Biogeochemical rates

The mathematical models used to infer rates of water motion from the conservative properties and biogeochemical rates from nonconservative ones were flrst developed in the 1960s. Although they require acceptance of several assumptions, these models represent an elegant approach to obtaining rate information from easily measured constituents in seawater, such as salinity and the concentrations of the nonconservative chemical of interest. These models use an Eulerian approach. That is, they look at how a conservative property, such as the concentration of a conservative solute C, varies over time in an infinitesimally small volume of the ocean. Since C is conservative, its concentrations can only be altered by water transport, either via advection and/or turbulent mixing. Both processes can move water through any or all of the three dimensions... 

Thus carbon metabolism on reefs has a tri-modal distribution (Table 2.2), and estimates of carbon production and calcification can be made by basic knowledge of bottom type. The partitioning of net carbon production and consumption, and the relationships to nutrient cycles, however, are not well understood, nor characterized, especially under field conditions. Further advances in this area of research will delineate kinetic constraints on the biogeochemical rates and their links with the carbon cycle. 

Both processes, with limits, will increase benthic faunal populations and bio-turbation, but sediments receiving excessive organic loading will tend to become anoxic and devoid of macrofauna. This matrix represents the variety of sediment types that might be found in various parts of the World and under various water depth and productivity conditions. These hypothetical types are used as a proxy for actual sediment variety, but if the World s sediments could be categorized in terms of quantity, quality and frequency of POM input, simulation could predict all the important biogeochemical rates and nutrient profiles. More continuous productivity... 

As described in the first part of this chapter, chemical thermodynamics can be used to predict whether a reaction will proceed spontaneously. However, thermodynamics does not provide any insight into how fast this reaction will proceed. This is an important consideration since time scales for spontaneous reactions can vary from nanoseconds to years. Chemical kinetics provides information on reaction rates that thermodynamics cannot. Used in concert, thermodynamics and kinetics can provide valuable insight into the chemical reactions involved in global biogeochemical cycles. 

Fig. 7-11 Compilation of the most important photochemical processes in the atmosphere, including estimates of flux rates expressed in moles per year between the earth s surface and the atmosphere and within the atmosphere. (Modified with permission from P. J. Crutzen, Atmospheric interactions - homogeneous gas reactions of C, N, and S containing compounds. In B. Bolin and R. Cook (1983). "The Major Biogeochemical Cycles and Their Interactions," pp. 67-112, John Wiley, Chichester.)...

Langdon, C., Takahashi, T., Sweeney, C., Chipman, D., Goddard, J., Marubini, F., Aceves, H., Barnett, H., and Atkinson, M.J., Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef, Global Biogeochem. Cy., 14, 639-654,2000. 

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