Calcium carbonate is the dominant component in the pelagic sediments of the South Atlantic; its distribution pattern can be explained by use of bottom-water circulation. Biogenous opal concentrations occur in two bands, near the Equator and around 50°S; these concentrations are associated with zones of high biological productivity in surface waters....
Ellis, David B., and T. C. Moore. 1973. "Calcium carbonate, opal, and quartz in Holocene pelagic sediments and the calcite compensation level in the South Atlantic Ocean." Journal of Marine Research 31, (3). https://elischolar.library.yale.edu/journal_of_marine_research/1269