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 ox ygen minimum zone across the Oman Margin continental slope ( similar to 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 se diments. The high abundance of compounds that can be ascribed to primary pr oducers, namely diatoms, dinoflagellates, coccolithophores, Eustigmatophyca e and cyanobacteria, reflects the high productivity of surface waters, but there is little direct molecular evidence of zooplankton reworking of organ ic material, except at the deepest water site ( similar to 1250 m). There i s, however, clear evidence of benthic re-working, probably by detritovore m egafauna, at one of the sites near the base of the oxygen minimum zone (sim ilar to 1000 m). The relative abundance of biological markers that can be a scribed to aerobic and anaerobic bacteria in the sediments, namely the hopa noids 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 an d from the complexity of sedimentation processes. 1999 Elsevier Science Ltd . All rights reserved.