OCEANOGRAPHIC CLIMATE OF HAWAHAN ISLAJTDS REGION 



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381 



FiouRE 8. — Southern limit of the 35 °/oo salinity isopleth 

 April to July and November to February, and mean 

 location of the 35 °/oo salinity isopleth April to August 

 and November to February. 



13° N., 16° N., 21° N., 26° N., and the approximate 

 salinity variation in the vicinit}^ of Midway Island 

 (28° N., 177° W.). Both at 16° N. and at 26° N. 

 the minimum occurs dm-ing March and April, 

 whereas at 21° N., within the island area, it occurs 

 in Juh'. The maximum sahnity at 16° N. occurs 

 during November and at 26° N. during November 

 and December, whereas at 21° N. it occurs some- 

 time during December, January, or February. 

 The movement of the 35°/oo isopleth, therefore, 

 coincides with the minimum and maximum 

 salinity period at 21° N., but is out of phase with 

 those to the north and south of the islands. 



At 13° N. the salinity reaches a maximum in 

 September and then in October begins to decrease 

 rapidly, reaching a minimum in November. In 

 the Midway Island region, beside the double 

 maximum and minimum, the rapid decrease in 

 salinity from a maximum between May and June 

 to a minimum in July should be noted . 



Finally, figure 9 shows that the seasonal salinity 

 range is .50°/oo, .35°/oo, .25°/oo and .45°/oo at 13°, 

 16°, 21° and 26° N., respectively. At 21° N. it is 

 therefore approximately 50 percent of that either 

 at 13° N. or 26° N. 



The salmity distribution between 155° and 160° 

 W. can be illustrated further by meridional pro- 

 files. The lack of observations made it necessary 

 to group the data for a number of months during 

 the minimum and maximum salinity period at 21° 

 N. Figure 10 shows the mean salinity profiles for 

 April through August and for November through 

 February. 





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JAN MAR MAY JUL SEP NOV JAN MAR 



Figure 9. — Seasonal variation of the surface salinity at 

 13°, 16°, 21°, 26° N., between 155° to 160° W., and in 

 the vicinity of Midway Island. 



The low salinity profile (fig. lOA), representative 

 of the June distribution, shows that the salinity 

 increases northward from 34. 65%© at 10° N. to 

 34.75°/oo at 20° N., or only by an average of 

 .01°/oo per degree of latitude. The salinity then 



