Sediment accumulation and bioturbation rates in the deep Northeast Atlantic determined by radiometric techniques

Abstract

Abstract Carvalho, F. P., Oliveira, J. M., and Soares, A. M. M. 2011. Sediment accumulation and bioturbation rates in the deep Northeast Atlantic determined by radiometric techniques. – ICES Journal of Marine Science, 68: . The upper layers of boxcore bottom-sediment samples from the Porcupine Abyssal Plain (five cores) and from the Iberian Abyssal Plain (eight cores) in the Northeast Atlantic were analysed for porosity, grain size, organic carbon, calcium carbonate, and radionuclides. Radiometric ages of sediment layers were determined using 230Th excess (the 230Thexc/232Th ratio method) and 14C radionuclides. Sediment accumulation rates were 0.14 and 3.2 cm kyear−1 at the Porcupine and Iberian Abyssal Plains, respectively. Sediment mixing, determined through 210Pb excess, was in the upper 5–11 cm sediment layer, likely as a result of infauna activity. Biodiffusion coefficients averaged 0.40 ± 0.37 and 1.05 ± 1.02 cm2 year–1 and were not significantly different in the sediments of either abyssal plain. The low rates of sediment accumulation and bioturbation in the abyssal depths of the Northeast Atlantic suggested that immobilization of sediment-reactive man-made radionuclides released near the seafloor will take place very slowly and with limited sediment burial.