[M-ZZ44] Marine manganese deposits - Genesis, exploration and development

[MZZ44-P02] Spatial characterization of ²¹⁰Pb- and ¹⁴C-derived bioturbation activities in surface sediments at northwestern Pacific seamounts

*Yuki Ota¹, Masahiro Suzumura¹, Ayumi Tsukasaki¹, Atsushi Suzuki¹, Koji Seike^1,2, Jumpei Minatoya³ (1.National Institute of Advanced Industrial Science and Technology, 2.Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, 3.Japan Organization for Metals and Energy Security (JOGMEC))

Keywords:marine sediment, northwestern Pacific, bioturbation, seamounts, 210Pb, 14C

obalt-rich ferromanganese crusts are present on seamount summits in the northwestern Pacific at various water depths. International Seabed Authority has issued the environmental guidelines and requires contractors to conduct an environmental and biological baseline survey around the seamounts. In this study, ²¹⁰Pb activity measurements and ¹⁴C dating were conducted in sediment cores collected from the seamounts to evaluate the spatial characteristics of bioturbation activity. The results indicate the shallower mixing layer depth and the smaller particle mixing coefficient of the surface sediment at the summit areas than at the foot of seamounts, which suggests a weak bioturbation activity in the peaks. This difference in bioturbation activity may be attributed to the differences in bottom-water dissolved oxygen and particulate organic matter concentrations between the summits and feet of the seamounts in the northwestern Pacific.