[B-PT01] Biomineralization and Geochemistry of Proxies

[BPT01-06] Calcification depths of planktic foraminifers constrained using geochemical signatures in the sediment trap samples collected from the Bay of Bengal

*Ayumi Maeda¹, Azumi Kuroyanagi², Toshihiro Yoshimura³, Birgit Gaye⁴, Tim Rixen⁵, Atsushi Suzuki¹, Hodaka Kawahata⁶ (1.National Institute of Advanced Industrial Science and Technology, 2.Tohoku University Museum, The Center for Academic Resources and Archives, Tohoku University, 3.Japan Agency for Marine-Earth Science and Technology, 4.Institute for Geology, Universität Hamburg, 5.Leibniz Centre for Tropical Marine Research, 6.Atmosphere and Ocean Research Institute, The University of Tokyo)

Keywords:planktic foraminifera, Bay of Bengal, oxygen isotope ratio

Mg/Ca and oxygen isotope ratios (δ¹⁸O) of planktic foraminifers revealed the hydrological conditions from the surface to thermocline using multiple species. Knowledge of apparent calcification depth (ACD) of planktic foraminifers plays a key role in reconstructing past environment, while the ACDs showed seasonal variations and are different at regional scale. We pursued revealing ACDs of Globigerinoides ruber, Trilobatus sacculifer, and Neogloboquadrina dutertrei in the Bay of Bengal using multiyear sediment trap samples collected approximately 900 m depth. The sediment traps were moored in the southwestern Bay of Bengal at ~950 m depth and 17-42 days intervals. The estimated temperature using δ¹⁸O and Mg/Ca patterns of G. ruber, T. sacculifer and N. dutertrei showed that G. ruber reflect the temperature within the surface mixed layer, whereas N. dutertrei precipitated tests in the upper thermocline and T. sacculifer calcify between them. The rapidly attenuating photosynthetically active radiation constrained living depth of the symbiont-bearing species within the euphotic zone of the upper 60 m in the southern Bay of Bengal. The flux-weighed δ¹⁸O values of each species corresponded to the mean annual δ¹⁸O values of respective species. Seasonal variations in species-specific test fluxes can be averaged out due to the recuring flux peaks in the NEM and the SWM.