Japan Geoscience Union Meeting 2018

Presentation information

[EE] Oral

B (Biogeosciences) » B-CG Complex & General

[B-CG07] Earth and Planetary Science Frontiers for Life and Global Environment

Mon. May 21, 2018 3:30 PM - 5:00 PM 101 (1F International Conference Hall, Makuhari Messe)

convener:Yoshinori Takano(Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Yohey Suzuki(Graduate School of Science, The University of Tokyo), Keisuke Fukushi(金沢大学環日本海域環境研究センター, 共同), Shingo Kato(RIKEN), Chairperson:Suzuki Yohey, Fukushi Keisuke

4:20 PM - 4:35 PM

[BCG07-09] Calibration between temperature and Mg/Ca and oxygen isotope ratios in high-magnesium calcite precipitated by asexually reproduced juveniles of large benthic foraminifera

*Ayumi Maeda1, Kazuhiko Fujita2, Keiji Horikawa3, Atsushi Suzuki4, Yoshikazu Ohno5, Hodaka Kawahata6 (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 2.Department of Physics and Earth Sciences, University of the Ryukyus, 3. Graduate School of Science and Engineering for Research, University of Toyama, 4.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 5.Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, 6.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:Temperature proxy, Large benthic foraminifera

The potential usefulness of test composition of reef-dwelling large benthic foraminifera as paleotemperature proxies was demonstrated by our previous study which reports that Mg/Ca and oxygen isotope ratios (δ18O) in the high-magnesium calcite tests represent a good correlation with seawater temperature. However, the distinction of temperature correlation with chemical composition in tests between perforate and imperforate species still remains unclear. We cultured asexual reproduced juveniles of four species among large benthic foraminifera at controlled temperatures (21°C–31°C). Neorotalia calcar, Baculogypsina sphaerulata, and Calcarina gaudichaudii were selected as the perforate species, whereas Amphisorus kudakajimensis was chosen as the imperforate species. The results of analyses and measurements suggest linear relations between Mg/Ca and temperature except at 31 °C, regarding A. kudakajimensis also except at 29°C, which is likely attributed to metabolic anomaly of foraminifera under chronic thermal stress. Additionally, A. kudakajimensis (imperforate species) exhibited different Mg/Ca–temperature equation from those of perforate species. The Mg/Ca–temperature and δ18O–temperature equations are yielded using the least square method as follows: Mg/Ca = 2.73 T + 74.71 for three perforate species, which is applicable to temperature range of 21°C–30°C. The temperature relations of δ18O differ across perforate species. We observed that the δ18O values were between the equilibrium of pure calcite and those of high-magnesium calcite. A species-specific calibration is necessary for the temperature relation of δ18O. Between perforate and imperforate species, respective calibrations are needed for Mg/Ca–temperature relationship, although the similar Mg/Ca range is observed in 21°C–30°C.