HR: 1340h
AN: PP23B-1439    [Abstracts]
TI: Stable Carbon and Oxygen isotopic analysis of sub-microgram quantities of CaCO$_{3}$ and the application to the analysis of single small foraminiferal shells.
AU: * Ishimura, T
EM: toyoho@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, 060-0810 Japan
AU: Tsunogai, U
EM: urumu@ep.sci.hokudai.ac.jp
AF: Graduate School of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, 060-0810 Japan
AU: Gamo, T
EM: gamo@ori.u-tokyo.ac.jp
AF: Ocean Research Institute,˙The University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AB: ~ We developed an analytical system to determine stable isotopic compositions ($\delta$$^{13}$C and $\delta$$^{18}$O) of sub-microgram quantities of CaCO$_{3}$ for the purpose of analyzing individual foraminiferal shells, using continuous-flow isotope ratio mass spectrometry (CF-IRMS). The system consists of a micro volume CaCO$_{3}$ decomposition tube, stainless steel CO$_{2}$ purification vacuum line with an introduction quantity regulating unit, helium-purged CO$_{2}$ purification line, gas chromatograph, and CF-IRMS. By using this system, we can determine stable carbon and oxygen isotopic compositions as low as 0.2 $\mu$g of CaCO$_{3}$, with standard deviations of $\pm$0.10 $\permil$ for $\delta$$^{13}$C and $\pm$0.18 $\permil$ for $\delta$$^{18}$O within a 4-hour reaction time and 30-minute analysis. Our method has the advantage that we do not have to regulate the weight of CaCO$_{3}$ to react with H$_{3}$PO$_{4}$ because we can regulate the introduced quantity of CO$_{2}$ within the stainless steel vacuum line. ~ By using the system, we can determine the $\delta$$^{13}$C and $\delta$$^{18}$O values for individual small foraminifera whose weight is below 10 $\mu$g (e.g. {\it Globocassidulina} sp.). That is to say, we can determine the $\delta$$^{13}$C and $\delta$$^{18}$O values for almost all kinds of calcareous foraminifera. Thus, we can apply the isotopic studies of foraminifera to seafloor sediments in which limited numbers of small shells are available (e.g. at high latitudes, in the deep sea around CCD, or in the seafloor fluid seepage area). In addition, in the case of large-sized calcareous foraminifera, we can determine the $\delta$$^{13}$C and $\delta$$^{18}$O differences between the fragments within a single shell. Partial analysis of their shells will be useful not only for paleoceanography but also for ecological research. ~ Using the system, we determined $\delta$$^{13}$C and $\delta$$^{18}$O values of a small-sized hyaline calcareous foraminifera {\it Globocassidulina} sp., about 210 $\mu$m in diameter and 3 $\mu$g of weight, collected from the top part (0-1cm) of a sediment core. The analytical result shows the isotopic compositions and dispersions of {\it Globocassidulina} sp. as -1.66$\pm$0.17 $\permil$ $_{PDB}$ for $\delta$$^{13}$C and +2.88$\pm$0.31 $\permil$ $_{PDB}$ for $\delta$$^{18}$O (1$\sigma$, n=10). Each measured value of single {\it Globocassidulina} sp. coincided well with those of multiple shells. No systematic difference was observed for the isotopic values between the living and the dead.
DE: 4825 Geochemistry
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting