Marine carbonates: Their formation and destruction

Abstract

For marine carbonates, an overwhelming amount of information exists in a variety of specialized journals addressing marine geochemistry and carbon cycling, as well as in many books summarizing the state of knowledge on this topic. Therefore it would be far beyond the scope of this chapter to try to completely review what is known about marine calcareous sediments and their diagenesis. On the other hand, although intensively investigated since the previous century (e.g. Murray 1897), marine carbonates have gained increasing attention by marine biologists, geochemists, paleoceanographers and paleoclimatologists over the last three decades. Among other reasons this is because marine carbonates, together with the oceanic CO2-carbonic acid-system, act as a sink or source of carbon within the global carbon cycle which has become a key topic of investigation and modelling related to the role of the greenhouse gas CO2 in future global climate change. Descriptions of sedimentary carbonates in different oceanic environments always have dealt with the formation of the calcium carbonate and the biologically, physically and chemically mediated processes governing the observed distribution of sedimentary carbonates in the marine realm. In this context special emphasis was often given to the complex pattern of inorganic and organic carbon exchange between the atmosphere, the world ocean and the continents. These are additional factors determining the distribution of inorganic carbon dissolved in seawater and the accumulation or destruction of calcium carbonate in marine sediments (Berger 1976; Andersen and Malahoff 1977; Broecker and Peng 1982; Sundquist and Broecker 1985; Morse and Mackenzie 1990). The intention of this chapter is furthermore to review the knowledge on the rate of calcium carbonate production in the ocean, the fluxes through the water column, as well as the rates of inorganic carbon accumulation and destruction in different marine environments. For this purpose this chapter summarizes studies dealing with the estimation of global carbonate reservoirs and fluxes in the state of ongoing production, accumulation and dissolution or physical erosion (Milliman 1993; Milliman and Droxler 1996; Wollast 1994). In addition, this chapter addresses the principles and presents examples for calculation of carbonate saturation conditions under variable boundary conditions in the oceanic CO 2-carbonic acid-calcite system, i.e. temperature, pressure, salinity, and CO2 exchange with the atmosphere.