[M-IS12] Paleoclimatology and paleoceanography

[MIS12-P06] Seasonal variation in planktonic foraminifera: sediment trap results from subtropical Northwest Pacific

*Yuri Hashimoto¹, Azumi Kuroyanagi², Atsushi Suzuki³, Kyoko Yamaoka³, Takeshi Fujii⁴, Shunsuke Kondo⁴, Hiroko Kamoshida⁵ (1.Tohoku Univ., 2.Tohoku University Museum, 3.AIST, 4.KANSO, 5.JOGMEC)

Keywords:planktonic foraminifera, sediment trap

Planktonic foraminifera are mainly calcareous shelled zooplankton that are used in paleoceanographic studies and paleoenvironmental analyses because the chemical composition and community composition of their shells record the environment of the ocean surface. However, there is a lack of reports on planktonic foraminifera, especially in the subtropical Northwest Pacific. In this study, we investigated seasonal changes in planktonic foraminifera flux and community composition using time-series sediment trap samples. A total of 22 species of planktonic foraminifera were identified, of which 11 species accounted for approximately 93.5% of the total. The planktonic foraminiferal fluxes showed distinct seasonal changes, with each species exhibiting different seasonal changes. This suggests that planktonic foraminifera fluxes are regulated by different factors depending on the species. Cluster analysis was used to categorize the patterns of seasonal changes, and three groups were identified. Group A represents approximately 66.1 % of the planktonic foraminifera in this study. It is composed of subtropical species, many of which have symbiotic algae. The flux of G. ruber, the most abundant species, showed two large maxima in December and July. Both of these peaks were observed during periods of higher water temperature (~28°C). Peaks during the high SST period were also observed in other warm, oligotrophic areas. Thus, it is suggested that in high SST and oligotrophic waters, the flux may reach its maximum during the optimum period for G. ruber (25-30℃). Group B consists of three species of Globorotalinidae, which inhabit relatively deep waters, and peak once a year during the summer season. This peak is considered to reflect the reproduction season of these species in this area. Group C consists of Globigerinella siphonifera, which showed no clear seasonal variation and remained low throughout the year.