OCEANOGRAPHY 



59 



Enewetak 

 Isl. 



Fig. 2 Location of islands and currents. See text for discus- 

 sion. [From Atkinson et al. with permission.] 



reef flats are shallow (0 to 2 m deep), and the deepest 

 part of the Deep Entrance is about 57 m. Because the sur- 

 face North Equatorial Water is well mixed to a depth of 

 75 m, water flowing into the lagoon, either over the reefs 

 or through the channels, is well-mixed ocean surface water. 

 Salinity, temperature, dissolved inorganic plant nutrients, 

 and dissolved carbon dioxide suggest little stratification 

 within the lagoon water (Table 1). For the data at hand, 

 surface water (0 to 10 m) appears to be slightly cooler 

 (0.2°C) and less saline (0.06 °/oo) than deeper water. 

 During the data collection period (July 26 to August 16, 

 1974), the weather was unusually rainy and cool 

 (S. V. Smith, personal communication). August is a period 

 of low wind; therefore, stratification should occur most 

 dramatically during this month, yet no major stratification 

 is evident in these data. There is only a slight indication of 

 the rain in the surface water. Nutrient data collected by 

 S. V. Smith and M. J. Atkinson during June 1979 in the 

 lagoon and passages also showed no vertical structure. 

 Several detailed nutrient profiles taken between to 2 m 

 above the bottom, at 10 cm intervals, revealed extremely 

 low and unchanging concentrations. Vertically averaged 

 phosphate and nitrate-nitrite concentrations are contoured 

 and suggest a weak minimum toward the center of the 

 lagoon (Fig. 3). 



and Biken, Buddemeier estimated that the water level is 



about 6.5 cm higher at Biken than at Japtan. CURRENTS 



LAGOON WATER 



The lagoon at Enewetak is well isolated from the gen- 

 eral westward flow of the North Equatorial Current. The 



Cross-Reef Currents 



Cross-reef currents involve shallow flow over the wind- 

 ward and leeward reef margins of the atoll. The area of 



TABLE 1 

 Chemical Data for Ocean and Lagoon Water* 



Temp 



(°C) 



Sal 



("/oo) 



Total 



alk 



(eq m^ 



PO« 



NO, 



NH^ 



(mmoles m ) 



Si 



pH 



Total 



CO2 Pco, 



(moles m ^) (uatm) 



Ocean 



'Data collected by S. V. Smith, July and August 1974. 



