DISTRIBUTION OF PHOSPHATE IN THE SEA 



11 



Section XI. stations 93 to 71: practically east and 

 west between latitudes 18° and 10° south, from the Sa- 

 moan Islands (longitude 168° west) to Callao, Peru (lon- 

 gitude 78° west. --In spite of the fact that this entire sec- 

 tion lies in the tropics, there are no extremely low 

 phosphate values. West of station 78 the surface water 

 has a temperature above 25°, yet in that region many 

 surface phosphate values are above 25 mg PO4 per cubic 

 meter. The highest quantities of phosphate were found 

 toward the east. 



The phosphate transition layer follows very closely 

 the isotherms of 15° and 20°, and rises to near the sur- 

 face toward the coast, where the richest surface water 

 is found. The intermediate layer of antarctic water is 

 not evident in the phosphate section but appears in the 

 station curves of the vertical distribution. The layer of 

 maximum phosphate lies between 600 and 1500 meters 

 with values between 225 and 325 mg PO4 per cubic me- 

 ter. The deeper water has a phosphate content of near- 

 ly 225 mg per cubic meter. 



Section XII. stations 45 to 40: in the equatorial 

 southeastern Pacific, extending approximately along 

 parallel 2° south from longitude 105° west to the South 

 American coast. --This section is another example of an 

 area in the tropics with comparatively large quantities 

 of phosphate at the surface. Although lying very close 

 to the equator, all the surface values were above 25 mg 

 PO4 per cubic meter. This is in accord, however, with 

 the low temperatures observed here. At stations 42 and 

 43, where the coldest surface water is encountered, the 

 phosphate values are highest, reaching 52 mg per cubic 

 meter at station 43. 



The transition zone lies very close to the surface, 

 above 200 meters in the western part of the section, and 

 in the upper 100 meters in the eastern part. The line of 

 maximum phosphate occurs between 500 and 1200 me- 

 ters, the quantities at most stations being between 225 

 and 275 mg PO4 per cubic meter. 



Section V. stations 162 to 148 and 134 to 130: ex- 

 tends northeastward from the Samoan Islands (latitude 

 14° south, longitude 168° west) to San Francisco (lati- 

 tude 37° north). --This section demonstrates that the 

 quantity of phosphate at the surface of the sea is not a 

 function of the latitude and that the tropical zone is not 

 necessarily a region of low fertility. It indicates, on 

 the other hand, that the phosphate content of the upper 

 water layers is intimately associated with vertical water 

 movements occurring in the troposphere. 



Beginning with station 130 at the northern end of 

 this section, we find 36 mg PO4 per cubic meter at the 

 surface in a region where there are upwelling of subsur- 

 face water, a strong surface current, and relatively low 

 temperatures. As the distance from the California coast 

 increases, the phosphate content of the surface water 

 decreases. Between stations 132 and 150 the phosphate 

 content is extremely low, less than 10 mg per cubic me- 

 ter, not only at the surface but usually to below 100 me- 

 ters. Where these low values occur, there are no prom- 

 inent currents. 



Continuing southward we find at station 152, in the 

 North Equatorial Current, 20 mg PO4 per cubic meter 

 at the surface, but at stations 153 and 154, in the Equa- 

 torial Countercurrent, the values are again low. Higher 

 values, about 25 mg PO4 per cubic meter, are found at 

 stations 155 and 156 which are near the southern border 

 of that current. As previously stated, at the borders of 

 the Equatorial Countercurrent there is probably irregu- 



lar water movement with vertical components. 



The relation of the phosphate content of the sea to 

 the hydrographic conditions is demonstrated by the tran- 

 istion zone in this section. For example, at stations 

 130 and 131 in the region of upwelling near the Califor- 

 nia coast, the increase in the phosphate content below 

 the surface layer is extremely rapid, as is also the case 

 from stations 150 to 156 in the North Equatorial Drift 

 and the Equatorial Countercurrent. Southwest of station 

 132 and northwest of station 150, the transition zone 

 widens until, at station 134, the changes in the phosphate 

 content are the most gradual. Similarly, southwest from 

 station 154 the change in the phosphate content with depth 

 becomes more gradual, although certain irregularities 

 are encountered. The thermocline shows similar varia- 

 tions with the different regions. 



The axis of the phosphate maximum lies at about 

 750 meters from stations 130 to 157, but south of this it 

 gradually descends, reaching 1200 meters at station 162. 

 The maximum phosphate values decrease more or less 

 regularly from 275 mg PO4 per cubic meter in the north- 

 east to less than 225 mg per cubic meter in the south- 

 west. The deeper water contains approximately 200 mg 

 PO4 per cubic meter with slightly higher values toward 

 the equator. 



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 line 

 representing 10 mg PO4 per cubic meter shows a 

 marked deficiency of phosphate in the upper layers, the 

 line reaching to a depth of 300 meters at station 140. 



The maximum phosphate content occurs at from 900 

 to 1600 meters, with over 300 mg PO4 per cubic meter. 

 Below 3000 meters this concentration is from 225 to 250 

 mg PO4 per cubic meter. 



Section XIV. stations 140 to 130: from the Hawaiian 

 Islands to San Francisco. --Except at stations 130 and 

 132 which have already been discussed (Section V), the 

 surface layer is extremely low in phosphate, the 10 mg 

 PO4 per cubic meter line being found at 100 meters at 

 station 133 and then gradually descending, reaching a 

 depth of almost 300 meters at station 140. 



The transition zone usually extends to about 500 me- 

 ters or more except at stations 130 and 132, where it 

 comes much nearer the surface. The line of maximum 

 phosphate runs for the most part between 500 and 1000 

 meters, with values between 250 and 325 mg PO4 per 

 cubic meter. Below a depth of 3000 meters the concen- 

 tration is approximately 250 mg PO4 per cubic meter. 



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 longitude 

 161° and 141° west. --The surface phosphate values are 

 low, with the 10 mg PO4 per cubic meter line running at 

 about 100 meters except at station 146, where it is at 

 200 meters. The maximum values, ranging from 275 to 

 300 mg PO4 per cubic meter, are found at 800 meters at 

 the easternmost station to about 1500 meters at the 

 westernmost station. Below the maximum layer there 

 are from 200 to 250 mg PO4 per cubic meter. 



Section VI. stations 130 to 125 : in the northeastern 

 Pacific, extending from San Francisco northwestward to 

 a point south of the Gulf of Alaska (latitude 52° north, 

 longitude 151° west). --In this section, which lies north 

 of longitude 37° north, the phosphate at the surface is 

 above 25 mg PO4 per cubic meter at all stations except 



