[M-ZZ44] Marine Manganese Minerals: Depositional environments, exploration, and development

[MZZ44-03] Rhythmical laminations of Ferromanganese Crust reveals a 6.5 million-year record of eolian dust flux to the Northwest Pacific

*Hitoshi Hasegawa^1,2, Nanako Koma¹, Akira Usui², Hirokuni Oda³, Hiroshi Kawabata¹, Norihiro Takahashi⁴, Takashi Ito⁴, Tomoyo Okumura², Go-Ichiro Uramoto², Teruhiko Kashiwabara⁵, Masanobu Yamamoto⁶ (1.Faculty of Science and Technology, Kochi University, 2.MaCRI, Kochi University, 3.AIST, 4.Ibaraki University, 5.JAMSTEC, 6.Hokkaido University)

Keywords:Ferromanganese crust, Rhythmical Lamination, Glacial-Interglacial cycle, Eolian dust, Northwest Pacific

Marine ferromanganese crusts are composed of iron-manganese oxide that were slowly deposited on deep sea floors and seamounts at a rate of a few millimeters per million years, and recording long-term paleoenvironmental changes. The ferromanganese crusts often exhibit submillimeter-scale rhythmical laminations, that are thought to reflect glacial-interglacial cycles, but the cause of their formation remains unknown. In this study, we analyzed a well-laminated ferromanganese crust collected from the Shotoku seamount (30°48.7′N, 138°19.14′E, water depth 1940 m) located in the Izu-Mariana Arc, northwest Pacific. Based on 3D micro-structural observation by X-ray CT and micro-scale chemical composition analysis by EPMA, we show that the rhythmical laminations in the ferromanganese crust is composed of alternating layers of manganese oxides with stromatolite-like columnar structures accumulated during interglacial periods and eolian dust deposited during the glacial periods. In addition, based on age constraints from paleomagnetic stratigraphy and orbital tuning, we reconstructed the variability of the eolian dust flux in the northwest Pacific over 6.5 million years. The variation of eolian dust flux is consistent with the records of quartz grain size variations in the Chinese Loess Plateau. Furthermore, the variability of eolian dust flux reveals a pronounced phase transition for 400-kyr long eccentricity cycles. Specifically, eolian dust flux shows an in-phase relationship with long-term eccentricity during 6.5-1.8 Myr ago, while it shows an anti-phase relationship during the last 1.8 Myr. Our finding suggests a switch in the response of the Asian interior hydroclimate to the 400-kyr eccentricity cycles due to the expansion of the Northern Hemisphere ice sheet in the early Pleistocene.