Aragonite carbonate compensation depth

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today s oceans. Below the lysocline is the level where no carbonate remains in the sediment this level is termed the carbonate compensation depth. 

Surface seawater is oversaturated with respect to CaCOa (calcite, aragonite) and biogenic CaCOa forms in surface seawater. Solubility of CaCOa increases with increasing pressure (depth). CaCOa dissolves below CCD (carbonate compensation depth). 

Berger W.H. (1978) Deep-sea carbonate Pteropod distribution and the aragonite compensation depth. Deep-Sea Res. 25,447-452. 

About 12% of the CaCOs flux made by Berner and Honjo (1981) consists of aragonite. A study of sedimentation of pteropods and foraminifera in the North Pacific by Betzer et ai (1984) using sediment traps confirmed that considerable dissolution of pteropods takes place in the water column. They estimate that —90% of the aragonite flux was dissolved in the upper 2.2 km of the water column. It should be noted that the depth for total dissolution of carbonates in the water column is considerably more than the aragonite compensation depth (ACD). This is probably due to the short residence time of pteropods in the water column because of their rapid rates of sinking. 

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