DISTRIBUTION OF CALCIUM CARBONATE IN AREA INVESTIGATED BY CARNEGIE 



121 



oozes, and red clays alone. The latter curve is repro- 

 duced in figure 44, together with the average data for all 

 pelagic samples collected in the Pacific. The general 

 similarity in the shapes of the two curves at depths 

 greater than 1000 meters is very striking. The dis- 

 crepancy at depths less than 1000 meters is probably 

 owing to the fact that only two pelagic samples from 

 these depths are available for the Pacific. There is a 

 marked quantitative difference, however, between the 

 two curves below 1500 meters; that is, the curve for the 

 Pacific samples at every depth shows a smaller calcium 

 carbonate content than at the corresponding depth in the 

 Atlantic. This is particularly marked below 3500 me- 

 ters, where the decrease shown by the curve for the 

 Pacific samples is rapid and almost linear from 49 per 

 cent at 3500 meters to 5 per cent at depths greater than 

 5000 meters. The curve for the Atlantic samples starts 

 to show a decrease from an average value of 71 percent 

 at 4000 meters to 6 per cent at 6400 meters. 



Irregularity ^ Depth Relation. The relationbetween 

 CaCOs and depth is a very irregular one and, as will be 

 shown later, it is complicated by many factors. The ir- 

 regularity of the relation was pointed out by Murray and 

 Chumley who showed that the maximum and minimum 

 carbonate values for Globigerina oozes of various depths 

 At any given latitudes in the Atlantic are very variable. 

 Pia, using Andr§e's data for depths between 4000 and 

 5000 meters, gives a short table showing the frequency 

 distribution of samples having different percentages of 

 carbonate and points out that the variations at any given 

 depth cannot be described in terms of the normal fre- 

 quency curve. This may also be seen from the writer's 

 table 35, in which the samples listed in table 36 for each 

 latitude and depth division are arranged in order of in- 

 creasing CaC03 content in ten groups of to 10 per cent, 

 10 to 20 per cent, etc. The samples have been divided 

 into pelagic and terrigenous types. When maximum fre- 

 quencies are present, they may be seen to be very wide 

 in extent, and in many cases secondary maxima are 

 shown. A rather extreme case, that for pelagic samples 

 collected at depths between 4000 and 5000 meters in lat- 

 itudes 0° to 10° north, is shown in figure 43. Of twenty- 

 eight pelagic samples, five have carbonate contents of 

 less than 10 per cent, two samples have between 20 and 

 50 pei" cent CaC03, and twenty-one samples, or 

 seventy-five per cent of the total number, have carbon- 

 ate contents between 50 and 90 per cent. 



Relation Between Carbonate Content and Bottom 

 Fauna . Mention has already been made of the fact that 

 samples which contain many individuals and many spe- 

 cies of benthonic foraminifera are usually, other things 

 being equal, those of relatively low content of pelagic 

 foraminifera (hence, low CaCOs content), higher organ- 

 ic matter, and greater proportions of broken pelagic 

 shells. In the south and central Pacific, far from land, 

 samples 13, 14, 31, 35, 79, 80, 81, and 82 are relatively 

 high in organic matter, in proportions of benthonic fora- 

 minifera, and broken to whole pelagic tests. They are 

 correspondingly low in carbonate content when compared 

 with other samples of the same depth and general loca- 

 tion. Samples 31 and 35 are red clays; samples 79 and 

 80 are radiolarian oozes; samples 13, 14, 81, and 82 are 

 siliceous Globigerina oozes. The latter, containing 67, 

 76, 40, and 85 per cent calcium carbonate, respectively, 

 lie either under the paths of the Peruvian Current or of 

 the Equatorial Current. Agassiz long ago pointed out 



that the sea bottom underlying these currents is high in 

 living organisms of many kinds, and the surface waters 

 above them are rich in living forms, in contrast with the 

 pelagic and benthonic faunas of the waters south and west 

 of the currents which are poor both in numbers of indi- 

 viduals and of species. He also noticed that the bottom 

 deposits from the area south and west of the currents 

 are relatively rich in manganese iron nodules. Agassiz 

 did not develop a correlation, however, between high 

 carbonate content and a small bottom fauna. 



The Globigerina oozes which contain the highest per- 

 centage of calcareous benthonic foraminifera are sam- 

 ples 22 and 27 and these, although they are not notably 

 high in organic matter, contain only slightly more than 

 42 per cent CaC03. The inverse relation between whole 

 tests of pelagic foraminifera and benthonic foraminifera, 

 and between benthonic foraminifera and carbonate con- 

 tent, may also be observed from a study of the average 

 composition of red clays and Globigerina oozes collected 

 by the Challenger . In the former, the proportion of cal- 

 careous benthonic to pelagic foraminifera is as 1 to 8, 

 namely, 0.59 to 4.77 per cent, whereas in Globigerina 

 oozes it is approximately 1 to 25, namely, 2.13 to 53.10 

 per cent. 



Two inferences are possible from these relations. 

 One, that living benthonic animals are more or less even- 

 ly distributed over the floor of the deep sea, but that their 

 remains are masked in some cases by the rapid accumu- 

 lation of calcareous shells of pelagic organisms, so that 

 they appear to be relatively few in number. This possi- 

 bility has been suggested by Cushman (1928) among 

 others, but since the quantity of animals living on the bot- 

 tom must be largely dependent, in the last analysis, on 

 the rate of accumulation of edible organic materials, 

 such a hypothesis would imply that the rate of accumula- 

 tion of organic material in the deep sea is everywhere 

 much the same. Furthermore, since the tests of ben- 

 thonic foraminifera must be about as soluble as those of 

 pelagic foraminifera, it would also imply that little so- 

 lution takes place on the ocean floor; otherwise, there 

 would be a direct relation between the CaC03 content and 

 the percentage of benthonic foraminifera. 



On the other hand, Agasslz's researches(1892,1906) 

 showed that areas in which the surface water is rich in 

 plankton also have rich bottom faunas. Therefore a 

 second inference seems more probable, namely, that 

 the apparently varying quantities in the samples of the 

 tests of benthonic foraminifera, as of the remains 

 of other bottom-living organisms, represent real 

 variations in the Iwttom faunas and are chiefly de- 

 pendent on varying rates of accumulation of available 

 organic materials. The high percentages of broken 

 pelagic shells and low carbonate contents of deposits 

 which support large communities of bottom-living 

 organisms might then be explained in part by assum- 

 ing that the shells had passed more frequently through 

 the alimentary tracts of mud eaters, and in part by 

 the fact that more carbon dioxide would be produced 

 by the metat>olism of the animals and the decomposition 

 of the organic matter; hence conditons would be more 

 favorable for solution of carbonates. Also the pres- 

 ence of such communities may mean that the bottom 

 deposits are more or less continually churned over, 

 thus allowing more rapid interchange between the 

 presumably saturated interstitial water of the sedi- 

 ments and the overlying presumably unsaturated water. 



