Organic carbon export from euphotic

As shown in Fig. 10-13, there is also a flux of O2 produced during net photosynthesis from the ocean to the atmosphere and an export flux of particulate and dissolved organic matter out of the euphotic zone. For a steady-state system, new production should equal the flux of O2 to the atmosphere and the export of organic carbon (Eppley and Peterson, 1979) (when all are expressed in the same units, e.g., moles of carbon). Such an ideal state probably rarely exists because the euphotic zone is a dynamic place. Unfortunately, there have been no studies where all three fluxes were measured at the same time. Part of the difficulty is that each flux needs to be integrated over different time scales. The oxygen flux approach has been applied in the subarctic north Pacific (Emerson et al, 1991) and subtropical Pacific (Emerson et al, 1995, 1997) and Atlantic (Jenkins and Goldman, 1985). The organic carbon export approach has... 

The quantity of primary production that is exported from the upper ocean is said to be equivalent to new production (18, 19) New primary production is that associated with allocthonous nutrients (i.e., those upwelled or mixed into the euphotic zone or input via rivers and rain). In order for steady state to be maintained, an equivalent flux out of the euphotic zone is required. Earlier studies (19) suggested that sediment-trap measurements of particulate organic carbon (POC) flux were equivalent to new primary production however, recently it has become clear that these measurements probably represent only a... 

Measurements of radionuclides are also used to determine removal mechanisms and controls for carbon and metal cycling in the ocean. For example, the removal of Th from the euphotic zone is closely coupled to the vertical flux of particulate organic carbon. The deficiency of Th with respect to its parent—near-surface waters is used to estimate the export flux of particulate organic carbon (Buesseler, 1991). Measurements of Th and in the upper water column provided the primary data relahng to particulate carbon fluxes during JGOFS. 

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