Impact of depositional and biogeochemical processes on small scale variations in nodule abundance in the Clarion‐Clipperton Fracture Zone

摘要: Manganese nodules of the Clarion–Clipperton Fracture Zone (CCFZ) in NE Pacific Ocean are highly enriched Ni, Cu, Co, Mo and rare-earth elements, thus may be subject future mining operations. Elucidating depositional biogeochemical processes that contribute to nodule formation, as well respective redox environment, both water column sediment, supports our ability locate deposits evaluate potential ecological environmental effects deep-sea mining. For these purposes we studied local hydrodynamics pore-water geochemistry with respect coverage at four sites eastern CCFZ. Furthermore, carried out selective leaching experiments order assess mobility Mn solid phase, compared them spatial variations sedimentation rates. We found oxygen penetration depth is 180–300 cm all sites, while reduction NO3− only significant below small or no on sediment surface. At site without nodules, microbial respiration rates, determined by incubation using 14C-labeled acetate, slightly higher than nodules. Leaching showed surface sediments covered big medium-sized mobilizable Mn. Our deep measurements data suggest hydrogenetic oxic-diagenetic control present-day growth since free manganese from deeper unable reach propose observed strong lateral contrasts size abundance sensitive which turn, controlled small-scale seafloor topography bottom-water current intensity.