Dissolved organic matter sediment porewater

Another oxidant near the sediment-water interface capable of oxidizing Mn(II) is iodate (I03 ), which occurs in the dissolved form as well as adsorbed onto particles (Ullman and Aller, 1985). Iodine is known to be released in porewaters during the remineralization of organic matter (Ullman and Aller, 1983, 1985 Kennedy and Elderfield, 1987). Once produced, iodine is then believed to be oxidized to 103 through microbial processes, where it adsorbs onto metal oxides (Ullman and Aller, 1985). Recent work has shown that an iodide peak can be maintained in sediments through the reduction of 103 by Mn(II), with reoxidation of iodide to IO3 above the iodide peak thus, iodide production is adequate to account for the oxidation of all the upward diffusing Mn(II) via 1 (>3 (Ansch u tz et al., 2000). 

Comparative elemental analyses of the upper and lower sections of two sediment cores collected on the MAP abyssal plain show that organic concentrations decreased at both locations from values of 0.93-1.02 wt% OC below the oxidation front to values 0.16-0.21 wt% within the surface oxidized layer (Fig. 12.9). PoUen abundances decreased in the same samples from about 1600 grains g below the oxidation front to zero above it. Overall, 80% of the organic matter and essentiaUy all of the pollen that has been stable for 140 000 y in the presence of porewater sulfate was degraded in the upper section of the MAP cores as a result of long-term exposure to dissolved O2. 

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