the deepest area of the Adriatic Sea. The suite of sensors deployed on the surface buoy allows for the characterization of water mass properties, biogeochemical cycles, dense water formation process, and ocean acidification, particularly in relation to carbon sequestration dynamics. Here, time series of meteorological data (e.g., wind speed, wind direction), sea surface physical parameters (e.g., temperature, salinity), dissolved oxygen and partial pressure of CO2 (pCO2sw) and pH from 2014 to 2024 will be presented (https://doi.org/10.13120/y2hw-1j63, Cardin et al., 2025). In particular, quality check and correction and post-processing methods applied to the data will be discussed. The validated surface dataset provides a consistent pCO2sw time series for the Adriatic Sea, with values and seasonal variability in agreement with previous observations across the Mediterranean. Associated temperature, salinity, oxygen, and wind measurements reproduce expected regional patterns, confirming the robustness and suitability of the presented dataset for further biogeochemical and climate-related analyses.
Continue reading ‘Surface pCO2 and hydrography in the dense water formation area of the southern Adriatic’Ocean acidification in the Bay of Biscay: two decades of data reveal a silent shift
Published 26 November 2025 Press releases ClosedTags: chemistry, North Atlantic
The sea along the Basque coast is changing quietly. An analysis of more than 21,700 measurements collected between 2002 and 2022 shows that the pH of seawater is steadily decreasing—clear evidence of ocean acidification driven by rising atmospheric carbon dioxide.
According to the study, published in Continental Shelf Research, the pH of waters from the surface down to 100 meters is declining by 0.022 to 0.041 units per decade. “If this trend continues at the same pace, the impacts on the health of marine ecosystems could be significant,” explains Ernesto Villarino, AZTI researcher and lead author of the study.
Conducted by AZTI with the support of the Naturklima Foundation, as part of the Gipuzkoa Marine Climate Change Observatory, and in collaboration with the Institute of Marine Sciences of Andalusia (ICMAN-CSIC), this research analyzes the longest continuous pH monitoring series ever recorded along the Basque coast. The data, provided by the Basque Water Agency (URA), confirm that the Bay of Biscay is also affected by ocean acidification, underlining the need to strengthen mitigation and climate-adaptation strategies.
Continue reading ‘Ocean acidification in the Bay of Biscay: two decades of data reveal a silent shift’Compound marine heatwaves and acidity extremes in the Southern Ocean
Published 21 November 2025 Science ClosedTags: Antarctic, chemistry, modeling, regionalmodeling
Abstract
Compound extremes of temperature and acidity that extend over substantial fractions of the water column can be particularly damaging to marine organisms, as they experience not only additional stress by the potentially synergistic effects of these two stressors, but also a reduction in habitable vertical space. Here, we detect and analyze such column-compound extremes (CCX) in the Southern Ocean between 1980 and 2019, and characterize their duration, intensity, and spatial extent. To this end, we use daily output from a hindcast simulation of the Regional Ocean Modeling System (ROMS), coupled with the Biological Elemental Cycling (BEC) model. We first detect extremes in temperature and acidity ([]) within the top 300 m using a relative threshold of 95% and then identify CCX where conditions are extreme for both stressors for at least 50 m of the water column. When analyzed on a fixed baseline, positive trends in ocean warming and acidification caused CCX to last longer, intensify, and expand throughout the Southern Ocean. In the Antarctic zone, CCX expanded between 1980 and 2019 more than ten times in volume, lasted up to 120 days longer, and doubled in anomaly. Some of the largest and longest events occurred in Antarctic Marine Protected Areas (MPAs), covering more than 200,000 km2 and persisting for over 500 days. CCX in the Subantarctic and Northern zones quadrupled in volume and increased by more than 30% in anomaly. Across the Southern Ocean, the increasing occurrence of CCX exacerbates the risks to marine ecosystems from warming and acidification.
Plain Language Summary
Extreme heat events in the ocean, known as Marine HeatWaves (MHW), are becoming more common due to climate change. These events can be even more harmful when they occur at the same time as Ocean Acidity eXtreme (OAX) events, synergistically causing stress for marine life. In this study, we looked at how often these combined events in the upper ocean, called Column-Compound eXtremes (CCX), occurred in the Southern Ocean between 1980 and 2019. We used a numerical model simulation to investigate changes in CCX during the study period. Compared to conditions in 1980, we find that CCX in the Antarctic zone have expanded more than 10 times in volume and lasted up to 120 days longer. In addition, expansive and intense CCX are found in Antarctic Marine Protected Areas (MPAs), posing a threat to vulnerable ecosystems. These events covered more than 200,000 km2 and lasted more than 500 days. The increasing occurrence of CCX across the Southern Ocean exacerbates the risks to marine ecosystems arising from ocean warming and acidification.
Key Points
- In the Antarctic zone, Column-Compound eXtremes (CCX) occupied in 2019 relative to 1980 ten times more volume and doubled in anomaly
- Marine Protected Areas in the Ross Sea and Antarctic Peninsula are disproportionately affected by the largest, longest, most intense CCX
- More than 70% of surface marine heatwaves contain CCX in 2019, although up to 60% of CCX occur without any surface expression
