[M-IS18] Paleoclimatology and paleoceanography

[MIS18-P23] Establishment of a diatom purification method by taxon for accurate geochemical analysis of diatom frustules

★Invited Papers

*Yuji Kato¹, Yuki Morono², Akira Ijiri³, Takeshi Terada⁴, Minoru Ikehara⁵ (1.Faculty of Life and Environmental Sciences, University of Tsukuba, 2.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 3.Kobe University, 4.Marine Work Japan, 5.Center for Advanced Marine Core Research, Kochi University)

Keywords:diatom, Southern Ocean, cell sorter, IODP

In order to perform accurate geochemical analysis on diatom fossils preserved in sediments, it is necessary to extract diatom frustules by taxon. However, due to the small size of diatoms, the purification of diatom taxa has not been achieved so far, and therefore, previous geochemical analysis on diatom frustules has been performed with a mixture of various taxa. In order to solve this problem, we attempted to extract diatom fossils by taxon using a cell sorter, an instrument that has been used in the field of life sciences. We used six samples from a sediment core International Ocean Discovery Program (IODP) Expedition 382 Hole U1538A, which was drilled in the Scotia Sea, Atlantic sector of the Southern Ocean. After the pretreatment process including removal of organic matter, carbonates, and clay minerals, which was followed by sieving to select 20–32 μm fraction, we conducted cell sorter experiments focusing on both optical and fluorescence characteristics of the particles (diatom fossils). As a result, we succeeded in extracting five diatom taxa with high purity: (1) discoid diatoms (mainly genus Thalassiosira) that have moderate degree of fluorescence; (2) pennate diatoms (mainly Fragilariopsis) that have the highest fluorescence values; (3) genus Rhizosolenia; (4) Eucampia antarctica; (5) needle-shaped diatoms (genus Thalassiothrix). The establishment of diatom purification method enables us to conduct more accurate geochemical analysis such as oxygen isotope ratio δ¹⁸O of diatom frustules, which is likely to lead to significant advance of paleoceanography especially at high latitudes or upwelling zones where diatoms are abundant.