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’Posts Tagged 'Indian'
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
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’Impact of land-based freshwater inflows on coastal ocean acidification in the Arabian Sea
Published 20 August 2025 Science ClosedTags: chemistry, field, Indian
Highlights
- Seasonal data from 75 rivers, 47 groundwater sources used to assess land input.
- Groundwater causes 85% of pH drop from freshwater in coastal seawater.
- Air-sea CO2 exchange has minimal effect as this coast is a perennial CO2 source.
- Freshwater lowers pH comparable to upwelling in central Arabian Sea nearshore.
Abstract
Coastal ocean acidification is a growing global concern, especially in densely populated regions where terrestrial inputs complicate its dynamics. Unlike the open ocean, coastal waters are heavily influenced by freshwater inflows. This study investigates the impact of riverine and groundwater inputs on seawater pH variability in the coastal Arabian Sea. River discharge leads to greater pH reduction during the monsoon (0.170 ± 0.021), while groundwater, despite its high alkalinity, causes a stronger decline in the non-monsoon season (0.296 ± 0.036) due to elevated pCO2 levels (27,318 ± 5076). Groundwater alone accounts for 85 % of the freshwater-induced pH drop. The effect of atmospheric CO2 exchange is negligible, as the region remains a perennial CO2 source throughout the year. These findings highlight the need to account for coastal biogeochemical processes, particularly aerobic respiration and photosynthesis, in acidification assessments. Understanding these drivers is critical for managing coastal acidification under increasing anthropogenic pressures and climate-driven changes in freshwater inputs.
Continue reading ‘Impact of land-based freshwater inflows on coastal ocean acidification in the Arabian Sea’New observations confirm the progressive acidification in the Mozambique Channel
Published 7 August 2025 Science ClosedTags: chemistry, field, Indian, modeling, regionalmodeling
New observations obtained in 2021 and 2022 are presented and used to investigate the trend of the carbonate system (including pH and aragonite saturation state, Ωar) in the southern sector of the Mozambique Channel. Using historical and new data in April–May we observed an acceleration of the acidification ranging from -0.012 TS.decade-1 in 1963–1995 to -0.027 (±0.003) TS.decade-1 in 1995–2022. Result from a neural network (FFNN) model for all seasons also suggests faster pH trend in recent decades, -0.011 TS.decade-1 over 1985–1995 and -0.018 TS.decade-1 over 1995–2022. In May 2022 we estimated Ωar of 3.49, about 0.3 lower than observed in May 1963 (Ωar = 3.86). The lowest Ωar value of 3.23 was evaluated from the FFNN model in September 2023 that corresponds to the hypothetical critical threshold value (3.25) for coral reefs. In 2025 a marine heat wave was observed in this region (sea surface temperature up to 30 °C) and data from a BGC-Argo float indicate that sea surface pH was low in January 2025 (pH = 7.95) whereas War was low in Mach 2025 (Ωar = 3.2). A projection of the CT concentrations based on observed anthropogenic CO2 in subsurface water and emissions scenario, suggests that a risky level for corals (Ωar < 3) could be reached as soon as year 2034.
Continue reading ‘New observations confirm the progressive acidification in the Mozambique Channel’Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans
Published 2 July 2025 Science ClosedTags: abundance, biogeochemistry, biological response, community composition, growth, Indian, laboratory, multiple factors, North Pacific, otherprocess, physiology, phytoplankton
Abstract
Key roles of marine dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2) in the sulfur cycle and/or atmospheric chemistry, alongside the rapid environmental changes in marine ecosystems, underscore the need to understand their responses to dynamic ecosystem shifts. We conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans to explore how dust deposition, ocean acidification, and microplastic exposure impact these compounds. Our results demonstrate that these stressors not only alter phytoplankton community but also modify per-cell DMSP production capacity and DMSP degradation pathways, subsequently influencing DMSP, DMS, and MeSH concentrations. CS2‘s response closely mirrors phytoplankton abundance and species. Initial physical-chemical conditions, such as carbonate system and nutrient availability, may mediate the sensitivity of phytoplankton and sulfur compounds to environmental shifts. This study enhances our understanding of biogenic sulfur responses in dynamic marine ecosystems and provides essential basis for future climate modeling.
Key Points
- External stressors alter algal communities and production and degradation of dimethyl sulfoniopropionate, thus affecting biogenic sulfides
- Response of carbon disulfide to different environmental stressors is closely linked to algal abundance
- Initial physical-chemical conditions of seawater mediate algae and biogenic sulfides’ sensitivity to environmental stressors
Plain Language Summary
Biogenic sulfur-containing compounds in the ocean, such as dimethyl sulfoniopropionate (DMSP), dimethyl sulfide (DMS), methyl mercaptan (MeSH), and carbon disulfide (CS2), play critical roles in the global sulfur cycle and have the potential to influence the Earth’s climate. For instance, DMS released from the ocean into the atmosphere contributes to cloud formation, which in turn affects weather patterns. Over recent decades, rapid environmental changes in marine ecosystems may have significantly impacted marine biogeochemical processes. To investigate how these compounds respond to such changes, we conducted two ship-based incubation experiments in the Northwest Pacific and Eastern Indian Oceans. We assessed the effects of dust deposition, ocean acidification (due to increased carbon dioxide), and microplastic pollution on the production of DMSP, DMS, MeSH, and CS2 by marine organisms. Our results demonstrate that these stressors alter phytoplankton growth and community composition and impact the pathways through which DMSP is degraded. Consequently, the concentrations of sulfur compounds in seawater are affected. Notably, changes in CS2 levels were more closely related to shifts in phytoplankton abundance. These findings enhance our understanding of how marine sulfur compounds may respond to future oceanic changes and offer valuable data for improving climate models.
Continue reading ‘Effects of different environmental stressors on marine biogenic sulfur compounds in the Northwest Pacific and Eastern Indian Oceans’Microzooplankton community dynamics under ocean acidification: key observations and insights
Published 30 April 2025 Science ClosedTags: abundance, biological response, BRcommunity, community composition, Indian, laboratory, otherprocess, phytoplankton, prokaryotes, zooplankton
Microzooplankton (MZP) community dynamics under ocean acidification were studied through pH manipulated microcosm experiments conducted in the coastal waters of the Bay of Bengal (off Vishakhapatnam) during the months of July and October 2022 (Experiment 1 and Experiment 2). The total abundance of phytoplankton and microzooplankton (MZP) communities was varied from 3.66 × 104 to 5.27 × 105 Cells. L−1 and 0.06 × 103 to 1.53 × 103 Cells. L−1, respectively, and a significant difference in phytoplankton and MZP abundance was found between the initial and final day of the entire experimental samples (control and acidified). The initial seawater samples were dominated with centric diatom species Dactyliosolen fragilissimus (Experiment 1 and Experiment 2: 72–82%) and shifted to pennate diatoms such as Pseudo-nitzschia sp. (Experiment 1: 60–68%) and Amphora sp. (Experiment 2: 80–94%) at the end of the experiments (all acidified and control samples). The initial MZP community composition consisted of four different groups LC: loricate ciliates, ALC: aloricate ciliates (heterotrophy and mixotrophy), HDS: heterotrophic dinoflagellates and copepod nauplii, and at the end of the experiments, it was shifted entirely to the dominance of aloricate ciliates (16–73%) and heterotrophic dinoflagellates (67–100%) in all the samples (control and acidified) in Experiments 1 and 2, respectively. Statistical analysis (Spearman’s rank correlation) results showed a relative and significant inverse relation of MZP with phytoplankton biomass and abundance and heterotrophic bacterial counts in all the samples (control and acidified). Besides, the LC showed a weak correlation with Chl-a, and the HDS showed a significant correlation with LC, phytoplankton biomass and abundance, and bacterial counts (picocyanobacteria and heterotrophic bacteria). These results indicate that the MZP may graze on both picocyanobacteria and heterotrophic bacteria, and also, HDS may graze on their relative community like LC. Canonical correlation analysis (CCA) revealed that prey abundance such as phytoplankton biomass (Chl-a), picocyanobacteria, and heterotrophic bacterial communities are most influencing variables on the MZP assemblages than other environmental variables such as pH, temperature, and salinity. Thus, these findings show that the MZP community dynamics under ocean acidification may vary with different species and groups due to their food availability (indirect effect) and individual competence (direct effect) to different environmental conditions, such as pH variations.
Continue reading ‘Microzooplankton community dynamics under ocean acidification: key observations and insights’An improved long-term high-resolution surface pCO2 data product for the Indian Ocean using machine learning
Published 16 April 2025 Science ClosedTags: chemistry, Indian, modeling, regionalmodeling
Accurate estimation of surface ocean pCO2 is crucial for understanding the ocean’s role in the global carbon cycle and its response to climate change. In this study, we employ a machine learning algorithm to correct the deviations in high-resolution (1/12°) model simulations of surface pCO2 from the INCOIS-BIO-ROMS model (pCO2model) for the period 1980–2019, using available observations (pCO2obs). We train the XGBoost model to generate spatio-temporal deviations (pCO2obs − pCO2model) of pCO2model. The interannually and climatologically varying deviations are then added back to the original model separately, which results in an improved surface pCO2 data product. A comparison of our surface pCO2 data product with moored observations, gridded SOCAT, CMEMS-LSCE-FFNN, and OceanSODA demonstrates an improvement by approximately 40% ± 3.31% in RMSE. Further analysis reveals that adding climatological deviations to pCO2model results in greater improvements than adding interannual deviations. This analysis underscores the ability of machine learning algorithms to enhance the accuracy of model-simulated surface pCO2 outputs.
Continue reading ‘An improved long-term high-resolution surface pCO2 data product for the Indian Ocean using machine learning’Warmer oceans, acidification endanger Sri Lanka’s maritime heritage
Published 8 April 2025 Media coverage ClosedTags: Indian
Sri Lanka’s waters are home to over 200 shipwrecks, each holding a unique story of trade, war, and maritime heritage. Among the most significant are the Godawaya Shipwreck, which dates back over 2,000 years, and HMS Hermes, the world’s first purpose-built aircraft carrier built by British and sunk by Japanese dive bombers during World War II (1931-1945).
Over time, these shipwrecks have transformed into artificial reefs, supporting marine biodiversity and playing a crucial role in ocean ecosystems. However, climate change is now emerging as a major threat to their survival, potentially shortening their lifespan.
“Shipwrecks face multiple threats from climate change,” says Prof. Sevvandi Jayakody of the Department of Aquaculture and Fisheries at Wayamba University of Sri Lanka. “These include extreme weather events, ocean acidification, invasive species, and rising sea temperatures, all of which can accelerate the degradation of wrecks.”
…
Human-induced climate change, driven by greenhouse gas emissions such as carbon dioxide (CO₂), not only warms the planet but also increases ocean acidity when the ocean absorbs carbon dioxide from the atmosphere, which lowers the ocean’s pH.
“Globally, research has shown that ocean acidification speeds up the corrosion rate of iron and steel wrecks,” notes Prof. Jayakody. “This is especially concerning for wrecks like HMS Hermes, which may still contain live ammunition. As the metal weakens, there is a risk of explosive materials being exposed.”
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Although ocean acidification studies in Sri Lanka are still in their early stages, the National Aquatic Resources Research and Development Agency (NARA) is monitoring pH levels in coastal waters.
“We take regular measurements from stations on both the east and west coasts,” says Dr. Kanapathipillai Arulananthan director general of NARA. “Additionally, the Norwegian research vessel Nansen is expected to provide further insights into changing ocean parameters in the Northern Indian Ocean.”
Another hidden threat is the rise of invasive species that could now establish in different areas due to warming waters. Changes in ocean temperature and acidity alter microbial activity, leads to faster decomposition of wooden shipwrecks according to research.
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Ballast water from ships can introduce these invasive species to new environments. While differences in salinity, temperature, and acidity once prevented their survival, climate change is making new habitats more suitable for these species, increasing the risk of bioerosion.
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As climate change intensifies, Sri Lanka’s shipwrecks face an uncertain future. Without proactive measures, these historical and ecological treasures could deteriorate beyond recognition, taking with them invaluable insights into the past —and a crucial refuge for marine life in the present.
Mr. Mutukumarana said every shipwreck is unique and when one disintegrates so goes its story, too. The only way forward would be to reduce the rate of global warming.
Continue reading ‘Warmer oceans, acidification endanger Sri Lanka’s maritime heritage’Safeguarding South-East Asia’s marine ecosystems from ocean acidification threats
Published 28 March 2025 Newsletters and reports ClosedTags: Indian, policy, South Pacific
The increasing carbon dioxide emissions from human activities are being absorbed by the oceans, leading to a decrease in seawater pH levels worldwide. South-East Asia is particularly vulnerable to this problem, as the projected trend of ocean acidification severely threatens marine life in the region, as well as marine industry productivity and food safety. Urgent action must be taken by the Association of Southeast Asian Nations (ASEAN) Secretariat and its Member States to sustain coastal populations’ livelihoods and economic prosperity.
Recommendations:
- Improve marine protected areas (MPAs) by applying science-based design and grass-roots community participation
- Establish a regional task force and collaborative funding
- Increase public awareness and implement marine educational programmes through curriculum integration
Carbonate chemistry and CO2 dynamics in the Persian Gulf
Published 14 March 2025 Science ClosedTags: chemistry, field, Indian
Highlights
- The T-S diagram identifies four distinct water types in the Persian Gulf study area.
- Alkalinity loss equals 31 Mt. CaCO3 or 3.72 Mt. inorganic carbon deposited annually.
- A ΔOrgC:ΔCaCO3 ratio of 2.6:1 indicates higher photosynthesis over calcification.
- Dissolved inorganic carbon and total alkalinity, dominate the pCO2 distribution.
- 85 % of surface waters of the Persian Gulf acted as CO2 sinks in late summer.
Abstract
This study examines the carbonate chemistry of the Persian Gulf within the Iranian Exclusive Economic Zone, using datasets collected during the PGE2102 expedition in September 2021. The water column was stratified, with a warm, oxic upper layer (0–25 m: 33.2 °C, salinity 38.9 psu, O2 177 μmol/kg) and a cooler, low-oxygen deep layer (> 25 m: 24.4 °C, salinity 40.2 psu, O2 94.3 μmol/kg). Four water types were identified: Indian Ocean Surface Water (IOSW), Surface Persian Gulf Water (Surface-PG), Deep Persian Gulf Water (Deep-PG), and Northwest Persian Gulf Water (NW-PG). The lowest normalized alkalinity (NAT) was found in NW-PG (2427 ± 29 μmol/kg), suggesting alkalinity loss, while IOSW exhibited the highest NAT (2551 ± 9 μmol/kg). Deep-PG had lower NAT (2460 ± 18 μmol/kg) than surface waters, with surface NAT decreasing westward. Organic matter decomposition in Deep-PG resulted in the lowest pH (7.924 ± 0.030) and highest pCO2 (592.8 ± 47 μatm). Surface waters showed reduced dissolved inorganic carbon (DIC ~2047 μmol/kg) and undersaturated pCO2 (403.9 ± 69 μatm) due to photosynthesis. Hypoxic zones in western and central areas exhibited elevated DIC (up to 2305.6 μmol/kg) and the lowest pH (7.832), reflecting remineralization. Calcium carbonate precipitation contributed to significant alkalinity losses (66.2 μmol/kg), translating to 31 million tons of annual deposition. A ΔOrgC:ΔCaCO3 ratio of 2.6:1 in surface waters suggests higher photosynthetic activity relative to calcification. Despite localized pCO2 hotspots, 85 % of surface waters acted as CO2 sinks, highlighting unique carbonate dynamics shaped by stratification, biogeochemical processes and regional conditions.
Continue reading ‘Carbonate chemistry and CO2 dynamics in the Persian Gulf’Effect of thermal and non-thermal processes on the variability of ocean surface pCO2 and buffering capacity in the North Indian Ocean
Published 24 February 2025 Science ClosedTags: biogeochemistry, chemistry, Indian, modeling, regionalmodeling
Highlights
- A coupled atmosphere–ocean-biogeochemistry model is customised for NIO.
- High surface pCO2 in upwelling regions of NIO are controlled by non-thermal processes.
- Surface pCO2 changes in upwelling regions of NIO are more sensitive to changes in DIC.
- Diffusion, CO2 flux and Phytoplankton uptake primarily control DIC variability in NIO.
Abstract
The oceans have absorbed nearly 30% of the anthropogenic CO2 that alters the ocean carbon chemistry. The oceanic processes are highly complex, which mandate approaches that couple its physical, chemical and biological states. Here, we use a coupled atmosphere–ocean-biogeochemistry model, incorporating spatially and temporally varying atmospheric CO2 to simulate the north Indian Ocean (NIO) carbon dynamics for the period 2013–2020. We assess the seasonal variability of Dissolved Inorganic Carbon (DIC), total Alkalinity (ALK), ocean surface pCO2 and buffering capacity. To assess the mechanisms that control carbon dynamics in the region, we segregate the ocean surface pCO2 into temperature-driven (thermal) and bio-physical processes induced (non-thermal) pCO2. We find that the thermally driven pCO2 is dominant in summer (June, July, August and September; JJAS), but the non-thermal component in winter (December, January and February; DJF) in the northern Arabian Sea (AS). The northern AS is characterised by a deep mixed layer and convection-induced vertical mixing during winter. DIC from the subsurface layer is uplifted to the surface, which results in high ocean surface pCO2 in winter. Off the Oman coast, the non-thermal processes control the surface pCO2 in summer. In the northern bay, the thermal component of pCO2 is dominant in summer and non-thermal component is prominent in winter as in northern AS, but their magnitudes are lower due to large riverine flux. The budget analysis reveals strong influence of diffusion, CO2 flux and biological processes in controlling DIC variability in NIO. Low buffering capacity in upwelling regions indicates that pCO2 changes are more sensitive to changes in DIC, primarily due to the upwelled DIC-rich surface waters. Therefore, it results in a reduced ability to absorb CO2. This warrants the need to address recent changes in carbon dynamics in response to the increased levels of atmospheric CO2.
Continue reading ‘Effect of thermal and non-thermal processes on the variability of ocean surface pCO2 and buffering capacity in the North Indian Ocean’
