HR: 17:45h
AN: V54B-08    [Abstracts]
TI: New technical developments in silicon isotope measurements by MC-ICP-MS
AU: * Reynolds, B C
EM: reynolds@erdw.ethz.ch
AF: IGMR, ETH Zurich, ETH Zentrum NO Sonneggstr 5, Zurich, CH-8092 Switzerland
AU: Georg, R B
EM: georg@erdw.eth.ch
AF: IGMR, ETH Zurich, ETH Zentrum NO Sonneggstr 5, Zurich, CH-8092 Switzerland
AU: Frank, M
EM: frank@erdw.ethz.ch
AF: IGMR, ETH Zurich, ETH Zentrum NO Sonneggstr 5, Zurich, CH-8092 Switzerland
AU: Halliday, A N
EM: halliday@earth.ox.ac.uk
AF: IGMR, ETH Zurich, ETH Zentrum NO Sonneggstr 5, Zurich, CH-8092 Switzerland
AU: Halliday, A N
EM: halliday@earth.ox.ac.uk
AF: University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AB: The fractionation of silicon (Si) isotopes during biological uptake and opal biomineralization allows silicic acid utilization in aquatic environments to be quantified from the geological record. The use of this direct nutrient proxy has been hampered by analytical difficulties in the measurement of Si isotopes in biogenic silica. The recent development of high-resolution multi-collector ICP-MS and novel sample introduction techniques now allow for the rapid and precise measurement of Si isotope abundances from very small amounts of biogenic opal. However, interferences and matrix effects can make Si isotopic measurements by MC-ICP-MS difficult, and considerable care must be taken to overcome these technical difficulties. Refined techniques also allow for the measurement of small samples of silica and silicate minerals to be analysed in a routine fashion, enabling the study of Si isotope fractionation between different mineral phases in terrestrial and extra-terrestrial materials. Using the Nu1700 high resolution MC-ICP-MS allows for the resolution of all significant interferences during measurements, and matrix effects have been studied for a range of sample introduction systems and chemical preparation methods allowing for different running conditions. We will review current techniques and analytical capabilities for the measurement of Si isotope ratios using MC-ICP-MS and show how these can be applied to a range of silicate mineral phases. Results will focus on the Si isotope composition of biogenic opal from cleaned diatom frustules and also on water samples. The developed techniques allow for high precision measurements to be obtained, which require re-examination of the stability of monomeric silicic acid solutions and ways of storing standard solutions needed for intra- and inter-laboratory calibrations of silicon isotopic analyses.
DE: 4825 Geochemistry
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting