Carbon Isotope Studies Research Articles

Sequestration of 12C in the deep ocean during the early Wenlock (Silurian) positive carbon isotope excursion

Marine carbonates from three biostratigraphically well-dated Silurian sections from the mid-continent of North America were analyzed for carbon isotopic (δ 13C carb) study. The early Wenlock positive carbon isotope excursion (Ireviken Excursion) is recorded in three sections from Tennessee, Iowa, and Ohio, with values of >+4.5‰. This global shift in the carbon isotopic ratio of marine waters began during a protracted extinction event (Ireviken Event) that spanned the Llandovery–Wenlock boundary. Although several oceanographic models have been developed to account for the coincident changes in lithology, biology, and carbon isotope stratigraphy during this interval of the Silurian, their proposed causal connections among glaciation, oceanography, primary productivity, and the global carbon cycle remain a matter of debate. This investigation provides carbon isotopic and lithologic evidence that the Ireviken Excursion occurred during a time of relatively oligotrophic conditions, a third order transgressive–regressive cycle, and increased carbonate production throughout the mid-continent of North America. The Ireviken Excursion is recorded in relatively pure carbonate sequences and is immediately preceded by a significant unconformity in each of the measured sections. It is proposed that the Ireviken Excursion was the product of sequestration and burial of 12C in deep water as a result of altered deep ocean circulation.

Palatability trials on hardwood leaf litter grown under elevated CO 2: a stable carbon isotope study

The palatability to isopods and microbes of a broad range of hardwood leaf litter, derived from three field CO 2-enrichment experiments in the USA, was investigated, using δ 13C, to trace the C flow from litter to isopods and to CO 2 respired by microbial decomposition. Leaf litter grown under elevated CO 2 had δ 13C values ranging from −39 to −45‰, which were significantly different from ambient litter δ 13C values of around −30‰. Litter palatability to isopods of the Porcellio sp. was tested by incubating ambient- and elevated-CO 2 litter, and a mixture of the two, in the presence of isopods for 14 days, under environmentally controlled conditions; δ 13C was measured on litter and isopods' body before and after incubation. In an additional experiment, litter was incubated in the absence of fauna for 30 days, and on five occasions the δ 13C of the CO 2 respired from litter was measured. The 13C label was clearly carried from the litter source to the isopods' bodies, and their faeces. For microbial-respired CO 2, δ 13C was significantly higher than that of the litter source, suggesting preferential degradation of substrates enriched in 13C as compared to those in the overall litter. With the exception of Quercus myrtifolia leaf litter, elevated CO 2 did not affect the palatability to isopods nor the microbial degradation of any of the litters, possibly as a result of unaltered litter N concentration. However, significant differences in litter palatability and decay rates were observed among the different species. With this study, the use of isotopically labelled litter material was confirmed as a key methodology that can significantly contribute to the advancement of the understanding of litter decomposition and of the quantification of C fluxes in the process.

Catalysis and Prebiotic Synthesis

Little is know about the origins of life on Earth. Most scientists believe this event occurred some time within a billion years after the Earth formed 4.6 billion years ago (Ga). It is also possible that the Earth was “seeded” by life transported here by another body like a meteorite or by extra-terrestrials. Most scientists in this field assume that life originated on Earth or in our solar system because there would be little data on which to base a proposal for the origin of life at a location outside our solar system. As it is we have a very rudimentary knowledge of the environments on the primitive Earth in the first billion years on our planet. Some relevant books and reviews include Brack (1998), Fry (2000), Zubay (2000), Orgel (2004), and Ferris (2005). Ten years ago it appeared that we had made good progress on understanding about when life arose and what the environmental conditions on the Earth were at that time. Carbon isotope studies on rocks present on the Earth 3.8 Ga suggested life arose in or slightly after that time period (Mojizsis et al. 1996). In addition, microfossils found in rocks dated to be 3.5 Ga suggested were consistent with the presence of life 3.5 Ga (Schopf 1993). These data have been challenged recently (Brasier et al. 2002) so it is not certain the proposed microfossils were originally living organisms. Also the carbon isotope studies have been challenged (Moorbath 2005). But new and entirely different findings suggest that that the Earth had liquid water and an environment suitable for life 4.3 Ga. (Watson and Harrison 2005). In addition it has been proposed that the early Earth had an atmosphere with a mixing ratio of hydrogen of 0.3 (Tian et al. 2005). This …

The carbon and oxygen isotope study of the youngest and oldest carbonatites of the world

The carbon and oxygen isotope study of the youngest and oldest carbonatites of the world

Carbon Dioxide Capture Using a Zeolite Molecular Sieve Sampling System for Isotopic Studies (13C and 14C) of Respiration

A method for collecting an isotopically representative sample of CO2 from an air stream using a zeolite molecular sieve is described. A robust sampling system was designed and developed for use in the field that includes reusable molecular sieve cartridges, a lightweight pump, and a portable infrared gas analyzer (IRGA). The system was tested using international isotopic standards (13C and 14C). Results showed that CO2 could be trapped and recovered for both δ13C and 14C analysis by isotope ratio mass spectrometry (IRMS) and accelerator mass spectrometry (AMS), respectively, without any contamination, fractionation, or memory effect. The system was primarily designed for use in carbon isotope studies of ecosystem respiration, with potential for use in other applications that require CO2 collection from air.

Sulfur and carbon isotope study for environmental perturbations at the mass-extinction events

Sulfur and carbon isotope study for environmental perturbations at the mass-extinction events

The bio-barite in witherite deposits from Southern Qinling and its significance *

Abstract Being stratiform or stratoid, the Huangboshuwan witherite deposit at Zhiyang and the Wenyuhe witherite-barite deposit at Zhushan occur in the lower Lower Cambrian siliceous rocks and the orebodies are remarkably controlled by lithological character and petrography. Carbon and oxygen isotopic studies of witherite, barytocalcite and calcite have shown that the carbon, involved in the formation of these minerals, was derived largely from organic carbon resultant from degradation, polycondensation and dehydroxylation of bio-organic matter in sediments at the early stage of diagenesis. Extensive occurrence of bio-barite strongly evidenced that Ba2+ was concentrated and settled down in the form of bio-barite on the seafloor as a result of biological processes, thereafter forming the initially enriched orebodies of barium deposits. The witherite was metasomatic products of bio-barite under the action of sulfate-reducing bacteria and organic and inorganic reduction.

Holocene vegetation dynamics in the northeastern Rub' al‐Khali desert, Arabian Peninsula: a phytolith, pollen and carbon isotope study

AbstractThe Holocene vegetation history of the Arabian Peninsula is poorly understood, with few palaeobotanical studies to date. At Awafi, Ras al‐Khaimah, UAE, a 3.3 m lake sediment sequence records the vegetation development for the period 8500 cal. yr BP to ∼3000 cal. yr BP. δ13C isotope, pollen and phytolith analyses indicate that C3 Pooid grassland with a strong woody element existed during the early Holocene (between 8500 and 6000 cal. yr BP) and became replaced by mixed C3 and C4 grasses with a strong C4 Panicoid tall grass element between 5900 and 5400 cal. yr BP. An intense, arid event occurred at 4100 cal. yr BP when the lake desiccated and was infilled by Aeolian sand. From 4100 cal. yr BP the vegetation was dominated by C4 Chloridoid types and Cyperaceae, suggesting an incomplete vegetation cover and Aeolian dune reactivation owing to increased regional aridity. These data outline the ecosystem dynamics and carbon cycling in response to palaeomonsoon and north‐westerly variability during the Holocene. Copyright © 2004 John Wiley & Sons, Ltd.

Carbon isotopic studies of individual lipids in organisms from the Nansha sea area, China

Carbon isotopes of individual lipids in typical organisms from the Nansha sea area were measured by the GC-IRMS analytical technique. delta(13)C values of saturated fatty acids in different organisms examined are from -25.6parts per thousand to -29.7parts per thousand with the average values ranging from -26.4parts per thousand to -28.2parts per thousand and the variance range of 11.8parts per thousand, between different organisms is also observed. Unsaturated fatty acids have heavy carbon isotopic compositions and the mean differences of 2.9%.9-6.8parts per thousand compared to the same carbon number saturated fatty acids. delta(13)C values of n-alkanes range from -27.5%o to -29.7parts per thousand and their mean values, ranging from -28.6parts per thousand, to -28.9parts per thousand, are very close in different organisms. The mean difference in delta(13)C between the saturated fatty acids and n-alkanes is only 1.5parts per thousand, indicating that they have similar biosynthetic pathways. The carbon isotopic variations between the different carbon-number lipids are mostly within +/-2.0parts per thousand, reflecting that they experienced a biosynthetic process of the carbon chain elongation. At the same time, the carbon isotopic genetic relationships between the biological and sedimentary lipids are established by comparative studies of carbon isotopic compositions of individual lipids in organisms and sediments from the Nansha sea area, which provides scientific basis for carbon isotopic applied research of individual lipids.

Geochemistry of natural gases in deep strata of the Songliao Basin, NE China

Chemical composition and stable carbon isotopic studies were undertaken for 27 gas samples from deep strata of the Xujiaweizi Depression in the Songliao Basin to investigate their origin. Gas molecular and carbon isotopic compositions show great variety. Methane is the main component for all studied samples and its content ranges from 57.4% to 98.2% with an average of 90.1%. Gas wetness ranges from 0.8% to 16.7% with an average of 2.7%. The main non-hydrocarbon gases are carbon dioxide and nitrogen with an average of 4.0% and 3.2%, respectively. Carbon isotope data suggest that these deep strata gases are mainly coal-type gases mixed with minor amounts of associated (oil-type) gases. Coal-type gases are characterized by heavier carbon isotopic values and drier chemical compositions. These gases were generated from the Lower Cretaceous Shahezi Formation coals interbedded shales with type III kerogen during the postmature stage of hydrocarbon generation. Oil-type gases are characterized by lighter carbon isotope and higher wetness, which were generated from the Lower Cretaceous shales with type II kerogen in the shallow strata during the early mature stage of hydrocarbon generation. Mixing of two different gases causes unusual carbon isotopic distribution patterns, with lighter isotopic values in higher numbered carbons in most gases. The discovery of coal-type gases in the Songliao Basin provides new prospects for the exploration in this region.

Taxonomic versus trophic structure of mesozooplankton: a seasonal study of species succession and stable carbon and nitrogen isotopes in a coastal upwelling ecosystem

Abstract Seasonal variations in mesozooplankton (>200 μm) stable carbon and nitrogen isotope abundances were compared with the seasonal species succession pattern off A Coruña (Galicia, NW Spain). Mesozooplankton biomass, numerical abundance, species composition, and natural abundance of stable isotopes, along with water column temperature, salinity, chlorophyll a and dissolved nitrate concentrations, were studied in monthly samples during the years 2000 and 2001 at a coastal station (80-m depth). Biomass and abundance of mesozooplankton followed the annual cycle with maxima in spring and summer (year 2000) and occasionally also in autumn (year 2001). The succession pattern shown by the taxonomic assemblages was recognized in both years of study, despite differences in the timing of upwelling and the large input of continental water during most of 2000. Variations in neither carbon nor nitrogen isotopes were correlated with either abundance or biomass at annual time scales, but heavy isotopes significantly accumulated during periods of zooplankton increase (spring and early summer). The consumption of nitrate during the spring can explain in part the progressive accumulation of heavy nitrogen isotopes during this period. In addition, the abundance of carnivorous zooplankton (mainly carnivorous copepods, siphonophores, and chaetognaths) was linearly related to the increase in heavy isotopes during the spring and, in the case of nitrogen, also during the whole study period. The computed linear relationships between isotope abundances and plankton species composition provided a way to further analyse the pelagic foodweb through the estimation of isotope reference values for primary consumers.

Carbon, oxygen and boron isotopic studies of Huangbai-shuwan witherite deposit at Ziyang and Wenyuhe witherite deposit at Zhushan

Carbon, oxygen and boron isotopic studies of Huangbai-shuwan witherite deposit at Ziyang and Wenyuhe witherite deposit at Zhushan

A stable carbon isotope and biological marker study of Polish bituminous coals and carbonaceous shales

Biological marker and carbon isotopic compositions of coals and carbonaceous shales from the Upper Carboniferous strata of the Upper Silesian (USCB), Lower Silesian (LSCB), and Lublin (LCB) coal basins were determined to assess depositional conditions and sources of the organic matter. n-Alkane, sterane, and isoprenoid distribution, and carbon isotope ratios are consistent with an origin from higher plants. In some cases, pristane/phytane (Pr/Ph) ratios of carbonaceous shales (roof and floor shales) are <1.0, while the associated coals have high ratios (≫1.0). This suggests that reducing conditions prevailed during deposition of the shales, but a period of oxidizing conditions accompanied deposition of the coals. Steranes present in coal extracts are dominated by the 14α(H)17α(H)20R C 29 stereoisomers, typical, but not conclusive, of higher plant origin. Carbonaceous shales exhibit a wider range of sterane composition, suggesting local, significant input of algal organic matter. Significant amounts of benzohopanes and gammacerane are present in some coals. Although benzohopanes are present at least in small amounts in samples from many different environments, they have been reported to occur most commonly in marine environments. The present study seems to provide the first example where benzohopanes have been reported in significant amounts in terrestrial organic matter. Gammacerane is abundant in rocks or sediments deposited in carbonate or highly saline marine environments. The finding of high gammacerane concentrations in the coals expands the depositional settings in which it has been observed and questions its utility as an independent indicator of hypersaline carbonate environments. Stable carbon isotope composition of coals, and type III kerogen in carbonaceous shales as well as correlation of stable carbon isotope composition of saturated and aromatic hydrocarbons in carbonaceous shales from both the USCB and the LSCB indicate terrigenous origin. Bitumens are always co-genetic with associated coals and kerogens. Isotopic data reveal that Sofer's genetic classification of oils is not applicable to organic matter in coals.

Paleodiet studies using stable carbon isotopes from bone apatite and collagen: examples from Southern Ontario and San Nicolas Island, California

Stable carbon isotope studies using the mineral portion of bone have shown that this is a feasible area of research for providing paleodietary data. Stable carbon isotopes in collagen ( δ 13C CO) reflect primarily the protein portion of diet, whereas stable carbon isotopes in carbonate from bone mineral ( δ 13C CA) reflect the whole diet. While spacing between stable carbon isotopes in carbonate and diet is thought to be constant, spacing between stable carbon isotopes in collagen and diet may be variable depending on whether the carbon isotope value of protein equals that of the whole diet. In order to elucidate these patterns skeletal remains of prehistoric human groups utilizing different subsistence strategies, from southern Ontario and San Nicolas Island, Channel Islands, southern California, were analysed for stable carbon isotopes in both bone carbonate and collagen. Southern Ontario provides an example where C 4 plants are consumed in combination with indigenous C 3 plants and C 3-consuming animals; whereas San Nicolas Island provides an example where marine foods are consumed in combination with terrestrial C 3 foods. Results indicate that, in southern Ontario, maize was consumed at an earlier date than is indicated by the analysis of collagen alone, and that, on San Nicolas Island, marine food consumption did not decrease over time as occurred on nearby Channel Islands. The analysis of stable carbon isotopes from bone carbonate provides additional paleodietary information to the analysis of stable isotopes from collagen. Protein-poor foods will be reflected in carbon isotopes in carbonate when consumed in small amounts, whereas they will be reflected in collagen only when consumed in sizeable proportions.

Structure studies of neutron-rich beryllium and carbon isotopes

We have investigated the structure of the neutron-rich beryllium isotopes 10–12Be using transfer reactions and found excited rotational bands with pronounced molecular structure. In the spectroscopy of 16C we could identify 14 new states, most of them with a three-particle-one-hole structure for the neutron configuration.

The carbon isotope ecology and diet of Australopithecus africanus at Sterkfontein, South Africa

The stable carbon isotope ratio of fossil tooth enamel carbonate is determined by the photosynthetic systems of plants at the base of the animal's foodweb. In subtropical Africa, grasses and many sedges have C(4)photosynthesis and transmit their characteristically enriched 13C/(12)C ratios (more positive delta13C values) along the foodchain to consumers. We report here a carbon isotope study of ten specimens of Australopithecus africanus from Member 4, Sterkfontein (ca. 2.5 to 2.0Ma), compared with other fossil mammals from the same deposit. This is the most extensive isotopic study of an early hominin species that has been achieved so far. The results show that this hominin was intensively engaged with the savanna foodweb and that the dietary variation between individuals was more pronounced than for any other early hominin or non-human primate species on record. Suggestions that more than one species have been incuded in this taxon are not supported by the isotopic evidence. We conclude that Australopithecus africanus was highly opportunistic and adaptable in its feeding habits.

Relationship between light rare earth deposits and mantle processes in Panxi rift, China

Many light rare earth deposits, such as Maoniuping, Dalucao, Panzhihua deposits, are collectively distributed in Panxi rift of Sichuan Province, China, and closely associated with the aegirine quartz syenite-carbonatite complex. Carbon and oxygen isotope studies demonstrate that the carbonatites in the complex are of typical igneous origin related to mantle processes. Electronic microprobe studies show that the fluid-melt inclusions found in the complex are enriched in light rare earth elements (LREE), which suggests that the magma was rich in LREE and could serve as the ore source for the regional LREE mineralization. Both the aegirine quartz syenite-carbonatite complex and the LREE mineralization found therein were derived from the mantle. The rare gas isotope analyses also support that there is a genetic association between the LREE mineralization and mantle processes.

Carbon and oxygen isotope profiles from the terminal precambrian Marwar Supergroup, Rajasthan, India

Results of carbon and oxygen isotope studies from early Cambrian unfossiliferous carbonates belonging to the Marwar Supergroup, western Rajasthan, India are presented. The carbonates are enriched in “heavy” δ18O values (upto +6.50‰ PDB) and rules out the diagenetic modifications of isotope signals. The multiple, shortterm negative (upto −10.31‰ PDB) and positive (upto +2.80‰ PDB) carbon isotope oscillations observed in Marwar carbonates well matches with the lower Cambrian (Nemakit-Daldynian) carbonates reported world wide and these oscillations have been attributed to the result of climatic oscillations either from glaciations or from “cold house phases” that did not involve major glaciations.

Nitrogen isotope and content record of Mesozoic orogenic gold deposits surrounding the North China craton

As an effective tracer, nitrogen isotopes have been used to determine the source of ore materials in recent years. In this study, the nitrogen isotopes and contents were measured on K-feldspar and sericite of gold deposits and some related granitic intrusions in Jiaodong, Xiao-qinling-Xiong’ershan, west Qinling, the west part of North Qilian and the Zhangjiakou-Xuanhua district around the North China craton (NCC). Although the gold deposits around the NCC are hosted in Precambrian metamorphic rocks, Phanerozoic sedimentary rocks, mafic volcanic rocks or granite, comparison of which with the nitrogen contents and isotope data of previous studies on mantle-derived rocks, granites, metamorphic rocks and gold deposits indicates that those deposits are closely related to granitic rocks. In addition, mantle-derived materials may have been involved in the ore-forming processes to a certain degree. This conclusion is consistent with the result of previous hydrogen, oxygen and carbon isotopic studies of those gold deposits.

Carbon, oxygen and boron isotopic studies of Huangbaishuwan witherite deposit at Ziyang and Wenyuhe witherite deposit at Zhushan

Being stratiform or stratoid, the Huangbaishuwan witherite deposit at Ziyang and the Wenyuhe witherite-barite deposit at Zhushan occur in the lower Lower Cambrian siliceous rocks and the orebodies are remarkably controlled by lithological character and petrography. Boron, carbon and oxygen isotopic studies of witherite, barytocalcite and calcite have shown that the car-bon, involved in the formation of these minerals, was derived mainly from hydrocarbons and bio-genetic gases resulting from degradation, polycondensation and dehydroxylation of bio-organic matter in sediments at the early stage of diagenesis; the boron was a mixture of boron in pore wa-ter and that released in the process of degradation of organic matter, with a minor amount of boron from cycling brines in the deep interior of the basin. Boron, carbon and oxygen isotopic studies unanimously demonstrated that witherite was precipitated in this sort of organic carbon-rich pore water medium during the early stage of diagenesis. Extensive occurrence of biodetritus and clastic texture in witherite ores strongly evidenced that Ba 2+ was concentrated and settled down in the form of bio-barite on the seafloor as a result of biological processes, thereafter forming the initially enriched orebodies of barium deposits. Biological processes in seawater and early diagenesis in sediments are the major ore-forming mechanisms of witherite deposits in the region studied.