EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

High-resolution carbon and oxygen isotope record in modern brachiopod Pictothyris picta collected off Okinoshima, Japan

Kazuma Oikawa1, Hideko Takayanagi1, Kazuyoshi Endo2, Masa-aki Yoshida3, and Yasufumi Iryu1
Kazuma Oikawa et al.
  • 1Tohoku University, Graduate School of Science, Department of Earth Science, Sendai, Aoba-ku, Japan (
  • 2Univ Tokyo, Grad Sch Sci, Dept Earth & Planetary Sci, Tokyo, Japan
  • 3Shimane Univ, Oki Marine Biol Stn, Matsue, Shimane, Japan

Carbon (δ13C) and oxygen (δ18O) isotope composition of Rhynchonelliformea brachiopods (hereafter, called ‘brachiopods’) have been regarded as useful paleoenvironmental indicators throughout the Phanerozoic. However, recent studies have revealed that the isotopic composition in modern brachiopod shells records not only environmental changes in ambient seawater but also is influenced by biological controls such as the chemical/isotopic composition of calcifying fluids and physiological processes (e.g., growth rates, metabolism). The latter is known as biological isotope fractionation effects, such as kinetic, metabolic, and pH effects. Recently, a new calcification mechanism in brachiopod shell formation, ion transport mechanism, was proposed. In this study, we measured δ13C and δ18O values of the primary (PL) and secondary (SL) shell layers of three Pictothyris picta (one male and two female specimens) collected at a water depth of~61 m off Okinoshima to improve our understanding of biological isotope fractionation effects during their shell secretion. We obtained ontogenetic-series δ13C and δ18O profiles from the PL (PL-Ont) and the uppermost SL (SL-Ont) at the sampling resolution of 3 days to 8 months per sample. We obtained inner-series δ13C and δ18O profiles from the innermost SL (SL-In) as well. The variations in the δ13C and δ18O profiles of the PL-Ont showed similar trends to those of the SL-Ont. However, the PL-Ont values mostly exhibited relatively lower δ18O values than those of the SL-Ont. Cross plots between the δ13C and δ18O values of the PL-Ont indicated a strong positive correlation and were lower than those of calcite precipitated in isotopic equilibrium with ambient seawater at the fast growth stage, suggesting the significant influence of the kinetic isotope fractionation effect. The SL was precipitated in oxygen isotopic equilibrium with ambient seawater regardless of the growth stage and/or the seasonal changes in living environments. Furthermore, the PL-Ont, SL-Ont, and SL-Inshowed similar δ18O values during the cold season, indicating negligible influences of the kinetic, pH, and magnesium effects on δ18O composition. The δ13C values of the PL-Ont formed at the cold season (= micro-portion formed under the least kinetic isotope fractionation effect) were lower than those of the SL, indicating the stronger metabolic effect on the PL secretion. Our isotopic data showed that the time lag of the PL and the SL formation varies among specimens.

How to cite: Oikawa, K., Takayanagi, H., Endo, K., Yoshida, M., and Iryu, Y.: High-resolution carbon and oxygen isotope record in modern brachiopod Pictothyris picta collected off Okinoshima, Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14032,, 2021.


Display file

Comments on the display

to access the discussion