Isotope Dataset Research Articles

Lithological and glacial controls on sulfide weathering and the associated CO2 budgets in the Tibetan Plateau: New constraints from small catchments

The Tibetan Plateau, a region that hosts low to middle-latitude glaciers and a high density of metasedimentary rocks, is a hotspot of continental weathering and carbon cycling. However, quantitative estimations of sulfide oxidation and how it affects CO2 budgets from the plateau weathering are lacking. Here we use chemical and isotopic datasets from the studied small catchments in the Tibetan Plateau to estimate that 69.1% to 77.0% of stream SO42– originates from sulfide oxidation. Thus, more than 80% of the CO2 consumed by silicate weathering is counterbalanced by transient CO2 release from H2SO4-driven carbonate dissolution in the study area. In addition, the sulfide oxidation rate for glacial catchments is 5 times that of nonglacial catchments. The CO2 release rate from acid generated by sulfide oxidation in metasedimentary catchments is approximately 3 times that of granitic catchments. We propose that sulfide oxidation has greatly modified the CO2 budget of chemical weathering of the Tibetan Plateau. This study reveals new constraints on the CO2 budget in the Tibetan Plateau weathering, and will provide important insights into the carbon cycle during the plateau uplifting in Cenozoic.

AGE AND SOURCES OF DETRITAL MATERIAL FOR THE METASEDIMENTARY ROCKS OF THE NILAN TERRANE OF THE MONGOL-OKHOTSK OROGENIC BELT

The paper presents the first results of U-Th-Pb (LA-ICP-MS) isotopic dating of detrital zircons from the Paleozoic (?) metasedimentary rocks of the Nilan Terrane of the Mongol-Okhotsk orogenic belt to refine the age estimates and determine their probable correlation with earlier dated sediments of this belt. It has been stated that the metasedimentary rocks of the Olga, Salarin and Rovnen formations and of the Sivak formation of the Nilan terrane are characterized by the almost complete absence of the Early Precambrian zircons, slightly negative ε Nd(t) values, and Mesoproterozoic t Nd(DM) and t Nd(С) values. The isotope dataset obtained shows that most of the detrital sediments were carried from continental massifs of the Amur superterrane.

Strategies towards robust interpretations of in situ zircon oxygen isotopes

Oxygen isotopes are a versatile tool to address a wide range of questions in the Earth sciences. Applications include geothermometry, paleoclimatology, tracing of geochemical reservoirs, fluid-rock interaction, magmatic petrogenesis, and identification of extra-terrestrial materials. Zircon arguably provides one of the most robust records of primary magmatic O isotope ratio due to low diffusion rates in crystalline grains. The ability to correlate zircon O isotopes with temporal and petrogenetic information (e.g. U-Pb geochronology, Lu-Hf isotopes, and trace elements) makes this mineral a key archive for understanding Earth’s crustal evolution. Consequently, zircon O isotope geochemistry has found widespread usage to address fundamental questions across the earth and planetary sciences. The general apparent ease of O isotopic acquisition through the advancement of rapid in situ techniques (i.e. secondary ion mass spectrometry; SIMS) and associated dedicated national laboratories has led to the generation of large O isotopic data sets of variable quality, highlighting the importance of a coherent workflow for data collection, reduction, and presentation. This paper presents a set of approaches for measurement, assessment, and reporting of zircon O isotope data. The focus in this contribution is on in situ analysis via secondary ion mass spectrometry using large geometry instruments, but other commonly used techniques are briefly reviewed for context. This work aims to provide an analytical framework necessary for geologically meaningful interpretation of O isotope data. In addition, we describe inherent geological (e.g. radiation-induced disturbance of the zircon O isotopic system) and analytical (e.g. fractionation due to sample topography effects) challenges and outline means to identify and avoid such issues as a prerequisite to the generation of robust primary O isotopic signatures for geological interpretation.

Presenting the AfriArch Isotopic Database

AfriArch is an archaeological and paleoenvironmental data community designed to integrate datasets related to human-environmental interactions in Holocene Africa. Here we present a dataset of bioarchaeological stable isotope (C/N/O) and radiocarbon measurements from African archaeological sites spanning the Holocene. Modern measurements, when reported together with archaeological data in original publications, are also included. The dataset consists of 5568 entries and covers the entirety of Africa, though most isotopic research has been concentrated in southern Africa. The AfriArch isotopic dataset can be used in paleodietary, paleodemography, paleoclimatic, and paleoenvironmental studies. It can also be employed to highlight data gaps across space and time and set future research agendas.

Tracing the role of Arctic shelf processes in Si and N cycling and export through the Fram Strait: insights from combined silicon and nitrate isotopes

Abstract. Nutrient cycles in the Arctic Ocean are being altered by changing hydrography, increasing riverine inputs, glacial melt and sea-ice loss due to climate change. In this study, combined isotopic measurements of dissolved nitrate (δ15N-NO3 and δ18O-NO3) and silicic acid (δ30Si(OH)4) are used to understand the pathways that major nutrients follow through the Arctic Ocean. Atlantic waters were found to be isotopically lighter (δ30Si(OH)4=+ 1.74 ‰) than their polar counterpart (δ30Si(OH)4=+ 1.85 ‰) owing to partial biological utilisation of dissolved Si (DSi) within the Arctic Ocean. Coupled partial benthic denitrification and nitrification on Eurasian Arctic shelves lead to the enrichment of δ15N-NO3 and lighter δ18O-NO3 in the polar surface waters (δ15N-NO3= 5.44 ‰, δ18O-NO3= 1.22 ‰) relative to Atlantic waters (δ15N-NO3= 5.18 ‰, δ18O-NO3= 2.33 ‰). Using a pan-Arctic DSi isotope dataset, we find that the input of isotopically light δ30Si(OH)4 by Arctic rivers and the subsequent partial biological uptake and biogenic Si burial on Eurasian shelves are the key processes that generate the enriched isotopic signatures of DSi exported through Fram Strait. A similar analysis of δ15N-NO3 highlights the role of N-limitation due to denitrification losses on Arctic shelves in generating the excess dissolved silicon exported through Fram Strait. We estimate that around 40 % of DSi exported in polar surface waters through Fram Strait is of riverine origin. As the Arctic Ocean is broadly N-limited and riverine sources of DSi are increasing faster than nitrogen inputs, a larger silicic acid export through the Fram Strait is expected in the future. Arctic riverine inputs therefore have the potential to modify the North Atlantic DSi budget and are expected to become more important than variable Pacific and glacial DSi sources over the coming decades.

Zircon Hf-O isotopic constraints on the origin and temporal evolution of the Toba volcanic system, Indonesia

Combined U-Pb-Hf-O isotopic analyses of zircons are useful probes to investigate the origin and temporal evolution of long-lived magma reservoirs feeding large eruptions. This study presents a complete dataset of zircon Hf-O isotopes of the latest five Toba eruptions in Quaternary. The new isotopic data differ slightly within and between eruptive units, with the majority of zircons having ε Hf values between −8 to −5 and δ 18 O values between 6 and 6.8. These Hf-O isotopic compositions of zircons were considered to inherit from an enriched and slightly heterogenous magma source. Specifically, zircons of the Oldest Toba Tuff (OTT) have rather restricted and constant Hf-O isotopes, which may crystallize from a reservoir protractedly supplied from the same magma source. Zircons of the Middle Toba Tuff (MTT) have a large range of δ 18 O values varying from ~6 to 8, with low ε Hf values extending to −14, indicating shallow-level crustal contamination. The largely negative correlations between ε Hf and δ 18 O for zircons from the MTT is indicative of contamination of high-δ 18 O crustal materials, whereas those of the positive correlations for zircons from the Youngest Toba Tuff (YTT) implies contamination of hydrothermally altered low-δ 18 O crustal materials. It is important that the Hf-O isotopes of all the zircons do not record any single batch of magma that was derived from partial melting of depleted mantle peridotites, but are consistent with an enriched and heterogenous mantle source hybridized by the subducted sediments, followed by contamination of low-δ 18 O or high-δ 18 O materials during their ascent to the surface or storage in the shallow magma reservoirs. The increase of zircon δ 18 O values towards eruptions in both the MTT and YTT suggests that the two eruptions may be accompanied by roof collapse that added high-δ 18 O materials to the magma. Thus, assimilation of high-δ 18 O crustal materials could be a possible trigger for the MTT and YTT eruptions. • Toba volcanic rocks were derived from an isotopically enriched and heterogenous mantle source with significant crustal contamination. • Hf-O isotopes of MTT zircon crystals exhibit characteristics of shallow-level crustal contamination. • The YTT magma reservoir was contaminated by both high- and low-δ 18 O crustal materials. • Assimilation of high-δ 18 O materials by roof collapse could be a likely eruption trigger for the MTT and YTT eruptions.

UID: The uranium isotope database

As the parent element in the U-Pb and Pb-Pb radiochronometers, uranium (U) was one of the first heavy elements whose isotopic composition was carefully determined. Thought to be constant until the end of the 20th century, the ratio of the long-lived isotopes of U (238U/235U) has since been shown to be variable at the permil to sub-permil levels in natural materials. Today, the study of U isotopes has found applications in a variety of fields including geo/cosmochronology, oceanic paleoredox reconstruction, magmatic differentiation, environmental remediation, and forensic studies. With thousands of newly reported U isotopic data each year, a real need exists for a comprehensive U isotope database.Here, we introduce a global, updatable, U isotope database (UID), which not only contains the most expansive, internally consistent U isotopic dataset to date (14,591 entries from more than 320 papers), but also includes all other sample data from the original publications, as well as the relevant metadata and sample information to facilitate further analysis. The UID is freely accessible and will be updated regularly. All data are normalized to the widely-used CRM-145 standard, and all assumptions used to convert the published data are explicitly detailed in the paper and the database itself. New data can be easily formatted and submitted for incorporation into the database. Using the UID we provide new recommended δ238U values for certified U standards and geostandards and discuss important applications and future directions for U isotope studies.

Water stable isotopes reveal the hydrological response of Costa Rican glacial lakes to climate variability

Lakes are generally considered a key information source for understanding paleoclimate. Here, we use stable water isotopes (δ2H and δ18O) in a high-elevation tropical glacial lake to inform about modern climate variability and local hydrological conditions. We report a data set of water isotopes in precipitation and lake water collected between June 2015 and November 2020 in the Chirripó National Park, Costa Rica. Using a linear resistance model, the isotopic information coupled with lake water temperature and hydrometeorological data allowed the calculation of seasonal evaporation to inflow ratios (E/I) for Lake Ditkevi. Isotopic variations (δ18O and d-excess) reflect seasonal changes in the evaporative conditions, with E/I ratios ranging from 2.7 ± 1.3% to 10.8 ± 5.4%. Significant correlations between lake d-excess, lake water temperature, and sea surface temperature anomalies in El Niño 3.4 region revealed the sensitive hydrological response of this high elevation tropical glacial lake to the cyclic deviations in the ocean-atmosphere domain of warm/cold El Niño Southern Oscillation episodes. Our findings contribute to i) a better understanding of the climatic controls on high-elevation precipitation and surface water systems in the tropics and ii) inform paleoclimate reconstructions in Central America.

Was that my meal? Uncertainty from source sampling period in diet reconstruction based on stable isotopes in a syngnathid fish

Stable isotopes can be used to reconstruct diet in fishes, an approach that is particularly useful in threatened or endangered species where lethal sampling needs to be avoided To apply this method stable isotopes need to be measured both in the consumers and dietary sources As turnover rates may largely differ across tissues, the reconstruction should consider the uncertainty associated with sampling timing for both consumers and dietary sources. The present study investigated for the first time the application of a time lag for the estimation of the trophic position and the dietary regime in the greater pipefish Syngnathus acus (Family Syngnathidae). For that, two isotopic (δ13C and δ15N) data sets from dorsal fin-clipped tissues were used, including values in potential sources sampled (a) concomitantly with consumers (Unshifted approach) or (b) in the season sampled preceding consumer sampling (Shifted approach). The results attained indicate that the trophic position of the species was not affected (< 0.6% change) by shifting when analyzed for the annual dataset (global assessment). However, the trophic level estimated in the shifted treatment was ca. 6% higher than in the unshifted approach when the analysis was performed using a seasonal dataset (seasonal assessment including exclusively specimens collected in summer). Regarding the reconstruction of the dietary regime and in comparison to the unshifted approach, the results attained with shifted sampling revealed a higher preference for amphipods (43.7%), isopods (19.5%) and mysidaceans (12.1%), and a reduction in the reconstructed abundance for harpacticoid copepods (5.1%). These findings were similar to those attained for specimens and food web components collected in the same sampling period (seasonal dataset), both in females and males. This study demonstrates (1) the variability of estimates in the reconstruction of diet regimes depending on the data time shifting applied, and (2) the importance of considering adequate time lags in the assessment for syngnathid fishes.

Hydrometeorological Processes and Moisture Sources in the Northeastern Tibetan Plateau: Insights from a 7-Yr Study on Precipitation Isotopes

Abstract The northeastern Tibetan Plateau is located in a climatic junction, which is considered an ideal region to explore the interactions between the summer monsoons and the westerly circulation patterns. However, to date, the needed long-term precipitation-based isotopic dataset is too limited to predict the interactions and patterns. This paper presents an evaluation of hydrometeorological processes and climate dynamics in the northeastern Tibetan Plateau based on a 7-yr precipitation isotope dataset covering the summer monsoon periods from 2012 to 2018. Results illustrated remarkable seasonal isotopic variability, characterized by lower δ18O and δ2H values in June with an average of −10‰ and −66.7‰, respectively. Higher δ18O and δ2H values in July averaged −6.7‰ and −39.5‰, respectively. This clear isotopic variability is largely related to seasonal changes of moisture sources and hydrometeorological processes. These precipitation isotopic values were primarily determined by the amount of precipitation, relative humidity, and convective activity, but showed no correlation with air temperature. Backward trajectory model results showed that Xinjiang, northern China, the Arctic, central Asia, and the South China Sea (SCS) were the primary sources of precipitation for the study site with varying seasonal contributions. The maritime moisture source of the SCS primarily resulted in the lowest precipitation δ18O values during the prevailing summer monsoon, which is mainly as a result of the strong convective activity and rainout processes along the air trajectory. The higher average deuterium excess (d-excess) value of precipitation in September indicated continental sources from central Asia (e.g., 75.4%) as land vapor recycling increases d-excess concentration in the atmosphere. These findings provide further insights into the main factors of precipitation isotopic variability related to atmospheric processes along the trajectory and the relevant factors in the monsoon regions. Significance Statement Recently, scientists and policy makers have become aware that Tibetan hydroclimate variability provides evidence of changes in regional and global circulation patterns that may result in the intensification of climate-driven extremes. However, these studies largely depend on crucial paleoclimate records of past precipitation isotopes in monsoon regions, which contain great uncertainties because of the complex relationship between climatic variability and precipitation isotopes. This study first presented a 7-yr isotopic dataset to understand the hydrological processes and climate dynamics controlling the isotopic variability in the northeastern Tibetan Plateau. The findings reveal important factors on the isotopic variability associated with atmospheric processes and their key climatic variables, which can enhance our interpretation of the paleoclimate records in monsoon regions.

Dual clumped isotope thermometry of coral carbonate

The stable (δ18O and δ13C) and clumped (Δ47) isotope compositions of coral carbonate are valuable archives for paleoclimate reconstructions. However, the Δ47-temperature relationships of warm and cold-water corals deviate from that of inorganic carbonate precipitated at equilibrium. Dual clumped isotope thermometry of carbonates (i.e., simultaneous Δ47 and Δ48 measurements on a single carbonate) has the potential to achieve more accurate paleotemperature reconstruction, identifying and correcting for kinetically driven isotopic disequilibrium. Here we present the first extensive dual clumped isotope dataset of coral carbonate, spanning a broad range of cold and warm-water coral species. We confirm that corals are enriched in Δ47 and depleted in Δ48 relative to equilibrium, a pattern corresponding to the mixing of an equilibrium DIC pool with kinetically derived HCO3– produced by hydration and hydroxylation of CO2. Dual clumped isotope measurements of cold-water corals fall on the initial linear portion of model (IsoDIC) predicted departure from equilibrium. The dual clumped isotope composition of cold-water corals, corrected by the model-predicted Δ47/Δ48 offset slope (−0.78), yield accurate reconstruction of coral growth temperature with a precision of <3 °C at the 68% confidence level. In contrast, disequilibrium offsets in the Δ47 and Δ48 of warm-water corals correspond to precipitation from a more equilibrated DIC pool, which we attribute to the action of carbonic anhydrase in the calcifying fluid. It may be possible to correct warm-water coral growth temperatures, using an empirically derived correction (Δ47/ Δ48 offset slope of −0.4). Dual clumped isotope thermometry of coral carbonate opens new possibilities to reconstruct both sea surface temperatures and ocean dynamics of intermediate to deep water masses.

A strontium isoscape of inland southeastern Australia

Abstract. The values and distribution patterns of the strontium (Sr) isotope ratio 87Sr/86Sr in Earth surface materials are of use in the geological, environmental, and social sciences. Ultimately, the 87Sr/86Sr ratios of soils and everything that lives in and on them are inherited from the rocks that are the parent materials of the soil's components. In Australia, there are few large-scale surveys of 87Sr/86Sr available, and here we report on a new, low-density dataset using 112 catchment outlet (floodplain) sediment samples covering 529 000 km2 of inland southeastern Australia (South Australia, New South Wales, Victoria). The coarse (&lt;2 mm) fraction of bottom sediment samples (depth ∼ 0.6–0.8 m) from the National Geochemical Survey of Australia were milled and fully digested before Sr separation by chromatography and 87Sr/86Sr determination by multicollector-inductively coupled plasma mass spectrometry. The results show a wide range of 87Sr/86Sr values from a minimum of 0.7089 to a maximum of 0.7511 (range 0.0422). The median 87Sr/86Sr (± median absolute deviation) is 0.7199 (± 0.0071), and the mean (± standard deviation) is 0.7220 (± 0.0106). The spatial patterns of the Sr isoscape observed are described and attributed to various geological sources and processes. Of note are the elevated (radiogenic) values (≥∼ 0.7270; top quartile) contributed by (1) the Palaeozoic sedimentary country rock and (mostly felsic) igneous intrusions of the Lachlan geological region to the east of the study area; (2) the Palaeoproterozoic metamorphic rocks of the central Broken Hill region; both these sources contribute radiogenic material mainly by fluvial processes; and (3) the Proterozoic to Palaeozoic rocks of the Kanmantoo, Adelaide, Gawler, and Painter geological regions to the west of the area; these sources contribute radiogenic material mainly by aeolian processes. Regions of low 87Sr/86Sr (≤∼ 0.7130; bottom quartile) belong mainly to (1) a few central Murray Basin catchments; (2) some Darling Basin catchments in the northeast; and (3) a few Eromanga geological region-influenced catchments in the northwest of the study area; these sources contribute unradiogenic material mainly by fluvial processes. The new spatial Sr isotope dataset for the DCD (Darling–Curnamona–Delamerian) region is publicly available (de Caritat et al., 2022; https://dx.doi.org/10.26186/146397)​​​​​​​.

Multivariate statistical analysis of chemical and stable isotopic data as indicative of groundwater evolution with reduced exploitation

Groundwater resources in the North China Plain (NCP) are undergoing tremendous changes in response to the operation of groundwater exploitation reduction (GWER) project. To identify groundwater evolution in this complex context, hierarchical cluster analysis (HCA) and principal component analysis (PCA) were combined to interpret an integrated dataset of stable isotopes and chemical data from four sampling campaigns in a pilot area of groundwater control. We proposed a novel HCA approach integrating stable isotopes and chemical signals, which successfully partitioned the groundwater samples into the unconfined and the confined water samples. Stable isotopic evidence showed that the lateral inflow and the surface water may contribute more to groundwater recharge in this region than local modern precipitation. The unconfined water’s main hydrochemical types were Na type with mixed anions, and Na–Cl–SO4 type, while the confined water was mainly Na–Cl and Na–SO4 types. Geochemical processes mainly involved the dissolution/precipitation of halite, gypsum, Glauber's salt, feldspar, calcite and dolomite, as well as the cation exchange. PCA results showed that water–rock interaction (i.e., salinity-based and alkalinity-based processes) predominated the hydrochemical evolution, along with local nitrate contamination resulting from fertilizers and domestic sewage. The GWER project regulated the natural evolution of unconfined water chemistry, and significantly reduced the unconfined water’s salinity (mainly Na+, Mg2+, SO42−). This may be attributed to upward leakage from low-salinity confined water at some parts of the aquifer. Additionally, insignificant changes in the confined water’s salinity reflected that the impact of GWER on the confined aquifer was negligible. This study facilitates the groundwater classification effectively in the areas lack of geological data, and enhances the knowledge of groundwater chemical evolution in such a region where groundwater restoration is in progress, with important implications for groundwater sustainable management in similar basins worldwide.

Climate changes as recorded in stable carbon isotopic compositions of the Late Jurassic marine sedimentary succession in the Qiangtang Basin, Northern Tibet

The Jurassic oceanographic and climatic evolution is considered to be related to the breakup of Pangaea. As a crucial component of the carbon cycle, atmospheric CO2 concentration (pCO2) has been postulated as a main driver for climate change during the Jurassic, and concomitant changes in paleo-oceanographic conditions occurred as a result. In this study, we present a high-resolution organic matter (kerogen) carbon isotope dataset (δ13Ckerogen) from Upper Jurassic marine sedimentary rocks in the Qiangtang Basin, Tibet. The δ13Ckerogen result contains a genuine record concerning the response of the eastern Tethys to exogenic carbon cycle perturbations in both marine and atmospheric reservoirs and is also consistent with the high-resolution bulk carbonate and organic matter carbon-isotope records from the Atlantic and western Tethys. The relative fractionation of carbon isotopes in organic matter vs. carbonate species, defined as Δ13C (δ13Ccarb-δ13Ckerogen), and the secular trend of atmospheric pCO2 over the Late Jurassic that is calculated from the high-resolution δ13Ckerogen values indicate a cold Callovian-Oxfordian transition, a long-term increasing but fluctuating Kimmeridgian and a prominent early Tithonian cooling event (ETCE). The pronounced temperature plateau during the late Kimmeridgian-early Tithonian was contemporaneous with the occurrence of major magmatic events during the Late Jurassic, while the ETCE has been possibly attributed to major changes in oceanic circulation patterns. Additionally, reconstructed atmospheric pCO2 values show very small differences to values using phytane- and stomatal density-based pCO2 calculations, providing an alternative estimate for accurate identification of the paleoclimatic framework of this enigmatic interval in the Mesozoic.

Using dual water isotopes to quantify the mixing of water masses in the Pearl River Estuary and the adjacent northern South China Sea

The mixing of different water masses is important for local physical and biogeochemical processes as well as for ecosystems in the ocean. In this study, a new dataset of stable water isotopes (δD and δ18O) combined with temperature–salinity profiles was used to quantitatively understand the mixing of water masses in the Pearl River Estuary (PRE) and the adjacent northern South China Sea (SCS). Based on hydrographic characteristics and the isotope–salinity relationships in the water column, three water masses, namely, low isotopic values (&amp;lt;1.5‰ for δD and &amp;lt;0‰ for δ18O) with a salinity of &amp;lt;33.20 for PRE water (PREW), high isotopic values (&amp;gt;2.0‰ for δD and &amp;gt;0.6‰ for δ18O) with a salinity of &amp;gt;34.60 for SCS Kuroshio Branch (SCSKB), and higher isotopic values (&amp;gt;3.0‰ for δD and &amp;lt;0.4‰ for δ18O) with a salinity of &amp;gt;33.30 for SCS water (SCSW), were identified in the PRE and the adjacent SCS. The mixing of the three water masses in the PRE and the adjacent SCS was mainly from SCSW (71%), followed by the SCSKB (23%), and the proportion of PREW only accounted for 6%. However, different water layers and regions are affected differently by these three water masses. The surface water is mainly influenced by the PREW, whereas the subsurface water is mainly influenced by the intrusion of SCSKB (100–300 m). The mixing process of water masses in the west side of the study area (&amp;lt;115°E) is mainly contributed by the SCSW (86%), whereas the contributions of PREW and SCSKB are only 4% and 10%, respectively. By contrast, the mixing of water masses in the east side (&amp;gt;115°E) is mainly influenced by the Kuroshio intrusion (50%). This study reveals that dual water isotopes are exquisitely sensitive to determine the complex hydrological process in the PRE and the adjacent SCS, and water masses on marine environment should deserve more attention.

Evaluation of shallow-water corals and associated carbonate sediments as seawater Ba isotope archives in the South China Sea

Barium isotopes (δ138Ba) obtained in carbonates have a great potential for reconstructing past changes in marine productivity and associated biogeochemical cycling. Although coral skeletons and inorganic carbonates have been used as archives for seawater Ba isotopes, few studies have investigated other confounding factors that influence Ba isotope fractionation (e.g., vital effects and carbonate mineralogy), hindering their use as paleo-proxies. In this paper, we report Ba isotope data for multi-species corals, including paired sets of living and fossil coral skeletons in the inner shelf (Paipu Reef, Hainan Island) and the open-sea (Jiuzhang Reef corals) in the South China Sea (SCS). We also present Ba isotope datasets of bulk carbonate sediments from two shallow-water drill cores (A and B) in the Jiuzhang Reefs, SCS. The δ138Ba data for the Paipu Reef corals have a relatively narrow range of values (0.12‰ to 0.21‰, mean 0.17 ± 0.06‰; 2 SD, n = 8) regardless of living and fossil coral skeletons. The corals of Jiuzhang Reef show a relatively consistent δ138Ba value (0.30 ± 0.04‰; 2 SD, n = 4). The coral skeletal δ138Ba values show no significant differences across multiple species within the individual colony, which suggests that vital effects do not affect coral δ138Ba records. These findings, together with the fact that a relatively constant δ138Ba offset exists between coral skeletons and seawater, indicate that coral skeletons may be reliable archives for past seawater δ138Ba. All bulk carbonate sediment samples yield constant δ138Ba values of 0.38 ± 0.04‰ (2 SD, n = 30) with a fairly consistent deviation (Δ138Babulk_carb-sw = −0.21 ± 0.04‰) from the reported typical surface seawater of SCS. In addition, mass balance calculation suggests that Ba isotope fractionation between inorganic High-Mg calcite (HMC) and seawater is derived to be Δ138BaHMC-sw = −0.13 ± 0.12‰, exhibiting a difference less than Δ138Baaragonite-sw = −0.28 ± 0.04‰ in aragonite precipitation. Our findings suggest that shallow-water carbonates are reliable archives of past seawater δ138Ba when considering Ba isotope deviations during marine carbonate deposition.

Zinc, sulfur and cadmium isotopes and Zn/Cd ratios as indicators of the origin of the supergiant Broken Hill Pb–Zn–Ag deposit and other Broken Hill-type deposits, New South Wales, Australia

AbstractVarious genetic models have been proposed for the supergiant Proterozoic Broken Hill Pb–Zn–Ag deposit largely based on geological and geochronological evidence. Here we present Zn, Cd and S isotope compositions as well as Zn/Cd ratios of sphalerite from Broken Hill and minor Broken Hill-type deposits (Australia) to help constrain these models but focus on syngenetic and magmatic–hydrothermal processes, since epigenetic models can be rejected because the orebodies were deformed and metamorphosed by the Olarian Orogeny. Values of δ34SVCDT, δ66ZnAA-ETHand δ114CdNIST SRM 3108for sphalerite from Broken Hill range from +0.27 to +4.73 ‰, −1.15 to +0.46 ‰ and −0.48 to +0.01 ‰, respectively, while those for the smaller Broken Hill-type deposits range from −5.11 to +1.28 ‰, −0.97 to +0.10 ‰ and −1.02 to +2.59 ‰, respectively. By combining published S isotope data of sulfides from the Broken Hill district with those obtained here, the sources of sulfur via thermochemical sulfate reduction, bacterial sulfate reduction and a magmatic origin cannot be distinguished. However, when the S isotope compositions are considered along with the broad range of Cd and Zn isotope data for sphalerite, which are among the lightest and heaviest yet reported for a sulfide deposit, the isotopic datasets are consistent with low-temperature biogenic processes associated with syngenetic deposition of sulfides. Cadmium isotope compositions when coupled with Zn/Cd ratios of sphalerite have previously been used to classify Pb–Zn deposits, including low-temperature, high-temperature and exhalative ores. However, the Zn/Cd ratios of sphalerite from Broken Hill cannot be used for such classification purposes.

Formation of juvenile continental crust in northern Nubian Shield: New evidence from granitic zircon U-Pb-Hf-O isotopes

The Neoproterozoic Arabian-Nubian Shield (ANS) consists of continental crust formed prior to and during the collision between East and West Gondwana. The Eastern Desert of Egypt (i.e., northern Nubian Shield) constitutes the north-western part of the ANS. Neoproterozoic magmatism in the Eastern Desert region occurred between ∼ 800 Ma and ∼ 550 Ma. Although there is a broad consensus that ∼ 800–650 Ma pre-collisional igneous rocks comprise the main magmatic stage contributing to Eastern Desert crustal evolution, whether this crust is purely of a juvenile composition, or was generated by recycling/reworking of much older continental crust, remains debated. Here, we present new whole-rock geochemical and Sr-Nd isotopic data and an integrated zircon U-Pb-Hf-O-trace element dataset for two granitoids (Um Khariga and Genina Gharbia) from the Eastern Desert. Samples from the Um Khariga granitoids yield zircon U-Pb ages of 746 ± 4 and 753 ± 4 Ma that overlap within error, and the Genina Gharbia granitoids have an age of ∼ 690 Ma, indicating that both granitoids belong to different phases of pre-collisional magmatism. Zircon hafnium isotopic data of both granitoids yield weighted mean εHf(t) values ranging from + 8.01 ± 0.23 to + 10.52 ± 0.13, indicating that both granitoid suites were derived by melting of a juvenile source. SIMS oxygen isotope data for zircon show that the magmatic zircon has mantle-like δ18O values with weighted means ranging from 4.73 ± 0.02 to 5.04 ± 0.08 ‰. Based on previously published zircon U-Pb-Hf-O-trace element data for granitoids and volcanic rocks of the Eastern Desert, plus our new isotopic datasets obtained from the Um Khariga and Genina Gharbia granitoids, we show that the ∼ 800–650 Ma magmatism is characterized by high zircon εHf(t) (+8 to + 15), and mantle-like zircon δ18O values (∼+5‰), implying that the continental crust of the Eastern Desert was either extracted directly from a depleted mantle and/or reworked from accreted juvenile oceanic crust or oceanic arc with no evidence for the input of old continental material. The overall zircon εHf(t) and δ18O evolution trends for the northern Nubian Shield show that juvenile mantle input dominated the early phases (ca. 800–670 Ma) of crustal growth and evolution in this part of the ANS, coinciding with the break-up stage of the supercontinent Rodinia. The involvement of continental crustal recycling only started to play a significant role since the ca. 670 Ma regional collisional event during the early stage of Gondwana assembly.

Quantification of the Seasonal Intrusion of Water Masses and Their Impact on Nutrients in the Beibu Gulf Using Dual Water Isotopes

AbstractA new data set of seasonal stable water isotopes (δD and δ18O) and temperature‐salinity profiles was applied to improve our understanding of water mass distributions and their impact on the environment of the Beibu Gulf (BG). Our study revealed that the coastal current (CC), West‐Guangdong coastal current (WGCC), and South China Sea water (SCSW) were the three dominant water masses in the BG, and their influence was exhibited in seasonal variations. The CC was the dominant contributor to the BG water during summer (43%) and fall (45%), while it changed to the intrusion of SCSW with higher salinity in winter (57%). The contribution of WGCC to the BG was relatively stable during the three seasons (24%–31%). In addition, the nutrients in the BG were greatly affected by different water mixing occurring in the gulf. The nutrients mainly originated from the CC in summer (52%–68%) and fall (32%–69%), while the dominant source shifted to the WGCC in winter (36%–69%). Moreover, the contribution of SCSW to the nutrients loading (15%–49%) in the BG was relatively high due to its high contribution (57%) to the BG water during winter. These indicated that the BG has a stable input of external nutrients from different water masses to sustain primary production in the BG. Our study uses dual water isotopes to quantify the seasonal intrusion of water masses and their impact on nutrients, providing a new method to study the impact of the distribution of water masses on nutrients in the gulf.

Towards the Third Millennium Changes in Siberian Triple Tree-Ring Stable Isotopes

Significant air temperature and precipitation changes have occurred since the 2000s in vulnerable Siberian subarctic regions and urged updates of available chronologies towards the third millennium. It is important to better understand recent climatic changes compared to the past decades, centuries and even millennia. In this study, we present the first annually resolved triple tree-ring isotope dataset (δ13C, δ18O and δ2H) for the eastern part of the Taimyr Peninsula (TAY) and northeastern Yakutia (YAK) from 1900 to 2021. We found that the novel and largely unexplored δ2H of larch tree-ring cellulose was linked significantly with δ18O for the YAK site, which was affected by averaged April–June air temperatures and evaporation. Simulated by the Land Surface Processes and Exchanges (LPX-Bern 1.0) model, the water fraction per year for soil depths at 0–20 and 20–30 cm was significantly linked with the new eco-hydrological tree-ring δ2H data. Our results suggest increasing evapotranspiration and response of trees’ water relation to rising thaw water uptake from lower (20–30 cm) soil depth. A positive effect of July air temperature on tree-ring δ18O and a negative impact of July precipitation were found, indicating dry conditions. The δ13C in larch tree-ring cellulose for both sites showed negative correlations with July precipitation and relative humidity, confirming dry environmental conditions towards the third millennium.