Carbon 13C Research Articles

Temporal variability of 14C reservoir effects and sedimentological chronology analysis in lake sediments from Chibuzhang Co, North Tibet (China)

Abstract Chronological analysis is the basic premise for paleoenvironmental research on lake sediment cores. It mainly employs bulk organic matter as a mixed dating material, although terrestrial plant remains are believed to provide reliable radiocarbon (14C) ages. 14C reservoir effects (REs) are generally problematic in establishing a final chronology and are usually recorded in aquatic macrophytes by the incorporation of dissolved inorganic carbon in high-altitude lakes of the Tibetan Plateau. We present a typical case of a 5.48 m-long core sampled from Chibuzhang Co, a lake in north Tibet, China, which contained two obvious obstacles: high REs and age reversals. The 14C RE was recently as much as ∼3500 years in the upper part according to total organic carbon (TOC) 14C ages and related dating from 210Pbex activity. It notably changed during the climatic transition to the Holocene due to carbonate input from catchment erosion and glacial meltwater, resulting in reversed 14C ages in the lower section of the core. 14C-dead carbon (or old carbon) dissolved in lake water was incorporated in the dating materials, as inferred from the 14C ages of plant samples. By combining data on grain size and carbonate content changes, two sedimentary units were identified with a boundary at 390 cm depth. These were used to estimate individual sediment accumulation rates (SARs) for the final age-depth models, instead of using a constant RE-corrected chronology. Our results provide an environmental history of ∼12.7 kyr in a long sediment core, based on an optimized SAR model of conventional 14C ages, which is supported by related lacustrine records and Bacon models. Use of separate 14C SAR analyses can solve the problem of age inversion in sediment cores, as sedimentological chronology analysis.

Stable carbon and nitrogen isotope ratios of surface food residues in pre-Columbian ceramics from the southern Pacific of Costa Rica as evidence of prehistoric human diets

Introduction: to understand and interpret the consumption of plants and animals by humans in the past requires the investigation of different lines of evidence. Identifiable macroscopic remains of plants and animals, for example seeds and bones, are frequently found at archaeological sites and provide key data on food resources. Their analysis is complemented by the study of pollen grains or phytoliths of cultivated plants within archaeological horizons or in sediment cores recovered from lakes and wetlands near archaeological sites. Another important source of information on human diets in the past consists of food residues preserved in or on artefacts excavated from archaeological sites. Objective: to examine food residues in archaeological pottery from coastal and interior sites in the southern Pacific region of Costa Rica. Methods: we focus on isotopic analysis of carbonized food residues preserved on the inner surfaces of ceramic pots, plates, and other ceramic pieces from archaeological excavations in the intermediate zone (elevations 500-1500m) and coastal zone of the southern Pacific region of Costa Rica. Isotopic analysis of surface food residues on pottery relies on the fact that stable isotopes of carbon (12C and 13C) and nitrogen (14N and 15N) in foods differ based on the photosynthetic pathway of plants and on trophic level. Results: in our analysis of material from twelve sites we found evidence of diets with high amounts of C4 plants (likely maize), legumes, herbivores, and mixtures, but we did not find robust evidence of food residues with isotopic signatures characteristic of reef animals and mollusks, even though some sites are shell mounds. Conclusion: our research represents one of the first studies of surface food residues from Costa Rican pottery, and indicates the potential for studies of this type to strengthen understanding of indigenous subsistence patterns through time and across Costa Rican archaeological regions.

ДИФУЗІЯ У ЗАЛІЗІ ТА ЙОГО СПЛАВАХ ПІСЛЯ НАСИЧЕННЯ ПОВЕРХНІ ІОНАМИ АРГОНУ ТА КРИПТОНУ ПРИ ВІДПАЛАХ ТА ІМПУЛЬСНИХ НАВАНТАЖЕННЯХ

The effect of the preliminary introduction of inert gases (argon and krypton) into iron and its alloys in a glow discharge plasma on diffusion (mass transfer) under various external influences was studied using methods based on the use of radioactive isotopes and xrays. The studies were carried out by methods of x-ray diffraction analysis, layered radiometric analysis of residual integral activity, macro-, micro-, electron-microscopic and activation autoradiography. Isotopes of iron 55Fe, nickel 63Ni, carbon 14C, argon 41Ar and krypton 85Kr were used. The following external effects were applied to the metal (alloy) in the initial state and after saturation with an inert gas: galvanic coating, isothermal annealing, athermal martensitic transformation with explosive kinetics and a large volume effect (~ 3%), ultrasonic impact treatment, compression due to deformation when the load falls, magnetic pulse deformation, etc. It is shown that the presence of a pre-introduced inert in iron and alloys based on it leads to a decrease in the mobility of atoms during annealing, low-temperature pulsed loading in a wide range of deformation rates, and further ion bombardment in a glow discharge. No difference was found in the effect of the type of inert gas — argon or krypton — on the change in atomic mobility, surface distribution, and the shape of the concentration profile. The barrier effect of the introduced gas is associated with structural-phase changes in the surface layers by the occurrence of gas-filled pores and a subtraction solid solution in the surface layers, which transforms into a substitutional solid solution away from the surface. Additional studies have shown that the barrier effect of the introduced inert gas on diffusion during subsequent exposures is observed not only on iron, but also on copper and aluminum. This effect is especially pronounced during the subsequent ion bombardment of copper and aluminum saturated with one or another inert gas in a krypton or argon medium as compared to the subsequent pulsed compression or deformation under martensitic transformations. This suggests the universal nature of the discovered regularity. It should be noted according to autoradiographic studies that the presence of an inert gas, which slows down the transfer of matter during subsequent treatments, does not change the nature of the distribution of atoms. There is diffusion over the grain volume with some depletion of the surface layer, and the concentration profiles are described by an exponential dependence on the square of the penetration depth. Therefore, the mechanism of volume diffusion is preserved over the entire range of temperatures and strain rates, and also does not depend on the type of external influence applied. This is true for native atoms and atoms forming solid solutions of various types: substitution (nickel), interstitial (carbon), subtraction (argon and krypton).

Show us your beaks and we tell you what you eat: Different ecology in sympatric Antarctic benthic octopods under a climate change context

Show us your beaks and we tell you what you eat: Different ecology in sympatric Antarctic benthic octopods under a climate change context

Use of Random forest in the identification of important variables

Random Forest (RF) technique has been shown to be promising in the supervised classification applied in different matrices. However, approaches to identifying significant variables that weight the model are scarce, in the classification problems. In this paper, we propose a methodology for the selection of variables of greater relevance in the construction of RF models. For the application of this methodology, classification models were developed to discriminating crude oil samples, about to their maximum pour point (MPP). In this sense, data from MPP (ASTM D5853) of 105 crude oil samples, their hydrogen (1H) NMR spectra and carbon (13C) NMR spectra were acquired. With MPP ranging from −54 °C to 39 °C, two classes were assigned: the first containing 43 samples with MPP value ≤ −9 °C, and, the second, 62 samples with MPP value > −9 °C. The 1H NMR models, with 90% accuracy, and 13C NMR, with 71% accuracy, were used in the selection of variable method. The results showed that the methodology proposed to select variables was effective in the distinction of the variables that best contributed to the discrimination of oils. Therefore, this new tool enabled a greater understanding of the interest chemical information, contained in the spectra and its relationship with the MPP property of the crude oil samples.

Artificial lighting at night alters aquatic-riparian invertebrate food webs.

Artificial lighting at night (ALAN) is a global phenomenon that can be detrimental to organisms at individual and population levels, yet potential consequences for communities and ecosystem functions are less resolved. Riparian systems may be particularly vulnerable to ALAN. We investigated the impacts of ALAN on invertebrate community composition and food web characteristics for linked aquatic-terrestrial ecosystems. We focused on food chain length (FCL), a central property of ecological communities that can influence their structure, function, and stability; and the contribution of aquatically derived energy (i.e., nutritional subsidies originating from stream periphyton). We collected terrestrial arthropods and emergent aquatic insects from a suite of stream and wetland sites in Columbus, Ohio, USA. Stable isotopes of carbon (13 C) and nitrogen (15 N) were used to infer FCL and contribution of aquatically derived energy. We found that moderate-to-high levels of ALAN altered invertebrate community composition, favoring primarily predators and detritivores. Impacts of ALAN, however, were very taxon specific as illustrated, for example, by the negative impact of ALAN on the abundance of orb-web spiders belonging to the families Tetragnathidae and Araneidae: key invertebrate riparian predators. Most notably, we observed decreases in both invertebrate FCL and reliance on aquatically derived energy under ALAN (although aquatic energetic contributions appeared to increase again at higher levels of ALAN), in addition to shifts in the timing of reciprocal nutritional subsidies. Our study demonstrates that ALAN can alter the flows of energy between aquatic and terrestrial systems, thereby representing an environmental perturbation that can cross ecosystem boundaries. Given projections for global increases in ALAN, both in terms of coverage and intensity, these results have broad implications for stream ecosystem structure and function.

Biophysical oceanography of tidally-extreme waters of the southern Kimberley coast, Western Australia

The continental shelf of the South Kimberley region of Western Australia is wide (~300 km) and interactions with the Indian Ocean culminate in extreme tides. This results in some of the largest tropical tides in the world (reaching 11 m on spring tide) measured in King Sound (KS), a large embayment which opens to the Indian Ocean. This remote area of Australia is very rich in natural resources and under increasing developmental pressures, but despite this the marine environment has been poorly studied. In Austral autumn (April/May) 2010, we examined phytoplankton biomass and production across four onshore-offshore transects from coastal waters (also within KS) to the 1000 m isobath, and their responses to physical and chemical environmental variables associated with tidal forces during a four week voyage aboard the RV Southern Surveyor. Using temperature and salinity relationships we found three distinct water masses; KS, Kimberley Shelf, and Kimberley Shelf break waters. The highest chlorophyll-a biomass in the study area was measured in a band along the 200 m isobath (27–46 mg Chl a m−2), and associated with greater concentrations of nutrients (332–392 mmol NO3- m−2, 650–823 mmol Si m−2, 21–39 mmol PO43- m−2). Phytoplankton biomass inside KS was dominated by large diatoms (as determined from accessory pigment analyses), shifting to a community largely comprised of picophytoplankton offshore. Rates of primary production (PP) on the shelf, via measurements of phytoplankton carbon (14C) uptake from photosynthesis versus irradiance incubations, decreased from coastal areas (222–560 mg C m−2 d−1) to offshore waters (45–78 mg C m−2 d−1). In KS, PP was highest (1692 mg C m−2 d−1) despite low standing stock nutrient concentrations (0.02–1.5 mmol NO3- m−2) and relatively high concentrations of suspended particulate material reducing light availability (Kd = 0.27 m−1).

Extreme 13C,15N and 17O isotopic enrichment in the young planetary nebula K4-47.

Carbon, nitrogen and oxygen are the three most abundant elements in the Galaxy after hydrogen and helium. Whereas hydrogen and helium were created in the Big Bang, carbon, nitrogen and oxygen arise from nucleosynthesis in stars. Of particular interest1,2 are the isotopic ratios 12C/13C, 14N/15N and 16O/17O because they are effective tracers of nucleosynthesis and help to benchmark the chemical processes that occurred in primitive interstellar material as it evolved into our Solar System3. However, the origins of the rare isotopes 15N and 17O remain uncertain, although novae and very massive stars that explode as supernovae are postulated4-6 to be the main sources of 15N. Here we report millimetre-wavelength observations of the young bipolar planetary nebula K4-47 that indicate another possible source for these isotopes. We identify various carbon-bearing molecules in K4-47 that show that this object is carbon-rich, and find unusually high enrichment in rare carbon (13C), oxygen (17O) and nitrogen (15N) isotopes: 12C/13C=2.2±0.8, 16O/17O=21.4±10.3 and 14N/15N=13.6±6.5 (uncertainties are three standard deviations); for comparison, the corresponding solar ratios7 are 89.4±0.2, 2,632±7 and 435±57. One possible interpretation of these results is that K4-47 arose from a J-type asymptotic giant branch star that underwent a helium-shell flash (an explosive nucleosynthetic event that converts large quantities of helium to carbon and other elements), enriching the resulting planetary nebula in 15N and 17O and creating its bipolar geometry. Other possible explanations are that K4-47 is a binary system or that it resulted from a white dwarf merger, as has been suggested for object CKVul8. These results suggest that nucleosynthesis of carbon, nitrogen and oxygen is not well understood and that the classification of certain stardust grains must be reconsidered.

The use of radiocarbon <sup>14</sup>C to constrain carbon dynamics in the soil module of the land surface model ORCHIDEE (SVN r5165)

Abstract. Despite the importance of soil as a large component of the terrestrial ecosystem, the soil compartments are not well represented in land surface models (LSMs). Indeed, soils in current LSMs are generally represented based on a very simplified schema that can induce a misrepresentation of the deep dynamics of soil carbon. Here, we present a new version of the Institut Pierre Simon Laplace (IPSL) LSM called ORCHIDEE-SOM (ORganizing Carbon and Hydrology in Dynamic EcosystEms-Soil Organic Matter), incorporating the 14C dynamics into the soil. ORCHIDEE-SOM first simulates soil carbon dynamics for different layers, down to 2 m depth. Second, concentration of dissolved organic carbon and its transport are modelled. Finally, soil organic carbon decomposition is considered taking into account the priming effect. After implementing 14C in the soil module of the model, we evaluated model outputs against observations of soil organic carbon and modern 14C fraction (F14C) for different sites with different characteristics. The model managed to reproduce the soil organic carbon stocks and the F14C along the vertical profiles for the sites examined. However, an overestimation of the total carbon stock was noted, primarily on the surface layer. Due to 14C, it is possible to probe carbon age in the soil, which was found to be underestimated. Thereafter, two different tests on this new version have been established. The first was to increase carbon residence time of the passive pool and decrease the flux from the slow pool to the passive pool. The second was to establish an equation of diffusion, initially constant throughout the profile, making it vary exponentially as a function of depth. The first modifications did not improve the capacity of the model to reproduce observations, whereas the second test improved both estimation of surface soil carbon stock as well as soil carbon age. This demonstrates that we should focus more on vertical variation in soil parameters as a function of depth, in order to upgrade the representation of the global carbon cycle in LSMs, thereby helping to improve predictions of the of soil organic carbon to environmental changes.

Anaerobic methane oxidation by nitrate: kinetic isotope effect

The ratio of stable carbon isotopes (13C/12C) in different environments serves as a significant limitation in estimating the global balance of methane [Hornibrook et al., 2000]. In this case, the value of 13C/12C largely depends on the kinetic isotope effect associated with the metabolism of microorganisms that produce and consume CH4. The article suggests a dynamic model of the processes of methane formation and its anaerobic oxidation with nitrate by methanotrophic denitrifying microorganisms (DAOM), which allowed estimating the fractionation factor of stable carbon isotopes. In the experiment with peat from the minerotrophic bog [Smemo, Yavitt, 2007], the dynamics of the amount of methane and was measured. The dynamic model showed that the introduction of nitrate leads to a slow decrease in the partial pressure of methane. Since methane in the DAOM process is a substrate, methane is enriched with heavier carbon 13C in the system under study. This leads to an increase in the value . The carbon isotope fractionation factor during methane oxidation with nitrate was equal to 1.018 and comparable with the fraction of carbon isotope fractionation in the process of acetoclastic methanogenesis (1.01). Model calculations have shown that during incubation the apparent fractionation factor of carbon isotopes with the simultaneous formation of methane and DAOM slowly decreases. The ratio of 13C/12C isotopes in dissolved and gaseous methane practically does not differ. The model showed that an increase in the initial concentration of nitrate increases the rate of DAOM, which leads to a decrease in the concentration of dissolved methane. In this case, the value of 13C/12C increases. In field studies, Shi et al. (2017) showed that the presence of DAOM in peat bogs in which fertilizers penetrate can be controlled by the amount of nitrate used and the depth of penetration into the anoxic layer. Two MATLAB files describing DAOM are attached to the article.

Application of in vivo MR methods in the study of breast cancer metabolism.

In the last two decades, various in vivo MR methodologies have been evaluated for their potential in the study of cancer metabolism. During malignant transformation, metabolic alterations occur, leading to morphological and functional changes. Among various MR methods, in vivo MRS has been extensively used in breast cancer to study the metabolism of cells, tissues or whole organs. It provides biochemical information at the metabolite level. Altered choline, phospholipid and energy metabolism has been documented using proton (1 H), phosphorus (31 P) and carbon (13 C) isotopes. Increased levels of choline-containing compounds, phosphomonoesters and phosphodiesters in breast cancer, which are indicative of altered choline and phospholipid metabolism, have been reported using in vivo, in vitro and ex vivo NMR studies. These changes are reversed on successful therapy, which depends on the treatment regimen given. Monitoring the various tumor intermediary metabolic pathways using nuclear spin hyperpolarization of 13 C-labeled substrates by dynamic nuclear polarization has also been recently reported. Furthermore, the utility of various methods such as diffusion, dynamic contrast and perfusion MRI have also been evaluated to study breast tumor metabolism. Parameters such as tumor volume, apparent diffusion coefficient, volume transfer coefficient and extracellular volume ratio are estimated. These parameters provide information on the changes in tumor microstructure, microenvironment, abnormal vasculature, permeability and grade of the tumor. Such changes seen during cancer progression are due to alterations in the tumor metabolism, leading to changes in cell architecture. Due to architectural changes, the tissue mechanical properties are altered; this can be studied using magnetic resonance elastography, which measures the elastic properties of tissues. Moreover, these structural MRI methods can be used to investigate the effect of therapy-induced changes in tumor characteristics. This review discusses the potential of various in vivo MR methodologies in the study of breast cancer metabolism.

Isolation and radiocarbon analysis of elemental carbon in atmospheric aerosols using hydropyrolysis

Radiocarbon (14C) analysis is a powerful tool that can unambiguously distinguish fossil and non-fossil sources of carbonaceous particles. However, one of the big challenges of this method is to isolate elemental carbon (EC) or black carbon (BC) for 14C analysis. Hydropyrolysis (hypy) has proven to be an effective method for separating BC in environmental matrices. The potential of hypy for isolation of EC from atmospheric aerosols is evaluated using typical combustion products from non-fossil (biomass), fossil fuel (coal and petroleum), and ambient aerosol samples collected in Beijing and Guangzhou. Using solid state nuclear magnetic resonance (NMR) along with measurement of carbon content and 14C, hypy conditions of 15 MPa hydrogen pressure and 550 °C temperature was confirmed to effectively separate EC from aerosol samples. Consequently, a comparison study of EC 14C in aerosol samples separated using the two-step heating method (CTO-375), thermal-optical method and hypy was conducted. The results show that hypy is an effective and stable approach for matrix-independent 14C quantification of EC in aerosols.

Relationships between grain size and organic carbon 14C heterogeneity in continental margin sediments

The deposition and long-term burial of sedimentary organic matter (OM) on continental margins comprises a fundamental component of the global carbon cycle. A key unknown in interpretation of carbon isotope records of sedimentary OM is the extent to which OM accumulating in continental shelf and slope sediments is influenced by dispersal and redistribution processes. Here, we present results from an extensive survey of organic carbon (OC) characteristics of grain size fractions (ranging from <20 to 250 μm) retrieved from Chinese marginal sea surface sediments in order to assess the extent to which the abundance and isotope composition of OM in shallow shelf seas is influenced by hydrodynamic processes. Our findings show that contrasting relationships exist between 14C contents of OC and grain size in surface sediments associated with two different hydrodynamic modes, suggesting that transport pathways and mechanisms imparted by the different hydrodynamic conditions exert a strong influence on 14C contents of OM in continental shelf sediments. In deeper regions and erosional areas, we infer that bedload transport exerts the strongest influence on (decreases) OC 14C contents of the coarser fraction, while resuspension processes induce OC 14C depletion of intermediate grain size fractions in shallow inner-shelf settings. We use the inter-fraction spread in Δ14C values, defined here as H14, to argue that the hydrodynamic processes amplify overall 14C heterogeneity within corresponding bulk sediment samples. The magnitude and footprint of this heterogeneity carries implications for our understanding of carbon cycling in shallow marginal seas.

A global compilation of coccolithophore calcification rates

Abstract. The biological production of calcium carbonate (CaCO3), a process termed calcification, is a key term in the marine carbon cycle. A major planktonic group responsible for such pelagic CaCO3 production (CP) is the coccolithophores, single-celled haptophytes that inhabit the euphotic zone of the ocean. Satellite-based estimates of areal CP are limited to surface waters and open-ocean areas, with current algorithms utilising the unique optical properties of the cosmopolitan bloom-forming species Emiliania huxleyi, whereas little understanding of deep-water ecology, optical properties or environmental responses by species other than E. huxleyi is currently available to parameterise algorithms or models. To aid future areal estimations and validate future modelling efforts we have constructed a database of 2765 CP measurements, the majority of which were measured using 12 to 24 h incorporation of radioactive carbon (14C) into acid-labile inorganic carbon (CaCO3). We present data collated from over 30 studies covering the period from 1991 to 2015, sampling the Atlantic, Pacific, Indian, Arctic and Southern oceans. Globally, CP in surface waters ( &lt; 20 m) ranged from 0.01 to 8398 µmol C m−3 d−1 (with a geometric mean of 16.1 µmol C m−3 d−1). An integral value for the upper euphotic zone (herein surface to the depth of 1 % surface irradiance) ranged from &lt; 0.1 to 6 mmol C m−2 d−1 (geometric mean 1.19 mmol C m−2 d−1). The full database is available for download from PANGAEA at https://doi.org/10.1594/PANGAEA.888182.

Ab Initio Simulation of pH-Sensitive Biomarkers in Magnetic Resonance Imaging.

An ab initio simulation scheme is introduced as a theoretical prescreening approach to facilitate and enhance the research for pH-sensitive biomarkers. The proton 1H and carbon 13C nuclear magnetic resonance (NMR) chemical shifts of the recently published marker for extracellular pH, [1,5-13C2]zymonic acid (ZA), and the as yet unpublished ( Z)-4-methyl-2-oxopent-3-enedioic acid (OMPD) were calculated with ab initio methods as a function of the pH. The influence of the aqueous solvent was taken into account either by an implicit solvent model or by explicit water molecules, where the latter improved the accuracy of the calculated chemical shifts considerably. The theoretically predicted chemical shifts allowed for a reliable NMR peak assignment. The p Ka value of the first deprotonation of ZA and OMPD was simulated successfully whereas the parametrization of the implicit solvent model does not allow for an accurate description of the second p Ka. The theoretical models reproduce the pH-induced chemical shift changes and the first p Ka with sufficient accuracy to establish the ab initio prescreening approach as a valuable support to guide the experimental search for pH-sensitive biomarkers.

A Copper10-Paclitaxel crystal; a medicinally active drug delivery platform

Paclitaxel is a well-known cancer drug that functions as a mitotic inhibitor. This work focuses on a copper based crystal that encapsulates the pharmaceutical agent and serves as a drug delivery agent. A Copper10-Pacitaxil1 chloride (CU10PAC1) complex is synthesized and tested against the National Cancer Institute’s sixty cell line panel. The 10:1 ratio results in a crystal that was examined by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spec (MALDI-TOF-MS), Scanning Electron Microscopy (SEM) and Proton (1H) and Carbon (13C) Nuclear Magnetic Resonance (NMR). The potential attributes of a copper based crystal as an in vivo drug carrier for Paclitaxel are discussed.

An improved method for the sealed-tube zinc graphitization of microgram carbon samples and 14C AMS measurement

Advances in accelerator mass spectrometry (AMS) and environmental chemistry techniques have increased demand for the natural abundance 14C analysis of ultra-small (<25 µgC) and compound-specific samples. The sealed-tube zinc (Zn) method is used for the reduction of sample CO2 to graphite on an iron catalyst. This method provides reliable, low AMS 14C backgrounds and high measurement precision over a wide range of sample sizes (1000 µgC to <15 µgC). Recently, Rinyu and co-workers demonstrated improved ion beam currents and 14C backgrounds when performing sealed-tube Zn graphitization by applying a thermal gradient (from room temperature to 550 °C) on 25–100 µgC samples [1]. However, many compound-specific radiocarbon analysis (CSRA) measurements are limited to smaller sample sizes – often <10 µgC per analyte with repeated collection by gas or liquid chromatography. Using a similar thermal gradient setup, we present an improved sealed-tube Zn method for the graphitization of samples ranging from ultra-small mass (2 µgC) and up to 100 µgC in the Keck Carbon Cycle AMS facility (KCCAMS) at the University of California, Irvine. Our improved method produces high AMS currents (he12C+ ∼1 µA µgC−1), a low extraneous C blank (0.5–0.7 µgC), high measurement precision (2–10% as relative % error) and accuracy (95–97%, as an absolute % difference of measured vs. consensus fraction modern values) for modern 2–5 µgC samples. These improvements have resulted in a sealed-tube Zn method which equals the performance of the ultra-small mass H2 reduction method for 2–10 µgC samples [2].

Investigating the complex hydrogeological settings in the northeastern slope of the West Bank to the Jordan Graben (Malih and Jeftlik)

The northeastern part of the West Bank is located between brackish water sources in the Jordan Rift to the east, and the freshwater drainage from the mountain ridge, where the complex geological structure can facilitate a possible flow-path connecting different fresh and saline water bodies, saline sources, and the regional aquifers, which are the sources of their freshwater. Integrated stable and radioactive isotopic tools of tritium (3H), carbon (14C), carbon (δ13C), sulphur (δ34S) deuterium (δ2H) and oxygen (δ18O) were used to investigate the effect of complex geologic structure on the groundwater residence times, and respective potential sources, mixing, and recharge mechanisms. The low 14C values in the Malih and Marj Najeh area suggest mixing signatures between the old brine and the fresh water that conveyed from Cretaceous rocks and Eocene mountain aquifer in the west through the faults that intersect the water flow path to the north, toward the study area. The study differentiates between two salinity mechanisms, one that is coming from dissolution of saline sediments and salinized the triggered freshwater along with Faria flow path with high 14C pMC values and positive δ34Ssulphate and the second is the deep-seated pressurized CaCl2 brine, the upflow of which causes salinization of fresh groundwater bodies entering the system.

Different pretreatment methods for 14C dating of Younger Dryas and Allerød pine wood (Pinus sylvestris L.)

Abstract An analysis was performed on samples from a series of well-preserved tree trunks and in situ stumps of Allerod/Younger Dryas age found in Koźmin and Kwiatkow, Kolska Basin, Central Poland. Five different types of wood preparation methods were investigated in three Polish radiocarbon laboratories (Gliwice, Poznan and Krakow) in order to find the most stable, repeatable and reliable procedure. Their effect was tested on the stable carbon isotope ratio (δ13C) and 14C age. Additionally, FTIR spectroscopy was used as a simple technique for obtaining rapid information on the structure of wood constituents and chemical changes taking place in wood due to various chemical treatments. The results of AMS measurements did not show statistically significant differences in radiocarbon ages of samples prepared according to the tested methods. On the other hand, δ13C measurements showed that the smallest scattering results gave α-cellulose obtained by the method BABA + Bleaching (with NaClO2 and HCl) + strong base. Moreover, the mean δ13C values for holo-cellulose samples are higher than those for α-cellulose samples. Studies evidenced that the methods of preparation leading to holo- or α-cellulose gave the same FTIR spectra, while the standard method of the chemical pretreatment of samples for 14C measurements (ABA) preceded by mercerization is insufficient for removing compounds containing aromatic rings.

Metagenomic and 13C tracing evidence for autotrophic atmospheric carbon absorption in a semiarid desert

Atmospheric carbon dioxide (CO2) absorption by desert soils has received increasing interests in recent years; however, the underlying physical and chemical mechanisms are not commonly acceptable. Here, we hypothesised that autotrophic carbon fixation of soil microbes contributes to this process. To test this postulate, we investigated the genomic and biochemical potential of autotrophic carbon fixation and traced atmospheric autotrophic carbon absorption using metagenomics and 13CO2 labelling approaches in the Mu Us Desert in northern China. More than 30000 genes involved in the six carbon fixation pathways (approximately 2% of the assembled metagenomes, in relative abundance) were found in the metagenome of the desert soil, and the relative abundance for genes encoding for the reductive citrate cycle was the highest among the six pathways. The main autotrophic microbes employing the six pathways belong to Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Firmicutes, Thaumarchaeota, Nitrospirae, Planctomycetes, and Bacteroidetes, respectively. 13CO2 labelling revealed that the contents of microbially incorporated soil organic carbon (13C-SOC) and dissolved organic carbon were 0.572–1.45 mg kg−1 and 0.290–0.914 mg kg−1, respectively. Further, the 13C-SOC correlated with the relative abundance of genes of the total six pathways, reductive citrate cycle, 3-hydroxypropionate bi-cycle, and reductive acetyl-CoA pathway. Another in situ labelling experiment showed a significant increase in δ13C of SOC, and the incorporated carbon (13C) in SOC accounted for 3.85% of total atmospheric carbon absorption. These results showed that desert soil microbes containing genetic potential for autotrophic carbon fixation spread over a broad taxonomic range, and incorporated atmospheric carbon into organic components, which contributed to atmospheric carbon absorption. Although more research is required to accurately evaluate the portions of autotrophic carbon in the amount of atmospheric carbon absorption, the biotransformation of carbon from the atmosphere to soil via autotrophic carbon fixation represents a microbial pathway for persistent atmospheric CO2 absorption in desert soils, and further implicates an important carbon biochemical cycle for carbon accumulation in oligotrophic desert soils.