Stable Oxygen Isotope Composition Research Articles

桂西北喀斯特小流域降雨稳定氢氧同位素组成及影响因素

气候变化背景下，降雨稳定氢氧同位素的变化对以快速的地表-地下水文过程为主要特征的喀斯特生态水文研究有重要意义。以桂西北典型喀斯特峰丛洼地小流域为研究对象，测定2013年至2018年日尺度及2019年至2020年8场大雨或特大暴雨的雨水稳定氢氧同位素组成，分析降雨稳定氢氧同位素变化特征及其影响因素。结果表明，研究区夏半年以海洋性水汽为主，冬半年以干燥的大陆性气团为主，导致夏半年降水δD、δ¹⁸O和氘盈余值显著（P<0.05）低于冬半年。降水的稳定氢氧同位素存在显著的反温度效应和雨量效应，即δ¹⁸O值与温度呈显著（P<0.001）负相关，与降雨量呈显著（P<0.001）正相关。次降雨过程中，持续时间较长（>9.5 h）的降雨存在显著的（P<0.05）雨量效应，特大暴雨则不存在雨量效应，与大气或地理因素有关。研究区水汽来源及降水强度存在明显的时间差异，因此在开展喀斯特小流域生态水文过程研究时，需要关注降水稳定氢氧同位素组成在不同时间尺度上的变化特征。;In the context of global climate change, the variation of stable hydrogen and oxygen isotopes during rainfall is of great significance to study of the rapid surface-to-subsurface hydrologic processes in karst areas. We measured the hydrogen-oxygen isotope composition of water samples during the inter-annual scale rainfall from 2013 to 2018 and eight typical rainfalls (heavy rain to extremely heavy rain) from 2019 to 2020 in the karst area of northwest Guangxi. We also analyzed the variation characteristics of hydrogen-oxygen isotope and its influencing factors. The results show that the δD, δ¹⁸O, and d-excess in the summer half-year is significant (P<0.05) lower than the winter half-year. Hydrogen and oxygen isotopes stable in precipitation have anti-temperature effect and rainfall effect, that is, δ¹⁸O value has a significantly (P<0.001) negative linear relationship with temperature and a significantly (P<0.001) positive linear relationship with rainfall. In the process of rainfall, the rainfall effect was only observed in the long-duration (> 9.5 h) rainfall events. Extremely heavy rain does not have a rainfall effect and is related to atmospheric or geographical factors. These results suggest that studies on eco-hydrological processes should focus on the various characteristics of stable hydrogen and oxygen isotopic compositions of precipitation at different time scales.

Hydrological differences between the Lutetian Paris and Hampshire basins revealed by stable isotopes of conid gastropods

During the Eocene greenhouse (56.0–33.9 Ma), northwest Europe was dominated by a semi-arid para-tropical climate but the paleohydrological conditions are poorly known. To gain more insight into seasonal hydrological conditions in the region, we compare Lutetian (middle Eocene, ∼ 44–45 Ma) mollusk δ18O records from two shallow marine basins on either side of the English Channel,i.e., the Paris and Hampshire Basins. The semi-circular Paris Basin was open to the Atlantic Ocean, while the Hampshire Basin was more enclosed and influenced by the draining of several rivers. The proximity of the basins and the similarity of their faunal assemblages suggest that they experienced roughly similar seawater temperatures but the seasonal hydrology is expected to have been different between these basins. Among the numerous mollusks present in both basins are several members of Conidae, a gastropod family that is particularly well-suited for paleoseasonality reconstructions. To assess the paleohydrological differences between these basins we analyzed the stable oxygen isotopic composition of three specimens ofEoconus deperditusfrom the Banc à Verrains in the middle part of the Calcaire Grossier Formation of the Paris Basin (France), and three specimens ofEoconus edwardsifrom the Shepherd’s Gutter Bed in the upper part of the Selsey Formation of the Hampshire Basin (United Kingdom). While the seasonal variability appears to have been similar between these basins, the δ18O values of the Hampshire Basin specimens are consistently lower than those in the Paris Basin, suggesting a regional difference in δ18Oswof 1–2‰ between the basins. This difference in δ18Oswwas likely related to the greater influence of fluvial discharge within the Hampshire basin, compared to the Paris Basin.

Atmospheric nitrate formation pathways in urban and rural atmosphere of Northeast China: Implications for complicated anthropogenic effects

Effects of human activities on atmospheric nitrate (NO3-) formation remain unclear, though the knowledge is critical for improving atmospheric chemistry models and nitrogen deposition reduction strategies. A potentially useful way to explore this is to compare NO3- oxidation processes in urban and rural atmospheres based upon the oxygen stable isotope composition of NO3- (Δ17O–NO3-). Here we compared the Δ17O–NO3- from three-years of daily-based bulk deposition in urban (Shenyang) and forested rural sites (Qingyuan) in northeast China and quantified the relative contributions of different formation pathways based on the SIAR model. Our results showed that the Δ17O in Qiangyuan (26.2 ± 3.3‰) is significantly higher (p < 0.001) than in Shenyang (24.0 ± 4.0‰), and significantly higher in winter (Shenyang: 26.1 ± 6.7‰, Qingyuan: 29.6 ± 2.5‰) than in summer (Shenyang: 22.7 ± 2.9‰, Qingyuan: 23.8 ± 2.4‰) in both sites. The lower values in the urban site are linked with conditions that favored a higher relative contribution of nitrogen dioxide reaction with OH pathway (0.76-0.91) than in rural site (0.47-0.62), which should be induced by different levels of human activities in the two sites. The seasonal variations of Δ17O–NO3- in both sites are explained by a higher relative contribution of ozone-mediated oxidation chemistry and unfavorable conditions for the OH pathway during winter relative to summer, which is affected by human activities and seasonal meteorological condition change. Based on Δ17O, wintertime conditions led to a contribution of O3 related pathways (NO3 + DMS/HC and N2O5 hydrolysis) of 0.63 in Qingyuan and 0.42 in Shenyang, while summertime conditions led to 0.15 in Qingyuan and 0.05 in Shenyang. Our comparative study on Δ17O–NO3- between urban and rural sites reveals different anthropogenic effects on nitrate formation processes on spatial and temporal scales, illustrating different responses of reactive nitrogen chemistry to changes in human activities.

Estimates of the contribution of fog to wet atmospheric deposition in Czech mountain forests based on its stable hydrogen and oxygen isotope composition: preliminary results

Stable isotopes are increasingly being used in many scientific fields, including environmental sciences. In this study we measured the variation in the stable hydrogen and oxygen isotope composition of fog water, rain water (in the form of bulk falling precipitation) and throughfall water in the Šumava (the Bohemian Forest), Krkonoše (the Giant Mts.) and Jizerske hory (the Jizera Mts.) Mts. in October-November 2017. In total, 46 cumulative two-week samples were collected and analysed. Our results indicate that the overall stable hydrogen and oxygen isotope composition of fog and rain samples differed significantly, fog being isotopically enriched in the heavier isotopes 2H and 18O relative to rain. In contrast to our assumption, throughfall water was generally depleted in the heavier isotopes 2H and 18O relative to rainwater. Hence, the simple mixing model for most samples yielded an unrealistic percentage outside the reasonable range of 0–100%. For few samples, however, the estimated contribution of fog to throughfall ranged between 3 and 8% based on δ2H and 4 and 7% based on δ 18O, which is lower than that estimated for the same mountain regions by other authors using different methods and significantly lower than that reported for mountain ranges in neighbouring countries. Although using stable isotopes is a promising tool for determining the contribution of fog to the hydrological budget when assessing atmospheric deposition, the critical limitations are in the collection, manipulation and storing of the samples.

A bone to pick: stable isotope compositions as tracers of food sources and paleoecology for notosuchians in the Brazilian Upper Cretaceous Bauru Group

Notosuchia is a highly diverse group of crocodyliforms that peaked during the Cretaceous period. Their taxonomic abundance and morphological disparity in the Upper Cretaceous Bauru Group (Bauru Basin, Brazil) is remarkable, with over 20 species reported. The stable carbon and oxygen isotope composition of notosuchian bioapatite from two sites (i.e., the Ponto 1 do Price and Fazenda Três Antas) in west Minas Gerais State was analyzed to evaluate differences in feeding habits among the taxa found in both localities. Possible environmental stressors are examined, in parallel to sedimentological, paleopedological, and paleontological studies, which indicate a semi-arid to arid climate for the Bauru Group. Multiple tissues of notosuchian crocodyliforms were included in our study, as well as a testudines carapace fragment, lepisosteiform fish teeth and scales, and host rocks. The mineral textures, X-ray diffraction and stable isotope data support preservation of tooth enamel and scale ganoin bioapatite. The δ13C results point to different feeding habits between two terrestrial, carnivore notosuchians, namely a terrestrial source diet for Uberabasuchus terrificus and an aquatic source diet for Campinasuchus dinizi. The δ18Ow for the crocodyliform data was calculated and compared to other Upper Cretaceous sites. Values support dry conditions during the formation of the bioapatite for the Fazenda Três Antas site and point to the Hateg Basin in Romania, yet likely younger, as a good paleoclimatic analogue.

Pronghorn (Antilocapra americana) enamel phosphate δ18O values reflect climate seasonality: Implications for paleoclimate reconstruction.

Stable oxygen isotope (δ18O) compositions from vertebrate tooth enamel are widely used as biogeochemical proxies for paleoclimate. However, the utility of enamel oxygen isotope values for environmental reconstruction varies among species. Herein, we evaluate the use of stable oxygen isotope compositions from pronghorn (Antilocapra americana Gray, 1866) enamel for reconstructing paleoclimate seasonality, an elusive but important parameter for understanding past ecosystems. We serially sampled the lower third molars of recent adult pronghorn from Wyoming for δ18O in phosphate (δ18OPO4) and compared patterns to interpolated and measured yearly variation in environmental waters as well as from sagebrush leaves, lakes, and rivers (δ18Ow). As expected, the oxygen isotope compositions of phosphate from pronghorn enamel are enriched in 18O relative to environmental waters. For a more direct comparison, we converted δ18Ow values into expected δ18OPO4* values (δ18OW‐PO4*). Pronghorn δ18OPO4 values from tooth enamel record nearly the full amplitude of seasonal variation from Wyoming δ18OW‐PO4* values. Furthermore, pronghorn enamel δ18OPO4 values are more similar to modeled δ18OW‐PO4* values from plant leaf waters than meteoric waters, suggesting that they obtain much of their water from evaporated plant waters. Collectively, our findings establish that seasonality in source water is reliably reflected in pronghorn enamel, providing the basis for exploring changes in the amplitude of seasonality of ancient climates. As a preliminary test, we sampled historical pronghorn specimens (1720 ± 100 AD), which show a mean decrease (a shift to lower values) of 1–2‰ in δ18OPO4 compared to the modern specimens. They also exhibit an increase in the δ18O amplitude, representing an increase in seasonality. We suggest that the cooler mean annual and summer temperatures typical of the 18th century, as well as enhanced periods of drought, drove differences among the modern and historical pronghorn, further establishing pronghorn enamel as excellent sources of paleoclimate proxy data.

The spatial patterns and impact factors of stable oxygen and hydrogen isoscapes in pond water: A case study on the water-source forests of the Hani terraced fields in Yunnan, China

Isoscapes are useful tools for studies concerned with hydroclimatic processes, at multiple scales, and their effects on water resources. However, few studies have been conducted on the application of landscape ecology methods for the characterization of isoscape patterns and their impact factors. In this work, measurements of stable hydrogen and oxygen isotope composition were performed on 112 pond-water samples from the water-source forest of the Hani terraced fields. The spatial gradients of pond-water isotope compositions, and the altitude factor of these gradients, were then analysed according to the topography of the study area, using spatial interpolation and gradient analysis methods. It was found that: 1) The pond-water evaporation line (PWEL) of the study area was δD = 6.28δ18O − 5.5 (R2 = 0.96, n = 112). The gradient and intercept of the PWEL were lower than those of the global meteoric water line (GMWL) and local meteoric water line (LMWL), indicative of intense evaporation. 2) Inverse distance weighting (IDW) interpolation, natural neighbourhood interpolation, spline interpolation, Kriging and Co-Kriging (with altitude as an auxiliary variable) were compared, and IDW interpolation was demonstrated to be the most precise of these methods. IDW interpolation demonstrated that pond-water δ18O values generally increased with decreased altitude, in E-W, S-N and SE-NW directions across the study area. 3) Gradient analysis demonstrated that δ18O generally decreased with increased altitude across the whole-region and at watershed-scales. The δ18O was significantly correlated with altitude on virtually all transects. Therefore, altitude is one of the key factors for the spatial pattern in the stable isotope compositions of the study area’s pond water. This was less pronounced in the E-W transect across the study area, as its isotope compositions were affected by watershed-level patterns. In summary, this work has established a new approach for the analysis of water-body isoscapes and their altitude factor by adopting methods of pattern analysis from landscape ecology.

Climatic quantification and seasonality of the late MIS 3 in North China: A perspective from carbon and oxygen isotopes of fossil mammal teeth

Marine Isotope Stage 3 (MIS 3, at 60–25 ka B.P.) was a short interstadial within the Last Glacial period. A generally warm and wet climatic condition during the MIS 3 period has been suggested by many previous studies. Quantitative climatic reconstruction and studies of seasonality, however, have been seldom attempted given the scarcity of useful proxy indicators. A full understanding the climatic characteristics during this period is hampered by their absence. This is especially the case in the East Asian monsoon region in North China, which is very sensitive to climatic change. To help fill this knowledge gap, we have determined the stable carbon (δ13C) and oxygen isotope (δ18O) compositions of tooth enamel from fossil mammals (Bubalus sp [buffalo] and Cervus elaphus [red deer], dated at ∼33–31 ka B.P.) recovered from Longquan Cave in North China. We use these data to constrain ecology, local air temperature and precipitation amounts during the late MIS 3. The average δ13C (VPDB) of tooth enamel (−14.4‰ and −8.8‰, respectively for buffalo and red deer) indicate that C3 plants comprised the main diet of animals living in this area. Pollen assemblages demonstrated that vegetation mainly consisted of grasses and herbs (∼64%) with trees only accounting for about 26%. These results indicate a landscape of open steppe with sparsely distributed trees. The reconstructed climate derived from tooth enamel δ18O was relatively colder and drier than present-day condition, with mean annual air temperature ranging from 4 to 13 °C and mean annual precipitation ranging from 360 to 670 mm. Moreover, the inferred summer and winter half-year temperatures were respectively 8–24 °C and −2 to 5 °C, which represents either similar or weaker seasonality than at the present time. The inferred cold and dry climate suggested by our study contrasts with the warm and wet conditions previously reconstructed using proxy indicators from bulk soil samples in North China. In comparison to the long-term, time-averaged climatic condition reflected by those soil proxies, the stable isotope compositions of fossil more likely recorded climatic conditions at annual or seasonal time-scale. The inferred annual cold/dry climate at Luanchuan Cave suggested by our data may indicate a short climatic cooling event from Greenland Interstadial (GIS) 5 to its following stadial. Mean annual temperature fluctuated by ∼8 °C during this interstadial-stadial cycle.

Combined paleohistological and isotopic inferences of thermometabolism in extinct Neosuchia, usingGoniopholisandDyrosaurus(Pseudosuchia: Crocodylomorpha) as case studies

AbstractThe evolution of thermometabolism in pseudosuchians (Late Triassic to the present) remains a partly unsolved issue: extant taxa (crocodilians) are ectothermic, but the clade was inferred ancestrally endothermic. Here we inferred the thermometabolic regime of two neosuchian groups, Goniopholididae (Early Jurassic to Late Cretaceous) and Dyrosauridae (middle Cretaceous to late Eocene), close relatives of extant crocodilians, in order to elucidate the evolutionary pattern across Metasuchia (Early Jurassic to the present), a clade comprising Neosuchia (Early Jurassic to the present) and Notosuchia (Middle Jurassic until the late Miocene). We propose a new integrative approach combining geochemical analyses to infer body temperature from the stable oxygen isotope composition of tooth phosphate and paleohistology and phylogenetic comparative methods to infer resting metabolic rates and red blood cell dimensions. †Dyrosaurusand †Goniopholisshare with extant crocodilians similar lifestyles, body forms, bone tissue organization, body temperatures, metabolic rates, and red blood cell dimensions. Consistently, we infer ectothermy for †Dyrosaurusand †Goniopholiswith the parsimonious implication of neosuchians and metasuchians being primitively ectothermic.

Accuracy of Otolith Oxygen Isotope Records Analyzed by SIMS as an Index of Temperature Exposure of Wild Icelandic Cod (Gadus morhua)

Global warming is increasing ocean temperatures, forcing marine organisms to respond to a suite of changing environmental conditions. The stable oxygen isotopic composition of otoliths is often used as an index of temperature exposure, but the accuracy of the resulting temperature reconstructions in wild, free-swimming Atlantic cod (Gadus morhua) has never been groundtruthed. Based on temperatures from data storage tags (DST) and corresponding salinity values, the stable oxygen isotope (δ18O) value was predicted for each month of tagging and compared with δ18Ootolith values measured in situ with secondary ion mass spectrometry (SIMS). Paired-sample Wilcoxon tests were applied to compare measured and predicted δ18O values. The difference between measured and predicted mean and maximum δ18Ootolith values was not significant, suggesting a good correspondence between SIMS-measured and DST-predicted δ18Ootolith values. However, SIMS-measured and predicted minimum δ18Ootolith values were significantly different (all samples: p &amp;lt; 0.01, coastal and frontal cod: p &amp;lt; 0.05), resulting in overestimation of maximum temperatures. Our results confirm that otoliths are well-suited as proxies for mean ambient temperature reconstructions. A possible matrix effect and the absence of a reliable aragonite standard for SIMS measurements appeared to cause a small divergence between measured and predicted δ18Ootolith values, which affected the estimation accuracy of absolute temperature. However, relative temperature changes were accurately estimated by SIMS-analyzed δ18Ootolith values.

Chemometric approaches for determining the geographical origin of Japanese Chardonnay wines using oxygen stable isotope and multi-element analyses

Determining the geographical origin of wines is a major challenge in wine authentication, but little information is available regarding non-parametric statistical approaches for wines. In this study, we collected 33 domestic Chardonnay wines vinified on a small scale from grapes cultivated in Japan, and 42 Chardonnay wines imported from 8 countries, for oxygen stable isotope and multi-element analyses. Non-metric multidimensional scaling (NMDS), kernel principal component analysis (KPCA) and principal component analysis (PCA) were applied to the oxygen stable isotopic compositions (δ18O) and the concentrations of 18 elements in the wines to compare the extractions by parametric and non-parametric methods. The non-parametric methods, NMDS and KPCA, separated domestic from imported Chardonnay wines better than the parametric method, PCA. Of 19 variables, 18 were important for geographical discrimination, with the δ18O value being the most significant in all statistic methods. Non-parametric multivariate analyses will help discriminate domestic from imported Chardonnay wines.

Stable isotope geochemistry of Gwebin mammalian fauna with implications for late Neogene paleoenvironmental changes in central Myanmar

To explore the paleoenvironmental changes in SE Asia during the late Neogene, we examined the stable carbon and oxygen isotope compositions of tooth enamel from mammals of the late Pliocene/earliest Pleistocene Gwebin area in central Myanmar and compared the results with those of the latest Miocene Chaingzauk mammals in Myanmar. The stable carbon isotope values (δ13C) of Gwebin mammals indicate that they inhabited mosaic environment ranging from woodland to grassland. The relative abundance of C3-browsing versus C4-grazing bovids as well as other C3-consuming anthracotheriids, porcupine, rhinoceroses, suids, and stegodontids suggest the dominance of wooded environment. In central Myanmar, it is assumed that floral transition from C3 to C4 plants has occurred since the latest Miocene to Early Pliocene relating to the Himalayan Orogeny. However, stable isotope data at present indicate that paleoenvironment of central Myanmar did not change considerably in the Pliocene and served as a refugium for several forest/woodland dwellers at least until the early Pleistocene. The development of the proto-Ayeyarwady and proto-Chindwin drainage systems in the late Neogene of Myanmar induced the riparian environment, probably buffering against the rain shadow effect of the Indo-Myanmar Ranges. The onset of the present day aridification in central Myanmar is probably related to the Middle to Late Pleistocene sea-level changes in SE Asian region, which have had a major impact on climate, vegetation and megafauna of SE Asia.

Late Pleistocene human paleoecology in the highland savanna ecosystem of mainland Southeast Asia

The late Pleistocene settlement of highland settings in mainland Southeast Asia by Homo sapiens has challenged our species’s ability to occupy mountainous landscapes that acted as physical barriers to the expansion into lower-latitude Sunda islands during sea-level lowstands. Tham Lod Rockshelter in highland Pang Mapha (northwestern Thailand), dated between 34,000 and 12,000 years ago, has yielded evidence of Hoabinhian lithic assemblages and natural resource use by hunter-gatherer societies. To understand the process of early settlements of highland areas, we measured stable carbon and oxygen isotope compositions of Tham Lod human and faunal tooth enamel. Our assessment of the stable carbon isotope results suggests long-term opportunistic behavior among hunter-gatherers in foraging on a variety of food items in a mosaic environment and/or inhabiting an open forest edge during the terminal Pleistocene. This study reinforces the higher-latitude and -altitude extension of a forest-grassland mosaic ecosystem or savanna corridor (farther north into northwestern Thailand), which facilitated the dispersal of hunter-gatherers across mountainous areas and possibly allowed for consistency in a human subsistence strategy and Hoabinhian technology in the highlands of mainland Southeast Asia over a 20,000-year span near the end of the Pleistocene.

What Speleothems Tell Us about Long-Term Rainfall Oscillation throughout the Holocene on a Planetary Scale

Within the context of anthropogenic warming, rainfall oscillations may induce especially important societal impacts worldwide. In this article, we propose to study potential underlying mechanisms related to precipitation changes on a planetary scale by taking advantage of the recent theory of Rossby waves of long periods winding around subtropical gyres, the Gyral Rossby Waves (GRWs). The stable oxygen isotopic compositions of speleothems are used to regionalize and reconstruct the evolution of long-term rainfall oscillation during the Holocene. The method applied here consists in estimating the wavelet power of dated series of stable oxygen isotopic composition (δ18O) in speleothems within period bands representative of subharmonic modes. Our findings highlight: (1) hydrological processes resulting from friction between the North Equatorial Current (NEC) and the North Equatorial Counter Current (NECC) to explain the weakening of ENSO activity in mid-Holocene, and (2) the quasi-resonance of the equatorward migration of the summer Inter Tropical Convergence Zone (ITCZ) during the Holocene, because of the progressive decrease of the thermal gradient between the low and high latitudes of the gyres. The results of this study suggest that the spatial and temporal variations in the amplitude of the rainfall oscillations are related both on the acceleration/deceleration phases of the western boundary currents and on the shrinkage of the Hadley cell. The latitudinal shift of the summer ITCZ in response to changes in the thermal gradient is of the utmost importance in predicting the expansion of deserts resulting from anthropogenic warming.

Holocene Evolution of Sea‐Surface Temperature and Salinity in the Gulf of Mexico

AbstractFlows into and out of the Gulf of Mexico (GoM) are integral to North Atlantic Ocean circulation and help facilitate poleward heat transport in the Western Hemisphere. The GoM also serves as a key source of moisture for most of North America. Modern patterns of sea‐surface temperature (SST) and salinity in the GoM are influenced by the Loop Current, its eddy‐shedding dynamics, and the ensuing interplay with coastal processes. Here, we present sub‐centennial‐scale records of SST and stable oxygen isotope composition of seawater (18Osw; a proxy for salinity) over the past 11,700 years using planktic foraminiferal geochemistry in sediments from the Garrison Basin, northwestern GoM. We measured O and magnesium‐to‐calcium ratios in tests of Globigerinoides ruber (white) to generate quantitative estimates of past sea‐surface conditions. Our results replicate and extend late Holocene reconstructions from the Garrison Basin, using which we then create composites of SST and 18Osw. We find considerable centennial and millennial‐scale variability in both SST and 18Osw, although their evolution over the Holocene is distinct. Whereas mean‐annual SSTs display pronounced millennial‐scale variability, 18Osw exhibits a secular trend spanning multiple millennia and points to increasing northwestern GoM surface salinity since the early Holocene. We then synthesize the available Holocene records from across the GoM and alongside the Garrison Basin composite uncover substantial, yet regionally consistent, spatiotemporal variability. Finally, we discuss the role of the Loop Current and coastal influx of freshwater in imposing these heterogeneities. We conclude that dynamic surface‐ocean changes occurred across the GoM over the Holocene.

Stadial‐Interstadial Temperature and Aridity Variations in East Central Europe Preceding the Last Glacial Maximum

AbstractLast glacial North Atlantic climate is characterized by abrupt, centennial‐millennial scale climate oscillations, called Dansgaard‐Oeschger (D‐O) events. Understanding the cause and propagation of these D‐O events into Eurasia is hampered by the scarcity of quantitative paleotemperature estimates from continental archives with precise, independent age models. Here, we present land snail shell carbonate clumped isotope‐based active season paleotemperature estimates and δ13C/δ18O‐based aridity reconstructions from Greenland stadial/interstadials (GS/GI) between 31 and 26.5 ka from the 14C‐dated Dunaszekcső loess section (Hungary). This reconstruction is complemented with a new 230Th‐dated flowstone stable isotope record covering 30‐26 ka. Our snail shell clumped isotope (Δ47) data indicate growing season temperatures (GSTs) of 16°C–18°C and 7°C–14°C for the investigated interstadials and stadials, respectively. Stable carbon and oxygen stable isotope compositions of shells and flowstone calcite reveal milder interstadials with drier summers and more available moisture over the winter season, and colder stadials with annually/seasonally (winter) drier conditions, promoting increased loess/dust deposition. We propose that large‐scale ocean‐atmospheric variability, characterized by NAO phases, may have imparted a major control on transmitting abrupt North Atlantic climate event signals into continental Europe during the last glacial.

Isotope Signature Of The Massive Ice Bodies On The Northeast Coast Of Chukotka Peninsula

The massive ice (MI) bodies are widespread phenomena on Chukotka coastal plains. Although they have been studying since 1930s, stable isotope method was applied for the ice beds quite recently. In this study cryostratigraphy and stable oxygen and hydrogen isotope composition of MI bodies on the extreme North-Eastern Chukotka (near Lavrentiya settlement and Koolen’ lake) have been studied in detail. It was concluded that studied MI bodies have intrasedimental origin and most likely are dated back to the Late Pleistocene age. Mean δ18O values range from –18.5 ‰ to –15 ‰ whereas mean δ2 H values range from –146‰ to –128 ‰ that is higher than expected for the Late Pleistocene ice bodies in this region, which most likely resulted from isotopic fractionation during freezing of water-saturated sediments in a closed system when forming ice became isotopically enriched compared with initial water. The analysis of co-isotope ratios for MI shows that initial water is mainly of meteoric origin (precipitation, water of lakes and taliks).

Effects of plastic mulch on soil water migration in arid oasis farmland: Evidence of stable isotopes

In arid areas, where water resources are extremely scarce, the consumption of agricultural water resources is generally higher than 80% of the total water resources. Reasonable irrigation practices and effective water conservation methods are critical to the efficient utilization of water resources. In order to analyze the rationality of existing irrigation mode and evaluate the effect of plastic mulch on irrigation water migration, this research monitored the hydrogen and oxygen stable isotopic composition of soil water in Minqin oasis farmland located in the arid area of Northwest China. We used the soil water balance equation and the Craig-Gordon model to quantify the infiltration and evaporation of soil water. The result shows: (1) After irrigations in the corn growing season, the average irrigation water of 29.9 ± 4.2% (29.0 ± 6.7 mm), 29.6 ± 2.9% (28.4 ± 2.7 mm) and 30.3 ± 4.3% (29.0 ± 3.5 mm) penetrated into the soil layer of 0–10 cm, 10–50 cm, and 50–100 cm respectively. The field drainage under plastic film mulching was higher than that of no film mulching. (2) Plastic film mulching is the main reason for the difference in SWlc-excess of the surface layer. The evaporative loss of 0–5 cm soil water in non-mulched soil was generally higher than that of plastic-mulched soil. During the whole corn growing season, plastic film mulching effectively reduces evaporation losses of surface soil water and improves water use efficiency. The results of the reserch are very useful for understanding the hydrological process of agricultural lands in arid oases, improving agricultural irrigation water utilization rates, and optimizing water conservation models.

Application of the Data on δ13C and δ18O of Carbonates for the Study of Unconventional Reservoirs on the Example of the Bazhenov Source Rocks, Western Siberia, Russia

This paper addresses potential application of data on stable carbon and oxygen isotope composition of carbonates for study of organic rich source rocks on the example of the Late Jurassic–Early Cretaceous Bazhenov Formation (West Siberian petroleum basin, Russia). Geochemical studies were conducted for sections located in central (most productive) and peripheral (northern and southern) regions of the Bazhenov Formation distribution area, containing deposits formed under different conditions. We identified key factors impacting stable isotope composition of carbonate minerals and established relation of their isotope composition to the formation conditions. Using a thermodynamic model of carbon and oxygen isotope exchange in the carbonate–water–carbon dioxide system, it is shown that variations in the isotope composition of secondary carbonates are affected by isotopic composition of primary carbonates in sediments and by the isotope exchange reactions with water and carbon dioxide, generated during the source rocks transformation. Our results demonstrate that stable isotope data for carbonates in the Bazhenov Formation together with standard geochemical methods can be efficiently applied to determine sedimentation conditions and secondary alteration processes of oil source rocks.

Stable oxygen and hydrogen isotope compositions of the Messoyakha and Pestsovoe pingos in northwest Siberia as markers of ice core formation

AbstractPingos are indicators of modern and past conditions of permafrost. In total, 1,620 pingos have been identified on the Yamal and Gydan peninsulas in western Siberia. The main purpose of this study is to consider the distribution of stable isotopes in pingo ice cores formed under conditions of open and closed systems. Two pingos from ice cores of different origin in the continuous permafrost zone of northwest Siberia have been considered: the Messoyaha‐1 pingo (10.5 m in height) and the Pestsovoe pingo (17 m in height). Drilling of the ice core was performed with continuous sampling of an undisturbed frozen core. Ice formation was estimated according to the Rayleigh fractionation in a closed‐system versus an open‐system framework. For the Pestsovoe pingo, a pronounced decrease in δ18O values with corresponding increase in dexc with depth indicates a closed system upon freezing of the lake talik from the top down. For the Messoyakha‐1 pingo, the values of δ18O and δ2Н showed a weak tendency to decrease with depth, with values of dexc varying randomly. Ice that was segregated in the overlying and underlying sediments had similar values of δ18O and δ2Н and a low slope. Isotopically nonequilibrium ice formation was established for ice which had been segregated in a closed system and for ice cores formed in an open to semiclosed system. The vacuum mechanism of water suction from the surrounding lake or lake talik may have played a significant role during the formation of the upper ice core of the Messoyakha‐1 pingo and its additional growth.