Search

Representations of the changing global carbon cycle under climatic and environmental perturbations require highly detailed accounting of all atmosphere and biosphere exchange. These fluxes remain unsatisfactory, as a consequence of only having data with limited spatiotemporal coverage and precision, which restrict accurate assessments. Through the nature of intimate coupling of global carbon and oxygen cycles via O 2 and CO 2 and their unique triple oxygen isotope compositions in the biosphere and atmosphere, greater insight is available. We report analysis of their isotopic compositions with the widest geographical and temporal coverage (123 new measurements for CO 2 ) and constrain, on an annual basis, the global CO 2 recycling time (1.5 ± 0.2 year) and gross primary productivities of terrestrial (~ 170-200 PgC/year) and oceanic (~ 90-120 PgC/year) biospheres. Observed inter-annual variations in CO 2 triple oxygen isotopic compositions were observed at a magnitude close to the largest contrast set by the terrestrial and oceanic biospheres. The seasonal cycles between the east and west Pacific Ocean were found to be drastically different. This intra-annual variability implies that the entire atmospheric CO 2 turnover time is not much longer than the tropospheric mixing time (less than ~ 5 months), verifying the derived recycling time. The new measurements, analyses, and incorporation of other global data sets allow development of an independent approach, providing a strong constraint to biogeochemical models., (© 2023. The Author(s).)

Vehicular catalytic converters are used to regulate, reduce, and convert toxic and environmentally unfriendly compounds in exhaust gases into relatively inert and less harmful chemical species. The efficiency, however, is largely affected by the operating temperature of the converter which is set by the hot exhaust gas released from the combustion chamber. A major gas released during combustion is CO 2 , and its multiply substituted isotopocule, namely, 13 C 16 O 18 O, provides a window of opportunity to probe directly the effective temperature of the converter in operation. Here, we report multiple isotopic measurements in exhaust CO 2 (δ 13 C, δ 17 O, δ 18 O, and Δ 47 ) of diesel (trucks and buses) and gasoline (sedans, trucks, and two-wheel motorcycles)-powered vehicles. For investigating the efficiency of a converter in reducing toxic compounds, we studied NO x processes through isotopic analysis of the exhaust N 2 O. We found that the degree of N 2 O reduction to N 2 in gasoline-powered vehicles is high when the temperature is above 200 °C (inferred by Δ 47 ). In contrast, diesel-powered vehicles produce N 2 O in abundance, probably a consequence of selective catalytic reduction of NO x , and the reduction efficiency depends on the converter temperature. In other words, the catalytic converters act as sinks and sources of N 2 O to the atmosphere in gasoline- and diesel-operated vehicles, respectively. We also report a new set of field data by measuring the isotopic compositions of CO 2 and N 2 O in the Hsuehshan tunnel, a ∼13 km long highway tunnel in Taiwan. Elevated N 2 O concentrations inside the tunnel indicate that the emission of N 2 O by heavy-duty diesel vehicles is much higher compared to the reduction by gasoline-operated passenger cars, making the vehicular exhausts a net source of N 2 O to the atmosphere. The combined study of clumped isotopes and N 2 O concentration in exhaust gases suggests that it is useful to probe the operational temperature of catalytic converters and monitor the pollution level in operation, thus providing an opportunity for manufacturers to optimize the catalytic efficiency to reduce the level of toxic pollutants to the environment.

The thermal physiology of non-avian dinosaurs, especially the endothermic/ectothermic nature of their metabolism, inferred indirectly using body mass, biophysical modelling, bone histology and growth rate, has long been a matter of debate. Clumped isotope thermometry, based on the thermodynamically driven preference of 13 C- 18 O bond in carbonate minerals of fossilized eggshells, yields temperature of egg formation in the oviduct and can delineate the nature of thermoregulation of some extinct dinosaur taxa. In the present study, the clumped isotope thermometry was applied to the eggshells of a few species of modern birds and reptiles to show that it is possible to obtain the body temperatures of these species in most of the cases. We then used this method to the fossil eggshells of Late Cretaceous sauropods and theropods recovered from western and central India. The estimated body temperatures varied between 29 °C and 46 °C, with an overall average of 37 °C, significantly higher than the environmental temperature (about 25 °C) of this region during the Late Cretaceous. The results also show that the theropod species with low body masses (~800 kg) had high body temperature (~38 °C), while some gigantic (~20000 kg) sauropods had low body temperatures that were comparable to or slightly higher than the environmental temperature. Our analyses suggest that these Late Cretaceous giant species were endowed with a capacity of variable thermoregulation to control their body temperature., (© 2020 The Authors.)

Air quality in the megacity Delhi is affected not only by local emissions but also by pollutants from crop residue burning in the surrounding areas of the city, particularly the rice straw burning in the post monsoon season. As a major burning product, gaseous CO 2 , which is rather inert in the polluted atmosphere, provides an alternative solution to characterize the impact of biomass burning from a new perspective that other common tracers such as particulate matters are limited because of their physical and chemical reactiveness. Here, we report conventional ([CO 2 ], δ 13 C, and δ 18 O) and unconventional (Δ 17 O) isotope data for CO 2 collected at Connaught Place (CP), a core area in the megacity Delhi, and two surrounding remote regions during a field campaign in October 18-20, 2017. We also measured the isotopic ratios near a rice straw burning site in Taiwan to constrain their end member isotopic compositions. Rice straw burning produces CO 2 with δ 13 C, δ 18 O, and Δ 17 O values of -29.02 ± 0.65, 19.63 ± 1.16, and 0.05 ± 0.02‰, respectively. The first two isotopic tracers are less distinguishable from those emitted by fossil fuel combustion but the last one is significantly different. We then utilize these end member isotopic ratios, with emphasis on Δ 17 O for the reason given above, for partitioning sources that affect the CO 2 level in Delhi. Anthropogenic fraction of CO 2 at CP ranges from 4 to 40%. Further analysis done by employing a three-component (background, rice straw burning, and fuel combustion) mixing model with constraints from the Δ 17 O values yields that rice straw burning contributes as much as ∼70% of the total anthropogenic CO 2 , which is more than double of the fossil fuel contribution (∼30%), during the study days., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Rationale: The doubly substituted isotopologues (e.g., 18 O 18 O, 17 O 18 O) in atmospheric O 2 are potential tracers for ozone photochemistry and atmospheric temperatures. Their low abundances and isobaric interference are the major analytical challenges. The 253 Ultra high-resolution stable isotope ratio mass spectrometer is suitable for resolving isobaric interferences., Methods: O 2 from air is purified using gas chromatography on a packed column filled with molecular sieve 5 Å and cooled to -78°C. The δ 17 O, δ 18 O, Δ 17 O, Δ 35 and Δ 36 values are measured on the extracted O 2 with the 253 Ultra at medium mass resolution (M/ΔM ~10000) using Faraday detectors for the singly substituted isotopologues and ion counters for the doubly substituted isotopologues., Results: Interferences from isobars, mainly 35 Cl for 17 O 18 O and H 35 Cl and 36 Ar for 18 O 18 O, are sufficiently resolved to enable high-precision determination of Δ 35 and Δ 36 . The Δ 35 and Δ 36 values of O 2 after photochemical isotope equilibration at -63°C and heating to 850°C agree with the theoretical prediction. The stratospheric Δ 35 and Δ 36 values are close to isotopic equilibrium at the ambient temperatures. However, the values for tropospheric O 2 differ from those expected at equilibrium., Conclusions: The 253 Ultra allows interference-free clumped isotope measurements of O 2 at medium mass resolution. The Δ 35 and Δ 36 signatures in atmospheric O 2 are mainly governed by O 3 photochemistry, temperature and atmospheric transport. Tropospheric O 2 is isotopically well mixed and retains a significant stratospheric signature., (© 2019 The Authors Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.)

To assess sources and processes that affect the variability of CO 2 at local to regional scales, we have analyzed the mixing ratio [CO 2 ] and stable isotopic compositions (δ 13 C and δ 18 O) of atmospheric CO 2 for three years (2014-2016) in urban and sub-urban areas in Taipei, Taiwan. The data are compared with those from some background sites, viz., Lulin, Mauna Loa, and Minamitorishima, to evaluate how local emissions affect CO 2 level regionally. [CO 2 ] over the urban and sub-urban stations are significantly higher than that observed at the three aforementioned remote sites mainly due to local emissions, which partly mask the seasonal cycle caused by photosynthesis and respiration. Likewise, significantly low δ 13 C and δ 18 O values observed at two Taipei stations also point to anthropogenic emissions. The seasonal cycles in [CO 2 ] and in the isotopic compositions are retrieved using the ensemble empirical mode decomposition method. Regional impact is assessed using CO 2 products from the Orbiting Carbon Observatory-2 satellite, the NOAA/EARL CarbonTracker project, and meteorological data from European Centre for Medium range Weather Forecast-Interim. We found that besides local emissions, Taiwan is largely affected by external CO 2 in winter and spring originated from north, west and southwest landmasses. In winter air masses with elevated CO 2 concentrations, originated in eastern China influence Taipei. In spring season, about 2 ppmv enhancement in CO 2 observed at the top of Lulin, a high mountain station (2.8 km), could be linked to CO 2 produced by biomass burning in the southeast Asian countries and transported to the region by easterly winds.

The abundance variations of near surface atmospheric CO 2 isotopologues (primarily 16 O 12 C 16 O, 16 O 13 C 16 O, 17 O 12 C 16 O, and 18 O 12 C 16 O) represent an integrated signal from anthropogenic/biogeochemical processes, including fossil fuel burning, biospheric photosynthesis and respiration, hydrospheric isotope exchange with water, and stratospheric photochemistry. Oxygen isotopes, in particular, are affected by the carbon and water cycles. Being a useful tracer that directly probes governing processes in CO 2 biogeochemical cycles, Δ 17 O (=ln(1 + δ 17 O) - 0.516 × ln(1 + δ 18 O)) provides an alternative constraint on the strengths of the associated cycles involving CO 2 . Here, we analyze Δ 17 O data from four places (Taipei, Taiwan; South China Sea; La Jolla, United States; Jerusalem, Israel) in the northern hemisphere (with a total of 455 measurements) and find a rather narrow range (0.326 ± 0.005‰). A conservative estimate places a lower limit of 345 ± 70 PgC year -1 on the cycling flux between the terrestrial biosphere and atmosphere and infers a residence time of CO 2 of 1.9 ± 0.3 years (upper limit) in the atmosphere. A Monte Carlo simulation that takes various plant uptake scenarios into account yields a terrestrial gross primary productivity of 120 ± 30 PgC year -1 and soil invasion of 110 ± 30 PgC year -1 , providing a quantitative assessment utilizing the oxygen isotope anomaly for quantifying CO 2 cycling.

Quantification of contributions from various sources of CO 2 is important for understanding the atmospheric CO 2 budget. Considering the number and diversity of sources and sinks, the widely used proxies such as concentration and conventional isotopic compositions (δ 13 C and δ 18 O) are not always sufficient to fully constrain the CO 2 budget. Additional constraints may help in understanding the mechanisms of CO 2 production and consumption. The anomaly in triple oxygen isotopes or 17 O excess (denoted by Δ 17 O) and molecules containing two rare isotopes, called clumped isotopes, are two recently developed tracers with potentials to independently constrain some important processes that regulate CO 2 in the atmosphere. The clumped isotope for CO 2 , denoted by Δ 47 , is the excess of 13 C 16 O 18 O over a random distribution of isotopes in a CO 2 molecule. We measured the concentrations of δ 13 C, δ 18 O, Δ 17 O, and Δ 47 in air CO 2 samples collected from the Hsuehshan tunnel (length: 12.9 km), and applied linear and polynomial regressions to obtain the fossil fuel end-members for all these isotope proxies. The other end-members, the values of all these proxies for background air CO 2 , are either assumed or taken as the values obtained over the tunnel and ocean. The fossil fuel (anthropogenic) CO 2 end-member values for δ 13 C, δ 18 O, Δ 17 O, and Δ 47 are estimated using the two component mixing approach: the derived values are -26.76 ± 0.25‰, 24.57 ± 0.33‰, -0.219 ± 0.021‰, and 0.267 ± 0.036‰, respectively. These four major CO 2 isotope tracers along with the concentration were used to estimate the anthropogenic contribution in the atmospheric CO 2 in urban and suburban locations. We demonstrate that Δ 17 O and Δ 47 have the potential to independently estimate anthropogenic contribution, and the advantages of these two over the conventional isotope proxies are discussed.

Rationale: The elucidation of chemical reaction mechanisms has attracted tremendous interest in recent years. Here, gravitational sampling electrospray ionization mass spectrometry (GS-ESI-MS) is used to explore a simple method for the real-time monitoring of chemical and biochemical reactions., Methods: A sample solution in a stainless steel sample well is directly delivered through a fused-silica capillary due to the forces of gravity, capillary action, and electroosmotic flow (EOF). Analyte ions are continuously generated via electrospray ionization from the capillary tip when a high voltage is applied on the sample well., Results: Liquid solutions (<5 μL) of small organic compounds (e.g., crystal violet) and large biomolecules (e.g., reserpine, angiotensin II, and insulin) were directly analyzed via GS-ESI-MS. In addition, the technique was successfully applied to continuously monitor chemical [e.g. chelation of ethylenediaminetetraacetic acid (EDTA) with copper(II), and addition-elimination of aminophenol and acetic anhydride] and biochemical (e.g., unfolding of cytochrome c) reactions in real time, where chelation complexes, reaction intermediates, and protein conformation changes were observed., Conclusions: GS-ESI-MS is a very simple modification of the ESI technique that does not require sample delivery pumps or nebulizer gases. It is particularly suitable for the analysis of liquid samples and the real-time monitoring of inorganic/organic chemical or biochemical reactions., (Copyright © 2014 John Wiley & Sons, Ltd.)

We present a comparative study of two offline methods, a newly developed method and an existing one, for the measurement of the stable carbon isotopic composition (δ(13)C) of dissolved inorganic carbon (DIC; δ(13)CDIC) in natural waters. The measured δ(13)CDIC values of different water samples, prepared from laboratory Na2CO3, ground and oceanic waters, and a laboratory carbonate isotope standard, are found to be accurate and reproducible to within 0.5 ‰\ (1σ). The extraction of CO2 from water samples by these methods does not require pre-treatment or sample poisoning and can be applied to a variety of natural waters to address carbon cycling in the hydrosphere. In addition, we present a simple method (based on a two-end-member mixing model) to estimate the silicate-weathering contribution to DIC in a river system by using the concentration of DIC and its δ(13)C. This approach is tested with data from the Krishna River system as a case study, thereby quantifying the contribution of silicate and carbonate weathering to DIC, particularly during peak discharge.