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

[MZZ44-P02] Ferromanganese Crusts - Reconstruction of Dissolved Oxygen Concentration in the Pacific Ocean since the Miocene

*Masanobu Yamamoto¹, Akira Usui², Hirokuni Oda³, Teruhiko Kashiwabara⁴, Hitoshi Hasegawa⁵ (1.Faculty of Environmental Earth Science, Hokkaido University, 2.Marine Core Research Institute, Kochi University, 3.National Institute of Advanced Industrial Science and Technology, 4.Japan Agency for Marine-Earth Science and Technology, 5.Faculty of Science and Technology, Kochi University)

Keywords:Ferromanganese crust, The Pacific Ocean, Oxygen concentration, Miocene, CO2, Ocean carbon storage

Decreased atmospheric CO₂ concentration is one of the most likely causes of the transition from the warmer Miocene-Pliocene to the colder Pleistocene. There are two possibilities for the cause of the decrease in CO₂ concentration: (1) a decrease in the total carbon amount of the atmosphere-ocean system or (2) an increase in the proportion of carbon stored in the oceans without a change in total carbon amount. Ocean carbon storage and atmospheric CO₂ concentrations are synchronized in the former case. In the latter case, atmospheric CO₂ concentration decreases as ocean carbon storage increases. Since carbon is transferred from the surface to the deep ocean as organic matter, which produces inorganic carbon by consuming oxygen, the oxygen concentration is related to how the ocean carbon is stored.
In this study, we reconstruct changes in dissolved oxygen concentrations in deep Pacific Ocean water since the Miocene by ultra-high resolution analysis of the remnant magnetics, structure, and chemical composition of ferromanganese crusts collected from 965 m to 5373 m depth on the slope of the Takuyo Daigo seamount in the North Pacific Ocean. Based on the reconstructed data, we will identify the depths of the deep ocean water that have been responsible for carbon sequestration, capture changes in the circulation patterns of the deep Pacific Ocean, the world's largest carbon storage, and estimate the evolution of carbon sequestration in the Pacific Ocean, and identify the causes of long-term changes in atmospheric CO₂ concentration. In this presentation, we will present the results of geomagnetic reversals using scanning SQUID magnetic microscopy (Oda et al., presented at this conference) and existing elemental analyses (Usui et al., 2017 Ore Geology Reviews, 87, 71-87) to discuss the possibility of reconstructing changes in dissolved oxygen concentration in deep Pacific waters since the Miocene.