Black Sea chemocline oscillations during the Holocene: molecular and isotopic studies of marginal sediments

We measured delta C-13 values of free and sulfur-bound lipids and framboida l pyrite-size distributions in three sediment cores from the southern margi ns of the Black Sea. The margin cores show a marked difference in the occur rence of biomarkers from green sulfur bacteria compared with the deep-basin cores, as a result of deepening of the chemocline resulting from enhanced mixing and/or decreased light-penetration as a consequence of high turbidit y and productivity in shelf waters. Quantitation of biomarkers suggests tha t photic-zone anoxia along the shelf margin was generally absent during the deposition of unit I, although occurred during the deposition of Unit IIb at two sites. (C) 2000 Elsevier Science Ltd. All rights reserved.