Biological production removes nutrients from surface waters

C-values in planktonic and benthic foraminifera can be used to monitor CO2 variations in the atmosphere by measuring the vertical carbon isotope gradient, which is a function of the biological carbon pump. This approach was pioneered by Shackleton et al. (1983), who showed that enhanced contrast between surface waters and deeper waters was correlated with intervals of reduced atmospheric CO2 contents. Increased organic carbon production in surface waters (possibly caused by enhanced nutrient availability) leads to the removal of carbon from surface waters, which in turn draws down CO2 from the atmospheric reservoir through re-equilibration. 

Biological cycling not only removes some ions from surface waters, it also transforms them. The stable form of iodine (I) in seawater is iodate (IOf), but biological cycling results in the formation of iodide (F) in surface waters, because the production rate of the reduced species is faster than the rate of its oxidation. Biological uptake of IOf in surface water results in a nutrient-like profile, contrasting with the conservative behaviour of most halide ions, for example CP and Br . The biological demand for NCp also involves transformation. Phytoplankton take up NO3 and reduce it to the -3 oxidation state (see Box 4.3 Fig. 5.12) for... 

Patterns of chemical distributions within the ocean are primarily controlled by biological processes and ocean circulation. Major features of this biogeochemical mosaic include removal of nutrients from warm surface ocean waters, concentration of these same nutrients in deep-ocean waters, and depletion of dissolved oxygen at intermediate water depths. These patterns are imprinted as mixing and advection carry nutrient-laden water from ocean depths into the sunlit upper water. These nutrients are used during photosynthesis to generate particulate and dissolved products that sink or are mixed into the interior ocean, where they are respired back into dissolved metabolites. Interactions of these physical and biological processes occur on time scales of days to hundreds of years and are expressed by the vertical concentration profiles of a variety of dissolved chemical... 

An efficient biological pump means that a large fraction of the system s net production is removed from the surface waters via export mechanisms. Factors that affect the efficiency of the biological pump are numerous and include nutrient supply and plankton community structure. 

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