OCEANOGRAPHY 



65 







2.4 - ^ J T ■ 16 



2 4 6 



Fig. 7 Vertical current profiles. Number at end of arrow 

 gives depth in meters. Arrow gives direction of the current. 

 Circled number gives the depth of the bottom in meters. 

 [From Atkinson et al. with permission.] 



TRADES 



Surface 

 current 

 (0-10m) 



Deep-water 

 current 

 (30-50m) 



_L 



_L 



_L 



cm s-1 



A 0-10m 

 A 10- 20m 

 O 20- 30m 

 • 30- 40m 

 ■ 40- 50m 



Fig. 8 Summary of drogue results. The shaded spiral 

 represents the approximate endpoints of current vectors from 

 the origin. [From Atkinson et al. with permission.] 



Windward Reef 



jy peep 

 ;^;; Entrance 



South Channel 



Fig. 9 General current patterns in the lagoon. See text for 

 key. 



increase toward the south end of the atoll to 

 acconnmodate the inflowing water across the windward 

 reef. Figure 11 shows the relative increase in southerly 

 volume transport versus distance from the north end of the 

 atoll. These relative volume transports are based on 

 cumulative transport across the windward reef. These are 

 reported as relative values, since variation in swell and 

 wind direction alter this relationship an unknown amount. 



Wind 



The wind creates the downwind drift of the surface 

 water and the upwind drift of the mid-depth water. These 

 can be qualitatively described as a special case of Ekman 

 wind-driven circulation. This pattern is superimposed on 

 the net drift of the entire water column toward the South 

 Channel. This southerly drift can be observed in the deep 

 water, below surface layers affected by the wind. 



The northern end of the atoll has a relatively small 

 southerly drift based on cumulative net input (Fig. 11); 

 therefore, the effect of the wind can be observed at a 

 deeper depth in the north end than in the south end of the 

 atoll. Drogues suspended at 38 m in the north end moved 

 northeast to east, whereas drogues at a similar depth in 

 the southern end moved south. The increasing volume 

 transport from north to south, due to the increasing net 

 input over the windward reef, creates a southerly deep 

 current that thickens toward the southern end of the 

 lagoon. Figure 12 is a plot of the 38 m drogue directions 

 versus distance from the north end of the atoll. By the 

 middle of the lagoon, the layer at 38 m is well within the 

 southerly deep current (Fig. 12). 



