126 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



high CO2 content, and hence by a greater degree of 

 undersaturation of calcium carbonate. 



An interesting light on the fate of calcium carbonate 

 in the deep waters of the Pacific is given by figure 45, 

 in which the available base chloride ratios for two sta- 

 tions in the north Pacific are plotted against depth and 

 compared with the average base chloride ratios for wa- 

 ters of the same depth in the Atlantic, given by Watten- 

 berg. For the Atlantic curve Wattenberg's average data 

 for the base chloride ratios of water samples collected 

 by the Mete or expedition between 19^ south and 2.5° 

 south down to depths of 3000 meters have been used. 

 The curve has been extended below 3000 meters by the 

 use of one of the curves given in Wattenberg's figure 13 

 which shows the average vertical distribution of the 

 base chloride ratio between 3000 and 4000 meters for 

 stations in which the average depth of the bottom is 4000 

 meters. One of the two Pacific curves shown represents 

 determinations of the titratable base made by Dr. P. H. 

 Mitchell on samples which the writer collected in 1933 

 aboard the U.S.C. and G.S.S. Pioneer in latitude 34° 33' 

 north and longitude 122° 31' west, about 150 miles off 

 the California coast. The bottom depth was 3975 meters. 

 The other curve represents the base chloride ratio of 

 samples the writer collected in 1934 aboard the U.S.S. 

 Bushnell in latitude 31° 49' west, longitude 163° 24' west 

 in the mid-Pacific about 600 miles north of the Hawaiian 

 Islands. The bottom depth here was approximately 3270 

 meters. The determinations^ were carried out at the 

 Scripps Institution by Miss Katherine Gehring. In the 

 first 500 meters below the surface the curves for both 

 the Atlantic and the Pacific are similar, although the 

 base chloride ratios of the Pacific surface water are 

 somewhat higher than the average given by Wattenberg, 

 and a much more marked diminution of the base content 

 takes place below the surface. Below 500 meters, how- 

 ever, the curves rapidly diverge. The average base 

 chloride ratio of the Atlantic water reaches a constant 

 value of 0.1225 at about 1000 meters; this is maintained 

 to a depth of 3000 meters. After this a marked increase 

 takes place to the bottom where a value of 0.1258 was 

 obtained. The Pacific samples show a much more 

 marked increase to a depth of about 1000 meters at 

 which values of 0.1258 and 0.1281 were obtained, and 

 then a slow increase to bottom values of 0.1278 and 

 0.1304. The high base chloride ratios of the Pacificdeep 

 waters shown by these curves almost certainly mean a 

 correspondingly high calcium content. If the sum of the 

 titratable base contents of the entire water column, in- 

 cluding both the surface and the deep water, were the 

 same in the two oceans, the excess of base in the deep 

 water would be counterbalanced by a depletion at or near 

 the surface. The excess base at depth might then be ex- 

 plained on the basis of a slower cycle of interchange of 

 deep and surface water in the Pacific, that is, the deep 

 water would have been at depth for a longer period of 

 time and hence would have had more time to dissolve 

 calcium carbonate whereas, correspondingly, the waters 

 nearer the surface would have had more time in which to 

 lose calcium by the precipitation and settling of solid 



The results of the titratable base analyses of the 

 Bushnell and the Pioneer samples have been confirmed 

 by determinations of the vertical distribution of titrata- 

 ble base in certain recent deep Scripps stations in south- 

 ern California waters, and by. calcium analyses of the 

 samples collected by the B ushnell . 



particles. Pacific subsurface waters, in fact, do show a 

 more pronounced decrease in the base chloride ratios, 

 relative to Pacific surface waters, than do Atlantic sub- 

 surface waters in comparison with Atlantic surface water. 

 In other words, more CaCOs has been removed from any 

 given volume of subsurface water in the Pacific than in 

 the Atlantic. Furthermore, it has been suggested on 

 other grounds by Sverdrup (1931) and Moberg (1930) that 

 there is less interchange of surface and deep water in 

 the Pacific than in the Atlantic. 



The base chloride ratios, however, at all depths in 

 the Pacific from the surface to the bottom, are higher 

 than at the corresponding depths in the Atlantic, and the 

 total base in the entire water column is much greater. 

 There is an especially marked divergence in the deep 

 water. The excess of base in the deep water of the Pa- 

 cific is probably owing to two causes. (1) As suggested 

 by the authors referred to, it seems probable that the 

 deep water of the Pacific has originated in the southern 

 Atlantic and Indian oceans from the mixing of Antarctic 

 and subtropical deep waters, hence has not been at or 

 near the surface for a long time, and owes part of its 

 high calcium content to its having passed under large 

 amounts of subsurface waters from which CaC03 parti- 

 cles have settled and been dissolved. (2) Owing to the 

 greater amounts of CO2 in the water and the lower pH, 

 any given volume of Pacific deep water has been capable 

 of dissolving more carbonates than a corresponding vol- 

 ume of Atlantic deep water. 



The fact that, in spite of the calcium brought into the 

 Pacific from the Atlantic and Indian oceans by the deep 

 water, there is a greater degree of undersaturation in 

 the Pacific than in the Atlantic, can only mean that the 

 rate of precipitation of CaCOs in waters near the surface 

 is slower in the Pacific. This must be owing primarily 

 to the much smaller amount of calcium-bearing river 

 water which is emptied into the Pacific. 



An examination of the pH data obtained by the Car - 

 negie shows no pronounced differences between the deep 

 waters of the north and the south Pacific, but on the con- 

 trary a rather symmetrical distribution of pH values 

 with respect to the equator. No carbon dioxide or titrat- 

 able base determinations are available for the south Pa- 

 cific. The results of the Carnegie (Moberg and Graham 

 [1935]) and of the Dana (Thomsen [1931]), however, show 

 that there is much more oxygen In the deep waters of the 

 central south Pacific than in the north. Presumably, 

 therefore, there is less carbon dioxide since, as already 

 stated, the sum of the dissolved oxygen and carbon dioxide 

 In any given water mass is usually constant. Now the pH 

 of the water is a function of the relative contents of car- 

 bon dioxide and titratable base. Since there probably is 

 less carbon dixoide in the south Pacific than in the north, 

 though the pH values in the two regions are the same, 

 probably there is also less titratable base (less dissolved 

 calcium) in the south Pacific. We may consequently infer 

 that the deep waters of the south Pacific have dissolved 

 less calcium carbonate than the deep waters of the north 

 Pacific, and that, consequently, more calcium carbonate 

 has settled to the bottom. It is obvious that this explana- 

 tion for the difference between the sediments of the north 

 and the south Pacific is far from satisfactory. There is 

 an urgent need for further investigation of the physical 

 and chemical conditions of the waters of the central east- 

 ern and southeastern Pacific if the problems of dis- 

 tribution of calcium carbonate are to be satisfactorily 

 solved. 



