Challenges to deep sea paleoceanography by establishing oxygen isotope proxy of siliceous sponge spicules

2023 Fiscal Year Final Research Report

• Project/Area Number: 20H02017
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17050:Biogeosciences-related
• Research Institution: Kochi University
• Principal Investigator: Ikehara Minoru 高知大学, 教育研究部自然科学系理工学部門, 教授 (90335919)
• Co-Investigator(Kenkyū-buntansha): 井尻 暁 神戸大学, 海事科学研究科, 准教授 (70374212)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 海綿骨針 / 酸素同位体 / 深海 / 古海洋学 / 北太平洋

Outline of Final Research Achievements

Paleoceanographic research in the North Pacific and polar oceans has not progressed because foraminiferal oxygen isotope ratios are not available due to poor carbonate preservation. To overcome this problem, the usefulness of oxygen isotope ratios from siliceous sponge spicules was tested in this study. After checking the cleaning method using a modern siliceous sponge from Okinawa Trough, the oxygen isotope ratios of sponge spicules retrieved from surface sediments (533 m to 2679 m depth) east of Okinawa, Japan were analyzed. The oxygen isotope ratios showed a constant correlation with the water temperature at the site, although there was some variation, and the relationship was found to be almost the same as the previously reported temperature dependence (-0.2‰/C). Although the analysis could not be applied to the marine core because it took time to secure the sponge spicules, we will continue preparation and analysis to extract palaeoenvironmental information from the deep sea.

Free Research Field

古海洋学

Academic Significance and Societal Importance of the Research Achievements

深海堆積物に普遍的に存在する珪質海綿骨針の酸素同位体比の有用性について検証した結果、データはまだ少ないものの一定の温度依存性を保持していることが明らかとなった。北太平洋と極域海洋は有孔虫の産出が悪いため、珪質微化石の酸素同位体比への期待が大きい。我々のグループが確立した珪藻殻の酸素同位体比のルーチン分析に加えて、本研究によりベントスとしての海綿骨針の酸素同位体比分析ができる環境が整いつつある。炭酸塩補償深度CCDより深い海底がほとんどを占める北太平洋における古海洋変動研究にブレークスルーをもたらす端緒となる成果である。