[B-PT02] Biotic History

[BPT02-02] Depth habitat of the late Eocene planktic foraminifers

*Kazuyoshi Moriya¹, Taku Oyama², Toyoho Ishimura³ (1.Department of Earth Sciences, Faculty of Education and Integrated Arts and Sciences, Waseda University, 2.Major in Earth Sciences, Resources and Environmental Engineering, Graduate School of Creative Science and Engineering, 3.Department of Interdisciplinary Environment, Graduate School of Human and Environmental Studies, Kyoto University)

Planktic foraminifers (Rhizaria) are widely distributed in modern ocean from equatorial to sub-polar oceans. Especially for surface dwelling species, distribution of those species is related to sea surface temperatures. For example, Globigerinoides sacculifer and Neogloboquadrina pachyderma predominantly inhabit tropical and polar oceans, respectively. In addition to this geographic variation, depth of habitat is also segregated from species to species. Globigerinoides ruber is well known as the shallowest dwelling species, Globorotalia menardii is deeper, and Globorotalia truncatulinoides is the deepest dwelling species. When calcifying their tests, oxygen isotope ratio (δ¹⁸O) of their test carbonates records temperature of their habitat. Therefore, δ¹⁸O of each species occurred from a given sample shows variation from positive to negative, hence, cooler to warmer. Using this temperature segregation, we can identify the depth of habitat of each species. This temperature/isotope segregation can be found in fossils species as well. Here, we report isotope segregation of the late Eocene planktic foraminifers in north Atlantic Ocean. We have determined δ¹³C and δ¹⁸O of 15 species at most within one sediment sample. The difference in δ¹⁸O between species showing the most negative and positive δ¹⁸O is approximately 3‰, corresponding to 12 degree C. Turborotalia ampliapertura show the most negative δ¹⁸O, indicating surface dwelling nature of this species. On the other hand, the most positive δ¹⁸O is recorded by Globorotaloides quadrocameratus.