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Intrashell oxygen isotope (δ18Os) analyses of terrestrial snails have been carried out over two decades. However, the intraspecies/interspecies differences are not yet well understood. Here, we conducted a high‐resolution intrashell δ18Os study on 43 shells from Cathaica fasciola and Bradybaena ravida, and 1449 δ18Os data were obtained. These large amounts of data demonstrate the reproducibility of intrashell δ18Os. Our results suggest that C. fasciola and B. ravida have similar growing seasons mainly from March to October in the studied region. The ecological habits of the two species could explain the distinctive variations in their δ18Os sequences. Therefore, our study may interpret the discrepancy between the studies of land snail species and the stable/clumped isotopes of their shells. Moreover, the calculated average growth rate is ∼290 μm/day (from 250 to 330 μm/day) for nonadult C. fasciola. Thus, the use of snail shells for reconstructing high‐resolution terrestrial climate changes is promising. Plain Language Summary: Land snails are sensitive to climatic and environmental changes. Therefore, the oxygen isotopic composition of snail shells (δ18Os) has often been used to study environmental changes. Researchers started to collect multiple samples from a single shell for δ18Os analyses about two decades ago. However, it is still unclear whether high‐resolution intrashell δ18Os results are repeatable and whether the influences of different individuals/species may exist. To address these issues, we collected 43 snail shells from Cathaica fasciola and Bradybaena ravida. In total, 1449 δ18Os data were obtained. The large amount of data showing similar variations in the intrashell δ18Os from different shells demonstrates the repeatability. Accordingly, our data suggest that the two species have similar growing seasons, mainly from March to October, although their ecological habits are different. In addition, the ecological habits of these two species could explain the subtle differences in their δ18Os. Taken together, our study could resolve the discrepancy between previous work on land snail species and stable/clumped isotopes. Furthermore, the estimated average growth rate is ∼290 μm/day (from 250 to 330 μm/day) for nonadult C. fasciola. Overall, snail shells are promising records for exploring high‐resolution terrestrial climate changes in the future. Key Points: The intrashell δ18Os of land snails is reproducible, which mainly records the δ18O of precipitationCathaica fasciola and Bradybaena ravida have different ecological habits but similar growing seasonEcological habits could explain the discrepancy between studies of land snail species and stable/clumped isotopes [ABSTRACT FROM AUTHOR]

Stable carbon isotopes of long-chain n-alkanes in lake sediments have been used for reconstructing past environmental changes. Gas chromatography isotope ratio mass spectrometry coupled to a combustion unit is the commonly applied technique for compound-specific carbon isotope analysis. This paper shows that sulfur in the lacustrine sediment can cause severe interference during the mass spectrometric measurement, leading to significant biases in δ13C of n-alkane. The δ13C deviation could be resulted from additional 12C33S+, 13C32S+ at mass-to-charge ratio (m/z) 45, and 12C34S+, H2C32S+at m/z 46, respectively. Such elemental sulphur interference can be eliminated by the activated copper in the pretreatment procedure. [ABSTRACT FROM AUTHOR]

Rationale: Gas chromatography‐combustion‐isotope ratio mass spectrometry (GC/C/IRMS) is widely used for compound‐specific carbon isotopic analysis. However, current isotopic analysis systems utilize the GC IsoLink combustion reactor, and independent reduction furnaces are not implemented. Therefore, whether this limitation in furnace use affects the precision of compound‐specific carbon isotopic analysis needs to be evaluated. Methods: We attempted to add a separate reduction furnace to the GC IsoLink interface and compared the δ13C values of n‐alkanes (including C and H elements), fatty acid methyl ester (including C, H, and O elements), caffeine (USGS61 and USGS62, including C, H, O, and N elements), and 9‐ethylcarbazole (including C, H, and N elements) before and after the addition of the reduction furnace using the GC IsoLink combustion reactor. Results: For n‐alkanes and fatty acid methyl esters, the δ13C differences between the measured values and their standard values were basically falling within 0.5‰ whether or not an independent reduction furnace was added. However, for the nitrogen‐containing compounds (caffeine and 9‐ethylcarbazole), the δ13C differences between the measured values and their standard values were much larger without an independent reduction furnace (1.0–3.71‰ for USGS61, 1.78–2.19‰ for USGS62, and 0.39–1.13‰ for 9‐ethylcarbazole) than with a reduction furnace (−0.31–0.68‰ for USGS61, −0.44–0.06‰ for USGS62, and −0.04–0.25‰ for 9‐ethylcarbazole). Conclusions: The addition of an independent reduction furnace had no significant effect on the δ13C of n‐alkanes and fatty acid methyl esters, but it had a significant effect on the δ13C of nitrogen‐containing compounds. It is suggested that GC IsoLink needs an independent reduction furnace to effectively eliminate the interference of NOx on CO2 isotopic determination to improve the accuracy of δ13C for nitrogen‐containing compounds. [ABSTRACT FROM AUTHOR]

Contrasting moisture evolutions between westerlies‐dominated Central Asia and monsoonal Asia since the mid‐Holocene have been widely recognized. Yet, inconsistent hydrological records over the early Holocene from both regions hamper our understanding of hydroclimatic changes and associated mechanisms. Here we present isotopic and biomarker (alkenone) records from three Chinese lakes located at both regions to address a possible meltwater role in lake water budget. Our results show the occurrence of particularly depleted isotopic values of lake water associated with lake freshening within the deglaciation and early Holocene. Together with anomalously old 14C dates, which were also documented in many other Asian lakes, our observations likely indicate substantial meltwater contribution to mid‐latitude Asian lake water budget, along with the climatic warming. Hence, the potential meltwater effect should be considered when inferring Asian summer monsoon and westerlies behavior over this critical period, with important implications to Holocene hydrological reconstructions and future hydroclimatic projections. Plain Language Summary: Although meltwater events have been well documented in marine records, the effects of meltwater on Asian lake water budget and regional hydrological cycle during the deglaciation and warm early Holocene remain poorly investigated. Our isotopic and biomarker records from Lake Sayram, Yanhaizi, and Qinghai in northern China, together with anomalously old 14C dates from investigated lakes and other Asian lakes, likely indicate substantial meltwater contribution to lake water budget within the deglaciation and early Holocene, which appears to be a large‐scale phenomenon in mid‐latitude Asia. This suggests that the potential meltwater effect on Asian lake hydrology should be assessed in climatic reconstructions and simulations, which may shed light on accurate interpretation of westerlies and summer monsoon circulation over the early Holocene. Key Points: Isotopic records likely indicate meltwater contribution to Asian lake water budget within the deglaciation and early HoloceneAnomalously old 14C dates summarized from mid‐latitude Asian lakes also support substantial meltwater input during this periodMeltwater effects should be considered when inferring early Holocene Asian summer monsoon and westerlies behavior [ABSTRACT FROM AUTHOR]

Record of long‐term land temperature changes remains ephemeral, discontinuous, and isolated, thus leaving the common view that Pleistocene land temperature evolution should have followed ocean temperatures unconfirmed. Here, we present a continuous land surface temperature reconstruction in the Asian monsoon region over the past 3.0 Myr based on the distribution of soil bacterial lipids from the Chinese Loess Plateau. The land temperature record indicates an unexpected warming trend over the Pleistocene, which is opposite to the cooling trend in Pleistocene ocean temperatures, resulting in increased land‐sea thermal contrast. We propose that the previously unrecognized increase of land‐sea thermal contrast during much of the Pleistocene is a regional climate phenomenon that provides a likely mechanism in favor of the long‐term enhancement of the Pleistocene East Asian summer monsoon. Plain Language Summary: Numerous sea surface temperature (SST) records indicate long‐term gradual cooling over the Pleistocene, whereas the East Asian summer monsoon (EASM) appears to have strengthened during this period. Land‐sea thermal contrast is thought to have an important influence on the intensity of the EASM, but the lack of land surface temperature (LST) records from monsoonal regions prevents the assessment of its role in driving monsoonal changes. Here, we present a 3‐Myr‐long LST record from the Chinese Loess Plateau, displaying a unique long‐term warming trend over the Pleistocene, different from the trajectories of SST records. We propose that the decoupling of long‐term land and sea temperatures, and thus the increase of land‐sea thermal contrast, provides a simple interpretation for the otherwise paradox, strengthening of the EASM over the Pleistocene. This study presents much needed original LST data that support novel interpretations on a mechanism for important paleoclimate phenomenon in East Asia with implications to the entire terrestrial ecosystem during the critical period of earth history. Key Points: Three million years of continuous land surface temperatures reconstructed based on soil bacterial lipidsThe land temperature record indicates an unexpected warming trend over the PleistoceneIncreasing land‐sea thermal contrast facilitated the long‐term intensification of Pleistocene East Asian summer monsoon [ABSTRACT FROM AUTHOR]

The expansion of plants using the [C.sub.4] photosynthetic pathway is one of the most prominent changes in the global ecosystem during the Cenozoic Era. A significant late Miocene expansion is well documented. However, the existence and cause of subsequent expansions are still not clear, owing in part to the lack of long, continuous climate-vegetation records. Here we present two high-resolution carbon isotope time series, covering the past 7 m.y., derived from eolian deposits on the Chinese Loess Plateau. The data indicate three intervals of significant [C.sub.4] plant expansions within the semiarid monsoonal region of East Asia (ca. 2.9-2.7 Ma, 1.3-0.9 Ma, and 0.6 Ma-present). These expansions covary with strengthened East Asian summer monsoon circulation. We conclude that in East Asia, large-scale late Miocene [C.sub.4]/[C.sub.3] vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation. Keywords: [C.sub.4] plant expansion, carbon isotope, summer monsoon, Chinese Loess Plateau, Miocene.

Reconstruction of the paleoaltitude history of the Tibetan Plateau is critical for understanding the linkage between tectonics and its effect on regional and global climate change. Presently, most of the paleoaltitude studies are concentrated on the southern and southeastern part of the Tibetan Plateau, and few studies have been conducted in the central‐northern part. In this paper we focused on the Wudaoliang Formation in the Tuotuohe Basin, central to northern Tibetan Plateau, to reconstruct paleoaltitude based on carbonate oxygen isotopes. The carbonate samples are primary or have experienced an early stage of digenesis. Based on the thermodynamic and empirical model results, the paleoaltitude of the Wudaoliang Formation is found to be around 2700–3260 m (average of 2980 ± 280 m) in the early Miocene (∼24 Ma). Integrating paleoaltitude results from Wudaoliang Basin and our results, we conclude that crustal shortening and tectonic activity were strong during the late Eocene to late Oligocene‐early Miocene and relatively weak during the early Miocene in the central‐northern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We have investigated carbon isotopic compositions of four plant genus/species, Bothriochloa ischaemum (C4), Stipa bungeana (C3), Lespedeza sp. (C3) and Heteropappus less (C3), along a precipitation gradient in northwest China in order to assess the impact of water availability on the carbon isotopic discrimination against 13C during carbon assimilation in this area. This information is necessary for reconstruction of paleovegetation, particularly paleo-C3/C4 plant ratios using δ13C value of organic matter in loess and paleosols in the Chinese Loess Plateau. The δ13C of C3 plants, as a group, exhibits a negative correlation with the annual precipitation amount with a total change and sensitivity of 5‰ and −1.1‰/100 mm, respectively, for the precipitation range from 200 to 700 mm. The C4 grass, B. ischaemum responds to aridity by decreasing 1.7‰ for over the precipitation range from 350 to 700 mm; the plant δ13C is significantly correlated with annual precipitation with a slope −0.61‰/100 mm. This result implies that without considering the effect of water availability on the plant δ13C values, reconstruction of percent C4 vegetation during the last glaciation can be overestimated by about a factor of two. [ABSTRACT FROM AUTHOR]

Hydrogen isotopic compositions (δD) of fatty acids (FAs) in lake sediments have been widely used in palaeoenvironmental reconstruction, but investigations on FA δD values in algae and submerged plants from natural lakes are still limited, greatly hampering the application and interpretation of their δD values in lacustrine environments. Here, we systematically investigated δD values of short-chain (C 14 –C 18 ), mid-chain (C 20 –C 24 ), and long-chain (C 26 –C 30 ) FAs in four algae and submerged macrophytes, two algal genera Chara and Cladophora and two angiosperm genera Potamogeton and Ruppia , that commonly occur in six lakes on the north-eastern Tibetan Plateau. We obtained the following results: (i) C 20 –C 30 FAs in each algal and submerged plant sample have similar variation patterns in δD values, suggesting that δD values of C 20 –C 30 FAs have consistent responses to their source water δD. In C 4 -like taxa ( Potamogeton , Ruppia , and Chara ), the C 16 and C 26 FAs have minor differences in their δD values, while in the C 3 -like Cladophora , δD values of C 16 FAs are significantly more negative (avg. –48 ± 7‰) than that of the C 26 FAs. We propose that different photosynthetic mechanisms in these algae and submerged plants account for the different inter-molecular δD variations between C 16 and C 26 FAs; (ii) δD values of C 26 FAs in the carbonate-coated alga Chara are significantly correlated with the δ 18 O values of carbonate encrustations – such a co-variance suggests that in addition to lake water, other factors may also influence both lipid synthesis and carbonate encrustation building up in Chara , leading to a significantly positive apparent hydrogen isotope fractionation factors (ε FA-W ) between C 26 FAs of Chara and lake water; (iii) δD values of C 26 FAs from Potamogeton , Ruppia and Cladophora are correlated well with lake water δD values ( R 2 = 0.84, p  < 0.001, n = 19), suggesting that the δD values of long-chain FAs potentially record δD variations of lake water with the apparent hydrogen isotope fractionation factors (ε FA-W ) of C 26 FAs ranging from −153‰ to −134‰. Our results highlight the impact of different photosynthetic pathways on the inter-molecular difference of FA δD values in algae and submerged plants and illustrate both the potential and the challenge of applying their FA δD values as a palaeo-hydrology proxy. [ABSTRACT FROM AUTHOR]

The hydrogen isotopic composition of plant wax (δD wax ) inherits the isotopic values of the source water and isotopic fractionation that take place in lipid biosynthesis. The δD wax values of n -alkanes or n -acids in sediment records are considered to be effective paleo-δD for precipitation proxies for different timescales. However, the vegetation effect also contributes substantially to the apparent fractionation values (ε w-p ) between the precipitation and plant. Therefore, a method for evaluating the dominant plant source in the sediment records is key for reconstructing a reliable paleo-δD p record. In this study, based on field data from the extremely arid Qaidam Basin and the semi-arid central Chinese Loess Plateau (CLP), a plant type index (Pta), based on the traditional P aq and n -alkane C 31 /C 29 index, was used to evaluate the dominant plant type that contributed to the sediments. In the arid and semi-arid region, the Pta values of the aquatic plants were <90, while the shrub Pta ranged from 90 to 180 and the grass Pta was >180. A test on contemporary soils and surface lake sediments also showed that the Pta index could estimate the regional vegetation distribution in modern environments. We also evaluated the dominant n -alkane source for four sediment records in China during the last millennium and reconstructed a regional paleo-δD p by choosing a different ε w-p . The estimated paleo-δD p values showed a good correlation with the modern regional summer δD p . We suggest that a large number of field studies are needed to improve the Pta index for quantitatively calculating the precise ratios for various plant sources. Such data would play a key role in improving hydrogen isotopic hydroclimatic research. [ABSTRACT FROM AUTHOR]

• δ13C of minute land snail shell could record the local vegetation signals. • Shell δ13C has the potential to be a reliable precipitation proxy. • Spatially scattered shell δ18O reflects the dominant control of precipitation δ18O. Land snails are abundant and well preserved in loess-paleosol sequences on the Chinese Loess Plateau (CLP) and are often regarded as valuable climatic indicators in paleoclimate reconstruction. To date, many stable isotope investigations have been carried out on land snail shells (e.g., δ13C shell and δ18O shell) from diverse geographical and climatic regions. However, few studies have been conducted on modern minute land snails (2–10 mm) on the CLP, and their climatic significance has not been adequately understood. Here, we present new δ13C shell and δ18O shell data from four minute modern land snails (Pupilla aeoli , Gastrocopta armigerella , Opeas striatissimum , Vallonia tenera), and analyses of their correlations with climatic factors (growing season temperature, precipitation and relative humidity) were conducted to examine their climatic significance across the CLP. The results show that δ13C shell can record local vegetation information and has the potential to be a reliable precipitation proxy. Interestingly, δ18O shell exhibits spatially scattered values in the studied region, and these data yielded poor correlations with various climatic parameters, such as precipitation amount, temperature and relative humidity. Given the similar spatial characteristics of observed precipitation δ18O (δ18O p), these phenomena may support the dominant control of δ18O p on δ18O shell. [ABSTRACT FROM AUTHOR]

[Display omitted] • δ13C of CO 2 in lake water was in situ measured from three Tibetan Plateau lakes. • δ13C of CO 2 in lake water at different water depths show small variations. • δ13C of CO 2 /HCO 3 – cannot fully explain δ13C difference of measured aquatic plants. The carbon isotope values (δ13C) of aquatic plants are of great significance for recognizing carbon cycles and tracing environmental changes in lakes. Yet, the influence of δ13C values of their utilizing carbon sources (especially in the case of CO 2 separated from the HCO 3 – in water) on their δ13C differences have never been evaluated, which is mainly due to the lack of CO 2 δ13C investigations in lake water. In this study, we used a newly developed fast-response automated gas equilibrator for real-time concentration and δ13C determination of dissolved CO 2 in the surface and bottom lake water of Lake Tuosu, Lake Qinghai and Lake Keluke, China. Moreover, we determined the corresponding δ13C values of total organic carbon (TOC) of a submerged plant (Potamogeton) and an alga (Cladophora), as well as the δ13C values of dissolved inorganic carbon (DIC) in bottom lake water. The results showed that the CO 2 δ13C values of bottom and surface water in these three lakes did not show significant differences and the δ13C values of CO 2 at different water depths also did not show significant differences. However, Potamogeton had higher TOC δ13C values (average 14–16‰) than Cladophora in these lakes. Although Potamogeton and Cladophora could utilize HCO 3 – as an additional carbon source whose δ13C values were more positive (ca. 7–8‰) than CO 2 , this effect on their δ13C values was no >4‰ after evaluation. Thus, our results show that the δ13C values of carbon sources (including CO 2 and HCO 3 –) are not the main factors in determining the TOC δ13C difference between Potamogeton and Cladophora , which could be primarily related to the biosynthetic fractionation for different aquatic plant species. Our results benefit further understanding and interpretations of δ13C variations in carbon cycles and paleoenvironment reconstructions for lakes. [ABSTRACT FROM AUTHOR]

The expansion of plants using the C4 photosynthetic pathway is one of the most prominent changes in the global ecosystem during the Cenozoic Era. A significant late Miocene expansion is well documented. However, the existence and cause of subsequent expansions are still not clear, owing in part to the lack of long, continuous climate-vegetation records. Here we present two high-resolution carbon isotope time series, covering the past 7 m.y., derived from eolian deposits on the Chinese Loess Plateau. The data indicate three intervals of significant C4 plant expansions within the semiarid monsoonal region of East Asia (ca. 2.9-2.7 Ma, 1.3-0.9 Ma, and 0.6 Ma-present). These expansions covary with strengthened East Asian summer monsoon circulation. We conclude that in East Asia, large-scale late Miocene C4/C3 vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation. [ABSTRACT FROM AUTHOR]

The nitrogen and oxygen isotopes of NO 3 - are effectively used to trace the main nitrogen sources and migration processes in the atmosphere, water and soil. NO 3 - can be converted into N 2 O by the bacterial denitrification method, which is an advanced method with high sensitivity. However, due to the existence of a small but inevitable blank during the whole experimental process, the N isotopic signal of N 2 O produced by denitrification superimposes on that of the N blank. Currently, the standard curve correction method is used to correct measured nitrogen isotope results to mitigate blank interference. It has been reported that high variability of the nitrogen isotope results have been produced by the denitrifier method by conducting an interlaboratory comparison of denitrifier methods and other methods on standards and environmental samples, and to reduce this problem, the nitrogen isotope calibration process with a standard curve is examined in depth in this paper, which uses PreCon-GC-IRMS to determine the nitrogen isotopes in N 2 O. We demonstrate for the first time that reliable results can be obtained without correction for samples with nitrogen isotope composition ranging from -9.9 to 19.5‰, which covers the natural sample range. This study establishes the double test approach for the bacterial denitrification method, ensuring the accuracy and long-term stability of different batches of nitrogen isotope results., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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 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., 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 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., Conclusions: 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., (Copyright © 2012 John Wiley & Sons, Ltd.)