Critical carbonate levels in the Indian Ocean

Publisher Website
Google Scholar
Abstract
One half of the ocean bottom is covered by carbonate sediments, the other deeper areas contain sediments with less than 10% CaCO3. The boundary between carbonate and noncarbonate sediments is associated with an increase in the rate of solution of calcium carbonate. This boundary is the critical carbonate compensation depth (CCD). Recent investigations of the carbonate distribution over the seafloor has revealed one more level, connected with depth and reflecting a sharp increase in dissolution rate of carbonate on the sea bottom. This sharp change in the content of CaCO3 is the carbonate lysocline (CL). The locations of the CCD and CL are mapped for different regions of the World Ocean. Study of the distribution patterns of planktonic foraminifera, which are an important part of carbonate sediments, has made it possible to establish the existence of another, bathymetrically higher level: the foraminiferal lysocline (FL). Pronounced changes in planktonic foraminiferal assemblages are confined to this level. Thus, three levels are distinguished which are important for understanding processes of carbonate accumulation: CCD, CL and FL. We have mapped the location of the FL in the Pacific and Indian oceans, and described the latitudinal and longitudinal variations in its depth. The data on CaCO3 content and planktonic foraminiferal assemblages are used to characterize the zones between the FL, CL and CCD. Biological productivity, planktonic foraminiferal productivity, dilution by biogenic noncarbonate and terrigenous material, rate of sedimentation, water chemistry (the degree of saturation of calcium carbonate), and bottom water circulation patterns are the main factors influencing the FL, CL and CCD changes, and the vertical range of zones between these levels.