[B-PT03] [EE] バイオミネラリゼーションと環境指標

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

*前田 歩^1,2、吉村 寿紘²、荒岡 大輔^4,3、鈴木 淳^4,3、藤田 和彦^3,4、豊福 高志⁵、大河内 直彦⁵、川幡 穂高^1,2 (1.東京大学大学院　理学系研究科地球惑星科学専攻、2.東京大学　大気海洋研究所、3.産業技術総合研究所、4.琉球大学　理学部物質地球科学科地学系、5.独立行政法人海洋開発研究機構)

キーワード：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.