1,721,045 research outputs found
Study of the Seasonal Water Cycle over the Indian Subcontinent and the Southern Ocean using Stable Isotopes in Rainwater and Water Vapor
Full text linkStable isotope ratios in rainwater and water vapor act as a tracers of the hydrological cycle. The data on stable isotopic composition in rainwater and water vapor are limited due to the lack of observational studies across the Indian subcontinent and over the ocean. These present day observations are important database to deduce the paleo-climatic condition from geological archives. In majority of the cases, isotopic records are translated into physical factors with the present background knowledge where relationships with physical variables are well established. In case of tropical region, the primary controlling factor identified behind the stable isotopic variations is the amount of rainfall. However recent observations contradict such relationships challenging the role of amount effect and identified source moisture effect on stable isotope ratios in rainwater at Indian stations.
The thesis investigated the amount effect relationship of isotopes at seasonal time scales. The long period observation covering 4 years, where daily time interval rainwater samples collected were used for our study. We used two different station locations; Thiruvananthapuram and Bangalore, where monsoonal rainfall is received for Southwest and Northeast periods. The role of mesoscale and synoptic convection and rainout along the transport pathways were found responsible for the isotopic variance. The role of moisture source regions, rainout over the advection pathways, high rainfall producing systems such as depression and cyclones, and continental recycling of water on rainwater and water isotopes ratios were major findings of the thesis work which are detailed in the chapters. Upon knowing the atmospheric and oceanic condition at the moisture source region based on satellite data and reanalysis data set we modeled our observations using the governing equations of isotope fractionation and well accepted Rayliegh’s distillation model. The observations on rainwater and water vapor isotope ratios in oceanic region are extremely limited due to difficulties in conducting sampling. Water vapor and rainwater observations over the Southern Ocean during the expedition of 2013 and estimation of the moisture recycling across the latitudes over the oceanic regions is a novel work in this thesis
CO2 Ventilation, Hydrological Cycle over Southern Ocean and Clumped Isotope Thermometry in Biogenic Carbonates
Full text linkThe thesis presents observations on the CO2 concentration and carbon isotopes in air CO2 (δ13C) to constrain the inter-annual variability of carbon inventory over the Southern Ocean between the years 2011-2013. Based on the observation, the region of CO2 venting was identified over the Southern Ocean. Further, isotopic characterization allowed inferring about the possible sources of CO2 degassing and contribution from the dissolved inorganic carbon (DIC) that exsolved to generate CO2. It is concluded that the origin CO2 is mainly from the degassing of CO2 available from the dissociation of DIC or organic degradation.
Live Foraminiferal samples of Globigerina bulloides from towing were captured, separated and analysed for δ18O and δ13C from various locations across the Southern Ocean between 10°N−60°S. A large similarities in the estimated values (deduced from simultaneous composition of ocean water 18O, δ13C in DIC and temperature i.e. SST under equilibrium condition) and measured δ18O and δ13C values were observed until 40°S from the equator, and hence it was concluded that the calcification depth of G. bulloides is confined to a depth of ~75-200m till 40°S latitude. However, further south (>40oS) disequilibrium from the estimates was detected. A number of possible reasons were cited for the observed disequilibrium such as (1) Deeper depth habitat (2) Partial dissolution (3) Non-equilibrium
calcification (4) Oceanic Suess Effect and (5) Genetic Variability. A box model of isotopic mass balance was presented in this study to explain the pattern of enrichment in the 13C values of sea water DIC with latitude (up to about 43°S). The model shows that a steady state of the carbon isotope ratio of water is achieved in a relatively short time of ~5000 days. Rainwater isotope
in the open marine condition across the latitudinal transects over Southern Ocean marking zone of precipitation and evaporation is another element of this thesis. A variation with excess lighter isotopes in rainwater was observed in high latitude rain in this study. Observed isotopic depletion is attributed to rainout process over the ocean. The average rainout fraction over the Southern Ocean in the region of zone of precipitation is ~44%, while it drops to ~25% in the zone of evaporation. Second part of the thesis presents a novel method of isotope thermometry which is called “clumped isotope (13C18O16O16O-2 in the calcite structure) thermometry”. A revision in the thermometry equation relating 47 vs T in synthetic carbonates precipitates and otoliths was proposed. The revised calibration was used on fish otoliths from the modern and past environment to estimate the temperatures. Together with the clumped isotope, conventional stable isotopes in the shell carbonates were measured to effectively reconstruct the seasonal fresh water fraction at seasonal time scales
Ab initio Quantum Chemical Studies on Kinetic Fractionation during the analysis of Carbonates for the Clumped Isotope Thermometry
No full textStable and clumped isotopic compositions of molecules and minerals carry the signatures of temperatures and other physical and chemical conditions of the time of their formation. Isotopic compositions of such precipitate are preserved in carbonate that provides information about the climate through geological time. The carbonates formed in the aquatic environment serve as an archive for past climate and temperature reconstruction. In nature, sedimentary carbonate rocks are primarily composed of minerals calcite (CaCO3) and dolomite (CaMg(CO3)2). They comprise ~20% of the surface sedimentary rocks on Earth and are also found in other planets, with the oldest being ~3.5 Ga, almost as primitive as the Earth itself. The majority of them form in the aquatic environments that ranged from the warm, sunlit shallow seafloor to the cold, perpetually dark, deep ocean. Carbonate rocks are also traced in the terrestrial and extraterrestrial environment, which includes terrestrial spring waters, rivers and lakes, caves, soils, and meteorites from outer space.
Ab initio quantum chemical simulations are used to calculate the extent of equilibrium and kinetic isotope fractionations, which provided additional theoretical references in clumped isotope paleothermometry. Ab initio quantum chemical simulations provide the inputs in terms of vibration frequencies and thermal energies of the optimized stable molecules and the transition state structures for the partition function calculations of equilibrium and kinetic fractionations. Ab initio calculations using density functional theory (DFT) are performed using 'Gaussian09' computational chemistry packages. Equilibrium constant and partition function calculations are performed using scripts in Matlab and Python.
Though the clumped isotope proxy is based on the temperature dependence of 13C-18O bonding preference in the mineral lattice, which is captured in the product CO2, there is limited information on the phosphoric acid reaction mechanism and the magnitude of clumped isotopic fractionation (mass 63 in CO32- to mass 47 in CO2) during the acid digestion. We explored the reaction mechanism for phosphoric acid digestion of calcite using first-principles density functional theory. We identified the transition state structures for each protonation reaction involving different isotopologues and used the corresponding vibrational frequencies in reduced partition function theory to estimate Δ47 acid fractionation. We showed that the acid digestion reaction, which results in the formation of CO2 enriched with 13C-18O bonds, commences with the protonation of calcium carbonate in the presence of water. Our simulations yielded a relationship between Δ47 acid fractionation for calcite and reaction temperature as Δ47 acid fractionation in calcite = -0.30175 + 0.57700*105/ T2 - 0.10791* (105/ T2)2, with T varying between 298.15 K and 383.15 K. This relationship shows a higher slope (Δ47 acid fractionation vs. 1/T2 curve) than previous studies based on the H2CO3 model. The theoretical estimates from the present and earlier studies encapsulate experimental observations from both 'sealed vessel' and 'common acid bath' acid digestion methods from literature.
Previous theoretical models for determining clumped isotopic fractionation in product CO2 during acid digestion of carbonates are independent of the cations present in the carbonate lattice. Hence further study is required to understand the cationic effect. We studied the acid reaction mechanism and calculated the acid fractionation factor for dolomite using partition functions and vibrational frequencies obtained for the transition state structure, and determined the effect of cations on the acid fractionation factor. Theoretically obtained acid fractionation factor for dolomite can be expressed as Δ47 acid fractionation in dolomite = -0.28563 + 0.49508*(105/ T2) - 0.08231* (105/ T2)2 for a temperature range between 278.15 K and 383.15 K. The theoretical slope of the dolomite-acid digestion curve is lower than that of the calcite-acid digestion curve obtained using the identical reaction mechanism. Our theoretical slope is consistent with the result from the common acid bath experiments but higher than the slope obtained in the experimental study using the sealed vessel and modified sealed vessel method and previous theoretical study using the H2CO3 model. Transition state structure, obtained in our study, includes the cations present in the carbonate minerals and provides distinct acid fractionation factors for calcite and dolomite. The observed gentler slope of theoretically calculated dolomite-acid digestion curve compared to calcite is expected considering the stronger Mg-O bond.
In the present theoretical study, we provided the acid digestion reaction mechanism based on the protonation and determined a quantitative acid digestion correction factor for a range of reaction temperature for the experimental protocols where the product CO2 is immediately removed from the system, and there is not enough chance of post-digestion isotope exchanges. We suggest using appropriate acid digestion correction factors depending on the experimental techniques used for acid digestion of carbonates.CSIR-UGC NET JRF & SRF Fellowshi
Reconstruction of temperature for Cenozoic and Proterozoic Ocean water using clumped isotope thermometry
No full textClumped isotope thermometry is a novel tool which is used for the determination of formation temperature for carbonates of diverse origin and understanding different marine and terrestrial processes. The primary interest of this study is to develop use clumped as well as stable isotope as the tool to deduce temperature of ocean water from Cenozoic and Proterozoic time window. Stable and clumped isotope studies have previously shown that both of these isotopes experience different degrees of fractionation for different mineralogy of carbonates (e.g., calcite, dolomite, aragonite etc.) during the sample preparation procedures conducted at different temperature conditions. Major highlights of my research work include development of analytical procedure and revisiting the numerical equation for thermometry using aragonite and dolomite minerals. Exclusive, experiments are conducted at different temperatures to understand the isotopic fractionation during sample preparation and analysis.
As a part of the present study, the natural aragonite specimens with well characterized temperature information are analysed in order to study the fractionation during acid digestion and clumped isotope thermometry calibration using sealed vessel or Break-seal method developed at IISc. Calcite and aragonite react or fractionate in a similar manner during phosphoric acid digestion which is evident from the previous theoretical and experimental studies. However, the protocol specific variation of temperature sensitivity and intercept values of the clumped isotope thermometric calibrations demarcates the existence of inconsistencies associated with the acid digestion protocols. This study proposes revised calibration for aragonite clumped isotope thermometry using the otoliths. As an application of the calibration study, palaeo-otoliths and travertine are analysed for temperature estimates infer about the freshwater availability near coastal United States covering the time from early Cretaceous, Eocene, Oligocene and Pleistocene time. Further, we validated the temperature of travertine formation analysing modern day tufa with known temperature record extending the thermometry to 40°C. A second analytical accomplishment includes designing and executing a new isotope dilution method for the clumped isotope analysis for small carbonate powder (2-3 mg).
We have also established acid fractionation for dolomite during reaction with the phosphoric acid digestion at 25℃ using seal vessel method. We proposed acid fractionation correction factor of 0.069 for the break seal method, suitable for our experimentation. Using this approach, we determined clumped isotope ratio in the pristine relic carbonate mud from the Vempalle Formation of Proterozoic Ocean. Our observation revealed lowest temperature value of 21.7℃ and δ18OVSMOW value of water as -9.96‰. This is the first evidence documenting lighter oxygen isotopic composition of Proterozoic Ocean The overlying stromatolites with dolomites registered consistently higher temperatures (72.8-106.2℃) that might suggests precipitation from hydrothermal fluid or early phase burial diagenesis promoting water-rock interaction. Our observations resolved long-standing dispute about existence of mild and lighter composition of water in the Proterozoic Ocean
Stable Isotopic Composition of Rice Grain Organic Matter as an Archive of Monsoonal Climate
No full textRice grows in saturated soil water condition and its requirement for water is highest amongst other cereal crops. In India, the southwest monsoon wind regime brings rainfall that provides a favourable environment for rice cultivation. Thus, there is significant dependency ofrice production on the southwest monsoon rainfall. Being a crop that grows across diverse climatic regions in India ranging from the humid to semi-arid, it offers possibility to explore therelationship between stable isotopic compositions in the grain organic matter with the climaticfactors relevant for its growth.
In this thesis, we measured the isotopic compositions of oxygen, hydrogen and carbon of several rice genotypes that were cultivated during the southwest monsoon in diverse climatic regions across the Indian landmass. These isotopic values were then compared with the seasonalaverage values of climate factors such as relative humidity and temperature. Together with thiswe also studied the dependency of the oxygen isotope composition of the grain OM (δ18OOM) onthat of the source water (δ18OSW). Upon removal of δ18OSW effect from δ18OOM, we obtained astrong and significant relationship between the 18O enrichment in grain organic matter (definedas 18OOM) with relative humidity. The gradient recorded was 0.45‰ shift in 18OOM with 1%change in the relative humidity level. This relationship can potentially be used to estimate thepast variations in relative humidity (and by extension, can provide a measure of monsoon rainfallvariations). We further validated this relationship based on experiments carried out in aglasshouse where all the physical factors were well-monitored. Together with this, carbonisotopic composition measured in the rice grain organic matter were used to infer the water useefficiency of rice grown in different climatic settings. The stable isotope approach was furtherimplemented for studying the archaeological rice grains recovered from archaeological sites.
Analysis of carbon isotopic composition of archaeological rice grains from seven archaeologicalsites (Balu, Kanmer, Ojiyana, Lahuradewa, JognaKhera, Hulas and Kunal), belonging to theHarappan civilization and other contemporary cultures provided a new suit of data on quantitativeestimate of the hydroclimatic condition (specifically relative humidity) and water availabilityduring the existence of this civilizatio
On the spatio-temporal distribution of stable isotope ratios in the hydrological cycle over India and the Southern Ocean
No full textThe isotopic composition of water vapor and precipitation at continental and oceanic sites
depends on factors such as: the geographical location of the sampling site, meteorological
conditions at the moisture source areas, local meteorological conditions, rainout history
of air-masses along their trajectory, large-scale moisture recycling below cloud evaporation,
etc. The present study aims at identification and quantification of such processes
over the Indian subcontinent and the Southern Ocean based on observed stable isotopic
composition in precipitation and atmospheric moisture.
The oxygen and hydrogen isotopic composition of precipitation at Srinagar, Kashmir,
allowed delineating the respective role of large-scale moisture transport processes vs that
of other meteorological factors such as temperature and precipitation amount. The time
integrated, large-scale convective activity over several days, constitutes a major factor
governing the isotopic composition of precipitation at Srinagar, whereas local meteorological
factors play a minor role. Over the Southern Ocean, as opposed to local factors,
atmospheric pressure and air temperature majorly govern the precipitation isotopic composition.
The isotopic data was further used to estimate the moisture sources contributing to
the summer precipitation at Kolkata and summer/winter precipitation at Srinagar. A
simple box model was developed to simulate the moisture transport and mixing to estimate
the contribution of sources to precipitation at Srinagar and Kolkata. Precipitation
at Srinagar, during the active period of the Western Disturbances, carries 80% of moisture
from the Mediterranean region while the balance originates from the Arabian area.
Adopting moisture source isotope signatures observed over a long-time span at the New
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Abstract ix
Delhi station, the Rayleigh’s distillation model explains the observed variability in the
isotopic data at Kashmir Valley during the Indian Summer Monsoon. At Kolkata, the
Bay of Bengal is a major moisture contributor to precipitation supplying overall 65-75%
of the total precipitation during the south west and the continental contribution varies
from 25-35%.
Over the Himalayan region, a discrepancy was noted between the measured isotopic
composition of precipitation and that simulated by an isotope enabled general circulation
model. The model underestimates the number of precipitation days as well as the magnitude
of isotopic values. This may be attributed to deficiencies in the meteorological inputs
or inadequate estimates of other parameters used in the model, as distinct hydrological
parameterizations do lead to large differences in isotopic responses.
The Craig and Gordon models are used to calculate the isotopic composition of evaporation
flux in many isotope enabled general circulation models. The parameters governing
the isotopic composition of evaporation flux can be considered separately or simultaneously
in the Traditional and the Unified Craig-Gordon (CG) models. These models were
tested for different molecular diffusivity ratios and ocean surface conditions to identify the
parameterizations that best match the observed relationships between the meteorological
parameters and the isotopic composition of water vapor. The model that matches best
is used to calculate the isotopic composition of the local evaporation along the Southern
Ocean sampling transect. The advected end member isotopic composition is assumed
from the previous observations along the path followed by the air trajectories. Solving in
a two-component mixing framework, the relative contribution of advected and evaporated
vapor along the sampling transect is established. The advected moisture is a prominent
component of the ambient vapor and its contribution becomes greater with increasing
latitudes. South of 65 S the amount of moisture present in the atmosphere is less and is
majorly local in origin with a small mixing of light Antarctic moisture.
Results from this study should be useful to tune the models, and further help in the
interpretation of regional paleo-climate data based on isotope proxies
High Resolution Reconstruction of Rainfall Using Stable Isotopes in Growth Bands of Terrestrial Gastropod
Full text linkReconstruction studies of seasonal rainfall utilizing stable isotope based proxy approach suffer from the limitations of time resolutions. Conventional methods and archives limit the achievable resolution to annual scales. However, high resolution reconstruction (seasonal to sub-weekly scale) can be achieved in proxy records where growth rates are high enough to leave spatial signatures in an organically or inorganically deposited layer such as growth bands. In this study, aragonitic skeleton of the gastropod Lissachatina fulica (Bowdich, Giant African Land Snails) is investigated with an aim to achieve sub-weekly scale reconstruction of the Indian monsoon rainfall. These terrestrial gastropods are native of Africa and highly invasive. Their evolution in the geological time period dates back to the Pliocene and is presently distributed across the tropical belt. They exhibit a high growth rate in the presence of water and high relative humidity in the environment. As a result, they are ideally suited for the task of palaeo seasonality reconstruction. The isotopic patterns recorded in their growth bands reveal composition of environmental water at seasonal time scales. In vitro studies were carried out on L. fulica to estimate their growth rates and growth responses to changes in the physical conditions within the
culture chamber.
The Indian monsoon rainfall exhibits characteristic dry spells that are generally sandwiched between periods of active phases of high rainfall during the South West monsoon season. These dry spells are typically characterized by rainfall with low intensity. Isotope fingerprinting of the rain water at daily time resolution, covering the years of 2007-10 exhibited distinct isotopic ratios for the dry and wet spells. Dry spells were clearly demarcated in the
record with isotopically enriched signature. In addition, the study indentified the role of three distinct moisture sources on δ18O of rain water at Bangalore, India. The variability in the oxygen isotopic composition of the Indian monsoon rainfall is predominantly controlled by this source moisture variability at inter annual time scales, while temperature and amount of rainfall tend to dominate the variability in the precipitation isotopes at seasonal and weekly scales.
Simultaneous isotopic analyses of both rainwater and shell carbonates growth bands were undertaken to understand their relationship to aid in high resolution reconstruction. Carbonate found in the growth bands of the gastropods, which is precipitated under equilibrium condition from rainwater, preserves the signature of rainfall. This provides an opportunity to reconstruct rainfall parameters (i.e. amount and moisture sources) knowing the variability in shell carbonates. Stable isotopic ratios measured across the growth bands of live shell specimens collected from the southern and eastern Indian regions (Bangalore and Kolkata, respectively) were compared with the rainfall isotope ratios at these two locations; signature of dry spells were clearly identified from the study of isotopic composition in the growth bands of the gastropod specimens.
The approach was also extended to older samples from historical archives from eastern Indian region (Kolkata, East India). Individual specimens belonging to the same species of gastropod, which were collected during the monsoon season of the year 1918 were used for reconstructing the seasonal pattern in monsoon rainfall over the region. The record of variation in the isotopic composition seen in the shell was compared with the rainfall data from Indian Metrological Division observatory at Kolkata station. The year 1918 was characterized as a
major drought year and the signature of dry period was seen preserved in the specimen. The work under taken in this thesis will widen the scope of seasonality reconstruction using terrestrial shell fossils from palaeo records, which have been rarely investigated in paleoclimate studies from the perspective of understanding the seasonal precipitation variability
Establishment of an Experimental System in India to Measure the Mixing Ratio and Stable Isotopic Composition of Air CO2 & Observations from Urban and Marine Environments
Full text linkThe thesis presents observations on the CO2 mixing ratio and the carbon isotopic ratio (13C/12C i.e. δ13) of atmospheric CO2 from the Indian region, for the period 2008 - 2011. An experimental system was established at the Centre for Earth Sciences, Indian Institute of Science, Bangalore. The experimental protocol involves collection of air samples, extraction of CO2 from the air samples collected, and finally the measurement of the CO2 mixing ratio and isotopic ratios of the extracted CO2 using pressure gauge readings and the dual inlet peripheral of the isotope ratio mass spectrometer, IRMS MAT 253. The isotopic ratios measured are scaled to VPDB and corrected for their N2O contribution. The experimental set up is calibrated with primary carbonate standards (NBS19) and an air CO2 reference mixture. The analytical precision (reproducibility of paired samples) obtained for the atmospheric CO2 measurement is ±7 µ mol.mol-1, ±0.05‰ and ±0.17‰ for the mixing ratio, δ 13C and δ 18Oof atmospheric CO2 respectively. The present study lays emphasis on the CO2 mixing ratio and the δ 13C of atmospheric CO2.
There are very few atmospheric CO2 monitoring stations in India. There exists only one long-term monitoring station, Cabo de Rama, on the west coast of India. Of late, a few new stations for measuring atmospheric trace gases have been in operation, with the major focus being on remote locations. Urban stations in India have never been monitored before for both the mixing ratio and the δ13C of atmospheric CO2 together. Monitoring urban stations in India is crucial today as they have become prime emitters of CO2 due to industrial activity. The emission from the sources varies seasonally and is influenced by factors like the Indian monsoon. The Indian subcontinent is surrounded by the Arabian Sea, the Indian Ocean and the Bay of Bengal which act differentially in terms of CO2 uptake or release.
There is also a differential transport of CO2 to and from the open ocean. Thus, understanding the spatial pattern of CO2 in the marine region close to the Indian subcontinent is essential to understand the oceanic uptake/release of CO2.
As part of this thesis, an urban area was monitored during 2008 - 2011 and the marine region was observed during the southwest monsoon of 2009. The temporal variation of the CO2 mixing ratio and δ13C of atmospheric CO2 was observed over an urban station, Bangalore (12° 58′ N, 77° 38′ E, masl= 920 m), India. Since Bangalore is one of the developing urban cities in India, it is interesting to monitor Bangalore air to understand the impact of anthropogenic emissions on atmospheric CO2 variability. The region has four distinct seasons, dry summer (March – May), southwest monsoon (June – September), post monsoon (October – November) and winter (December – February). Thus, it is also an ideal location to identify the effect of different seasons on the contribution of CO2 from various sources. Air samples were collected from the Indian Institute of Science campus, Bangalore, during 2008 - 2011. Both the diurnal and seasonal variations of the mixing ratio and δ13C of CO2 were observed in Bangalore. On the diurnal scale, a higher mixing ratio with lighter carbon isotopes (negative value) of δ13C of CO2 was recorded in the air-CO2 analyzed during the early morning compared to the late afternoon samples. The observations suggest that coal combustion, biomass burning and car exhausts are possible sources for CO2 identified based on the Keeling plot method. The nocturnal boundary layer (NBL) is found to influence the buildup of CO2 concentration in the early morning. The presence of the NBL in the early morning prevents the mixing of locally produced air with the CO2 from the free atmosphere above. Thus, the free air contribution of CO2 is reduced during the early morning rather than in the afternoon. The effect of seasonal variability in the height of the NBL on the air CO2 mixing ratio and the 13C of atmospheric CO2 were documented in the present study. On a seasonal scale, the free air contribution of CO2 was
found to be higher during the southwest monsoon and winter compared to the dry hot summer and post monsoon period. On a seasonal time scale, a sinusoidal pattern in both the mixing ratio and δ13C has been recorded in the observations. While compared with nearby CO2 monitoring stations like the coastal station, Cabo de Rama, and the Open Ocean station, Seychelles, maintained by CSIRO Australia and NOAA-CMDL respectively, Bangalore recorded higher amplitudes of seasonal variation. Seasonal scale variations have revealed an additional source i.e. emission from the cement industry along with other sources identified from diurnal variations. The emission of CO2 from these different sources is not constant; rather it was found to vary with different seasons. The enhanced biomass burning during the dry season drives the δ13C of atmospheric CO2 towards more negative values, while during the southwest monsoon; the increased biosphere cover pushes the δ13C value of atmospheric CO2 towards positive values. The effect of La Nina in 2011 is also prominent in the observation.
The study also intends to identify the spatial variability of both the mixing ratio and δ 13C air-CO2 close to the urban station, Bangalore based on the simultaneous sampling of air from three locations, Bangalore and two coastal stations, Mangalore and Chennai, which are equidistant from Bangalore. Samples were collected during the southwest monsoon and winter of 2010 - 2011. The observations documented a similar source of CO2 for all the three stations irrespective of the season. The factor responsible for the variability in the mixing ratio and the δ 13C of air CO2 among these stations is the differential transport of air from the marine region and its mixing with locally produced air.
To identify the variability of atmospheric CO2 over the marine region, the atmosphere over the Bay of Bengal was monitored during the southwest monsoon of 2009 as part of the Continental Tropical Convergence Zone (CTCZ) Cruise expedition. The ocean surface water was also monitored simultaneously for the δ18O of water and the δ13C of dissolved
inorganic carbon measurement. The combined observations of both air and water have shown the transport of continental air to the marine region and its uptake by the ocean during the period.
The variability of atmospheric-CO2 is also observed during special events like the solar eclipse. During the annular solar eclipse of 15th January, 2010 an unusually depleted source value was identified for Bangalore air. The role of the boundary layer and a change in photosynthesis were identified as possible factors affecting air CO2 composition.
In conclusion, the thesis has provided the first observations on air CO2 variability from an urban station in India. The observations have identified the possible sources of CO2 and have demonstrated the role of climatic phenomena like the Atmospheric Boundary Layer, Indian Monsoon, and La Nina in controlling the behaviour of sources and sinks and thus affecting the air CO2 variability over land and ocean. The seasonal scale variation based on day-to-day variability in the afternoon samples has revealed the important contribution of emissions from the cement industry whose contribution was absent in the diurnal variability. Thus, it is evident from this study that the timing of air sampling is crucial while identifying the sources. The per capita emission of individual urban stations in India is different; thus, it is essential to monitor more urban stations to identify sources and their different contributions. In future, the simultaneous monitoring of both continental and marine air over both the Arabian Sea and the Bay of Bengal will enable us to understand the long range transport of atmospheric CO2. The long term monitoring of CO2 from the Indian region can give us a better perspective on the effect of the Indian monsoon on air CO2 variability and vice versa
Lab Experiment Documenting Growth of Microbes in an Extreme Condition
No full textBacterial population during 3.2 billion years of early earth was responsible for modifying the greenhouse gas concentration in the early earth. Here we studied the primitive facultative anaerobe E.coli K12, known to contain pathways of mixed acid fermentation in stressed oxygen deficient environment. We carried out chamber experiments where bacteria were grown in M9 minimal media containing 0.4% glucose in crimp sealed chambers for a period of 7 days-12 days. Growth rate for the bacteria were monitored using optical density measurements and CFU values on LB agar. δ13C of CO2 was analysed using Gas Bench peripheral connected with IRMS MAT 253. We observed an approximate enrichment of 3‰ in the 13C data of respired CO2 from the 1st day of incubation till 12 days of incubation under stressed conditions. We suggest that enrichment in δ13C captured a shift in the carbon source from glucose to acetate
Stable isotope geochemistry of carbonatites: New insights into the petrogenesis and evolution
No full textCarbonatites are carbonate-rich magmatic rocks that are commonly thought of having a mantle origin and are thus, of great interest to geologist for understanding the chemical evolution of the upper mantle. This thesis provides new perspectives on processes related to the origin, formation, and evolution of carbonatites using a multi-isotope approach. In the first of several studies in this thesis, variations in the stable carbon and oxygen isotope record of carbonatites through geologic time were assessed from newly acquired and the available literature data. Using the classic Amba Dongar carbonatite-alkaline complex of India as a case study, age constraints were placed on carbonatite magmatism which revealed its temporal relation to the peak Deccan volcanism. U-Pb dating of apatite in the carbonatites and associated nephelinites yielded 65.4 Ma as the emplacement age of the alkaline rocks, which reasserts the contemporaneity of alkaline magmatism and the Deccan volcanism. In a further study, an improved low-temperature acid digestion method was developed by employing a break seal vessel technique which yielded good precision and reproducibility in the long term for a suite of carbonate reference materials in clumped isotope measurements. On the application of the abovementioned technique that was developed, the abundance of multiply substituted “clumped” isotopologues in carbonate minerals (calcite, ankerite, dolomite) was used to derive the apparent equilibrium temperatures of carbonatites. These results reveal that the clumped-isotope temperatures derived for the carbonatites are much lower than typical magmatic temperatures, providing additional mechanistic insights into the formation and modification of the primary rocks due to fluid-rock interaction, recrystallisation, closed-system isotope exchange, and mineralisation of rare earth elements. The thesis further evaluates the effective use of triple oxygen isotope variations in carbonates (methods and applications) in understanding the isotopic fractionations in Earth surface processes and the interaction between different reservoirs. The findings clearly demonstrate the traceability of the isotopic ratios to the different origins and mechanisms of formation of the carbonates. Finally, the thesis work assesses the mantle origin of carbonatites using triple oxygen isotope compositions of several other global carbonatites. It was established that primary igneous carbonatites define a range of triple oxygen isotope values that are independent of mineralogy and overlaps with commonly investigated mantle rocks and minerals
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