Marine carbonate system functions

Figure 6.12. Calculated saturation states with respect to aragonite of marine pore waters undergoing anoxic diagenesis as a function of the original C/N ratio of labile organic matter. The extent of diagenesis is represented by the organic C oxidized in the sediment-pore water system, shown as inorganic carbon added to pore waters.

Apparently, there are many studies about the distribution, content, transfer, and transformation of carbon in sediment or soil to be performed. As one of three interdependent basic links in sediment (including soil-water-atmosphere systems), marine sediment plays an important role in oceanic or global environments. From now on, more attention should be paid to research into the functions of sediments in carbon biogeochemical cycles (Sun and Song, 2002). 

The volume terminates with Chapter 16 in which also the essentiality of Cd " for certain diatoms is pointed out. The distribution of Cd " in the ocean is very similar to that of major nutrients suggesting that it may be taken up by marine phytoplankton at the surface and remineralized at depth. At high concentration, Cd is toxic to phytoplankton as it is for many organisms. However, at relatively low concentrations, Cd " can enhance the growth of a number of phytoplankton species under Zn limitation possibly Cd is taken up either by the Mn or the Zn transport system. The otdy known biological function of Cd is to serve as a metal ion cofactor in cadmium-carbonic anhydrase (CDCA) in diatoms. The expression of CDCA is regulated by the availabilities of Cd " and Zn " both Zn " and Cd can be used as the metal ion cofactor and be exchanged for each other in certain marine phytoplankton species. 

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