Continental margins organic matter

Ransom, B., Bennett, R. J., Baerwald, R., and Shea, K. (1997). TEM study of in situ organic matter on continental shelf margins Occurrence and the monolayer hypothesis. Marine Geol. 138,1-9. 

Hulthe, G., Hulth, S., and Hall, P.O.J. (1998) Effect of oxygen on degradation rate of refractory and labile organic matter in continental margin sediments. Geochim. Cosmochim. Acta 62, 1319-1328. 

Martine, W. R., and Sayles, F. L. (2004). Organic matter cycling in sediments of the continental margin in the northwest Atlantic Ocean. Deep-Sea Research Part I-Oceanographic Research Papers 51(3), 457-489. 

Potential processes that may be called upon to explain the large discrepancy between excess N2 and NOs deficits within the SNM are (1) sedimentary denitrification, (2) anammox, (3) metal (Fe, Mn)-catalyzed denitrification, and (4) non-Redfieldian organic matter mineralization (Codispoti et al., 2001 Devol et al., 2006a,b). The first of these possibilities requires a decoupling between nitrogen and phosphorus cycles (e.g. possible greater burial of phosphorus in continental margin sediments). The less likely additional requirement is that the maximal inputs from the sediments should occur at the same depth as the water column peak of N02. In other words, the exact coincidence of the extrema in NOs , N02, ... 

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... 

Approximately 100 Gt of organic matter is sequestered in the upper meter of marine sediments. In the modern ocean, —90% of OC burial occurs under oxygenated bottom waters along continental margins (e.g., Hedges and Keil, 1995). Up to 45% of OC burial occurs in deltaic sediments, which, in spite of nature as loci of major riverine inputs, appear to include a major... 

The broad implication of these observations is that somewhere between upper continental margins and the deep ocean, depositional conditions lead to greatly increased exposure times of sedimentary organic matter to O2 that are... 

Recent measurements of calcium and alkalinity in the ocean above the calcite saturation horizon (Milliman et ai, 1999 Chen, 2002) suggest dissolution in supersaturated waters. The proposed mechanisms are variations of the organic matter driven CaC03 dissolution mechanism. In these cases the authors suggest that microenvironments in falling particulate material (Milliman et al., 1999) or anerobic dissolution in sediments of the continental shelves and marginal seas (Chen, 2002) are locations of CaC03 dissolution. As the details and accuracy of measurements improve, thermodynamic and kinetic mechanisms required to interpret the results become more and more complex. 

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