RESTRICTED 



9 



is thicker than the surface current but slov/er and more coiapressed 

 laterally (occupying about the central one-half to tv/o-thirds of 

 the area of the lagoon]. Its iiiass transport is probably between 

 7(K and 90^ that of the surface current. Like the latter, it is 

 affected by the tide, the speed decreasing on the ebb and the 

 direction changing near the passes. 



(g) j^ron Bikini Island v;estv/ard there is a current v/hich 

 runs at iiid-depths just inside the northern reefs and :i.ore or 

 less parallel to them. It increases in size and thickness as 

 it progresses v/estv/ard. The salinity of the water in this cur- 

 rent (see section 3.21) indicates that it is reef v;ater of fair- 

 ly recent origin. Its final disposition in the western end of 

 the lagoon has not been studied, but presumably some small part 

 is lost over the western reefs or through the westernmost passes, 

 while the remainder joins the botton current. 



(h) Summarizing these observations*: The lagoon derives its 

 v;ater by continuous inflow over the northern and eastern reefs 

 and by tidal interchange along the rest of the periphery, of 

 which the southwestern passes are the r.iost important, the la- 

 goon has an active internal circulation v/hich consists priraarily 

 of a westerly v;ind-driven sui-face current and a return flow along 

 the bottom. 



The current rueasureiaents presented in this section are the 

 framevrork that will be used in fulfilling the practical require- 

 ments of the report, namely the deterLiination of the path of 

 contai.iination in the lagoon and the rate of flushing. However, 

 before preparing the final estiiaate it is necessary to exatiine the 

 variations in temperature and salinity in the lagoon, which add to 

 the gene^ -^1 knowledge of lagoon circulation and serve as an in- 

 dependent check on the quantitative results. 



3.2 Measurements of tei.iperature and chemical constituents 



3.21 Plorizontal variatiuuib in temperature and chemical 

 constituents 



Since the waters of Bikini lagoon are derived from the rela- 

 tively homogeneous surface layer of the surrounding ocean and are 

 subject to continual interchange with it, it is not to be ex- 

 pected that a high degree of variability would occur in the la- 

 goon. However, the small variations that have been observed are 

 useful in analyzing the general system of circulation. 



Variability can arise in three v/ays: (a) In the surface 

 water of the surrounding ocean there are slight north-south 

 gradients in temperature and salinity, the temperatiire increas- 



