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In situ Ge/Si and d30Si determination in phytoliths - advancing laser ablation ICP-MS techniques to analyse novel biogeochemical weathering archives

English title In situ Ge/Si and d30Si determination in phytoliths - advancing laser ablation ICP-MS techniques to analyse novel biogeochemical weathering archives
Applicant Frick Daniel
Number 168836
Funding scheme Early Postdoc.Mobility
Research institution Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum GFZ
Institution of higher education Institution abroad - IACH
Main discipline Inorganic Chemistry
Start/End 01.11.2016 - 30.04.2018
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All Disciplines (2)

Discipline
Inorganic Chemistry
Geochemistry

Keywords (6)

LA-ICP-MS; metal stable isotope fractionation; germanium silicon ratio; silicate weathering; phytoliths; fs-LASS-MC-ICP-MS

Lay Summary (German)

Lead
Die abiotische und biotische Verwitterung von Silikatmineralien in der Erdkruste beeinflusst den CO2 Gehalt in der Erdatmosphäre. Es ist deshalb von grosser Bedeutung, den Kreislauf von Silizium zu quantifizieren, sowie die Veränderungen in den Massenflüssen in geologischen Zeiträumen zu bestimmen. Hierfür werden stabile Metallisotope eingesetzt. Für die Verwitterung sind dies insbesondere Siliziumisotopenverhältnisse (d30Si) und das Ge/Si Verhältnis. Da jedoch nicht alle Kompartimente über geologische Zeiträume erhalten bleiben, werden die Verhältnisse auch über Proxys bestimmt. Hierfür eignen sich Phytolithe, mikroskopisch kleine, sehr stabile SiO2-Kristalle, welche von Pflanzen gebildet werden. Bisher fehlen jedoch analytische Routinen, um die Isotopen- und Elementverhältnisse einzelner Phytolithe zu bestimmen.
Lay summary

Inhalt und Ziel des Forschungsprojektes
Die Forschungsziele sind die (i) Entwicklung und Verwendung einer analytischen Routine zur Charakterisierung einzelner Phytolithe und (ii) experimentell die Fraktionierung von δ30Si sowie des Ge/Si Verhältnisses in Pflanzen zu bestimmen. Aufgrund der geringen Grösse und Masse von Phytolithe kommen für die analytische Routine nur in situ Methoden, wie zum Beispiel Laser Ablation induktiv gekoppeltes Plasma Massenspektrometrie, in Frage.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojektes
Diese analytische Entwicklung eröffnet ein unergründetes Verwitterungsarchiv, um vergangene Umweltbedingungen auf der Erde zu erforschen. Die analytische Routine, sowie die aus diesem Projekt gewonnen Informationen zur Fraktionierung von Isotopen- als auch Elementverhältnissen während des Wachstums von Pflanzen, wird es Geochemikern ermöglichen, vergangene Massenflüsse durch das Ökosystem zu erkunden und daraus Voraussagen über den zukünftigen Klimawandel zu treffen.

Direct link to Lay Summary Last update: 16.08.2016

Responsible applicant and co-applicants

Publications

Publication
Laser Ablation In Situ Silicon Stable Isotope Analysis of Phytoliths
Frick Daniel A, Schuessler Jan A, Sommer Michael, von Blanckenburg Friedhelm (2018), Laser Ablation In Situ Silicon Stable Isotope Analysis of Phytoliths, in Geostandards and Geoanalytical Research, 12243.

Datasets

Data supplement to: Laser ablation in situ silicon stable isotope analysis of phytoliths

Author Frick, Daniel A.; Schuessler, Jan A.; Sommer, Michael; von Blanckenburg, Friedhelm
Persistent Identifier (PID) 0000-0002-8530-3064
Repository GFZ Data Services
Abstract
Silicon is a beneficial element for many plants, and is deposited in plant tissue as amorphous bio-opal (phytoliths). The biochemical processes of uptake and precipitation induce isotope fractionation: the mass-dependent shift in the relative abundances of the stable isotopes of silicon. At the bulk scale, the silicon isotope composition reported as δ30Si span from -2 to +6 ‰. To further constrain these variations, at the scale of individual phytolith fragments we applied in situ femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS) to a set of 7 natural phytolith samples.Two phytoliths samples (Norway spruce Picea abies and European beech Fagus sylvatica L.) were extracted from the organic-rich topsoil horizon (O) of two studies sites in Germany (Beerenbusch, close to village Rheinsberg and Wildmooswald, in the southern Black Forest). The other five phytolith samples (bushgrass Calamagrostis epigejos, common reed Phragmites australis, common horsetail Equisetum arvense, annual and perennial rough horsetail Equisetum hyemale) were separated from plant materials.The individual phytolith fragments were analysed by fsLA-MC-ICP-MS and Si isotope results are reported in the δ-notation (delta) as permil deviation relative to NIST SRM610, which is isotopically indistinguishable from the reference material NBS28 (quartz NIST SRM8546 alias NBS28, δ29Si ≡ 0 and δ30Si ≡ 0). Raw data processing and background corrections were made according to the protocol described in Schuessler and von Blanckenburg (2014) that also involves application of several data rejection/acceptance criteria. Of these, the most important ones are that A) only 30/28Si and 29/28Si ratios are used for the calculation which deviate less than 3 standard deviation from the mean and B) only results which follow the mass-depended terrestrial fractionation line in a three-isotope-plot of δ29Si vs. δ30Si within analytical uncertainties and C) have a mass bias drift between the two bracketing standards of less than 0.30 ‰ in 30/28Si are accepted and reported in this study.Detailed description of the sample origin, preparation steps, and the measurement protocol can be found in Frick, D. A.; Schuessler, J. A.; Sommer, M.; von Blanckenburg, F. (2018): Laser ablation in situ silicon stable isotope analysis of phytoliths. Geostandards and Geoanalytical Research. https://doi.org/10.1111/ggr.12243. With this supplement we aim to provide a comprehensive...

Collaboration

Group / person Country
Types of collaboration
Silizium-Biogeochemie/Leibniz-Zentrum für Agrarlandschaftsforschung (ZALF) e. V. Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Metal Stable Isotope Geochemistry Workshop Poster Silicon isotope composition of single phytoliths 08.01.2018 Sorèze, France Frick Daniel;
Goldschmidt 2017 Poster Silicon isotope composition of single phytoliths 13.08.2017 Paris, France Frick Daniel;


Abstract

In this research project I will establish a novel method to analyse single phytoliths (biogenic silica) for their stable metal isotopic and elemental composition, as currently available methods are not suitable. To achieve this goal, I will develop a novel analytical routine, by using state-of-the-art femtosecond-Laser Ablation Split Stream Inductively Coupled Plasma Mass Spectrometry (fs-LASS-ICP-MS), to determine in situ the stable metal isotope ratios (using a multicollector ICP-MS) and elemental composition (using a quadrupole ICP-MS) of individual phytoliths simultaneously. The chemical and isotopic characteristic of individual phytoliths discloses intrinsic information on the environmental conditions under which the plant host grew. With this newly developed routine, the geological record of past soil environments, as preserved in the form of the phytolith’s chemical and isotope composition, will be accessible.Atmospheric carbon dioxide concentrations are modulated by abiotic and biotic silicate weathering that occurs in the Critical Zone - the narrow zone between unweathered bedrock and the top of the vegetation. Thus understanding the Si cycle and assessing mass fluxes in the Critical Zone is essential to understand past climate variations. To distinguish abiotic from biotic processes in the Critical Zone, novel metal stable isotope tracers are employed by geochemists. Two frequently used tracers for silicate weathering are Si stable isotope ratios and Ge/Si ratios. In soil and river water, opposing trends in these ratios are generated by abiotic weathering and biotic uptake, respectively. However, not all compartments in the Critical Zone are easily probed; especially (soil)-water is not preserved over weathering time scales. Here, phytoliths could act as an archive from which the past water composition can be inferred, provided the associated fractionation factors are known. Multicollector ICP-MS in combination with fs-LASS, having a micrometre resolution, will be used to determine simultaneously the Si isotope and Ge/Si composition of individual phytoliths. Within consecutive experiments, I will use the developed analytical method to investigate all three different Si uptake plant types (active, passive and rejective) with the aim to determine experimentally their Si isotope and Ge/Si fractionation factors between soil water and plants.The proposed analytical development will render an unexploited archive for past-environmental Critical Zone conditions accessible, for the first time. Access to such past weathering archives enables geochemists to explore past mass fluxes through ecosystems and thus to constrain predictions for future climate change.
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