Key Biogeochemical Processes of Carbon in Seawaters

Carbon has a lifetime in the sedimentary reservoir measured in hundreds of millions of years and is released to the atmosphere by volcanic eruptions and 

The overall cycle of carbon among the atmosphere, biota, soils, and ocean has an associated residence time of about 100,000 years, with most of this time spent in deep seas. The cycle involving the atmosphere, biota, soils, and upper ocean is mediated, for the most part, by biological processes, limited in many cases by the supply of constituents other than C, N, P, and water. The biogeochemical cycles of these elements are thus inextricably connected. 

Enhanced by abundant substrate, high biological productivity with seasonal and spatial variation has been observed in the ECS. High primary production tends to enhance the biological pump and draws down the concentration of dissolved CO2. 

On the basis of the sea-air Pco2 difference, the sea-air flux was calculated by three methods. The results were greatly different, but the trend was identical (Table 4.3, Gao and Song, 2006). The ECS is a sink of atmospheric CO2 in spring and summer and a source in autumn and winter. 

The distribution of the sea-air net flux of CO2 is inhomogeneous in continental marginal seas. Because of the influence of the Changjiang River input, the character of the carbon sink/source for the Changjiang River Estuary was clearly different from those of the other regions of the ECS. We calculated the CO2 sea-air flux of the Changjiang River Estuary (Fig. 4.10, Gao et al., 2008) The results indicated that the flux values varied between —10.0 and 

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