ON THE MINIMUM OXYGEN LAYER IN THE 

 NORTH PACIFIC OCEAN 



By Takeo Kawamoto 

 Kobe Marine Observatory, Japan 



Oxygen in the sea is supplied by contact with the atmosphere and 

 by photosynthesis. On the other hand, dissolved oxygen is consumed 

 by the respiration of marine organisms and the reduction of bacterial 

 action or the reducing agents of both inorganic or organic matters dis- 

 solved in water. Thus the oxygen contents in sea water are always af- 

 fected by the reactions of general oxidation and reduction taking place 

 in the sea. Besides the oxygen content in the sea are influenced by 

 the mixing with other waters. Therefore, if there is no supply of oxy- 

 gen in sea water, the dissolved oxygen will be diminished gradually. 

 Then, if we observed a water mass which contained low oxygen value 

 in the intermediate waters, we generally consider that the water mass 

 had taken a long run and many times before reaching that region. 



So when we discuss the property of the water mass or its movement 

 in ocean, it is important and interesting to know the distribution of 

 dissolved oxygen in sea waters. Though the causes of the variations 

 in the dissolved oxygen content are not explained completely, but by 

 tracing the distribution of poor oxygen layer in the ocean some aspects 

 of the oceanic general circulation in the intermediate waters will be 

 given. 



We have much interest in the oxygen minimum layer observed 

 at the depths between 400 and 1000 meters in the North Pacific Ocean. 

 This paper is an attempt to obtain the general aspects of the general 

 oceanic circulation in the intermediate waters in the North Pacific 

 Ocean by the distribution of poor oxygen layer. Figures show the hori- 

 zontal distribution of the dissolved oxygen at 250, 500 and 1000-meter 

 layers, respectively. 



These oceanographical data were obtained from the following re- 

 ports: 



The "Carnegie" in 1928, 1929. 



The "Soyo Maru" in 1933, 1934, 1935. 



The "E. W. Scripps" in 1938, 1939, 1940, 1941. 



The U. S. S. "Bushnell" in 1939. 



The "H. M. Smith" in 1950. 



The "Tenyo Maru" in 1951. 



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