590 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 2 Americium-241 Associated with Components in 

 Core Samples of Sediment 



*The values in parentheses are the la counting errors expressed as the percent of the value listed. 



with depth in sediment cores from other lagoon locations (Noshkin et al., 1978a). The 

 concentrations of ^^^ ^"^^Pu and ^^^ Am associated with the carbonate components in 

 four cores taken along a 1 .5-km transect across Mike and Koa craters are shown in Fig. 6. 

 The concentrations in the sediments from the Atolls' largest craters are surprisingly 

 nonhomogeneous. Turbulence and large-scale mixing of the sediments during and after 

 testing should have produced a much more uniform distribution than that found. The 

 2 39 24 0pjj concentration in the sediment column at station 17E is fairly uniform to a 

 depth of 50 cm. At station 16E, the concentration increases with depth to 35 cm. The 

 ^'^^ Am concentration in the sediment column at station 16E decreases with depth. No 

 correlation is obvious between the ^"^^Am and 2 39+240p^ concentrations associated 

 with the components of these crater sediments. The craters should act as natural sediment 

 traps, but little sedimentation in the Mike and Koa craters has occurred since the bottom 

 depths were redetermined in 1964. In 1964 the maximum bottom depth of Mike crater 

 was 27.4 m below sea level (U. S. Atomic Energy Commission, 1973). We have found no 

 measurable change in the depth of the crater bottom during the period 1972 to 1977. 

 Only small quantities of resuspended or reef-generated particulate material are then 

 transported in the water masses to the western reef. Very little sedimentary material 

 therefore escapes from the lagoon, and any resuspended bottom material probably settles 

 out again on the lagoon floor close to its origin. The complex areal and vertical patterns 



