Light oceanic flux

Tans (1980) laid out a useful approach to assess the isotopic mass balance of atmospheric CO2 as a function of the fluxes, isotopic compositions and isotopic fractionations involved in the transfer of CO2 between the atmosphere, the ocean and the biosphere. The simple formulation shown below involves some approximation that is justihed in light of the uncertainties in the system (Tans, 1980). Accordingly, the mean temporal change in atmospheric CO2 content (Cf) can be described by... 

Fig. 3. The variation of photon flux with depth in different water types. Types I, lA, IB, II, and III represent different oceanic waters and types 1, 3, 5, 7 and 9 represent coastal waters (Jerlov, 1968). Surface light flux was calculated from data of Pettit (1932) for 10 nm spectral band centered at 350 nm. The measurement was made at latitude 32°N with the sun in the zenith.

It is also clear that eolian and riverine sources alone are insufficient to yield such short residence times and there must be additional sources of REEs in the ocean. The most likely candidate of the potential REE source is remineralization of nearshore, coastal and shelf sediments as described earlier. The magnitude of this remineralization flux required to balance each REE in the ocean is given in Table 3. Those fluxes are quite large particularly for the light REEs, whereas the relative importance of remineralization decreases and becomes somewhat comparable with the sum of eolian and riverine inputs for the heavy REEs. This REE fractionation during remineralization on the shelf may contribute the different NPDW-normalized REE patterns observed in the surface waters (Figure 9), although the mechanism is not well understood. 

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