A STUDY ON THE PROPERTY OF THE COASTAL WATER 

 AROUND HACHIJO ISLANDS 



By Yasuo MiYAKE, Y. Sugkra and K. Kameda 



Meteorological Research Institute, Tokyo, Japan 



It is interesting to study how the property of the ocean water is 

 affected by the presence of a tiny island in the far-off sea, and to w'hat 

 extent the coastal water of such an island is changed by land water 

 pouring into the sea. Since the land ^vater contains more nutrient 

 matter than the offshore water, it may contribute more or less to the 

 biological productivity around the island. Accordingly, a study of this 

 problem will give also a basic knowledge for the coastal fisheries and 

 the growth of sea weeds near the island. 



For such a program, the chemical properties of the coastal sur- 

 face water around Hachijo Island (33°05'N, 139°48'E) were studied 

 in July, 1951, December, 1952, and in October, 1953, 



Land waters of the island were also chemically investigated during 

 the observation periods. In summer (from 13 to 28 July, 1951) , the 

 surface water temperature varied from 23.7 °C to 27.4°C, pH of sea 

 water averaged 8.3 and the mean chlorinity was 18.75°/oo- The con- 

 centrations of most of the nutrients in this season were so low that am- 

 monia-N v/as less than 3/xg atoms per liter, nitrite-N was also less than 

 O.OBjig atoms per liter, and phosphate-P could be found only in traces. 

 Only silicate-Si was present in an appreciable amount. The amoimt 

 was about 10/j,g atoms per liter in the offshore water, but increased 

 as the shore was approached until a quantity of 20 to 70/ag atoms per 

 liter was present. In winter (from 6 to 14 Dec, 1952) , the water tem- 

 perature of the surface was about 20°C and the chlorinity averaged 

 ]9.02Voo. which was comparatively higher than in summer. The 

 amounts of the nutrient salts were also larger. Nitrite-N and nitrate-N 

 were contained from 0.05 to 0.70 and from 1 to lOO^ig atoms per liter 

 respectively. Phosphate-P was from 0.05 to 4.0^g atoms per liter. Sil- 

 icate-Si was from 10 to 70^g atoms per liter. The distribution patterns 

 of these compounds around the island were like that of the chlorinity 

 shown in Figure 1. As shown in Figure 1, the effect of the island on 

 the ocean water was greater in the region from the eastern to the 

 southern coast owing to the different amount of the outflowing land 

 water as well as to the direction of the current. The effect of the ocean 



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