Microbial degradation of the marine prymnesiophyte Emiliania huxleyi under oxic and anoxic conditions as a model for early diagenesis: long chain alkadienes, alkenones and alkyl alkenoates

To investigate the effect of bacterial diagenesis on the distributions of algal lipids, the marine haptophyte Emiliania huxleyi was incubated with estuarine sediment slurries under defined conditions (oxic, sulfate reducing and methanogenic). Rapid initial degradation of lipids corresponded to increased bacterial populations, both of which subsequently declined. Under oxic conditions the algal C-31 dienes were rapidly and completely degraded within 178 days. Extensive degradation of the characteristic C-37 methyl alkenones occurred under all conditions (up to 85% under oxic conditions); however, the U-37(K)' index remained essentially constant, except for a slight increase at the longest oxic incubation time. Under anoxic conditions the alkyl alkenoates were preferentially degraded relative to the alkenones and changes in the AA(36) index occurred. These results demonstrate that lipids are part of the "labile" organic matter; however, they were generally degraded at multiple rates which slowed during incubation, resulting in their partial preservation. Hence, laboratory experiments conducted over only short periods cannot predict the preservation potential of lipid components. Furthermore, preservation differed between sulfate reducing and methanogenic conditions, so the roles of anaerobic processes need to be considered individually with regard to oxic vs. anoxic preservation. (C) 1998 Elsevier Science Ltd. All rights reserved.