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Ceratitis capitata (Wiedemann) is a polyphagous plant pest organism causing serious damage on more than 300 fruit types. Although the medfly is present in Europe, it is so far not established in Germany. In the years 2015–2017, an official survey was conducted by the German Federal Plant Protection Organisations to elucidate the current occurrence of this organism in Germany. While in 2015 only small numbers of flies were captured in traps situated in all German Federal States, a peak of 188 specimens could be trapped in 2016 with a decline to 29 specimens in 2017. Highest abundance of the fruit fly was detected in Southern Germany and at a single spot east of Berlin. The present study aimed to identify the origin of the trapped fruit flies and to assess the general potential of the species for overwintering in Germany. Using two approaches with cytochrome oxidase subunit I (COI), Sanger barcoding sequencing first and subsequent analysis of ten small simple repeat microsatellite loci from literature, the worldwide spread of C. capitata describing three phases could be retraced by analysing samples from Germany and 11 other countries. German and French populations were found to build the most recent stage of this species distribution. Specimens trapped in Germany obviously resulted from different introduction events. They most strongly resembled populations from France and Croatia but were not identical to these populations. We found strong evidence that specimens captured between 2016 and 2017 could not overwinter in Germany.

Cyst producing nematodes are persistent soil-born organisms causing severe damage to cultivated plants. Persistence of the economically relevant cyst nematode species Globodera pallida, G. rostochiensis and Heterodera schachtii was investigated at different stages during a large-scale industrial composting process to evaluate its efficiency to prevent spread of these nematodes into natural and agricultural habitats. Using reference cyst nematodes incorporated into organic waste from households and the processing industry the effect of anaerobic fermentation as well as aerobic composting processes were investigated. Treated cysts were analysed for viability and reproductive potential by performing hatching tests and bioassays on susceptible host plants. The investigated composting plant showed maximum temperatures between

Selenium behaves as a chalcophile and moderately volatile element during planetary accretion and magmatic processes on Earth. Together with the geochemically similar S and Te, Se is more volatile than most other moderately volatile elements and thus potentially becomes a new tracer to constrain the mechanism of volatile depletion in the Earth's mantle and other planetary bodies. As previously observed for several volatile elements, stable isotopes of Se are expected to fractionate upon eruptive outgassing of magmas. To understand the degassing behavior of Se and associated isotope fractionation, we report on Se and Te contents and Se isotope compositions (δSe) of submarine glasses across a range of distant ridge depth intervals along the Reykjanes Ridge and subglacial/subaerial basalts on Iceland (51–65°N; N = 22). Selenium (150–399 ng/g) and Te (2.61–14.5 ng/g) contents of the submarine glasses display progressive enrichment along the Reykjanes Ridge towards Iceland. This can be explained either by enhanced mantle melting towards Iceland or by enrichment of Se–Te contents in the mantle source due to the Icelandic plume–Reykjanes Ridge interaction. Both scenarios are equally plausible. The δSe values of submarine Reykjanes Ridge glasses range between −0.20 ± 0.08‰ and −0.08 ± 0.08‰ (on average −0.15 ± 0.07‰; 2SD, N = 15), which are unaffected by the Icelandic plume contribution and remain strictly within the previously reported average for depleted MORBs. These new data combined with literature δSe for depleted MORBs define a highly homogeneous depleted mantle composition δSe = −0.15 ± 0.11‰ (2SD, N = 44). On the other hand, we observed degassing of Se and Te to a variable extent (~40–95%) in submarine Reykjanes glasses at depths shallower than ~250 m and in subaerial/subglacial basalts on Iceland. Degassing-induced Se isotope fractionation shifted δSe of subaerial lavas towards heavier values (by up to ~0.44‰) well outside the range of submarine MORBs. However, when Se outgassing is associated with subglacial eruption, the outer glass rim of basalt preserves the primary/undegassed Se isotopic signature; whereas the pillow interior experiencing further Se loss (~50%) is enriched in heavier isotopes (−0.01 ± 0.12‰) relative to the outer glass rim (−0.22 ± 0.08‰). These observations are complemented by measurements of BHVO-2G from high-temperature heating experiments of the natural Hawaiian basalt BHVO-2, which show evaporation of 40% Se and 85% Te and resulting shift in δSe by ~+0.74‰. Degassing-induced Se isotope fractionation during volcanic eruption may be well explained by a simple Rayleigh distillation model with an empirical fractionation factor α of ~0.9998 (between volcanic gas and silicate melt). The results presented here show that Se isotope and Se–Te systematics can potentially contribute further constraints on degassing of chalcophile and volatile elements during terrestrial volcanism and large-scale planetary processes., We are especially grateful to Jean-Guy Schilling for his initial support and encouragement of the project, and to Katherine A. Kelley for providing us with all the samples. We acknowledge fruitful discussions with Ronny Schoenberg, Jabrane Labidi, and Timon Kurzawa, and lab support from Elmar Reitter and Maria Isabel Varas-Reus. We also thank Frances Jenner, Alex McCoy-West, and an anonymous reviewer for their through reviews and constructive suggestions, and Julie Prytulak for the efficient editorial handling. S. K. acknowledges financial support by the ERC Starting Grant O2RIGIN (636808).

Anoplophora glabripennis (Motschulsky 1853) (Coleoptera: Cerambycidae), the Asian Longhorned Beetle, is native to temperate and subtropical areas of China and the Korean peninsula. Due to its wide range of host plants, it is considered among the most economically important invasive plant pests. The morphological identification of A. glabripennis larvae can be confirmed by DNA barcoding, but obtaining the specimens from infested trees can be a demanding and challenging task. Therefore, non-invasive diagnostic tools based on DNA extracted from frass samples can be of key importance in phytosanitary surveys. In this study, an in silico generated real-time quantitative PCR test was developed for the detection of A. glabripennis DNA from frass material, which is naturally extruded from larval tunnels through cracks in the bark. Specificity was confirmed against a wide range of other wood-boring insect species frequently encountered during phytosanitary surveys and inclusivity was demonstrated for different populations of A. glabripennis from all main European outbreak areas. The test proved sensitive and reliable in detecting A. glabripennis DNA extracted from woody frass material of Acer saccharinum and Aesculus hippocastanum at least up to the 100-fold dilution. Furthermore, the test allowed the molecular identification of any life stage of the insect, including eggs and young larvae, whose morphological identification is impossible or very challenging. This study provides a reliable and sensitive molecular tool to detect A. glabripennis DNA in woody frass material, thus allowing a non-invasive sampling approach.

The later stages of Earth’s transition to a permanently oxygenated atmosphere during the Great Oxidation Event (GOE; ∼2.43–2.06 Ga) is commonly linked with the suggestion of an “oxygen overshoot” during the ∼2.22–2.06 Ga Lomagundi Event (LE), which represents Earth’s most pronounced and longest-lived positive carbon isotope excursion. However, the magnitude and extent of atmosphere-ocean oxygenation and implications for the biosphere during this critical period in Earth’s history remain poorly constrained. Here, we present nitrogen (N), selenium (Se), and carbon (C) isotope data, as well as bio-essential element concentrations, for Paleoproterozoic marine shales deposited during the LE. The data provide evidence for a highly productive and well-oxygenated photic zone, with both inner and outer-shelf marine environments characterized by nitrate-and Se oxyanion-replete conditions. However, the redoxcline subsequently encroached back onto the inner shelf during global-scale deoxygenation of the atmosphere-ocean system at the end of the LE, leading to locally enhanced water column denitrification and quantitative reduction of selenium oxyanions. We propose that nitrate-replete conditions associated with fully oxygenated continental shelf settings were a common feature during the LE, but nitrification was not sufficiently widespread for the aerobic nitrogen cycle to impact the isotopic composition of the global ocean N inventory. Placed in the context of Earth’s broader oxygenation history, our findings indicate that O2levels in the atmosphere-ocean system were likely much lower than modern concentrations. Early Paleoproterozoic biogeochemical cycles were thus far less advanced than after Neoproterozoic oxygenation., University of Tubingen, German Research Foundation (DFG) SCHO1071/11-1 VA 1568/1-1, UK Research & Innovation (UKRI), Natural Environment Research Council (NERC) NE/V004824/1, University of Lausanne, European Research Council (ERC) 636808, National Research Foundation of South Africa (NRF Grant) 75892, Spanish Government RYC2020-030014-I, Natural Sciences and Engineering Research Council of Canada (NSERC), ACS PF grant 624840ND2, NERC Frontiers grant NE/V010824/1, Royal Society of London

In plant pest diagnosis, Sanger sequencing of marker genes (DNA-barcoding) is the most applied and appropriate method for the identification of insects. Standard PM7/129 of the European and Mediterranean Plant Protection Organization (EPPO) includes a number of primers and PCR protocols for diagnosing insect pests. LCO1490 and HCO2198 primers recommended herein were shown to be excellent tools for amplifying a fragment of the COI gene from a vast range of arthropods. The COI barcoding region is available for thousands of arthropod taxa in public databases and ready-to-use for evolutionary studies. However, we found that LCO1490 and HCO2198 primers are not working for bark beetles of genus Ips. The attempt to amplify this gene fragment from an individual organism using the barcoding primers led to DNA amplification of associated wasps and nematodes, which were apparently vectored by the beetle. Thus, new primers for Ips that bind specifically to another (non-barcoding) region of the COI gene were developed in the past years. These primers were successfully applied in phylogenetic analyses of this genus, resulting in the adverse effect that COI-based Ips phylogenies cannot be expanded to higher systematic categories without sequencing the outgroups (as they are not available in databases yet). Here we provide new primers for Ips that differ significantly from DNA sequences of Ips-associated wasps and nematodes and bind to a COI fragment that largely overlaps with the barcoding region proposed in the EPPO standard. Furthermore, using these primers we developed a quick PCR-based test for detecting Ips duplicatus, a quarantine pest currently emerging in many European countries.

Significant Mo mobility and isotope (δ98/95Mo) fractionation is induced during prograde metamorphism at present-day subduction zones. Depending on the redox conditions during early subduction and accompanied slab dehydration, isotopically heavy Mo is released towards the overlying mantle wedge, leaving behind a depleted, and isotopically light subducted slab. This isotopically light Mo signature has been detected in slab-melt influenced volcanic rocks and potentially will be traceable in ocean-island basalts, if their geochemical signatures are affected by previously subducted lithologies (i.e. slab and overlying sediments). Thus, the isotope composition of mantle plume-influenced volcanic rocks might reveal the nature of subducted and re-incorporated lithologies and possibly redox conditions during subduction.In this study, we present new Mo isotope data for South-Mid Atlantic Ridge basalts that partly interacted with the enriched Discovery and Shona mantle plumes. Isotopically heavier Mo isotope ratios (δ98/95Mo > ambient depleted mantle) are observed in samples tapping a more enriched mantle source. Furthermore, δ98/95Mo correlates with radiogenic isotopes (Sr, Nd, Hf) indicating recycling of a Proterozoic sedimentary components with a Mo isotopic composition that was not modified during and before subduction by Mo mobility under oxidising conditions. Rather, the new Mo isotope data supports and expands on previous stable Se and S isotope evidence that suggests the incorporation of subducted anoxic Proterozoic deep-sea sediments into the mantle of the South-Mid Atlantic Ridge basalts.

The first dramatic rise in atmospheric oxygen to concentrations above 10-5 present atmospheric level (PAL), known as the Great Oxidation Event (GOE), was initiated during the early Proterozoic Eon c. 2.43-2.32 billion years (Gyrs) ago [1,2]. Although atmospheric O2 concentrations are generally accepted to have remained below 1% PAL for at least 1.5 Gyrs following the GOE [3], high atmospheric O2 build up occurred during the Lomagundi carbon isotope excursion (LE) at the latest stage of the GOE [4]. The LE is the most pronounced and longest-lived carbon isotope excursion in Earth’s history that took place c. 2.22-2.06 Gyrs ago [4,5]. It reflects increased organic carbon (Corg) burial resulting from high primary productivity at the time of high phosphorous flux to the ocean associated with intense acidic chemical weathering of landmasses. However, mechanisms responsible for such high Corg sequestration are not yet fully resolved, nor has it been possible to precisely quantify the magnitude and expansion of oxygenation within the coeval atmosphere-ocean system.Here, we studied diagenetic concretions of pyrite and carbonate and their host black shales of the Francevillian Group, southeast Gabon, deposited during the LE. Light sulfur (δ34S ‰, VCDT) and carbon (δ13Ccarb ‰, VPDB) isotope ratios indicate that both pyrite and carbonate formed in sediments through microbial sulfate reduction and Corg remineralization, respectively. Selenium isotopic ratios (δ82/76Se ‰, NIST3149) of the pyrite concretions and their host shales are dominated by highly negative values as low as –3‰, which is strong evidence for partial reduction of selenium oxyanions (SeOx2-) in the sediment below an oxygenated seawater column. Collectively, the data suggests an oxygenated water column in the Francevillian Basin with a large SeOx2- reservoir that continuously resupplied these electron acceptors to the sediment and prevented their quantitative reduction. The studied black shales host putative, fossilized large colonial multicellular organisms that had the ability to laterally and vertically migrate within the sediments [6]. We propose that bioturbation by these organisms allowed an increased flux of electron acceptors (e.g., O2, NO3–, SeOx2-, SO4-) into the sediments and pushed the microbial sulfate reduction and methanogenesis zones downward. As a consequence, CH4 and H2S generated in these zones were re-oxidized in more oxic upper levels of the sediments, which prevented them from escaping to the water column. An increase in ecosystem complexity thus likely aided Corg sequestration to the sediments and O2 accumulation in the atmosphere-ocean system during the LE. [1] Bekker et al. (2004), Nature, 427, 117–120. [2] Holland (2006), Philos. Trans. R. Soc. B 361, 903–91. [3] Colwyn et al. (2014), Geobiology, DOI: 10.1111/gbi.12360. [4] Karhu and Holland (1996), Geology, 24, 867–870. [5] Bekker (2014), Encyclopedia of Astrobiology, Springer-Verlag, 1–6. [6] El Albani et al. (2019), Proc. Natl. Acad. Sci. USA, 116, 3431–3436.

Abstract Negatively charged tin clusters offer a broad range of decay products, as observed after electron-cluster interactions [S. König, M. Wolfram, S. Bandelow, G. Marx, L. Schweikhard, Eur. Phys. J. D 72, 153 (2018)]. To get further insight into their decay pathways, size and charge-state selected clusters Snn- and Snn2- were photo-excited at the ClusterTrap setup by 532 nm Nd:YAG laser pulses. For small mono-anionic precursor clusters containing up to n ≃ 45 atoms, Snn-7- and Snn-10- are observed as preferred ionic fragments. For bigger clusters a transition to neutral monomer evaporation was found. In the case of di-anionic precursors, preferred decay products are Sn10- and Snn-10-, indicating fission similar to the case of the group 14 neighbor element lead [S. König, A. Jankowski, G. Marx, L. Schweikhard, M. Wolfram, Phys. Rev. Lett. 120, 163001 (2018)]. Furthermore, doubly charged fragment clusters such as Snn-72- are observed, originating from break-off of neutral heptamers Sn7, a behavior which has not been observed previously for di-anionic clusters. Graphical abstract

Our understanding regarding the behaviour of the fluid mobile element Zn at destructive plate margins is limited. In particular the fractionation mechanisms and input-output mass-balance remains to be investigated due to implications for the spatio-temporal cycling of this vital and socio-economically relevant element. In this study, we investigate the Zn isotope systematics of subduction input provided by IODP samples from the SW Pacific in comparison to lavas from the central Tonga arc, addressed as a worldwide endmember in terms of pre-subduction mantle wedge depletion. With an improved analytical precision, we report subtle, yet resolvable Zn isotope variations between the central Tongan islands, with an overall statistically relevant variation of 0.05‰ (at ±0.014‰ 2SD). The signatures are all > 0.1‰ lighter than the subduction input at this site, suggesting a fractionation process during subduction. After careful extraction of the isotopic effect caused by mantle melting processes (using DMM δ66/64Zn JMC-Lyon provided by Sossi et al. (2018) and Wang et al. (2017) and melt extraction indices such as Sm/La, Zr/Nb, and Zn/La), a pronounced negative correlation is observed between the Zn isotopic composition of the lavas and key fluid indicators such as Ba/Th and Ce/Pb. Together with predictions from ab initio calculations and mixing models performed between Indian DMM and Rayleigh dehydration of the subducting slab, we attribute the remaining, subtle Zn isotope variations to additions by Cl-rich fluids to the individual mantle wedges. A maximum of 5% chlorine-fluid contribution is suggested for the magmatic source of Tofua, whereas smaller proportions are estimated for Kao, Late and Ata. Overall, this study sheds new light on Zn fractionation mechanisms in sediment-poor subduction zones. Implications for the long-term Zn recycling will be addressed in this presentation.References:Sossi, P.A., Nebel, O., O’Neill, H.S.C., Moynier, F., 2018. Zinc isotope composition of the Earth and its behaviour during planetary accretion. Chemical Geology 447, 73-84.Wang, Z.-Z., Liu, S.-A., Liu, J., Huang, J., Xiao, Y., Chu, Z.-Y., Zhao, X.-M., Tang, L., 2017. Zinc isotope fractionation during mantle melting and constraints on the composition of Earth’s upper mantle. Geochimica et Cosmochimica Acta 198, 151- 167.

Element transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter. The precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains. The transfer of selenium to solids likely occurred through a similar pathway, allowing the formation of iron selenides concomitantly with sulfides. The formation rate of sulfide however remains difficult to assess. Here we investigate whether the Se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system. We present high precision Se concentration and δ 82 / 78 Se data for 23 chondrites as well as the first δ 74 / 78 Se , δ 76 / 78 Se and δ 77 / 78 Se data for a sub-set of seven chondrites. We combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites. Our Se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites. Our overall average δ 82 / 78 Se value for chondrites is − 0.21 ± 0.43 ‰ ( n = 23 , 2 s.d.), or − 0.14 ± 0.21 ‰ after exclusion of three weathered chondrites ( n = 20 , 2 s.d.). These average values are within uncertainty indistinguishable from a previously published estimate. For the first time however, we resolve distinct δ 82 / 78 Se between ordinary ( − 0.14 ± 0.07 ‰ , n = 9 , 2 s.d.), enstatite ( − 0.27 ± 0.05 ‰ , n = 3 , 2 s.d.) and CI carbonaceous chondrites ( − 0.01 ± 0.06 ‰ , n = 2 , 2 s.d.). We also resolve a Se isotopic variability among CM carbonaceous chondrites. In addition, we report on δ 74 / 78 Se , δ 76 / 78 Se and δ 77 / 78 Se values determined for 7 chondrites. Our data allow evaluating the mass dependency of the δ 82 / 78 Se variations. Mass-independent deficits ro excesses of 74Se, 76Se and 77Se are calculated relative to the observed 82Se/78Se ratios, and were observed negligible. This rules out poor mixing of nucleosynthetic components to account for the δ 82 / 78 Se variability and implies that the mass dependent Se isotopic variations were produced in a once-homogeneous disk. The mass-dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high H2S–H2Se contents in the region of enstatite chondrite formation. Experimental studies showed that high H2S contents favor the formation of compact sulfide layers around metallic grains. This decreases the reactive surface, which tends to inhibit the continuation of the sulfidation reaction. Under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light S and Se isotopes in solids; This hypothesis provides an explanation for our Se isotope as well as for previously published S isotope data. On the other hand, high δ 82 / 78 Se values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration, or could reflect the contribution of ices carrying photo-processed Se from the outer solar system.

Polyanionic lead clusters have been produced by electron attachment in a Penning trap. The smallest dianionic and trianionic lead clusters observed were of size n = 28 and n = 69, respectively and the appearance sizes following the definition of Martinez et al. (2015) are n = 39 and n = 80, respectively. In addition, and in contrast to previous measurements on clusters of several other metals, decay reactions are observed in the cluster size range of n = 14–49. The decay products are similar, but not identical, to those reported for the photodissociation of Pb n − .

The isotopic signature of the chalcophile, redox-sensitive and moderately volatile element Se in geological materials may offer valuable new insights into the origin and evolution of volatiles in planetary systems. Here, we report a new method for Se isotope determination of low Se containing samples relevant to the Earth's mantle reservoir. We present a method that combines a double spike and hydride generation sample introduction system with a ThermoFisher Scientific® NeptunePlus™ MC-ICP-MS. The measurement routine takes advantage of methane injection in the instrument source during measurement, resulting in enhanced Se signals and suppression of polyatomic interferences. Purification of Se from natural samples was simplified by employing conventional ion exchange chromatography procedures. An external reproducibility of 0.15‰ (2σ) on δ82/76Se values for measurements performed on natural samples with Se abundances down to ~5 ng is obtained. We demonstrate that our technique allows the determination of Se isotope signatures of low Se-bearing geological materials with complex matrices such as mafic igneous rocks, which is essential to extend the Se isotopic investigation to Se-depleted planetary reservoirs such as the Earth's mantle.

Oceanic lavas erupting today trace ocean-atmosphere oxygenation in Earth’s middle ages., Oxygenation of Earth’s oceans and atmosphere through time has consequences for subducted surface signatures that are now stored in the mantle. Here, we report significant mass-dependent selenium isotope variations in modern hot spot–influenced oceanic lavas. These variations are correlated with tracers of mantle source enrichment, which can only be explained by incorporation of abyssal pelagic sediments subducted from a redox-stratified mid-Proterozoic ocean. Selenium geochemical signatures of these sediments have mostly been preserved during long-term recycling and may therefore complement the global surface sediment record as ancient oxygen archives. Combined deep mantle and surface perspectives, together with emerging models for atmospheric oxygen based on selenium systematics, further imply a significantly oxygenated ocean-atmosphere system throughout the mid-Proterozoic.

Molybdenum isotopes have emerged as novel tracers for high-temperature igneous and metamorphic processes. The debate remains to what extent different subducted slab lithologies, such as oceanic crust and marine sediments, contribute to the Mo isotope signature of arc magmas and, hence, exert different controls on the terrestrial Mo cycle. Here we investigate Mo isotope systematics from input to output at the Tongan subduction zone: Arc lavas from different Tongan islands, pelagic sediments and altered oceanic crust (AOC) samples from DSDP site 595/596 on the subducting Pacific plate. For complementary insights into the fate of Mo and its isotopic signatures during prograde subduction metamorphism, we also present data of metasediments and variably altered AOC-type eclogites from the Zermatt-Saas ophiolite, Switzerland and Italy, and the Schistes Lustres Complex in Alpine Corsica. Manganese oxide-rich pelagic sediments from DSDP site 595/596 show variable, depth-dependent Mo/Mn ratios and Mo isotope compositions controlled by diagenetic reactions. As subducted equivalents, Mn-rich eclogitic metapelites display lower Mo contents and δ98/95Mo ratios compared to their non-subducted protolith. This indicates prominent loss of Mo along with isotope fractionation during early subduction metamorphism. In comparison to unaltered MORB, low temperature seafloor alteration has shifted Mo/Ce and δ98/95Mo in studied AOC samples towards lower ratios, in the range of most mafic eclogites published so far. However, some mafic eclogites show even lower Mo/Ce and δ98/95Mo ratios compared to AOC, likely due to fluid-related Mo loss upon early subduction and preferential incorporation of light Mo into residual rutile. Our data document a prominent loss of isotopically heavy Mo before and upon early subduction metamorphism at shallow depths in the forearc region. Moreover, when prograde rutile crystallizes at ~30 km depth, it fixes the largest fraction of Mo in the subducting material. This creates an “arc Mo-conundrum” as devolatization of the slab at subarc depths is not able to account for the fluid-mobile Mo source responsible for observed higher Mo/Ce and δ98/95Mo in Tongan arc lavas compared to the mantle. As an alternative scenario, Mo mobilization by slab-derived aqueous fluids during the early stages of subduction into the forearc mantle produces serpentinites enriched in Mo with a possible heavy Mo isotopic signature. Mechanical transport and devolatization of forearc serpentinites at subarc regions is a plausible alternative recycling process accounting for the observed Mo systematics in Tongan arc lavas. This is supported by positive covariations of Mo/Ce and δ98/95Mo with elements such as As, Sb, and Cs, which are thought to be mostly released from the subducting material during early stages of subduction. We propose that a multi-stage recycling of metasomatized forearc mantle can be an important process in recycling of Mo and possibly other elements.

A series of multi-reflection time-of-flight (MR-ToF) spectra is recorded with increasing ion flight times and added up to a single transient. It shows periodic ToF-signal trains for each ion species revolving between the MR-ToF analyzer’s mirrors. This is used to perform a “comb-sampling” evaluation previously devised for analysis of capacitive-pickup signals (Greenwood et al., Rev. Sci. Instrum. 82 (2011), 043103). The recording and evaluation focuses on simultaneously measuring the full range of trapped ions for wide-band mass spectrometry. The comb-sampling technique is revisited for the present transients, as it is the first time it is used for comparatively background-free single-ion-counting data.

The catalytic activity of the allosteric enzyme pyruvate decarboxylase from yeast is strictly controlled by its own substrate pyruvate via covalent binding at a separate regulatory site. Kinetic studies, chemical modifications, cross-linking, small-angle X-ray scattering, and crystal structure analyses have led to a detailed understanding of the substrate activation mechanism at an atomic level with C221 as the core moiety of the regulatory site. To characterize the individual role of the residues adjacent to C221, we generated variants H92F, H225F, H310F, A287G, S311A, and C221A/C222A. The integrity of the protein structure of the variants was established by small-angle X-ray scattering measurements. The analyses of both steady state and transient kinetic data allowed the identification of the individual roles of the exchanged side chains during allosteric enzyme activation. In each case, the kinetic pattern of activation was modulated but not completely abolished. Despite the crucial role of C221, the covalent binding of pyruvate is not obligate for enzyme activation but is a requirement for a kinetically efficient transition from the inactive to the active state. Moreover, only one of the three histidines guiding the activator molecule to the binding pocket, H310, specifically interacts with C221. H310 stabilizes the thiolate form of C221, ensuring a rapid nucleophilic attack of the thiolate sulfur on C2 of the regulatory pyruvate, thus forming a regulatory dyad. The influence of the other two histidines is less pronounced. Substrate activation is slightly weakened for A287G and significantly retarded for S311A.

Fragmentation of cationic (Pbn+, n = 6–41) and anionic (Pbn–, n = 9–56) lead clusters by photoabsorption at 532 nm is investigated. For small (Pbn+, n 24, Pbn–, n > 30) lead clusters the fragmentation is dominated by evaporation of monomers, but at the intermediate sizes the main fragmentation pathways seem to include the breaking off of a neutral heptamer, Pb7. Under the same conditions as for all other clusters being investigated, Pb14+ shows a peculiar behavior, as no decay products are detected.

This study presents Mo isotope data for arc lavas from different subduction zones that range between δ 98 / 95 Mo = − 0.72 and + 0.07 ‰ . Heaviest isotope values are observed for the most slab fluid dominated samples. Isotopically lighter signatures are related to increasing relevance of terrigenous sediment subduction and sediment melt components. Our observation complements previous conclusions that an isotopically heavy Mo fluid flux likely mirrors selective incorporation of isotopically light Mo in secondary minerals within the subducting slab. Analogue to this interpretation, low δ 98 / 95 Mo flux that coincides with terrigenous sediment subduction and sediment melting cannot be simply related to a recycled input signature. Instead, breakdown of the controlling secondary minerals during sediment melting may release the light component and lead to decreasing δ 98 / 95 Mo influx into subarc mantle sources. The natural range between slab dehydration and hydrous sediment melting may thus cause a large spread of δ 98 / 95 Mo in global subduction zone magmas.

The origin of Earth's volatiles has been attributed to a late addition of meteoritic material after core-mantle differentiation. The nature and consequences of this 'late veneer' are debated, but may be traced by isotopes of the highly siderophile, or iron-loving, and volatile element selenium. Here we present high-precision selenium isotope data for mantle peridotites, from double spike and hydride generation multi-collector inductively coupled plasma mass spectrometry. These data indicate that the selenium isotopic composition of peridotites is unaffected by petrological processes, such as melt depletion and melt-rock reaction, and thus a narrow range is preserved that is representative of the silicate Earth. We show that selenium isotopes record a signature of late accretion after core formation and that this signature overlaps only with that of the CI-type carbonaceous chondrites. We conclude that these isotopic constraints indicate the late veneer originated from the outer Solar System and was of lower mass than previously estimated. Thus, we suggest a late and highly concentrated delivery of volatiles enabled Earth to become habitable.

This study presents the first combined S and Se isotope investigation of sulfide suited to explore differences in fractionation between these two redox sensitive isotope systematics as recorded in the same mineral. A case study of Cretaceous Navajun pyrite from the Mesozoic Cameros Basin, Spain, with known petrogenesis and geological context shows systematic decoupling at the microscale: Variable S isotope values within the analyzed pyrite coincide with rather constant Se isotope values and vice versa. These signatures were not generated during pyrite growth but record previous redox induced fractionations in fluids that each contributed both elements from two sources. It is likely that both S and Se isotope fractionation occurred during strong reduction from one fully oxidized source whereas only S but no Se isotope fractionation occurred during minor reduction following sulfide dissolution via H2O from another source. Subsequent mixing of these two H2S-H2Se fluids at different elemental S-Se ratios during incorporation into the pyrite can then explain the S-Se isotope variations in the investigated specimen. These inferences are in accordance with a larger range in the redox potential Eh of Se relative to S, resulting in coupled or decoupled Se and S isotope fractionation depending on the oxygen fugacity during the reduction process. If extended to other sulfides of diverse origin, for a given pH, combined Se and S isotope studies may allow to investigate the magnitude of redox variations and place more robust constraints on minimum and maximum oxygen concentrations in the source. We therefore suggest combined S-Se isotope analyses in sulfide as a new powerful proxy for studying Earth’s redox evolution beyond the bulk rock scale.

The selenium stable isotope system emerges as a new potential tracer of volatile origin and evolution of the terrestrial planets. Accurate determination of the mantle Se isotope composition requires an assessment of Se isotopic behavior in magmatic processes and potential variations across all mantle reservoirs. Here we report the first high-precision Se isotope and Se–Te abundance data for a suite of basaltic glasses from the Pacific–Antarctic ridge. These MORBs display a narrow range in δ82/76Se values (deviation of 82Se/76Se relative to NIST SRM 3149) between −0.30 ± 0.09‰ and −0.05 ± 0.09‰, with an average of −0.16 ± 0.13‰ (2 s.d., n = 27). We quantify the main processes relevant to MORB petrogenesis in order to better understand the Se–Te elemental behavior in the mantle and investigate if these are systematically related to Se isotope variations. We show that both Se isotopes and S–Se–Te abundances of MORB melts remain unaffected by assimilation of high-temperature hydrothermal fluids and sulfides, whereas the latter has been shown to overprint the 34S/32S ratios. MORB differentiation involving sulfide segregation (sulfide liquid and monosulfide solid solution) significantly fractionates Se and Te (Se/Te ratio ∼ 45–190), with no systematic Se isotope variation. The Se–Te contents of the primary MORB melt corrected for magmatic differentiation can be successfully reproduced by near-fractional decompression melting of a mantle with 170–200 μg g−1 S (as sulfide liquid), which has either (1) “fertile lherzolite-like” Se and Te contents (80 ± 17 and 11 ± 1.7 ng g−1, respectively; 1 s.d.) or (2) distinctly lower Se (49 ± 11 ng g−1) and Te (3.5 ± 1.3 ng g−1) contents depending on the choice of experimental partition coefficients published by different studies. Regardless, our model shows that Se-Te systematics of “fertile” lithospheric peridotites preserve little primary melt depletion signatures and reflect significant, if not complete, metasomatic overprinting. Finally, based on the observed negligible Se isotopic fractionation between sulfide phase and silicate melt, we suggest that MORBs preserve their mantle source isotopic signature (δ82/76Se = −0.16 ± 0.13‰). Our MORB average is similar within uncertainty to chondritic values but significantly lighter than previously published δ82/76Se data for basalts from a variety of geodynamic settings. The subtle but significant Se isotope variation observed within the investigated MORB suite (up to ∼0.25‰) and between other mantle samples analyzed so far may reflect intrinsic source heterogeneity and potential isotopic differences across various mantle reservoirs.

Investigating the isotope systematics and behavior of selenium in subduction zones provides valuable insights into mechanisms that contribute to chalcophile and moderately volatile element distribution between terrestrial reservoirs. In this study, we present high-precision Se isotope and Se–Te elemental data on subduction zone lavas from the Mariana arc system. Our results indicate that Se–Te concentrations are unaffected by submarine degassing but are affected by magmatic differentiation. In contrast, Se isotopes of submarine lavas are unaffected by both magmatic differentiation and degassing and thus may preserve their magmatic source signature. Compared to the average Se isotope composition previously obtained for mantle-derived samples (δ82/76Se = 0.23 ± 0.12‰, 2 s.d., n = 5), suitable to represent the Mariana pre-subduction wedge, Mariana lavas show a larger overall range (δ82/76Se from 0.03 to −0.33‰, n = 21) with a clear tendency towards lighter Se isotope compositions. The variable Se isotope signatures within the Mariana suite can further be attributed to different slab-derived fluid and melt-like subduction components. This provides evidence for a significant role of subduction recycling of hydrothermal sulfide-containing altered oceanic crust and pelagic sediments with possible implications for the Se isotope evolution of the crust-mantle system throughout geological time.

Recent studies report a large Mo isotope variability of up to 1‰ (expressed in δ98/95MoNIST3134) in convergent margin lavas. These isotopic variations have been associated with subduction zone processes and ultimately may account for heavy and variable isotope signatures in evolved continental crust. Arc lavas show both lighter and heavier Mo isotopic values when compared to the chondritic average (δ98/95MoNIST3134 −0.16 ± 0.02‰), with a concentration weighted mean isotopic composition (δ98/95MoNIST3134 +0.03‰) distinctly heavier than that of the mantle (δ98/95MoNIST3134~−0.21 to −0.16‰). The absence of isotopic fractionation during tholeiitic igneous differentiation indicates that heavy Mo isotope signatures in convergent margin rocks are intrinsic to subduction zone processes, caused either by recycling of subducted components, by Mo isotope fractionation during magmatic differentiation, or by a combination thereof. In order to gain a more detailed understanding of the Mo isotope variability in arc lavas, we have studied Mo isotopes and concentrations in calc-alkaline lavas sampled along the Banda Arc in Indonesia, an intra-oceanic subduction zone well known for variable contributions of subducting continental meterial. Banda Arc lavas exhibit Mo isotopic compositions covering a large range from −0.48 to +0.24‰ in δ98/95MoNIST3134. We find that, combined with published data from other subduction zones, the majority of arc data are isotopically heavier compared to its presumed mantle wedge source or mid-ocean-ridge basalts. Furthermore, arc lava Mo isotope signatures show an apparent covariation between indices of amphibole-clinopyroxene fractionation from the melt. Generally, heavier Mo isotopic signatures are associated with higher degrees of REE fractionation expressed as λ1, λ2, and Dy*/Dy, high Ca/Al, and higher Sc contents. These observations can be best explained with an open system magma reservoir where fractional crystallisation, recharge and eruption are tightly linked. Notable exceptions in the Banda region are four samples with isotopically light Mo. Three of these isotopically light lavas indicate the assimilation of an isotopically light Mo reservoir with heavy δ18O and radiogenic 87Sr/86Sr-206Pb/204Pb, tentatively identified as lower arc crust. Together, our data demonstrate, in line with previous findings, that magmatic processes modify the Mo isotopic composition in arc lavas, thus adding complexity to the Mo isotope systematics inherent to subduction zones.

The composition of the Earth’s upper mantle is a function of melt depletion and subsequent metasomatism; the latter obscuring many of the key characteristics of the former, and potentially making predictions of Primitive Upper Mantle (PUM) composition problematic. To date, estimates of PUM abundances of highly siderophile element (HSE = platinum group elements (PGE) and Re) and the strongly chalcophile elements Se and Te, have been the subject of less scrutiny than the lithophile elements. Critically, estimates of HSE and strongly chalcophile element abundances in PUM may have been derived by including a large number of metasomatized and refertilized samples whose HSE and chalcophile element abundances may not be representative of melt depletion alone. Unravelling the effects of metasomatism on the S–Se–Te–HSE abundances in peridotite xenoliths from Kilbourne Hole, New Mexico, USA, potentially provides valuable insights into the abundances of HSE and strongly chalcophile element abundances in PUM. Superimposed upon the effects of melt depletion is the addition of metasomatic sulfide in approximately half of the xenoliths from this study, while the remaining half have lost sulfide to a late S-undersaturated melt. Despite these observations, the Kilbourne Hole peridotite xenoliths have HSE systematics that are, in general, indistinguishable from orogenic peridotites and peridotite xenoliths used for determination of PUM HSE abundances. This study represents the first instance where Se-Te-HSE systematics in peridotite xenoliths are scrutinized in detail in order to test their usefulness for PUM estimates. Despite earlier studies attesting to the relative immobility of Se during supergene weathering, low S, Se, Os and Se/Te in peridotite xenoliths suggests that Se may be more mobile than originally thought, and for this reason, peridotite xenoliths may not be suitable for making predictions of the abundance of these elements in PUM. Removal of Se, in turn, lowers the Se/Te in basalt-borne xenolithic peridotites to subchondritic values. This is in contrast to what has been recently reported in kimberlite-borne peridotite xenoliths. Moreover, Te added to melt depleted peridotite in metasomatic sulfide is more difficult to remove in a S-undersaturated melt than the HSE and Se due to the generation of micron-scale tellurides. The effects of these processes in orogenic peridotites and xenoliths, from which PUM abundances have been calculated, require further scrutiny before unequivocal Se-Te-Re-PGE values for PUM can be derived.

The Re–Os isotopic system is the geochronometer of choice to constrain the timing of lithospheric mantle root formation and reconstruct the evolution of Earth’s dynamics from the “mantle” perspective. In order to constrain the effects of metasomatic processes on the Re–Os isotopic system, eleven peridotites from the Letlhakane kimberlite pipe were investigated for whole rock major and trace elements, highly siderophile elements (HSE), Se, Te and 187Os/188Os signatures. These spinel peridotites (SP), garnet peridotites (GP), garnet-phlogopite peridotites (GPP) and phlogopite peridotites (PP) experienced cryptic metasomatism and the GP–GPP–PP additionally constitute a sequence of increasing modal metasomatism. The cryptically metasomatised SP appear devoid of base metal sulphides (BMS) and show suprachondritic Se/Te ratios (15–40) and extremely Pd- and Pt-depleted HSE patterns. These features are characteristic of high-degree partial melting residues. Their 187Os/188Os signatures are thus considered to be inherited from the partial melting event. This implies a Neoarchean (2.5–2.8 Ga, TRD eruption) stabilisation of the Letlhakane mantle root and supports the Letlhakane mantle root being a westerly extension of the Zimbabwe cratonic root. The modally metasomatised peridotites contain BMS whose abundance significantly increases from the GPP to the GP and PP. The BMS-poor GPP are only slightly richer in Pt and Pd than the BMS-free SP but have similarly high Se/Te ratios. The BMS-rich GP and PP exhibit significant enrichments in Pt, Pd, Se, Te resulting in HSE–Se–Te signatures similar to that of the Primitive Upper Mantle (PUM). Addition of 0.001–0.05 wt.% metasomatic BMS ± PGM (platinum group minerals, i.e., Pt-tellurides) to highly refractory residues, such as the Letlhakane SP, reproduce well the HSE–Se–Te systematics observed in the BMS-poor and BMS-rich modally metasomatised peridotites. In the GPP, the negligible addition of metasomatic BMS ± PGM did not disturb the 187Os/188Os signatures, indicating TRD eruption ages identical with those of the SP. By contrast, the PP and GP, which suffered significant BMS ± PGM addition, have 187Os/188Os considerably shifted toward more radiogenic values. As a result, unrealistically young TRD eruption ages are obtained that cannot be used to constrain the time frame of the stabilisation of the cratonic roots and the mechanisms of craton formation. The Se–Te and incompatible HSE (i.e., Pt, Pd) are powerful geochemical tools to assess the robustness of the Re–Os isotopic system in mantle peridotites. Specifically, Se/Te and Pd/Ir ratios provide complementary insights into the complex metasomatic history of mantle peridotites. The Se/Te ratio is very sensitive to Os-free PGM metasomatism producing highly variable Se/Te >15 at low, relatively constant Pd/Ir 0.4), at constant but low Se/Te