Bioturbation in near-surface sediments from the COMRA Polymetallic Nodule Area: evidence from excess 210Pb measurements

In order to evaluate bioturbation in sediments from the COMRA Polymetallic Nodule Area in the northeast tropical Pacific, excess 210 Pb profiles in sediments cores col- lected with multiple corers during R/V DAYANGYIHAO Environmental Program Cruise in 1998 were measured by direct gamma assay using Ortec HPGe GWL series well-type coaxial low background intrinsic germanium detectors. A steady-state diffusion model of excess 210Pb profiles suggests that bioturbation mixing depths and biodiffusion coefficients are 16 cm and 2.75 cm2/a in East Zone, and 6 cm and 0.26 cm2/a in West Zone, respectively. Furthermore, the observa- tions of macrofauna and measurements of total organic car- bon (TOC) content in sediments suggest that bioturbation is directly controlled by species and abundance of benthic fauna, such as polychaete, and the bioturbation mixing depth and intensity are positively correlated with the organic mat- ter content.