MEDITERRANEAN SAPROPEL FORMATION, DYNAMIC AND CLIMATIC VIEWPOINTS

Sapropels, i. e. discrete, black and organic-rich layers sedimented in the Eastern basin in anoxic conditions, constitute record, over the p ast 500,000 years, of eleven particular interactions between marine ci rculation and biology during glacial as well as temperate climates. Co nsidering climatic and dynamic aspects, we argue that this formation i s preconditioned by the stoppage of dense water formation in the Adria tic Sea, following sea-level and/or freshwater input changes. In this case, oxygenation of eastern deep water depends solely on the dense wa ter formation in the South Aegean Sea, a process modified by episodic freshwater inputs. This scheme explains correlations between sapropel events and the strong African monsoons responsible for Nile river floo ding over several thousand years (Rossignol-Strick, 1983). At the time of sapropel formation, Mediterranean general dynamics and planktonic productivity were not drastically changed. The deciphering of Mediterr anean climatic records needs to take into account northern ice sheet c hanges (via sea-level, temperature and salinity in the adjacent Atlant ic), as well as tropical climatic oscillations (via increased freshwat er inputs and sapropel events).