Determination of radium, thorium, uranium isotopes, and /sup 210/Pb in sediments and sediment pore waters from North Equatorial Pacific deep-sea clay-silicous oozes shows that the radium and uranium isotopes are mobile in the pore water. The concentration-depth profiles of radium can be understood in terms of a diagenetic model which takes into account mixing of sediment particles by bioturbation, molecular diffusion in the pore water, adsorption onto particle surfaces, as well as radioactive production and decay. The /sup 234/U//sup 238/U activity ratios in several samples are higher than the seawater value, indicating some enrichment of /sup 234/U in the pore water. However, the absolute concentrations of /sup 238/U and /sup 234/U are 25% lower than those in seawater, suggesting that the sediments form a sink for uranium isotopes. /sup 210/Pb is present in the pore water at concentrations approx. 20% that of /sup 226/Ra. The origin of /sup 210/Pb in the pore water is uncertain and could be due either to its in situ mobilization in the sediments or subsequent production in the laboratory from the decay of /sup 222/Rn. /sup 230/Th is present in measurable concentrations in the pore waters, but its distribution does not show any systematic trendmore » with depth or other parameters. The most likely source of /sup 230/Th appears to be minute amounts of sediment particles collected in the pore waters during the squeezing operation.« less
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Cochran et al. (1980) studied this question.