120 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



5000 meters. The curve for pelagic samples in these 

 latitudes is somewhat similar in form to that for all 

 samples but shows a higher percentage of calcium car- 

 bonate at any given depth. 



Between 10° and 20° south the average amounts of 

 calcium carbonate for depths of 1000 to 4000 meters are 

 approximately 50 to 65 per cent for all samples com- 

 bined, and 66 to 74 per cent for pelagic samples alone. 

 Below 4000 meters there is a marked diminution in 

 CaCOs content to less than 20 per cent. From 10° to 20° 

 north the curves, though much more irregular than in 

 the corresponding southern latitudes, tend to show a de- 

 crease with depth from 47 per cent CaCOs in the upper 

 thousand meters to 1 per cent at depths greater than 

 5000 meters. 



There is a good correlation between depth and car- 

 bonate content for the pelagic samples collected between 

 20° and 30° south, the amount of carbonate decreasing in 

 a regular manner from over 90 per cent for one sample 

 less than 2000 meters in depth to an average of 18 per 

 cent for eleven samples between 4000 and 5000 meters, 

 and per cent for one sample collected below 5000 me- 

 ters. In the north Pacific at the same latitudes no sam- 

 ples have been analyzed containing more than 48 per cent 

 calcium carbonate and the average for even the shallow- 

 est depths is less than 20 per cent, the percentage of 

 carbonate then decreasing in a more or less regular 

 manner to average values of 1.9 per cent between 4000 

 and 5000 meters and 0.8 per cent for depths greater than 

 5000 meters. 



Between 30° and 40° south there is a decrease with 

 depth for the eighteen pelagic samples analyzed from 75 

 per cent CaCOs between 2000 and 3000 meters to 19 per 

 cent between 4000 and 5000 meters. South of 40° south 

 only four samples have been analyzed from the area in- 

 vestigated by the Carnegie, so that the average curve, 

 though given for the sake of completeness, has little sig- 

 nificance. 



Between 30° and 50° north the average values of 

 CaCOs, although low throughout, tend to have a maximum 

 at intermediate depths. North of 50° north ninety sam- 

 ples were collected by the Albatross and have been ana- 

 lyzed byTrask (1932). These are all terrigenous sam- 

 ples and contain, on the average, very little calcium car- 

 bonate, but nevertheless they exhibit a good correlation 

 between CaCOs and depth, the average values ranging 

 from 5.8 per cent for twenty-eight samples collected be- 

 tween and 1000 meters to considerably less than 1 per 

 cent for thirty-five samples collected at depths greater 

 than 3000 meters. 



In figure 41 the distribution of calcium carbonate 

 content with latitude for each depth division is shown. 

 As before, two curves are usually plotted, one for the 

 averages of all available samples and the other for pe- 

 lagic samples. The number of samples entering into 

 each average value is also given. The average carbon- 

 ate values for each latitude interval are plotted at the 

 mid-point, halfway between the two limiting latitudes; 

 for example, the average latitude of samples collected 

 between the equator and 10° north has been assumed to 

 be 5° north. 



For depths between and 1000 meters the maximum 

 average carbonate content of all samples lies between 

 10° and 20° north latitude, and the average values de- 

 crease sharply both to the north and to the south. All 

 but two of these samples are terrigenous. 



Between 1000 and 2000 meters the maximum average 



carbonate content of all samples analyzed lies between 

 20° and 30° south and the curve for all samples taken 

 together first shows a sharp drop and then an irregular 

 decrease in CaC03 content to the northward. 



Between 2000 and 3000 meters the curve for pelagic 

 samples shows a more or less regular decrease in 

 CaC03 content from latitudes 40° to 50° south to 20° to 

 30° north, with a slight secondary maximum being evi- 

 dent between 0° and 10° south. The curve for all sam- 

 ples combined is more irregular but shows a pronounced 

 decrease of calcium carbonate north of the equator, and 

 relatively constant values to the southward. 



For depths between 3000 and 4000 meters the maxi- 

 mum average carbonate content lies between 10° and 20° 

 south, the average carbonate values being almost con- 

 stant to 40° south, but decreasing markedly to 20° north. 

 North of 30° very little carbonate is present except in 

 one pelagic sample. , 



The curves for depths between 4000 and 5000 me- 

 ters show a pronounced maximum in CaC03 between 0° 

 and 10° north, with a regular decrease of average car- 

 bonate contents in both directions toward the higher lat- 

 itudes, and an increase south of 30° to a secondary max- 

 imum of 37.5 per cent between 40° and 50° south. 



The curve for samples obtained at depths greater 

 than 5000 meters is somewhat similar in general shape 

 to the last curve, but the average values of carbonate 

 content are all much smaller. There is a maximum be- 

 tween 0° and 10° north of 24.2 per cent CaC03, and a 

 secondary maximum between 10° and 20° south of 17 per 

 cent. North of 10° north the average carbonate content 

 of all samples never rises above 1 per cent. 



Comparison of Atlantic and Pacific. That there is a 

 correlation between decreasing calcium carbonate con- 

 tent and increasing depths was pointed out by Murray 

 and Renard (1891), and this relation has since been con- 

 firmed by the results of other oceanographic expeditions. 

 Andree (1920), however, was able to find very little cor- 

 relation between depth and carbonate content when con- 

 sidering Globigerina oozes of the Atlantic alone, and 

 Pratje (1932) has suggested that there is no significant 

 influence of depth, as such, on the carbonate content of 

 sediments. Pia (1933), using the data collected by 

 Andr6e, found a Bravais correlation coefficient between 

 CaCOs content and depth of -0.3179±0.0762 for the Glo- 

 bigerina oozes collected by the Challenger . Valdivia , and 

 other expeditions in the Atlantic. Using Gebbing's data 

 (1909) from the Challenger . Gazelle , and Gauss he cal- 

 culated a correlation coefficient of -0.3047±0.0821. From 

 these calculations he concluded that "die Korr elation ist 

 also negativ, nicht sehr vollkommen, aber sehr sicher. 

 From a compilation given by Murray and Chumley (1924), 

 however, of the data for all samples collected from the 

 Atlantic previous to 1922, Pia was able to calculate 

 somewhat higher correlation coefficients as follows: 



For all samples at depths greater than 



1500 fathoms -0.3884+0.0283 



For Globigerina oozes, pteropod oozes, 



and red clay at depths greater than 



1500 fathoms -0.6312±0.0221 



For Globigerina oozes alone (thus reducing 



the influence of terrigenous materials) at 



depths less than 1500 fathoms -0.3316*0.0360 



Pia has plotted his average data for calcium carbonate 

 content against depth for all the 1426 samples given by 

 Murray and Chumley and for Globigerina oozes, pteropod 



