[M-IS16] Paleoclimatology and paleoceanography

[MIS16-P18] Changes in carbonate dissolution and preservation in Southern Ocean sediment off Chilean margin during the last 140 kyrs based on fragmentation and size-normalized weight of planktic foraminiferal tests.

*Takuto Kasuya¹, Yusuke Okazaki², Shinya Iwasaki³, IODP Expedition 383 Scientific Party (1.Department of Earth and Planetary Sciences, School of Science, Kyushu University , 2.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, 3.MARUM Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen)

Keywords:Carbonate preservation / dissolution, Southern Ocean, MIS 5, Planktonic foraminifera

The Southern Ocean plays an important role in global climate change as a reservoir of heat and carbon. Glacial atmospheric carbon dioxide concentrations were 80-100 ppm lower than the interglacial level. Changes in CaCO₃ dissolution and preservation in the deep-sea particularly for the Southern Ocean is thought to be a key factor for glacial carbon reservoir. In this study, we investigated change in dissolution and carbonate preservation in Southern Ocean sediment for the last 140 kyrs based on two proxies, fragmentation index and size-normalized weight of planktic foraminiferal tests. Fragmentation index represents a ratio of the number of fragments to the intact planktic foraminiferal tests. Two planktic foraminiferal species, Neogloboquadrina pachyderma and Globigerina bulloides were employed. For size-normalized weight of planktic foraminiferal tests, Globigerina bulloides tests were picked up from the 212-250 µm, 250-300 µm, and 300-355 µm sieve fractions. Sediment core samples used in this study were obtained at Site U1543 (54°35.06’S; 76°40.58’W; 3864 m water depth) in the eastern South Pacific west of the Chile Trench during the International Ocean Discovery Program (IODP) Expedition 383 in 2019. At U1543, foraminiferal tests in the sediment have been preserved only during glacial terminations to early interglacials during the last 140 kyrs, which is consistent with expected deep-sea carbonate ion response to atmospheric CO₂ elevations during the glacial terminations. During the last interglacial period (marine isotope stage 5e), both fragmentation ratio and size-normalized weight of planktic foraminiferal tests suggested two carbonate dissolution events at millennial time-scale.