DISTRIBUTION OF CALCIUM CARBONATE IN AREA INVESTIGATED BY CARNEGIE 



101 



Table 34. Average calcium carbonate content 



of pelagic bottom samples of all latitudes in 



the area investigated by the Carnegie. 



according to depth 



Depth in 

 meters 



Average 

 per cent 

 CaC03 



the Albatross of the sea bottom in the southeast Pacific, 

 there are still areas covering many thousands of square 

 miles in which no soundings of any kind have been made. 

 Until quite recently, one of these unexplored regions was 

 that between 120° and 140° west longitude and 10° north 

 and 15° south latitude. Murray and Lee considered that 

 this area contains very little calcium carbonate, even 

 though all the bottom samples collected by the Albatross 

 on both sides of it were rich in lime. It will be noticed 

 that on chart 10 the sediments of this region are repre- 

 sented as having more than 50 per cent calcium carbon- 

 ate. Both points of view were purely speculative, how- 

 ever, until the circumnavigating trip of the Danish ship 

 Dana, during which echo soundings were made at fre- 

 quent intervals across the center of this questionable 

 area from latitude 5° south, longitude 120° west, to lati- 

 tude 9° south, longitude 140° west. (See Dana Report 

 no. 1, 1934). A representative series of these soundings 

 is plotted in the author's figure 42. At the eastern side 

 of the course the depth is about 4300 meters, corre- 

 sponding to an Albatross sounding in this location of 429f 

 meters. The depth then gradually increases to an aver- 



age maximum of about 4700 meters and afterwards de- 

 creases to about 4200 meters near the Marquesas Is- 

 lands. A study of figure 42 will show that in this region 

 the percentage of CaC03 in depths between 4000 and 

 5000 meters is usually well over 60 per cent, so that it 

 is probable that the average CaC03 content of the whole 

 area is greater than 50 per cent, as indicated on chart 

 10. 



In general the results of later work show that the 

 areas of high CaCOs content in the southeast Pacific are 

 much larger than had previously been supposed. For 

 example, the two areas given by Murray and Lee as hav- 

 ing more than 75 per cent CaCOs in latitudes 3° to 19° 

 south and 38° to 51° south, and longitudes 113° to 124° 

 west and 86° to 129° west, respectively, are probably 

 continuous, if the Carnegie samples collected between 

 them may be taken as representative. Similarly, the 

 small area indicated by Murray and Lee in latitudes 5° 

 to 7° north and longitudes 160° to 163° west has been 

 considerably extended. 



On the other hand, those regions which are underlain 

 by deposits having between 15 and 50 per cent calcium 

 carbonate usually form only rather narrow borders 

 around regions in which carbonate content is high. In 

 other words, the boundaries between regions of high and 

 low carbonate are relatively sharp when considered on a 

 small scale chart. There are two notable exceptions to 

 this statement. A region of intermediate calcium car- 

 bonate content between 30 and 50 per cent lies across 

 the equator between longitude 96° west and the South 

 American coast. According to Schott (1934) the Peruvian 

 Current here swings westward to become the Southern 

 Equatorial Stream and, as will be shown below, areas 

 underlying these currents tend to be low in calcium car- 

 bonate. A second large region of calcium carbonate 

 content between 30 and 50 per cent lies between the Car- 

 oline and Gilbert archipelagoes. Since no CaCOs deter- 

 minations are available, the 30 per cent CaCOs contour 

 is here based on the boundary given by Hanzawa (1928) 

 for Globigerina ooze. It is probable that many of the 

 Globigerina oozes of this region contain more than 50 

 per cent CaCOs. 



