Isotopic Results Research Articles

Preparation of La2Zr2O7 composite oxides with fluorite/pyrochlore phases by excluding element influences for catalyzing oxidative coupling of methane.

To elucidate the effect of the A2B2O7 phase on the oxidative coupling of methane (OCM) while excluding elemental influences, La2Zr2O7 compounds with a disordered defect fluorite (La2Zr2O7-F) structure and an ordered pyrochlore phase (La2Zr2O7-P) have been synthesized. Irrespective of their element composition, the catalytic performance of La2Zr2O7-F exceeds that of La2Zr2O7-P. Furthermore, the La2Zr2O7-F surface has more oxygen vacancies/defects than the La2Zr2O7 surface because La2Zr2O7-F exhibits a higher lattice disorder degree and lower B-O bond strength, which leads to the formation of more reactive oxygen anions (O2- and O22-) and basic sites for OCM. Isotopic exchange results have testified that surface-active oxygen sites are generated due to the gaseous O2 adsorption/activation occurring on the surface vacancies via both simple and multiple hetero-exchange mechanisms. In conclusion, crystal structure is the primary factor that governs the catalytic performance of A2B2O7 compounds, with the disordered defect fluorite phase being the most optimal structure for OCM.

안정동위원소 분석을 통한 신석기시대 생업에 관한 연구의 성과와 방향

Although the question of the subsistence strategies in the Neolithic period is a central topic in Korean archaeology, the changes in subsistence activities have been investigated on the basis of preserved fauna and floral remains. Most previous studies on subsistence patterns have focused on the quantitative analysis of floral and fauna remains preserved in the shell middens. In contrast to traditional methods such as quantitative analysis of floral and fauna remains, stable isotope analysis provides a direct measurement of past human diets. This method provides information about whether individuals derived the protein in their diet from plant or animal sources.
 Until now, stable isotopic results of humans from Neolithic period (Ando, Janghang, Daepo, Tongsamdong humans) revealed that the Neolithic people were mainly dependent on marine food resources as hunter-gatherers. Based on the stable isotope data, we can propose that marine resource exploitation was the main subsistence strategy in the Neolithic period. However, there is also a regional difference in stable isotope values between west (Konamri human) and east-south coast. This indicates that there might be a possibility to have regional difference in subsistence strategies during Neolithic period.

Assessment of groundwater recharge sources and its dynamics using environmental isotope and hydrochemical approaches in coastal aquifers of Peninsular Malaysia

The aims of this study are to investigate the interconnection and the dynamics between groundwater and surface water in the coastal area in the eastern part of Peninsular Malaysia using isotope technique integrated with the hydrochemical and hydrogeological approach. Using stable isotopic composition (d2H and d18O), it was shown that there is no relationship between the mid–deep and deep groundwater indicating that they came from different aquifers. Based on the two–component mass balance for oxygen, the source of groundwater salinity was determined. The results showed that 12% of the groundwater is recharged by the seawater while 88% is from both rainwater and river water. This reveals that one of the deep groundwater (UMPB) was affected by seawater intrusion. However, the deep groundwater in the southern part of the study area was not influenced by saline water because of the geological conditions. As a result of the seawater intrusion, UMPB is showing the characteristics of shallow groundwater due to mixing with modern saline water which was also supported by the natural radioactive isotope (3H and 14C) and hydrochemical results.

Petrogenesis and tectonic setting of TTG rocks from the Katoro area, Sukumaland Greenstone Belt, NW Tanzania: Evidence from zircon U-Pb geochronology, Lu-Hf isotopes, whole-rock geochemistry, and Sr-Nd isotopes

The northern part of the Tanzania Craton is mainly comprised of several low-grade metamorphic granite-greenstone belts that are exposed on the east and south shores of Lake Victoria. Due to their gold-endowment, these greenstone belts have been the main focus of research and were interpreted to form in various tectonic settings involving back-arc basin, island arc or continental arc, and oceanic plateau. However, the TTG gneiss, as the dominant component of Archean crust, has received far less attention from the scrutiny of modern analytical methods than its counterpart, the mafic volcanics of the greenstone belts. Here, we present a comprehensive geochemical dataset including zircon U-Pb age, zircon Lu-Hf isotope results, as well as bulk-rock geochemical compositions and Sm-Nd isotopic analyses for TTG suites from the Katoro area in northwestern part of Tanzania. Zircon U-Pb dating for three TTG samples yielded 207Pb/206Pb ages of 2688 ± 19 Ma, 2717 ± 19 Ma and 2695 ± 15 Ma, respectively, and the results fall within the peak crustal growth period in northern part of the Tanzania Craton. The Katoro TTGs have relatively high contents of SiO2 (70.77–74.69 %) and Na2O (4.74–5.16 %), high ratios of Sr/Y (59.49–167.25) and (La/Yb)N (17.27–50.72), but low MgO (0.24–0.70 %) and K2O (1.71–3.26 %) contents, low Nb/Ta ratios (8.50–16.60), and most of them belong to the trondhjemitic series rocks. They are characterized by strong enrichment of LILEs and LREEs with slightly positive Eu anomalies (Eu/Eu*=1.05–1.38), but depleted in Nb-Ta and Ti, as well as heavy REEs and Y. They have positive εHf(t) values (average εHf(t) = +1.90 ± 0.50 or + 2.07 ± 0.33) and εNd(t) values (+1.19 to + 2.40) but lower than the contemporaneous depleted mantle, which is inconsistent with a subducting slab signature, and it is proposed that the Katoro TTGs most likely originated from partial melting of rutile-free, garnet- and amphibole-bearing lower mafic crust of an oceanic plateau. The results presented here suggest that the tectonic evolution in this part of Tanzania Craton needs to invoke a scenario in which crustal growth caused by subduction-related modification of an oceanic plateau.

Experimental constraints on siderite clumped isotope thermometry

We present results from chemostatic siderite precipitation experiments conducted using a modified constant composition method at temperatures between 15 and 75 °C and compare these results with previous temperature relationships to obtain a composite low temperature relationship for siderite clumped isotope ratios (Δ47) from 8.5 to 75 °C:Δ47=0.0364±0.004∗106T2+0.1672±0.046±95%CL,R2=0.708The slope of this line is statistically indistinguishable from those reported for aragonite, calcite, and dolomite clumped isotopes, but differs in its intercept. To test whether this difference results from mineralogical differences in phosphoric acid fractionation factors (AFF) between siderite and Ca-Mg carbonates, we heated siderite to 625 °C at 1 GPa, which yielded a statistically indistinguishable Δ47 value from that predicted by published clumped isotope calibrations populated by Ca-and Mg-carbonate data at higher temperatures. Thus, the apparent difference between siderite clumped isotope behavior and that of other carbonate minerals may not be well explained by differences in AFF. Despite differences in precipitation methods, our results are entirely consistent with published inorganic and microbially-mediated experimental siderite clumped isotope data, suggesting that siderite Δ47-temperature dependence differs from Ca-Mg carbonates for reasons unrelated to precipitation methods. Our isotopic results are also consistent with published isotopic measurements on natural siderites precipitated at known environmental temperatures. Our analysis leads us to conclude that supersaturation-related kinetic effects likely play an important role in clumped isotope fractionation in natural and experimentally precipitated siderite.

The Origin of Carbonate Components in Carbonate Hosted Pb-Zn Deposit in the Sichuan-Yunnan-Guizhou Pb-Zn Metallogenic Province and Southwest China: Take Lekai Pb-Zn Deposit as an Example

The Lekai lead–zinc (Pb-Zn) deposit is located in the northwest of the Sichuan–Yunnan–Guizhou (SYG) Pb-Zn metallogenic province, southwest China. Even now, the source of the metallogenic fluid of Pb-Zn deposits in the SYG Pb-Zn metallogenic province has not been recognized. Based on traditional lithography, rare earth elements (REEs), and carbon–oxygen (C–O) isotopes, this work uses the magnesium (Mg) isotopes of hydrothermal carbonate to discuss the fluid source of the Lekai Pb-Zn deposit and discusses the fractionation mechaism of Mg isotopes during Pb-Zn mineralization. The REE distribution patterns of hydrothermal calcite/dolomite are similar to that of Devonian sedimentary carbonate rocks, which are all present steep right-dip type, indicating that sedimentary carbonate rocks may be serve as the main source units of ore-forming fluids. The C–O isotopic results of hydrothermal dolomite/calcite and the δ13CPDB–δ18 OSMOW diagram show that dolomite formation is closely related to the dissolution of marine carbonate rocks, and calcite may be affected to some extent by basement fluid. The Mg isotopic composition of dolomite/calcite ranges from −3.853‰ to −1.358‰, which is obviously lighter than that of chondrites, mantle, or seawater and close to that of sedimentary carbonate rock. It shows that the source of the Mg element in metallogenic fluid of Lekai Pb-Zn deposit may be sedimentary carbonate rock rather than mantle, chondrites, or seawater. In addition, the mineral phase controls the Mg isotope fractionation of dolomite/calcite in the Lekai Pb-Zn deposit. Based on the geological, mineralogical, and hydrothermal calcite/dolomite REE, C–O isotope, and Mg isotope values, this work holds that the mineralization of the Lekai Pb-Zn deposit is mainly caused by basin fluids, influenced by the basement fluids; the participation of basement fluids affects the scale and grade of the deposit.

Palaeomagnetic investigations across Hinlopenstretet border zone: from Caledonian metamorphosed rocks of Ny Friesland to foreland facies of Nordaustlandet (NE Svalbard)

New demagnetization results of 286 palaeomagnetic specimens from 15 sites in Neoproterozoic–Lower Paleozoic sequences of Ny Friesland–Nordaustlandet (the Caledonian Eastern Svalbard Terrane) are presented. New in situ 40 Ar/ 39 Ar ultraviolet mass spectrometry (Uv-MS) age determinations on amphibolites and mylonites from the Ny Friesland cluster in the 340–460 Ma interval correspond broadly to the Caledonian thermal event. Older ages are observed but are more scattered and probably reflect partial resetting or argon gain of Proterozoic micas. Palaeomagnetic, petrological and structural data confirm a west to east decrease in the degree of the Caledonian metamorphism and remagnetization across Hinlopenstretet, which is interpreted here to coincide with the limit of Caledonian east-directed overthrusting. No pre-Caledonian palaeomagnetic record was identified in investigated amphibolites and metacarbonates of Ny Friesland. Pre-folding pre-Caledonian, potentially Neoproterozoic (primary?) magnetization was recognized only in non-metamorphosed Murchisonfjorden (Nordaustlandet) carbonates. However, selective palaeomagnetic palaeopoles from Murchisonfjorden also fall into Caledonian sensu lato and Mesozoic sectors of the Laurussia reference path. This also indicates that regions east of Hinlopenstretet and east of the Caledonian front could be partially subjected to Caledonian remagnetization. Mesozoic palaeomagnetic overprints are potentially related to the injection of Mesozoic dolerites in eastern Svalbard. Here, we discuss two concepts of post-Caledonian rotations that could affect the palaeomagnetic record of the Eastern Svalbard Terrane: rotations around vertical axes related to strike-slip faults and rotations around horizontal axes related to normal listric faults that originated during extension in the Devonian basin and the opening of the Atlantic and Arctic oceans. Supplementary material: (1) A detailed description of applied rock-magnetic and palaeomagnetic procedures, (2) detailed description of investigated geochronological samples, (3) in situ Uv-MS 40 Ar/ 39 Ar isotopic age determination results, (4) mineralogy of ferromagnetic phases, (5) hysteresis parameters, (6) distribution of the NRM components and great circles in palaeomagnetic sites and (7) anisotropy of magnetic susceptibility are available at https://doi.org/10.6084/m9.figshare.c.6132018

Environmental and hydrologic controls on sediment and organic carbon export from a subalpine catchment: insights from a time series

Abstract. Studies engaging in tracking headwater carbon signatures downstream remain sparse, despite their importance for constraining transfer and transformation pathways of organic carbon (OC) and developing regional-scale perspectives on mechanisms influencing the balance between remineralization and carbon export. Based on a 40-month time series, we investigate the dependence of hydrology and seasonality on the discharge of sediment and OC in a small (350 km2) Swiss subalpine watershed (Sihl River basin). We analyze concentrations and isotopic compositions (δ13C, F14C) of particulate OC and use dual-isotope mixing and machine learning frameworks to characterize and estimate source contributions, transport pathways, and export fluxes. The majority of transferred OC is sourced from plant biomass and soil material. The relative amount of bedrock-derived (petrogenic) OC, abundant in headwater streams, progressively decreases downstream in response to a lack of source material and efficient overprinting with biospheric OC, illustrating rapid organic matter alteration over short distances. Large variations in OC isotopic compositions observed during baseflow conditions converge and form a homogenous mixture enriched in OC and characterized by higher POC-F14C values following precipitation-driven events. Particulate OC isotopic data and model results suggest that storms facilitate surface runoff and the inundation of riparian zones, resulting in the entrainment of loose plant-derived debris and surficial soil material. Although particle transport in the Sihl River basin is mainly driven by hydrology, subtle changes in bedrock erosivity, slope angle, and floodplain extent likely have profound effects on the POC composition, age, and export yields.

Biomarkers and Carbon Isotope of Monomer Hydrocarbon in Application for Oil-Source Correlation and Migration in the Moxizhuang-Yongjin Block, Junggar Basin, NW China.

Different opinions on the oil-source correlation and migration of the Moxizhuang-Yongjin block in the Junggar Basin, NW China, have seriously affected oil and gas exploration in this area. This research is based on the results of biomarker analysis and carbon isotope of monomer hydrocarbon on crude oil and source rock samples from different blocks. Two oil families (A1, A2, and B) are classified by cluster analysis on nine typical biomarker ratios. Typically, sub-family A1 oils are distributed in the Zhuang 102 well block of the Moxizhuang block, and their gammacerane index is the highest. The abundance of C24 tetracyclic terpanes is the lowest, the C27 regular steranes are dominant, and the organic matter is mainly input by lower aquatic organisms. Sub-family A2 oils are distributed in the Zheng 1-1 well block of the Moxizhuang block. The gammacerane index of oils is lower than the former, and the abundance of C24 tetracyclic terpanes is higher. In the dual input of lower aquatic organisms and terrestrial higher plants, the input of terrestrial higher plants accounted for a larger proportion. Family B oils are distributed in the Yong 2 well block of the Yongjin block, and their gammacerane index is the lowest. They have a high abundance of C24 tetracyclic terpanes, and C29 regular steranes are dominant, reflecting the characteristics of terrigenous organic matter contribution. Based on the biomarker compound composition, at least two oil charges are indicated: Sub-family A1 oils are likely sourced from the Wuerhe formation, sub-family A2 oils may be a mixture of Wuerhe formation and Badaowan formation, and family B oils are likely sourced from the Badaowan formation. The oil families with typical genetic affinities may indicate two major petroleum systems or multiple oil systems existing in the study area. In addition, the characteristics of hydrocarbon accumulation and migration are also discussed, the oil and gas in the West Sag of Well Pen 1 and Changji Sag are filled from deep to shallow in the vertical direction and migrated from south to north in the horizontal direction, at the same time, with the help of sand bodies and faults, and they migrated to the north and northeast. This work provides a scientific basis for oil and gas exploration in the hinterland of the Junggar Basin.

Complex Late Triassic-Middle Jurassic Subduction-Related Magmatic History from Detritus of Nominal Middle Jurassic Brooks Range Ophiolite, Northern Alaska

Abstract In northern Alaska, the Early Cretaceous sedimentary Yukon-Koyukuk basin documents the progressive unroofing of the adjacent Brooks Range orogen. Igneous clasts in the lower conglomerate are believed to originate from ophiolitic rocks of the two uppermost allochthons in the Brooks Range, the Brooks Range ophiolite and the Angayucham terrane. The emplacement of these oceanic terranes onto the continental margin of the Arctic Alaska terrane documents the initiation of Brookian orogenesis. While most agree that the Angayucham terrane represents a widespread distribution of Late Devonian oceanic crust and Triassic-Early Jurassic oceanic plateau(s)/island(s), the age and origin of the Brooks Range ophiolite remains controversial. We present new age, whole-rock chemistry, and isotopic data from igneous clasts as well as a few Angayucham terrane outcrop samples from the NE Yukon-Koyukuk basin. Our results show that the igneous clasts are mostly subduction-related and more likely to represent eroded material from the Brooks Range ophiolite rather than the Angayucham terrane. Our Late Triassic, and Early and Middle Jurassic zircon crystallization ages for the igneous clasts, combined with their immobile trace element compositions documenting various stages of oceanic subduction (mature arc and later rifting), suggest a long-lived subduction system that was active in the Late Triassic and throughout the Middle Jurassic. Radiogenic lead and neodymium isotopic results yield juvenile signatures for both the igneous clasts and the Angayucham terrane, pointing to their formation in an intraoceanic setting distal from the continental rocks and sediments of the Arctic Alaska terrane. These new data, combined with the published data of others, allow us to propose a revised tectonic model that integrates Late Triassic island arc formation with the tectonic development and emplacement of the Brooks Range ophiolite.

Seasonal variations in diet (δ13C) and climate (δ18O) inferred through toxodonts enamel teeth during the Late Pleistocene in the brazilian intertropical region

To access the annual isotopic variation of Toxodon platensis Owen, 1837, tooth enamel samples found in tanks in two localities in the Brazilian Intertropical Region (Puxinanã, Paraíba and Caruaru, Pernamuco) was analyzed isotopically (δ13C, δ18O). We suggest that one annual growth cycle of toxodonts could be represented by 11–17 mm of enamel. The carbon and oxygen isotopic values of the studied samples (LEG 2249–2253) are statistically different, interpreted as reflecting different climatic conditions in both localities. The interpretation of the carbon isotopic results shows little variation in the diet. The oxygen isotopic values of all samples represent the record of at least three years under different climate regimes. The carbon and oxygen isotopic values suggested that the feeding behaviour of these toxodonts were not influenced by the prevailing climatic conditions in both localities.

The Age and Genesis of Fe–Mn Nodules in Gray Forest Soils of the Southern Taiga Based on the Results of Isotope and Metagenomic Studies

The Age and Genesis of Fe–Mn Nodules in Gray Forest Soils of the Southern Taiga Based on the Results of Isotope and Metagenomic Studies

Positive response of nitrite-dependent anaerobic methane oxidation to both gradual and abrupt increases of atmospheric CO2 concentration in paddy soils

The global ongoing increase in the atmospheric CO2 concentration is a gradual rather than an abrupt process. Although the abrupt increase in atmospheric CO2 concentration has been reported to greatly affect nitrite-dependent anaerobic methane oxidation (n-damo), the effect of a gradual increase in atmospheric CO2 concentration on n-damo remains unclear. To better evaluate the role of n-damo in paddy soils, this study investigated the responses of n-damo to different CO2 treatments: the ambient CO2 concentration (CK), a gradual increase (GI), and an abrupt increase (AI) in the CO2 concentration across different growth periods and soil depths. The 13CH4 stable isotope and quantitative PCR results revealed that compared to the CK, GI and AI significantly increased the activity of n-damo by 91.6 % and 90.0 % (p < 0.05), respectively, and also significantly increased the abundance of Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria by 67.7 % and 98.6 % (p < 0.05), respectively. Although there was no significant variation between GI and AI. In addition, the activity and abundance differed significantly between growth period and soil depth. The high-throughput sequencing results showed that GI and AI had little effect on bacterial community, while the soil depth had a significant impact on bacterial community. The changes in several soil physiochemical factors (e.g., the contents of soil water, organic carbon, and inorganic nitrogen) had important impacts on n-damo activity and the bacterial community structure. Overall, the results indicate a positive and similar response of n-damo to both gradual and abrupt increases in the atmospheric CO2 concentration in paddy soils.

Metallogenic Material Source and Genesis of the Jilinbaolige Pb-Zn-Ag Deposit, the Great Xing’an Range, China: Constraints from Mineralogical, S Isotopic, and Pb Isotopic Studies of Sulfide Ores

The Jilinbaolige Pb-Zn-Ag polymetallic deposit is located in the eastern part of Inner Mongolia and in the central-southern part of the Great Xing’an Range, in which several large-sized Pb-Zn-Ag deposits have been found. The Jilinbaolige deposit, which occurs mainly at the contact zone between Yanshanian granite intrusion and sedimentary strata, shows strong NE-to-NNE structural control. The deposit includes three ore-forming stages: (1) the arsenopyrite–pyrite–chalcopyrite–sphalerite stage, (2) the galena–sphalerite–quartz stage, and (3) the pyrite–calcite–quartz stage. In this study, we present a systematic study on the mineralogical and geochemical characteristics (including major elements, S isotopes, and Pb isotopes) of the main sulfide ore minerals in the Jilinbaolige Pb-Zn-Ag deposit in order to evaluate the metallogenic environment, ore-forming material source, and genesis of this polymetallic deposit. The sulfide typomorphic characteristics, ore fabric, and thermometry suggest that the genesis of sulfides in the deposit is closely related to magmatic-hydrothermal activity. The early stage of mineralization might have evolved from a high-temperature hydrothermal environment. The sulfur isotopic results show that the δ34S values in the Jilinbaolige deposit range from 2.3‰ to 6.1‰, with an average value of 3.98‰, indicating that the sulfur originated from magmas with both mantle and crustal components. The Pb isotopic compositions (206Pb/204Pb = 18.214–18.330, 207Pb/204Pb = 15.478–15.615, 208Pb/204Pb = 37.957–38.292, μ = 9.24–9.50, ω = 34.49–36.49) of the sulfide ores suggest that that the lead is of crust-mantle mixed origin. The comparison between the S and Pb isotopic compositions of the Jilinbaolige deposit and the polymetallic deposits from the central-southern parts of the Great Xing’an Range suggests that these deposits have a similar metallogenic source, which is closely related to the Yanshanian granite and medium-temperature hydrothermal fluids. These ore-bearing hydrothermal fluids that evolved from deep magmatic sources migrated along the contact and fracture zones and during the subsequent gradual decrease in temperature, and the metallogenic components were deposited in the relatively open fracture and fissure space. Our results provide insights for further mineral prospecting in the south-central part of the Great Xing’an Range.

U-PB AND LU-HF IN ZIRCON DECIPHERING MAGMATIC PULSES OF THE JUÍNA KIMBERLITE: IMPLICATIONS FOR THE LITHOSPHERIC MANTLE ISOTOPIC COMPOSITION OF THE AMAZONIAN CRATON

This work aims to analyze U-Pb and Lu-Hf ages in zircons formed together with diamonds from the kimberlite province of Juína, in Mato Grosso state, Brazil. Fourteen megacryst (2-3 cm) of zircon were imaged by cathodoluminescence to evaluate the internal structure of the zircon grains and zoning features related to structures of reactions and resorption indicative of magma mixture during evolution. According to the taken images, most of the investigated crystals have a non-metamict structure, with rare fractures, inclusions, and overgrowths, which generates a small degree of heterogeneity. Analyses by Laser Ablation- Multi-Collector- Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) were performed to determine grain ages. Concordia diagrams indicate ages ranging from 99.8 ± 1.6 Ma to 89.5 ± 5.6 Ma with two clusters indicating different magmatic pulses. The analyzed zircons displayed total concentrations of U and Th ranging from 108 to 673 mg kg-1 and 26 to 194 mg kg-1, respectively, and U/Th values varying between 4 and 0.3. The concentrations of U and Pb suggest the occurrence of magmas with two distinct signature components. One hundred and twenty Lu-Hf isotopic results obtained by LA-MC-ICP-MS indicate homogeneity in the isotopic composition, with εHf values ranging from +2.2 to -1.9, and depleted mantle model ages (TDM) between 1.45 Ga and 2.55 Ga. The results suggest that the kimberlite magma derives from a mantle source enriched with an Hf isotopic signature equivalent to the chondritic unfractionated reservoir (CHUR).

Trophic structure and biomagnification of cadmium, mercury and selenium in brown smooth hound shark (Mustelus henlei) within a trophic web

Stable isotopic values of carbon (δ13C) and nitrogen (δ15N) were used to characterize the trophic structure and biomagnification of Cadmium (Cd), Mercury (Hg) and Selenium (Se) in a trophic web of 18 taxa namely zooplankton, crustaceans, mollusks, fishes, and Mustelus henlei shark collected off the western coast of Baja California Sur, Mexico. Isotopic results indicated interspecies variations in the trophic web structure with mean δ13C values of – 20.0‰ (zooplankton) < − 18.2 ‰ (M. henlei) < − 14.1 ‰ (Thaisella kiosquiformis, mollusk). In general, δ15N and δ13C values increased from primary consumers (zooplankton) to predators, following the isotopic patterns of other trophic webs. The concentrations of Cd, Hg and Se were relatively less in most of the organisms except mollusks that presented high concentrations of Cd. The biomagnification factors of the trophic web showed biodilution of Cd (Food Web Magnification Factor, FWMFCd = 0.2), biomagnification of Hg (FWMFHg = 3.34) and Se (FWMFSe = 1.45) respectively. However, the concentrations of Se did not increase consistently from the lower trophic levels to the higher ones. This study documents the dynamics of a marine trophic structure and demonstrates that biodilution/biomagnification processes of metal contaminants are largely species specific and are closely related to physical - chemical and food web structure.

NanoSIMS as an analytical tool for measuring oxygen and hydrogen isotopes in clay minerals from palaeosols: Analytical procedure and preliminary results

Oxygen and hydrogen isotope composition of neoformed clay minerals is commonly used as a palaeoclimatic proxy. Usually, sediments and rocks (including palaeosols) contain not only neoformed clay minerals, but also detrital and/or diagenetic ones. Together with the usually small size (micro- or nanometric) of the clay minerals in these materials, this can generate difficulties during isotopic analyses by conventional spectrometry. To avoid this problem, we used nanoscale secondary ion mass spectrometry (NanoSIMS) to analyse neoformed clay minerals included in palaeosol levels in early Barremian continental profiles located in NE Spain. The bottom levels of the profiles are rich in kaolinite, whereas the top levels contain smectite (beidellite-type). The isotopic compositions of pure powder standards of kaolinite and beidellite were measured in bulk by conventional mass spectrometry to obtain reference values for calibrating the instrumental mass fractionation. Two common preparation techniques for geological samples were tested (thin sections and thick polished sections), revealing that thin sections are more suitable for NanoSIMS analysis due to their lower resin content. The high spatial resolution of the instrument allowed the elemental mapping of the samples, permitting the localization of the minerals of interest and the measurement of isotopic ratios at selected points (1 x 1 μm2) within the samples. The preliminary isotopic results allowed to distinguish a decrease in the average 18O/16O and D/H ratios from the kaolinite in the bottom levels to the smectite in the top levels, reflecting a change in the climatic conditions. The average δ18O and δD values obtained for kaolinite (δ18OSMOW=18±15‰; δDSMOW=-82±36‰ and δ18OSMOW=14±4‰; δDSMOW=-97±37‰) and smectite (δ18OSMOW=13±14‰; δDSMOW=-167±87‰ and δ18OSMOW=11±6‰; δDSMOW=-180±40‰;), respectively, are consistent with the crystallization of the clays in weathering conditions. Despite the uncertainties of these preliminary isotopic measures, the results obtained allowed to estimate an average temperature for kaolinite formation of 21-22°C, and of 16-17°C for smectite. Given suitable calibration using pure isotopic standards and adequate sample preparation, NanoSIMS can thus have a great applicability in palaeoclimatic studies involving the oxygen and hydrogen isotopic composition of nanometre-sized clay minerals from palaeosols samples.

Disentangling the Contribution of Moisture Source Change to Isotopic Proxy Signatures: Deuterium Tracing with WRF-Hydro-Iso-Tag and Application to Southern African Holocene Sediment Archives

Abstract It is well accepted that global circulation models equipped with stable water isotopologues help us better understand the relationships between atmospheric circulation changes and isotope records in paleoclimate archives. Still, isotope-enabled models do not disentangle the different processes affecting precipitation isotopic compositions. Furthermore, the relevance of this model-oriented approach relies on the realism of the modeled isotope results, which would support the interpretation of the proxy records in terms of modeled climate changes. To alleviate these limitations, the newly developed WRF-Hydro-iso-tag, a version of the isotope-enabled regional coupled model WRF-Hydro-iso enhanced with an isotope-tracing procedure, is presented. Physics-based WRF-Hydro-iso-tag ensembles are used to regionally downscale the isotope-enabled Community Earth System Model for southern Africa, for two 10-yr slices of mid-Holocene and preindustrial times. The isotope-tracing procedure is tailored to assess the origin of the hydrogen isotope deuterium contained in southern African precipitation, between the Atlantic and Indian Oceans. In comparison to the global model, WRF-Hydro-iso-tag simulates lower precipitation amounts with more regional details, as well as mid-Holocene-to-preindustrial changes in precipitation isotopic compositions that better match plant-wax deuterium records from two marine sediment cores off the Orange and Limpopo River basins. Linear relationships between mid-Holocene-to-preindustrial changes in temperature, precipitation amount, moisture source, and precipitation deuterium compositions are derived from the ensemble results. A deuterium enrichment in the Orange River-related sediment core may not be related to an aridification but rather indicate a summer circulation change enabling a larger contribution of more isotopically enriched moisture from the Atlantic Ocean. Significance Statement The knowledge of past climates is crucial for understanding our Earth system and apprehending future climate change. Plant materials in sediment archives contain atoms of hydrogen from past precipitation that allow paleoclimate reconstructions, using compositions of the hydrogen isotope deuterium. However, in the tropics, deuterium-depleted plant remains can either denote a wetter climate phase or a change in atmospheric circulation patterns with longer distances between ocean evaporation and land precipitation. This work provides an innovative dynamical downscaling method of global paleoclimate models to disentangle the effects of precipitation amount change and moisture source change on deuterium records, and ultimately to improve paleoclimate reconstructions. The interpretation of a deuterium enrichment in a marine sediment core as a marker for aridification is revised. The enrichment caused by an atmospheric circulation change bringing a larger amount of more isotopically enriched moisture flow from the Atlantic Ocean to southern African precipitation would be a more physically sound explanation.

Infancy, childhood, and puberty on the Silk Road revealed with isotopic analysis of incremental dentine

Childhood is a unique phase in human life history, in which newborns are breastfed and weaned, and are progressively familiarized to adult diets. By investigating dietary changes from infancy to adolescence, valuable information regarding past cultural behaviors and aspects of human lives can be explored and elucidated. Here, in conjunction with published isotopic results of serial dentine (n = 21) from Yingpan Man, new δ13C and δ15N results are obtained from 172 samples of incremental dentine from 8 teeth of 8 individuals of the Yingpan cemetery, located in Xinjiang, China. The δ13C values range from – 18.2 to – 14.6‰ with a mean ± SD value of – 16.3 ± 0.9‰, and the δ15N results range between 13.4 and 19.9‰ with a mean ± SD value of 16.0 ± 1.4‰. This indicates that the childhood diets were mixtures of C3 and C4 dietary resources and were clearly influenced by breastfeeding and weaning practices. In particular, the findings indicate that there were significant inter-individual differences in terms of the timing and duration of breastfeeding and weaning practices as well as childhood dietary practices at Yingpan. For instance, three individuals were exclusively breastfed after birth, while, two individuals and Yingpan Man were not. In addition, the post-weaning diets of most Yingpan individuals were relatively stable, but one individual and Yingpan Man displayed clear evidence of increased consumption of C4 foods, likely millet, during late and post-weaning periods. Further, 7 individuals had unique dietary changes between 9 to 14 years old. Potential factors related to this are presented from the perspective of changes in social roles that might be caused by their early participation in the social division of labor or puberty and marriage.

Influencing factors and significance of organic and inorganic nitrogen isotopic compositions in lacustrine sedimentary rocks

Comprehensive nitrogen biogeochemical cycle has been reconstructed for representative lacustrine organic-rich sedimentary rock in China, namely the Triassic Yanchang Formation (YF, 199–230 Ma) in Ordos and the Cretaceous Qingshankou Formation (QF, 86–92 Ma) in Songliao basins, by evaluating the organic and inorganic nitrogen isotopic compositions rather than only organic or bulk nitrogen isotopic compositions. The results indicate that the nitrogen isotope values of bulk rock (δ15Nbulk) in the non-metamorphic stage are significantly different from that of kerogen, which challenge the conceptual framework of sedimentary nitrogen isotope interpretation. The δ15Nbulk from the YF and QF were lower than their respective the nitrogen isotope values of kerogen (δ15Nker), with offsets up to ∼5.1‰, which have the inverse relationship for the metamorphosed rock. Thermal evolution did not significantly modify the δ15N of bulk rock and kerogen. The δ15N of sediments from the YF (δ15Nbulk, 1.6‰–5.6‰) were lower than that of rock from the QF (δ15Nbulk, 10.2‰–15.3‰). The nitrogen isotope values of silicate incorporated nitrogen (δ15Nsil) were slightly lower than those of the δ15Nker in the YF and obviously lower for the QF. The fact that different nitrogen cycles occur in the YF and QF due to the different depositional redox conditions leads to different isotopic results. The YF water environment dominated by oxic conditions is not conducive to the occurrence of denitrification and anammox, and no abundant N2 loss leads to the relatively light δ15Nbulk. In the stratified water for the QF, redox transition zone promotes denitrification and anammox, resulting in the heavy δ15Nbulk of rock and promotes the DNRA, resulting in heavy δ15Nker and low δ15Nsil.