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An understanding of past climatic variability at regional to local scales is mandatory for a proper evaluation of current and potential future repercussions from global climate change. The Southeast Asian tropics remain severely under-represented in paleoenvironmental and paleoclimatic reconstructions, although a few recent paleoclimate studies evaluated the variability, position and strength of the main Asian monsoon systems at different timescales from modern records to the last 15,000 years. Comparable data from Việt Nam, however, are scarce although Việt Nam and its Central Highlands are critically located at the intersection of the East Asian Summer Monsoon and the Indian Summer Monsoon with highly important socio-ecological consequences from changes in the climate system. This study presents a high-resolution sedimentary climate record from Ea Tyn Lake in Việt Nam’s Central Highlands covering the last 1250 years. Using geochemical and sedimentological proxies and principal component analysis, we reconstructed at least 12 drought events, some of which appear to be of supraregional significance as they coincide with historically documented droughts in India, China, and Cambodia. Beyond tracking short-term climate events, the Rb/Sr elemental ratio along the Ea Tyn Lake sediment sequence reflects long-term monsoon variability throughout the last millenium, which was previously only reconstructed via δ18O speleothem records from China and India. Our Ea Tyn Lake record shows that the East Asian Summer Monsoon was relatively strong between ~1000 and 1350 cal CE and weaker between 1350 and 1850 cal CE, followed by renewed intensification after ~1850 cal CE.

Global warming enhances atmospheric moisture loading and will likely affect the East-Asian monsoon system across Vietnam. The absence of a long written climate history from Vietnam creates a reliance on geological archives of past monsoon history and regional paleoenvironmental changes to provide a framework for evaluating current climatic trends. Biển Hồ lake (14°03′ N, 108°00′ E) is a volcanic crater (i.e. maar) in Vietnam's Central Highlands that has been accumulating sediment since the Pleistocene. Field campaigns between 2016 and 2018 recovered an abundance of gravity and piston sediment cores extending to a depth of ~15 m, covering approximately the last 30 ka BP. The paleoenvironmental interpretation of Pleistocene and Holocene sediment requires knowledge of modern lacustrine and sedimentary conditions, as well as the origin and transport pathways of the catchment material. Here, we focus on a high-resolution sedimentological and geochemical reconstruction of the recent environmental history - from 1950 AD to the present - based on sediment cores from Biển Hồ maar, in direct comparison with local and regional weather and historic records. The uppermost sedimentary record reflects a substantial anthropogenic influence such as deforestation, military use, crater breaching, dam and sill construction, and reforestation that strongly modified the maar's morphology and hydrology. A strong increase in sedimentation rate during the 1960–70s in Biển Hồ cores coincided with U.S. military activities and water withdrawal. A breach in the maar's rim and the connection to a new external reservoir in 1983-1984 AD increased Biển Hồ water level. Reforestation around most of Biển Hồ’s rim in the 1990s curbed erosion and sedimentation rate. Nutrient availability in Biển Hồ declined in the past ~10 years after the installation of a concrete sill between Biển Hồ and the reservoir to limit water exchange with the more nutrient-rich reservoir. This paper is a calibration study on modern sediment to provide an empirical basis for the interpretation of Biển Hồ’s deeper Holocene and pre-Holocene sedimentary record.

2H/1H ratios in animal biomass reflect isotopic input from food and water. A 10-week controlled laboratory study raised 48 mice divided in two generations (8 mothers Mus musculus and their offspring). The mice were divided into four groups based on the combination of 2H, 13C, 15N-enriched and non-enriched food and water. Glycine, the most common amino acid in bone collagen, carried the 2H, 13C, 15N-isotopic spike in food. ANOVA data analysis indicated that hydrogen in food accounted for ∼81 % of the hydrogen isotope inventory in collagen whereas drinking water hydrogen contributed ∼17 %. Air humidity contributed an unspecified amount. Additionally, we monitored 13C and 15N-enrichment in bone collagen and found strong linear correlations with the 2H-enrichment. The experiments with food and water indicate two biosynthetic pathways, namely (i) de novo creation of non-essential amino acids using hydrogen from water, and (ii) the integration of essential and non-essential amino acids from food. The lower rate of isotope uptake in mothers' collagen relative to their offspring indicates incomplete bone collagen turnover after ten weeks. The variance of hydrogen stable isotope ratios within the same cohort may limit its usefulness as a single sample proxy for archaeological or palaeoenvironmental research.

Summary The conventional paradigm for generation of economically viable petroleum reserves involves thermal cleavage of C-C bonds within sedimentary organic matter. However, there is evidence for alternative chemical pathways yielding non-microbial methane generation at low temperatures. In addition, assessing the role of water in methane generation at temperatures lower than those required for it to form by thermal cracking represents a critical step for evaluating processes likely involved in catalytic methanogenesis. Previous pyrolysis experiments of source rocks in the presence and absence of water have yielded insights on the role of water in CH4 generation at a range of maturities including late-stage thermogenesis. Our studies explore the role of catalytic pathways in CH4 generation by experiments simulating maturation of immature source rocks at temperatures insufficient to achieve thermal cleavage of C-C bonds. These hydrous maturation experiments demonstrate that immature shales can generate CH4 at temperatures (80–100 °C). They establish the potential to yield δ13C values

The radiation and extinction of East African vertebrate fauna have been linked to key climatic changes that occurred around 2.8, 1.7, and 0.5 Ma. This study tests whether vegetation and diet changes were linked to these climatic fluctuations, focusing on the climatic event at 1.7 Ma, by analyzing the stable isotope composition of fossil herbivore teeth from the Olduvai Gorge's stratigraphic units Upper Bed I, Lower Bed II, and Upper Bed II, which span ~1.83–1.33 Ma, in order to detect shifts in herbivore diets from C3 to C4 plants in conjunction with their drinking water isotope geochemistry. C4 grass expansion is known to be favored by drier conditions, and this study tests whether herbivore diets permanently changed to being C4 dominant at this key time period. Crocodile teeth are also tested to determine if they may be used as paleoclimatic indicators, since large crocodiles prey on terrestrial herbivores in wetland settings. Vertebrate bioapatite carbon and oxygen isotope compositions are found to show similar trends as those of pedogenic carbonates (carbonate nodules, or concretions), which reflect a drying environment that was changing from C3 woodland dominated habitats to mixed woodlands and grasslands from Bed I to Lower Bed II times. While a return to more humid conditions in Upper Bed II might be expected to lead to a reversal to C3 plants, herbivores in this study retained mostly the drought-resistant C4 plant diet. These results indicate that vegetation and ecosystems passed through a threshold to C4 domination that did not revert to C3 despite partial reversals in climate that occurred later. Crocodile teeth were not useful in tracking C4 plant expansion, but the oxygen isotopes from modern crocodiles are able to show seasonal cycles from wet to dry seasons, and Bed I crocodiles indicate a degree of annual seasonal changes during that time as well.

The cause of rapid hydrological changes in the tropical West Pacific during the last deglaciation remains controversial. In order to test whether these changes were triggered by abrupt climate change events in the North Atlantic Ocean, variations in precipitation during the last deglaciation (18–10 ka) were extracted from proxy records of chemical weathering and terrigenous input in the western Philippine Sea (WPS). The evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration (CIA), elemental ratios (K/Al, TOC/TN and Ti/Ca), δ13Corg, terrigenous fraction abundance and flux data from International Marine Global Change Study Program (IMAGES) core MD06-3054 collected on the upper continental slope of eastern Luzon (northern Philippines). Sediment deposited during the Last Glacial Maximum (LGM) shows weathering equal to or slightly greater than Holocene sediment in the WPS. This unusual state of chemical weathering, which is inconsistent with lower air temperatures and decreased precipitation in Luzon during the LGM, may be due to reworking of poorly consolidated sediments on the eastern Luzon continental shelf during the LGM sea-level lowstand. Rapid changes in chemical weathering, characterized by higher intensity during the Heinrich event 1 (H1) and Younger Dryas (YD) and lower intensity during the Bolling-Allerod (B/A), were linked to rapid variations in precipitation in the WPS during the last deglaciation. The higher terrigenous inputs during the LGM relative to those of the Holocene were controlled by sea-level changes rather than precipitation. The terrigenous inputs show a long-term decline during the last deglaciation, punctuated by brief spikes during the H1 and YD related to sea-level rises and rapid precipitation changes in the WPS, respectively. The proxy records of chemical weathering and terrigenous input from eastern Luzon suggest high rainfall during the H1 and YD events, consistent with inferred rainfall patterns based on Fe/Ca records from offshore Mindanao. Rapid precipitation changes in the WPS did not coincide with migrations of the Intertropical Convergence Zone (ITCZ) but, rather, were related to state shifts of the El Nino-Southern Oscillation (ENSO) during the last deglaciation. Based on proxy records and modeling results, we argue that the Atlantic meridional overturning circulation (AMOC) controlled rapid precipitation changes in the tropical West Pacific through zonal shifts of ENSO or meridional migration of the ITCZ during the last deglaciation. Our findings highlight the dominant role of the North Atlantic Ocean in the tropical hydrologic cycle during the last deglaciation.

Over the past century, numerous discoveries throughout East Africa have advanced our understanding of hominin evolution and provided substantive evidence that climatic and environmental variability played a critical role in evolutionary developments. Stratigraphic records with high temporal resolution aid in testing evolutionary hypotheses that invoke changes in climate and environment at various timescales as drivers of hominin evolution. Olduvai Gorge, Tanzania has a rich history of hominin fossil discoveries from its ~2.0 Ma sedimentary sequence, which includes multiple deep lake intervals. In 2014, the Olduvai Gorge Coring Project (OGCP) recovered a sequence of sediment cores that provide an extensive record of the Pleistocene sedimentary history, including paleolacustrine systems in this area. With >94% core recovery, these cores are ideally suited for high-resolution analyses of organic geochemical proxies and provide an exceptional opportunity to build on previously published outcrop-based paleoenvironmental data from Olduvai. The OGCP core 2A section between 76.6 and 86.9 m depth is considered as a time-stratigraphic equivalent of strata that host the hominin fossils OH24 and OH56 at the Olduvai DK archaeological site. This depositional interval age-bracketed between ~1.88 Ma (Bed I Basalt) and ~1.85 Ma (Tuff IB) was sampled for organic geochemical analyses. The carbon isotopic composition of organic matter (δ13CTOC) from this section varies between values representative of more forested and open grassland ecosystems over ~21 kyr. This observation is consistent with the Milankovitch precession cycle driving the availability of water, which was previously observed in lower resolution studies of outcrop samples. Complementary organic geochemical proxies provide further evidence of these shifts in environmental conditions and record sub-Milankovitch scale changes superimposed on the precession cycle. This suggests the occurrence of short-term fluctuations in the environments inhabited by hominins, which opens new lines of investigation on how environmental scenarios may affect particular evolutionary mechanisms that drove various evolutionary responses.

The Santa Barbara Basin (SBB) preserves a high-resolution sediment record that is varved down to ca. 1700 CE and laminated for at least 2500 years. The distributions of 25 polycyclic aromatic hydrocarbons (PAHs) were investigated in a suite of samples from sediment cores representing different depositional scenarios – varves/laminae, terrigenous flood layers, and marine turbidites. The concentrations of these PAHs were determined using gas chromatography–mass spectrometry in selected ion mode and evaluated in terms of their distributions, diagnostic ratios, and loadings recognized by principal component analysis (PCA). Two biogenic PAHs, perylene and retene, provided the greatest variation in their downcore concentration values. Perylene concentrations increased downcore exhibiting markedly higher abundance in sediments older than 300 CE, consistent with the interpretation that perylene is formed diagenetically in reducing sediments. A modest increase in perylene concentrations in sediments from the late 1960s may be associated with flood-derived transport of higher amounts of degraded terrestrial organic matter from fire-denudated landscapes into the coastal environment. The markedly higher concentrations of retene in flood layers and turbidites relative to varves/laminae suggest that these lithologies are more effective in transporting pyrogenic PAHs and can be interpreted as a proxy for wildfires in SBB. Changes in key diagnostic ratios reveal the shift from a dominance of petrogenic PAHs in older sediments to a strong pyrogenic signal beginning in the latter half of the 20th century. Statistical analysis using PCA of the PAH distributions in the samples revealed that modern sediments showed a strong, positive relationship with PC1, which represents the greatest variation among the samples, whereas flood layers showed a strong relationship with the second major variable (PC2). Thus, statistical approaches provide the capability to elucidate modern, anthropogenic signatures within the complex PAH distributions of SBB and also establish a PAH profile that characterizes the lithological signature of flood layers.

The paper presents the first systematic geochemical study on the content of natural gas (methane, heavier alkanes, CO2), and isotopic composition of methane dissolved in natural springs in Romania, from various tectonic and geological settings. The dissolved methane concentrations in the investigated areas range between 0.08 and 16,359 μg/L. Based on isotopic analyses, the origin of methane in the gas mixture released by the investigated springs has been inferred. The highest concentrations of methane have been measured in the Transylvanian Basin and Carpathian Foredeep. Ethane in relatively high concentrations has been detected in Herculane and Calimanesti-Caciulata areas. Very high concentrations of dissolved CO2 were determined in the Eastern Carpathians volcanic chain area. Lower amounts of dissolved CO2 were detected in the Carpathian Foredeep, Southern Carpathians, Transylvanian Basin, and Pannonian Basin. The measured values of δ13C-CH4 range between − 67‰ and + 4‰. The methane from the investigated areas is biotic, microbial in the Transylvanian Basin, Pannonian Basin, and Moldavian Platform, and thermogenic in the Carpathian Foredeep. We report for the first time the presence of a presumably abiotic methane component in Romania, from geothermal sources, in the areas of Ciomadul Volcano and Herculane area.

International audience; Of the most abundant elemental constituents of organic matter, hydrogen has received the least attention due to its exchangeability with ambient water. The development of steam equilibration using two isotopically distinct waters can enable the user to calculate the proportion of exchangeable H and generate a δ2H value of the non-exchangeable H. Three fossil faunal assemblages from Europe were selected in order to investigate collagen δ2H with respect to body mass, diet and to compare chronological periods in the Quaternary. δ15N values in each suite of fauna show trophic level enrichment, a trend which was also observed in δ2H values. In the case of predatory species with lower δ15N values than other carnivore species, the use of hydrogen isotopes could help to infer the consumption of prey with lower δ15N values rather than a significant dietary contribution of plant foods. For example, a cave bear which exhibits low δ2H values are consistent with low δ15N and therefore point to an herbivorous diet and not omnivory. The combination of δ2H, with δ15N and δ13C, from archaeological and ecological studies of humans and fauna could help reconstruct prey preference; which is especially important when trying to distinguish the quantity of marine versus freshwater resources in diets. Relative to dietary influences, climate variability seems to be a minor control on δ2H in the faunal assemblages studied here.

Recent observations suggest that karst landscapes may be an unaccounted sink for atmospheric CH4, but questions remain about the processes contributing to sub-atmospheric CH4 mole fractions in caves. The CH4 dynamics associated with karst environments were studied over 18 months at 6 locations in Buckner Cave, Southern Indiana by measuring the mole fractions and stable isotopic composition of CH4 and carbon dioxide (CO2). CO2 mole fractions were used to infer seasonal changes in airflow. Samples were obtained on a monthly basis. CH4 mole fractions ranged from 1.9 ± 0.1 ppm near the cave entrance to 0.1 ± 0.1 ppm in the more remote parts of the cave. The carbon and hydrogen stable isotopic compositions of CH4 in the cave ranged from − 58.7 to + 7 ‰ (VPDB) and − 170 to + 10 ‰ (VSMOW), respectively. The isotopic data suggest that the CH4 dynamics of Buckner Cave can be described by a seasonally variable mixing system in which atmospheric CH4 enters primarily through the main entrance and is subsequently consumed by methanotrophs. Additionally, at least two smaller CH4 sources are evident when air has been stagnant. The results suggest that subterranean karst cavities are an important sink for atmospheric CH4.

Small lakes in northern latitudes represent a significant source of CH4 to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH4 budgets are lacking as are measurements of δ13C-CH4 and δ2H-CH4. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH4 and corresponding δ13C-CH4 and δ2H-CH4 in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH4 flux was highly variable, ranging from an average flux of 7 mg CH4 m−2 d−1 in the deep-water zone to 154 mg CH4 m−2 d−1 along the lake margin. Diffusive flux accounted for ~8.5 % of mean net CH4 flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean ± SD 10 ± 17 %) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH4 emissions varied widely throughout the system, with δ13C-CH4 ranging from −66.2 to −55.5 ‰, and δ2H-CH4 ranging from −345 to −258 ‰. Carbon isotope composition of CH4 in ebullitive flux showed wider variation compared to net flux, ranging from −69.2 to −49.2 ‰. Dissolved CH4 concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH4 in the hypoxic deep water coincided with decreasing dissolved O2 concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ13C-CH4 and δ2H-CH4. The most depleted 13C- and 2H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ13C and δ2H observations of CH4, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH4 in deeper sediments were consistent with mixing/transition between CH4 production pathways, indicating a higher contribution of the CO2 reduction pathway. The large spatial variability in fluxes of CH4 and in isotopic composition of CH4 throughout a single lake system indicates that the underlying mechanisms controlling CH4 cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH4 emissions in these systems. Future studies of whole-lake CH4 budgets should consider this significant spatial heterogeneity.

Microbial oxidation of methane (CH4) plays a central role in carbon cycling in Arctic lakes, reducing potential CH4 emissions associated with warming. Isotopic signatures of CH4 (δ13C and δ2H) are indicators of microbial oxidation, wherein the process strongly enriches 13C and 2H in residual CH4. We present δ13C and δ2H measurements obtained from sampling the water column and sediment for dissolved CH4 from three, small Arctic lakes in western Greenland under both open-water and ice-covered conditions from 2013 to 2014. Despite substantial variations in aquatic chemistry among the lakes, δ13C and δ2H of CH4 suggested that CH4 was produced predominantly by acetoclastic methanogenesis in the littoral sediments and hydrogenotrophic methanogenesis in the profundal sediments in all of the lakes. Surprisingly large variations for both δ13C and δ2H of CH4 were observed, with δ13C extending from −72‰ to +7.4‰ and δ2H from −390‰ to +250‰. The CH4 isotopic values reported here were significantly more enriched (p

Species-specific responses of plant intrinsic water-use efficiency (iWUE) to multiple environmental drivers associated with climate change, including soil moisture (θ), vapor pressure deficit (D), and atmospheric CO2 concentration (ca ), are poorly understood. We assessed how the iWUE and growth of several species of deciduous trees that span a gradient of isohydric to anisohydric water-use strategies respond to key environmental drivers (θ, D and ca ). iWUE was calculated for individual tree species using leaf-level gas exchange and tree-ring δ13 C in wood measurements, and for the whole forest using the eddy covariance method. The iWUE of the isohydric species was generally more sensitive to environmental change than the anisohydric species was, and increased significantly with rising D during the periods of water stress. At longer timescales, the influence of ca was pronounced for isohydric tulip poplar but not for others. Trees' physiological responses to changing environmental drivers can be interpreted differently depending on the observational scale. Care should be also taken in interpreting observed or modeled trends in iWUE that do not explicitly account for the influence of D.

Summary: Hydrogen (H) isotope ratio (δ2H) analyses of plant organic compounds have been applied to assess ecohydrological processes in the environment despite a large part of the δ2H variability observed in plant compounds not being fully elucidated. We present a conceptual biochemical model based on empirical H isotope data that we generated in two complementary experiments that clarifies a large part of the unexplained variability in the δ2H values of plant organic compounds. The experiments demonstrate that information recorded in the δ2H values of plant organic compounds goes beyond hydrological signals and can also contain important information on the carbon and energy metabolism of plants. Our model explains where 2H‐fractionations occur in the biosynthesis of plant organic compounds and how these 2H‐fractionations are tightly coupled to a plant's carbon and energy metabolism. Our model also provides a mechanistic basis to introduce H isotopes in plant organic compounds as a new metabolic proxy for the carbon and energy metabolism of plants and ecosystems. Such a new metabolic proxy has the potential to be applied in a broad range of disciplines, including plant and ecosystem physiology, biogeochemistry and palaeoecology.

Although the Late Devonian extinctions were amongst the largest mass extinction events in the Phanerozoic, the causes, nature and timing of these events remain poorly restrained. In addition to the most pronounced biodiversity loss at the Frasnian–Famennian (F–F) boundary and the end Famennian, there were also less extensively studied extinction pulses in the Middle to Late Givetian and the Frasnian. Here we used a combination of palynological, elemental, molecular and stable isotope analyses to investigate a sedimentary record of reef-systems from this time period in the Canning Basin, Western Australia. The acquired data generally showed distinct variations between sediments from (i) the time around the Givetian–Frasnian (G–F) boundary and (ii) later in the Frasnian and indicated a distinct interval of biotic stress, particularly for reef-builders, in the older sediments. Alterations of pristane/phytane ratios, gammacerane indices, Chlorobi biomarkers, δDkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic/euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column. Simultaneous excursions in δ13C profiles of carbonates, organic matter (OM) and hydrocarbons in the older sediments reflect the stratification-induced enhancement of OM-recycling by sulfate reducing bacteria. Alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans (MTTCs) and perylene indicate an increased terrigenous nutrient input via riverine influx, which would have promoted stratification, phytoplankton blooms and the development of lower water column anoxia. The detected palaeoenvironmental conditions around the G–F boundary may reflect a local or global extinction event. Our data furthermore suggest a contribution of the higher plant-expansion and photic zone euxinia to the Late Devonian extinctions, consistent with previous hypotheses. Furthermore, this work might contribute to the understanding of variations in Devonian reef margin and platform-top architecture, relevant for petroleum exploration and development in the global Devonian hydrocarbon resources.

a b s t r a c t Molecular hydrogen produced through iron oxidation during formation of serpentine and magnetite can sustain terrestrial subsurface ecosystems. The Fe 3+ in serpentine partitions into octahedral and tetrahedral sites differently as serpentinization proceeds, and tetrahedral Fe 3+ is present toward the end of serpentinization. We map Fe oxidation states in a serpentinite to determine the degree to which serpentinization progressed and where hydrogen production has been maximized to assess habitability at an abandoned chrysotile mine in Norbestos, Quebec, in association with the Canadian Space Agency's Mars Methane Analogue Mission. We also analyzed stable isotopes of carbon and oxygen in carbonates to constrain the conditions of water-rock interaction during serpentinization. Iron oxidation and coordination was determined through field imaging of rock walls with a visible hyperspectral imager (420-720 nm), and samples collected from imaged rocks and elsewhere in the mine were imaged in the laboratory (420-1100 nm). Sample chemistry, mineralogy, and oxidation state were determined with laboratory measurements of visible through mid-infrared reflectance spectra, major element chemistry, mineralogy, and Mossbauer spectroscopy. Mapping with hyperspectral imaging of outcrops and hand samples shows that tetrahedral Fe 3+ is common in serpentinites at this site, and results are confirmed through other measurements. Major element chemistry and mineralogy are consistent with serpentine plus minor carbonate. Carbonate samples show an exceptional range in δ 13

The air in subterranean karst cavities is often depleted in methane (CH4) relative to the atmosphere. Karst is considered a potential sink for the atmospheric greenhouse gas CH4 because its subsurface drainage networks and solution-enlarged fractures facilitate atmospheric exchange. Karst landscapes cover about 14 % of earth’s continental surface, but observations of CH4 concentrations in cave air are limited to localized studies in Gibraltar, Spain, Indiana (USA), Vietnam, Australia, and by incomplete isotopic data. To test if karst is systematically acting as a global CH4 sink, we measured the CH4 concentrations, δ13CCH4, and δ2HCH4 values of cave air from 33 caves in the USA and three caves in New Zealand. We also measured CO2 concentrations, δ13CCO2, and radon (Rn) concentrations to support CH4 data interpretation by assessing cave air residence times and mixing processes. Among these caves, 35 exhibited subatmospheric CH4 concentrations in at least one location compared to their local atmospheric backgrounds. CH4 concentrations and δ13CCH4 and δ2HCH4 values suggest that microbial methanotrophy within caves is the primary CH4 consumption mechanism as the atmosphere exchanges with subsurface air. The pattern of δ13CCH4 and δ2HCH4 values along CH4 concentration gradients in cave air provides evidence for incomplete oxidation by methanotrophy. Only 5 locations from 3 caves showed elevated CH4 concentrations compared to the atmospheric background and could be ascribed to local CH4 sources from sewage and outgassing swamp water. Several associated δ13CCH4 and δ2HCH4 values point to carbonate reduction and acetate fermentation as biochemical pathways of limited methanogenesis in karst environments and suggest that these pathways occur in the environment over large spatial scales. Our data show that karst environments function as a global CH4 sink. Estimates of CH4 flux in karst landscapes are needed in order to include the subterranean CH4 sink in climate models.

[1] On 24 August 2013 a sudden gas eruption from the ground occurred in the Tiber river delta, nearby Rome's international airport of Fiumicino. We assessed that this gas, analogous to other minor vents in the area, is dominantly composed of deep, partially mantle-derived CO2, as in the geothermal gas of the surrounding Roman Comagmatic Province. Increased amounts of thermogenic CH4 are likely sourced from Meso-Cenozoic petroleum systems, overlying the deep magmatic fluids. We hypothesize that the intersection of NE-SW and N-S fault systems, which at regional scale controls the location of the Roman volcanic edifices, favors gas uprising through the impermeable Pliocene and deltaic Holocene covers. Pressurized gas may temporarily be stored below these covers or within shallower sandy, permeable layers. The eruption, regardless the triggering cause—natural or man-made, reveals the potential hazard of gas-charged sediments in the delta, even at distances far from the volcanic edifices.

The hydrogen isotope composition of plant waxes preserved in lacustrine sediments is a potentially valuable tool for reconstructing paleoenvironmental changes in the Arctic. However, in contrast to ...

Organic deuterium/hydrogen stable isotope ratios (i.e., 2H/1H, expressed as δ2H value in ‰) in animal tissues are related to the 2H/1H in diet and ingested water. Bone collagen preserves the biochemical 2H/1H isotopic signal in the δ2H value of collagen’s non-exchangeable hydrogen. Therefore, δ2H preserved in bone collagen has the potential to constrain environmental and trophic conditions, which is of interest to researchers studying of both living and fossil vertebrates. Our data examine the relationship of δ2H values of collagen with geographic variation in δ2H of meteoric waters, with local variations in the ecology and trophic level of species, and with the transition from mother’s milk to adult diet. Based on 97 individuals from 22 marine and terrestrial vertebrates (predominately mammals), we found the relationships of collagen δ2H to both geographic variation in meteoric water δ2H (R2 = 0.55) and to δ15N in bone collagen (R2 = 0.17) statistically significant but weaker than previously reported. The second strongest control on collagen δ2H in our data is dietary, with nearly 50 percent of the variance in δ2H explained by trophic level (R2 = 0.47). Trophic level effects potentially confound the local meteoric signal if not held constant: herbivores tend to have the lowest δ2H values, omnivores have intermediate ones, and carnivores have the highest values. Body size (most likely related to mass-specific metabolic rates) has a strong influence on collagen δ2H (R2 = 0.30), by causing greater sensitivity in smaller animals to seasonal climate variations and/or high evapotranspiration leading to 2H-enrichment in tissues. In marine mammals weaning produces a dramatic effect on collagen δ2H with adult values being universally higher than pup values (R2 = 0.79). Interestingly, the shift in δ15N at weaning is downward, even though normally hydrogen and nitrogen isotope ratios are positively correlated with one another in respect to trophic level. Our findings suggest that in carnivores, which have an especially high variance in δ2H, large samples are needed to separate signals from precipitation, trophic level, body size, and age. For δ2H of fossil collagen to be useful as a proxy of environmental or dietary information, these confounding effects need to be understood, which means careful selection of a study species. Further, δ2H from a single fossil bone collagen is likely to be uninterpretable.

An international project developed, quality-tested, and determined isotope-delta values of 19 new organic reference materials (RMs) for hydrogen, carbon, and nitrogen stable isotope-ratio measurements, in addition to analyzing pre-existing RMs NBS 22 (oil), IAEA-CH-7 (polyethylene foil), and IAEA-600 (caffeine). These new RMs enable users to normalize measurements of samples to isotope-delta scales. The RMs span a range of delta H-2(VSMOW-SLAP) values from -210.8 to +397.0 mUr or parts per thousand, for delta C-13(VPDB-LSVEC) from -40.81 to +0.49 mUr and for delta N-15(Air) from -5.21 to +61.53 mUr. Many of the new RMs are amenable to gas and liquid chromatography. The RMs include triads of isotopically contrasting caffeines, C-16 n-alkanes, n-C-20-fatty acid methyl esters (FAMEs), glycines, and L-valines, together with polyethylene powder and string, one n-C-17-FAME, a vacuum oil (NBS 22a) to replace NBS 22 oil, and a H-2-enriched vacuum oil. A total of 11 laboratories from 7 countries used multiple analytical approaches and instrumentation for 2-point isotopic normalization against international primary measurement standards. The use of reference waters in silver tubes allowed direct normalization of delta H-2 values of organic materials against isotopic reference waters following the principle of identical treatment. Bayesian statistical analysis yielded the mean values reported here. New RMs are numbered from USGS61 through USGS78, in addition to NBS 22a. Because of exchangeable hydrogen, amino acid RMs currently are recommended only for carbon- and nitrogen-isotope measurements. Some amino acids contain C-13 and carbon-bound organic H-2-enrichments at different molecular sites to provide RMs for potential site-specific isotopic analysis in future studies.

RATIONALE The condition of the pyrolysis reactor is very important for obtaining stable, precise hydrogen isotopic ratios using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC/TC/IRMS). However, few studies of the conditioning process have been conducted, and little is known about the best methods for high-precision hydrogen isotope analysis. METHODS We investigated δ2H variations and observed the changes in carbon coating using six different conditioning methods for the pyrolysis alumina tube: (i) no treatment; (ii) conditioning with 4 μL hexane; (iii) conditioning with 2 μL hexane; (iv) conditioning with 2 μL hexane followed by backflushing overnight; (v) conditioning with 10 s of backflushing with methane; (vi) conditioning with 3 s of backflushing with methane. RESULTS Conditioning the alumina tube can improve the pyrolysis efficiency of organic compounds because a moderate amount of carbon acts as a catalyst in high-temperature regions of the alumina tube. Carbon actually flows in the tube and is difficult to confine to the high-temperature region. Insufficient amounts of carbon in the high-temperature regions lead to incomplete pyrolysis of organic compounds and lower δ2H values due to kinetic fractionation of hydrogen isotopes. In contrast, excess hexane or methane can lead to higher δ2H values, probably due to enrichment of deuterium in the hydrocarbon residue. CONCLUSIONS The δ2H values obtained by Method 6 are closest to the TC/EA δ2H values and are more precise than those obtained by other methods, perhaps because this method introduces a moderate, consistent amount of carbon with each sample injection. Copyright © 2012 John Wiley & Sons, Ltd.

RATIONALE In recent experiments, we found that compound-specific δ2H values can vary as a result of changing the gas chromatography temperature program under common pyrolysis conditions. To achieve better precision, it is necessary to examine the details and find a solution to this problem when using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC-TC-IRMS) for hydrogen isotope analysis. METHODS A test was designed to find the possible temperature effect under four different GC temperature ramp rates using n-alkanes (n-C21, n-C27, and n-C31) and fatty acids (n-C12, n-C18, and n-C24). The common 'hexane' method was used initially to condition the pyrolysis reactor. Experiments were then carried out using the 'methane condition' method because it was considered to improve pyrolysis efficiency. RESULTS Under the 'hexane condition' the measured hydrogen isotope ratios of the n-alkanes and n-fatty acids became more positive with increasing GC temperature ramp rate. The ion current intensity of hydrogen also generally increased. However, when the 'methane condition' method was used, the measured δ2H values of the n-alkanes and n-fatty acids showed little change under different GC temperature ramp rates. CONCLUSIONS Higher pyrolysis efficiency could reduce the tailing of the H2 peak and the related isotopic variations at increased GC temperature ramp rates. In addition, too slow a temperature ramp rate could broaden the peak width and thus increase the background effect and possible isotopic fractionations in the split interface; this could also influence the hydrogen isotope values. We therefore suggest that the appropriate temperature ramp rate is an important factor in improving the precision in analyzing compound-specific hydrogen isotopes. Copyright © 2012 John Wiley & Sons, Ltd.

A vertical δ18O profile was measured through a glacio-lacustrine confining unit on Nantucket Island (USA) in order to constrain vertical infiltration rates when Glacial Lake Nantucket was filled (17–19 thousand years (ka) BP) and after the lake drained. Pore fluids throughout the deposit were found to have a nearly uniform δ18O isotopic composition (−9.3 to −6.3‰) similar to modern precipitation. The porosity (0.35), permeability (10–15 m2), and solute diffusivity (2 × 10–10 ± 1 × 10–10 m2/s) of these silt-dominated glacio-lacustrine deposits were measured in order to quantify flow rates. A paleohydrologic model was developed across Nantucket Island to reconstruct vertical flow rates through the glacio-lacustrine sediments between 19 and 0 ka BP. Results indicate that the vertical Darcy flux through this confining unit varied by a factor of about 16, from about 0.08 m/y during lake-level high stands (17–19 ka BP) to 0.005 m/y once the lake drained. Models of Holocene isotope transport through these lacustrine deposits suggest that all of the isotopically depleted (δ18O < −20‰) glacial meltwater would have been flushed by advection in less than 200 years. These findings suggest that significant amounts of glacial meltwater (~64 million m3/y over 2,000 years) could have recharged the continental shelf.

This paper describes results of chemical and isotopic analysis of inorganic carbon species in the atmosphere and precipitation for the calendar year 2008 in Wrocław (SW Poland). Atmospheric air samples (collected weekly) and rainwater samples (collected after rain episodes) were analysed for CO2 and dissolved inorganic carbon (DIC) concentrations and for δ13C composition. The values obtained varied in the ranges: atmospheric CO2: 337-448 ppm; δ13CCO2 from -14.4 to -8.4‰; DIC in precipitation: 0.6-5.5 mg dm(-3); δ13CDIC from -22.2 to +0.2‰. No statistical correlation was observed between the concentration and δ13C value of atmospheric CO2 and DIC in precipitation. These observations contradict the commonly held assumption that atmospheric CO2 controls the DIC in precipitation. We infer that DIC is generated in ambient air temperatures, but from other sources than the measured atmospheric CO2. The calculated isotopic composition of a hypothetical CO2 source for DIC forming ranges from -31.4 to -11.0‰, showing significant seasonal variations accordingly to changing anthropogenic impact and atmospheric mixing processes.

For the first time we report δD of kerogen (δDkerogen) for three Permian–Triassic (P–Tr) sequences (Hovea#3, Perth Basin, Western Australia; Jameson Land, East Greenland and Lusitaniadalen, Spitsbergen). We have compared δDkerogen with δ13C of kerogen (δ13Ckerogen) and δ34S of total reduced inorganic sulfur (TRIS, essentially pyrite; δ34Spyrite) of all the sections and for one sample set with δ13C of carbonate (δ13Ccarbonate) to establish (i) similarities between the sections and (ii) evaluate whether these signals are local and/or global. Stable isotope shifts occur for all three sample sets either at the P–Tr transition (Western Australia) or coinciding with the marine ecosystem collapse (Spitsbergen and East Greenland). δDkerogen reflects organic matter (OM)/ kerogen type and is not sensitive to the low level of thermal maturation. Reliable palaeoenvironmental information in terms of the use of δD can therefore only be obtained for the P–Tr transition from hydrogen compound-specific isotope analyses (CSIA) of biomarkers (Nabbefeld et al., 2010b). The negative shifts in δ13Ccarbonate (primary) and δ13Ckerogen are attributed to the release of 13C-depleted carbon into the atmosphere, whereas the isotopic excursions in δ34Spyrite relate to palaeoredox changes. However, the global coincidence in timing of the shifts in δDkerogen, δ34Spyrite and δ13Ckerogen suggests a relation between the sulfur, carbon and hydrogen cycles. The negative shifts in δ13Ccarbonate (primary) are in general attributed to the release of 13C-depleted source of carbon into the oceans and atmosphere, whereas δ13Ckerogen can reflect the latter in certain cases, but can also be superimposed by varying sources of OM/kerogen type. Isotopic excursions in δ34Spyrite relate to global changes in the palaeoredox conditions that affect sulfur cycling in the ancient seas.

Unlike long-term heating in subsiding sedimentary basins, the near-instantaneous thermal maturation of sedimentary organic matter near magmatic intrusions is comparable to artificial thermal maturation in the laboratory in terms of short duration and limited extent. This study investigates chemical and H, C, N, O isotopic changes in high volatile bituminous coal near two Illinois dike contacts and compares observed patterns and trends with data from other published studies and from artificial maturation experiments. Our study pioneers in quantifying isotopically exchangeable hydrogen and measuring the D/H (i.e., 2 H/ 1 H) ratio of isotopically non-exchangeable organic hydrogen in kerogen near magmatic contacts. Thermal stress in coal caused a reduction of isotopically exchangeable hydrogen in kerogen from 5% to 6% in unaltered coal to 2–3% at contacts, mostly due to elimination of functional groups (e.g., OH, COOH, NH 2 ). In contrast to all previously published data on D/H in thermally matured organic matter, the more mature kerogen near the two dike contacts is D-depleted, which is attributed to (i) thermal elimination of D-enriched functional groups, and (ii) thermal drying of hydrologically isolated coal prior to the onset of cracking reactions, thereby precluding D-transfer from relatively D-enriched water into kerogen. Maxima in organic nitrogen concentration and in the atomic N/C ratio of kerogen at a distance of ∼2.5 to ∼3.5 m from the thicker dike indicate that reactive N-compounds had been pyrolytically liberated at high temperature closer to the contact, migrated through the coal seam, and recombined with coal kerogen in a zone of lower temperature. The same principle extends to organic carbon, because a strong δ 13 C kerogen vs. δ 15 N kerogen correlation across 5.5 m of coal adjacent to the thicker dike indicates that coal was functioning as a flow-through reactor along a dynamic thermal gradient facilitating back-reactions between mobile pyrolysis products from the hot zone as they encounter less hot kerogen. Vein and cell filling carbonate is most abundant in highest rank coals where carbonate δ 13 C VPDB and δ 18 O VSMOW values are consistent with thermal generation of 13 C-depleted and 18 O-enriched CO 2 from decarboxylation and pyrolysis of organic matter. Lower background concentrations of 13 C-enriched carbonate in thermally unaffected coal may be linked to 13 C-enrichment in residual CO 2 in the process of CO 2 reduction via microbial methanogenesis. Our compilation and comparison of available organic H, C, N isotopic findings on magmatic intrusions result in re-assessments of majors factors influencing isotopic shifts in kerogen during magmatic heating. (i) Thermally induced shifts in organic δ D values of kerogen are primarily driven by the availability of water or steam. Hydrologic isolation (e.g., near Illinois dikes) results in organic D-depletion in kerogen, whereas more common hydrologic connectivity results in organic D-enrichment. (ii) Shifts in kerogen (or coal) δ 13 C and δ 15 N values are typically small and may follow sinusoidal patterns over short distances from magmatic contacts. Laterally limited sampling strategies may thus result in misleading and non-representative data. (iii) Fluid transport of chemically active, mobile carbon and nitrogen species and recombination reactions with kerogen result in isotopic changes in kerogen that are unrelated to the original, autochthonous part of kerogen.

Lake sediment cores and cosmogenic exposure (CE) dates constrain the pattern of deglaciation and evolution of climate across Baffin Island since the last glacial maximum (LGM). CE dating of erratics demonstrates that the northeastern coastal lowlands became ice-free ca.14 ka as the Laurentide Ice Sheet (LIS) receded from its LGM margin on the continental shelf. Coastal lakes in southeastern Baffin Island started to accumulate sediment at this time, whereas initial lacustrine sedimentation was delayed by two millennia in the north. Reduced organic matter in lake sediment deposited during the Younger Dryas chron, and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall. Ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the LIS and local mountain glaciers ∼9.6 ka (Cockburn Substage). A second readvance occurred just before 8 ka during a period of unusually cold summers, corresponding to the 8.2 ka cold event in the Greenland Ice Sheet. Most local glaciers were behind their present margins before 7 ka, and in some instances much earlier, although the Foxe Dome of the LIS continued to slowly retract toward the present day Barnes Ice Cap throughout the Holocene. Pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka. Subsequently, grass tundra became established, followed by modern tundra vegetation ca. 8 ka, with subtle changes in pollen assemblages in the late Holocene. Lake primary productivity peaked in the early Holocene, before terrestrial vegetation or marine surface waters reached their apparent thermal maxima. Lacustrine, marine, and glacial proxies all reflect significant late Holocene cooling. The onset of Neoglaciation is well dated in lacustrine records at ca. 6 ka, with intensification after 2.5 ka. The expansion of local glaciers during the Little Ice Age represents the most extensive advance since 7 ka. We suggest that the replacement of Atlantic surface waters by cold, low-salinity Arctic Ocean water, coupled with the steady reduction of summer insolation, resulted in a significant positive sea-ice feedback that produced a larger late Holocene summer temperature depression over the Baffin region than in the Pacific sector of the Arctic.

Our conceptions of the NE sector of the Laurentide Ice Sheet (LIS) at the Last Glacial Maximum (LGM) have evolved through three major paradigms over the past 50 years. Until the late 1960s the conventional view was that the Eastern Canadian Arctic preserved only a simple deglacial sequence from a LIS margin everywhere at the continental shelf edge (Flint Paradigm). Glacial geologic field studies began in earnest in this region in the early 1960s, and within the first decade field evidence documenting undisturbed deposits predating the LGM led a pendulum swing to a consensus view that large coastal stretches of the Eastern Canadian Arctic remained free of actively eroding glacial ice at the LGM, and that the most extensive ice margins occurred early in the last glacial cycle. This Minimalist Paradigm dominated until the late1980s when an expanded data set from shallow marine studies indicated LGM ice at least locally reached the continental shelf. Within the past decade the marine data, coupled with new evidence from lake sediments and cosmogenic exposure dates on moraines and glaciated terrain in the Eastern Canadian Arctic has led to a new paradigm that better reconciles the terrestrial and marine evidence. Collectively, these lines of evidence indicate that all of southern Baffin Island was glaciated at the LGM, but that some coastal uplands north of Cumberland Sound remained above the limit of actively eroding glacial ice, even though outlet glaciers reached the continental shelf in front of most fiords and sounds. The most plausible explanation for the observed glacial limits is that low-gradient, relatively fast-moving outlet glaciers sliding on deformable sediments occupied marine embayments and fiords, contrasting with slower moving ice frozen to its bed on the intervening crystalline terrain. Slow-moving ice frozen to its bed would have had steeper surface gradients, hence would have terminated inland from the coast. This scenario is consistent with observations indicating high-elevation coastal terrain remained unglaciated even though outlet glaciers reached the continental shelf. LGM summer temperatures were apparently much lower than present, as lakes in the ice-free regions were permanently frozen.

Paleoclimate research based on the stable isotopic composition of lake sediments is often hampered by the lack of preservation of suitable material for isotopic analysis. We examined organic material as a proxy for past water isotopic composition in a series of experiments. First, we cultured aquatic moss under constant illumination, temperature, and water δ18O, and show that new cellulose records source water δ18O precisely (r2 = 0.9997). Second, we analyzed paired lakewater and vegetation samples collected from sites spanning strong climatic gradients. In field conditions, the relationship between organic δ18O and water δ18O is more variable, though it is still controlled by environmental water isotopic composition. However, terrestrial mosses in the arctic are often significantly enriched in δ18O relative to aquatic mosses in nearby lakes due to their use of different water sources. Third, we measured δ18O of cellulose extracted from disseminated sedimentary organic material. In the majority of the middle- to high-arctic lakes in this study, the δ18O of disseminated sediment cellulose is greatly enriched relative to the expected values based on lakewater δ18O, suggesting a significant component of terrestrial cellulose. This interpretation is supported by radiocarbon dates from a Holocene sediment core in which 14C ages of sediment cellulose are 700-5000 yrs older than the enclosing sediments. We conclude that aquatic cellulose can be used as a reliable tracer of lakewater isotope ratios, but terrestrial cellulose often dominates the sedimentary cellulose pool in places such as Baffin Island where sedimentation rates are low enough to allow the degradation of aquatic cellulose. Care must be taken when interpreting sediment cellulose δ18O records where diagenesis has played a role, because terrestrial cellulose is more resistant to degradation, and therefore can predominate in environments with low organic carbon burial.

Hydrogen isotope ratios (D/H) of lipid biomarkers extracted from aquatic sediments were measured to determine whether they can be used as a proxy for D/H of environmental water. Values of δD were determined by using a recently developed isotope-ratio-monitoring gas chromatograph-mass spectrometer system (irmGCMS) and were confirmed by conventional hydrogen isotopic measurements (i.e., combustion followed by reduction) on individual compounds isolated by preparative capillary gas chromatography. Diverse lipids (alkanes, n-alkanols, sterols, and pentacyclic triterpenols) were analyzed to examine hydrogenisotopic controls on lipids of varying origin and biosynthetic pathway. For algal sterols (24-methylcholest- 3β-ol, 24-ethylcholest-5,22-dien-3β-ol, and 4,23,24-trimethylcholesterol, or dinosterol), the fractionation between sedimentary lipids and environmental water was -201 ± 10‰ and was similar in both marine and freshwater sites. In a sediment from a small lake in a forested catchment, triterpenols from terrestrial sources were enriched in D by 30‰ relative to algal sterols. Apparent fractionation factors for n-alkyl lipids were smaller than those of triterpenols and were more variable, probably reflecting multiple sources for these compounds. We conclude that hydrogen-isotopic analyses of algal sterols provide a viable means of reconstructing D/H of environmental waters. Results are less ambiguous than reconstructions based on analyses of kerogen or other operationally defined organic matter fractions.

Thirteen of 18 piston cores recovered from ‘Robinson Lake’ in the mid-Arctic vegetation zone of Baffin Island, Arctic Canada, penetrated stratified lacustrine sediment beneath a thin over-consolidated diamict (till) and postglacial lacustrine sediment. The sub-till lacustrine units are up to 120 cm thick, of which the upper several decimeters frequently contain thick, layered mats of aquatic moss; pollen and diatoms are common throughout both lacustrine units. A series of 23 AMS 14C dates defines the chronology of the postglacial sequence, which records a succession from a pioneer grass- and Oxyria-dominated tundra between 10.4 and 8 ka BP, to a sedge-dominated tundra after 8 ka BP. Limiting 14C dates place the sub-till lacustrine sediments more than 40 ka BP; 10 luminescence dates centered on 85 ka indicate they were deposited late in oxygen isotope stage (OIS) 5. The dominance of shrub and tree pollen, especially shrub birch and alder, in sub-till lacustrine samples, indicates low-arctic tundra farther north than at any time during the Holocene. Pollen concentrations are comparable to or higher than in the Holocene units. Cooling late in the interglacial is indicated by declining birch and alder pollen percentages in the upper part of the section. Diatom floras in both the sub-till and postglacial lacustrine sequences indicate similar development of lake-water chemistry, but input of silica and weathering products was greater in the older lake cycle, suggesting more vigorous catchment processes. Macrofossils in the sub-till units are characteristic of lakes ice-free in summer. Based on pollen assemblages indicating local and regional vegetation diagnostic of summer temperatures higher than the Holocene, we interpret the sub-till lacustrine units to be of interglacial character. By analogy with Holocene plant succession in central and eastern Canada, all of Keewatin and Labrador/Ungava must have been ice free throughout this interval, suggesting essentially complete deglaciation of the Laurentide Ice Sheet at the time.

The condition of the pyrolysis reactor is very important for obtaining stable, precise hydrogen isotopic ratios using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC/TC/IRMS). However, few studies of the conditioning process have been conducted, and little is known about the best methods for high-precision hydrogen isotope analysis.We investigated δ(2)H variations and observed the changes in carbon coating using six different conditioning methods for the pyrolysis alumina tube: (i) no treatment; (ii) conditioning with 4 μL hexane; (iii) conditioning with 2 μL hexane; (iv) conditioning with 2 μL hexane followed by backflushing overnight; (v) conditioning with 10 s of backflushing with methane; (vi) conditioning with 3 s of backflushing with methane.Conditioning the alumina tube can improve the pyrolysis efficiency of organic compounds because a moderate amount of carbon acts as a catalyst in high-temperature regions of the alumina tube. Carbon actually flows in the tube and is difficult to confine to the high-temperature region. Insufficient amounts of carbon in the high-temperature regions lead to incomplete pyrolysis of organic compounds and lower δ(2)H values due to kinetic fractionation of hydrogen isotopes. In contrast, excess hexane or methane can lead to higher δ(2)H values, probably due to enrichment of deuterium in the hydrocarbon residue.The δ(2)H values obtained by Method 6 are closest to the TC/EA δ(2)H values and are more precise than those obtained by other methods, perhaps because this method introduces a moderate, consistent amount of carbon with each sample injection.

In recent experiments, we found that compound-specific δ(2)H values can vary as a result of changing the gas chromatography temperature program under common pyrolysis conditions. To achieve better precision, it is necessary to examine the details and find a solution to this problem when using gas chromatography/thermal conversion/isotope ratio mass spectrometry (GC-TC-IRMS) for hydrogen isotope analysis.A test was designed to find the possible temperature effect under four different GC temperature ramp rates using n-alkanes (n-C(21), n-C(27), and n-C(31)) and fatty acids (n-C(12), n-C(18), and n-C(24)). The common 'hexane' method was used initially to condition the pyrolysis reactor. Experiments were then carried out using the 'methane condition' method because it was considered to improve pyrolysis efficiency.Under the 'hexane condition' the measured hydrogen isotope ratios of the n-alkanes and n-fatty acids became more positive with increasing GC temperature ramp rate. The ion current intensity of hydrogen also generally increased. However, when the 'methane condition' method was used, the measured δ(2)H values of the n-alkanes and n-fatty acids showed little change under different GC temperature ramp rates.Higher pyrolysis efficiency could reduce the tailing of the H(2) peak and the related isotopic variations at increased GC temperature ramp rates. In addition, too slow a temperature ramp rate could broaden the peak width and thus increase the background effect and possible isotopic fractionations in the split interface; this could also influence the hydrogen isotope values. We therefore suggest that the appropriate temperature ramp rate is an important factor in improving the precision in analyzing compound-specific hydrogen isotopes.

The broad scope of isotopic applications of bone collagen ranges from modern ecological and physiological investigations to learning about living conditions of animals in the past (Ambrose & DeNiro, 1989; Chisholm et al., 1982; DeNiro & Epstein 1978, 1981; DeNiro & Weiner, 1988; Hare et al., 1991; Hedges & Law, 1989; Leyden et al., 2006; Lis et al., 2008; Reynard & Hedges, 2008). Bone collagen represents one of the best preserved proteins in fossilized animal remains that in some cases has been chemically preserved for up to 120,000 years (Bocherens et al., 1999). Collagen is protected from degradation by being encapsulated into the bone mineral bioapatite. In comparison to other biopolymers found in the archaeological record, bone collagen is relatively abundant, easily extracted, and offers a long-term record of the life of humans and animals (Collins et al., 2002). Stable isotope ratios in the living biomass directly relate to the stable isotope ratios of life-supporting substrates in the environment. Animals integrate stable isotopes into their biomass through the air we breathe, water we drink and food we eat. Despite the apparent permanence of mineral constituents of bone, the organic components undergo constant turnover through the life of a vertebrate and its collagen content represents a ‘running average’ of months, years, or a lifetime, depending on the specific bone and the animal. Bone collagen thus offers a valuable insight into the environmental conditions during part of or the entire life of an animal (LeeThorp, 2008; Tuross et al., 2008). Carbon and nitrogen stable isotopes of bone collagen have been in broad use in determining diets, paleodiets, trophic levels, and paleoenvironments associated with modern and fossilized bone samples (Ambrose & DeNiro 1989; Chisholm et al., 1982; Hare et al., 1991; Schwarcz, 2000; Walker & DeNiro, 1986; Walter & Leslie, 2009), while other isotopes are only recently finding useful applications. Hydrogen is unique among all elements in terms of the doubling of the atomic mass from the light hydrogen nuclide protium 1H to the less abundant, but heavier nuclide deuterium 2H (or traditionally also abbreviated as D). This large mass difference between the two stable hydrogen isotopes creates strong fractionation effects (i.e. the preferential use or participation of one of the two isotopes in chemical and physical processes) and generates an extremely wide natural isotopic range of hydrogen stable isotope ratios (Sessions et al., 1999). Available hydrogen stable isotope data from bone collagen suggest greater variability than the most of the earlier studies had presumed, a situation that would compromise the diagnostic value of individual forensic collagen δD values for many species.

Museum collections contain a wealth of insect remains originating from a wide geographic range, which can be used to investigate their utility as a proxy for environmental isotope ratios. Chitinous remains of insects such as beetles (Coleoptera) are chemically stable and their stable isotope composition is strongly related to that of environmental water in the period of cuticle formation. We present a dataset of chitin δD and δ18O in two genera of water beetles from a museum collection containing 40 locations for Helophorus (water scavenging beetles) and 48 locations for Hydroporus (predaceous diving beetles) that were selected from latitudes 27–82°N in North America. Only two genera were used to minimize inter-sample variation caused by species-specific differences in metabolic effects, feeding strategy, habitat, and life cycle. The isotopic composition of water beetle exoskeletons had a strong latitudinal trend (North–South) from −160 to +65 ‰ for δD and from 7 to 34 ‰ for δ18O, paralleling gradients of isotopes in precipitation. Strong relationships were observed between isotopic composition of beetles and modelled July precipitation (0.71 < R2 < 0.82, p < 0.001). The relationship between δD and δ18O in the beetle samples had a systematic offset from the global meteoric water line, which was likely caused by metabolic effects during chitin formation. The offset between δD values in beetles and in modelled precipitation was 33 ‰ larger, on average, for Hydroporus compared with Helophorus, suggesting fractionation of hydrogen isotopes during passage through the food chain. This trophic level effect was not observed for stable oxygen isotopes. Furthermore, the observed deviations between isotopic composition of water beetles and modelled precipitation at collection sites were not constant and indicated local hydrological deviations from modelled precipitation. The largest deviations were observed for sites in the Southern US and the Arctic that are highly evaporative and at sites in the Rocky Mountains and Coastal Mountains that were fed by snow melt. Our results indicated that the isotopic composition of water beetles from a museum collection was systematically related to δD and δ18O values of precipitation at the collection site.

Beetles, one of the most diverse and long-lived animal groups, provide a trove of ecological and palaeoenvironmental information largely because their exoskeletons contain chitin, a highly resistant biopolymer which preserves well in the geological record. In addition to palaeoenvironmental inferences that can be derived from presence or absence of particular taxa, beetle chitin records the hydrogen stable isotope ratios (D/H) of environmental water, which is related to temperature and other environmental variables. Because the vast majority of beetle fossils consists of incomplete body parts, the H isotopic variability within and between beetle specimens must be quantified. We provide data that show intra- and inter-specimen D/H variation in modern water beetles that may relate to systematic variations in chitin biosynthesis during exoskeleton development. A discussion of existing hydrogen-isotope studies of chitin are presented, including recent advances in hydrogen-isotope analysis that can enhance sample throughput.

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the d values of these reference materials should bracket the isotopic range of samples with unknown d values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for d 13 C and d 15 N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the ‘principle of identical treatment’. The new reference materials cover the following isotopic ranges: d 2 Hnicotine � 162 to � 45%, d 13 Cnicotine � 30.05 to R7.72%, d 15 Nnicotine � 6.03 to R33.62%; d 15 Nacetanilide R1.18 to R40.57%; d 13 Curea � 34.13 to R11.71%, d 15 Nurea R0.26 to R40.61% (recommended d values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different d 15 N values. Comparative d 13 C and d 15 N on-line EA-IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA-IRMS reference materials. Published in 2009 by John Wiley & Sons, Ltd. Semi-automated stable isotope ratios analysis (SIRA) in continuous flow by on-line elemental analysis (EA) or gas chromatography (GC) interfaced with isotope ratio massspectrometry (IRMS) has become a routine and invaluable approach to characterize and trace organic compounds. It is commonly used in studies of ecology, environmental sciences, food science, forensics, geochemistry, and medical sciences. Rapid advances in instrumentation have reduced sample size requirements and increased sample throughput, for example in the GC-IRMS of hydrogen, 1 carbon 1,2 and nitrogen, 2‐4 and in the EA-IRMS of hydrogen, 5 carbon 6 and

Hydrogen isotopic analysis of organic materials has been widely applied in studies of paleoclimate, animal migration, forensics, food and flavor authentication, and the origin and diagenesis of organic matter. Hydrogen bound to carbon (C-H) generally retains isotopic information about the water present during organic matter synthesis and associated biosynthetic fractionations, but hydrogen bound to other elements (O, S, or N) can readily exchange with atmospheric water vapor and reflects recent exposure to water or vapor. These two pools must be separated to obtain meaningful information from isotope ratios of organic materials. Previously published analytical methods either replace exchangeable H chemically or control its isotopic composition, usually by equilibration with water or waters of known isotopic composition. In addition, the fraction of H that is exchangeable can vary among samples and is itself of scientific interest. Here we report an improved and automated double-equilibration approach.Samples are loaded in a 50-position autosampler carousel in an air-tight aluminum equilibration chamber. Water vapor of known isotopic composition is pumped through the chamber at 115 degrees C for at least 6 h. After flushing with dry N(2) and being cooled, the carousel is rapidly transferred from the equilibration chamber to a He-purged autosampler attached to a pyrolysis elemental analyzer connected to an isotope ratio mass spectrometer. By equilibrating two aliquots of each sample with two isotopically distinct waters, it is possible to calculate both (1) the D/H ratio of non-exchangeable H, and (2) the fraction of H that is exchangeable. Relative to previous double-equilibration techniques, this approach offers significant reductions in sample size and labor by allowing simultaneous equilibration of several tens of samples.

Compound-specific deltaD and delta13C analyses of gas mixtures are useful indicators of geochemical and environmental factors. However, the relative concentrations of individual components in gas mixtures (e.g., H2, CO2, methane, ethane, propane, i-butane, n-butane) may vary over several orders of magnitude. The determination of hydrogen and carbon compound-specific stable isotope ratios requires that the hydrogen and carbon dioxide produced from each separated component has a concentration adjusted to match the dynamic range of the stable isotope mass spectrometer. We present a custom-built gas sampling and injection system (GASIS) linked with a Delta Plus XP mass spectrometer that provides flexibility, ease of operation, and economical use of small gas samples with wide ranges of analyte concentrations. The overall on-line GC-ox/red-IRMS (Gas Chromatography - oxidation/reduction - Isotope Ratio Mass Spectrometry) system consists of (i) a customized GASIS inlet system and (ii) two alternative reactors, namely an oxidative Cu-Ni-Pt reactor at 950 degrees C for production of CO2 and a reductive graphitized Al2O3 reactor at 1420 degrees C for production of H2. In addition, the system is equipped with (iii) a liquid nitrogen spray-cooling unit for cryo-GC-focusing at -20 degrees C, and (iv) a Nafion dryer for removal of water vapor from product CO2. The three injection loops of the GASIS inlet allow flexibility in the volume of injected analyte gas (e.g., from 0.06 to 500 microL) in order to measure reproducible deltaD and delta13C values for gases at concentrations ranging from 100% down to 10 ppm. We calibrate our GC-ox/red-IRMS system with two isotopically distinct methane references gases that are combusted off-line and characterized using dual-inlet IRMS.

A modification of a chemical preparation procedure for oxygen isotope analysis of cellulose has been developed which yields greater precision and requires less time for sample preparation. In the place of isoquinoline, zinc is used to remove HCl from the reaction products of the sample and HgCl 2 . The two methods give systematically different results because isoquinoline biases measurements by contaminating the sample with additional CO 2 . For the zinc method, precision is ±0.2% (1σ standard deviation) compared with ±0.9% for the isoquinoline method