Compared with traditional bulk foraminiferal analysis methods, in situ analysis of individual foraminiferal tests (individual foraminiferal analysis or IFA) offers several advantages over traditional bulk methods, including enhanced temporal resolution where fossiliferous sample material is limited as well as potentially resolving seasonal-scale climate variability in deep time. Despite these advantages, applications of element-to‑calcium (El/Ca) ratios and δ11B in benthic foraminifera using IFA remain limited, and the biogeochemical drivers of intra-test and inter-test geochemical variability are poorly constrained. In this study, we systematically evaluate El/Ca ratios and δ11B in individual benthic foraminifera. By analysing Holocene epifaunal benthic foraminiferal species Cibicidoides wuellerstorfi from a deep ocean core site (ODP Site 999), we conclude that intra- and inter-test variabilities are regulated by ontogenetic effects resulting in inter-test variabilities of ±0.14 mmol/mol Mg/Ca, ± 14 μmol/mol B/Ca, and ± 0.18 ‰ δ11B. Application of the IFA method to epifaunal benthic foraminifera species Cibicides lobatulus from a box core in the English Channel, UK reveals ~0.1 pH units acidification and ~ 1 °C warming since the mid-19th century. By demonstrating that individual-level variability in reconstructed temperature and pH tracks seasonal trends in the available contemporaneous water-column instrumental measurements at the same site, we provide a ground-truthing to our multi-proxy IFA methodology, and also demonstrate the potential for benthic IFA to provide seasonal-scale reconstructions of ocean climate over hundreds to millions of years.
Continue reading ‘Individual foraminiferal analysis: a promising tool for high-resolution temperature and pH reconstruction’Posts Tagged 'chemistry'
Individual foraminiferal analysis: a promising tool for high-resolution temperature and pH reconstruction
Published 27 March 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, field, methods, paleo, protists
Resilient adults but vulnerable larvae: demographic pathways of chiton decline under ocean acidification
Published 26 March 2026 Science ClosedTags: abundance, algae, biological response, BRcommunity, chemistry, field, laboratory, mollusks, morphology, mortality, North Pacific, otherprocess, phytoplankton, reproduction, vents
Highlights
- Natural CO₂ seep systems showed reduced intertidal chiton abundance.
- Adult chitons showed resilience to acidification in field and lab experiments.
- Larval survival and recruitment were strongly impaired under acidified seawater.
- Population declines are linked to early life-stage vulnerability.
- Loss of chitons may reduce grazing and bulldozing, reshaping intertidal communities.
Abstract
Ocean acidification (OA) is a major threat to marine calcifiers; however, the sensitivity across taxa and life stages remains elusive. In this study, we combined field surveys of natural CO₂ seeps with laboratory exposure, transplantation, and larval settlement experiments to assess the effect of OA on chitons, a group of calcifying grazers and bulldozers that play critical roles in the structure of rocky intertidal ecosystems. Field surveys revealed approximately 98.6% reduction in chiton (Acanthopleura loochooana, Liolophura japonica, and Acanthochitona rubrolineata) abundance at acidified habitats (pH 7.6), despite greater microalgal food availability and no detectable increase in predator abundance. Laboratory CO₂-exposure experiments showed no direct effect of OA on adult A. loochooana survival, which is consistent with the presence of protective structural features in the valves that confer resistance to dissolution. Transplant experiments revealed no evidence of increased adult A. loochooana mortality in the acidified habitats (pH 7.6). In contrast, larvae showed pronounced sensitivity to OA, with acidified seawater (pH 7.6) reducing larval settlement by approximately 81.5% compared to control conditions (pH 8.1); early life stages were the most vulnerable. These findings suggest that OA-associated decline in chiton abundance is mainly mediated by impaired recruitment rather than by direct adult mortality, predation, or food limitation. Given the role of chitons as grazers and bulldozers, their loss could substantially change intertidal community dynamics by decreasing grazing pressure and disturbing algal and microbial assemblages. Our findings underscore the criticality of considering life-stage vulnerability and ecological function when evaluating the ecosystem-level consequences of OA.
Continue reading ‘Resilient adults but vulnerable larvae: demographic pathways of chiton decline under ocean acidification’The role of seagrass in modifying dissolved oxygen and pH in coastal systems: a meta-analysis
Published 26 March 2026 Science ClosedTags: biological response, chemistry, field, phanerogams, review
Highlights
- Seagrass productivity drives diel pH–DO variation, enhancing local buffering capacity
- Oxygen–pH coupling highlights seagrass role in mitigating acidification during photosynthesis
- Studies should integrate temperature, salinity, and light to parse biological drivers
- Expanded geographic scope, especially tropics and Global South, is urgently needed
- Standardized pH scales and advanced sensors to improve comparability and monitoring
Abstract
Seagrass meadows, highly productive ecosystems, can influence local water chemistry by increasing dissolved oxygen in the water column and removing dissolved CO2 thus raising pH. This study provides the first quantitative synthesis of literature comparing pH and dissolved oxygen (DO) between systems with and without seagrasses. Through a systematic literature review and meta-analysis, we collated and analysed data from 63 studies reporting pH values and 70 studies reporting DO. Across studies, seagrass habitats were associated with slightly higher mean pH relative to non-seagrass habitats. Seagrass habitats showed the highest mean pH (8.11 ± 0.30) and the greatest diel variability (0.47 ± 0.65) of all habitats investigated with unvegetated areas exhibiting lower mean pH and reduced variability. The diel pH range was also significantly higher in seagrass habitats (p = 0.024). The pooled standardized mean difference was small (0.15), indicating a modest overall effect of seagrass presence on pH across studies. Although mean DO concentrations were slightly lower in seagrass habitats compared to other vegetated systems, they experienced fewer hypoxic events (12% of values < 2 mg/L) compared to other vegetated systems (55%). Generalized additive models identified DO as the strongest predictor of pH, with minor contributions from temperature and salinity. Overall, seagrass habitats are associated with increasing average pH and reducing hypoxia across multiple sites and regions. However, the magnitude and direction of effects vary widely among studies (I2 = 97%). These findings indicate that seagrass influences on water chemistry are context-dependent and likely driven by interactions among biological processes and local environmental conditions. Key knowledge gaps were identified; including the need for a greater focus on H+ concentration and the need for more research on seagrass ecosystems in underrepresented geographical regions.
Continue reading ‘The role of seagrass in modifying dissolved oxygen and pH in coastal systems: a meta-analysis’Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification on the coast of Korea
Published 25 March 2026 Science ClosedTags: abundance, biological response, chemistry, community composition, crustaceans, field, nematodes, North Pacific, otherprocess, zooplankton
This study aimed to investigate the meiofauna community characteristics in coastal waters affected by ocean acidification. Therefore, the meiofauna communities in the coastal waters of Hupo in Uljin-gun, which showed a high ocean acidification trend in the integrated data on the coastal areas of South Korea for the previous ten years, were monitored over five years. During the study period, the mean abundance of total meiofauna communities expressed in population density was 614 individuals (Inds.)/10 cm2. The most dominant taxa were nematodes (65–70%) and harpacticoids (7–20%); these two taxa accounted for approximately 80% of the total meiofauna abundance. Station (St.) 5 and 10, which had the lowest seawater pH values, showed the lowest average abundance values for harpacticoids (average 46 Inds./10 cm2) and nauplius (average 4 Inds./10 cm2) among the major meiofaunal groups over the 5-year period. In addition, St. 5 indicated the lowest meiofaunal diversity index of 0.54. To examine the effect of ocean acidification on meiofauna communities at the species level, species of nematodes, the most dominant taxon, were analyzed. The results indicated that the number of nematode species at St. 10, one of the two stations with the lowest pH, was the lowest compared to those at other stations. Analysis of c-p values for nematode species showed that both species sensitive to environmental disturbance and species resistant to environmental pollution appeared at high rates. According to the feeding type of nematodes, epistrate feeders accounted for a remarkably high proportion at St. 10. This study provides various data on meiofauna community characteristics to understand the effects of ocean acidification on coastal ecosystems.
Continue reading ‘Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification on the coast of Korea’Analysing the distribution and variability of dissolved inorganic carbon and alkalinity over the Bay of Bengal region using the coupled ocean biogeochemical modeling
Published 25 March 2026 Science ClosedTags: chemistry, Indian, modeling, regionalmodeling
Highlights
- High-resolution regional coupled ocean biogeochemical modeling in the Bay of Bengal.
- Spatio-temporal variability of Dissolved Inorganic Carbon and Alkalinity is studied.
- Aragonite (calcite) saturation depth in the Bay of Bengal is estimated.
- ENSO and IOD events significantly influence surface DIC of the BoB region.
Abstract
A prototype high-resolution regional coupled ocean biogeochemical modeling experiment is carried out in the Bay of Bengal (BoB) region to study the distribution and spatio-temporal variability of Dissolved Inorganic Carbon (DIC) and Alkalinity (Alk) during the period 2000-2021. It is found that in the eastern as well as head BoB, the DIC concentration remains less (1.6-1.7 mol/m3) as compared to the south-west and west-central BoB, where the DIC concentration remains particularly high (>1.9 mol/m3). The highest (lowest) DIC concentration in the BoB remains in the Mar-April (Oct) months. The seasonal variability of the DIC and Alk is studied vis-à-vis seasonal changes in the currents and freshwater flux. The depth profiles of DIC, Alk, and DIC/Alk ratio are also investigated across different sections in the BoB. The DIC remains stratified in the BoB, and the stratification becomes much more pronounced on moving from south to north (and west to east) part of the model domain. The aragonite (calcite) saturation depth ranges between approx. 100-400 m (500-4000 m) in the BoB. The particularly high (>8.1) and low (∼8) pH values are found in the head BoB and southwest BoB, respectively. It is shown that the influence of El Nino – Southern Oscillation (ENSO) event on the surface DIC concentration over the BoB region is much stronger as compared to the Indian Ocean Dipole (IOD) event.
Continue reading ‘Analysing the distribution and variability of dissolved inorganic carbon and alkalinity over the Bay of Bengal region using the coupled ocean biogeochemical modeling’Diel variability and decoupled pH-oxygen dynamics drive metabolic plasticity in kelp crabs from an upwelling seascape
Published 25 March 2026 Science ClosedTags: biological response, chemistry, crustaceans, laboratory, multiple factors, oxygen, physiology, respiration, South Pacific
Coastal upwelling zones, shaped by global change and human impacts, naturally impose hypoxia and acidification on marine species, creating selective pressures that influence physiological responses and drive phenotypic variability. Understanding these responses is crucial for predicting marine biodiversity dynamics in heterogeneous seascapes. We explored diel cycles of pH and dissolved oxygen (DO) and their influence on the metabolic performance of the kelp crab Taliepus dentatus, a species with limited larval dispersal. Kelp crabs from two environmentally contrasting sites along an upwelling seascape in central Chile—an upwelling shadow and an active upwelling zone—were studied using field sensor data and laboratory experiments. Active upwelling disrupted the regular diel pH cycle, resulting in persistently low pH (pHT ≈ 7.5) decoupled from oxygen dynamics. Experimental simulations of diel pH–DO fluctuations revealed that nocturnal low DO/low pH conditions (DO = 1 and 5 mg l⁻¹; pH = 7.5 and 7.8 for ‘upwelling’ and ‘downwelling’ conditions, respectively) reduced metabolic rates and respiratory quotient in crabs. Individuals from the active upwelling zone exhibited elevated metabolic rates, haemolymph pH and lactate accumulation under extremely low pH/low DO conditions compared with those from the upwelling shadow, suggesting site-specific physiological adjustments. These findings underscore the importance of incorporating natural variability into experimental designs and management frameworks aimed at predicting species resilience under climate change.
Continue reading ‘Diel variability and decoupled pH-oxygen dynamics drive metabolic plasticity in kelp crabs from an upwelling seascape’Long-term pH trends and spatiotemporal variability of the carbonate system in Jakarta Bay
Published 20 March 2026 Science ClosedTags: biogeochemistry, chemistry, field, South Pacific
Jakarta Bay, an industrialized and densely inhabited coastal area, presents considerable environmental issues as a result of excessive organic pollution and nutrient inflow. Understanding the spatiotemporal variability of the carbonate system in such an affected bay is critical for assessing marine ecosystem health. The spatiotemporal variability of the carbonate system, pH, partial pressure of carbon dioxide (pCO2), total alkalinity (TAlk), and dissolved inorganic carbon (DIC) was investigated in Jakarta Bay during the rainy and dry seasons of 2023. pH datasets from 2011 to 2023 were also collected from the Environmental Agency of DKI Jakarta (DLH DKI Jakarta) for trend analysis. The temporal analysis shows that during the SE monsoon, the lowest pH (mean: 8.06 ± 0.43); lowest TAlk (mean: 2099 ± 340 µmol kg-1); highest pCO2 (mean: 879 ± 1177 µatm); and highest DIC (mean: 2068 ± 806 µmol kg-1) were observed. The pH distribution gradually increased from the river outlet to the outer bay; inversely, pCO2, TAlk, and DIC gradually decreased. Furthermore, from 2011 to 2023, pH in Jakarta Bay showed a slight upward tendency that was statistically insignificant, reflecting high variability and the influence of local biogeochemical processes. The carbonate system variability reflects changes in biogeochemical (Chl-a, DO and nutrients) and physical (SST and Sal) parameters. In addition, the semi-enclosed hydrodynamic properties, together with the influence of human activities, including a continuous supply of nutrients and organic materials from the mainland through the incoming rivers, further affected the balance of the carbonate system in the bay.
Continue reading ‘Long-term pH trends and spatiotemporal variability of the carbonate system in Jakarta Bay’Contrasting effects of river and erosion-derived inputs on Arctic Ocean acidification
Published 18 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, modeling, regionalmodeling
Although the Arctic Ocean is relatively small in volume, its extensive coastline delivers large quantities of terrigenous material from rivers and coastal erosion. As a result, the Arctic Ocean is impacted more strongly by terrigenous material than most other parts of the global ocean. Yet the effect of this material on carbon cycling and ocean acidification remains poorly quantified. In this study, we use an ocean biogeochemical model driven by observation-based estimates of terrigenous carbon, alkalinity, and nutrients to evaluate their contribution to the mean state, depth pattern, and seasonal cycle of ocean acidification, as measured by the aragonite saturation state. Riverine alkalinity generally mitigates acidification, whereas organic carbon from coastal erosion intensifies it. Nutrients from both sources mitigate ocean acidification at the surface by stimulating primary production, but intensify it at depth through subsequent remineralisation. Together, riverine and erosion-derived inputs account for about 20–40 % of the seasonal variability in the saturation state of the surface ocean. This amplification of the natural seasonal cycle is primarily caused by an increase in the summertime maximum of the saturation state. Terrigenous inputs also reduce the Arctic Ocean’s capacity to absorb atmospheric CO2 by 17–25 %. Accurately representing carbon and nutrient inputs from rivers and coastal erosion in biogeochemical models is therefore important for reliable assessments of ocean acidification, ecosystem health, and carbon budgets in the Arctic Ocean.
Continue reading ‘Contrasting effects of river and erosion-derived inputs on Arctic Ocean acidification’Groundwater-derived carbon promotes hypoxia and acidification in a large tropical estuary
Published 18 March 2026 Science ClosedTags: biogeochemistry, chemistry, field, North Pacific
Abstract
Submarine groundwater discharge (SGD) derived nutrient inputs have been extensively documented. However, SGD-derived carbon fluxes remain largely unconstrained, representing a critical gap in most coastal carbon budgets. Here, we resolve SGD and dissolved carbon budgets in the Pearl River Estuary (PRE), the largest estuary in Southern China surrounded by the world’s largest urban conglomerate. Broadly-defined SGD contributes 89%–96% of the dissolved inorganic carbon (DIC) pool (2–4 times riverine inputs) and 20%–70% of the dissolved organic carbon (DOC) fluxes of the PRE. SGD transports DIC exceeding total alkalinity (TAlk) by 2.7–7 times, potentially driving pH decline and acidification of nearshore waters. Groundwater pCO2 values are 10–36 times higher than estuarine waters. SGD-derived DOC mineralization can decrease estuary water pH by 0.04–0.16 units and increase CO2 by 6.0–90.0 μmol L−1, affecting local coral populations and benthic organisms. SGD also reduces seawater dissolved oxygen (DO) by 12–150 μmol L−1 and fuels the development of hypoxic zones. Overall, SGD regionally intensifies seawater hypoxia and acidification, creating challenging conditions for coral reef survival in an already stressed ecosystem. Our findings demonstrate that SGD should be integrated into carbon budgets and ecological assessments of the land-ocean continuum.
Plain Language Summary
Submarine groundwater discharge can transport large amounts of dissolved carbon into the coastal ocean, but it is often overlooked due to challenges in quantification. Here, we investigate the contribution of groundwater to the dissolved carbon pool in a large tropical estuary using radium isotopes and carbon data. We found that groundwater is a significant source of estuarine dissolved carbon and has the potential to acidify seawater oxygen-depleted waters. These findings emphasize the importance of considering groundwater when evaluating carbon budgets and the ecological health of coastal ecosystems.
Continue reading ‘Groundwater-derived carbon promotes hypoxia and acidification in a large tropical estuary’Novel in situ CO2 enrichment system reveals seagrass meadows are a refugium against coastal acidification for North Atlantic bivalves
Published 18 March 2026 Science ClosedTags: biological response, BRcommunity, chemistry, growth, laboratory, mollusks, mortality, North Atlantic, phanerogams
While the accumulation of anthropogenic CO2 in the atmosphere is causing a decline in global ocean pH, many eutrophic estuaries are already experiencing acidification due to accelerated respiration driving the consumption of dissolved oxygen (DO) and production of CO2, decreasing available carbonate ions (CO32-) and threatening marine calcifiers. Here, a novel in situCO2 enrichment system was constructed to examine the effects of coastal acidification on the growth and survival of two species of North Atlantic bivalves (Argopecten irradians and Crassostrea virginica) in two distinct estuarine habitats: a seagrass meadow and an unvegetated sandy bottom in an open water estuary. The in-situ system captured natural diel dynamics as ambient chambers displayed chemistry nearly identical to the surrounding water, while CO2-enriched, acidified chambers maintained a consistent ~Δ 0.3–0.5 pH offset. At the unvegetated sandy bottom site, A. irradians and C. virginica displayed significant reductions in growth and survival in the acidified chambers (pHT = 7.3–7.5; saturation state of aragonite, ΩAr = 0.6–0.9) relative to ambient conditions (pHT = 7.6–7.9; ΩAr = 1.6–2). At the seagrass site, while growth of A. irradians and C. virginica in the acidified treatments (pHT = 7.3–7.7; ΩAr = 0.7) receiving the same delivery of CO2 was, again, significantly slowed compared to the control (pHT = 7.5–8.1; ΩAr = 2 – 2.8), the growth reduction, mortality rates, and levels of acidification were attenuated compared to the sandy bottom experiment, evidencing the ability of seagrass to buffer seawater and serve as a potential acidification refuge for bivalves. Collectively, the novel experimental CO2 enrichment system constructed for this project demonstrates that coastal acidification can have deleterious effects on marine bivalve populations, and that future conditions as well as the habitat refuge offered by seagrasses must be considered when developing management and restoration plans for temperate estuaries.
Continue reading ‘Novel in situ CO2 enrichment system reveals seagrass meadows are a refugium against coastal acidification for North Atlantic bivalves’Seasonal variations and key controls on seawater aragonite saturation state in the Northern Yellow Sea, China
Published 17 March 2026 Science ClosedTags: chemistry, field, North Pacific
Based on four field surveys conducted from August 2022 to May 2023, seasonal distribution and dynamics of the seawater aragonite saturation state (Ωarag) were investigated in the northern coastal zone of the Northern Yellow Sea, an important fishery region, to assess impacts of ocean acidification especially in river-dominated coastal systems. Results revealed seawater Ωarag had significant spatiotemporal variability with surface values ranging from 1.42 to 3.76 in summer, 1.22 to 2.34 in autumn, 1.71 to 2.48 in winter, and 2.03 to 3.56 in spring. Subsurface seawater Ωarag was generally lower than surface values, while seawater with Ωarag < 1.5—a critical threshold for severe biological stress—were predominantly found in the nearshore areas and in the southwestern offshore bottom waters. Persistent seasonal acidification was observed across the study area. While seawater temperature played an important role in seasonal Ωarag variation, its effect was masked in the nearshore zones by river-diluted water inputs, especially in summer, and in offshore bottom waters by community respiration during summer and autumn. These mechanistic insights clarify key drivers of coastal acidification and provide a scientific basis for developing targeted strategies to detect acidification trends and ecosystem responses in anthropogenically impacted coastal regions.
Continue reading ‘Seasonal variations and key controls on seawater aragonite saturation state in the Northern Yellow Sea, China’Coulometric readout of ion-selective electrodes for an aquatic pH probe
Published 17 March 2026 Science ClosedTags: chemistry, field, Mediterranean, methods
Ion-selective electrodes are widely used for the detection of ions in aqueous solutions such as natural waters. Their origin traces back to 1909 with the invention of the pH glass electrode. Nowadays, routine pH measurements are still performed by potentiometric measurements with glass electrodes. The phase-boundary potential difference at the glass membrane-sample interface, measured against a reference electrode, relates to solution pH following the Nernst equation. While being user-friendly, they suffer from multiple drawbacks. Firstly, their sensitivity is intrinsically dictated by the Nernst equation and is limited to 59.2 mV/pH at 25 °C. This might not be sufficient for applications where high precision pH sensing is required, such as ocean acidification monitoring. Secondly, a Nernstian response can only be obtained if all the other potential differences in the overall electrochemical cell are constant over the whole experimental procedure. This is not the case when, for example, the temperature or the ionic strength of the sample change during the measurement routine. The former influences the glass electrode itself, while the latter rather affects the reference electrode via liquid junction potential variations.
This thesis presents enhancements to the potentiometric experimental setup for pH sensing with glass or polymeric membrane pH electrodes, achieved through the integration of electronic components, chemical symmetry and open liquid junctions. A dynamic electrochemical readout called constant potential coulometry is explored for in situ pH sensing in coastal waters by implementation in a submersible probe deployed in the Krka River estuary in April 2025.
Continue reading ‘Coulometric readout of ion-selective electrodes for an aquatic pH probe’Environmental controls and nonlinear responses of the diatom-dinoflagellate ratio in Jiaozhou Bay
Published 13 March 2026 Science ClosedTags: abundance, biological response, BRcommunity, chemistry, community composition, field, North Pacific, otherprocess, phytoplankton
Highlights
- Dia/dino abundance, biomass, and diversity ratios exhibited similar temporal patterns;
- All ratios showed considerable heterogeneity without a consistent distributional trend;
- Dia/dino ratios responded distinctly to DO, nutrients, and their interactions;
- Shifting seawater properties exerted large influence on diatom-dinoflagellate dynamics.
Abstract
Diatoms and dinoflagellates are widely recognized as key indicators of marine ecosystem status and play central roles in ecosystem functioning and biogeochemical cycling. Yet how these two major phytoplankton groups adjust to changing coastal environments, and whether such adjustments occur coherently in different ecological dimensions, remains poorly constrained. Hence, we studied the temporal and spatial dynamics of diatom-dinoflagellate (dia/dino) ratios in Jiaozhou Bay during 2021 and 2024, integrating abundance-, carbon biomass-, diversity-, and richness-based metrics. Although abundance, biomass, and diversity ratios exhibited broadly similar temporal trajectories, the richness ratio displayed an opposite pattern, highlighting a decoupling between numerical dominance and species composition. Spatially, all four ratios exhibited significant heterogeneity, without a consistent nearshore-offshore gradient, reflecting complex local regulation. Correlation analyses revealed distinct controls on dia/dino ratios. The abundance ratio increased under conditions of elevated dissolved inorganic nitrogen (DIN) and reduced dissolved oxygen (DO), whereas the diversity ratio was associated with high DIN and low dissolved inorganic phosphorus (DIP). In contrast, the carbon biomass ratio was primarily linked to reduced DO and lower pH, while the richness ratio responded most strongly to the combined influence of low DO and elevated DIP. These contrasting responses indicated that dia/dino ratios captured different facets of phytoplankton community reorganization rather than reflecting a single environmental driver. Overall, our results suggested that the balance between diatoms and dinoflagellates in Jiaozhou Bay emerged from the coupled and nonlinear interactions among nutrient availability and oxygen dynamics. This study highlighted the dia/dino balance as an integrative indicator of coastal ecosystem condition and implied the importance of considering multiple ecological dimensions when assessing phytoplankton responses to ongoing eutrophication and environmental change.
Continue reading ‘Environmental controls and nonlinear responses of the diatom-dinoflagellate ratio in Jiaozhou Bay’Trophic status and climatic stressors in the shallow coral reefs of the Cuban marine shelf
Published 12 March 2026 Science ClosedTags: chemistry, field, North Atlantic
The “Bojeo a Cuba” expedition (summer 2023) provided a synoptic, national-scale snapshot of oceanographic conditions around Cuba’s shallow coral reefs during a regional marine heatwave. At 66 sites across six regions, we evaluated key climatic stressors (sea surface temperature, pH, alkalinity) and trophic status indicators. Satellite-derived SST during each site’s sampling week revealed significantly warmer waters on the southern shelf (mean = 30.93 °C) than the northern shelf (mean = 29.21 °C, P < 0.01). In situ SST was consistently high (mean = 30.52 °C), documenting the heatwave’s intensity. pH (mean = 8.12) and total alkalinity (mean = 2343 µmol kg⁻¹) indicated a currently balanced carbonate system. Concentrations of dissolved inorganic nitrogen and phosphorus were below our methods’ quantification limits (1.61 µmol L⁻¹ for P-PO₄³⁻), while chlorophyll-a (mean = 0.04 µg L⁻¹) consistently classified waters as oligotrophic. This study establishes a critical summer baseline, confirming oligotrophic conditions while documenting the severity of thermal stress during the 2023 heatwave—the most immediate and uniform threat to Cuban reefs. Our findings underscore the vulnerability of these ecosystems to extreme warming events within the context of long-term Caribbean warming trends.
Continue reading ‘Trophic status and climatic stressors in the shallow coral reefs of the Cuban marine shelf’Ocean acidification at the crossroads I: harmonizing unpurified and purified meta-cresol purple spectrophotometric pHT measurements based on absorbance data
Published 11 March 2026 Science ClosedTags: chemistry, field, methods
Consistent monitoring of seawater spectrophotometric pH on the total hydrogen ion scale (pHT) has been questioned by an evolving method, with changes in parameterization and the purity of the meta-cresol purple (mCP). Using real seawater samples, we demonstrate that spectrophotometric pHT measurements obtained with unpurified (UNPUR) and purified (PUR) mCP can be harmonized to within 0.003 pH units, the climate-goal threshold. This agreement is only achieved when mCP impurities at 434 nm are quantified for both the UNPUR and PUR mCP, assuming no impurities affect 545 nm absorbances, and impurity-corrected absorbance data at 434 nm are used in the same parameterization to calculate pHT. We applied this approach to a ship-based pHT time series transitioning from UNPUR to PUR mCP measurements. Our results show that previous claims suggesting that UNPUR mCP underestimates pHT in the upper pH range are misleading, as they were based on the inappropriate use of absorbances obtained with UNPUR mCP with a parameterization developed for PUR mCP. In fact, our data reveal better agreement between UNPUR and PUR pHT in the upper pH range of seawater, while UNPUR mCP tends to overestimate pHT in the lower pH range. These findings highlight the urgent need for the global chemical oceanography community to establish a spectrophotometric pHT method with full traceability to the International System of Units (SI), along with affordable and distributed certified reference materials and characterized purified mCP. This work supports the need for harmonization efforts to ensure the reliability of pHT data in global synthesis products.
Continue reading ‘Ocean acidification at the crossroads I: harmonizing unpurified and purified meta-cresol purple spectrophotometric pHT measurements based on absorbance data’Two decades of skeletal density decline in Pocillopora spp. corals in the Mexican Pacific Ocean: insight into a tropical eastern Pacific acidification scenario?
Published 10 March 2026 Science ClosedTags: biological response, chemistry, corals, field, morphology, North Pacific
Corals demonstrate vulnerability to environmental changes, exhibiting the capacity to substantially modify coral calcification. In this study, we estimated declines in the density of Pocillopora coral species in the Mexican Pacific. The samples utilized in this study encompass both recently collected corals and those stored in Mexican repositories collected in the northeastern and southern Mexican Pacific regions. Density estimates indicate a 28.6% decline in coral density over the past 23 years (−0.0227 g CaCO3 cm-3 y-1) in the southern Mexican Pacific, while at the entrance to the Gulf of California, density has decreased by 15.4% over the past 20 years (−0.017 g CaCO3 cm-3 y-1). A comprehensive evaluation of environmental data reveals that the observed decline in Pocillopora skeletal density in Mexican Pacific reefs is concomitant with decreases in Ωar and pH, and an increase in ocean temperature on a substantial regional scale. When considered in conjunction with the previously documented reductions in coral growth of Pocillopora spp. skeletons in the eastern Tropical Pacific, our findings indicate a potential decline in CaCO3 production within the region’s reef systems. The results of this study underscore the significance of generating long-term series of coral growth parameters for relevant reef-building species and the carbonate system in key and representative coastal areas, particularly those that are already challenging for coral survival and reef maintenance.
Continue reading ‘Two decades of skeletal density decline in Pocillopora spp. corals in the Mexican Pacific Ocean: insight into a tropical eastern Pacific acidification scenario?’Consequences of rising atmospheric CO₂ on ocean acidification and dissolved carbon cycling: a systematic review
Published 10 March 2026 Science ClosedTags: chemistry, review
Increasing atmospheric CO2 and temperature diminish ocean pH and raise the amounts of dissolved inorganic and organic carbons, causing wide-ranging shifts in marine water carbon chemistry and predicting the impacts on long-term ecosystems. This review aimed to determine the ocean chemistry and spatial variation of CO2 at a global scale, as well as to predict the influences of anthropogenic and natural changes on marine ecosystems. The literature has demonstrated that the southern polar oceans, Antarctica, and any coastal zone are predominantly susceptible to marine acidification and the dissolved carbon cycle. Based on 355 studies conducted over the last 30 years, this investigation found that marine acidification and the dissolved cycle are complex and poorly understood phenomena. These two facts and climate change are very interrelated, and the potential of these threats is very spatial, seasonal, stratified, and complex also. It was found that the atmospheric CO2 has increased by about 50% since preindustrial times and excess CO2 raise the seawater acidity through some equilibrium reactions in aqueous medium. The study observed that over the past half-century, the marine surface water acidity has risen by 30%, and predicted that by 2100, it will increase to 150. Moreover, this study critically reviewed the actual rules of marine dissolved organic and inorganic carbon on the global carbon cycle and marine acidification and vice versa. Such a major change in ocean chemistry will already have wide consequences for marine life and ocean ecosystems.
Continue reading ‘Consequences of rising atmospheric CO₂ on ocean acidification and dissolved carbon cycling: a systematic review’Introducing the first ocean carbonate chemistry products hub
Published 6 March 2026 Press releases ClosedTags: chemistry, review
The ocean plays a critical role in stabilizing Earth’s climate. As the planet’s largest active carbon sink, it absorbs about 25% of global carbon dioxide emissions and roughly 90% of the excess heat generated by those emissions. This critical role helps regulate the planet’s climate, but comes at a cost.
“As carbon dioxide enters the ocean, some of it reacts with water to form a weak acid that increases the acidity of the ocean and alters the natural chemical balance of seawater,” said Liqing Jiang, a research scientist at Earth System Science Interdisciplinary Center and NOAA’s National Centers for Environmental Information (NCEI), “As more carbon dioxide enters the ocean, seawater becomes increasingly acidic. In fact, ocean acidity has risen by about 30% since the beginning of the Industrial Revolution.”
A more acidic ocean reduces carbonate ions, which alongside calcium, is a building block for ocean creatures that form skeletons and shells like coral reefs and oysters. Higher acidity reduces coral larval survival, weakens reef structures, and increases ecosystem vulnerability to storms and bleaching. These creatures function as key marine health indicators, and their decline threatens the entire marine ecosystem.
However, the ocean is vast, and the interconnected physical, chemical, and biological processes require scientists like Jiang to integrate many different types of data to piece together the full picture of how ocean chemistry is changing.
To support researchers navigating this complexity, Jiang led a team of international researchers to publish a comprehensive review of over 60 major ocean carbonate chemistry data products. The catalog brings together a wide range of global datasets, including historical time series, model outputs, and aggregated products spanning multiple time periods, making it one of the most comprehensive compilations of ocean carbonate chemistry data products to date.
Jiang’s goal is to present all available ocean carbonate chemistry products. He continues to collect datasets through the catalog to widen the library of data.
“My hope is that researchers will use these products to better understand changes in ocean carbonate chemistry, to improve model inputs for more accurate projections of future ocean conditions, and to support more robust assessments of marine ecosystem vulnerability,” said Jiang.
The paper detailing this work, “Synthesis of data products for ocean carbonate chemistry”, has been published in Earth System Science Data. The full data product catalog is publicly accessible at the following link.
Continue reading ‘Introducing the first ocean carbonate chemistry products hub’Glacial meltwater impacts marine carbonate chemistry on Iceland’s continental shelf
Published 6 March 2026 Science ClosedTags: chemistry, field, North Atlantic
Increased meltwater runoff from glaciers may drive localized ocean acidification and impact carbon dioxide (CO2) uptake in the coastal ocean. However, the paucity of carbonate system observations from continental shelves receiving inputs from glaciers limits our understanding of cryosphere‐ocean connectivity. Here, we contrast meltwater impacts on seawater carbonate chemistry and stable isotopes (δ13C‐DIC) off marine‐ and land‐terminating glacier outflows off Iceland. On the shelf outside a marine‐terminating glacier, glacial meltwater reduced the seawater buffer capacity of receiving surface waters through dilution of total alkalinity, and increased CO2 uptake through salinity‐driven drawdown of pCO2. Primary production acted as a counterbalance to the lowered [TA‐DIC]. On the shelf area receiving meltwater from large glacial river deltas, CO2 uptake was almost halved and the saturation state of aragonite was 0.2 units lower than on the marine‐terminating glacier shelf. Reduced net autotrophy due to higher turbidity and upwelling of low‐pH deep waters off the delta‐dominated shelf likely explain those differences. The diverging carbonate dynamics on the two shelves build on previous observations that land‐terminating glaciers can reduce the buffer capacity as well as CO2 uptake potential of nearshore surface waters in comparison to marine‐terminating glaciers. The future retreat of many marine‐terminating glaciers onto land is likely to modify how meltwater will impact coastal seawater carbonate chemistry.
Continue reading ‘Glacial meltwater impacts marine carbonate chemistry on Iceland’s continental shelf’Applying omics techniques to examine microscopic life fueling Gulf region ecosystems
Published 6 March 2026 Press releases ClosedTags: biological response, chemistry, field, North Atlantic
Scientists at NOAA’s Atlantic Oceanographic & Meteorological Lab and the Northern Gulf Institute applied omics techniques to provide the first basin-scale assessment of the microbial communities at the base of marine ecosystems across the Gulf region. The new study from Dr. Luke Thompson’s group, conducted by Dr. Sean Anderson and co-authors, is the largest environmental DNA (eDNA) or microbiome survey of the Gulf of America ever performed.
Scientists collected environmental DNA (eDNA) – genetic material from whole microbes or shed by marine life into the environment – during the 2021 Gulf and Ocean Monitoring Ecosystems and Carbon Cruise (GOMECC). These samples unlock crucial new insights into the microscopic life across an entire basin – from nearshore coastal ecosystems out to the open Gulf. By analyzing the microbial communities throughout the water column, we can better understand how they are being impacted by changing environmental conditions.
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Changes in the composition of these microbial communities in any given region has cascading effects, influencing the biodiversity and feasibility of commercially viable species to survive and flourish in a specific region. Understanding how microbial diversity throughout the water column varies with changing conditions – changes in salinity, temperature, nutrient levels – could unlock key insights and provide early indicators of how entire ecosystems will be impacted by exacerbated environmental stressors, including ocean acidification.
Continue reading ‘Applying omics techniques to examine microscopic life fueling Gulf region ecosystems ‘
