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The mantle is Earth’s largest silicate reservoir and one of its fundamental characteristics is the chemical and isotopic heterogeneity that extends down to the mineral scale. These various-sized mantle domains reflect different proportions of multiple, superimposed depletion and enrichment events that affected the mantle in time and space. As such, each of these domains may therefore retain different and potentially unique information regarding the extent of mantle depletion as well as the role and nature of enrichment by crustal recycling. Owing to the reaction with other surface reservoirs before subduction, mantle domains that were enriched by recycled crust may additionally record ancient ocean-atmospheric conditions. The sustainable mantle thus maintains a certain rate of exchange between Earth’s interior and exterior, stores compositional heterogeneities that relate to this exchange and partly mirror global conditions of ancient Earth’s surface. This session welcomes contributions that address different scales, features and implications of the chemical and isotopic heterogeneity of the mantle, its role for geological resources and the perspective of mantle and mantle-derived components to elucidate ancient surface conditions that shaped a habitable planet over time.

Molybdenum isotope ratios (δ98/95Mo) of marine sediments constitute an important tracer for paleoredox reconstructions of the ancient ocean. Due to its redox-sensitivity, significant mass-dependent Mo isotope fractionation is induced in present-day low temperature environments leading to distinct Mo concentrations and isotope compositions in different marine lithologies. Subduction and recycling of such fractionated material can thus be potentially traced in arc magmas. Indeed, Mo isotope variations are observed in mafic arc lavas that are attributed to reflect recycled crustal components, but open questions remain to what extent different subducted lithologies contribute to the Mo isotope signature of arc magmas. We present a comprehensive Mo isotope dataset covering input to output at the Tongan subduction zone, together with exhumed eclogite-facies oceanic crust and sediments from the Western Alps and Alpine Corsica. Pelagic Mn-rich metapelites and MORB-type eclogites reveal that Mo is largely lost during early subduction metamorphism. Moreover, rutile hosts most of the remaining isotopically light Mo in the slab at higher metamorphic degrees where it remains fixed during slab-dehydration processes at subarc depths. Thus, direct recycling of this fractionated material cannot account for the observed positive covariations of Mo/Ce and δ98/95Mo with fluid indices (e.g., Ba/Th) in Tongan arc lavas. We propose that Mo systematics in Tongan arc lavas are the result of shallow fluid-induced Mo mobilization and forearc mantle serpentinization during early stages of subduction. Subsequent mechanical transport and devolatiziation of this metasomatized forearc mantle material towards subarc regions is a plausible alternative process to recycle Mo and other metals.

Eine nicht-invasive Diagnose holzzerstörender Schadorganismen ist von großer Bedeutung um Eingriffe in kostbare Holzprodukte und lebende Bäume auf ein Minimum zu beschränken. Hier stellen wir zwei ganz unterschied­liche Methoden vor, eine physikalische und eine molekularbiologische, die einen schonenden Nachweis von Insekten­larven im Holz ermöglichen. Beide Methoden sind bereits zum Teil erfolgreich zur Analyse des Asiatischen Laubholzbockkäfers (Anoplophora glabripennis, ALB) eingesetzt worden und eignen sich als Frühwarnsysteme in der Bekämpfung von Quarantäneschadinsekten., Journal für Kulturpflanzen, Bd. 72 Nr. 9 (2020)

Zwei Organismengruppen gehören zu den besonders wider­standsfähigen und ertragsmindernden Schadorganismen an der Kartoffel: (1) Zystennematoden der Gattung Globodera, wie der Weiße (G. pallida) und der Goldene Kartoffelzystennematode (G. rostochiensis), sowie (2) Synchytrium endobioticum, der Erreger des Kartoffelkrebses. Ihr Status als geregelte, schwer kontrollierbare Unions-Quarantäneschadorganismen ist ihren äußerst robusten Dauerstadien (Zysten bzw. Wintersporangien) zuzuschreiben sowie dem Auftreten einzelner Populationen mit hoher Virulenz. Ihre Verbreitung ist daher unbedingt zu vermeiden. Ein hohes Risiko einer Verschleppung bergen die jährlich mehreren hunderttausend Tonnen bei der Kartoffelverarbeitung anfallenden Resterden mit nicht zuzuordnender Herkunft. Um eine unbedenk­liche Rückführung der Erden auf Ackerflächen zu ermöglichen, wird im Projekt GlobRISK die Optimierung bzw. Ergänzung phytosanitärer Verfahren zur Dekontamina­tion der Resterden von Kartoffelzystennematoden vorangetrieben. Im Drittmittelprojekt INNOKA beabsichtigen wir, innovative Nachweisverfahren für S. endobioticum aus Resterden zu entwickeln und somit Grundlagen für weitere Forschungsarbeiten zur Dekontamination S. endo­bioticum belasteter Resterden zu schaffen., Journal für Kulturpflanzen, Bd. 72 Nr. 8 (2020): Themenheft Pflanzengesundheit

Detailed experimental methodology, table of primers, and additional data/figures

International audience; Transition metal stable isotope systematics of terrestrial igneous reservoirs may help to better understand the recycling behavior of these elements through Earth’s interior. However, isotopic variations of ‘heavy’ elements caused by magmatic processes are subtle and difficult to resolve. Within this scope we have improved our precision on MC-ICP-MS Zn isotope measurements to < ±0.02 ‰ on 66/64Zn for single runs (2SD, multiple digestions of reference materials) using a 64Zn-67Zn double spike. With this step forward we investigated the systematics governing the Zn transport and isotope fractionation at subduction zones. For this study, the focus was on volcanic rocks from the Tongan subduction zone - where the pre-subduction mantle wedge composition (Sm/La>1) is amongst the most depleted for worldwide arc settings. Additional analyses of samples from IODP site 595 provide an insight to the input to this subduction factory. Primitive lavas (basalts and basaltic andesites; MgO>5 %) display subtle, yet resolvable Zn isotopic variations between the central Tonga islands Tofua, Late, Kao and Ata, as well as differences to 66/64Zn values of MORB and the subduction input. In addition, Zn-isotopes and Zn/La are correlated with fluid indices such as Ba/Th, suggesting potential mobilization of Zn from the subducting plate and/or overlying sediments into the mantle wedge prior to melting. Yet, negative correlations observed between Zn-isotopes and Sm/La of the lavas point towards a link between Zn-isotopic composition and relative mantle depletion beneath individual volcanic edifices. Concomitant occurrence of these features complicates a straighforward deconvolution of the Zn-isotope variations seen in arc lavas and fluid-iduced transport cannot be simply ruled out. In this presentation we will discuss and expand the Zn-isotope fractionation problematic in subduction settings aiming to address the following: i) what are the main mechanisms triggering Zn-isotope fractionation and what is the result of their combined effects? ii) can we identify and possibly quantify the subduction component from the Zn-isotope composition of the arc lavas? iii) what are the long-term effects of Zn recycling into the mantle on the evolution of the terestrial Zn signal?

Selenium (Se) is an important micronutrient but also a strong toxin with a narrow tolerance range for many organisms. As such, a globally heterogeneous Se distribution in soils is responsible for various disease patterns (i.e. Se excess and deficiency) and environmental problems, whereby plants play a key role for the Se entrance into the biosphere. Selenium isotope variations were proved to be a powerful tracer for redox processes and are therefore promising for the exploration of the species dependent Se metabolism in plants and the Se cycling within the Critical Zone. Plant cultivation setups enable systematic controlled investigations, but samples derived from them-plant tissue and phytoagar-are particularly challenging and require specific preparation and purification steps to ensure precise and valid Se isotope analytics performed with HG-MC-ICP-MS. In this study, different methods for the entire process from solid tissue preparation to Se isotope measurements were tested, optimized and validated. A particular microwave digestion procedure for plant tissue and a vacuum filtration method for phytoagar led to full Se recoveries, whereby unfavorable organic residues were reduced to a minimum. Three purification methods predominantly described in the literature were systematically tested with pure Se solution, high concentrated multi-element standard solution as well as plant and phytoagar as target matrices. All these methods efficiently remove critical matrix elements, but differ in Se recovery and organic residues. Validation tests doping Se-free plant material and phytoagar with a reference material of known Se isotope composition revealed the high impact of organic residues on the accuracy of MC-ICP-MS measurements. Only the purification method with no detectable organic residues, hydride generation and trapping, results in valid mass bias correction for plant samples with an average deviation to true δ82/76Se values of 0.2 ‰ and a reproducibility (2 SD) of ± 0.2 ‰. For phytoagar this test yields a higher deviation of 1.1 ‰ from the true value and a 2 SD of ± 0.1 ‰. The application of the developed methods to cultivated plants shows sufficient accuracy and precision and is a promising approach to resolve plant internal Se isotope fractionations, for which respective δ82/76Se values of +2.3 to +3.5 ‰ for selenate and +1.2 to +1.9 ‰ for selenite were obtained.