[M-IS14] 古気候・古海洋変動

[MIS14-P02] Paleo-Ocean Reconstruction (11.6–9.6 Ma) Using Raman Spectroscopy on a Ferromanganese Nodule from the Tabletop of KC-8

*chanwoo park¹、Kiho Yang^1,2 (1.Department of Oceanography, Pusan National University、2.Institute for Future Earth, Pusan National University)

キーワード：Ferromanganese nodule, Raman spectroscopy, Magellan seamount, Paleoclimate

Ferromanganese (Fe-Mn) nodules generally have a very slow growth rate(few mm/Myr), with their geochemical and mineralogical characteristics varying depending on the oceanic environment. Therefore, these two characteristics have made them useful for paleoceanographic reconstruction studies. This study examines the geochemical and mineralogical characteristics of the Fe-Mn nodule from the tabletop of KC-8 Seamount to reconstruct the paleo-ocean conditions during its formation, using X-ray fluorescence (XRF), Raman spectroscopy, and Raman analysis for geochemical and mineralogical analysis. Morphological observations revealed that the nodule consists of four distinct layers. Porous L1 and L3, with an average Mn/Fe ratio below 2.5, exhibited vernadite characteristic Raman bands. In contrast, dense L2 and L4, with an average Mn/Fe ratio exceeding 2.5, displayed both vernadite bands and todorokite bands. The age of the nodule calculated using the Co chronology is 36.8 Ma. The variations in Mn/Fe ratios and mineral composition indicate change in the redox conditions of the water column and sediment. Notably, at the L1–L2 boundary (11.2–9.6 Ma), a drastic decrease in the Mn/Fe ratio was observed toward the outer layers(1.8-0.7), along with a decline in todorokite band intensity from L2 to L1. This transition corresponds to the period of the Indonesian seaway closure (11.6–9.6 Ma), during which the warm pool formation in the western Pacific led to an intensified thermocline and reduced surface productivity. Consequently, the oxygen minimum zone (OMZ) waned, resulting in a more oxidative environment. This study utilizes Raman analysis to obtain continuous data on these paleo-ocean changes during the formation of the warm pool, thereby enabling high-resolution reconstruction of the paleo-ocean redox condition changes recorded in the ferromanganese nodule.