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The age of a deep-sea clam, Tindaria caifisti-formis, from 3800 m depth has been determined by MRa (6.7 year half-life) chronology of separated size fractions of a captured population. A length of 8.4 mm is attained in about 100 years. Shells of this size fraction show about 100 regularly spaced bands, indicating that the growth feature may be an annual one.There are several reports indicating that the rate of metabolism on the deep ocean floor is extremely slow-generally one to two orders of magnitude slower than the rate for comparable organisms in shallow water systems (1-4). From small brood size and the high proportion of adult size classes observed for deep ocean benthos Grassle and Sanders (5) have postulated life histories with low rates of reproduction, growth, and mortality. The deep sea is an environment devoid of light, virtually invariant in ambient high pressure and low temperature, and probably subject to a slow food supply rate. These facts provide the basis for expectation of slow metabolic rates at depth but they also make the interpretation of growth features in the hard parts of deep-sea organisms difficult.The aim of our study was to explore the possibility of radiometrically determining the rates of growth of deep-sea benthic organisms that secrete a hard mineral shell. Our initial effort reported here is on a deep-sea clam, Tindaria callistiformis, an exclusively deep-sea species with regular growth bands. Our technique is to use the 228Ra (half-life = 6.7 years) concentrations in a number of growth stages and to infer from these data the growth rate of the organism.Radium-228 is produced from the decay of long-lived 232Th, which is found ubiquitously in clay-rich sediments at a concentration of about 10 parts per million although virtually absent in sea water. The 228Ra produced by a-decay is subject to release from sediments by diffusion or physical transport via the pore waters of the sediment into the overlying water. The distribution of 228Ra in the ocean after the initial study by Moore (6, 7) has been the subject of several intensive investigations (8, 9). Fig. 1 shows a profile from Trier et al. (9) for a North Atlantic Ocean station in the general vicinity of the site from which the clams used in this study were recovered.Radium-228 in surface waters of the deep ocean is derived from the sediment-water interactions in shallow coastal regions, especially where physical mixing knd bioturbation rates are high. Using 228Ra concentrations found in different layers of coral, Dodge and coworkers (10, 11) were able to date corals and determine that for several species the growth bands were indeed annual. Furthermore, by comparing the 228Ra/Ca ratio with 210Pb dating, they were able to demonstrate that this ratio was sensibly invariant in the surface ocean over at least 30 years.The 228Ra concentration at the water-sediment interface of the deep ocean floor is also high. Its concentration there is expected to be stabilized as well or better than in the surface waters. Thus the ...

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...

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