DISTraBUTION OF OXYGEN IN THE PACIFIC OCEAN 



33 



to higher levels and decreases in value but is still very 

 evident at station 157 at 400 meters. There will be a 

 general discussion of the oxygen minimum later (p. 34). 



The oxygen content of sea water can often be taken 

 as an index to dynamic conditions, but there are in- 

 stances when it cannot be so used. For example, the 

 intermediate antarctic water of low salinity penetrating 

 to station 151 at 100 meters cannot be seen in the oxygen 

 section because of the proximity of this water to the sur- 

 face. The oxygen maximum at about 150 meters at sta- 

 tions 159 and 160, however, may be caused in part by the 

 Inflow of water from the south. Such a flow is evidenced 

 also in the salinity distribution. Similarly, the maximum 

 at station 161 at 700 meters may be associated with the 

 influx of water of low salinity at this point. 



Below the depths at which the minimum occurs, the 

 oxygen content increases more or less regularly with 

 depth. Although the oxygen content is somewhat variable 

 at great depths, it definitely increases from north to 

 south at the 2000- and 3000-meter levels. The observa- 

 tions indicate that the bottom water has an oxygen con- 

 tent between 3.0 and 3.5 ml per liter or about 40 percent 

 of saturation. One observation made near 4000-meter 

 depth at station 152 shows 3.63 ml per liter. 



Section VII. stations 139 to 143; more or less north 

 and south in the central North Pacific, following approx- 

 imately meridian 160° west from the Hawaiian Islands 

 (latitude 22° north) to about latitude 34° north. --The ox- 

 ygen content at the surface throughout this section is 

 above 5.0 ml per liter. A maximimi is found with its 

 center at a level of about 100 meters at the north end 

 and 75 meters at the south end of the section. This max- 

 imum has a value between 5.0 and 6.0 ml per liter or 

 over 100 per cent of saturation. At station 143 more 

 than 6.0 ml per liter occurs, which represents an oxygen 

 saturation greater than 110 per cent. Below this maxi- 

 mum there is a clearly defined secondary minimum. 

 The level of this is indicated by the broken line on the 

 chart at about 250 meters. It is more clearly shown in 

 the vertical distribution curves than in the section. It 

 will be recalled that a double minimum was found at the 

 southern stations in Section V. 



The primary minimum occurs at 1000 meters at 

 station 143. From here southward it rises to 800 me- 

 ters and increases in value. In the north it is repre- 

 sented by less than 0.5 ml per liter (less than 5 per cent 

 saturation); south of station 141 it is between 0.5 and 

 1.0 ml per liter (10 to 20 per cent saturation). Below 

 this minimum the oxygen increases regularly. The only 

 observations made below 3000 meters were at station 

 142 where it is indicated that the bottom water contains 



more than 3.0 ml per liter of oxygen or is more than 40 

 per cent saturated. 



Section XIV. stations 140 to 130: from the Hawaiian 

 Islands to San Francisco. --Stations 130 to 134 already 

 have been discussed under Section V. South of station 

 134 the surface oxygen values vary between 4.0 and 5.0 

 ml per liter. The maximum at 100 meters at station 134 

 is continued west to station 140 with values generally 

 above 5.0 ml per liter or more than 100 per cent satu- 

 ration. The secondary minimum which was seen in sec- 

 tions V and VII, to the south and west of this section, 

 occurs here from station 140 eastward to station 137, 

 (latitude 24° 02' north, longitude 145° 33' west), although 

 it is apparent in the vertical oxygen section only at sta- 

 tion 139 at 225 meters. 



The marked minimum at 1000 meters at station 135 

 continues westward at a slightly lower depth and the ox- 

 ygen content increases slowly to above 0.5 ml per liter 

 or 10 per cent saturation. In the deep water there is a 

 definite increase in quantity of oxygen from northeast to 

 southwest. In this region the bottom water probably con- 

 tains from 3.0 to 3.5 ml of oxygen per liter. The high- 

 est value oI)served was 3.46 ml per liter at 4340 meters 

 at station 137. 



Section XV. stations 142 to 146: an east and west 

 section in the central North Pacific, extending approxi- 

 mately along the parallel 33° north between longitudes 

 161° and 141° west. --The surface oxygen content is 

 above 5.0 ml per liter, which represents 90 to 100 per 

 cent saturation. The layer of maximum oxygen values 

 lies at about 100 meters with water of more than 5.0 ml 

 per liter of oxygen, corresponding to more than 100 per 

 cent saturation. 



At about 250 meters there is a secondary minimum, 

 as represented on the oxygen section by a broken line. 

 To see this minimum more clearly, reference should be 

 made to the station curves (I-B, pp. 56-115). Theconcen- 

 tration of oxygen in this minindum layer is less than 5.0 ml 

 per liter. This minimum was observed in sections V, 

 VII, and XIV at all stations west of longitude 145° west 

 and south of latitude 16° north. Reference to the verti- 

 cal curves shows that it is only faintly evident at station 

 146 (latitude 31° 51' north, longitude 140° 50' west). It 

 is not seen in the curve for station 145 because no ob- 

 servations were made at the level at which it would be 

 expected to occur. 



The primary minimum is encountered at 1000 me- 

 ters with values below 0.5 ml per liter or about 5 per 

 cent of saturation. Below the minimum layer the oxygen 

 content increases, reaching 3.0 ml per liter, or more 

 than 40 per cent saturation, at 3500 meters. 



BUSHNELL SECTION 



Hawaiian Islands to Aleutian Islands: latitude 50° 

 30' north, longitude 175° 16' west to latitude 25° 33' 

 north, longitude 159° 38' west. --The Bushnell section is 

 constructed from data furnished by R. R. Revelle from 

 sixteen stations (Ba to Bp) occupied by the U. S. S. Bush - 

 nell on a line between the Aleutian Islands, latitude 50° 

 30' north, longitude 175° 16' west, to Hawaii, latitude 25° 

 33' north, longitude 159° 38' west. It is extended to the 

 south by one Carnegie station (140) and to the north by a 

 station (5055-17220) investigated jointly by the Hydro- 

 graphic Office of the U. S. Navy and the Oceanographic 

 Laboratories of the University of Washington (see 



Thompson, Thomas, and Barnes, 1934). The position of 

 the latter station is latitude 50° 55' north, longitude 177° 

 20' west. For comparison Carnegie stations 142 and 141 

 are also shown in the section between Bushnell stations 

 Bk and Bl, and Bm and Bn, respectively. The Bushnell 

 stations were occupied between August 18 and 26, 1934; 

 the University of Washington station on June 10, 1933; 

 and the Carnegie stations between October 3 and 7, 1929. 



This section in its northern part cuts across the 

 North Pacific West Wind Drift (sometimes called the 

 Japan Current) and continues southward through the cen- 

 ter of the North Pacific vortex. The currents in the 



