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• Land snail Δ 47 -derived temperature correlates well with growing season temperature. • Clumped temperatures of Cathaica are about 3 °C higher than those of Bradybaena. • A species-specific Δ 47 transfer function is needed to reconstruct paleotemperature. • Body water δ18O of Bradybaena shows a robust correlation with rainfall δ18O in northern China. Land snail fossils are abundantly distributed in geological deposits and their isotopic compositions provide a means to determine paleoclimatic changes. With the development of the clumped isotopes (Δ 47) geothermometer, many efforts have been made in recent years to study clumped isotopes in land snail shell carbonate. Although there have been several recent attempts, there is, as yet, no empirical calibration function to convert land snail Δ 47 to environmental temperature. Here, we systematically analyzed clumped isotopes (Δ 47) of two common land snail species (Bradybaena and Cathaica) from China. Results showed that temperatures calculated using the Δ 47 (T 47) of both species did not correlate with the mean annual temperatures (MAT) at the study sites. However, the T 47 -MAT offset is negatively correlated to MAT, suggesting that land snails tend to add shell during the warmer months at colder sites or modulate their body temperature differently in colder regions. Meanwhile, clumped temperatures of Cathaica are 3.4 ± 1.5 °C higher than those of Bradybaena at 18 sites, indicating that a species-specific transfer function is needed to reconstruct paleotemperature using land snail clumped isotopes. After determining the proper duration of the growing season for land snails at different locations, we developed a Δ 47 -growth season temperature (GST) transfer function for the two species. The calibration function for Bradybaena land snails is expressed by a linear regression between 1/T2 and absolute Δ 47 (R2 = 0.94): Δ 47 = (0.0513 ± 0.0036) × 106/T2 + (0.0930 ± 0.0413), where Δ 47 is expressed in ‰ and T in K. The calibration function for Cathaica is as follows (R2 = 0.80): Δ 47 = (0.055 ± 0.011) × 106/T2 + (0.035 ± 0.129). The function for Cathaica was successfully applied to reconstruct mean summer (June-July-August) temperatures during the Last Glacial Maximum and modern times on the central Chinese Loess Plateau, based on Δ 47 data of Cathaica sp. provided by Eagle et al (2013a). This testifies to the validity of the aforementioned constructed transfer function. In addition, the calculated δ18O of body water (δ18O BW) for Bradybaena showed a robust correlation with the δ18O of rainfall (δ18O p), particularly in northern China, which points to the potential to trace hydrological changes in the region. In contrast, Cathaica δ18O BW did not show a straightforward relation to δ18O p. This inter-species complexity warrants further study. [ABSTRACT FROM AUTHOR]

Abstract Lacustrine stromatolites serve as high-resolution and sensitive archives of palaeoenvironmental settings and palaeoclimatic conditions. An exceptionally well-developed stromatolite bed was discovered within nearshore shallow lacustrine sediments of the Lower Miocene Taxihe Formation on the southern margin of the Junggar Basin, north of the Tian Shan Range. We investigated the morphology, mineralogy, clumped and traditional stable isotope geochemistry of the stromatolites by using a multi-method approach with the application of X-ray diffraction analysis, advanced mineral identification and characterization (AMICSCAN), a clumped isotope palaeothermometer and modelling. The overall positive excursions and covariance of δ18O (varying from +10.61‰ to −5.82‰ V-PDB) and δ13C (ranging between −1.27‰ and +2.08‰ V-PDB) values are interpreted as the result of deposition in a closed-basin system under local progressive evaporation conditions during an episode of aridification. Clumped isotope proxy records display a significant decrease in water δ18O values and a decline of lake water temperature from ~38 to ~32 °C, suggesting a shift towards more arid and relatively cooler conditions during the course of stromatolite accretion. This interpretation agrees with lake volume and water level decreases inferred from isotope modelling results. The Late Cenozoic aridification of the southern margin of the Junggar Basin is thus interpreted from a new and unique perspective to have prevailed since the Early Miocene, driven by renewed uplift of the northern Tian Shan Range. The investigated stromatolite records reflect a snapshot of the local palaeoclimatic and palaeoenvironmental evolution, and our work provides references for potential studies of future discoveries of lacustrine microbialites in northwestern China. Graphical abstract Unlabelled Image Highlights • Petrology, mineralogy, traditional and clumped isotope are combined in stromatolites. • Stromatolite records provide snapshots in shrinkage of southern Junggar palaeolake. • Tectonic reactivation in Tian Shan favored a cooler and drier climate since Neogene. [ABSTRACT FROM AUTHOR]

Abstract Stable carbon isotope composition of soil organic matter (δ13C SOM) has been widely used to infer past environmental or vegetation (C 3 /C 4) changes. However, as a carbonaceous product of incomplete burning of biomass, the carbon isotope signature of black carbon (BC) has received little study and a limited usage on this purpose. Moreover, the environmental or vegetation indication of BC carbon isotope composition (δ13C BC) in sedimentary records remains ambiguous although the δ13C BC is supposed to reflect carbon isotope composition of vegetation being burnt. This deserves site-specific studies. Here we analyzed δ13C BC and δ13C SOM on loess-paleosol samples from Lijiayuan and Yangling sections on Chinese Loess Plateau (CLP) spanning the last glacial maximum to decipher the environmental (or vegetation) meaning of δ13C BC at each study site. Opposite changing patterns were observed on the δ13C BC values for the two sections. The δ13C BC at Yangling (in southern part of the CLP) varied from − 19.18‰ to − 21.93‰ (mean: − 20.62‰) with more positive values occurred during the middle Holocene than those during the LGM, demonstrating more C 4 plants occupied in the region during the warm-humid middle Holocene. This is consistent with the changing pattern widely-documented in δ13C SOM records over the CLP during the same period. By contrast, the δ13C BC at Lijiayuan (in northwestern part of the CLP) changed within the range of − 21.83‰ ~ − 24.64‰ (mean: − 23.34‰) and displayed more negative values during the early-middle Holocene with respect to the LGM period. The δ13C BC at Lijiayuan were about 2.5‰ lower than those at Yangling, indicating a northward decrease of C 4 plants on the CLP. The anti-phased changes of δ13C BC at Lijiayuan were considered to reflect variations in paleorainfall because the vegetation is dominated by C 3 plants at the study site and carbon isotope compositions of C 3 plants decrease as rainfall increases. Compared with δ13C SOM record at the same profile, δ13C BC seem biased against capturing C 4 signal during mid-Holocene possibly due to dominance of C 3 plants at the study site during fire seasons and a potentially extra source of BC from forest fires occurred on surrounding mountains. By contrast, δ13C BC tend to exaggerate C 4 signal during the LGM attributed to a possible shift of fire season from spring to summer. These findings suggest that we probably underestimate the abundance of C 4 plants during mid-Holocene and overestimate C 4 biomass during the LGM using BC carbon isotope composition. Highlights • Two δ13C BC records on CLP showed opposite trends of changes since the LGM. • The δ13C BC record on southeastern CLP showed similar C 4 change mode as δ13C SOM did. • The δ13C BC record on northwestern CLP reflected changes in monsoonal rainfall. • Signal of C 3 plant was exaggerated in the δ13C BC record on northwestern CLP. • C 4 plant is either underestimated or overestimated using δ13C BC on southeastern CLP. [ABSTRACT FROM AUTHOR]

In this study, we performed a detailed comparison of stable and clumped isotopic data for an extraction method passing CO 2 through a Porapak Q absorbent trap (PQT) driven by liquid nitrogen (LN method), an extraction method passing CO 2 through a PQT driven by liquid nitrogen and high vacuum pumping (LN + HV method) and an extraction method without a PQT (NAT method), to examine the effectiveness and reliability of these methods. Changes in raw Δ 47 values along with collection times were used to constrain the optimum collection time (OCT) for each method. The OCT for the LN method shortened considerably when the PQT was warmer, i.e., from ∼35 min to ∼30 min when the PQT temperature changed from −15 °C to −12.5 °C. In contrast, the OCT for the LN + HV method displayed little change with the PQT temperature and was reduced to 25 min for both −15 °C and −25 °C. The contaminant removal efficiency of these methods was evaluated by Δ 48 values, revealing that the LN method (with a −12.5 °C to −25 °C PQT) and the LN + HV method (at −25 °C) could effectively remove contaminants compared with the NAT method. Therefore, the LN + HV method (at −25.0 °C) may serve as a promising sample preparation method for routine measurement because it can save time without compromising sample cleaning efficiency. Nevertheless, the LN + HV method yielded Δ 47 values 0.04–0.05‰ higher than the LN method at the same temperature, possibly because of different absorption–desorption states of the PQT in these methods. These findings provide useful clues for optimizing CO 2 extraction methods for clumped isotope analysis. [ABSTRACT FROM AUTHOR]