Bioturbation in sediment cores from the Clarion-Clipperton Zone in the northeast Pacific: Evidence from excess 210Pb

Radioactivity levels of Pb-210 and Ra-226 were measured to evaluate the bioturbation coefficients and mixing depths in one sediment core collected from the polymetallic nodule area inside the Clarion-Clipperton Zone (CCZ), a contract area of the China Ocean Mineral Resources Association (COMR) in the eastern Pacific Ocean. With a steady-state diffusion mode, the bioturbation coefficient and mixing depth of the sediment core were estimated to be 81.5 cm(2)/a and 51.3 cm, respectively, higher than that of the sediment core from the previous results from abyssal or global areas, which may be attributed to the distribution of total organic carbon (TOC) abundance. In addition, the transport flux of TOC from the surface layer to the deep layer were evaluated to be 1.15 mmol/(cm(2)center dot a), resulting in 83,200 tons of carbon buried annually into the sediment in the CCZ, indicating that a potential carbon sink will be disturbed with future exploration.