The influence of oxygen exposure time on the composition of macromolecular organic matter as revealed by surface sediments on the Murray Ridge (Arabian Sea)
Nierop, K.G.J.; Reichart, G.-J.; Veld, H.; Sinninghe Damsté, J.S. (2017). The influence of oxygen exposure time on the composition of macromolecular organic matter as revealed by surface sediments on the Murray Ridge (Arabian Sea). Geochim. Cosmochim. Acta 206: 40-56. dx.doi.org/10.1016/j.gca.2017.02.032
In: Geochimica et Cosmochimica Acta. Elsevier: Oxford,New York etc.. ISSN 0016-7037; e-ISSN 1872-9533, more
The Arabian Sea represents a prime example of an open ocean extended oxygen minimum zone (OMZ) with low oxygenconcentrations (down to less than 2 mM) between 200 and 1000 m water depth. The OMZ impinges on the ocean floor, affectingorganic matter (OM) mineralization. We investigated impact of oxygen depletion on the composition of macromolecularOM (MOM) along a transect through the OMZ on the slopes of the Murray Ridge. This sub-marine high in the northernArabian Sea, with the top at approximately 500 m below sea surface (mbss), intersects the OMZ. We analyzed sedimentsdeposited in the core of OMZ (suboxic conditions), directly below the OMZ (dysoxic conditions) and well below theOMZ (fully oxic conditions). The upper 18 cm of sediments from three stations recovered at different depths were studied.MOM was investigated by Rock Eval and flash pyrolysis techniques. The MOM was of a predominant marine origin andinferred from their pyrolysis products, most biomolecules (tetra-alkylpyrrole pigments, polysaccharides, proteins and theirtransformation products, and polyphenols including phlorotannins), showed a progressive relative degradation with increasingexposure to oxygen. Alkylbenzenes and, in particular, aliphatic macromolecules increased relatively. The observed differencesin MOM composition between sediment deposited under various bottom water oxygen conditions (i.e. in terms ofconcentration and exposure time) was much larger than within sediment cores, implying that early diagenetic alteration oforganic matter depends largely on bottom water oxygenation rather than subsequent anaerobic degradation within the sediments,even at longer time scales.
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