. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] PELAGIC SEDIMENTS 689 meters. From the distribution of carbonate concentrations with depth in areas with different productivities, the combined influence of hydrostatic pressure and temperature and hkewise the influence of productivity are quite evident (Figs. 18 and 19). Further, at a higher total rate of deposition, providing rapid pro- Depth 3000 4000 - CaCO- 20 40 60 80 100% -•— Average for 500 m intervals from all available data-, present sediment 5000 6000 m. I / j^f Pacific 135°W) Fig. 18. Concentration of
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] PELAGIC SEDIMENTS 689 meters. From the distribution of carbonate concentrations with depth in areas with different productivities, the combined influence of hydrostatic pressure and temperature and hkewise the influence of productivity are quite evident (Figs. 18 and 19). Further, at a higher total rate of deposition, providing rapid pro- Depth 3000 4000 - CaCO- 20 40 60 80 100% -•— Average for 500 m intervals from all available data-, present sediment 5000 6000 m. I / j^f Pacific 135°W) Fig. 18. Concentration of calcium carbonate at the present sediment surface as a function of depth in the Pacific Ocean. The average curve shows a pronounced effect of depth on the rate of sokition of carbonate. In the central equatorial Pacific, characterized by a wide regional variability in biological productivity, this latter factor dominates the carbonate distribution. (From Bramlette, 1961.) tection of the carbonate, the disappearance of the carbonate occurs at greater water depths (Fig. 20). Finafly, the influence of the removal of the dissolved calcium ion is demonstrated by the carbonate distribution in the South Atlantic basins; at equal depths the dissolution of calcite is far more extensive in the Brazil Basin, which is flushed by Antarctic deep water, than in the neighboring Congo Basin, which has a slower renewal of the bottom water (Wattenberg, 1933, 1937; Correns, 1939). At shallow and intermediate depths where the rate of dissolution of calcium carbonate is low, calcite and aragonite are sometimes dolomitized. Outcrops of dolomitized limestone, such as on the Nasca Ridge in the South Pacific (Bram- lette, unpublished), are coated with manganese-iron oxide minerals, indicating that the dolomitization was active in the past, and that it has since been re- placed by oxide deposition. A similar sequence is observed in many oceanic limestones and phosphorite deposits, which also display
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