5:15 PM - 7:15 PM
[MZZ44-P01] Microstructures observed on the surface of ferromanganese crusts at the Takuyo-Daigo Seamount
Keywords:Ferromanganese crusts, Microstructures
Ferromanganese crusts are recognized as one of the next generations of mineral resources owing to their composition enriched with industrially valuable metals. Although research on their formation processes has been conducted extensively, a comprehensive understanding remains elusive because of their extremely slow growth rate (a few millimeters per million years) and their presence in the deep sea (1000 m-5500 m), which is not easily accessible. On the other hand, studies in the field of molecular biology have advanced in elucidating the types of microorganisms inhabiting on the surface of ferromanganese crusts and their metabolic functions, suggesting that these microorganisms may be involved in the formation of ferromanganese crusts (Kato et al.,2018; Kato et al.,2019).
The study focuses on samples from the Takuyo-Daigo Seamount, which has been investigated from various perspectives as a model seamount for ferromanganese crusts. Four samples collected from different depths (1432, 2988, and 5373 m) using the remotely operated vehicle “Hyper-Dolphin” during the KR16-01 cruise were used in this study. These samples were fixed overnight in 3.7% paraformaldehyde-filtered seawater, and preserved in 50% ethanol-phosphate buffer saline (PBS) at 4 degrees C. The samples were dehydrated in 99% ethanol and air-dried before observation. The microstructure of the surface (~1 cm) of each sample was observed using a scanning electron microscope (SEM), and its chemical composition was analyzed using energy-dispersive X-ray spectroscopy (EDS) attached to the SEM.
As a result of the observations, differences in the surface 3D structure were observed depending on the depth. These differences are considered to correspond to the differences in micro-growth textures observed in the cross-sections of each sample. On the surface of the samples above the carbonate compensation depth (CCD), many coccolithophorid scales and microparticles, which are presumed to be the skeletons of plankton with carbonate as the main components, were observed. Whereas such particles were not observed on the surface of the sample below the CCD. Furthermore, in the grooves where microorganisms’ cell-like microstructures were observed, manganese was found to be deficient compared to other areas. The manganese deficiency in the grooves was also reported by Kato et al. (2018) by SEM-EDS analysis of a thin section, suggesting that microorganisms may be involved in the local variation of elemental composition.
[Ref.]
Kato et al. (2018) Microbes Environ. 33, 366-377. Kato et al. (2019) PLoS ONE 14(11): e0224888
The study focuses on samples from the Takuyo-Daigo Seamount, which has been investigated from various perspectives as a model seamount for ferromanganese crusts. Four samples collected from different depths (1432, 2988, and 5373 m) using the remotely operated vehicle “Hyper-Dolphin” during the KR16-01 cruise were used in this study. These samples were fixed overnight in 3.7% paraformaldehyde-filtered seawater, and preserved in 50% ethanol-phosphate buffer saline (PBS) at 4 degrees C. The samples were dehydrated in 99% ethanol and air-dried before observation. The microstructure of the surface (~1 cm) of each sample was observed using a scanning electron microscope (SEM), and its chemical composition was analyzed using energy-dispersive X-ray spectroscopy (EDS) attached to the SEM.
As a result of the observations, differences in the surface 3D structure were observed depending on the depth. These differences are considered to correspond to the differences in micro-growth textures observed in the cross-sections of each sample. On the surface of the samples above the carbonate compensation depth (CCD), many coccolithophorid scales and microparticles, which are presumed to be the skeletons of plankton with carbonate as the main components, were observed. Whereas such particles were not observed on the surface of the sample below the CCD. Furthermore, in the grooves where microorganisms’ cell-like microstructures were observed, manganese was found to be deficient compared to other areas. The manganese deficiency in the grooves was also reported by Kato et al. (2018) by SEM-EDS analysis of a thin section, suggesting that microorganisms may be involved in the local variation of elemental composition.
[Ref.]
Kato et al. (2018) Microbes Environ. 33, 366-377. Kato et al. (2019) PLoS ONE 14(11): e0224888