y 115 radionuclides have been fractionated (by dissolution, leaching, diffusion, etc.) can thus only be made: (1) within samples (such as sediment cores) having had only one source term, (2) by comparison with previously determined radionuclide concentrations at specified locations, (3) by the comparison of sediment-water relationships, or (4) by comparison of these data with data collected in the future. With respect to (1) above, the notably more constant concentration of 6c, in the 12-40 cm region of the sediment core collected at Station B-2 may be a Signature of a rapid early time fractionation of the rapidly settling particles deposited. 60 “Co between the In the upper regions of the station B-20 sediment core, and in data presented by Nelson and Noshkin (1973) from Eniwetok Atoll, 2078; (relative to other radionuclides) is enriched in surface sediments, and 6c, and 1376. either decrease or are more constant in concentration with depth than are other radionuclides measured. In addition, in the core col- lected at Station B-21, 69¢5 is also relatively depleted in surface sediments. These distributions may result from slow diffusion of the 60¢, and 137 Cs, or by other chemically mediated losses and subsequent aqueous phase transport of the radionuclides away from particles suspended in transport. Further, the deple- tion of W370 (relative to 23942405, ) from the sediments away from the regions of high radionuclide concentrations in the northwest quadrant may also be an example of the chemical solubility of the Cs. Such an explanation for the anomalous distribution of 13766 may be preferred to explanations based on its volatile precursors (137 ye, VW37 yy. This follows because, in theory, !?"cs would be expected to enrich in smaller sized, later time fallout, which would appear to mean that its areal distribution would be less, instead of more, restricted to smal] geographical areas. With respect to the historical literature, only a few radionuclide concentrations measured in this work can be compared with those reported