[M-IS16] Paleoclimatology and paleoceanography

[MIS16-01] Recent progress of the microscale isotopic analytical technique of carbonate (MICAL) and the applications to the high resolution environmental analysis

★Invited Papers

*Toyoho Ishimura¹ (1.Graduate School of Human and Environmental Studies, Kyoto University)

Keywords:microscale analysis, stable isotope, carbonate

The stable carbon and oxygen isotopic compositions (δ¹³C and δ¹⁸O) of carbonate, especially biological calcite (e.g. foraminifera and coral), are useful as environmental tracers to reconstruct paleoclimate and paleo-oceanic circulations. In recent studies, stable isotopic analyses for sub-100 micrograms of carbonate are needed to reconstruct high-resolution environmental fluctuations. To analyze the stable isotopic compositions of carbonate, however, more than 10 – 400 micrograms of CaCO₃ are needed even with the latest methods. As a consequence, in case of foraminiferal study, we have had to prepare several to several tens of foraminiferal shells to determine the stable isotopic compositions, and the reported isotopic data of individual foraminiferal shells are limited to the taxa that have large and thick CaCO₃ shells (e.g. Uvigerina spp.). We could not utilize the δ¹³C and δ¹⁸O values of foraminifera for the sediments in which a limited number of small-sized shells are available, such as at high latitudes, in the deep sea around carbonate compensation depth, etc. If we can determine the isotopic compositions of individual small foraminifera, we can expand the area of the seafloor to which they can be applied.

Recently, Ishimura et al. (2004, 2008) have developed a stable carbon and oxygen isotopic analysis system for sub-microgram quantities of CaCO₃ (MICAL), and have applied it to the analysis of high-resolution environmental studies with collaborators in the field of paleoceanography, geology, biology, and fisheries sciences. By using the system we can determine the δ¹³C and δ¹⁸O values for almost all kinds of foraminifera, including foraminifera of the minimum size. We can apply the isotopic studies of foraminifera to seafloor sediments in which a limited numbers of small shells are available. In addition, in the case of large-sized calcareous foraminifera, we can determine the δ¹³C and δ¹⁸O differences between the fragments within a single shell. Foraminifera make their shells larger by adding new chambers at each growth stage, but little ecological information is known about foraminifera.
High resolution isotopic analysis of CaCO₃ will be useful not only for paleoceanography, but also for ecological research, for example, high-resolution stable isotopic analysis of CaCO₃ to clarify the life history recorded in fish otolith. In this presentation, we will introduce the applications not only to the field of paleoenvironmental analysis, but also to the other scientific fields.