MOLECULAR EVIDENCE FOR DEGRADATION AND PRESERVATION OF ORGANIC-MATTERIN THE ANOXIC BLACK-SEA BASIN

Lipids were measured in a short core covering the past 150 years in th e Black Sea, in order to examine the biogeochemical factors involved i n the degradation and preservation of organic matter in anoxic sedimen ts. Most of degradation of labile compounds occurs in the upper 20 mm of the sediment, although for some compounds there appeared to be insi gnificant loss with increasing depth. A diagenetic model consisting of two pools of organic matter, labile and refractory, was used to calcu late first-order degradation rate constants. From the rate constants, an order of relative reactivity was constructed for selected lipids in Black Sea sediment: fatty acids > neutral lipids; unsaturated and bra nched fatty acids > saturated fatty acids, isoprenoid alkenes > sterol s and n-alkanols > n-alkanes, long-chain alkenones, long-chain alkyldi ols, and long-chain alkylketo-ols. Degradation rate constants were als o used to estimate rain rates describing delivery of lipids to the sed iment and accumulation rates and burial efficiencies within the surfac e sediment. Degradation and preservation of the model lipids are discu ssed in terms of their molecular structures, autochthonous vs. allocht honous sources, and rates of delivery to the sediment.