DISTRIBUTION OF CALCIUM CARBONATE IN AREA INVESTIGATED BY CARNEGIE 



103 



Table 35. Frequency of occurrence of samples having the percentage content of CaCO^ indicated, 

 according to latitude and depth intervals — Concluded 



4000-5000 

 >5000 



1000-2000 

 2000-3000 

 3000-4000 

 4000-5000 

 >5000 



2000-3000 

 3000-4000 

 4000-5000 



2000-3000 

 4000-5000 



2 14 1 3 .. 3 

 ... 4 .... 1 



10° - 20° S--Concluded 

 . 1 .. 3 .. 1 



20° - 30° S 



40° - 50° S 



2 2 



The following abbreviations are used: t indicates terrigenous; p, pelagic samples. 



Along the South and Central American coasts, in the 

 eastern part of the path of the Peruvian Current, there 

 is a band of varying width which is low in CaCO^. It is 

 extended westward as a wide, curved tongue at about 20° 

 south in the Bowers Basin of Agassiz (1906), and at lon- 

 gitudes 100° to 105° west joins a narrow region of low 

 CaC03 between 5° and 25° south, which includes the 

 Bauer Deep discovered by the Carnegie . This tongue is 

 bounded on the southeast by the sediments of the Merri- 

 am Ridge, which are high in calcium. Another region of 

 low carbonate content surrounds the GalSpagos Islands, 

 even though the bottom here is relatively shallow and 

 plateau-like in character. A marked diminution of car- 

 bonate content occurs in a small area at about 100° west 

 longitude and 40° south latitude, and is probably to be 

 correlated with a depth depression. Between the Tua- 

 motu Archipelago and the high CaC03 area, which lies 

 across the equator at 160° west, there is a re-entrant 

 area of low CaC03 content. A similar re-entrant area 

 lies between 17° and 25° south, west of longitude 140°, 

 and a third larger area lies between 30° and 42° south, 

 west of longitude 125° west. 



These areas may be regarded as salients of a broad 

 band of deposits poor in calcium carbonate extending, 

 according to the map of Murray and Lee, from 50° south 

 to 10° north where it joins the low area covering almost 

 the entire north Pacific. In the south this band lies, in 

 general, between longitudes 150° and 176° west; toward 

 the north it becomes narrower and is shifted to the west- 

 ward between the meridians of 164° and 166° west on 

 the east side, and 180° to 174° east on the west side. 



A comparison of chart 10 with a bathymetric chart 

 of the Pacific shows that the areas of high calcium car- 

 bonate generally lie in the shallower depths, less than 

 4000 meters, except near the equator. The rather sharp, 

 relatively straight northern boundary of the high calcium 

 carbonate area of the southeast Pacific between longitudes 



90° and 155° west almost exactly parallels the average 

 southern limit of the Counter Equatorial Current and 

 does not follow the depth contours. (Compare also with 

 Schott's map [1934] of salinity in the Pacific, from which 

 it may be seen that this boundary follows closely the 

 34.5 per mille isohaline.) 



Relations Between CaCO;^ . Depth, and Latitude. Fig- 

 ures 38, 39, and 40 show the distribution for each ten 

 degrees of latitude of average calcium carbonate con- 

 tents with respect to depth. In most cases two curves 

 are plotted, one for all samples within a given latitude 

 division, and another which includes only the pelagic 

 samples. The number of samples entering into each 

 average value is given in the figures. The average car- 

 bonate value for a given depth interval is plotted at the 

 mid-point, halfway between the two limiting depths; for 

 example, the average depth of samples collected at depths 

 less than 1000 meters has been assumed to be 500 meters, 

 and the average depth of samples over 5000 meters has 

 been assumed to be 5500 meters. 



In latitudes 0° to 10° south the calcium carbonate 

 content of all samples, both pelagic and terrigenous, 

 markedly increases from an average of 12 per cent be- 

 tween and 1000 meters to 68 per cent between 2000 and 

 3000 meters, and then as sharply decreases to an aver- 

 age value of 11 per cent for samples at depths greater 

 than 5000 meters. In contrast, the curve for pelagic 

 samples alone shows a regular decrease with depth at all 

 levels. The difference between the two curves is owing 

 to the relatively low carbonate content of terrigenous 

 samples of moderate depth. Between latitudes 0° and 10° 

 north the curve for all samples combined is compara- 

 tively straight to depths between 3000 and 4000 meters 

 at about 22 to 32 per cent calcium carbonate, and then 

 shows an increase to an average of 51 per cent at depths 

 between 4000 and 5000 meters, after which there is a 

 decrease to about 24 per cent for depths greater than 



