[M-IS23] [JJ] Paleoclimatology and paleoceanography

[MIS23-P02] Grain-scale stable carbon and oxygen isotopic variations of the international reference materials IAEA-603 (newly released) and NBS 19

*Kozue Nishida¹, Toyoho Ishimura¹ (1.National Institute of Technology, Ibaraki College)

Keywords:stable isotopes, international reference material, carbonate, IAEA-603, SEM

The international reference material IAEA-603 prepared from Carrara marble (calcite) was newly released on 2016 to replace the reference material NBS19 (exhausted). From the reference sheet of IAEA-603 (Fajgelj and Assonov, 2016), assigned carbon and oxygen isotopic (δ¹³C and δ¹⁸O) values are +2.46±0.01‰ and -2.37±0.04‰, respectively at a sample size of about 120 µg. For sub-microgram scale isotopic analysis, we examined the grain-scale stable carbon and oxygen isotopic variations of IAEA-603. The individual grains of IAEA-603 (grain size: 200 to 760 µm) were measured with an IsoPrime100 isotope ratio mass spectrometer with customized continuous-flow gas preparation system (MICAL3c, Ishimura et al., 2004, 2008) at National Institute of Technology, Ibaraki College, Japan, and the individual weight of each grain estimated from the reacted CO₂ gas volume was 4-90μg. The standard deviations (1σ uncertainties) of δ¹³C and δ¹⁸O of the individual grains of IAEA-603 are ±0.07‰ and ±0.16‰, respectively (N = 16), and the grain-scale analytical results also indicated homogeneous values as same as stable isotopes of the single grains of NBS19 (the standard deviation: ±0.10‰ in δ¹³C, ±0.16‰ in δ¹⁸O, N = 16, Ishimura et al., 2008). In IAEA-603, δ¹³C and δ¹⁸O ranged within 0.2‰ and 0.4‰, respectively. Both δ¹³C and δ¹⁸O of the individual grains showed non-significant grain-size dependencies. From the scanning electron microscope observations, the individual grains of IAEA-603 were dominantly polycrystalline with translucent grains composed of coarse crystals, and contained a certain amount of white opaque grains containing fine crystals. On the other hand, NBS19 showed single-crystal-like grains. Thus, as the reference sheet of IAEA-603 (Fajgelj and Assonov, 2016) mentioned, the storage in sealed ampules is important for avoiding exchange with atmospheric moisture and atmospheric CO₂, especially in polycrystalline IAEA-603.