Organic matter euphotic zone

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... 

Fig. 2.10 Mean colloidal organic matter (COM - zooplankton+phytoplankton+dissolved organic carbon) burden [kmol P/m2], integrated over the uppermost 90 m (euphotic zone).

Fig. 2.13 Mean fraction of DDT bound on detritus (upper panels) and colloidal organic matter (lower panels) in the euphotic zone [%].

Some is released into seawater as an extracellular exudate or as a result of viral lysis and from sloppy feeding by the grazers. Consumption by grazers entrains the organic matter in the marine food web as shown in Figure 23.2. Cells that are not consumed or lysed by a virus can sink or be otherwise carried out of the euphotic zone by currents. 

Particulate organic matter (POM) in the ocean originates largely from plankton in the euphotic zone and reflects living plankton populations. Between 40°N and 40°S... 

The nature of the organic compounds in natural waters has been the subject of considerable study (15, 40, 52, 65, 66). Only a few general comments are pertinent here. The fact that the greater part of the organic matter present in natural waters is nonliving is often overlooked by workers in water chemistry. Parsons (52) reported that in the euphotic zone of the sea, the relative proportions of organic matter are ... 

Ammonium is considered a regenerated source of N, because it is produced in situ, in the euphotic zone, from ammonification of organic matter. The N in... 

Despite these observations, exceUent correlation is found between the d N of bulk surface sedimentary N and that of the local sub-euphotic zone nitrate at sites where export production is high and/or organic matter preservation is good (many of which are from continental margins. Fig. 34.6) (ThuneU et al, 2004). In these... 

The supplies of oxygen to waters below the euphotic zone are primarily physical advection and mixing. Removal of oxygen from these waters takes place through the oxidation of organic matter (Equations (2) and (3)) ... 

Roughly 90% of the organic matter that exits the euphotic zone of the ocean is degraded in the water column. Of the 10% of the organic carbon flux that reaches the seafloor, only about one-tenth escapes oxidation and is buried. Degradation of the organic matter that reaches the ocean sediments drives the reactions that control sediment diagenesis and benthic flux. 

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