SCOPE AND METHODS OF THE CHEMICAL INVESTIGATIONS 



Oxygen 



Dissolved oxygen was determined according to the 

 method of Winkler (1888). The water to be analyzed was 

 drawn from Nansen bottles (Oceanogr. 1-A,p.3)l through 

 a glass tube into green glass, patent -stoppered bottles 

 having a capacity of approximately 100 ml and calibrated 

 by weighing distilled water to 0.1 gram. When drawing 

 a sample, enough water was allowed to overflow to thor- 

 oughly flush out any air -contaminated water. As soon as 

 the bottle was filled with the sample, manganous chlo- 

 ride and a sodium hydroxide -potassium iodide mixture 

 was added. When the resulting precipitate had settled, 

 hydrochloric acid was added. The samples were titrated 

 within a few hours after collecting. The N/100 thlosul- 

 phate solution used for the titration was standardized 

 against N/100 potassium dichromate solution at every 

 second oceanographic station, that is, every four days. 

 The burette was read to 0.05 ml and the authors believe 

 that the results are accurate to about 0.03ml per liter. 

 The results are expressed in milliliters per liter and in 

 percentage of saturation. In computing the latter, the 

 saturation values given by Jacobsen (1905) were used. 

 His values are slightly below those of Fox (1909), and 

 Whipple and Whipple (1911). For temperatures higher 

 than those included in Jacobsen's table (0° to 25°), the sat- 

 uration values were obtained by extrapolation and by com- 

 parison with the tablesof Fox and Whipple and Whipple. 



Hydrogen-ion Concentration 



The hydrogen-ion concentration was determined 

 colorimetrically by means of a double-wedge compara- 

 tor similar to one used at the Scripps Institution of 

 Oceanography for a number of years (Moberg, 1926a), 

 The comparator consists essentially of a rectangular 

 glass box divided diagonally by a vertical glass partition 

 into two wedge-shaped compartments, the dimensions 

 being approximately those given by Barnett and Barnett 

 (1920), namely, 35 cm long and 1.5 cm wide. In making 

 a determination, one of the compartments is filled with 

 an acid- indicator solution and the other with an alkaline 

 solution of the same indicator. When viewed horizontal- 



ly, the comparator then presents the entire color range 

 of the indicator, with the center representing the hydro- 

 gen-ion concentration of the half -transformation point of 

 of the indicator. A scale attached to the comparator and 

 graduated into one hundred divisions thus gives the per- 

 centage of transformation or apparent dissociation of 

 the indicator. From the scale reading and the indicator 

 constant, the corresponding degree of indicator trans- 

 formation and hence the pH may be computed according 

 to the foUowing equation: 



pH = pK - log 



100 - X 



where pK is the negative logarithm of indicator constant 

 and X is the scale reading. 



After the addition of Indicator to give the same con- 

 centration as in the wedges, the sample to be analyzed 

 is placed in a small glass box having the same liquid 

 diameter as the total of the two wedges. This box is 

 placed above the large box, which is moved until the 

 colors in the two match, and then the scale reading is 

 taken. Both boxes are contained in a light-proof hous- 

 ing, and artificial light is used for illumination. The 

 instrument used on the Carnegie , with special modifica- 

 tions required for use at sea, was designed by R. H. 

 Seiwell. Cresol red was used as indicator and the value 

 8.14 was used for pK. This value previously had been 

 determined by Moberg and agrees well with that ob- 

 tained by Barnett and Barnett (1921), namely, 8.13. All 

 the pH readings were corrected for salt according to 

 Ramage and Miller (1925), the correction -0.27 being 

 used for all Carnegie samples. The determinations of 

 pH were made within a few hours after collecting the 

 samples. Since the cruise of the Carnegie , Buch (1929) 

 has shown that the pH of sea water changes slightly with 

 the temperature, and that there is a similar change in 

 the indicator constant. In the case of the Carnegie data, 

 corrections for the temperature effect were not made. 

 This, however, makes them comparable with most of 

 the data previously published and, because the temper- 

 ature values are available, corrections may be applied 

 when desired. 



PRESENTATION OF DATA 



The results of the chemical investigations carried 

 out by the Carnegie , together with those of the physical 

 investigations, are presented in table 2 (I-B, pp. 183-257) 

 and graphs 14 to 92 0-B, pp. 16-55). The vertical and 

 horizontal distribution of the chemical constituents are 

 further shown by sections constructed along the path of the 

 cruise. These correspond to the sixteen sections prepared 

 by Sverdrup (I-B) to illustrate the distribution of tem- 

 perature, salinity, and density. A chart showing the geo- 

 graphic positions of the sections is given in figure CI. 

 Frequent reference to this chart, which shows the various 

 stations included in each section, will be necessary for a 

 clear understanding of the discussions to follow. The 

 exact positions of these stations can be obtained from the 

 tables and graphs previously referred to. In the discus- 

 sions of the chemical data, each constituent is taken up 



1 Oceanography I-A and I-B, volumes of the same 

 series as the present volume, by H. U. Sverdrup, F. M. 

 Soule, J. A. Fleming, and C. C. Ennis (1944), hereafter 

 will be referred to in this report as I-A and I-B. 



separately and in the following order: phosphate, sili- 

 cate, hydrogen-ion concentration, and oxygen. 



For each chemical constituent, a brief description 

 of its distribution along the various sections is given at 

 the beginning of the discussion. These descriptions fol- 

 low, in general, a discussion of the vertical distribution 

 of the substance in question, the conditions being dis- 

 cussed in order from the surface downward. In examin- 

 ing the sections, it will be noted that the vertical distri- 

 bution of the chemical substances usually follows that of 

 the physical conditions, that is, certain more or less 

 distinct layers or zones can be recognized. The zones 

 included in the discussions are as follows. 



1. The convection or surface layer , in which the 

 conditions are relatively uniform with respect to depth 

 because of mixing of the water caused by temperature 

 changes, winds, and other agencies. This layer is usual- 

 ly less than 100 meters in thickness. 



2. The transition zone or discontinuity layer , in which 

 there is a rapid change from conditions prevailing in the 

 convection layer to those characteristic of deep water. 



