[M-IS12] Paleoclimatology and paleoceanography

[MIS12-19] Towards a reconstruction of the North Atlantic carbonate cycle over the past 400 Myr using Micro X-ray Computed Tomography Method

*Saran Takeda Lee^1,2, Katsunori Kimoto³, Shinya Iwasaki⁴, Naomi Harada², IODP Expedition 395 Scientific Party⁵ (1.Department of Natural Environmental Studies, The University of Tokyo, Japan, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, Japan, 3.Japan Agency for Marine-Earth Science and Technology, Japan, 4.Hokkaido University, Japan, 5.Texas A&M University)

Keywords:Planktic foraminifera, Ocean acidification, Bulk density of foraminiferal test, X-ray Microcomputed Tomography (µCT), North Atlantic Ocean

The carbonate ion ([CO₃^2-]) concentration in deep ocean depends on the amount of dissolved inorganic carbon and alkalinity. Since the dissolution and preservation of planktonic foraminiferal tests, a major component of marine carbonate sediments, is determined by deep-water [CO₃^2-], it has been thought that quantifications of the dissolution of planktonic foraminiferal tests preserved in the sediments can be used to reconstruct marine carbon storage during glacial/interglacial cycles. However, the previously used carbonate dissolution index such as size-normalized weight and shell fragmentation are limited in their quantitative reconstruction of changes in deep-water [CO₃^2-] concentration because the values are distorted by differences in shell size and shell wall thickness due to habitat conditions. To resolve these problems, a method to quantify planktonic foraminiferal tests density with high resolution using a Micro X-ray Computed Tomography (MXCT) system was recently developed (e.g., Iwasaki et al., 2019; Kimoto et al., 2023). This technique has been applied as an intensity of foraminiferal test dissolution indicator to quantitatively reconstruct ancient deep water [CO₃^2-] (Iwasaki et al., 2022; Iwasaki et al., 2023). In this study, we plan to observe the internal test structure and measure the test density of planktonic foraminifera by MXCT using sediment core samples from the Gardar Drift and the Erick Drift. Finally, we aim to quantitatively reconstruct the deep-water [CO₃^2-] concentration by the variability in test dissolution of planktonic foraminifera over the past 4 Ma covering the intensification of Northern Hemisphere Glaciation (iNHG). In this presentation, we will mainly outline the research plan, introduce the MXCT methodology, and report the preliminary results.