Ocean acidification (OA) is one of the quietest yet most profound changes unfolding in our seas. Caused mainly by the ocean’s absorption of excess carbon dioxide from the atmosphere, it steadily lowers seawater pH and depletes carbonate ions — the essential building blocks for shells, skeletons, and coral reefs. These chemical shifts ripple through marine ecosystems, weakening coral structures, slowing the growth of shellfish, disrupting plankton communities, and ultimately destabilising the food webs that sustain biodiversity and human livelihoods. Although OA is recognised as a global problem, its effects are not uniform. Some regions, particularly the Indian Ocean and other tropical waters, remain poorly studied despite being home to rich biodiversity and millions of people whose lives depend on healthy coastal ecosystems. This paper focuses on OA as a “silent” driver of biodiversity loss and addresses two major gaps: the lack of strong policy and governance integration, and the scarcity of regional data for Indian and tropical waters. To explore how OA is framed in global agreements such as the United Nations Convention on the Law of the Sea (UNCLOS) and the Paris Agreement, and examine its treatment in India’s environmental laws, including the Environment (Protection) Act, Coastal Regulation Zone rules, and the Biological Diversity Act. While these frameworks provide important protections, none directly target OA or mandate systematic monitoring. The shortage of long-term, high-resolution data on pH and carbonate chemistry in Indian waters makes it difficult to gauge the scale of the threat or design locally relevant solutions. The lack of species-specific studies in this region adds further uncertainty to impact predictions. This is mainly upon doctrinal studies. This study calls for integrating OA into national marine policies, creating dedicated monitoring networks in the Indian Ocean, and fostering interdisciplinary research that links chemical changes to ecological shifts and community livelihoods. Closing these gaps is vital not only for protecting marine biodiversity but also for ensuring food security and economic stability for coastal populations.
Continue reading ‘Ocean acidification: the silent threat to marine biodiversity’Posts Tagged 'Indian'
Ocean acidification: the silent threat to marine biodiversity
Published 8 April 2026 Science Leave a CommentTags: Indian, policy, review
Effects of upwelling-driven acidification and deoxygenation on the dissolved inorganic carbon system over the southeastern Arabian Sea shelf
Published 8 April 2026 Science Leave a CommentTags: chemistry, field, Indian
Highlights
- Summer monsoon upwelling drives strong acidification and deoxygenation over the EAS shelf.
- Non-upwelling DIC and TAlk variability is largely governed by conservative water-mass mixing.
- Elevated nDIC35 during upwelling confirms DIC enrichment beyond salinity stratification alone.
- AOU-nDIC35 coupling indicates respiratory amplification of upwelled CO2-rich source waters.
- Reduced buffering and lower ΩCa–ΩAr increase seasonal chemical stress on shelf ecosystems.
Abstract
Repeated measurements of inorganic carbon system parameters over one year along two coastal transects (Kochi in the southern EAS and Mangalore in the central EAS) in the eastern Arabian Sea (EAS) reveal strong seasonal coupling between upwelling, deoxygenation, acidification, and inorganic carbon accumulation on the shelf. During the non-upwelling (oxic) period, the variability of dissolved inorganic carbon (DIC) concentrations and total alkalinity (TAlk) was governed predominantly by conservative water-mass mixing, particularly between low-salinity Bay of Bengal-derived waters and more saline Arabian Sea shelf waters, as demonstrated by the marked reduction in salinity normalised DIC (nDIC35) and TAlk (nTAlk35). In contrast, during the summer monsoon (June–September), coastal upwelling transported oxygen-poor, DIC-rich subsurface waters onto the shelf, leading to pronounced subsurface inorganic carbon enrichment, hypoxia, and acidification. Vertical profiles of nDIC35 showed that elevated inorganic carbon concentrations persisted even after removing salinity effects, increasing from ∼1950–2000 μmol kg−1 at the surface to >2100–2200 μmol kg−1 below ∼40 m. Nearshore surface waters during peak upwelling exhibited a strong offset between measured DIC and nDIC35, indicating localized freshwater dilution, but salinity-normalised values confirmed that the underlying carbon inventory remained high. Apparent oxygen utilisation (AOU) and nDIC35 were positively correlated, indicating that a substantial fraction of the residual DIC enrichment was associated with oxygen consumption, although this relationship reflects the combined imprint of DIC-rich upwelled source waters and subsequent microbial remineralisation within the stratified shelf system. Thus, carbon accumulation during the summer monsoon is best explained by a two-stage mechanism: (i) physical advection of CO2-rich, oxygen-deficient upwelled waters, followed by (ii) secondary amplification through local respiration. In contrast, TAlk exhibited much weaker non-conservative modification, and the elevated alkalinity generated under low-oxygen conditions was insufficient to counteract the strong DIC-driven reduction in carbonate-system buffering capacity, thereby increasing the system’s vulnerability to pCO2 build-up and acidification. Consequently, calcite and aragonite saturation states declined sharply during upwelling, with ΩCa and ΩAr falling to ∼2.5 and ∼ 1.5, respectively, when pCO2 exceeded 1000 μatm under severe oxygen depletion. The co-occurrence of hypoxia, acidification, and weakened carbonate buffering characterises the eastern Arabian Sea shelf as a highly dynamic natural laboratory for understanding multi-stressor impacts on coastal biogeochemistry and ecosystem vulnerability.
Continue reading ‘Effects of upwelling-driven acidification and deoxygenation on the dissolved inorganic carbon system over the southeastern Arabian Sea shelf’Combined ecotoxicity of microplastics and crude oil co-pollutants: occurrence, distribution and its synergistic impact with ocean acidification on Artemia franciscana
Published 3 April 2026 Science Leave a CommentTags: biological response, crustaceans, Indian, laboratory, multiple factors, physiology, plastics, reproduction, toxicants, zooplankton
Microplastics (MPs) are recognized as a global concern, with specific attention shifted towards marine MPs pollution. This particular study investigates the abundance and distribution of crude oil-loaded microplastics (COMPs) along the Chennai coastline, Tamil Nadu, India and evaluates their combined toxicological effects with ocean acidification on Artemia franciscana. Spatial analysis revealed that Ennore Creek exhibited the highest MP concentration (10.82 ± 0.2 items/L). Polypropylene was recorded as the predominant polymer type followed by low density polyethylene and polyethylene terephthalate, with particle size ranging from 250 to 500 µm. COMPs were detected across all sampling sites, with concentrations declining from Ennore Creek (0.21 ± 0.03 items/L) to Kasimedu Beach (0.10 ± 0.02 items/L). The adsorption of crude oil on MPs is primarily mediated by physical interaction with multi-layer adsorption behaviour. The results highlighted that increase in MP concentration and decrease in seawater pH significantly induced acute toxicity and oxidative stress responses in A. franciscana. At pH 7.8, experimental groups exposed to 0.5 mg/mL of COMPs developed higher ROS, SOD and catalase activity (p<0.001). Whereas control groups alone showed significant increase in oxidative stress responses at lower pH level such as pH 7.8 and 8.0. Combined exposure of COMPs and low pH conditions significantly increased oxidative damages in A. franciscana and affected its hatching ability. The observations from this study emphasize the urgent need for integrated monitoring and further research to explore combined toxicological effects of MPs and ocean acidification to other marine organisms as well.
Continue reading ‘Combined ecotoxicity of microplastics and crude oil co-pollutants: occurrence, distribution and its synergistic impact with ocean acidification on Artemia franciscana’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’A systematic review of the ocean acidification research in India: research trends, gaps and recommendations
Published 11 February 2026 Science ClosedTags: biological response, Indian, policy, review, useOAICCresource
Ocean acidification, a consequence of climate change, has become a significant threat to marine organisms. Globally, tremendous efforts have been made to understand its impact on different ecological and biological processes. In India, this research area is still not fully explored, but expanding at an exponential rate. Hence, it is essential to consolidate the fragmented knowledge into a systematic review, which will assist future researchers to develop their work. In this study, we utilized the Scopus, Web of Science and Ocean Acidification-International Coordination Centre bibliography to conduct a systematic review of ocean acidification research in India. We used the Biblioshiny package in R to conduct a bibliometric analysis, identify spatial and temporal research trends, and highlight the growth of literature in ocean acidification research, as well as existing knowledge gaps. We used the following keywords: ocean acidification, lowered pH, acidifying ocean, elevated carbon dioxide, elevated CO2, marine carbonate chemistry, shell decalcification and affiliation as India to obtain relevant publications. We selected 353 publications by applying relevance filtering and adherence to PRISMA guidelines. Almost one-third of the publications were non-primary articles. Among research articles, only 71 publications were found to investigate the response of marine organisms to ocean acidification. Majority of them involved single stressors, for a short term on very limited taxa. Lack of molecular-level investigation, multifactorial experimental design, and long-term observations were major gaps. This review aims to support researchers, policymakers, and other stakeholders involved in the planning, monitoring, and developing adaptation strategies. Finally, it provides recommendations for future research and policy development.
Continue reading ‘A systematic review of the ocean acidification research in India: research trends, gaps and recommendations’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’Navigating uncertainty: an assessment of climate change risks to the marine and coastal environment of Sri Lanka
Published 7 January 2026 Science ClosedTags: biological response, fisheries, Indian, policy, review
Sri Lanka is highly vulnerable to the impacts of marine climate change due to the low coastal profile, which is densely populated with many rural areas dedicated to fishing and aquaculture. Motivated by this, this study aimed to compile and analyse the available evidence and identify steps to improve climate adaptation by undertaking an assessment of marine climate change risks for Sri Lanka. The stepwise approach consisted of a comprehensive literature review and synthesis of risks, followed by appraisal, validation and scoring by expert stakeholders. Here we present a summary of key findings regarding marine climate variables (temperature, sea-level rise, ocean circulation, salinity, ocean acidification, dissolved oxygen, storminess, precipitation and wind), and risks to marine biodiversity and ecosystem services. The most important biodiversity risks identified include decreasing plankton productivity; threats to sea turtles; changes in fish communities; increasing threats to coral reefs; changes to mangrove and seagrass habitats; shoreline erosion; and increasing risk of bio-invasions. Key risks to ecosystem services include declining fisheries; damage and disruption to critical infrastructure and services; threats to tourism; and loss of protective coastal habitats. We also identified important knowledge gaps and uncertainties involving lack of climate data and evidence of impacts. Finally, we provide recommendations regarding marine monitoring and research, and options to strengthen climate policies and climate adaptation in Sri Lanka.
Continue reading ‘Navigating uncertainty: an assessment of climate change risks to the marine and coastal environment of Sri Lanka’Acidification and plastic pollution threaten Bangladesh’s blue economy
Published 2 January 2026 Media coverage ClosedTags: fisheries, Indian, socio-economy
The Bay of Bengal has long been the engine of Bangladesh’s blue economy—a vast, resource-rich frontier that sustains millions of people and generates vital export earnings.
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Bangladesh’s total marine fish harvest fell to 628,622 tonnes in FY 2023–24, the lowest in nine years (Department of Fisheries – Annual Report 2024). Deep-sea trawler catches declined by 21% year-on-year (FAO), while catch per artisanal boat has dropped nearly 70% over the past two decades—from 13 tonnes in 2000 to barely 4 tonnes in 2020 (World Bank Fisheries and Aquaculture Review).
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Overfishing and IUU (Illegal, Unreported, and Unregulated) fishing are well-known problems. But two largely untold reasons lie behind this steady deterioration: acidification and plastic pollution—silent yet powerful forces that destabilise the marine ecosystem.
Acidification: An invisible enemy beneath the waves
The ocean has long served as Earth’s greatest climate regulator, absorbing nearly one-third of all carbon dioxide (CO₂) emitted by human activities (IPCC, 2023). While this process helps slow global warming on land, it comes at a devastating cost beneath the surface.
When CO₂ dissolves in seawater, it forms carbonic acid, lowering the ocean’s pH and disrupting marine chemistry.
In the early 1980s, Bay of Bengal surface waters averaged a pH of 8.3 (Indian Ocean Research Consortium). Today, coastal and estuarine zones measure between 7.9 and 8.0, with some readings as low as 7.73 (UNEP South Asia Marine Assessment). This 0.2–0.3 drop in pH represents nearly a 30% increase in ocean acidity over five decades (NOAA; IPCC).
Continue reading ‘Acidification and plastic pollution threaten Bangladesh’s blue economy’How rising ocean acidity is changing India’s coasts and fisheries
Published 1 January 2026 Press releases ClosedTags: Indian
The ocean has always seemed immeasurably vast and unchanging, a realm so deep and ancient that human activity could hardly make a dent in its rhythms. Scientists now warn that this assumption is outdated. While it might be calming to stand on a beach and watch the waves roll in, little do we realise that a quiet change is taking place within the familiar-looking ocean. The water is slowly turning more acidic, almost like a few extra drops of lemon in a glass of water. We cannot see it, but marine life feels it every day. For a country like India, where millions depend on the sea for food and income, this invisible change carries real consequences.
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A new scientific review from researchers at Amrita Vishwa Vidyapeetham shows ocean acidification may be just as disruptive, and in some regions even more immediate, than rising temperatures or sea level rise. Its consequences could reverberate for centuries.
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Why India cannot afford to ignore ocean acidification
India has one of the longest coastlines in Asia, and millions of people depend on the sea for income. Almost seventy percent of fishing households live near or below the poverty line, making adaptation difficult.
India’s four major coral reef systems already face temperature-related bleaching. Acidification slows coral growth and weakens reef structures, affecting shore protection, fish nurseries, and tourism.
India also has a large aquaculture sector that relies on species sensitive to pH and carbonate levels. Molluscs, crustaceans, and some finfish can face growth and survival challenges in more acidic waters. Yet India’s research output on OA remains low and scattered. Most studies focus on coral bleaching or warming. There is no national OA monitoring network, and only a few long-term coastal observations exist.
The review notes that India contributes only a fraction of global OA literature and lacks coordinated national monitoring. With 67.3 percent of India’s fishing households living at or below the poverty line, disruption to marine resources could undermine livelihoods, nutrition, and coastal stability. Without long-term pH and carbonate chemistry data, policymakers lack the scientific foundation needed to anticipate risks or design adaptation measures.
Continue reading ‘How rising ocean acidity is changing India’s coasts and fisheries’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’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’Exploring structural integrity of coralline algae in response to the environmental changes associated with the PETM: a tale of functional resistance
Published 11 December 2025 Science ClosedTags: algae, biological response, field, Indian, morphology, paleo
Coralline algae are key benthic components of shallow-marine ecosystems globally and as habitat-formers they support high biodiversity levels. Experiments on living coralline algae show internal growth changes in response to warming and higher CO2. These growth changes are leading to weakened structural integrity and increased breakage impacting their ecological function of habitat formation. Short-term experiments, though, raise questions about long term acclimation over multiple generations. Coralline algae have an extensive fossil record across the Cenozoic. Analysing growth changes within the geological record, specifically across hyperthermals, geologically abrupt environmental changes in the Earth’s history characterized by rapid ocean warming, acidification and sea level rise, can complement modern experiments. This allows us to quantify the vulnerability and response of habitat formers, such as coralline algae, to long-term environmental change. We evaluated cellular structure and structural integrity in species of the genera Sporolithon and Lithothamnion from Meghalaya, NE India (Eastern Tethys) before and during the Paleocene-Eocene Thermal Maximum, PETM (~55.8 Ma), the most pronounced hyperthermal of the Cenozoic. Cellular structural changes were not uniform between species, some species showed increased stress and strain due to larger cell sizes during the PETM, while other species revealed negligible changes in cell sizes. Unexpectedly, stresses and strains experienced by these Palaeogene taxa are comparable to contemporary species of the study genera. These findings suggest a resilience to long term warming and lower pH conditions resulting in a resistance to breakage. However, species differences in environmental change responses potentially highlight variations in phenotypic plasticity.
Continue reading ‘Exploring structural integrity of coralline algae in response to the environmental changes associated with the PETM: a tale of functional resistance’Monsoon-driven biogeochemical shifts and acidification risk in tropical estuarine ecosystems: a case study from the Indian coast
Published 17 November 2025 Science ClosedTags: biogeochemistry, chemistry, field, Indian
Tropical estuaries serve as biogeochemical hotspots where the interactions between monsoon hydrology and human activities significantly impact ecosystem health. However, limited information exists on their carbonate chemistry, which is crucial for assessing climate vulnerability. This study provides the first seasonal assessment of hydrography, nutrients, and carbonate system dynamics in the Haripur estuary, Bay of Bengal. Seasonal evaluation revealed significant variations in pH, carbonate system indicators, and nutrients (p < 0.001). During the monsoon, pH declined to 7.12 ± 0.17, dissolved oxygen dropped to near-hypoxic levels (2.95 ± 0.35 mg L−1), and nutrient enrichment was observed with elevated dissolved inorganic nitrogen (6.07 ± 0.74 μM) and phosphate (1.61 ± 0.39 μM). Carbonate saturation states remained persistently corrosive, reaching minima of ΩAr (0.03 ± 0.01) and ΩCa = 0.04 ± 0.01) among the lowest reported for Indian estuaries. Multivariate analysis identified nutrient enrichment and carbonate imbalance as the dominant stressors, explaining 32.4 % of the total variance. These findings clearly indicate that the Haripur estuary functions as a regional hotspot of monsoon-driven acidification and a global outlier exhibiting year-round carbonate undersaturation. Urgent management interventions are recommended to mitigate hypoxia and acidification risks in this vulnerable tropical estuary through nutrient load reduction, enhanced tidal flushing, and ecosystem-based adaptation. The results further provide a valuable basis for developing best management practices in the context of regional and global climate change, thereby supporting the objectives of Sustainable Development Goal 14 (Life Below Water).
Continue reading ‘Monsoon-driven biogeochemical shifts and acidification risk in tropical estuarine ecosystems: a case study from the Indian coast’Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective
Published 12 November 2025 Science ClosedTags: chemistry, field, Indian
This study comprehensively assesses the long-term variability of temperature, ocean acidity changes, and their implications on sound absorption and acoustic propagation in the Bay of Bengal. The analysis reveals a persistent warming trend in the Indian Ocean over the past 50 years, with a significant increase in temperature observed during the Sagar Maitri cruise in 2019. Thermal structure analysis using HadleySST EN4 data indicates warming in the upper 50m but a cooling trend in the 100-200m depth range. Oceanic Heat Content analysis highlights an increasing tendency of heat storage in the upper 50m, indicative of global warming.
In the context of surface ducted propagation, Sonic Layer Depth (SLD) and gradients in the Sound Speed Profile (SSP) were crucial factors influencing acoustic energy behavior. The study revealed a decreasing trend in in-layer gradient (Gr_SL) since 1990, intensifying after that period. The below-layer gradient (Gr_BL) also exhibited a decreasing trend, implying complex dynamics in the sonic layer with potential implications for sound propagation in the surface duct.
The investigation into pH changes spanning 65 years demonstrates a declining trend, particularly since the 1990s, attributed to increased atmospheric CO2 dissolution. The study linked this decrease to anthropogenic activities, aligning with global trends. The analysis of sound absorption illustrated a nonlinear relationship between absorption, frequency, and pH, emphasizing a significant impact of ocean acidification on sound absorption in the Bay of Bengal. The acoustic propagation modeling further highlighted a decrease in transmission loss with reducing pH, leading to increased sound travel and potentially noisier oceans. Salinity variations play a more significant role than temperature in influencing sound absorption.
Continue reading ‘Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective’Unprecedented carbon accumulation in the Indian Ocean during 2016–2017
Published 29 October 2025 Science ClosedTags: chemistry, Indian, modeling, regionalmodeling
Abstract
During 2016–2017, the Indian Ocean experienced a pronounced increase in dissolved inorganic carbon (∼0.39 PgC/yr), approximately four times greater than the annual mean air–sea CO2 flux. Using a reconstructed data product and a state-of-the-art ocean biogeochemical model, we attribute this anomaly to an enhanced Southern Ocean inflow and a weakened Indonesian Throughflow associated with an El Niño event accompanied by a positive Indian Ocean Dipole (IOD), and followed by a negative IOD during the El Niño-to-La Niña transition. The resulting carbon accumulation leads to a decline in aragonite saturation and a shoaling of the aragonite saturation horizon in the southeastern Indian Ocean. This subsurface acidification may pose risks to deep-water calcifying organisms. Our findings demonstrate that ocean carbon storage and acidification are strongly modulated by circulation-driven transport processes, highlighting the need for improved subsurface observations and model capabilities to better capture the interior carbon response to climate variability.
Plain Language Summary
Between 2016 and 2017, the Indian Ocean stored a much larger amount of carbon than usual—about four times more than the typical annual exchange of carbon between the ocean and atmosphere. Using reconstructed observations and an advanced ocean model, we show that this unusual carbon buildup was caused by stronger inflow from the Southern Ocean and a weaker Indonesian Throughflow, driven by El Niño and negative Indian Ocean Dipole events. This extra carbon made the water more acidic and caused the depth at which aragonite (a mineral important for shell-building organisms) remains stable to rise by nearly 20 m in the southeastern Indian Ocean. These chemical changes could threaten deep-water organisms that rely on stable chemical conditions. Our results highlight how ocean currents can strongly affect carbon storage and acidification, and point to the need for better subsurface measurements and models to understand how climate variability impacts the ocean interior.
Key Points
- Indian Ocean carbon storage varied unprecedentedly in 2016–2017, driven by circulation anomalies linked to climate variability
- Anomalous dissolved inorganic carbon inventory was mainly due to increased Southern Ocean inflow and weakened Indonesian Throughflow
- Anomalous carbon redistribution caused subsurface acidification, shoaling aragonite saturation depth by ∼20 m in the southeast Indian Ocean
Ocean acidification global perspectives and India’s path forward
Published 29 October 2025 Science ClosedTags: Indian, policy, review, socio-economy
Ocean acidification (OA) poses a significant global threat to marine ecosystems, fisheries, and coastal livelihoods. While several countries have established robust monitoring and mitigation strategies, many regions, including India, are still developing comprehensive responses. Given India’s heavy reliance on ocean-based resources, it is crucial to integrate OA considerations into national marine policies to safeguard biodiversity, support sustainable seafood production, and protect vulnerable coastal communities. In alignment with Sustainable Development Goal (SDG) Target 14.3, which calls for enhanced scientific cooperation and monitoring to address OA, this review highlights key gaps in India’s current OA research and policy landscape. It proposes a strategic framework encompassing improved monitoring systems, socio-ecological impact assessments, and targeted policy interventions. By fostering a holistic and collaborative approach, the study aims to strengthen India’s OA resilience and contribute to broader global mitigation efforts.
Continue reading ‘Ocean acidification global perspectives and India’s path forward’Remote sensing observation of sea surface temperature (SST) and pCO2 over the Bay of Bengal and Arabian Sea and its relation with chlorophyll variability
Published 13 October 2025 Science ClosedTags: chemistry, field, Indian, modeling, regionalmodeling
The study is carried out to estimate the satellite-derived partial pressure of carbon dioxide (pCO2) in the Bay of Bengal (BoB) and Arabian Sea (AS) using sea surface temperature (SST)-based algorithm. The relationship of satellite-derived pCO2 with SST and chlorophyll has been understood in different seasonal months and years. The SST images are generated for the Bay of Bengal and Arabian Sea during two distinct seasonal months, December 2013 and 2014 and April 2014 and 2015. The daily and 8 days, monthly composite SST images are generated using INSAT-3D, MODIS-Aqua, and GHRSST datasets. The corresponding overpass time of MODIS-Aqua and INSAT-3D 13:30Hrs SST data has been archived. The SST is observed in the range of 24–32 °C. The SST-based pCO2 algorithm is applied over the northern Indian ocean and the pCO2 variability in two different seasons monitored. The pCO2 ranged around 350–750 μatm. The INSAT-3D derived 30-min time interval images processed on intra-day basis having 48 passes per day. The pCO2 images observed directly proportional relationship with the SST images during summer and inverse trend during winter. With the increase in SST by 1–2 °C, there has been increase in pCO2 by 2–5% during summer. The comparison of pCO2 on weekly and monthly time scales using the INSAT-3D, MODIS and GHRSST data has been observed to be interesting and showed matching trend. This exemplifies the preliminary study to understand the hourly, daily, weekly, monthly, and seasonal trend of SST and pCO2 variability in the northern Indian Ocean basins using satellite datasets. The MODIS-Aqua monthly composite chlorophyll images indicate that the high chlorophyll (0.8–1.4 mg m−3) patches are matching well with the high pCO2 concentration (400–450 μatm) patches during winter month and similar trend is not observed during summer month. Main findings of the paper are to have the pCO2 estimation using SST data in Indian scenario using multiple satellite datasets from MODIS-Aqua, INSAT, and GHRSST datasets and the comparison with ocean productivity using satellite-derived chlorophyll data. This study has a strong relevance in terms of ocean acidification monitoring using satellite data- and model-based time-series map generation. The study is important from the point of view of air-sea interaction, ocean acidification, and ocean biogeochemistry. The in situ pCO2 measurements, data validation, and fine-tuning would rely on the scope for regional algorithm development as future study and trend analysis from climate change perspective.
Continue reading ‘Remote sensing observation of sea surface temperature (SST) and pCO2 over the Bay of Bengal and Arabian Sea and its relation with chlorophyll variability’Molecular responses of amphipod (Parhyale darvishi), to pH stress in Persian Gulf
Published 10 October 2025 Science ClosedTags: biological response, crustaceans, Indian, laboratory, molecular biology, zooplankton
Climate change is driving more frequent and extreme pH fluctuations in intertidal habitats, yet the molecular mechanisms by which small crustaceans cope with acid–base stress remain poorly understood. In this study, we evaluated the transcriptional responses of the intertidal amphipod Parhyale darvishi to acute low-pH (6.0) and high-pH (9.0) challenges, simulating the extremes observed in tide pools. Following a 7-day acclimatization in aerated seawater (salinity 40–42 ppt, 24–25 °C, 12:12 h light:dark), individuals (4–7 mm length) were randomly assigned to one of three treatments: control (ambient pH 7.50–7.60), low pH (adjusted to 6.0 with 20 mL 37% HCl), or high pH (adjusted to 9.0 with 3 mL NaOH), each with two 1-L replicates containing 50 animals. After 0h, 12h and 24 h of exposure, total RNA was extracted and reverse-transcribed to cDNA. Real-time PCR assays quantified expression of five target genes: catalase (CAT), glutathione S-transferase (GST), Na⁺/K⁺-ATPase, apoptosis signal-regulating kinase 1 (ASK1), and caspase-3, with tubulin serving as the reference gene. Both pH stressors elicited significant transcriptional changes relative to controls. Under low pH, antioxidant genes CAT and GST were upregulated by approximately 2.5- and 2.1-fold, respectively, indicating activation of oxidative defense pathways. In contrast, high pH induced a more moderate antioxidant response (1.8- and 1.5-fold for CAT and GST) but triggered a pronounced apoptotic signal, with caspase-3 expression increasing nearly 3-fold. Na⁺/K⁺-ATPase transcripts rose under both treatments, reflecting osmoregulatory adjustments, while ASK1 exhibited a stronger induction in acid-stressed amphipods, suggesting stress-activated kinase signaling. These findings demonstrate that P. darvishi mounts distinct molecular responses to acid versus alkaline challenges, engaging antioxidant defenses under low pH and apoptosis-related pathways under high pH. Such differential gene expression profiles provide mechanistic insight into how intertidal amphipods cope with rapid pH swings, and underscore the utility of molecular biomarkers for assessing the resilience of coastal invertebrates under future acidification and alkalinization scenarios.
Continue reading ‘Molecular responses of amphipod (Parhyale darvishi), to pH stress in Persian Gulf’Assessing the physiological and oxidative stress status of Etroplus suratensis under elevated temperature and ocean acidification
Published 27 August 2025 Science ClosedTags: biological response, fish, Indian, laboratory, multiple factors, physiology, temperature
Highlights
- Current study delves into the impacts of ocean warming (OW) and acidification (OA) on E. suratensis.
- Combined stressor-induced metabolic depression which indicated energy conservation strategy.
- Lower Scope for Growth advocates impaired energy allocation under stress.
- Oxidative stress biomarkers and apoptosis augmented due to combined stress.
- Anticipated OA and OW could threaten future fish populations and marine ecosystem balance.
Abstract
The incessant release of anthropogenic CO2 in the atmosphere has accentuated ocean warming (OW) and elevated the partial pressure of dissolved CO₂, culminating in a foreseeable decline in oceanic pH. Thus, the present study endeavors to elucidate the concomitant impacts of OW and ocean acidification (OA) on the eco-physiological responses of Etroplus suratensis over a 30-day mesocosm experiment. Physiological parametres, encompassing ingestion, absorption, respiration, and excretion rates, were measured to gauge the scope for growth (SfG). Additionally, a comprehensive evaluation of biomarkers, comprising antioxidant defenses, detoxification pathways, lipid peroxidation, and apoptotic markers, was assessed at various biological levels. Results revealed that combined stressors curtailed the feeding activity, as substantiated by a significant reduction in ingestion and absorption rate. Metabolic depression, illustrated by reduced respiration and excretion rates, insinuated an energy conservation strategy amidst dual stressors. Despite these adaptations, SfG remained depressed, accentuating the detrimental effects of the combined stressors on the energy allocation strategy of this fish. Furthermore, oxidative stress biomarkers, including superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST), exhibited heightened activities, albeit these defenses were insufficient to counteract persistent environmental stressors, resulting in increased lipid peroxidation (LPO) and apoptosis. Notably, cleaved caspase-3 expression was significantly upregulated, which suggested that apoptosis was a key cellular response against combined stressors. Overall, anticipated OA and OW significantly impacted the energy budget, oxidative stress biomarkers, and key cellular responses of E. suratensis, compromising growth, survival, and reproductive fitness. These potentially jeopardize population structure and disrupt trophic interactions which may impair functional integrity of estuarine ecosystem.
Continue reading ‘Assessing the physiological and oxidative stress status of Etroplus suratensis under elevated temperature and ocean acidification’Pteropods reliably record the aragonite compensation depth in the western Bay of Bengal
Published 21 August 2025 Science ClosedTags: abundance, biological response, community composition, field, Indian, mollusks, otherprocess, protists, zooplankton
Anthropogenic greenhouse gas emissions have a detrimental impact on the carbon sequestration by the oceans. Pteropods, a crucial component of the ocean’s planktic community, secrete aragonite shells that are sensitive to increasing atmospheric carbon dioxide levels, making them the first indicators of ocean acidification. Therefore, pteropods are often used to observe the changes in aragonite compensation depth (ACD). Intriguingly, in the major parts of the northern Indian Ocean, the chemically defined ACD is < 800 m, but pteropods have been reported in surface sediments collected from much deeper depths in the same region, which raises questions about the use of pteropods to trace ACD in this area. To address this ambiguity, we conducted a systematic and detailed evaluation of pteropods to trace the changes in ACD in the western Bay of Bengal, which is the first-ever such study. The pteropods population dominated by Heliconoides inflatus was low on the inner shelf, and isolated pockets of high pteropod abundance were restricted to the upper slope. Based on the pteropod abundance in the surface sediments and the ratio of pteropods to planktic foraminifera, we report the baseline ACD in the western Bay of Bengal at ~ 500 m. The aragonite compensation depth based on the pteropod abundance in the surface sediments correlates well with the chemically defined ACD in this region. These findings will help to assess the impact of ocean acidification on aragonite compensation depth in the western Bay of Bengal.
Continue reading ‘Pteropods reliably record the aragonite compensation depth in the western Bay of Bengal’
