DISTRIBUTION OF HYDROGEN IONS IN THE SEA 



27 



minimum values vary between 7.5 and 7.6. Below the 

 layer of minimum pH the values increase, reaching about 

 7.7 near 3000 meters, the greatest depth investigated. 



Section VIII. stations 94 to 104: in the tropical west- 

 ern Pacific, extending from the Samoan Islands (latitude 

 13° south, longitude 172° west) north and west to station 

 104 (latitude 20° north, longitude 161° east). --The pH of 

 the surface water is between 8.2 and 8.3 except at sta- 

 tions 97 and 98 where it is less than 8.2. Water with 

 nearly the same pH as at the surface extends to a depth 

 of 100 to 200 meters. At station 100 the transition zone 

 is concentrated between the 100- and 200-meter levels 

 and the pH gradient is steep, as is the case with the 

 phosphate gradient. At the other stations the change in 

 pH with depth is more gradual, extending to more than 

 500 meters at some stations farthest north. 



There is no pronounced minimum pH value although 

 at most stations slightly lower values were found at 

 about 1000 meters than elsewhere. Below 2000 meters 

 pH values are about 7.7. 



Section XIII. stations 107 to 101: In the tropical 

 western Pacific, extending eastward from Guam (latitude 

 14° north, longitude 146° east) to station 101 (latitude 

 13°23' north, longitude 177° 27' east). --At the surface 

 the pH is well above 8.2 at all the stations, these values 

 extending to a depth of about 100 meters except at the 

 two southernmost stations where they reach nearly 200 

 meters. 



The transition zone extends to about 600 or 700 me- 

 ters at the stations near the center of the section, ex- 

 cept at station 101 where it extends to about 400 meters 

 only. 



At stations 101 and 102 a minimum is practically 

 lacking, but at the other stations it is shown at a depth of 

 about 1000 meters with pH values between 7.6 and 7.7. 



Below 2000 and 3000 meters the pH is between 7.7 

 and 7.8. 



Section DC. stations 107 to 120: from Guam (latitude 

 14° north, longitude 146° east) north to station 113 near 

 Yokohama (latitude 35 ° north), thence northeast to sta- 

 tion 120 (latitude 47° 02' north, longitude 166° 20' east). 



--In this section the pH varies more from station to sta- 

 tion than in the other sections. The pH at the surface 

 fluctuates from less than 8.2 to nearly 8.3 except at the 

 two most northern stations where it is below 8.0. 



The change in pH with depth is fairly gradual in the 

 southern part of the section, stations 107 to 115, the 

 transition zone extending from 500 to 1800 meters. At the 

 other stations the change is more abrupt, the lower limit 

 of the transition zone being at about 200 meters at sta- 

 tions 119 and 120. 



The depth of the minimum pH layer, which at most 

 stations is well marked, varies in a similar manner; 

 ranging from 1500 meters at station 112 to 350 meters 

 at station 120. The minimum values are between pH 7.5 

 and 7.7, the lower values being found in the north. Be- 

 low 3000 meters the pH is above 7.7. 



Section XVI. stations 118 to 125: extends in an east- 

 northeasterly direction across the northern part of the 

 North Pacific from station 118 east of northern Japan 

 (latitude 42° 29' north, longitude 155° 24' east) to station 

 125 south of the GuLf of Alaska (latitude 51° 58' north, 

 longitude 150° 39' west), extending along the Aleutian 

 Islands from stations 122 to 124. --Stations 118 to 120 

 were discussed under Section DC with which they are in- 

 cluded. 



The distribution of pH in this section resembles that 

 of stations 119 and 120. The surface water has a pH be- 

 low 8.0 at stations 121 and 122 but is slightly higher at 

 the other stations. There is no layer of uniform pH at 

 the surface, the values usually being higher at 5 meters 

 than at the surface and then decreasing rapidly with 

 depth. The depth of the lower limit of the transition 

 zone is at 300 meters at station 122, at slightly more 

 than 100 meters at station 124, and at intermediate 

 depths at the other stations. 



There is no distinct layer of minimum pH, the low- 

 est value (between 7.5 and 7.6) being found at the lower 

 limit of the transition zone. From this level pH in- 

 creases, the values between 2000 and 3000 meters being 

 about 7.7. 



VERTICAL DISTRIBUTION 



It has already been pointed out that as in the case of 

 other plant nutrients biological activities affect the 

 quantity of carbon dioxide, and consequently the pH, in 

 the ocean. In the photosynthetic zone more carbon diox- 

 ide is ordinarily utilized by the plants than is liberated 

 by respiration or decomposition of organic material. 

 Similarly, carbon dioxide is liberated by animal respi- 

 ration and organic decomposition in the water strata be- 

 low the photosynthetic zone from where it may be carried 

 by the water to the upper levels where it again becomes 

 available for plant growth. The carbon dioxide cycle in 

 the sea differs from that of the other nutrients in that 

 carbon dioxide may be given off to the atmosphere or 

 absorbed from it. As to whether carbon dioxide is given 

 off from or absorbed by the water depends on the carbon 

 dioxide tension or pressure and this in turn depends on 

 a number of factors, the chief of which are the carbon 

 dioxide content of the water and the temperature. In the 

 Atlantic, south of latitude 20° north, Wattenberg (1933) in 

 most localities found the carbon dioxide tension of the sea 

 to be about the same as that of the atmostphere, except along 

 the coast of Africa where it was higher in the sea water . 



For one hundred and fifty-nine Carnegie stations in 

 widely separated regions the average surface pH value 

 is 8.22. In order to determine whether or not this value 

 represents equilibrium in the carbon dioxide tension 

 between the sea and the atmosphere, it would be neces- 

 sary to know the titratable base content and to consider 

 the temperature. According to Buch (1933) a pH of 8.22, 

 at a temperature of 30° and a salinity of 34 per mille, 

 represents a carbon dioxide tension in equilibrium with 

 the atmosphere. For a temperature of 20°, which would 

 probably be near the average for the Carnegie surface 

 observations, this equilibrium is represented by a pH of 

 8.20. 



The vertical distribution of pH in the surface or con- 

 vection layer at the Carnegie stations was rather vari- 

 able. In some cases the pH was constant throughout the 

 entire layer whereas in others it increased, decreased 

 below the surface, or varied in an irregular manner. 

 Similar irregiilarities were found in the distribution of 

 oxygen and undoubtedly were owing to biological activi- 

 ties. It will be remembered that gases do not readily 

 diffuse through the water and any irregularities in their 



