TY - JOUR

T1 - Micrometer silicon isotope diagnostics of soils by UV femtosecond laser ablation

AU - Steinhoefel, Grit

AU - Breuer, Joern

AU - von Blanckenburg, Friedhelm

AU - Horn, Ingo

AU - Kaczorek, Danuta

AU - Sommer, Michael

N1 - Funding Information: We thank A. Danilova, M. Zarei (Institut für Bodenkunde und Standortlehre, Universität Hohenheim, Germany) and P. Weidler (Forschungszentrum Karlsruhe GmbH, Karlsruhe, Germany) for performing and helping with the XRD-analysis and K. P. Jochum (MPI, Mainz) for organizing the preparation of fused glass beads. We appreciate thoughtful comments by two anonymous reviewers and the editorial handling by J. D. Blum. This study was founded by the German Research Foundation (DFG) – PAK 179 “Multiscale analysis of Si cycling in terrestrial biogeosystems”.

PY - 2011/7/22

Y1 - 2011/7/22

N2 - This study presents the first Si isotope data of the principle Si pools in soils determined by a UV femtosecond laser ablation system coupled to a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). This method reveals accurate and precise Si isotope data on bulk materials, and at high spatial resolution, on the mineral scale. The following Si pools have been investigated: a) the Si source to soils on all major silicate minerals on thin sections from bedrock fragments in the soil profiles; b) bulk soils (particle size <2mm) after fusion to glass beads with an iridium-strip heater or pressed into powder pellets; c) separated clay fractions as pressed powder pellets and e) separated phytoliths as pressed powder pellets. Multiple analyses of three rock standards, BHVO-2, AGV-1 and RGM-1 as fused glass beads and as pressed powder pellets, reveal -30Si values within the expected range of igneous rocks. The MPI-DING reference glass KL2-G exhibits the same Si isotope composition after remelting by an iridium-strip heater showing that this technique does not alter the isotope composition of the glass.We used this approach to investigated two immature Cambisols developed on sandstone and paragneiss in the Black Forest (Germany), respectively. Bulk soils show a largely uniform Si isotope signature for different horizons and locations, which is close to those of primary quartz and feldspar with -30Si values around -0.4‰. Soil clay formation is associated with limited Si mobility, which preserves initial Si isotope signatures of parental minerals. An exception is the organic horizon of the paragneiss catchment where intense weathering leads to a high mobility of Si and significant negative isotope signatures as low as to -1.00‰ in bulk soils. Biogenic opal in the form of phytoliths, exhibits negative Si isotope signatures of about -0.4‰. These results demonstrate that UV femtosecond laser ablation MC-ICP-MS provides a tool to characterize the Si isotope signature of the principle Si pools left behind after weathering and Si transport have altered soils. These results can now serve as a fingerprint of the residual solids that can be used to explain the isotope composition of dissolved Si in soil solutions and river water, which is mostly enriched in the heavy isotopes.

AB - This study presents the first Si isotope data of the principle Si pools in soils determined by a UV femtosecond laser ablation system coupled to a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS). This method reveals accurate and precise Si isotope data on bulk materials, and at high spatial resolution, on the mineral scale. The following Si pools have been investigated: a) the Si source to soils on all major silicate minerals on thin sections from bedrock fragments in the soil profiles; b) bulk soils (particle size <2mm) after fusion to glass beads with an iridium-strip heater or pressed into powder pellets; c) separated clay fractions as pressed powder pellets and e) separated phytoliths as pressed powder pellets. Multiple analyses of three rock standards, BHVO-2, AGV-1 and RGM-1 as fused glass beads and as pressed powder pellets, reveal -30Si values within the expected range of igneous rocks. The MPI-DING reference glass KL2-G exhibits the same Si isotope composition after remelting by an iridium-strip heater showing that this technique does not alter the isotope composition of the glass.We used this approach to investigated two immature Cambisols developed on sandstone and paragneiss in the Black Forest (Germany), respectively. Bulk soils show a largely uniform Si isotope signature for different horizons and locations, which is close to those of primary quartz and feldspar with -30Si values around -0.4‰. Soil clay formation is associated with limited Si mobility, which preserves initial Si isotope signatures of parental minerals. An exception is the organic horizon of the paragneiss catchment where intense weathering leads to a high mobility of Si and significant negative isotope signatures as low as to -1.00‰ in bulk soils. Biogenic opal in the form of phytoliths, exhibits negative Si isotope signatures of about -0.4‰. These results demonstrate that UV femtosecond laser ablation MC-ICP-MS provides a tool to characterize the Si isotope signature of the principle Si pools left behind after weathering and Si transport have altered soils. These results can now serve as a fingerprint of the residual solids that can be used to explain the isotope composition of dissolved Si in soil solutions and river water, which is mostly enriched in the heavy isotopes.

KW - MC-ICP-MS

KW - Silicon isotopes

KW - Soils

KW - UV femtosecond laser ablation

UR - http://www.scopus.com/inward/record.url?scp=79959806548&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2011.05.013

DO - 10.1016/j.chemgeo.2011.05.013

M3 - Article

AN - SCOPUS:79959806548

VL - 286

SP - 280

EP - 289

JO - Chemical geology

JF - Chemical geology

SN - 0009-2541

IS - 3-4

ER -