Oxygen Isotope Variations Research Articles

Hydrological Behavior of Karst Systems Identified by Statistical Analyses of Stable Isotope Monitoring Results

The article presents findings of a two-year systematic study of stable isotope content in two karst groundwater resources in Primorsko-goranska county (Croatia): the Martinšćica wells (MWs) and the Dobrica spring (DBC). The temporal and spatial variation of hydrogen and oxygen isotopes is commonly studied in conjunction with hydrogeological conditions such as groundwater dynamics and discharge conditions. However, since this information was incomplete, we were forced to work with limited data and rely on analyses of stable isotope monitoring results. The obtained results show that winter precipitation is the most common recharge source for the systems, and the average residence time of water in the subsurface is less than a year. Furthermore, the MWs system is a typical dual-porosity system with dominant base flow. The results of the nonparametric regression analysis show that the possibility of seawater intrusion into the spring affecting DBC isotope content cannot be ruled out. We believe that the results presented in the paper demonstrate that when combined with statistical analyses, environmental stable isotopes are a powerful tool for gaining insights in karst hydrogeology.

Climatic fluctuations during a mass extinction: Rapid carbon and oxygen isotope variations across the Permian-Triassic (PTr) boundary at Guryul Ravine, Kashmir, India

In one of the most extended Permo-Triassic (PTr) boundary sections at Guryul Ravine (Kashmir), both carbon and oxygen isotopes show no marked trend across the boundary, but do show zigzag variations at a scale not seen above and below. These are interpreted as major short-term variations in biological storage of carbon (δ13Ccarb), temperature (δ18Ocarb), and land/ocean carbon mixing (δ13Corg) which also occur in other sections with the required detail of analysis. Oxygen isotopes, though probably altered show that relative sea surface temperatures fluctuated greatly at Guryul Ravine; if unaltered they fluctuated between 22 °C and 42 °C, using a salinity-stratified model for the partially enclosed PTr Neotethys Ocean, about the same range as at Meishan and Shangsi in China at lower equatorial latitudes. Together with the carbonate isotopes, this suggests large fluctuations in climate and terrestrial biomass from the latest Permian event horizons to the fossil-defined base of the Triassic which lasted, on current estimates about 60 ± 48 ka, and, by analogy with Quaternary studies, fit a 100kyr eccentricity cycle, with the main end Permian extinction occurring within the cycle. The lack of consistent element geochemical changes across the boundary accompanied by significant carbon, sulphur, and other isotopic changes, here and elsewhere, suggests that atmospheric and oceanic chemistry rather than physical changes, such as provenance and sea‐level changes, drove the PTr environmental changes and extinctions at least on the mid‐latitude Tethyan shelf of northern India.

Enhanced aridification across the Eocene/Oligocene transition evidenced by geochemical record in the Tajik Basin, Central Asia

The Tajik Basin is an intermontane depression between the mountain ranges of Tian Shan, Pamir, and Hindukush, which is located in the northwestern part of the India-Asia collision zone. Due to the westward retreat of the Neotethys Sea, the paleoenvironment of the Tajik Basin has underwent change from a shallow-sea to a continental semiarid land during the Cenozoic era. This implies that the long-term climatic record in the Tajik Basin can potentially reflect the environmental effects of the changed land-sea distributions controlled by plate collision and global eustatic sea-level changes. In this paper, we present new results of stable oxygen and carbon isotopes of carbonates and chemical weathering indices of bulk samples from the Eocene-Oligocene terrestrial strata (ca. 39–30 Ma) in the center of the Tajik Basin. The temporal variations of oxygen and carbon isotopes of carbonates indicate an isotopic shift across the Eocene-Oligocene transition (~34 Ma), characterized by a relatively positive shift due to the isotopic enrichment in authigenic carbonates in an enhanced aridification episode in the Tajik Basin. This shift was also mirrored by the weakened chemical weathering indicated by the ratios of major oxides across the Eocene-Oligocene transition. Such a regional climatic shift was generally coincident with a remarkable global scale sea-level drop. We suggest that the isolated Paratethys Sea, which was mainly driven by global cooling due to the initial formation of the Antarctica Ice-sheet, together with the decreased seawater evaporation due to lower sea surface temperature, reduced water vapor transport by westerlies to the downwind region, and thus intensified the aridification in the Tajik Basin began at ~34 Ma. • Reconstructed paleoclimatic record between ~39 and 30 Ma in Central Tajik Basin. • Stable isotopes and chemical weathering indices reveal enhanced aridity at ~34 Ma. • Regression of the Paratethys played a major role in reducing moisture transport.

Tree-Ring Oxygen Isotope Variations in Subalpine Firs from the Western Himalaya Capture Spring Season Temperature Signals

We analyzed the tree-rings δ18O of Abies spectabilis (fir) growing at the subalpine treeline ecotone in the Magguchatti valley. The valley is located in the Indian summer monsoon (ISM) dominated region of western Himalaya and also receives snow precipitation derived by westerly disturbances (WDs) during the winter months. The 60 year developed (1960–2019 CE) tree-ring δ18O chronology revealed a strong positive correlation with the temperature of late winter and spring months (February to April). Strong negative correlations are also apparent for snowcover, soilmoisture, and relative humidity for the same spring season. Our findings partly contrast the significant correlation results of tree-ring δ18O with summer precipitation and drought indices recorded from other summer monsoon-dominated regions in the Himalayas. The spatial correlation analyses with sea surface temperatures (SSTs) and climate parameters showed subdued signals of tropical Pacific at the site, but with a shift to more moisture influx from the Arabian Sea during the last two decades. Moreover, a significant negative correlation with North Atlantic Oscillation further justifies the strongly captured spring temperature and snowcover signals and the weak effect of summer precipitation in fir trees. A temperature rising trend during the latter half of the 20th century and the elevation effect are taken as important factors controlling the moisture source at the treeline ecotone zones.

Termination 1 Millennial‐Scale Rainfall Events Over the Sunda Shelf

AbstractRecent paleoclimate reconstructions have suggested millennial‐scale variability in the Indo‐Pacific Warm Pool region coincident with events of the last deglaciation. Here, we present a new stalagmite oxygen isotope record from northern Borneo, which today is located near the center of the region's mean annual intertropical convergence zone. The record spans the full deglaciation, and reveals for the first time distinct oxygen isotope variations at this location connected with the Bølling‐Allerød onset and the Younger Dryas event. The full deglaciation in the Borneo stalagmite proxy reconstruction appears remarkably similar to a 20–11 ka transient simulation of rainfall over the area produced using the isotope‐enabled Community Earth System Model. In this model, periods of weakened Atlantic Ocean meridional overturning circulation are associated with an anomalous Western North Pacific anticyclone, which is produced in boreal autumn and shifts south over Borneo during boreal winter, causing dry conditions.

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.

Carbon and Oxygen Isotopic Characteristics of Longmendong Formation in Muxu River Section of Qishan, Shanxi Province and Its Significance

The lower and upper Longmen cave formation of Late Ordovician in the Muxu river section of Qishan in the southwest margin of Ordos are Sandaogou formation of Middle Ordovician and beiguoshan formation of Upper Ordovician respectively, with continuous and complete strata. The average values of carbon and oxygen isotopes of carbonate rocks are 0.57‰ and -10.73‰ respectively, with poor correlation, which basically preserves the characteristics of original isotopic composition. The paleosalinity Z is between 120 and 130, which reflects that the late Ordovician was a marine sedimentary environment, which is consistent with the geological research results. According to the base value characteristics and drift changes of carbon isotope curve of Longmenshan formation, it can be divided into XH1-XH4 cycle segments. Generally speaking, the early carbon isotope values are mainly positive drift, with large scale and long time; The late stage is dominated by negative drift, with small scale and short time. This reflects that the sea level fluctuated greatly in the early Late Ordovician, with strong activity, and the sea level fluctuated slightly in the late Ordovician, showing a downward trend as a whole. Carbon and oxygen isotope variation curve of longmendong formation and global Ordovician δ13C variation curves shows that longmendong formation is deposited in the late Ordovician, which is equivalent to Sandbian and Katian periods. There is a positive drift event of GICE carbon isotope, which is regionally comparable.

Oxygen isotope variations in Mg-rich olivines from type I chondrules in carbonaceous chondrites

Using high-resolution cathodoluminescence (HR-CL) panchromatic imaging for the location of high-precision oxygen three-isotope analyses by secondary ion mass-spectrometry (SIMS), this study is aimed at characterizing the oxygen-isotope variations in Mg-rich olivines (≥Fo99) of selected type I chondrules from the Yamato (Y) -81020 CO3.05 (Ornans-type) carbonaceous chondrite. Cathodoluminescence being extremely sensitive to faint changes in CL activator/quencher concentrations (Al, Cr, Mn, Fe) allows us to describe various overlooked cycles of growth and dissolution in Mg-rich olivines, which strongly suggest an intimate relationship with their gaseous environment during their formation. The present study confirms significant Δ17O variations of ten ‰ in Mg-rich olivines but does not support the relationship previously found between Mg# [MgO/(MgO + FeO) × 100, mol%] and Δ17O among type I chondrules, nor the interpretation of redox changes that has been made of it. We instead show that Mg-rich olivines in Y-81020 chondrules exhibit a prominent 16O-enriched and 16O-depleted bimodal distribution, which is considered as the most primordial signature of type I chondrules from Y-81020 and very likely other carbonaceous chondrites. This signature is interpreted as a snapshot of the early stages of a mixing occurring between two clouds/environments in which chondrules formed and evolved by gas–melt interaction and mixed according to hydrodynamical instabilities imposed by the process responsible for the mixing. As far as this study allows, O-isotope variations of Mg-rich olivines seems to account for large scale dynamical instabilities while chemical variations highlighted by HR-CL (dissolution/growth) bear witness of smaller scale instabilities very likely occurring in the immediate vicinity of the chondrules. Without being able to decide on plausible astrophysical settings yet, we note however that processes like disruptive and vaporizing collisions between planetesimals offer a range of processes and physicochemical conditions, e.g., expansion, decompression, dynamical instabilities, that deserve to be explored in more detail, some of which resembling those highlighted in this study, e.g., gas–melt interaction, partial pressure fluctuations, heterogeneous materials, gas mixing.

Absence of hydrothermal oxygen isotope variations in host rocks supports magmatic origin of the giant Gr\xe4ngesberg iron oxide\u2013apatite (IOA) deposit, Central Sweden

The origin of Kiruna-type iron oxide–apatite ores is controversial, and debate presently centres on a ‘magmatic’ versus a ‘hydrothermal’ mode of formation. To complement recent investigations on the Grängesberg iron oxide–apatite ore deposit in the northwestern part of the Palaeoproterozoic Bergslagen ore province in central Sweden, we investigated the oxygen isotope composition of the host rocks of this large iron oxide–apatite ore body. As the metavolcanic and metagranitoid country rocks around the Grängesberg ore body either pre-date or are coeval with ore formation, they would be expected to record an extensive isotopic imprint if the ore body had formed by large-scale hydrothermal processes involving an externally sourced fluid. A direct magmatic formation process, in turn, would have produced localized alteration only, concentrated on the immediate vicinity of the ore body. Here, we test these two hypotheses by assessing the oxygen isotope variations in the host rocks around the main Grängesberg iron oxide–apatite ore body. We analysed oxygen isotopes in quartz from metavolcanic (n = 17) and metagranitoid host rocks (n = 14) from the vicinity of the ore body, and up to 2 km distance along and across the strike of the ore body. Remarkably, we find no significant variation in δ18O values with distance from the ore body, or any deviations in country rock δ18O from common magmatic and/or regional values. Only two samples show shifts to values more negative than the common magmatic range, indicating highly localized hydrothermal overprint only. As a large-scale, low-temperature hydrothermal origin of the ore body through voluminous fluid percolation would be expected to have left a distinct imprint on the oxygen isotope values of the country rocks, our results are more consistent with an ortho-magmatic origin for the Grängesberg iron oxide–apatite ore.

Abundance and importance of petrological type 1 chondritic material

AbstractWe review the mineralogy, petrology, and abundance of petrological type 1 extraterrestrial material. Such material has been completely altered by aqueous processing on its parent bodies. As well as the four meteorite groups that contain type 1 members (CI, CM, CR, and CY), we summarize data from the 2019 fall Flensburg and a recent reanalysis of the “meteorite” Bench Crater found on the Moon, along with fine‐grained micrometeorites, interplanetary dust particles, and xenoliths in meteorites. Type 1 materials exhibit a remarkably high diversity of alteration conditions (temperature, water‐to‐rock [W/R] ratios, and fluid composition) and starting mineralogy. Type 1 material comprises a significant component of the modern extraterrestrial flux to the Earth and was likely common throughout the solar system during the whole course of its history, pointing to both widespread accretion with ices and heating of parent bodies. Type 1 materials are composed predominantly of various phyllosilicates, carbonates, sulfides, and magnetite. Some type 1 materials appear to be part of a “CM clan” typified by serpentine‐rich phyllosilicate compositions and an oxygen isotope composition that falls in the 16O‐rich part of the CM field. Others span a wide range in δ18O (&gt;30‰) and fall on or above the terrestrial fractionation line (+ve Δ17O). Positive Δ17O values are unusual for carbonaceous meteorites but are relatively common in type 1 materials. The wide variation in oxygen isotopes, as well as in textures, mineralogy, and bulk chemistry, points to multiple parent bodies that may originate in the inner and/or outer solar system. Cometary materials, or transition objects such as Main Belt comets or type D asteroids, are likely the source of much of the type 1 materials on Earth but relating them to specific parents requires more study.

Coupled Effects of Moisture Transport Pathway and Convection on Stable Isotopes in Precipitation across the East Asian Monsoon Region: Implications for Paleoclimate Reconstruction

AbstractThis study investigated the variations in stable oxygen isotopes in daily precipitation (δ18Op) collected between 2010 and 2013 at four sites across the East Asian monsoon region to address the controversy whether local meteorological factors, moisture transport pathway or convection dominates the δ18Op changes. We found that the δ18Op time series exhibit opposite seasonal patterns between the southern and northern sites; however, relatively low δ18Op values occur at each site during summer. The opposite seasonal patterns are closely related to the proportional change in the contributions from oceanic (&gt; 52% in the south) and continental (&gt; 85% in the north) moisture sources. Moisture transport distances also influence the seasonal δ18Op fluctuations. In the south, the moisture transported over short distances from the middle of the western Pacific Ocean results in relatively high δ18Op values during the pre-monsoon season. In contrast, long-distance transport of moisture from the Indian and Equatorial Pacific Oceans during the monsoon season results in relatively low δ18Op values. In the north, relatively low δ18Op values during the monsoon season can be attributed to an increase in relatively distant moisture originated from the middle of the western Pacific Ocean. Convection only plays a role in affecting δ18Op values in the south during the monsoon season. Our study suggests that moisture transport pathway (moisture sources and moisture transport distances) is a major factor that governs seasonal variations in δ18Op across the East Asian monsoon region, which has implications for the interpretation of paleoclimate records from this region.

Crystallographic and crystallochemical controls on oxygen isotope analysis of hematite by SIMS

Previous work on oxygen isotopic compositions of hematite samples by secondary ion mass spectrometry (SIMS) has yielded large oxygen isotopic variability (>3 ‰) within individual samples. Deconvolving instrumental effects from geological variation is of vital importance in correctly interpreting in situ SIMS δ18O isotope compositions recorded in hematite. Here, we demonstrate that the excess scatter in δ18O values acquired with SIMS results from a combination of true sample variability and crystallographically-induced instrument mass fractionation. The natural and crystallographically-induced isotopic variability of hematite was investigated by a combination of SIMS, laser fluorination, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) elemental mapping, and electron back-scattered diffraction (EBSD). We used the Sensitive High Resolution Ion Microprobe – Stable Isotopes (SHRIMP-SI) on a museum-quality hematite specimen from the Quadrilátero Ferrífero, Minas Gerais, Brazil, and orientation-induced analytical fractionation was found to contribute up to 5 ‰ to the observed SIMS δ18O isotopic scatter. Laser ablation ICP-MS elemental mapping of crystallographically uniform single hematite crystals revealed distinct chemical zonation patterns that indicate several discrete stages of crystal growth. Crystal zoning additionally coincides with abrupt shifts in δ18O ranging ca. 11 ‰ for a single crystallographic orientation. These results highlight an intimate link between crystal growth mechanism and isotopic evolution of the mineralizing fluid, showing the need for high spatial resolution analysis before the isotopic composition of hematite can be used to infer conditions of mineral precipitation and solution compositions. The results also demonstrate that an understanding of both crystallographic orientation and crystallochemical variability are needed to obviate problems previously encountered in oxygen isotope analysis of hematite by ion microprobe.

Dating of non-oak species in the United Kingdom historical buildings archive using stable oxygen isotopes

Stable oxygen isotope dendrochronology is an effective precision-dating method for fast grown, invariant (complacent) tree-rings and for trees growing in moist, temperate climatic regions where growth may not be strongly controlled by climate. The method works because trees preserve a strong common isotopic signal, from summer precipitation, and therefore do not need to be physiologically stressed to record a dating signal. This study explores the working hypothesis that whilst tree species may differ in their eco-physiology, leaf morphology and wood anatomy they will record an isotopic signal in their growth rings that is sufficiently similar to enable their precise dating against isotopic reference chronologies developed using dated oak tree rings from the same region. Modern and historical samples from six species (sweet chestnut, English elm, ash, alder, European beech and black poplar) were analysed and their oxygen isotopic variability was compared against an oak master chronology previously developed for central southern England. Whilst differences in the relative strength of the agreement between the different species and the master chronology are apparent, the potential for interspecies dating is demonstrated convincingly. The ability to date non-oak species using stable oxygen isotopes opens-up new opportunities for science-based archaeology and will improve understanding of a largely-unexplored, but significant part of the European historical buildings archive.

Carbon and oxygen isotope variations in shell beds from the Upper Ordovician (mid-Cincinnatian: Maysvillian to early Richmondian) of Ontario: Evaluation of the Warm Saline Deep Ocean hypothesis, paleoceanographic changes, and Milankovitch orbital cycles in the transition to the Hirnantian glaciation

Carbon and oxygen isotopes of both well-preserved articulate brachiopod Paucicrura rogata and cement in mid-Cincinnatian samples (Maysvillian to early Richmondian) on the eastern North American passive margin shelf in SW Ontario show no simple relationships. The δ13C trends of the brachiopods, organic matter and cements are little altered and vary little up section. The brachiopod δ13Cbrach pattern is very close to the American mid-continent whole rock δ13CWRcarb pattern across the Fairview excursions. The δ18Obrach variations, if primary, indicate fluctuating but generally slightly cooling temperatures upwards, though the actual temperatures depend on inferred salinities of the seawater. The temperature/ salinity relationships variations are compatible with the warm deep saline water hypothesis. The paleoceanography shows a change from a warm open passive carbonate margin to a fluctuating warmer/cooler enclosed clastic marginal basin with freshwater input, heralding the cold conditions of the Hirnantian ice age. The Milankovitch cyclicity determined from δ13Ccarb patterns, is practically identical to that from determined from magnetic intensities on the contemporary Yangtse Shelf.

Spatial and temporal variations of hydrogen and oxygen isotopes and sources of water vapour indicated from satellite precipitation products along the transection of 38°north latitude in North China

The variations of hydrogen and oxygen isotopes in rainfall are critical for understanding the sources of rainfall and the influence of local evaporation. Satellite precipitation products with high time resolution (for instance 1 h) could be helpful for testifying the accuracy of water sources, as it can clearly illustrate the route of cloud movement. In this study, we analyzed the composition of hydrogen and oxygen isotopes in different rainfall events in three stations from 2015 to 2018 along the transection of 38° N latitude from Taihang Mountains to the coastal region in North China, Taihang Mountain Station (mountainous area), Luancheng Station (pre-mountain plain) and Nanpi Station (coastal low plain). By selecting typical rainfall events, water vapor sources and its influence rainfall on hydrogen and oxygen isotopes were analyzed with hourly available CMORPH satellite precipitation products. Results showed that the hydrogen and oxygen isotopes of precipitation were cha-racterized by enrichment in the rainy season and depletion in the dry season. The hydrogen and oxygen isotopes in the rainy season showed a tendency of depletion with the increases of precipitation. The slope and intercept of the fitted relationship of hydrogen and oxygen isotopes in the piedmont region of the mountains were the lowest, indicating that precipitation in the piedmont plain was significantly affected by secondary evaporation fractionation. The effect of evaporation resulted in the largest variations of isotope ratio in the dry year. In the mountainous station, due to the heavy rainfall, large isotopic variation was found in rich precipitation year. Based on the route analysis of sate-llite precipitation products, dominant water vapor in the region was inland and northwest-oriented water vapor, while water vapor in the rainy season was from southwest and from the Pacific Ocean. There was a significant difference in the hydrogen and oxygen isotopes of precipitation in the mountainous and plain stations in 2016, owing to water vapor sources and effects of rainfall for the mountainous and evaporation for plain. The results from HYSPLIT model showed that during the rainstorm on 19th July in 2016, water vapor at the mountainous station was mainly from the southwest, while that in the coastal plain was a mixture of southwest and southeast sources. Overall, our results showed that spatial and temporal variations of hydrogen and oxygen isotopes were controlled by both water sources and evaporation processes along the transection of 38° north latitude in North China.

Interannual oxygen isotope variability in Indian summer monsoon precipitation reflects changes in moisture sources

The primary influences on the spatio-temporal variability of oxygen isotope compositions in precipitation over the Indian summer monsoon domain are inadequately constrained by the limited observational record. Consequently, the climatic significance of isotopic signatures of precipitation preserved in proxy archives from the region remains unclear. Here we present simulations with an isotope-enabled climate model (IsoGSM2) with the moisture-tagging capability to investigate the role of relative contributions of moisture from oceanic and terrestrial sources to the interannual variability in oxygen isotope composition in summer monsoon rainfall. During weak monsoon years, the moisture contribution from the Arabian Sea dominates precipitation over the Indian subcontinent while the remote oceanic and terrestrial sources have a greater influence during strong monsoon years. We suggest that changes in monsoon circulation, moisture source, and precipitation intensity are interrelated and that speleothem oxygen isotope records from the region can potentially help reconstruct interannual to decadal monsoon rainfall variability.

Origin of minerals in åkermanite-rich patch texture and oxygen isotopic evolution of compact Type A Ca-Al-rich inclusions from the Northwest Africa 7865 CV chondrite

We report the in-situ oxygen isotopic distributions corresponding to the petrographic-mineralogical observation on a compact Type A (CTA) Ca-Al-rich inclusion (CAI), KU-N-02, from a reduced CV3 chondrite, Northwest Africa 7865. The CTA has an igneous texture and mainly consists of spinel, melilite, and Al-Ti-rich clinopyroxene (fassaite). Oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. The spinel grains are poikilitically enclosed in the melilite and fassaite and are uniformly 16O-rich (Δ17O = approximately − 23‰). The fassaite is texturally classified into two types: blocky fassaite and intergranular fassaite. The blocky fassaite crystals exhibit growth zoning as they change from Ti-rich to Ti-poor along the inferred directions of crystal growth from core to rim, while the oxygen isotopic compositions change from 16O-poor (Δ17O = approximately − 6‰) to 16O-rich (Δ17O = approximately − 23‰) with crystal growth. The intergranular fassaite crystals exist between the melilite crystals and exhibit variable Ti abundance and oxygen isotopic compositions. Additionally, their relationships between Ti contents and oxygen isotopic composition are similar to those of the blocky fassaite. The melilite grains are homogeneously 16O-poor (Δ17O = approximately − 2‰), irrespective of their åkermanite (Åk) content. Each melilite grain generally exhibits growth zoning with increasing Åk contents from core to rim, although the melilite contains Åk-rich patches within single crystal. Åk-rich patches often include two types of fassaite: small blebby crystals attached to spinel crystals and round crystals. The oxygen isotopic compositions of the Åk-rich patch and blebby fassaite are 16O-poor (Δ17O = approximately − 2‰), similar to that of the host melilite. On the other hand, the round fassaite exhibits significant variation in oxygen isotopic compositions ranging from Δ17O = −23‰ to − 4‰, which are different from those of the host melilite. These petrographic textures and oxygen isotopic variations indicate the presence of a solid precursor with variable oxygen isotopic compositions for the CTA. The spinel and round fassaite grains are relicts of the precursor that melted in the 16O-poor nebular gas, resulting in the crystallization of the host melilite from the 16O-poor melt. The Åk-rich patches and blebby fassaite crystallized from melts trapped by the growing host melilite crystals. The blocky and intergranular fassaite crystallized after the melilite did, and the oxygen isotopic composition of the melt changed to 16O-rich during the crystallization process, suggesting that the oxygen isotopic composition of the surrounding nebular gas could be varied. The inferred oxygen isotopic evolution for CTA is consistent with those inferred for Type B CAIs, suggesting that coarse-grained igneous CAIs formed in a similar nebular environment regardless of precursor chemistry.

Isotope Fractionation of Gaseous-, Supercritical-, and Dual-Phase Carbon Dioxide in Pressurized Cylinders Exposed to Variable Temperatures.

This work examines the stable isotope fractionation of carbon and oxygen in gaseous, supercritical, and liquid carbon dioxide systems at temperatures from −27.1 to +43.5 °C. For pressurized single-, supercritical-, and dual-phase carbon dioxide, both carbon and oxygen isotope fractionations can be measured and are significant when subjected to variations within this temperature range. The δ13C and δ18O values ranged from −41.55 to −41.38 ‰ (VPDB) and −27.74 to −24.9 ‰ (VPDB), respectively, for gas-phase carbon dioxide from 9.3 to 39 °C. A pressure variation of 27.58 barg to 34.48 barg was measured throughout this temperature range. In order to evaluate the effect of supercritical formation and liquefaction on the stable isotope values, cylinders were filled to varying pressures. When stored at cold temperatures, the δ13C value as measured in the headspace of the liquid phase varied from −41.23 to −41.13 ‰ (VPDB) and −41.50 to −41.44 ‰ (VPDB) in the supercritical phase. The δ18O value was between −25.51 and −25.36 ‰ (VPDB) in the liquid phase and between −24.79 and −24.77 ‰ (VPDB) in the supercritical phase. Temperatures in these experiments were selected to mimic outdoor conditions (winter and summer) that stable isotope laboratory practitioners may encounter when storing compressed carbon dioxide cylinders containing stable isotope working reference gases. The carbon and oxygen isotope composition of carbon dioxide gas within these pressurized cylinders return to their precooled isotope values within ∼24 h when warmed to laboratory temperatures (∼24 °C). A headspace analysis performed immediately after the carbon dioxide cylinder was removed from the cold environment yielded δ13C values that were relatively enriched, while δ18O values were relatively depleted. This is likely an effect of 12C and 18O being preferentially partitioned in the liquid phase within the cylinder. As the cylinder warmed, both liquid and gas equilibrated, and carbon and oxygen homogenized isotopically. As the cylinder was heated into the supercritical phase, a slight opposite isotope effect at higher pressure and temperatures was noted. That is, a slight 13C depletion and 18O enrichment were observed in the gas phase. However, these isotope variations were just slightly outside of the analytical error. Additionally, a separate gas-phase carbon dioxide cylinder was kept at a constant laboratory temperature as a control. This carbon dioxide showed no measurable carbon or oxygen isotope variation throughout the duration of the experimental work. The measured isotope fractionation was significantly higher comparing the phase transition from the gaseous to liquid phase versus the gaseous phase to supercritical phase. The proper handling of pressurized carbon dioxide cylinders used as reference gases for an isotope ratio mass spectrometer includes using carbon dioxide at pressures of less than ∼34.88 barg to ensure that the gas is present as a single phase, storing the gas in a temperature-controlled environment, and allowing the gaseous carbon dioxide to equilibrate to ambient conditions for 24–48 h if storage in a controlled ambient environment is not feasible.

Investigating early husbandry strategies in the southern Caucasus: intra-tooth sequential carbon and oxygen isotope analysis of Neolithic goats, sheep, and cattle from Göytepe and Hacı Elamxanlı Tepe

The beginning of agriculture marks major changes in food acquisition technology in human history. In the southern Caucasus, agricultural villages emerged around 6000 cal. BC, 2000 to 3000 years later than in the Fertile Crescent despite their geographical closeness to each other. This study aims to provide isotopic evidence indicative of animal herding strategies in the early farming communities in the southern Caucasus. To analyze intra-individual sequential carbon and oxygen isotope variations, we used tooth enamel of five goats, four sheep, and three cattle from the Neolithic settlements, Göytepe and Hacı Elamxanlı Tepe (Azerbaijan). The analyses also included reference samples of modern domestic goat and sheep that are known to have grazed in the vicinity of the sites. As a result, the sequential carbon and oxygen isotope variations of the modern goat and sheep samples showed large amplitude and a synchronous pattern during the whole enamel maturation period. The same pattern was observed in some of the Neolithic goat and sheep samples, suggesting they may have grazed in the vicinity of the lowland site throughout the year. Other Neolithic goat and cattle samples exhibited relatively small amplitudes and inverse cyclical variation patterns. While these patterns may have been caused by multiple factors, such as drinking water and food/fodder, vertical transhumance has also been proposed for the similar isotope patterns. Despite the difficulty in specifying exact causes for the observed isotopic patterns, their diversity within/among the species implies multiple pastoral strategies that may have had adaptive advantages in new agricultural frontiers in the southern Caucasus.

Timing of Sierra Nevadan stadial/interstadial variations from 15 to 56 ka

We summarize proxy evidence for stadial/interstadial variability recorded in sediments of three Great Basin lakes – Owens, Mono, and Pyramid. These lakes lie along the eastern margin of the Sierra Nevada Ice Sheet and record environmental variability associated with it. We have applied new paleomagnetic secular variation measurements (PSV) to more carefully date the lake environmental variability. We have also used PSV to correlate the Great Basin environmental variability to North Atlantic records of oxygen isotope variability. We see evidence for 25 cycles in stadial/interstadial variability of the Great Basin lakes. These cycles can be correlated among all three lakes and are largely synchronous. We can also date the individual stadial and interstadial intervals present in the three lakes. They have an average cycle duration of 1430 ± 530 years. But, the cycle durations in all three lakes vary coherently from less than 1000 years to more than 2000 years between 20 and 56 ka. The variability in cycle duration suggests internal variability in the global climate engine as the cause of the observed variability rather than some (presumably more periodic) external forcing. We also correlate interstadial D/O cycles 2–16 recorded in the Atlantic Ocean region with interstadial intervals in the Great Basin lakes. These intervals are largely synchronous between the two regions. We see evidence of 5 more Great Basin lake interstadials synchronous with un-numbered light δ18O intervals in the Atlantic oxygen isotope stratigraphy. This suggests some kind of linkage between the North Atlantic and North Pacific climate variability during the period 15–56 ka.