Uranium and thorium decay series nuclides in plankton from the Caribbean1

Abstract

Zooplankton(predominantly calanoids and cyclopoids) from the Caribbean were analyzed for 'W, 254U, 23pTh, =Th, =Ra, **'Ra, aoPb, and zloPo. The concentration factor in the zooplankton relative to seawater is highest for 210Po. "'Pb and '"Th have similar concentration factors and are comparable (when normalized to 226Ra) to reported fiberscavenging experimental data on ""Pb and %'"Th. The dominant transport agent for =OPo and ""Pb from the mixed layer to depth cannot be unmodified zooplankton debris.The abundances of the members of the uranium and thorium decay series in the oceans can be used to understand both the dynamics of ocean circulation and the influence of particles in the water column on the distribution of elements in ocean water profiles and marine sediments. A major role is played by plankton both as an indicator of surface water radionuclide abundances and as one of the active agents modifying these abundances. We report in this paper a method of determining the abundances of several natural radionuclides in the same small plankton sample, together with data gathered over much of the Caribbean and the inferences drawn concerning the processes responsible for the observed distributions.The samples were collected on two cruises during the fall and winter of 1971-1972 as previously reported (Forster et al. 1972). All the samples (except stations 75 and 79) consist predominantly of calanoids and cyclopoids. This relative homogeneity may be expected to minimize effects of differential uptake of the radionuclides by the animals. Figure 1 is an index map of the stations at which samples were taken. Analytical methodsThe plankton samples were freeze-dried on ship and stored in plastic vials. On ar-1 This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by ONR under contract N00014-67-A-0097-0022. rival at Yale they were dried overnight at 105OC, and homogenized in an agate mortar. The available sample for radiochemical analyses, generally around 1 g, was used in the following radiochemical procedure for the determination of 238U, 234U, 232'-J-J,, 228Th, 228Ra, 226Ra, 210Pb, and 210Po.The dry homogenized sample was weighed and transferred to a Teflon dish, moistened with distilled water, and concentrated HN03 was added until effervescence ceased. Spikes of 208Po and 230Th or 232U-228Th and Pb carrier (ca. 40 mg as PbCr04) were added, and the sample was heated to dryness after the addition of 25 ml of HN03 and 5 ml of HClO*. This residue was taken to dryness again after the addition of 10 ml HCl, and then leached with aliquots each of 12 ml of 1 M HCI. The remaining solid ( generally siliceous ) was treated with 10 ml of HF and a few drops of HC104 and taken to dryness. This residue was again heated to dryness after the addition of HCl as before, and leached again with two aliquots each of 12 ml of 1 M HCl. The combined leaches from all treatments yield a clear solution in 1 M HCI. All apparatus used to this stage was Teflon or polypropy...

A two-tracer (210Po–234Th) approach to distinguish organic carbon and biogenic silica export flux in the Antarctic Circumpolar Current

“…Most of the 210 Pb that is bound to the cell walls is excreted with the feces. This is consistent with data reported by Shannon et al (1970), Kharkar et al (1976), Beasley et al (1978) and Heyraud and Cherry (1979), which indicated high 210 Po/ 210 Pb ratios in various plankton species. Fisher et al (1983) concluded that 210 Po/ 210 Pb ratios in fecal pellets of zooplankton are half those of their phytoplankton food supply in field samples.…”

“…The adsorption rate of a radionuclide is dependent on its physico-chemical behavior, its concentration in the water, the particle concentration and particle composition in the water. Kharkar et al (1976) and Heyraud et al (1976) found the following relative adsorption intensities:…”

“…Direct measurements of particle fluxes with sediment traps (Fischer et al, 1988;Wefer and Fischer, 1991) and indirect estimates from particle reactive radionuclide export rates are well known. Since these radionuclides are produced and decay at known rates, they provide a good tool to quantify particle export (Cherry et al, 1975;Kharkar et al, 1976;Bacon and Anderson, 1982;Fisher et al, 1988). With knowledge of the fluxes and the adsorption behavior of the radionuclides, it is possible to make good estimates of carbon export (Moore and Dymond, 1988;Buesseler et al, 1992).…”

Particle fluxes associated with mesoscale eddies in the Sargasso Sea

“…210 Pb and 210 Po are both particle-reactive, with varying affinities both in terms of efficiency and type of matter to which they associate and, indeed, different binding mechanisms: 210 Pb and 210 Po adsorb on particle surfaces, but 210 Po is also incorporated via biological activity and is preferentially enriched in organic tissue (Fisher et al, 1983;Kharkar et al, 1976;Shannon et al, 1970;Stewart and Fisher, 2003a&b;Stewart et al, 2005). As a consequence, 210 Po is more efficiently removed from surface waters than 210 Pb via sinking particles, and results in disequilibrium between the two radionuclides throughout the upper 500m (Figure 10 and from 40 to 60 dpm m -2 d -1 for E4 (Table 3).…”

Scavenging of 234Th and 210Po in surface water of Jinhae Bay, Korea during a red tide

“…234 Th and 210 Po are well known for being particle-reactive chemical property, although they may not follow the same geochemical pathway. 210 Po is more reactive with biogenic particles than other nuclides (Shannon et al, 1970;Kharkar et al, 1976;Beasley et al, 1978;Tanaka et al, 1983;Turekian et al, 1974). Shannon et al (1970) determined that the enrichment factors of 210 Po from seawater, phytoplankton and zooplankton were 1, 6 and 23, respectively.…”