Microbial degradation of the marine prymnesiophyte Emiliania huxleyi underoxic 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 a lgal lipids, the marine haptophyte Emiliania huxleyi was incubated with est uarine sediment slurries under defined conditions (oxic, sulfate reducing a nd methanogenic). Rapid initial degradation of lipids corresponded to incre ased bacterial populations, both of which subsequently declined. Under oxic conditions the algal C-31 dienes were rapidly and completely degraded with in 178 days. Extensive degradation of the characteristic C-37 methyl alkeno nes occurred under all conditions (up to 85% under oxic conditions); howeve r, the U-37(K)' index remained essentially constant, except for a slight in crease at the longest oxic incubation time. Under anoxic conditions the alk yl alkenoates were preferentially degraded relative to the alkenones and ch anges in the AA(36) index occurred. These results demonstrate that lipids a re part of the "labile" organic matter; however, they were generally degrad ed at multiple rates which slowed during incubation, resulting in their par tial preservation. Hence, laboratory experiments conducted over only short periods cannot predict the preservation potential of lipid components. Furt hermore, preservation differed between sulfate reducing and methanogenic co nditions, so the roles of anaerobic processes need to be considered individ ually with regard to oxic vs. anoxic preservation. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.