Centrte for Earth Sciences

The abundance of the doubly substituted CO 2 isotopologue, 13 C 18 O 16 O, in CO 2 produced by phosphoric acid digestion of synthetic, inorganic calcite and natural, biogenic aragonite is proportional to the concentration of 13 C-18 O bonds in reactant carbonate, and the concentration of these bonds is a function of the temperature of carbonate growth. This proportionality can be described between 1 and 50°C by the function: D 47 = 0.0592 AE 10 6 AE T À2 À 0.02, where D 47 is the enrichment, in per mil, of 13 C 18 O 16 O in CO 2 relative to the amount expected for a stochastic (random) distribution of isotopes among all CO 2 isotopologues, and T is the temperature in Kelvin. This relationship can be used for a new kind of carbonate paleothermometry, where the temperature-dependent property of interest is the state of ordering of 13 C and 18 O in the carbonate lattice (i.e., bound together vs. separated into different CO 3 2À units), and not the bulk d 18 O or d 13 C values. Current analytical methods limit precision of this thermometer to ca. ± 2°C, 1r. A key feature of this thermometer is that it is thermodynamically based, like the traditional carbonate-water paleothermometer, and so is suitable for interpolation and even modest extrapolation, yet is rigorously independent of the d 18 O of water and d 13 C of DIC from which carbonate grew. Thus, this technique can be applied to parts of the geological record where the stable isotope compositions of waters are unknown. Moreover, simultaneous determinations of D 47 and d 18 O for carbonates will constrain the d 18 O of water from which they grew.

In order to generate a reliable and long-lasting stable isotope ratio standard for CO 2 in samples of clean air, CO 2 is liberated from well-characterized carbonate material and mixed with CO 2 -free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO 2 is generated by a conventional acid digestion of powdered carbonate. Evolved CO 2 gas is mixed and equilibrated with a prefabricated gas comprised of N 2 , O 2 , Ar, and N 2 O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction/measurement systems, varied within very small margins of error appropriate for high-precision air-CO 2 work (about AE0.015% for d 13 C and AE0.025% for d 18 O). To establish a valid d 18 O relation to the VPDB scale, the temperature dependence of the reaction between 25 and 478C has been determined with a high level of precision. Using identical procedures, CO 2 -in-air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, d 13 C ¼ þ1.95% and d 18 O ¼ À2.2% exactly); (2) a local calcite similar in isotopic composition to NBS 19 ('MAR-J1', d 13 C ¼ þ1.97% and d 18 O ¼ À2.02%), and (3) a natural calcite with isotopic compositions closer to atmospheric values ('OMC-J1', d 13 C ¼ À4.24% and d 18 O ¼ À8.71%). To quantitatively control the extent of isotope-scale contraction in the system during mass spectrometric measurement other available international and local carbonate reference materials (L-SVEC, IAEA-CO-1, IAEA-CO-8, CAL-1 and CAL-2) were also processed. As a further control pure CO 2 reference gases (Narcis I and II, NIST-RM 8563, GS19 and GS20) were mixed with CO 2 -free synthetic air. Independently, the pure CO 2 gases were measured on the dual inlet systems of the same mass spectrometers. The isotopic record of a large number of independent batches prepared over the course of several months is presented. In addition, the relationship with other implementations of the VPDB-scale for CO 2in-air (e.g. CG-99, based on calibration of pure CO 2 gas) has been carefully established. The systematic high-precision comparison of secondary carbonate and CO 2 reference materials covering a wide range in isotopic composition revealed that assigned d-values may be (slightly) in error. Measurements in this work deviate systematically from assigned values, roughly scaling with isotopic distance from NBS 19. This finding indicates that a scale contraction effect could have biased the consensus results. The observation also underlines the importance of cross-contamination errors for high-precision isotope ratio measurements.

The ionisation efficiencies of N 2 O vs. CO 2 as well as their ratios were measured in detail introducing clean N 2 O and CO 2 into the electron impact ion source of an isotope ratio mass spectrometer. Changes in the ionisation efficiency ratio (IER) were found for different electron energy settings and compared with the ratios of literature ionisation cross-section values for pure N 2 O and CO 2 . To establish the influence of mixtures of N 2 O and CO 2 in a mass spectrometer, artificial air mixtures were prepared by mixing different amounts of N 2 O and CO 2 from well-calibrated spike cylinders with CO 2 -free air. The mixing ratios varied from 8-512 ppb for N 2 O and from 328-744 ppm for CO 2 . With these mixtures the effects of varying N 2 O concentrations on apparent CO 2 isotope ratios in air samples were determined. After applying a mass balance correction the d 13 C results were consistent within small error margins. The data seemed almost independent from a particular choice for the IER of N 2 O vs. CO 2 in the correction algorithm. For d 18 O a small effect of the ionisation efficiency ratio of N 2 O vs. CO 2 was found. Several sets of calculations were made varying the IER between 0.88 and 0.62. The dependence of d 18 O was the smallest with an adopted IER of 0.68-0.72 in the mass balance correction equation for isotopic analysis of CO 2 in air. For high-precision measurements of the CO 2 stable isotope ratios in air samples a careful assessment of the mass spectrometer performance is necessary. Different ion sources, even different ion source settings, alter the IER of N 2 O vs. CO 2 which is used in the N 2 O correction algorithm. Preferably, the specific mass spectrometric behaviour should be established with clean N 2 O/CO 2 mixtures or with air mixtures covering a larger range of N 2 O concentrations.

The ionisation efficiencies of N2O vs. CO2 as well as their ratios were measured in detail introducing clean N2O and CO2 into the electron impact ion source of an isotope ratio mass spectrometer. Changes in the ionisation efficiency ratio (IER) were found for different electron energy settings and compared with the ratios of literature ionisation cross-section values for pure N2O and CO2. To establish the influence of mixtures of N2O and CO2 in a mass spectrometer, artificial air mixtures were prepared by mixing different amounts of N2O and CO2 from well-calibrated spike cylinders with CO2-free air. The mixing ratios varied from 8–512 ppb for N2O and from 328–744 ppm for CO2. With these mixtures the effects of varying N2O concentrations on apparent CO2 isotope ratios in air samples were determined. After applying a mass balance correction the δ13C results were consistent within small error margins. The data seemed almost independent from a particular choice for the IER of N2O vs. CO2 in the correction algorithm. For δ18O a small effect of the ionisation efficiency ratio of N2O vs. CO2 was found. Several sets of calculations were made varying the IER between 0.88 and 0.62. The dependence of δ18O was the smallest with an adopted IER of 0.68–0.72 in the mass balance correction equation for isotopic analysis of CO2 in air. For high-precision measurements of the CO2 stable isotope ratios in air samples a careful assessment of the mass spectrometer performance is necessary. Different ion sources, even different ion source settings, alter the IER of N2O vs. CO2 which is used in the N2O correction algorithm. Preferably, the specific mass spectrometric behaviour should be established with clean N2O/CO2 mixtures or with air mixtures covering a larger range of N2O concentrations. Copyright © 2004 John Wiley & Sons, Ltd.

Stable isotope ratios of the life science elements carbon, hydrogen, oxygen and nitrogen vary slightly, but significantly in major compartments of the earth. Owing mainly to antropogenic activities including land use change and fossil fuel burning, the 13 C/ 12 C ratio of CO 2 in the atmosphere has changed over the last 200 years by 1.5 parts per thousand (from about 0.0111073 to 0.0110906). In between interglacial warm periods and glacial maxima, the 18 O/ 16 O ratio of precipitation in Greenland has changed by as much as 5 parts per thousand (0.001935-0.001925). While seeming small, such changes are detectable reliably with specialised mass spectrometric techniques. The small changes reflect natural fractionation processes that have left their signature in natural archives. These enable us to investigate the climate of past times in order to understand how the Earth's climatic system works and how it can react to external forcing. In addition, studying contemporary isotopic change of natural compartments can help to identify sources and sinks for atmospheric trace gases provided the respective isotopic signatures are large enough for measurement and have not been obscured by unknown processes. This information is vital within the framework of the Kyoto process for controlling CO 2 emissions.

The ratio of the measured abundance of 13 C-18 O bonding CO 2 to its stochastic abundance, prescribed by the d 13 C and d 18 O values from a carbonate mineral, is sensitive to its growth temperature. Recently, clumped-isotope thermometry, which uses this ratio, has been adopted as a new tool to elucidate paleotemperatures quantitatively. METHODS: Clumped isotopes in CO 2 were measured with a small-sector isotope ratio mass spectrometer. CO 2 samples digested from several kinds of calcium carbonates by phosphoric acid at 25 C were purified using both cryogenic and gas-chromatographic separations, and their isotopic composition (d 13 C, d 18 O, Δ 47 , Δ 48 and Δ 49 values) were then determined using a dual-inlet Delta XP mass spectrometer. RESULTS: The internal precisions of the single gas Δ 47 measurements were 0.005 and 0.02 % (1 SE) for the optimum and the routine analytical conditions, respectively, which are comparable with those obtained using a MAT 253 mass spectrometer. The long-term variations in the Δ 47 values for the in-house working standard and the heated CO 2 gases since 2007 were close to the routine, single gas uncertainty while showing seasonal-like periodicities with a decreasing trend. Unlike the MAT 253, the Delta XP did not show any significant relationship between the Δ 47 and d 47 values. CONCLUSIONS: The Delta XP gave results that were approximately as precise as those of the MAT 253 for clumped-isotope analysis. The temporal stability of the Delta XP seemed to be lower, although an advantage of the Delta XP was that no dependency of d 47 on Δ 47 was found.

The Cretaceous greenhouse climate was accompanied by major changes in Earth's hydrological cycle, but seasonally resolved hydroclimatic reconstructions for this anomalously warm period are rare. We measured the δO and CO clumped isotope Δ of the seasonal growth bands in carbonate shells of the mollusc Villorita cyprinoides (Black Clam) growing in the Cochin estuary, in southern India. These tandem records accurately reconstruct seasonal changes in sea surface temperature (SST) and seawater δO, allowing us to document freshwater discharge into the estuary, and make inferences about rainfall amount. The same analytical approach was applied to well-preserved fossil remains of the Cretaceous (Early Maastrichtian) mollusc Phygraea (Phygraea) vesicularis from the nearby Kallankuruchchi Formation in the Cauvery Basin of southern India. The palaeoenvironmental record shows that, unlike present-day India, where summer rainfall predominates, most rainfall in Cretaceous India occurred in w...

The solar salterns in Tuticorin, India, are man-made, saline to hypersaline systems hosting some uniquely adapted populations of microorganisms and eukaryotic algae that have not been fully characterized. Two visually different microbial mats (termed ‘white’ and ‘green’) developing on the reservoir ponds (53 PSU) were isolated from the salterns. Firstly, archaeal and bacterial diversity in different vertical layers of the mats were analyzed. Culture-independent 16S rRNA gene analysis revealed that both bacteria and archaea were rich in their diversity. The top layers had a higher representation of halophilic archaea Halobacteriaceae, phylum Chloroflexi, and classes Anaerolineae, Delta- and Gamma- Proteobacteria than the deeper sections, indicating that a salinity gradient exists within the mats. Limited presence of Cyanobacteria and detection of algae-associated bacteria, such as Phycisphaerae, Phaeodactylibacter and Oceanicaulis likely implied that eukaryotic algae and other photot...

A single locality of the Late Cretaceous (Maastrichtian) Lameta Formation at Pisdura in Central India has yielded a large number of coprolites attributed to titanosaurian dinosaurs. Internally the coprolites are dark grey and contain abundant plant tissues and other organic materials. The plant tissues are mostly of gymnospermous origin. In addition, remains of bacterial colonies, fungal spores and algae are seen in the macerated fraction under scanning electron microscope. The dark grey appearance is probably attributable to fine-grained organic matter within voids in tracheids or xylem. The average 13 C/ 12 C ratio of the organic matter in the coprolites is-24‰ (relative to PDB) suggesting that plants of C 3 type were the main diet of their producers. A comparison of 15 N value (about 4‰ w.r.t. air) of the coprolites with that of faecal matter of modern herbivores and carnivores suggests that gut fermentation may not have been an active mechanism in the digestion process of titanosaurs.

Presence of calcareous nodules in the upper part of the Talchir sedimentary sequence (Permo-Carboniferous) in Gondwana sediments of east-central India offers a chance to delineate the environment of deposition and the regional palaeo-climate. Carbon and ...

We present here, an experimental set-up developed for the first time in India for the determination of mixing ratio and carbon isotopic ratio of air-CO 2 . The set-up includes traps for collection and extraction of CO 2 from air samples using cryogenic procedures, followed by the measurement of CO 2 mixing ratio using an MKS Baratron gauge and analysis of isotopic ratios using the dual inlet peripheral of a high sensitivity isotope ratio mass spectrometer (IRMS) MAT 253. The internal reproducibility (precision) for the δ 13 C measurement is established based on repeat analyses of CO 2 ± 0.03 . The set-up is calibrated with international carbonate and air-CO 2 standards. An in-house air-CO 2 mixture, 'OASIS AIRMIX' is prepared mixing CO 2 from a high purity cylinder with O 2 and N 2 and an aliquot of this mixture is routinely analyzed together with the air samples. The external reproducibility for the measurement of the CO 2 mixing ratio and carbon isotopic ratios are ±7 (n = 169) μmol•mol -1 and ±0.05 (n = 169) based on the mean of the difference between two aliquots of reference air mixture analyzed during daily operation carried out during November 2009-December 2011. The correction due to the isobaric interference of N 2 O on air-CO 2 samples is determined separately by analyzing mixture of CO 2 (of known isotopic composition) and N 2 O in varying proportions. A +0.2 correction in the δ 13 C value for a N 2 O concentration of 329 ppb is determined. As an application, we present results from an experiment conducted during solar eclipse of 2010. The isotopic ratio in CO 2 and the carbon dioxide mixing ratio in the air samples collected during the event are different from neighbouring samples, suggesting the role of atmospheric inversion in trapping the emitted CO 2 from the urban atmosphere during the eclipse.

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Carbon dioxide (CO 2) and water vapor are major greenhouse gases in Earth's atmosphere that control the planet's surface temperature (Houghton and Wood 1989). Variations in CO 2 levels can lead to major changes in climate, surface processes, and biota. For example, over the past two centuries the combustion of fossil fuels has raised the atmospheric CO 2 level from about 275 ppmV (Barnola et al. 1987) to the current level of 365 ppmV (Keeling 1994); this has caused already discernible increases in Earth's near-surface temperature (IPCC 1990). Over a longer timescale, analysis of trapped gases in the polar icecores (Barnola et al. 1987) showed that during the past 150,000 years CO 2 levels have oscillated between approximately 200 and 300 ppmV. Knowledge of past carbon dioxide levels and associated paleoenvironmental and paleoecological changes is useful for predicting future consequences of the current increase in atmospheric CO 2. While it is possible to directly measure the CO 2 content of the late Pleistocene and Holocene atmosphere, direct estimation of CO 2 levels in the atmosphere is not possible for the pre-Pleistocene epoch.. Several indirect methods (proxy) to estimate the paleo-CO 2 concentration in the atmosphere have been proposed: for example, carbon isotopic analysis of pedogenic carbonates, stomatal index count of fossil leaves, and isotopic composition of marine sedimentary carbon and boron from carbonate fossils (Cerling 1991; McElwain and Chaloner 1996; Ekart

Approximately 140 million years ago, the Indian plate separated from Gondwana and migrated by almost 90° latitude to its current location, forming the Himalayan-Tibetan system. Large discrepancies exist in the rate of migration of Indian plate during Phanerozoic. Here we describe a new approach to paleo-latitudinal reconstruction based on simultaneous determination of carbonate formation temperature and δ(18)O of soil carbonates, constrained by the abundances of (13)C-(18)O bonds in palaeosol carbonates. Assuming that the palaeosol carbonates have a strong relationship with the composition of the meteoric water, δ(18)O carbonate of palaeosol can constrain paleo-latitudinal position. Weighted mean annual rainfall δ(18)O water values measured at several stations across the southern latitudes are used to derive a polynomial equation: δ(18)Ow = -0.006 × (LAT)(2) - 0.294 × (LAT) - 5.29 which is used for latitudinal reconstruction. We use this approach to show the northward migration of t...

The backward air mass trajectory analysis (HYSPLIT) during the summer monsoon suggests that the rain which precipitates at Kolkata is generated from a moisture parcel which originates from the Arabian Sea and moves inland over the dry Indian subcontinent or over the Bay of Bengal. We used monthly satellite and ground based measurements of the hydro-meteorological variables together with isotope data from Bangalore, Bay of Bengal and Kolkata and other locations to quantify the contribution of different moisture sources during the SW Monsoon. The vapor mass as it moves under the prevailing wind direction was subjected to isotopic modification due to addition of evaporated moisture from Bay of Bengal and rainout process. This was simulated using Craig and Gordon model and Rayleigh fractionation model respectively. The moisture generated during the process of evaporation from Bay of Bengal surface ocean gets advected towards the continent and precipitates as rainfall or snowfall over th...

Moisture sources responsible for rains over Kolkata during the summer monsoon can be traced using backward air-mass trajectory analysis. A summary of such trajectories between June and September suggest that these moisture parcels originate from the Arabian Sea and travel over the dry continental region and over the Bay of Bengal (BoB) prior to their arrival at Kolkata. We use monthly satellite and ground-based observations of the hydrometeorological variables together with isotopic data of rainwater from Bangalore and Kakinada to quantify the contributions of advected continental and oceanic water vapour in the Kolkata rains. The vapour mass is modified during its transit from its original isotopic value due to addition of evaporated moisture from the BoB, and further modification occurs due to the process of rainout during transport. The evaporated component is estimated using the Craig–Gordon equation. The rainout process is simulated using a Rayleigh fractionation model. In this...

The stable isotopic composition of water vapor over the ocean is governed by the isotopic composition of surface water, ambient vapor isotopic composition, exchange and mixing processes at the water-air interface as well as the local meteorological conditions. In this study we present water vapor and surface water isotope ratios in samples collected across the latitudinal transect from Mauritius to Prydz Bay in the Antarctic coast. The samples were collected on-board the ocean research vessel SA Agulhas during the 9 th (Jan-2017) and 10 th (Dec-2017 to Jan-2018) Southern Ocean expeditions. The inter annual variability of the meteorological factors governing water vapor isotopic composition is explained. The parameters governing the isotopic composition of evaporation flux from the oceans can be considered separately or simultaneously in the Craig-Gordon(CG) models. The Traditional Craig-Gordon (TCG) (Craig and Gordon, 1965) and the Unified Craig-Gordon (UCG) (Gonfiantini et al., 2018) models were used to evaluate the isotopic composition of evaporation flux for the molecular diffusivity ratios suggested by (Merlivat, 1978)(MJ), (Cappa et al., 2003)(CD) and (Pfahl and Wernli, 2009)(PW) and for different ocean surface conditions. We found that the UCG model with CD molecular diffusivity ratios where equal contribution from molecular and turbulent diffusion is the best match for our observations. By assigning the representative end member isotopic compositions and solving the two-component mixing model, a relative contribution from locally generated and advected moisture was calculated along the transect. Our results suggest varying contribution of advected westerly component with an increasing trend up to 65°S. Beyond 65°S, the proportion of Antarctic moisture was found to be increasing linearly towards the coast.

Indian Summer Monsoon is an integrated component of the global climate system. The spatial movement of ITCZ at seasonal and orbital time scales is revealed in the ensemble of terrestrial and marine records covering the last 50,000 years. We deduced an evolutionary shift in the precipitation pattern near western North America, Mediterranean and South East Asia based on the estimated water isotopic composition from the δ 18 O carbonate and Δ 47 thermometer. Record revealed three stages of climate transition: mid-Holocene optima, Younger Dryas and Last glacial maxima. Estimated mean arid air temperature was 9-21°C and 12-35°C during the glacial and interglacial periods respectively. The June summer solar insolation at 65°N is captured in the temperature record linked with ice volume, atmospheric CO 2 levels and sea surface temperature; factors influencing the monsoon precipitation near mid-latitude region worldwide.

Indian Summer Monsoon is an integrated component of the global climate system. The spatial movement of ITCZ at seasonal and orbital time scales is revealed in the ensemble of terrestrial and marine records covering the last 50,000 years. We deduced an evolutionary shift in the precipitation pattern near western North America, Mediterranean and South East Asia based on the estimated water isotopic composition from the δ Ocarbonate and Δ47 thermometer. Record revealed three stages of climate transition: mid-Holocene optima, Younger Dryas and Last glacial maxima. Estimated mean arid air temperature was 9–21°C and 12–35°C during the glacial and interglacial periods respectively. The June summer solar insolation at 65°N is captured in the temperature record linked with ice volume, atmospheric CO2 levels and sea surface temperature; factors influencing the monsoon precipitation near mid-latitude region worldwide.