Dissolved organic matter depth profile

Figure 6 The rate of organic matter oxidation as a function of depth below the sediment-water interface at two locations on the northwest Atlantic margin at 70° W (Martin and Sayles, submitted). The calculated organic C oxidation rates are based on fits to pore-water O2, NO, and NH4 profiles. The apparent discontinuity between the rates of oxidation by O2 and NOJ is most likely an artifact of the modeling procedure used to calculate the rates. Fits to dissolved O2 profiles were entirely independent of fits to NO profiles at sites where NOJ profiles could be used to calculate both the rate of oxidation by O2 and that of oxidation by NO, magnitudes of oxidation rates were similar to those shown here, but no discontinuity was present (Martin and Sayles, submitted). The small overlap in the zones of oxidation by O2 and NOJ is most likely due to the relatively poor resolution ( 0.5 cm) of the pore-water NOJ...

Oxygen profiles in the ocean do not continually decrease with depth (Fig. 1.4). A typical dissolved O2 profile exhibits a minimum that is positioned above 1000 m. The main processes that contribute to this profile are the rapid and efficient respiration of settling organic matter (with more than half being degraded between 100 and... 

So far, dissolved iron has been discnssed with respect to the assimilation by phytoplankton. The chemical state of bioavailable dissolved species is presently a matter of intensive stndies and discussions. Due to thermodynamic reasons concentrations of free ions of dissolved iron are extremely low under oxic and pH-nentral conditions. A discussion paper by Johnson et al. (1997) reviews regional distributions and depth profiles of dissolved iron and points ont that at greater depth the iron concentrations always remain constant of 0.6 nM. Other elements with such short residence time (100 to 200 years) typically continuously decrease with depth and age. This suggests a substantial decrease in the iron removal rate below this concentration. As organic ligands with a binding capacity of 0.6 nM Fe have been found (Rue and Bruland 1995 Wn and Luther... 

Fig. 8.1 Schematic representation of the biogeochemical zonation in marine sediments. The names of the main zones were proposed by Froelich et al. (1979) and Berner (1981, in parenthesis). The depth scale is quasi-logarithmic die exact depths, however, vary strongly and increase from the shelf to the deep sea. The pore water chemistry shows relevant dissolved species. Peak heights and concentration scales are arbitrary. The chemical profiles reflect the depdi sequence of the dominant mineralization processes through which organic matter is oxidized to CO, (Modified from Froelich et al. 1979).

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