[B-PT03] [EE] Biomineralization and the Geochemistry of Proxies -Field ecology, Laboratory culture and Paleo

[BPT03-03] Investigation of δ²⁶Mg in large benthic foraminifera as a temperature proxy

*Ayumi Maeda^1,2, Toshihiro Yoshimura², Daisuke Araoka^4,3, Atsushi Suzuki^4,3, Kazuhiko Fujita^3,4, Takashi Toyofuku⁵, Naohiko Ohkouchi⁵, Hodaka Kawahata^1,2 (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.National Institute of Advanced Industrial Science and Technology, 4.Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 5.Japan Agency for Marine-Earth Science and Technology)

Keywords:Temperature proxy, Large Benthic Foraminifera, Mg isotope fractionation

In the last decade, stable magnesium (Mg) isotope fractionation in biogenic carbonates has been attracted for a new paleoenvironmental proxy, along with technological advance in mass spectrometry. Although δ²⁶Mg has been expected to serve as more robust temperature proxy from the dawn of their evaluation, considerable differences were observed between various biogenic carbonates having various Mg content. In this study, we investigated δ²⁶Mg in large benthic foraminifers producing high-magnesium calcite tests in order to evaluate them as a temperature proxy. Amphisorus kudakajimensis and Calcarina gaudichaudii were cultured in six temperature conditions (21℃-30℃), and measured δ²⁶Mg by MC-ICP-MS. In a previous study, both species showed clear relationships of linearity between Mg/Ca and temperature. Regardless of the previous studies reporting positive relationships between δ26Mg and temperaturethe, the δ²⁶Mg in both species showed negative temperature dependency. There was no significant correlation with the growth rate of foraminifers. Evaluation of Mg isotope fractionation process in large benthic foraminifera may give a profound insight into a foraminiferal biomineralization.