5:15 PM - 7:15 PM
[MGI28-P04] Preliminary analytical results of Mn-microparticles in outer rise sediments off Nemuro, Hokkaido, northern Japan
Keywords:Mn-microparticle, Antarctic Bottom Watar, Subarctic Ocean Gyre
Manganese (Mn) is the third most abundant metallic element in the Earth's surface environment after iron and titanium1. It has drawn significant interest as an important element in understanding the behaviour of metallic elements in the environment owing to its redox-sensitive dynamics, often accompanied by trace metals1. In the ocean, manganese is found as spherical or plate-like oxides called 'manganese nodules' or 'manganese crusts' on the deep seafloor of the pelagic, oxygenated, and ultra-oligotrophic environment such as the Subtropical Ocean Gyre region. Previous studies focused on unraveling the processes underlying the vast formation of Mn minerals on the deep seafloor2,3. In addition, recent studies have shown that vast amounts of Mn minerals are varied in the deep subseafloor sedimentary environment as submillimeter-scale Mn micronodules4 or micrometer-scale Mn microparticles5. These studies have shown that each type of Mn mineral potentially accounts for up to half of the total Mn content in the deep subseafloor sediments. This underscores its significance in the global Mn budget on the Earth’s surface. However, the main studies of Mn minerals in deep-sea sediments in the past have focused on the analysis of samples from subtropical ocean gyre regions.
Recent studies have also shown that these Mn minerals are precipitated from bottom water6,7 indicating that the presence of oxygen-rich bottom water current in deep-sea plays a significant role. In this respect, investigations of the deep-sea sediment under oxygen-rich bottom water such as Antarctic Bottom Water (AABW)8 is critical for understanding of the actual extent and diversity of the Mn mineral formation environment.This case study showed the preliminary results of core sample analysis taken during JAMSTEC cruises MR24-02 and MR24-05 from outer-rise off Nemuro, Hokkaido, Japan. The lithology of the core is diatomaceous silt and top of the core (up to 6 cm) shows oxidized color which we focused on in this study. Resin-embedding method9 and the particle enrichment method7 were applied to the samples and SEM-EDS microstructural observation and elemental analysis revealed the presence of Mn-microparticles in these sediments. The results showed that the mineral particles, mainly composed of manganese, were discovered and classified into three morphological types: 1) particles attached to microfossil shells, 2) radially spread particles and 3) particles with no corners and a clear outline. The surface structure of these particles showed a structure similar to a tangle of frizzled fine threads, which is common to the surface microstructure of Mn-microparticles in sediment under Subtropical Ocean Gyre5,7, but with a finer frizzled thread-like structure. At present, it is considered that Mn-microparticles are formed and preserved on the deep-sea floor of the outer-rise sediment off Nemuro, Hokkaido, northern Japan under Subantarctic Ocean Gyre. Oxygen supply system is essential for the formation of manganese oxides in such sedimentary environment.
Reference: 1Post, 2000, PNAS; 2Hein et al., 2013, Mar. Geol.; 3Usui et al., 2017, Ore Geol. Rev.; 4Yasukawa et al., 2020, Ore Geol. Rev.; 5Uramoto et al., 2019, Nature Comm.; 6Usui et al., 2020, Sci. Rep; 7Uramoto et al., 2024, Geochem. J.; 8Yi et al., 2023, Sci. Adv.; 9Uramoto et al., 2014, Limnol. Oceanogr. Meth.
Recent studies have also shown that these Mn minerals are precipitated from bottom water6,7 indicating that the presence of oxygen-rich bottom water current in deep-sea plays a significant role. In this respect, investigations of the deep-sea sediment under oxygen-rich bottom water such as Antarctic Bottom Water (AABW)8 is critical for understanding of the actual extent and diversity of the Mn mineral formation environment.This case study showed the preliminary results of core sample analysis taken during JAMSTEC cruises MR24-02 and MR24-05 from outer-rise off Nemuro, Hokkaido, Japan. The lithology of the core is diatomaceous silt and top of the core (up to 6 cm) shows oxidized color which we focused on in this study. Resin-embedding method9 and the particle enrichment method7 were applied to the samples and SEM-EDS microstructural observation and elemental analysis revealed the presence of Mn-microparticles in these sediments. The results showed that the mineral particles, mainly composed of manganese, were discovered and classified into three morphological types: 1) particles attached to microfossil shells, 2) radially spread particles and 3) particles with no corners and a clear outline. The surface structure of these particles showed a structure similar to a tangle of frizzled fine threads, which is common to the surface microstructure of Mn-microparticles in sediment under Subtropical Ocean Gyre5,7, but with a finer frizzled thread-like structure. At present, it is considered that Mn-microparticles are formed and preserved on the deep-sea floor of the outer-rise sediment off Nemuro, Hokkaido, northern Japan under Subantarctic Ocean Gyre. Oxygen supply system is essential for the formation of manganese oxides in such sedimentary environment.
Reference: 1Post, 2000, PNAS; 2Hein et al., 2013, Mar. Geol.; 3Usui et al., 2017, Ore Geol. Rev.; 4Yasukawa et al., 2020, Ore Geol. Rev.; 5Uramoto et al., 2019, Nature Comm.; 6Usui et al., 2020, Sci. Rep; 7Uramoto et al., 2024, Geochem. J.; 8Yi et al., 2023, Sci. Adv.; 9Uramoto et al., 2014, Limnol. Oceanogr. Meth.