Rates of Benthic Mixing in Deep-Sea Sediment as Determined by Radioactive Tracers

A series of closely spaced radiocarbon measurements on a carbonate-rich box core from the western equatorial Pacific show a mixed layer at least 7 cm thick, with 14 C ages between 4000 and 5000 years, and an orderly progression of ages below this layer, indicating an average sedimentation rate of about 2 cm/10 3 yr. The profile can be simulated using a numerical extension of the mixing model of Guinasso and Schink (1975) and a numerical exponential mixing model. The best-fit iteration indicates an apparent mixing coefficient of K = 120 cm 2 /10 3 yr which also fits well the excess 210 Pb distribution. The best-fit also indicates that a small amount of sediment was lost on the top, and that there was a reduction in sedimentation rate within the early Holocene.