East Asian hydroclimate modulated by the position of the westerlies during Termination I.

Speleothem oxygen isotope records have revolutionized our understanding of the paleo East Asian monsoon, yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes. We report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle Yangtze region, which indicates a wetter central eastern China during North Atlantic cooling episodes, despite the oxygen isotopic record suggesting a weaker monsoon. We show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the Meiyu rains and shortened post-Meiyu stage, in accordance with a recent hypothesis. Model simulations support this interpretation and further reveal the role of the westerlies in communicating the North Atlantic influence to the East Asian climate

A solar wind-derived water reservoir on the Moon hosted by impact glass beads

The past two decades of lunar exploration have seen the detection of substantial quantities of water on the Moon’s surface. It has been proposed that a hydrated layer exists at depth in lunar soils, buffering a water cycle on the Moon globally. However, a reservoir has yet to be identified for this hydrated layer. Here we report the abundance, hydrogen isotope composition and core-to-rim variations of water measured in impact glass beads extracted from lunar soils returned by the Chang’e-5 mission. The impact glass beads preserve hydration signatures and display water abundance profiles consistent with the inward diffusion of solar wind-derived water. Diffusion modelling estimates diffusion timescales of less than 15 years at a temperature of 360 K. Such short diffusion timescales suggest an efficient water recharge mechanism that could sustain the lunar surface water cycle. We estimate that the amount of water hosted by impact glass beads in lunar soils may reach up to 2.7 × 1014 kg. Our direct measurements of this surface reservoir of lunar water show that impact glass beads can store substantial quantities of solar wind-derived water on the Moon and suggest that impact glass may be water reservoirs on other airless bodies

Simultaneous Quantification of Forsterite Content and Minor–Trace Elements in Olivine by LA–ICP–MS and Geological Applications in Emeishan Large Igneous Province

Olivine forsterite contents [Fo = 100 × Mg/(Mg + Fe) in mol%] and minor–trace element concentrations can aid our understanding of the Earth’s mantle. Traditionally, these data are obtained by electron probe microanalysis for Fo contents and minor elements, and then by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) for trace elements. In this study, we demonstrate that LA–ICP–MS, with a simplified 100% quantification approach, allows the calculation of Fo contents simultaneously with minor–trace elements. The approach proceeds as follows: (1) calculation of Fo contents from measured Fe/Mg ratios; (2) according to the olivine stoichiometric formula [(Mg, Fe)2SiO4] and known Fo contents, contents of Mg, Fe and Si can be computed, which are used as internal standards for minor–trace element quantification. The Fo content of the MongOLSh 11-2 olivine reference material is 89.55 ± 0.15 (2 s; N = 120), which agrees with the recommended values of 89.53 ± 0.05 (2 s). For minor–trace elements, the results matched well with the recommended values, apart from P and Zn data. This technique was applied to olivine phenocrysts in the Lijiang picrites from the Emeishan large igneous province. The olivine compositions suggest that the Lijiang picrites have a peridotitic mantle source

MK-1 Orthopyroxene—A New Potential Reference Material for In-Situ Microanalysis

Orthopyroxene, an important phase in mantle-derived rocks, has become a powerful tool to unravel mantle nature and magma processes. However, the applications have been hindered by the lag in the development of analytical techniques, such as shortage of reference materials. Orthopyroxene grains derived from an ultramafic intrusion at the Mogok metamorphic belt (Myanmar) were evaluated for the potential use of orthopyroxene as a reference material for in-situ microanalysis. Approximately 20 g of 0.5–3 mm pure orthopyroxene grains were separated under binocular microscope and analyzed using EPMA, LA-ICPMS, and bulk analytical methods (XRD, XRF, and solution-ICPMS) for major and trace elements at four institutions. Eleven core-to-rim profiles carried out using EPMA and twelve core-to-rim profiles determined using LA-ICPMS suggest that MK-1 orthopyroxene grains are sufficiently homogeneous, with RSD < ±2% (1σ) for major elements (Mg, Si, and Fe) and RSD < ±10% (1σ) for trace elements (Na, Al, Ca, Ti, Cr, Co, Zn, Ni, Mn, Sc, and V). In addition, the composition of MK-1 orthopyroxene was also measured by XRF and solution-ICPMS measurements in two different laboratories, to compare with the results measured using EPMA and LA-ICPMS. The results indicated a good agreement with RSE < ±2% (1σ) for major elements and RSE < ±5% (1σ) for most trace elements, except for Na (±9.73%) and Ti (±6.80%). In an overall assessment of these data, MK-1 orthopyroxene can be considered as a reference material for in-situ microanalysis, which would provide solid trace elements data for a better understanding of mantle source and magmatic evolution

Distributions of selenium and related elements in high pyrite and Se-enriched rocks from Ziyang, Central China

Pyrite-bearing volcanic tuff and carbonaceous slates of the Lower Cambrian Lujiaping Formation have been considered the source of selenium (Se) in high-Se soils in the area of the Naore Village of the Ziyang County, China, where acute Se toxicity occurred in the 1980s. For geochemical exploration, the accumulation and distribution of Se and trace elements within the pyrite grains are of great indicative significance for understanding the possible origin and forming mechanism of the Se enrichment. In this work, 7 rock samples and 89 pyrite grains were collected and analysed to investigate the element micro-distribution within the pyrite grains using EPMA and LA-ICP-MS. The whole-rock analysis shows that the pyrite-bearing Lower Cambrian rocks in Ziyang are commonly enriched in Se, As, Mo, Cd, Cr, Ni, Sb, Cu and Ba. In situ microanalysis indicates that Se (30-1880 mu g/g) and As (160-2960 mu g/g) concentrations within the pyrite grains are 1-2 orders of magnitude higher than those in the host rocks (Se: 0.56-73.1 mu g/g, As: 2.56-195 mu g/g) and that the Se contents are negatively correlated with pyrite mineral sizes. Grain-scale element mappings of fresh Se-enriched pyrites reveal two types of Se and As distribution patterns (type-I: high-Se 120-1870 mu g/g and low-As < 150-1580 mu g/g cores, type-II: low-Se 60-680 mu g/g and low-As < 150-1310 mu g/g cores) with alternating Se or As contents during the growth of zoned pyrite. The texture of pyrite element zoning reflects multi-stage hydrothermal pulses with changing trace element concentrations. Type-II pyrite formed later than type-I pyrite. Genetic analysis confirms that Se-enriched strata were strongly affected by hydrothermal submarine deposition and that Se in pyrite was mainly derived from hydrothermal fluids. Secondary hydrothermal erosion led to the formation of high-Se "fractures" (Se content 19.3 wt%). In summary, utilizing pyrite as an indicator for the Lower Cambrian Lujiaping Formation Se-bearing strata extends our understanding of selenium geochemical processes and highlights the mechanistic aspects of Se

Characterization of the potential reference material SA02 for micro-beam U–Pb geochronology and Hf–O isotopic composition analysis of zircon

In the present work, a natural zircon megacryst SA02 (the exact provenance unknown) is investigated as a new potential reference material for U–Pb geochronology and Hf–O isotopic composition analysis via micro-beam methods. The precise and accurate U–Pb age is determined by the chemical abrasion isotope dilution thermal ionization mass-spectrometry (CA-ID-TIMS) method. The resultant mean 206Pb/238U date is 535.10 ± 0.24 Ma (2s, n = 2), interpreted as the crystallization age of the zircon megacryst. The mean ID-TIMS 206Pb/238U date of 533.7 ± 3.7 Ma (2s, n = 8) is recommended as the working value for micro-beam analyses when using untreated SA02 zircon grains as the primary reference material. 206Pb/238U dates of 533.0 ± 6.2 Ma (2s, n = 57) and 534 ± 8 Ma (2s, n = 101) obtained by secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) respectively are reproducible and in agreement with the results of ID-TIMS within < 0.3% relative analytical errors. Solution data of Hf isotope compositions measured by multi-collector ICP-MS (MC-ICP-MS) from SA02 zircon yield a mean 176Hf/177Hf of 0.282287 ± 0.000016 (2s, n = 31), which is recommended as a reference value for microbeam analysis. Hf isotope analyses by LA-MC-ICP-MS yield homogeneous Hf isotopic compositions with a mean 176Hf/177Hf of 0.282289 ± 0.000033 (2s, n = 142) identical to the solution value. The mean δ18O value measured by laser fluorination is 6.03 ± 0.28‰ (2s, n = 13), which is consistent with the result of SIMS analysis

A Single Amino Acid Substitution in RFC4 Leads to Endoduplication and Compromised Resistance to DNA Damage in <i>Arabidopsis thaliana</i>

Replication factor C (RFC) is a heteropentameric ATPase associated with the diverse cellular activities (AAA+ATPase) protein complex, which is composed of one large subunit, known as RFC1, and four small subunits, RFC2/3/4/5. Among them, RFC1 and RFC3 were previously reported to mediate genomic stability and resistance to pathogens in Arabidopsis. Here, we generated a viable rfc4e (rfc4−1/RFC4G54E) mutant with a single amino acid substitution by site-directed mutagenesis. Three of six positive T2 mutants with the same amino acid substitution, but different insertion loci, were sequenced to identify homozygotes, and the three homozygote mutants showed dwarfism, early flowering, and a partially sterile phenotype. RNA sequencing revealed that genes related to DNA repair and replication were highly upregulated. Moreover, the frequency of DNA lesions was found to be increased in rfc4e mutants. Consistent with this, the rfc4e mutants were very sensitive to DSB-inducing genotoxic agents. In addition, the G54E amino acid substitution in AtRFC4 delayed cell cycle progression and led to endoduplication. Overall, our study provides evidence supporting the notion that RFC4 plays an important role in resistance to genotoxicity and cell proliferation by regulating DNA damage repair in Arabidopsis thaliana

In situ calcite U−Pb geochronology by high-sensitivity single-collector LA-SF-ICP-MS

U−Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method, with potential applications to a vast array of geological problems. Due to the low levels of U and Pb in calcite, measurement using higher-sensitivity instruments, such as sector field (SF) ICP-MS, have advantages over more commonly used quadrupole (Q) ICP-MS instruments. Using a Thermo Element XR ICP-MS, we demonstrate that the Jet+X cone combination with the N2 enhancement technique provides the best sensitivity for measuring U and Pb isotopes. This higher sensitivity improves the precision of calcite U−Pb isotope measurements, and permits dating at high spatial resolutions (<110 µm) and for samples containing low contents of 238U (<1 µg g−1) and/or 207Pb (i.e., young samples <10 Ma). Using a spot size of 85 µm with a low fluence (∼2.0 J cm−2), the laser-induced elemental fractionation of 206Pb/238U in the NIST SRM 614, ARM-3 and WC-1 reference materials are insignificant (<2.2%). Adopting the optimized instrument parameters, we analysed four commonly-used calcite U−Pb reference materials (WC-1, Duff Brown Tank, JT, and ASH-15). The results match well with published isotope dilution data, demonstrating the reliability of our technique. ARM-3, an andesitic glass, is shown to be an appropriate reference material for both 207Pb/206Pb calibration and instrument optimization because of its moderate contents of U (∼3.75 µg g−1) and Pb (∼12.7 µg g−1). We further demonstrate that the image-guided approach using LA-ICP-MS elemental mapping is an efficient tool in obtaining robust ages

Beryl Reference Materials for In Situ Oxygen Isotope Determination

The mineral beryl (Be3Al2(SiO3)6) has the most abundant phase with industrial value for extracting a critical metal—beryllium. Due to multi-stage, fluid-induced growth, individual beryl grains may yield complex geochemical records, revealing variations in the oxygen isotopes of the fluids from which they crystallize. Secondary ion mass spectrometry (SIMS) with high sensitivity and high spatial resolution represents a good tool for in situ isotopic analysis. SIMS oxygen analyses require matrix-matched reference materials to calibrate instrumental mass fractionations during measurement. In this work, the oxygen isotope homogeneities of six beryl samples with different compositions (BS1, BS2, BS3, BS4, BS5, and BS6) were documented by SIMS. These samples’ recommended oxygen isotope compositions were characterized by laser fluorination isotope ratio mass spectrometry (IRMS). This study suggests that there is no matrix effect related to composition variation in beryl SIMS oxygen isotope analysis. The recommended δ18O values of the four reference materials, BS1, BS2, BS4, and BS5, were 15.01 ± 0.34‰ (2 standard deviations, 2 SD), 7.53 ± 0.16‰ (2 SD), 2.38 ± 0.14‰ (2 SD), and 10.72 ± 0.44‰ (2 SD), respectively. Therefore, BS1, BS2, BS4, and BS5 are recommended as suitable reference materials for in situ mineral beryl oxygen isotope microanalysis