Molecular characterisation of organic matter in sediments underlying the oxygen minimum zone at the Oman Margin, Arabian Sea

Lipids in replicate sediment cores collected from a transect through the oxygen minimum zone across the Oman Margin continental slope (∼400, 800, 1000 and 1250 m), have been analysed in order to assess the relative contributions of primary and secondary producer-derived material to the sediments. The high abundance of compounds that can be ascribed to primary producers, namely diatoms, dinoflagellates, coccolithophores, Eustigmatophycae and cyanobacteria, reflects the high productivity of surface waters, but there is little direct molecular evidence of zooplankton reworking of organic material, except at the deepest water site (∼1250 m). There is, however, clear evidence of benthic re-working, probably by detritovore megafauna, at one of the sites near the base of the oxygen minimum zone (∼1000 m). The relative abundance of biological markers that can be ascribed to aerobic and anaerobic bacteria in the sediments, namely the hopanoids and branched fatty acids, respectively, mirrors the concentrations of oxygen in overlying water. Considerable intra- and inter-site variability probably results from the spatial and temporal variability in production and from the complexity of sedimentation processes.