LA-ICP-MS; metal stable isotope fractionation; germanium silicon ratio; silicate weathering; phytoliths; fs-LASS-MC-ICP-MS
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
Data supplement to: Laser ablation in situ silicon stable isotope analysis of phytoliths
||Frick, Daniel A.; Schuessler, Jan A.; Sommer, Michael; von Blanckenburg, Friedhelm
|Persistent Identifier (PID)
GFZ Data Services
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...
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.