Over the past decade, sinking particulate organic matter (POM) samples from depth profiles in the equatorial Pacific have been analyzed by multiple techniques to evaluate the organic matter preservation mechanisms most dominant in the oceanic water column. How the samples were analyzed strongly influenced which organic matter preservation scheme appeared to dominate. Bulk functional group analysis by solid-state 13C-NMR showed that organic matter composition varied very little in light of the extreme degree of remineralization (>98%) that occurred with water column depth. This indicates preservation by a physical mechanism, such as sorption to mineral grains or protection within a mineral aggregate. However, detailed lipid studies of the characterizable fraction showed that selective preservation was important, with lipid structure being correlated with preservation over depth. However, the characterizable fraction decreases greatly with depth. Therefore, in this paper, direct temperature-resolved mass spectrometry (DT-MS), was used to further characterize POM, with the assumption that this approach could "see" a substantial proportion of the "uncharacterized" organic matter. DT-MS, which provides compositional information at an intermediate level between the detailed wet chemical studies and one-dimensional solid-state C13-NMR, also indicates an intermediate view between the mechanistic extremes of selective preservation and physical protection.
Bibliographical noteFunding Information:
This research was supported by Old Dominion University (E.C.M.) and National Science Foundation collaborative research grants to S. G. W. (OCE 90-22238), to C. L. (OCE 90-24372) and to the late John Hedges (OCE 90-22319), who paved the way for our continued research into the uncharacterized organic matter in the marine environment.
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