Nitrogen isotopes in mantle-derived diamonds: indications of a multi-component structure

Mantle nitrogen trapped in diamonds is commonly defined by an isotopic composition (δ15N) of ~-5% based on the central tendency of total combustion diamond data that vary from -25 to +18%. We present here the nitrogen isotopic data from stepped combustion of diamonds, which together with data from other mantlederived materials suggest a multi-component structure of diamond-nitrogen. Mantle nitrogen sampled in diamonds apparently has δ15N ~-15%, similar to that observed in mantle xenoliths and mid-oceanic ridge basalts (MORBs), while nitrogen in a minor population of diamonds from China is consistent with contributions from an ocean island basalt like mantle source

Noble gases in mineral separates from three shergottites: Shergotty, Zagami, and EETA 79001

This study provides a complete data set of all five noble gases for bulk samples and mineral separates from three Martian shergottites: Shergotty (bulk, pyroxene, maskelynite), Zagami (bulk, pyroxene, maskelynite), and Elephant Moraine (EET) A79001, lithology A (bulk, pyroxene). We also give a compilation of all noble gas and nitrogen studies performed on these meteorites. Our mean values for cosmic-ray exposure ages from 3He, 21Ne, and 38Ar are 2.48 Myr for Shergotty, 2.73 Myr for Zagami, and 0.65 Myr for EETA79001 lith. A. Serious loss of radiogenic 4He due to shock is observed. Cosmogenic neon results for bulk samples from 13 Martian meteorites (new data and literature data) are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic-ray effects. While a contribution of this low-energy irradiation is strongly indicated for all of the shergottites, spallation Ne in Chassigny, Allan Hills (ALH) 84001, and the nakhlites is fully explained by galactic cosmic-ray spallation. Implanted Martian atmospheric gases are present in all mineral separates and the thermal release indicates a near-surface siting. We derive an estimate for the 40Ar/36Ar ratio of the Martian interior component by subtracting from measured Ar in the (K-poor) pyroxenes the (small) radiogenic component as well as the implanted atmospheric component as indicated from 129Xe* excesses. Unless compromised by the presence of additional components, a high ratio of ~2000 is indicated for Martian interior argon, similar to that in the Martian atmosphere. Since much lower ratios have been inferred for Chassigny and ALH 84001, the result may indicate spatial and/or temporal variations of 40Ar/36Ar in the Martian mantle

Nitrogen isotopic composition of the MORB mantle: a reevaluation

Nitrogen in the mantle source of mid oceanic ridge basalts (MORBs) is commonly believed to have δ15N~−5‰. This is based on a (selective) statistical average drawn from nitrogen isotopic data obtained simultaneously with argon from MORBs. However, on critical evaluation, using the accompanying 40Ar/36Ar data, we show this approach to be somewhat ambiguous. Considering the fact that MORBs can have a number of geochemical components in them, as has been shown by several recent studies, the approach of statistical averaging may actually point to a mixture rather than the true mantle end-member. A more reasonable approach, also used for deriving the mantle noble gas signatures, suggests nitrogen in the MORB mantle to be much lighter (~−15‰) in its isotopic composition. Such a signature is consistent with nitrogen data from MORBs as well as from other mantle derived samples that are believed to have sampled volatiles from the MORB mantle

Origin of air-like noble gases in oceanic basalts

Noble gas studies of oceanic basalts show the ubiquitous presence of an air-like component, which is usually attributed to a simple atmospheric contamination. However, simultaneous nitrogen and argon isotopic study shows the presence of heavy nitrogen with an isotopic composition (δ15N) ~ +18%, accompanied by 40Ar/36Ar values much lower than the mantle value. Such a component can be attributed to recycled materials from subduction zones, which are incorporated into these basaltic magmas during their ascent through a shallow enriched region in the mantle. This suggests that a part of the air-like noble gases in oceanic basalts is due to recycled atmospheric gases. Thus the air-like noble gases in the oceanic basalts, hitherto considered a hindrance, provide useful clues for understanding the geochemical evolution of these samples

Precursors of Mars: constraints from nitrogen and oxygen isotopic compositions of martian meteorites

We present an approach to assess the nature of materials involved in the accretion of Mars by the planet's nitrogen (δ15N) and oxygen (Δ17O) isotopic compositions as derived from data on martian meteorites. δ15N for Mars has been derived from nitrogen and xenon systematics, while Δ17O has been taken from the literature data. These signatures indicate that Mars has most probably accreted from enstatite and ordinary chondritic materials in a ratio of 74:26 and may not have a significant contribution from the carbonaceous (CI, CM, or CV) chondrites. This is consistent with the chromium isotopic (ε53Cr) signatures of martian meteorites and the bulk planet Fe/Si ratio for Mars as suggested by the moment of inertia factor (I/MR2) obtained from the Mars Pathfinder data. Further, a simple homogeneous accretion from the above two types of materials is found to be consistent with the planet's moment of inertia factor and the bulk composition of the mantle. But, it requires a core with 6.7 wt% Si, which is consistent with the new results from the high pressure and temperature melting experiments and chemical data on the opaque minerals in enstatite chondrites

Noble gases and nitrogen in Martian meteorites Dar al Gani 476, Sayh al Uhaymir 005 and Lewis Cliff 88516: EFA and extra neon

Meteorite “finds” from the terrestrial hot deserts have become a major contributor to the inventory of Martian meteorites. In order to understand their nitrogen and noble gas components, we have carried out stepped heating experiments on samples from two Martian meteorites collected from hot deserts. We measured interior and surface bulk samples, glassy and non-glassy portions of Dar al Gani 476 and Sayh al Uhaymir 005. We have also analyzed noble gases released from the Antarctic shergottite Lewis Cliff 88516 by crushing and stepped heating. For the hot desert meteorites significant terrestrial Ar, Kr, Xe contamination is observed, with an elementally fractionated air (EFA) component dominating the low temperature releases. The extremely low Ar/Kr/Xe ratios of EFA may be the result of multiple episodes of trapping/loss during terrestrial alteration involving aqueous fluids. We suggest fractionation processes similar to those in hot deserts to have acted on Mars, with acidic weathering on the latter possibly even more effective in producing elementally fractionated components. Addition from fission xenon is apparent in DaG 476 and SaU 005. The Ar–Kr–Xe patterns for LEW 88516 show trends as typically observed in shergottites – including evidence for a crush-released component similar to that observed in EETA 79001. A trapped Ne component most prominent in the surface sample of DaG 476 may represent air contamination. It is accompanied by little trapped Ar (20Ne/36Ar > 50) and literature data suggest its presence also in some Antarctic finds. Data for LEW 88516 and literature data, on the other hand, suggest the presence of two trapped Ne components of Martian origin characterized by different 20Ne/22Ne, possibly related to the atmosphere and the interior. Caution is recommended in interpreting nitrogen and noble gas isotopic signatures of Martian meteorites from hot deserts in terms of extraterrestrial sources and processes. Nevertheless our results provide hope that vice-versa, via noble gases and nitrogen in meteorites and other relevant samples from terrestrial deserts, Martian secondary processes can be studied

High Resolution Mapping of QTLs for Heat Tolerance in Rice Using a 5K SNP Array

Abstract Background Heat stress is one of the major abiotic threats to rice production, next to drought and salinity stress. Incidence of heat stress at reproductive phase of the crop results in abnormal pollination leading to floret sterility, low seed set and poor grain quality. Identification of QTLs and causal genes for heat stress tolerance at flowering will facilitate breeding for improved heat tolerance in rice. In the present study, we used 272 F8 recombinant inbred lines derived from a cross between Nagina22, a well-known heat tolerant Aus cultivar and IR64, a heat sensitive popular Indica rice variety to map the QTLs for heat tolerance. Results To enable precise phenotyping for heat stress tolerance, we used a controlled phenotyping facility available at ICAR-Indian Institute of Wheat and Barley Research, Karnal, India. Based on ‘days to 50% flowering’ data of the RILs, we followed staggered sowing to synchronize flowering to impose heat stress at uniform stage. Using the Illumina infinium 5K SNP array for genotyping the parents and the RILs, and stress susceptibility and stress tolerance indices (SSI and STI) of percent spikelet sterility and yield per plant (g), we identified five QTLs on chromosomes 3, 5, 9 and 12. The identified QTLs explained phenotypic variation in the range of 6.27 to 21. 29%. Of these five QTLs, two high effect QTLs, one novel (qSTIPSS9.1) and one known (qSTIY5.1/qSSIY5.2), were mapped in less than 400 Kbp genomic regions, comprising of 65 and 54 genes, respectively. Conclusions The present study identified two major QTLs for heat tolerance in rice in narrow physical intervals, which can be employed for crop improvement by marker assisted selection (MAS) after development of suitable scorable markers for breeding of high yielding heat tolerant rice varieties. This is the first report of a major QTL for heat tolerance on chromosome 9 of rice. Further, a known QTL for heat tolerance on chromosome 5 was narrowed down from 23 Mb to 331 Kbp in this study

Additional file 2: Table S1. of High Resolution Mapping of QTLs for Heat Tolerance in Rice Using a 5K SNP Array

List of genes in the five QTL intervals identified. Table S2. Non-synonymous SNPs in the mapped QTL intervals. Table S3. Reported QTLs related to heat stress tolerance in rice. (XLSX 52 kb

Experience of establishing and coordinating a nationwide network for bidirectional intussusception surveillance in India: lessons for multisite research studies

Objectives To document and share the process of establishing the nationally representative multisite surveillance network for intussusception in India, coordination, data management and lessons learnt from the implementation.Design This study combined both retrospective and prospective surveillance approaches.Setting 19 tertiary care institutions were selected in India considering the geographic representation and public and private mixParticipants All children under-2 years of age with intussusceptionPrimary and secondary outcome measures The experience of site selection, regulatory approvals, data collection, quality assurance and network coordination were documented.Results The site selection process involved systematic and objective four steps including shortlisting of potential institutions, information seeking and telephonic interaction, site visits and site selection using objective criteria. Out of over 400 hospitals screened across India, 40 potential institutions were shortlisted and information was sought by questionnaire and interaction with investigators. Out of these, 25 institutes were visited and 19 sites were finally selected to participate in the study. The multistep selection process allowed filtering and identification of sites with adequate capacity and motivated investigators. The retrospective surveillance documented 1588 cases (range: 14–652 cases/site) and prospective surveillance recruited 621 cases (range: 5–191 cases/site). The multilayer quality assurance measures monitored and ensured protocol adherence, complete record retrieval and data completeness. The key challenges experienced included time taken for obtaining regulatory and ethical approvals, which delayed completion of the study. Ten sites continued with another multisite vaccine safety surveillance study.Conclusion The experience and results of this systematic and objective site selection method in India are promising. The systematic multistep site selection and data quality assurance methods presented here are feasible and practical. The lessons from the establishment and coordination of this surveillance network can be useful in planning, selecting the sites and conducting multisite and surveillance studies in India and developing countries