Carbonate compensation depth CCD

Calcium carbonate compensation depth (CCD) The depth below which calcium carbonate is not found in marine sediments due to its dissolution. 

Figure 10.20. Comparison of some trends through the Cenozoic. A. The 8180 content of benthic foraminifera (Savin et al., 1975 see also Prentice and Matthews, 1988). If the 5180 trend is primarily due to temperature, Cretaceous deep water temperatures were about 12°C warmer than today. B. Progressive change of the North Atlantic and Pacific carbonate compensation depth (CCD van Andel, 1975). C. The Sr/Ca ratio of planktonic foraminifera (Graham et al., 1982). D. Ridge volume (Pitman, 1978).

There are several other topics that would be equally appropriate to consider in a review of this type. Some of these, such as the record of seawater and the history of the calcium carbonate compensation depth (CCD), are mentioned briefly as they relate to records that are discussed in greater detail. Other topics have been omitted. We hope readers will recognize that the topics covered here are determined not only by the scientific interests of the authors, but also by the practical limits of what can be covered in a single review. 

The carbonate compensation depth (CCD) occurs where the rate of calcium carbonate dissolution is balanced by the rate of infall, and the calcium carbonate content of surface sediments is close to Owt.% (e.g., Bramlette, 1961). The CCD has been confused with the calcium carbonate critical depth (sometimes used interchangeably with the lysocline discussed next), where the carbonate content of the surface sediment drops below 10 wt.%. A similar marker level in deep-sea sediments is the ACD, below... 

A sketch of the carbonate content of deep sea sediments as a function of depth. Lighter shades indicate greater CaC03 content in the sediments. Horizontal arrows indicate theoretical relations among the depths of the lysocline (where CaCOs shows visible signs of dissolution), the carbonate compensation depth, CCD (where the CaCOs concentration drops to zero) and the saturation horizon (S =l). 

Below the lysocline a depth is reached at which the rate of supply of carbonate particles equals the rate of dissolution, termed the carbonate compensation depth (CCD). Below the CCD no carbonate is de-... 

The Peru Basin is a relatively shallow oceanic basin with depths typically in the range 3,900-4,300 mwhich is close to the depth of the Carbonate Compensation Depth (CCD) (4,250 m) and lies in a region of high biological productivity. Manganese nodules were initially recovered during cruises SO-04 and SO-11 of... 

Observations from studies of surface sediments have allowed definition of regionally varying levels in the ocean at which pronounced changes in the presence or preservation of calcium carbonate result from the depth-dependent increase of dissolution on the seafloor. The first such level to be identified was simply the depth boundary in the ocean separating carbonate-rich sediments above from carbonate-free sediments below. This level is termed the calcite (or carbonate) compensation depth (CCD) and represents the depth at which the rate of carbonate dissolution on the seafloor exactly balances the rate of carbonate supply from the overlying surface waters. Because the supply and dissolution rates of carbonate differ from place to place in the ocean, the depth of the CCD is variable. In the Pacific, the CCD is typically found at depths between about 3500 and 4500 m. In the North Atlantic and parts of the South Atlantic, it is found... 

Figure 4 Comparison of carbonate saturation profiie for the eastern equatorial Indian Ocean with measurements of foraminiferal fragmentation and carbonate content (weight-%) from depth-distributed modern sediment samples in this region. The saturation horizon with respect to caicite (ACOa " = 0) occurs iocaiiy in the water column at a depth of 3800 m. This level corresponds with both the foraminiferai iysociine and carbonate iysociine as recognized in the sediments. The carbonate compensation depth (CCD) in this region is found at a depth of approximateiy 5000 m. increased foraminiferal fragmentation and decreases in sedimentary carbonate content are the resuit of dissoiution and carbonate ioss beiow the iysociine. Carbonate saturation data are from GEOSECS Station 441 (5°2 S, 91°47 E Takahashi et al. 1980) modern sediment data are from Peterson and Prell (1985).

Atlantic Ocean Nodule abundance in the Atlantic Ocean appears to be more limited than in the Pacific or Indian Oceans, probably as a result of its relatively high sedimentation rates. Another feature which inhibits nodule abundance in the Atlantic is that much of the seafloor is above the calcium carbonate compensation depth (CCD). The areas of the Atlantic where nodules do occur in appreciable amounts are those where sedimentation is inhibited. The deep water basins on either side of the Mid-Atlantic Ridge which are below the CCD and which accumulate only limited sediment contain nodules in reasonable abundance, particularly in the western Atlantic. Similarly, there is a widespread occurrence of nodules and encrustations in the Drake Passage-Scotia Sea area probably due to the strong bottom currents under the Circum-Antarctic current inhibiting sediment deposition in this region. Abundant nodule deposits on the Blake Plateau can also be related to high bottom currents. 

Figure 3 Reconstructed Carbonate Compensation Depth (CCD) through the Cenozoic (Van Andel, 1975 Broecker and Peng, 1982). Timescale as Figure 1.

As well as around the K/T Boundary, there were earlier ones, for instance at the Permian/ Triassic (P/T) Boundary about 248 million years ago. When the former took place, there may have been an alteration in sea-floor spreading rates and a drop in the carbonate compensation depth (CCD) in the Atlantic, succeeded by a rise. Another such drop occurred in the Early Tertiary and may have been the result of a supernova. Four episodes were recognized in the... 

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