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’Posts Tagged 'biogeochemistry'
Quantifying the role of land-based inputs on coastal ocean acidification from a tropical semi-arid region
Published 15 April 2026 Science Leave a CommentTags: biogeochemistry, chemistry, Indian
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
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’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’Enhanced carbon burial in seagrass meadows under ocean acidification revealed by carbon dioxide vents
Published 16 March 2026 Science ClosedTags: algae, biogeochemistry, biological response, field, Mediterranean, phanerogams, vents
Seagrass meadows are natural carbon sinks, yet the effect of ocean acidification on their carbon burial capacity remains poorly understood. Here we investigated natural carbon dioxide vents in Ischia, Italy to assess how seawater pH influences carbon burial in an area dominated by the seagrass Posidonia oceanica. Organic carbon burial rates (mean ± standard error) between 1954 – 2021 were low under ambient conditions (1.5 ± 0.5 g m-2 yr-1) but increased sharply under acidified conditions (7 ± 1 g m-2 yr-1), reaching sevenfold higher values under extreme acidification (10 ± 3 g m-2 yr-1). Stable isotopes suggest that these patterns reflect changes in the relative contribution of seagrass, macroalgae, and epiphytes to buried carbon. These findings reveal that ocean acidification can substantially alter coastal carbon cycling, potentially through shifts in community composition, with important implications for understanding past and future feedbacks between seagrass ecosystems and the marine carbon cycle.
Continue reading ‘Enhanced carbon burial in seagrass meadows under ocean acidification revealed by carbon dioxide vents’Neglecting organic alkalinity introduces greater error than assuming boron to salinity ratios in Arctic sea ice brine carbonate system calculations
Published 3 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, methods
While total alkalinity (AT) is traditionally attributed to dissolved inorganic constituents, dissolved organic matter (DOM) can significantly contribute to AT as organic alkalinity (OrgAlk), introducing errors in calculated carbonate parameters, such as the CaCO3 saturation state (Ω) and partial pressure of CO2 (pCO2). This study presents measurements of OrgAlk in the Arctic Ocean sea ice system and assesses its influence on carbonate speciation, with OrgAlk contributing 0.1–1.0% to AT. Sea ice brine exhibited elevated DOM and OrgAlk, with an OrgAlk/DOC ratio of 0.13 ± 0.06 µmol kg− 1 µM− 1, consistent with global ocean values. Correcting AT for OrgAlk increased computed pCO2 up to 84 µatm and decreased Ω ≤ 0.2 for aragonite and ≤ 0.3 for calcite compared to un-adjusted values. Elevated brine pCO2 suggests that conventional estimates of Arctic sea ice CO2 uptake may be overestimated when AT is used as an input parameter, particularly in spring as OrgAlk is released. The omission of OrgAlk contributed greater errors to calculated carbonate parameters than the differences in boron from using direct measurements versus salinity based ratios, highlighting the necessity of accounting for even minor OrgAlk to refine predictions of surface pCO2, net air-sea CO2 flux, and the fate of CaCO3 minerals.
Continue reading ‘Neglecting organic alkalinity introduces greater error than assuming boron to salinity ratios in Arctic sea ice brine carbonate system calculations’Ocean acidification and changes in biological production in the western subarctic region of the North Pacific over the quarter century, 1999–2023
Published 2 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, North Pacific
Changes in the physical and biogeochemical conditions of the ocean over time can affect marine ecosystems. In this study, we use biogeochemical observational data for the past 25 years (1999–2023) to investigate ocean acidification and changes in biological production at site K2 (47˚ N, 160˚ E) in the western subarctic region of the North Pacific Ocean. During this period, satellite-derived sea surface temperatures increased at a rate of 0.056 °C yr–1, while the surface mixed-layer salinity decreased by 0.004 yr−1. As a result of the oceanic uptake of anthropogenic CO2 from the atmosphere, the deseasonalized annual mean surface mixed-layer pH and saturation states of calcium carbonate minerals of calcite and aragonite decreased at rates of 0.0013 ± 0.0004, 0.007 ± 0.003, and 0.004 ± 0.002 yr−1, respectively. These rates are consistent with those calculated for winter. Under these acidification conditions, no significant trends were observed in either the annual mean or winter concentrations of nutrients (phosphate, nitrate, and silicate), or in total alkalinity in the surface mixed layer. However, the decadal trends in nutrient concentrations show a significant increase in May and decrease in July. Net community production (NCP), which is an index of biological production, was estimated from differences in nutrient concentrations between winter and May or July. This analysis revealed significant decreasing trends in NCP from winter to May, followed by increasing trends from winter to July. The stoichiometric molar ratio of Si associated with the July NCP increase (P:N:Si = 1:15:55) is higher than the previously reported ratio (1:16:40). A significant decreasing trend in satellite-derived photosynthetically active radiation (PAR) was observed in May (0.20 ± 0.08 yr−1), which may be linked to reduced biological production during that month. This decrease may be offset by increased production in summer that is likely due to a shift in the timing of the diatom bloom. These findings highlight the effects of long-term changes of potential drivers of both atmospheric and deep oceanic origin on oceanic biological production.
Continue reading ‘Ocean acidification and changes in biological production in the western subarctic region of the North Pacific over the quarter century, 1999–2023’Wind control of the interannual ocean‐biogeochemical variability in the South Atlantic Bight
Published 23 February 2026 Science ClosedTags: biogeochemistry, chemistry, modeling, North Atlantic, regionalmodeling
Abstract
In the South Atlantic Bight (SAB), changes in the Gulf Stream (GS), particularly its strength and proximity to the coast, are thought to be primary factors determining the shelf-break upwelling rate. However, it is still not entirely clear if and to what extent those factors influence cross-shelf nutrient fluxes and shape the ocean biogeochemistry at interannual and longer timescales. Here, we use a high-resolution regional ocean-biogeochemical model and an ocean reanalysis product (1993–2022), along with a satellite-derived chlorophyll data set (1997–2022), to investigate the interannual ocean-biogeochemical variability in the SAB. Regional model outputs suggest that year-to-year changes in phytoplankton production are indeed largely driven by upwelling of cold and nutrient-rich water to the shelf-break. The upwelling variability, reflected in bottom temperature and vertically integrated production patterns, is strongly linked to surface velocity changes in the GS near the shelf break, but weakly related to the depth-integrated GS transport. The GS’s velocity changes, and the temperature and production anomalies, are well correlated to the alongshore wind stress, suggesting that local wind is the leading driver of the shelf-break upwelling variability at interannual timescales. Those relationships are also supported by circulation patterns from ocean reanalysis and satellite chlorophyll anomalies. Finally, examining the simulated shelf-slope interchanges in the carbonate system, we find that shelf-break upwelling significantly increases bottom acidification, a pattern linked to the low carbonate concentration in the slope waters. This study thus provides new insight for understanding and predicting GS and winds impacts on biogeochemical patterns from the SAB.
Plain Language Summary
The ocean current known as the Gulf Stream (GS) can induce upwelling of subsurface cold and nutrient-rich waters into the coastal margin of the South Atlantic Bight, influencing coastal temperature and phytoplankton growth. Previous studies suggested that the GS strength and its proximity to the coast are key factors determining the intensity of upwelling events. However, the degree to which these factors impact the year-to-year changes in phytoplankton production and other ocean properties remains unclear. Here we use numerical models of ocean currents and seawater biogeochemistry, as well as chlorophyll records derived from satellite measurements, to investigate that impact. The patterns showed that interannual changes in coastal temperature, phytoplankton production, water acidity, and dissolved oxygen are strongly modulated by upwelling changes in the outer edge of the continental margin (about 70 m depth in this region). This interannual upwelling variability is tightly coupled to variations in the surface alongshore GS velocity close to that outer edge, which is modulated by alongshore wind variability. Our study characterizes GS patterns associated with high and low productivity years, and highlights the role of surface wind as ultimate driver of the interannual upwelling variability in the South Atlantic Bight.
Key Points
- A regional ocean model is used to investigate interannual variability of ocean-biogeochemistry in the South Atlantic Bight
- Year-to-year changes in primary production, chlorophyll, and carbonate system patterns respond to shelf-break upwelling anomalies
- Shelf-break upwelling is closely linked to the Gulf Stream velocity near the shelf break, modulated by alongshore wind variability
A biogeochemical perspective on acidification and buffering capacity in the Piscataqua Estuary
Published 18 February 2026 Science ClosedTags: biogeochemistry, chemistry, field, laboratory, North Atlantic, sediment
Coastal acidification is influenced not only by rising atmospheric CO2 and river-ocean mixing, but also by metabolic processes that alter seawater carbonate chemistry and buffering capacity. This study examines how sedimentary biogeochemical processes contribute to carbonate system variability in the Piscataqua Estuary, a tidally dynamic channel connecting Great Bay to the Gulf of Maine. The biogeochemical processes considered include sedimentary aerobic respiration, denitrification, sulfate reduction, and carbonate dissolution or precipitation. Two incubation experiments were conducted in September and October of 2024 at the University of New Hampshire’s Coastal Marine Laboratory (CML) to quantify changes in pH, dissolved inorganic carbon (DIC), and total alkalinity (TA) in the overlying water arising from sediment-water biogeochemical exchange. Sediment cores were collected to be paired with overlying water from slack low and slack high tides during each month. Across both experiments, sediment cores consistently exhibited greater acidification and larger shifts in DIC and TA concentrations compared to water-only cores, indicating strong sedimentary biogeochemical influence. Among the processes considered, sulfate reduction is likely the most influential driver of carbonate system variability, contributing to increases in both DIC and TA. Linking experimental results to in-situ measurements at CML revealed that variability observed over individual ebb or flood tides primarily reflected processes associated with tidal advection (ie, river-ocean mixing and water-column biogeochemical activity). However, when evaluating net changes over both tidal transitions (ebb and flood), contributions from sedimentary biogeochemical processes were comparable in magnitude to those of the other processes during September and October. Sedimentary biogeochemical processes also appear to exert more consistent contributions to DIC and TA than water-column biogeochemical processes. Together, these findings demonstrate that sedimentary biogeochemical processes play a major role in regulating carbonate system variability in the Piscataqua Estuary. This study underscores the importance of examining carbonate system variability across multiple timescales to obtain a more comprehensive understanding of estuarine carbonate dynamics. Additional experimental work is needed to further resolve the influence of metabolic processes on coastal carbonate systems under changing environmental conditions.
Continue reading ‘A biogeochemical perspective on acidification and buffering capacity in the Piscataqua Estuary’Acute microbial and nutrient responses to elevated temperature and pCO2: a coastal UK microcosm study
Published 13 February 2026 Science ClosedTags: abundance, biogeochemistry, community composition, laboratory, multiple factors, North Atlantic, nutrients, otherprocess, phytoplankton, temperature
The coastal ocean’s ecosystem resilience is consistently hampered by the compounding impacts of projected climate change and anthropogenic perturbation. In this microcosm study, we investigated how elevated temperature and pCO2, together with episodic nutrient pollution and a short-term marine heatwave, affect the nano- and picoplanktonic community of primary producers and subsequent changes in coastal biogeochemistry. Our study demonstrates that future elevated temperature and pCO2 conditions impact the planktonic community, first by a ∼ 50 % decreased autotrophic abundance, and second by a shift from larger eukaryotic to smaller cells. When combined with a heatwave, total primary producers experienced an additional 37–38 % decrease, indicative of a negative synergistic effect beyond either stressor alone. Picoeukaryotes were particularly sensitive, declining by 44–50 %. Short-term nutrient pollution under ambient conditions induced a 41 % increase in cell abundance, but failed to stimulate biomass under elevated temperature and pCO2, and instead led to altered organic matter dynamics, including significantly lower carbon fixation. These findings emphasize the need for further evaluation of multi-stressor interactions to better understand biogeochemical vulnerability, nutrient retention, and ecological functioning in coastal ecosystems undergoing rapid climatic and anthropogenic change.
Continue reading ‘Acute microbial and nutrient responses to elevated temperature and pCO2: a coastal UK microcosm study’Microbial community dynamics over large spatial and environmental gradients in a subtropical ocean basin
Published 9 February 2026 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, community composition, field, molecular biology, North Atlantic, otherprocess, prokaryotes, protists
Microbes are fundamental to ocean ecosystem function, yet they remain understudied across broad spatial and environmental scales in dynamic regions like the Gulf of America/Gulf of Mexico (GOM). We employed DNA metabarcoding to characterize prokaryotes (16S V4–V5) and protists (18S V9) across 51 stations, spanning 16 inshore–offshore transects and three depths. Cluster analysis revealed three clusters corresponding to depth zones that integrated vertical and horizontal sampling: photic zone (inshore near surface–bottom and offshore surface), deep chlorophyll maximum (offshore), and aphotic zone (offshore near bottom). We applied group-specific generalized additive models (GAMs) to log-transformed abundance data of major taxa in the photic zone, identifying key environmental factors that explained 42%–82% of the variation in abundance. SAR11 and SAR86 were positively associated with temperature and dissolved inorganic carbon, while cyanobacterial genera (Prochlorococcus and Synechococcus) were differently impacted by nutrients, salinity, and pH in ways that often followed their expected ecological niches. Representatives of protist parasites (Syndiniales) and grazers (Sagenista) showed group-specific nonlinear associations with salinity, oxygen, nutrients, and temperature. Using GAMs, we expanded the spatial resolution of DNA sampling and predicted surface log abundances at 84 cruise sites lacking amplicon data. Indicator analysis was performed with sequence-level data, revealing several protists that were indicative of more acidic waters and the absence of any significant prokaryote indicators. Our results provide the first basin-scale survey of microbes in the GOM and highlight the need for coordinated omics and environmental sampling to improve predictions of microbial responses to changing conditions.
Continue reading ‘Microbial community dynamics over large spatial and environmental gradients in a subtropical ocean basin’Y/Ho ratios in marine sediments unveil Neoproterozoic ocean acidification
Published 28 January 2026 Science ClosedTags: biogeochemistry, chemistry, field, methods, paleo
Understanding Precambrian seawater pH is critical for unraveling Earth’s early marine environments and biospheric evolution. Yet, quantitative constraints remain elusive due to the lack of robust proxies. Here, we demonstrate that yttrium/holmium (Y/Ho) fractionation during adsorption onto marine sediments serves as a novel and reliable pH proxy. Experimental results reveal that Y/Ho fractionation in ferruginous sediments follows a pH-dependent power-law relationship, while in argillaceous sediments, it is jointly controlled by pH and salinity at low salinities (< 29‰) but stabilizes (KdY/Ho ≈ 0.4) at higher salinities (≥ 29‰). Temperature exerts a negligible influence, ensuring broad applicability across geological timescales. Leveraging these relationships, we develop a quantitative method to reconstruct paleo-seawater pH using Y/Ho ratios from coexisting ferruginous and argillaceous sediments. Validation against modern and Phanerozoic records confirms the proxy’s accuracy (e.g., pH 8.21 ± 0.22 for modern Pacific sediments). Application to Neoproterozoic meta-pelites and iron formations reveals prolonged oceanic acidification (pH 5.9–6.4), deviating from previous model-based neutral-to-alkaline estimates. This acidic state, likely sustained by CO2 outgassing from carbonatite-alkaline volcanism during Rodinia’s breakup, challenges conventional views of Precambrian ocean chemistry. Our findings provide a transformative tool for probing early Earth’s environmental dynamics and highlight the interplay between tectonics, magmatism, and marine pH evolution.
Continue reading ‘Y/Ho ratios in marine sediments unveil Neoproterozoic ocean acidification’Coastal eutrophication and freshwater inputs drive acidification in the Indian River Lagoon, Florida
Published 22 January 2026 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
Highlights
- First quantification of acidification throughout the IRL using Ωarag.
- A positive relationship was found between Ωarag and salinity.
- Ωarag had a negative relationship with dissolved nutrients.
- Nutrients, algal blooms, and freshwater are drivers of acidification in the IRL.
- Ωarag is important to understand eutrophication in estuaries.
Abstract
The additive effects of eutrophication and acidification in coastal environments have a wide range of implications for the health of organisms and ecosystems. In the eutrophic waters of the Indian River Lagoon (IRL), FL, USA, decreases in overall shellfish size have been reported, which may be related to coastal acidification. To better understand the relationship between acidification and eutrophication in the IRL, environmental parameters, dissolved nutrients, and aragonite saturation state (Ωarag) were monitored along the entire IRL in the 2016–2017 wet and dry seasons. Additionally, three sites in the central IRL were sampled approximately weekly from June 2016–June 2017 to observe temporal variability. For the IRL-wide survey, northern sites with higher dissolved nutrient concentrations had lower Ωarag due to nutrient pollution and harmful algal blooms, while southern sites with lower salinity had lower Ωarag related to freshwater inputs (i.e., discharges and rainfall). In the time series sampling, there was a positive correlation between Ωarag with salinity and negative correlations with dissolved nutrient concentrations. This work suggests that freshwater inputs and associated dissolved nutrients and organics have implications for acidification in the IRL, which will be important considerations for restoration efforts in the IRL and beyond.
Continue reading ‘Coastal eutrophication and freshwater inputs drive acidification in the Indian River Lagoon, Florida’Spatial dynamics of aragonite saturation state and blue carbon stocks in seagrass meadows of the Palk Bay, Southeast Coast of India
Published 19 January 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, community composition, Indian, otherprocess, phanerogams
Seagrass meadows are increasingly recognized for their role in mitigating climate change through blue carbon sequestration and their influence on local carbonate chemistry. This study investigates the spatial variability of aragonite saturation state (Ωarag) and assesses the blue carbon storage potential of seagrass meadows along the Palk Bay, Southeast Coast of India. Subsurface water samples were collected across multiple seagrass-dominated stations between May and June 2024. Key seawater carbonate system parameters, including pH, temperature, total alkalinity (TA), and salinity, were measured to calculate Ωarag using CO2SYS software. Sediment cores were analyzed for organic carbon content and bulk density to estimate carbon stock. Results revealed significant spatial variation in Ωarag, influenced by seagrass density, species composition (Cymodocea serrulata and C. rotundata), and hydrodynamic conditions. Stations with dense C. serrulata beds showed elevated Ωarag values, suggesting local amelioration of acidification stress. The mean carbon stock was estimated at 1.97 Mg C/ha−1, with higher values in more mature (> 60% cover) and dense seagrass patches. These findings highlight the dual ecological function of seagrass meadows in enhancing local carbonate saturation and functioning as effective carbon storage systems, underlining their significance in coastal ecosystem-based climate mitigation strategies.
Continue reading ‘Spatial dynamics of aragonite saturation state and blue carbon stocks in seagrass meadows of the Palk Bay, Southeast Coast of India’Seasonal and regional dynamics of carbonate chemistry and buffering capacity in contrasting marine systems: the Northeastern Mediterranean and the Sea of Marmara
Published 12 January 2026 Science ClosedTags: biogeochemistry, chemistry, field, Mediterranean
This thesis investigates seasonal and spatial variability in carbonate system dynamics and buffering capacity across two contrasting semi enclosed Turkish seas: the oligotrophic Northeastern Mediterranean and the eutrophic Sea of Marmara. Data were collected in winter and summer on research cruises conducted in 2022–2023. High quality multi-index measurements included total alkalinity (TA), nutrients, and spectrophotometric pH. Derived carbonate system parameters were calculated with PyCO2SYS, and a standardized, layer-based approach was applied to reflect regional hydrography and vertical structure. The Sea of Marmara showed high TA, often above 2700 μmol kg⁻¹, together with elevated dissolved inorganic carbon (DIC) below the halocline due to respiration and weak ventilation. Revelle factors were high, vertical gradients in pH and aragonite saturation state were strong, and hypoxia was present in sub halocline and deep waters. In the Northeastern Mediterranean, TA and DIC were lower and more stable. Revelle factors were lower, and buffering was stronger in surface and intermediate layers, with only modest sensitivity increases at depth. Advanced indices added diagnostic value beyond the Revelle factor. In the Sea of Marmara, βDIC and γDIC were highest below the halocline, identifying where small DIC additions most strongly raise the partial pressure of carbon dioxide (pCO₂) and lower pH. γAlk and ωAlk indicated greater benefit of marginal TA gains at depth. ωDIC isolated saturation state sensitivity to carbon loading in respiration dominated layers. In the Northeastern Mediterranean, the Revelle factor captured first order seasonal shifts in well mixed winter layers, while the advanced indices flagged narrow coastal and subsurface windows of rising sensitivity. These results provide the first multi seasonal, multi-index baseline for Turkish seas. They show that eutrophication, stratification, and ventilation control local acidification risk and that advanced buffer indices sharpen process attribution. The study supports monitoring that couples carbonate chemistry with oxygen and nutrients and guides management toward nutrient reduction and protection of sub halocline habitats where buffering is weakest.
Continue reading ‘Seasonal and regional dynamics of carbonate chemistry and buffering capacity in contrasting marine systems: the Northeastern Mediterranean and the Sea of Marmara’Ocean acidification in Massachusetts bay and Boston harbor: insights from a 1-D modeling approach
Published 8 January 2026 Science ClosedTags: biogeochemistry, chemistry, modeling, North Atlantic, regionalmodeling
Highlights
- NeBEM, an ERSEM-based biogeochemical and ecosystem model, is established for the U.S. Northeast.
- NeBEM provides process-based insights into carbonate system variability beyond the capability of empirical data-fitting methods.
- Biological processes strongly influence TA and DIC variability in outer Massachusetts Bay.
Abstract
Massachusetts Bay (MB)/Boston Harbor (BH) in the northeastern United States has reduced buffering capability, making it highly vulnerable to ocean acidification (OA). We applied the U.S. Northeast Biogeochemistry and Ecosystem Model (NeBEM), integrating the unstructured grid, Finite Volume Community Ocean Model with a modified European Regional Seas Ecosystem Model (ERSEM), to investigate seasonal and interannual OA variability through one-dimensional (1-D) experiments. Objectives were to (a) evaluate model skill in reproducing observed seasonal cycles of OA-related variables, particularly pCO2 and pH, in shallow and deep regions, and (b) assess sensitivity to parameterizations and algorithms for calculating dissolved inorganic carbon (DIC), total alkalinity (TA), pCO2, and pH. The 1-D NeBEM reproduced variability of nutrients, dissolved oxygen, chlorophyll-a, pCO2, and pH at the deep outer bay site, where air-sea interactions dominate, but failed at the shallow inner bay site due to the absence of river discharge-driven advection. Of TA algorithms tested, the semi-diagnostic method best captured observed seasonal pCO2 variation, achieving the highest correlation and lowest root mean square error, although all methods performed similarly for pH. Comparisons with multi-linear regression methods showed that empirical models are highly sensitive to calibration set. Mechanistic analysis indicated that TA variability is mainly regulated by nitrification and net community production (NCP), while DIC variability is driven primarily by NCP. Atmospheric CO₂ loading was the first-order contributor to DIC change in magnitude. However, it has decreased in MB over the past two decades, in contrast to regional and global trends. Therefore, it is not a major driver of OA progression in this system.
Continue reading ‘Ocean acidification in Massachusetts bay and Boston harbor: insights from a 1-D modeling approach’Assessing the influence of ocean acidification on the deterioration of coral reefs in Sri Lanka
Published 1 January 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, Indian, review
Rising atmospheric CO2 levels have significantly increased ocean acidification (OA), endangering coral reefs, and nutrient (nitrate (NO3−), and phosphate (PO43−)) pollution also weakens the coral 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 Ω Ar 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. The NO3− concentrations of 2–5 µmol L− 1, from human activities, may intensify coral bleaching during heat stress. Results showed that SC (2.19±1.28 µmol L− 1) and WC (3.52±1.48 µmol L− 1) had NO3− above the permissible range, which may be due to waste discharge and high runoff. The significantly higher PO43− concentrations were reported in EC (0.35±0.07 µmol L− 1). Coral bleaching hotspot (HS) identification emphasizes how spatially distributed HS are from January to June. The OA risk assessment confirmed that climate change brought high risk to the coral reef ecosystems, which impact on the ecology and economy of Sri Lanka.
Continue reading ‘Assessing the influence of ocean acidification on the deterioration of coral reefs in Sri Lanka’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’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’
