[M-ZZ47] Marine Manganese Deposits - Genesis, environment, and development -

[MZZ47-P01] Morphological analysis of bioturbation structures in northwestern Northwestern Pacific seamounts

*Koji Seike^1,2, Atsushi Suzuki¹, Yuki Ota³, Jumpei Minatoya⁴ (1.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 2.Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, 3.Environmental Management Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 4.Japan Oil, Gas and Metals National Corporation (JOGMEC))

Keywords:burrow, X-ray CT scan, deep-sea, benthos

Biological sediment mixing by benthic invertebrates, or bioturbation, is one of the most important controls on biogeochemical cycling in seafloor ecosystems. Revealing the nature of bioturbation is thus important if we are to better understand benthic marine environments. In this study, we obtained sediment core samples from Northwestern Pacific seamount summits and bases to investigate the nature of bioturbation in the area. Bioturbation structures (burrows produced by endobenthic invertebrates) preserved within the core samples were examined by using an X-ray CT scanner (Supria Grande, Hitachi Ltd., Japan) installed at the Geological Survey of Japan, AIST. The X-ray CT images were visualized and analyzed with the software Amira 3D with the XImagePAQ Extension, which enabled observation of bioturbation structures in the cores. All recognizable biogenic sedimentary structures were manually traced and analyzed with the Amira software, and burrow diameters and inclinations were estimated from the traces. Among the observed sites, the cores taken from seamount bases contained abundant biogenic sedimentary structures (burrows). Burrow diameters were approximately 2 mm, and burrow inclinations were approximately 30°. Burrow diameter negatively correlated with burrow inclination, suggesting that larger burrows tended to be oriented horizontally. By contrast, cores from seamount summits contained almost no clearly identifiable burrow structures.