124 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



and depth previously referred to. The deeper the water 

 column the more water must be passed through by cal- 

 careous skeletons settling from the surface, and there- 

 fore more solution of these skeletons will occur. The 

 rate of deposition of calcareous skeletons on the bottom 

 will consequently be slower and the calcareous material 

 lying on the bottom surface will be exposed longer to the 

 dissolving action of the sea water above the bottom. The 

 relative amounts of solution taking place both during the 

 settling of CaC03 particles and on the bottom surface 

 will thus be greater than in shallower waters where the 

 sediments have a shorter period of settling and are bur- 

 ied more quickly. 



This explanation of the correlation between carbon- 

 ate content and depth is not accepted by some workers, 

 notably Wattenberg (1933), and Buch and Gripenberg 

 (1932), who state that the increasing hydrostatic pres- 

 sure at greater depths increases the ability of the water 

 to dissolve calcium carbonate. A similar suggestion 

 was also made by Murray and R6nard (1891) and by Reid 

 (1888). The effect of hydrostatic pressure is still some- 

 what problematical since no data are available as to the 

 effect of pressure on the solubility product of calcium 

 carbonate. The known effects of hydrostatic pressure on 

 the factors involved in the carbonate equilibrium of sea 

 water are, however, quite small (Revelle, 1934). 



With regard to the influence of currents, it is obvi- 

 ous, as pointed out by Pia (1933), that horizontal currents 

 alone cannot affect the time of settling of calcium car- 

 bonate particles, but that only the vertical components of 

 these currents and the turbulence induced by them can 

 be effective. Defant (1932) has shown that the deep cur- 

 rents of the Atlantic exhibit considerable turbulence. 



The degree of under saturation of deep waters, with 

 respect to calcium carbonate, is probably of greatest 

 importance for the distribution of calcium carbonate in 

 marine bottom sediments. For example, it is known that 

 the Antarctic deep waters are very high in CO2 and, as 

 WQst (1934) has shown, the boundaries of deep water of 

 Antarctic origin in the Atlantic, indicated by potential 

 temperature differences, are also the boundaries of low 

 CaCOs content in the bottom sediments. In the western 

 basin of the south Atlantic, where the Antarctic deep cur- 

 rent penetrates far to the north, the percentages of 

 CaC03 in the sediments are much less than in the east- 

 ern Atlantic where the current is cut off by the Walfish 

 Ridge. Likewise, according to Pratje (1932), the sedi- 

 ments even in the two halves of the eastern south Atlan- 

 tic basin are very different as far as their contents of 

 CaC03 are concerned, the sediments in the western half 

 being much higher in CaC03 for any given depth than 

 those in the eastern part of the basin. This is to be cor- 

 related, Pratje claims, with the fact that in the. west the 

 bottom topography is very uneven, and tends to retard 

 the Antarctic Current, whereas in the east the compara- 

 tively flat nature of the bottom allows it to pass over the 

 sediments. The relation between the presence of Ant- 

 arctic deep water and low CaC03 content also holds for 

 the Indian Ocean, according to Wust, who postulates a 

 ridge in the western half of this ocean which cuts off the 

 Antarctic water and, therefore, prevents the solution of 

 CaC03, whereas in the eastern half the Antarctic Cur- 

 rent moves farther north so that the CaC03 is dissolved. 

 Wiist, basing his statement on data given by Schott and 

 Schu (1910), claims that Antarctic bottom water covers 

 most of the floor of the Pacific, but Sverdrup (1931), 

 employing the later data of the Carnegie, believes that 



Pacific deep water also contains a considerable mixture 

 of the subtropical deep water of the Indian Ocean, a sug- 

 gestion first made by M611er (1929). It will be shown 

 below that this deep water of the Pacific is of low pH and 

 high CO2 content, and is probably markedly undersatu- 

 rated with respect to CaC03. Murray and Philippi (1908) 

 were the first to point out the relation between deep wa- 

 ters of Antarctic origin and the low CaC03 content in 

 the sediments underlying them. 



Solution after Deposition. Besides the solution of 

 CaC03 particles which takes place as they settle through 

 the water, there is probably also considerable removal 

 of CaC03 from the bottom sediments themselves, for 

 which suggestive evidence was first obtained by Dittmar 

 (1884) and Brennecke (1921). These authors found that 

 the amounts of dissolved calcium in waters immediately 

 above the bottom seem to be somewhat higher than the 

 normal values for the ocean as a whole. The evidence 

 was not conclusive, however, since the variations were 

 of about the same magnitude as the analytical errors in- 

 volved. Wattenberg's careful determinations of the re- 

 lation between titratable base, which he claims is a very 

 sensitive measure of variations in the calcium content, 

 and the chlorinity, definitely showed an increase in the 

 ratio of titratable base to chlorinity directly above the 

 bottom, at depths greater than 2000 meters. The fact 

 of interchange between the interstitial waters of the sed- 

 iments and the superjacent bottom water was also shown 

 by a decrease in the oxygen content of the latter. Anoth- 

 er type of evidence of solution within the sediments is 

 given by Andree, who claims that normally there is a 

 decrease in CaC03 content with increasing depth within 

 a sediment. Many of the bottom cores collected by the 

 Michael Sars (see Chumley, 1930), however, showed an 

 increase with depth in the sediment, but these are be- 

 lieved to be "abnormal"! by Andree, and to indicate 

 changes of the conditions of sedimentation. A third type 

 of evidence of carbonate solution on the sea floor has 

 been mentioned previously, namely, the inverse relation 

 between contents of organic mattgr and of benthonic for- 

 aminifera, on the one hand, and the percentage of CaC03 

 on the other. 



The Meteor workers also believe that in some cases 

 there may be a relative increase in CaC03 on the sea 

 bottom owing to the removal by bottom currents of the 

 clay fractions, which are presumably low in CaC03. 

 Correns (1927) claims that coarser sediments tend to be 

 higher in CaC03 than those of finer particle size and he 

 believes that this is owing to the removal by currents of 

 some of the finer -grained noncalcareous material. An 

 alternative explanation may be that coarser particles, 

 since they have less surface in proportion to volume than 

 fine-grained particles, tend to dissolve more slowly, 

 wast (1934) thinks that a partial explanation of the rela- 

 tion between CaCOs and depth is that in deep waters the 

 bottom currents move more slowly than in shallower 

 waters, therefore not removing as much of the fine frac- 

 tions. On the other hand, it should be pointed out that the 

 more slowly a current moves the less solution of CaC03 

 can take place, since the water becomes more nearly 

 saturated; furthermore, the stirring up of sediments by 

 relatively rapid currents allows fresh water to come in 



^W. Schott (1935) has shown that the relatively low 

 carbonate contents of the lower parts of core samples of 

 Atlantic deep-sea sediments may be owing to deposition 

 during the glacial period. 



