PELAGIC SEDIMENTS 



355 



Murray and Renard (1891), and all since, have recognized that 

 solution of calcium carbonate is important on the deeper parts of 

 the ocean floor, and is a factor in the decreasing carbonate content 

 below depths of about 4000 m. What may be called a compensation 

 condition, where supply does not exceed the solution, and thus 

 with no net accumulation of calcium carbonate, includes obvious 

 factors other than depth and rate of supply. Data presented here, 

 however, appear to indicate that factors related to a rather narrow 

 depth difference are more important than has previously been 

 indicated, and largely control the pattern of carbonate percentages 

 in pelagic sediments. Conditions related with marked deviations 

 to unusually great depths, or rates of supply, or other factors will 

 be apparent, but the depth of compensation remains surprisingly 

 near limits between 4000 and 5000 m. The sharp decrease in CaC02 

 and compensation depth appears even more limited, within a range 

 of about 500 m in localized regions where depth differences are 

 greater than differences in the other factors. This poses a problem 

 on the solubility conditions in the bottom waters that a depth 

 below 4000 to 5000 m appears so important. 



Figure 4 shows CaCOs per cent plotted against depth in meters 

 for an area near 10-27° S Lat in the Pacific. The curve shows a 



2000 



3000 



*i^ 4000 



£] 5000]^ 



6000 



20 



40 



60 



80 



100 



Co CO,, wt 7o 



Fig. 5. Calcium carbonate versus depth of the Pacific. Central equatorial 



Pacific, 15° X to 5° S Lat, 120°-135° W Long. Average for 500-meter inter- 

 vals from all available data for top of core samples. 



