Carbon cycles, global residence time

Figure 15. Diagram showing the major components of the global calcium cycle with b Ca values (denoted as 5). The modem residence time of Ca in the oceans is about 1 million years (Holland 1978 1984). Abbreviations used are SW = seawater, Sed = sedimentation, clastic = clastic sediments, carb = marine carbonate sediments, hydrol = mid-ocean ridge hydrothermal systems, lith = continental lithosphere.

Finally, we must somehow resolve the vexing problem of the chemical speciation of trace elements in seawater what is the chemical nature of the various metal chelators whose existence has been demonstrated by electrochemistry Is the chemistry of several metals in surface seawater really controlled by metallophores released by prokaryotes Or are dissolved metals chiefly present as parts of metalloproteins in the process of remineralization How do metal chelators affect the residence times of metals (in particular, scavenged elements such as iron and cobalt) and in turn how do those chelators influence the global carbon cycle via changes in marine primary productivity ... 

Figure 15.19 gives a description of the global carbon cycle. The inventories of the various reservoirs were already given in Table 4.1, where we noticed that the atmosphere is a relatively small reservoir with large fluxes, so that the residence time of C in the atmosphere is only a few years. The carbon system is not at steady state. Because of fossil fuel combustion and possibly also because of deforestation, the inventories of C in the atmosphere and hydrosphere are increasing. The flux related to fossil fiiel combustion is nearly 1 % of the total atmospheric CO2 reservoir. The flux due to land use is more con-troversal but is probably 1-2 X 10 mol C . As the summary at the bottom... 

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