[M-IS10] Global climate change driven by the Southern Ocean and the Antarctic Ice Sheet

[MIS10-P05] Chrysophyte cysts collected in the Atlantic sector of the Southern Ocean

*Yuji Kato¹, Akira Ijiri², Minoru Ikehara¹ (1.Marine Core Research Institute, Kochi University, 2.Graduate School of Maritime Sciences, Kobe University)

Keywords:chrysophyte cysts, diatoms, Southern Ocean, siliceous microfossils

Chrysophytes are known as an important and diverse group of freshwater phytoplankton, which are characterized by the endogenous formation of siliceous cysts during their resting stages. Recently chrysophyte cyst fossils preserved in marine sediments have been proposed to have a potential as a new paleo-indicator of the inflow of glacial meltwater (Kato and Suto, 2019). However, the application of chrysophyte cyst fossils in the field of paleoceanography or paleolimnology is still limited because of the lack of fundamental information such as modern biogeographic distribution of the taxa. In this study, we carried out microscopic observation of surface seawater samples (filtered through a 0.45 μm-mesh membrane filter) from approximately 30 sites in the Atlantic sector of the Southern Ocean, collected during R/V Hakuho-Maru cruise KH-19-6 Leg 4 (December 2019 - January 2020). As a result, the biogeographic distribution of present chrysophyte cysts in the area was successfully illustrated for the first time. In addition, oxygen isotope ratio (δ¹⁸O) of the seawater samples was also measured and compared with the biogeographic distribution of chrysophyte cysts. This experiment showed a tendency that the δ¹⁸O-seawater values were relatively low at sites where chrysophyte cysts were abundant. Since glacial meltwater generally has lower δ¹⁸O values, the results obtained in this study would support the hypnotized relationship between abundant chrysophyte cysts and meltwater inputs.