Posts Tagged 'Indian'

Reviews and syntheses: carbon biogeochemistry of Indian estuaries

The goal of this review is to provide a comprehensive overview of the magnitude and drivers of carbon cycling dynamics in the major estuaries of India. Data from a total of 32 estuaries along the Bay of Bengal (BB) and the Arabian Sea (AS) were compiled from the literature and re-analysed based on changes in season (wet vs. dry) and marine end-members (e.g., BB vs. AS). The estuaries are generally undersaturated in dissolved oxygen relative to the atmosphere and strongly influenced by local and regional precipitation patterns. Speciation of the dissolved inorganic carbon (DIC) pool is dominated by bicarbonate and primarily variability in DIC is controlled by a combination of carbonate weathering, the degree of precipitation, the length of the estuaries, in situ respiration, and mixing. Carbonate dissolution had the largest influence on DIC during the wet season, while respiration was the primary control of DIC variability in the estuaries connected with BB during the dry season. Interestingly, the influence of anaerobic metabolism on DIC is observed in the oxygenated mangrove dominated estuaries, which we hypothesize is driven by porewater exchange in intertidal sediments. Dissolved organic carbon (DOC) generally behaves non-conservatively in the studied estuaries. The DOC-particulate organic carbon (POC) inter-conversion and DOC mineralization are evident in the BB during the dry season and AS estuaries, respectively. The wet season δ13CPOC shows dominance of freshwater algae, C3 plant material, as well as marine organic matter in POC. However, anthropogenic inputs are evident in some estuaries in eastern India during the dry season. POC respiration was identified in the AS; however, a link between POC and CH4 is identified throughout both the regions. pCO2 is controlled principally by respiration with freshwater discharge only playing a marginal important role in the BB. The AS estuaries act as a CO2 source to the atmosphere; however, the BB estuaries vary between a source and sink. POC together with methanotrophy and dam abundance appear to control CH4 concentrations, and all of the studied estuaries act as a CH4 source to the atmosphere. Additionally, anthropogenic inputs and groundwater exchange also show potential influences in some cases. The Indian estuaries contribute 2.62 % and 1.09 % to the global riverine DIC and DOC exports to the ocean, respectively. The total CO2 and CH4 fluxes from Indian estuaries are estimated as ~9718 Gg yr-1 and 3.27 Gg yr-1, which contributes ~0.67 % and ~0.12 %, respectively, to global estimates of estuarine greenhouse gas emissions. While a qualitative idea on the major factors controlling the carbon biogeochemistry in India is presented through this work, a more thorough investigation including rate quantification of the above-mentioned mechanisms is essential for precise accounting of the C budget of Indian estuaries.

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Effects of acidification on fish larval abundance at Teknaf coast, Bangladesh

The study aimed to investigate the effects of acidification on fish larvae abundance at the Teknaf coast. From January 8 to December 14, 2021, samples of fish larvae were collected at every month from the Teknaf coast. From the bottom to the surface, Bongo-Net with a 500 µm mesh size was being towed. A total of 1,120 larvae were gathered from the research area during the survey. In the study region, 93 larvae/1,000 m3 were found to be the mean density of all fish larvae. The hydrological parameters such as water temperature, pH, salinity, and total alkalinity were determined to find out the effects of these variables on the larvae abundance along the Teknaf coast. The average values of the parameters including water temperature, pH, salinity, and total alkalinity were found at 28.41°C, 8.36, 23.57 PSU, and 113.25 mg/l respectively. The ocean acidification factors including pCO2, HCO3-, CO32-, DIC, ΩAragonite, and ΩCalcite were also determined by using the “seacarb” package of R programming to find out the effects of these variables on the larvae abundance along the Teknaf coast. The average values of the factors including pCO2, HCO3-, CO32-, DIC, ΩAragonite, and ΩCalcite were found 128.72 µatm, 0.000751 mole/kg, 0.000138 mole/kg, 0.000892 mole/kg, 2.3544 and 3.7028 respectively. The results showed an insignificant relationship between pCO2 and fish larvae abundance throughout the Teknaf coast. However, there was a negative correlation between pCO2 and pH. The findings of this research indicate that OA affects fish larvae abundance at Teknaf coast. Regional fisheries management organizations will be better able to make decisions about the management of the extremely valuable fish larvae as a result of future population-level predictions of the impacts of ocean acidification.

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Do global environmental drivers’ ocean acidification and warming exacerbate the effects of oil pollution on the physiological energetics of Scylla serrata?

Global climate change–induced ocean warming and acidification have complex reverberations on the physiological functioning of marine ectotherms. The Sundarbans estuarine system has been under threat for the past few decades due to natural and anthropogenic disturbances. In recent years, petroleum products’ transportation and their usage have increased manifold, which causes accidental oil spills. The mud crab (Scylla serrata) is one of the most commercially exploited species in the Sundarbans. The key objective of this study was to delineate whether rearing under global environmental drivers (ocean acidification and warming) exacerbates the effect of a local driver (oil pollution) on the physiological energetics of mud crab (Scylla serrata) from the Sundarbans estuarine system. Animals were reared separately for 30 days under (a) the current climatic scenario (pH 8.1, 28°C) and (b) the predicted climate change scenario (pH 7.7, 34°C). After rearing for 30 days, 50% of the animals from each treatment were exposed to 5 mg L−1 of marine diesel oil for the next 24 h. Physiological energetics (ingestion rate, absorption rate, respiration rate, excretion rate, and scope for growth), thermal performance, thermal critical maxima (CTmax), acclimation response ratio (ARR), Arrhenius activation energy (AAE), temperature coefficient (Q10), warming tolerance (WT), and thermal safety margin (TSM) were evaluated. Ingestion and absorption rates were significantly reduced, whereas respiration and ammonia excretion rates significantly increased in stressful treatments, resulting in a significantly lower scope for growth. A profound impact on thermal performance was also noticed, leading to a downward shift in CTmax value for stress-acclimated treatment. The present results clearly highlighted the detrimental combined effect of global climatic stressors and pollution on the physiological energetics of crabs that might potentially reduce their population and affect coastal aquaculture in forthcoming years.

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Biotic and paleoceanographic changes across the Late Cretaceous Oceanic Anoxic Event 2 in the southern high latitudes (IODP sites U1513 and U1516, SE Indian Ocean)

Abstract

Oceanic Anoxic Event 2, spanning the Cenomanian/Turonian boundary (93.9 Ma), was an episode of major perturbations in the global carbon cycle. To investigate the response of biota and the paleoceanographic conditions across this event, we present data from International Ocean Discovery Program sites U1513 and U1516 in the Mentelle Basin (offshore SW Australia; paleolatitude 59°–60°S in the mid-Cretaceous) that register the first complete records of OAE 2 at southern high latitudes. Calcareous nannofossils provide a reliable bio-chronostratigraphic framework. The distribution and abundance patterns of planktonic and benthic foraminifera, radiolaria, and calcispheres permit interpretation of the dynamics of the water mass stratification and provide support for the paleobathymetric reconstruction of the two sites, with Site U1513 located northwest of the Mentelle Basin depocenter and at a deeper depth than Site U1516. The lower OAE 2 interval is characterized by reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer as indicated by the fluctuations in abundance of the intermediate dwelling planktonic foraminifera. The middle OAE 2 interval contains lithologies composed almost entirely of radiolaria reflecting extremely high marine productivity; the low CaCO3 content is consistent with marked shoaling of the Carbonate Compensation Depth and ocean acidification because of CaCO3 undersaturation. Conditions moderated after deposition of the silica-rich, CaCO3-poor rocks as reflected by the microfossil changes indicating a relatively stable water column although episodes of enhanced eutrophy did continue into the lower Turonian at Site U1516.

Key Points

  • Documentation of first complete record of the Late Cretaceous Oceanic Anoxic Event 2 (OAE 2) at southern high latitudes (60°S) in the Indian Ocean
  • Dynamics of the water mass stratification inferred from distribution patterns of foraminifera, radiolaria, calcispheres
  • OAE 2 is characterized by alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer
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Variable pH and subsequent change in pCO2 modulates the biofilm formation, synthesis of extracellular polymeric substances, and survivability of a marine bacterium Bacillus stercoris GST-03

Biofilm-forming bacteria adhere to the substrates and engage in the nutrient cycling process. However, environmental conditions may interrupt the biofilm formation ability, which ultimately may affect various biogeochemical cycles. The present study reports the effect of varying pH and subsequent change in pCO2 on the survivability, biofilm formation, and synthesis of extracellular polymeric substances (EPS) of a biofilm-forming marine bacterium Bacillus stercoris GST-03 isolated from the Bhitarkanika mangrove ecosystem, Odisha, India. Understanding the pH-dependent alteration in EPS constituents, and associated functional groups of a marine bacterium will provide better insight into the adaptability of the bacteria in future ocean acidification scenarios. The strain was found to tolerate and form biofilm up to pH 4, with the maximum biofilm formation at pH 6. EPS yield and the synthesis of the key components of the EPS, including carbohydrate, protein, and lipid, were found maximum at pH 6. Changes in biofilm formation patterns and various topological parameters at varying pH/pCO2 conditions were observed. A cellular chaining pattern was observed at pH 4, and maximum biofilm formation was obtained at pH 6 with biomass of 5.28582 ± 0.5372 μm3/μm2 and thickness of 9.982 ± 1.5288 μm. Structural characterization of EPS showed changes in various functional groups of constituent macromolecules with varying pH. The amorphous nature of the EPS and the changes in linkages and associated functional groups (-R2CHOR, –CH3, and –CH2) with pH variation was confirmed. EPS showed a two-step degradation with a maximum weight loss of 59.147% and thermal stability up to 480 °C at pH 6. The present work efficiently demonstrates the role of EPS in providing structural and functional stability to the biofilm in varying pH conditions. The findings will provide a better understanding of the adaptability of marine bacteria in the future effect of ocean acidification.

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Phytoplankton community shift in response to experimental Cu addition at the elevated CO2 levels (Arabian Sea, winter monsoon)

Understanding phytoplankton community shifts under multiple stressors is becoming increasingly important. Among other combinations of stressors, the impact of trace metal toxicity on marine phytoplankton under the ocean acidification scenario is an important aspect to address. Such multiple stressor studies are rare from the Arabian Sea, one of the highest productive oceanic provinces within the North Indian Ocean. We studied the interactive impacts of copper (Cu) and CO2 enrichment on two natural phytoplankton communities from the eastern and central Arabian Sea. Low dissolved silicate (DSi < 2 µM) favoured smaller diatoms (e.g. Nitzschia sp.) and non-diatom (Phaeocystis). CO2 enrichment caused both positive (Nitzschia sp. and Phaeocystis sp.) and negative (Cylindrotheca closterium, Navicula sp., Pseudo-nitzschia sp., Alexandrium sp., and Gymnodinium sp.) growth impacts. The addition of Cu under the ambient CO2 level (A-CO2) hindered cell division in most of the species, whereas Chla contents were nearly unaffected. Interestingly, CO2 enrichment seemed to alleviate Cu toxicity in some species (Nitzschia sp., Cylindrotheca closterium, Guinardia flaccida, and Phaeocystis) and increased their growth rates. This could be related to the cellular Cu demand and energy budget at elevated CO2 levels. Dinoflagellates were more sensitive to Cu supply compared to diatoms and prymnesiophytes and could be related to the unavailability of prey. Such community shifts in response to the projected ocean acidification, oligotrophy, and Cu pollution may impact trophic transfer and carbon cycling in this region.

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Modeling the sea-surface pCO2 of the central Bay of Bengal region using machine learning algorithms

Highlights

  • Performance of MLR, ANN, and XGboost for emulating sea-surface pCO2 is evaluated.
  • XGBoost outperforms MLR and ANN in reproducing sea-surface pCO2.
  • The pCO2 reproducibility using satellite-derived SST and SSS is best using XGBoost.
  • The central BoB has been warming at a rate of 0.0175°C per year during 2010–2019.
  • The sea-surface pCO2 decreases at a rate of −0.4852 μatm per year in the BoB.

Abstract

The present study explores the capabilities of advanced machine learning algorithms in predicting the sea-surface pCO2 (partial pressure of carbon dioxide) in the open oceans of the Bay of Bengal (BoB). We collect the available observations (outside EEZ (Exclusive Economic Zone)) from the cruise tracks and the mooring stations. Due to the paucity of data in the BoB, we attempt to predict pCO2 based on the Sea Surface Temperature (SST) and the Sea Surface Salinity (SSS). Comparing the MLR, the ANN, and the XGBoost algorithm against a common dataset reveals that the XGBoost performs the best for predicting the sea-surface pCO2 in the BoB. Using the satellite-derived SST and SSS, we predict the sea-surface pCO2 using the XGBoost model and compare the same with the in-situ observations. The model performs satisfactorily, having a correlation of 0.75 and the RMSE of ±12.23μatm. Further using this model, we emulate the monthly variations in the sea-surface pCO2 for the central BoB between 2010-2019. Using the satellite data, we show that the central BoB is warming at a rate of 0.0175 °C per year, whereas the SSS decreases at a rate of -0.0088 PSU per year. The modeled pCO2 shows a declination at a rate of −0.4852 μatm per year. We perform sensitivity experiments to find that the variations in SST and SSS contribute ≈ 41% and ≈ 37% to the declining trends of the pCO2 for the last decade. Seasonal analysis shows that the pre-monsoon season has the highest rate of decrease of the sea-surface pCO2.

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Calcification response of reef corals to seasonal upwelling in the northern Arabian Sea (Masirah Island, Oman) (update)

Tropical shallow-water reefs are the most diverse ecosystems in the ocean. Their persistence rests upon adequate calcification rates of the reef building biota, such as reef corals. Coral calcification is favoured in oligotrophic environments with high seawater saturation states of aragonite (Ωsw), which leads to an increased vulnerability to anthropogenic ocean acidification and eutrophication. Here we present Porites calcification records from the northern Arabian Sea upwelling zone and investigate the coral calcification response to low Ωsw and high nutrient concentrations due to seasonal upwelling. The calcification rate was determined from the product of skeletal extension rate and bulk density. Skeletal  Ba/Ca and  Li/Mg proxy data were used to identify skeletal portions that calcified during upwelling and non-upwelling seasons, respectively, and to reconstruct growth temperatures. With regard to sub-annual calcification patterns, our results demonstrate compromised calcification rates during the upwelling season. This is due to declining extension rates, which we attribute to light dimming caused by high primary production. Interestingly, seasonal variations in skeletal density show no relationship with temporally low Ωsw during upwelling. This suggests relatively constant, year-round saturation states of aragonite at the site of calcification (Ωcf) independent of external variability in Ωsw. Although upwelling does not affect seasonal density variability, exceptionally low mean annual density implies permanent Ωcf adjustment to the lowest sub-annual Ωsw (e.g. upwelling). In the Arabian Sea upwelling zone, the mean annual calcification rate is similar to Porites from non-upwelling regions because low skeletal density is compensated by high extension growth. Variable responses of reef coral extension to nutrients, which either exacerbate or compensate negative effects of diminished skeletal density associated with ocean acidification, may therefore be critical to the maintenance of adequate carbonate accumulation rates in coral reefs under global change.

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Role of abiotic factors in enhancing the capacity of mangroves in reducing ocean acidification

The present study investigated the effects of rising carbon dioxide levels in nature and the carbon sequestration potential of dominant mangrove species for reducing the toxic effects of ocean acidification. The study was conducted on the east coast of Odisha, in the western Bay of Bengal. To determine the effect of these ambient parameters on the absorption of carbon dioxide by the mangroves, water temperature, salinity, pH levels of seawater along with soil texture and pH, salinity expressed in electrical conductivity, compactness expressed in bulk density, and soil organic carbon were simultaneously monitored. The aboveground biomass and carbon of the selected species were studied for 2 consecutive years at 10 designated stations. The total carbon calculated for the study area varied from 242.50 ± 49.00 to 1321.29 ± 445.52 tons with a mean of 626.68 ± 174.81 tons for Bhitarkanika and Mahanadi mangrove chunks. This is equivalent to 2299.92 ± 641.55 tons of CO2 absorbed from the atmosphere. A total of 27 equations were selected as the best fit models for the study area. The equations between mangrove biomass and carbon along with aquatic and edaphic factors governing the pH of water and soil strongly support the positive influence of mangrove photosynthetic activity in shifting the equilibrium toward alkalinity. This calls for conservation of mangrove ecosystem to minimize the pace of acidification of estuarine water. The results indicate that Excoecariaagallocha and Avicennia marina as are the most capable species for combatting maximum carbon dioxide toxicity from the atmosphere; which will be helpful in REDD + programs and carbon-based payments for ecosystem services (PES).

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Shallow water records of the PETM: novel insights From NE India (eastern Tethys)

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) is associated with major extinctions in the deep ocean, and significant paleogeographic and ecological changes in surface ocean and terrestrial environments. However, the impact of the associated environmental change on shelf biota is less well understood. Here, we present a new PETM record of a low paleolatitude shallow-marine carbonate platform from Meghalaya, NE India (eastern Tethys). The biotic assemblage was distinctly different to other Tethyan PETM records dominated by larger benthic foraminifera and calcareous algae both in the Paleocene and Eocene. A change in taxa and forms indicating deeper waters with a concurrent decrease in abundance of shallow water algae suggests a sea-level rise during the onset of the PETM. The record is lacking the ecological change from corals to larger foraminiferal assemblages and the Lockhartia dominance, characteristic of several other sections in the Tethys. Comparison with a global circulation model (GCM) indicates high regional temperatures in the Thanetian which may have excluded corals from the region. Furthermore, the regional circulation pattern is isolating the site from the wider Paratethys. Our study highlights the need for a diverse global perspective on shallow-marine response to the PETM and the strength of coupling data to global climate models for interpretation.

Key Points

  • Shallow-marine Paleocene-Eocene Thermal Maximum (PETM) successions are rare; here, we presented from the low paleolatitude NE India (eastern Tethys)
  • The absence of coral reefs in NE India, in contrast to other Tethyan records, was driven by very high temperatures
  • Linking biotic records of this section with climate modeling allow to interpret the biotic differences across the Tethyan region
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Recent ocean acidification trends from boron isotope (δ11B) records of coral: role of oceanographic processes and anthropogenic CO2 forcing

Abstract

Anthropogenic CO2 emission has resulted in lowering of surface ocean pH referred as ‘Ocean acidification (OA)’ which posed a serious threat to calcifying marine organisms. Several attempts have been made to assess the role of anthropogenic CO2 forcing against oceanographic factors/processes contributing to the recent OA trend; however, such attempts were hindered by the dearth of long-term pH records. Boron isotopic composition (δ11B) of corals has been used as a robust proxy for seawater pH records. In the present study, we have compiled available coral δ11B-pH records from the Indian, Pacific and Atlantic oceans and assessed regional trends, variability, forcing factors and their relative roles. Most of these δ11B-pH records show a discernable decline trend in recent decades with large variability. Our assessment of the Pacific records reveals that atmospheric CO2 forcing explains maximum pH variability followed by physical oceanographic factors/processes modulated by Pacific oscillations, e.g., ENSO and PDO. In addition, coral metabolic processes might control a large portion of the pH variability; however, they require detailed laboratory-based studies. Further, our investigation reveals a significant increase in pH variability (pH extremes) since ~1970s associated with ENSO events which might be critical for the resilience and adaptability of corals and other calcifiers.

Research Highlights

  • Since the industrial era (~1850), Coral δ11B-pH records show a discernible decreasing trend and a rapid decline since 1970.
  • Oceanographic processes control large inter-annual pH variability, whereas the long-term declining trend is driven by atmospheric CO2 forcing.
  • The pH extremes are predicted to increase in future warming scenarios, a threat to coral ecosystem.
Continue reading ‘Recent ocean acidification trends from boron isotope (δ11B) records of coral: role of oceanographic processes and anthropogenic CO2 forcing’

Phytoplankton growth and community shift over a short-term high-CO2 simulation experiment from the southwestern shelf of India, Eastern Arabian Sea (summer monsoon)

The southwestern shelf water of India (eastern Arabian Sea) experiences high seasonality. This area is one of the understudied regions in terms of phytoplankton response to the projected ocean acidification, particularly, during the summer monsoon when phytoplankton abundance is high. Here we present the results of a short-term simulated ocean acidification experiment (ambient CO2 424 µatm; high CO2, 843, 1138 µatm) on the natural phytoplankton assemblages conducted onboard (R. V. Sindhu Sadhana) during the summer monsoon (Aug 2017). Among the dissolved inorganic nutrients, dissolved silicate (DSi) and nitrate + nitrite levels were quite low (< 2 µM). Phytoplankton biomass did not show any net enhancement after the incubation in any treatment. Both marker pigment analysis and microscopy revealed the dominance of diatoms in the phytoplankton community, and a significant restructuring was noticed over the experimental period. Divinyl chlorophylla (DVChla) containing picocyanobacteria and 19‘-hexanoyloxyfucoxanthin (19′HF) containing prymnesiophytes did not show any noticeable change in response to CO2 enrichment. A CO2-induced positive growth response was noticed in some diatoms (Guinardia flaccidaCylindrotheca closterium, and Pseudo-nitzschia sp.) and dinoflagellates (Protoperidinium sp. and Peridinium sp.) indicating their efficiency to quickly acclimatize at elevated CO2 levels. This is important to note that the positive growth response of toxigenic pennate diatoms like Pseudo-nitzschia as well as a few dinoflagellates at elevated CO2 levels can be expected in the future-ocean scenario. The proliferation of such non-palatable phytoplankton may impact grazing, the food chain, and carbon cycling in this region.

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Assessment of ocean acidification in a selected tropical coastal lagoon in Mauritius

This assessment of ocean acidification at Flic-en-Flac (FF), located in the west of Mauritius, is a first-time study conducted from 2017 to 2021. The variations of pH and total alkalinity (AT) were monitored. Over the course of this study, temperature varied from 23 °C to 31 °C, whereas salinity was constant at 35 %. The summer season lasted from October to March and the winter season from April to September. The lowest mean pH value, (7.94 ± 0.02), was noted in April 2019 winter month whereas the highest mean pH value (8.17 ± 0.03) was noted in October 2017 summer month. The overall mean pH values (8.06 ± 0.06) were slightly higher in all summer periods compared to winter ones (8.01 ± 0.07). However, it was observed that the mean pH values in summer 2018 (7.97 ± 0.03), were lower than in 2017 (8.06 ± 0.06) and 2019 (8.03 ± 0.05) due to a tropical storm. The mean AT for the three sampling periods was (2404.1 ± 174.8) µmolkg−1 , in line with the global mean of (2300 ± 200) µmolkg−1 . The mean alkalinity varied from (2094.8 ± 68.0) µmol/kg (September 2019) and the highest mean AT of (2880.0 ± 14.1) µmol/kg (November 2018). In most cases, results following the t-test show that they were significant when the pH values of summer and winter were compared. However, all the t-test results were not significant with regards to alkalinity. 

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Biogeochemistry of carbon, nitrogen and oxygen in the Bay of Bengal: new insights through re-analysis of data

Primary production is reported to be a fraction of heterotrophic carbon demand in the Bay of Bengal (BoB), and it is attributed to the unavailability of inorganic nutrients and faster sinking of organic matter in association with mineral particles. The contribution of nutrients through external sources to total primary production is low (<5%), suggesting internal cycling of nutrients is important in the BoB. Organic nutrients support primary production in the absence of inorganic nutrients in the BoB. It was noticed that about 45% of particulate organic carbon (POC) production is exudated as dissolved organic carbon (DOC). Therefore, the total organic carbon production is revised to twice that of the earlier estimate and it is sufficient to support heterotrophic carbon demand. Balance among the ventilation of oxygen by anticyclonic eddies, strengthening due to cyclonic eddies and salinity stratification controls the oxygen levels in the OMZ than hitherto hypothesized as ballasting of organic matter. The stable isotopic composition of nitrogen in nitrate and particulate organic nitrogen (PON) does not evidence a significant contribution of anthropogenic nitrogen in the BoB. This negates the hypothesis that anthropogenic inputs modify the biogeochemistry of BoB. The deposition of anthropogenic aerosols decreases the pH of surface waters in the western BoB, whereas a decrease in salinity due to an increase in freshwater flux due to warming of the Himalayan glacier may increase pH and decrease pCO2 levels. As a result, BoB is turning into more sink for atmospheric CO2, which is contrasting to that of elsewhere in the global ocean.

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Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.

Highlights

  • Negative δ13C excursion at onset of OAE1a recorded in carbonate-ramp deposits.
  • Time-series analysis shows relative complete record of C3 segment of OAE1a.
  • Evidence for short-lived carbonate dissolution event at the negative δ13C peak of C3.
  • Discussion of effects of seawater temperature, pH, and diagenesis on δ18O record.

Abstract

We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. Stable oxygen-isotope ratios of bulk carbonates are interpreted to indicate two episodes of cooling, separated by rapid warming during the peak of the negative CIE. The contributions of diagenesis and seawater pH on the bulk oxygen-isotope record will have affected the palaeoclimatic signal and are critically discussed. A major shift in oxygen isotope values at the peak of the negative CIE in the C3 segment coincides with relatively carbonate-poor, marly deposits, time-equivalent with other, global evidence for a reduction of carbonate saturation of sea-surface water. According to our chemo- and cyclostratigraphic calibration, this episode of low carbonate saturation of seawater reflects a pulse of major volcanic CO2 release from the Ontong-Java large igneous province that was sufficiently short to have escaped internal buffering by the dynamics of the ocean lysocline.

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Impact of atmospheric dry deposition of nutrients on phytoplankton pigment composition and primary production in the coastal Bay of Bengal

Atmospheric deposition of pollutants decreases pH and increases the nutrient concentration in the surface water. To examine its impact on coastal phytoplankton composition and primary production, monthly atmospheric aerosol samples were mixed with coastal waters in the microcosm experiments. These experiments suggested that the biomass of Bacillariophyceae, Dinophyceae and Chlorophyceae were increased and primary production of the coastal waters increased by 3 to 19% due to the addition of aeolian nutrients. The increase in primary production displayed significant relation with a concentration of sulphate and nitrate in the atmospheric aerosols suggesting that both decreases in pH and fertilization enhanced primary production. The impact of acidification on primary production was found to be 22%, whereas 78% was contributed by the nutrient increase. The atmospheric pollution is increasing rapidly over the northern Indian Ocean since past two decades due to rapid industrialization. Hence, it is suggested that the impact of atmospheric pollution on the coastal ecosystem must be included in the numerical models to predict possible changes in the coastal ecosystem due to climate change.

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Ocean acidification impact on haematological and serum biochemical parameters in Lates calcarifer

Introduction

Ocean acidification (OA) is a long-term drop in the pH of the ocean caused mostly by atmospheric carbon dioxide (CO2). It is a consequence of climate change that poses a direct threat to life on earth by affecting the marine ecosystem (Panchang and Ambokar, 2021). The ocean has absorbed around 30% of the carbon dioxide emitted by human activities since the beginning of the industrial revolution (Sabine et al., 2004). The elevated partial pressure of carbondioxide (pCO2) causes seawater pH and CaCO3 staturation to decrease (Feely et al, 2004). The pCO2 value is now at 375 atm (Rhein et al., 2013) which is expected to reach 420 to 940 atm by 2100, and pH may decline by 0.13 to 0.42 units scenario (Rhein et al., 2013). The pH of sea water has declined from 8.17 units in pre-industrial periods (Key et al., 2004) to 8.06 units now (Rhein et al., 2013), indicating a decrease of 34.91%. Due to eutrophication and amplification of natural CO2 some coastal locations may see shifts H+ that are at least 2–3 times the world average (Melzner et al., 2012). Many marine organisms’ physiological activities are predicted to be influenced by such changes in ocean chemistry, potentially having far-reaching effects on marine biodiversity and ecological processes (Murugan et al., 2005Vijayakumaran et al., 2005Fabry et al., 2008Pörtner, 2008Kumar et al., 2009Gattuso et al., 2011).

Ocean acidification thought to harm marine fish performance, owing to changes in oxygen availability and delivery capabilities (Pörtner, 2008). Individual survival may be harmed by acidic pH because less energy is allocated to digestion, growth, and reproduction (Munday et al., 2009Munday et al., 2014). The OA has the ability to change the outcomes of ecologically important processes and the structure of ecological communities (Pörtner, 2008). Given that abiotic variables such as oxygen availability, temperature, and salinity are known to have the greatest influence on aquatic species’ early life stages (Bonk, 2005), the possible impact of acidified seawater on their development should be taken into account. Only a few studies on the impact of OA on early life stages of aquatic animals have been conducted, with the majority focusing on invertebrates (Kurihara et al., 2004Havenhand et al., 2008Dupont and Thorndyke, 2009Ellis et al., 2009 Dupont et al., 2010) indicating that the impact of OA on the early life history of vertebrates is scanty.

Because blood is the channel of intercellular transfer and comes into direct contact with multiple organs and tissues of the body, it plays an important part in all physiological systems and hence, an animal’s physiological status at any given time is reflected in its blood. Any type of environmental stress induces oxidative stress in a normal organism, which is reflected in blood proteins and causes haematological changes, and may be used as a method for biological monitoring (Martinez and Souza, 2002). Although organisms are resistant to the harmful effects of oxidative stress caused due to reactive oxygen species, prolonged exposure can cause oxidative damage, including the loss of compensatory mechanisms due to changes in enzyme function (Galloway and Handy, 2003Dogan and Can, 2011Narra, 2017). Adverse changes in the haematological and biochemical markers indicate toxicity, and their use in environmental monitoring and aquatic biota health has a wide variety of applications (Thilagam et al., 2009Narra, 2017).

A few research on the consequences of hypercapnia on various life stages of marine teleosts have been published in recent years (Checkley et al., 2009Munday et al., 2009Munday et al., 2014). Increased pCO2 levels were employed by Kikkawa et al. (2003) to explore the acute lethal effect of pCO2 on the early life stages of marine fishes. The whole world’s seas, especially coastal estuaries and streams, are being affected by OA. Many economies rely on fish and shellfish, and people all over the world use seafood as their major source of protein. Considering the need of the hour and importance of fisheries sector, an experiment was designed to study seawater acidification impacts on the growth rate of Indian seabass at various stages of their lives (Fry and Fingerlings). In both fry and fingerlings, we investigated how acidified medium alter haematological, biochemical markers in blood and consequently affect the growth. Thus, this study will help in designing the long-term effects of ocean acidification on the growth of Indian seabass, which might have implications on coastal and marine ecosystem organisms.

Continue reading ‘Ocean acidification impact on haematological and serum biochemical parameters in Lates calcarifer’

Modeling the seasonal variability and the governing factors of ocean acidification over the Bay of Bengal region

The Bay of Bengal (BoB) is a high recipient of freshwater flux from rivers and precipitation, making the region strongly stratified. The strong stratification results in a thick barrier layer formation, which inhibits vertical mixing making this region a low-productive zone. In the present study, we attempt to model the pH of the BoB region and understand the role of different governing factors such as sea-surface temperature (SST), sea-surface salinity (SSS), dissolved inorganic carbon (DIC), and total alkalinity (TALK) on the seasonality of sea-surface pH. We run a set of sensitivity experiments to understand the role of each of the governing factors. The results show that the SST, SSS, and DIC are the principal drivers affecting the sea-surface pH, while TALK plays a buffering role. The SST and DIC are consistently found to be opposite to each other. The pre-monsoon season (MAM) has shown to have an almost equal contribution from all the drivers. In the pre-monsoon season, the SST and DIC are balanced by TALK and SSS. The role of SSS is significantly dominant in the second half of the year. Both SST and SSS counter the role of DIC in the southwest monsoon season. The strong stratification plays an essential role in modulating the pH of the BoB region. The thickness of the barrier layer formed in the sub-surface layers positively affects the sea-surface pH. The northern BoB is found to be more alkaline than the southern BoB. Our study highlights the complexity of ocean acidification in the BoB region compared to the other part of the world ocean.

Continue reading ‘Modeling the seasonal variability and the governing factors of ocean acidification over the Bay of Bengal region’

Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.

Highlights

  • Negative δ13C excursion at onset of OAE1a recorded in carbonate-ramp deposits.
  • Time-series analysis shows relative complete record of C3 segment of OAE1a.
  • Evidence for short-lived carbonate dissolution event at the negative δ13C peak of C3.
  • Discussion of effects of seawater temperature, pH, and diagenesis on δ18O record.

Abstract

We report the first high-resolution sedimentological and geochemical record of the negative carbon-isotope excursion (CIE) at the onset of the early Aptian oceanic anoxic event (OAE) 1a from a carbonate-ramp depositional environment, analysed from a well core from c. 2500 m depth, 100 km offshore Abu Dhabi, United Arab Emirates. Time-series analysis of stable oxygen isotope values and concentrations of Si, Al, and Ti resulted in durations of the C3 and C4 segments of the CIE that support relative completeness of the C3 segment and high sediment preservation rates of c. 13 cm/kyr of the studied sedimentary sequence. Stable oxygen-isotope ratios of bulk carbonates are interpreted to indicate two episodes of cooling, separated by rapid warming during the peak of the negative CIE. The contributions of diagenesis and seawater pH on the bulk oxygen-isotope record will have affected the palaeoclimatic signal and are critically discussed. A major shift in oxygen isotope values at the peak of the negative CIE in the C3 segment coincides with relatively carbonate-poor, marly deposits, time-equivalent with other, global evidence for a reduction of carbonate saturation of sea-surface water. According to our chemo- and cyclostratigraphic calibration, this episode of low carbonate saturation of seawater reflects a pulse of major volcanic CO2 release from the Ontong-Java large igneous province that was sufficiently short to have escaped internal buffering by the dynamics of the ocean lysocline.

Continue reading ‘Environmental change and carbon-cycle dynamics during the onset of Cretaceous oceanic anoxic event 1a from a carbonate-ramp depositional system, Abu Dhabi, U.A.E.’

Summer trends and drivers of sea surface fCO2 and pH changes observed in the southern Indian Ocean over the last two decades (1998–2019) (update)

The decadal changes in the fugacity of CO2 (fCO2) and pH in surface waters are investigated in the southern Indian Ocean (45–57 S) using repeated summer observations, including measurements of fCO2, total alkalinity (AT) and total carbon (CT) collected over the period 1998–2019 in the frame of the French monitoring programme OISO (Océan Indien Service d’Observation). We used three datasets (underway fCO2, underway ATCT and station ATCT) to evaluate the trends of fCO2 and pH and their drivers, including the accumulation of anthropogenic CO2 (Cant). The study region is separated into six domains based on the frontal system and biogeochemical characteristics: (i) high-nutrient low-chlorophyll (HNLC) waters in the polar front zone (PFZ) and (ii) north part and (iii) south part of HNLC waters south of the polar front (PF), as well as the highly productive zones in fertilised waters near (iv) Crozet Island and (v) north and (vi) south of Kerguelen Island. Almost everywhere, we obtained similar trends in surface fCO2 and pH using the fCO2 or ATCT datasets. Over the period 1998–2019, we observed an increase in surface fCO2 and a decrease in pH ranging from +1.0 to +4.0 µatm yr−1 and from −0.0015 to −0.0043 yr−1, respectively. South of the PF, the fCO2 trend is close to the atmospheric CO2 rise (+2.0 µatm yr−1), and the decrease in pH is in the range of the mean trend for the global ocean (around −0.0020 yr−1); these trends are driven by the warming of surface waters (up to +0.04 C yr−1) and the increase in CT mainly due to the accumulation of Cant (around +0.6 µmol kg−1 yr−1). In the PFZ, our data show slower fCO2 and pH trends (around +1.3 µatm yr−1 and −0.0013 yr−1, respectively) associated with an increase in AT (around +0.4 µmol kg−1 yr−1) that limited the impact of a more rapid accumulation of Cant north of the PF (up to +1.1 µmol kg−1 yr−1). In the fertilised waters near Crozet and Kerguelen islands, fCO2 increased and pH decreased faster than in the other domains, between +2.2 and +4.0 µatm yr−1 and between −0.0023 and −0.0043 yr−1. The fastest trends of fCO2 and pH are found around Kerguelen Island north and south of the PF. These trends result from both a significant warming (up to +0.07 C yr−1) and a rapid increase in CT (up to +1.4 µmol kg−1 yr−1) mainly explained by the uptake of Cant. Our data also show rapid changes in short periods and a relative stability of both fCO2 and pH in recent years at several locations both north and south of the PF, which leaves many open questions, notably the tipping point for the saturation state of carbonate minerals that remains highly uncertain. This highlights the need to maintain observations in the long-term in order to explore how the carbonate system will evolve in this region in the next decades.

Continue reading ‘Summer trends and drivers of sea surface fCO2 and pH changes observed in the southern Indian Ocean over the last two decades (1998–2019) (update)’

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