[H-CG23] Earth surface processes related to deposition, erosion and sediment transport

[HCG23-02] Assessment of endobenthic activities around deep-sea hydrothermal vents

*Koji Seike¹, Kyoko Yamaoka¹, Akira Iguchi¹, Minako Tanaka², Tatsuo Fukuhara², Kato Kodai², Yuya Yamamoto², Akiyuki Ishida³ (1.Geological Survey of Japan, AIST, 2.KANSO TECHNOS Co., Ltd., 3.Japan Organization for Metals and Energy Security (JOGMEC))

Keywords:burrow, bioturbation, deep-sea, benthos

Benthic activities in the seafloor sediments, or bioturbation, are one of the most essential factors in an ecosystem of the deep-sea hydrothermal vent. Although the major methods in ecological studies on the benthos are counting occurrence species and measuring the biomass of the ecosystem, we are recently developing a new approach to evaluate benthic activities in the sediment using X-ray CT scanning of the seafloor sediments. We investigated sediment core samples collected from northwestern Pacific hydrothermal vents. Bioturbation structures (burrows produced by endobenthic invertebrates) preserved within the core samples were examined 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 using the visualization and analysis software Amira 3D Pro, which allowed observation of bioturbation structures in the cores. All recognizable biogenic sedimentary structures were manually traced and analyzed with the Amira software, i.e., burrow diameter and inclination were analyzed for the core samples. Using this method, we revealed the following findings: 1) Measuring bioturbated sediment volume is possible based on 3D observation of the cores, 2) Burrow diameter negatively correlated with burrow inclination, suggesting that the larger burrows tend to be oriented horizontally, 3) we can distinguish active burrows from those produced in the near past, and 4) We can distinguish abiotic sedimentary structures from biogenic structures based on 3D morphological investigation using the CT data.