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

Lipids were measured in a short core covering the past 150 years in the Black Sea, in order to examine the biogeochemical factors involved in the degradation and preservation of organic matter in anoxic sediments. Most of degradation of labile compounds occurs in the upper 20 mm of the sediment, although for some compounds there appeared to be insignificant loss with increasing depth. A diagenetic model consisting of two pools of organic matter, labile and refractory, was used to calculate 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 branched fatty acids > saturated fatty acids, isoprenoid alkenes > sterols and n-alkanols > n-alkanes, long-chain alkenones, long-chain alkyldiols, and long-chain alkylketo-ols. Degradation rate constants were also used to estimate rain rates describing delivery of lipids to the sediment and accumulation rates and burial efficiencies within the surface sediment. Degradation and preservation of the model lipids are discussed in terms of their molecular structures, autochthonous vs. allochthonous sources, and rates of delivery to the sediment.