782 EIGHTH PACIFIC SCIENCE CONGRESS 



current is seen clearly on the southern coast where the shadow of the 

 current is iormed. 



The daily variations in the concentrations of some chemical sub- 

 stances were observed at a fixed point A in Figure 1. 



It was found that the chlorinity change showed a good correlation 

 with the tide, increasing and decreasing in the same direction as the 

 elevation of the water level (Fig. 2). The relation between the silicate 

 content and the chlorinity is almost linear as shown in Figure 3. Using 

 these facts, we can calculate the mixing ratio of ocean water and land 

 water. The result of calculation shows that the rate of mixing in the 

 surface water at the distance of 100 m. from the coast line is about 25% 

 in winter and the effect of land water seems to extend as far as to about 

 5 km. from the land. 



The diurnal variation of the dissolved oxygen content is shown in 

 Figure 4. It is maximum at about 14 h. and minimal in the early morn- 

 ing. Such a type of variation resembling somewhat that of air tem- 

 perature may be regarded as a normal one as pointed out by one 

 (Miyake i) of the present authors previously. 



In summer the lange of variation is greater than in winter, as the 

 popidation of living matter and the intensity of the sunshine are larger 

 in summer. 



Since most of nutrient matter near the shore is supplied from the 

 land, the chemical analysis of land water is also necessary. 



There are a number of wells, small springs and a few stieamlets in 

 the island. These may be classified into two groups from a chemical 

 point of view. The first group (A) of waters contains much chloride 

 and nutrient matter while the second one (B) contains a considerably 

 lesser amount. 



It is interesting to note that the content of the silicate-Si in land 

 water was comparatively larger in summer than in winter. In compar- 

 ing the land water with regard to the nutrient matter, it is seen that 

 the first group has a remarkably richer silicate and nitrate content than 

 the second. 



The average concentrations of both groups are shown in Table I. 



TABLE I 



Amm.-N Nitrite-N Nitrate-N Phosphate-P Silicatr-Si Chlorinity 



(Ug at/L us at/L ^g at/L MS at/L mk at/L % 



A 0.0 0.00 7.3 0.5 180 0.02 



B 3.0 0.05 95. 1.7 190 0.60 



' Y. Miyake: Ccophys. May.. Ifi, (194S). 66-70. 



