REDOX-CONTROLED MEDITERRANEAN SAPROPEL- S1, FORMATION, PRESERVATION, AND INTERRUPTION
Abstract:The repetitive formation of distinctly organic-rich sedimentary units (sapropels) in the Mediterraneran is known to be related to precession-minima, i.e. humid climate conditions. The most-recent sapropel S1 formed basin-wide, synchronously between 9.8 and 5.7 14C ky BP at all water depths greater than ~200m. Increased fresh water (monsoon) input, and associated stratification resulted in the deep (> 1.8 km) eastern Mediterranean Sea to be devoid of oxygen during most of the 4,000 years of S1 formation. This resulted in a differential basin-wide preservation of S1 determined by water depth, as a result of different predominant ventilation/climate-related redox conditions above and below 1.8 km.
The end of this period was marked by a basin-wide sedimentary manganese-oxide peak representing abrupt re-ventilation and remaining oxic conditions thereafter. Other, short-term ventilation events occurred during S1, notably the 8.2 ka event. This basin-wide event marks a brief episode of not only re-oxygenated deep water thus reduced preservation, but also decreased primary productivity thus lower nutrient supply. Ventilation is closely linked to Aegean/Adriatic deepwater formation.
Sapropel formation and preservation mechanisms are related to a sensitive interplay between N-African monsoonal and northern climate systems.