Spatial and Temporal Variability in 5 Different Sapropel S5 Layers From the Eastern Mediterranean: Common Features and Peculiarities

Sapropel S5 in the Eastern Mediterranean was deposited during the last interglacial climatic optimum (MIS5e, ca. 125 kyrs BP). Here we present a high resolution geochemical and micropaleontological study of the temporal and spatial evolution of 5 sapropel S5 layers identified in Eastern Mediterranean deep-sea cores (SIN97-GC05, central Ionian Sea; UM94-PC31, Urania basin area west of Crete; SIN97-GC01, Urania basin area north-west of Crete; BAN84-GC27 and BAN89-GC09, south of Crete). In some cores organic carbon and nitrogen determinations and oxygen and carbon isotopic composition of selected foraminifera species integrate the data-set. The visible sapropel layer thickness ranges from 5 cm in core SIN97-GC05 to 64 cm in core UM94-PC31, but all the analysed sapropels underwent post depositional oxidation that reduced the original thickness (e.g., 11 cm SIN97-GC01 , 66 UM94-PC31 cm). Planktonic foraminifera bioevents (as defined by Cane et al., 2002 and Capotondi et al., in press) within the S5 were used to correlate the cores and provide a time frame for the evolution of sapropel deposition. The bioevents used are: disappearance of Globorotalia inflata (f8), disappearance of Globigerinoides sacculifer (f5), disappearance of Globorotalia scitula (f4), re-appearance of G. scitula (f1). Results indicate a spatial variability in productivity (as detected with biogenic Ba, Corg) with higher values in the cores south of Crete and in the Urania basin and lowest values in the westernmost core. Marked temporal changes occurs within the sapropels, as suggested by many proxies investigated. An increase of temperature and the development of a Deep Chlorophyll Maximum characterise the onset of the sapropel layer, which is followed by surface water stratification and productivity sudden develop, together with strong seafloor dysoxia/anoxia. Maxima in productivity occur in all the cores below the f4 bioevent, although in core SIN97GC05, the westernmost core the f4 bioevent was not detected. Afterwards, a partial oxygenation takes place, changing the main features of the sapropel and a decrease in productivity occurs in the cores south of Crete. A different evolution characterize the core UM94-PC31, from the Urania basin in the anoxic lakes region, after bioevent f4: productivity does not seem to change, remaining at high levels; diatoms are present and very abundant; organic matter concentration and enrichments in redox-sensitive trace metals still increase in contrast with all the other sapropel studied. The evolution of the sapropel in the Urania basin is thus different from other areas of the Eastern Mediterranean but sapropel deposition ended almost at the same time, as suggested by bioevent f1, which suggests that localized anoxic bottom water conditions might be longer present at high water depth (3291 m), but then disappear when oxic conditions are re-established at a basin scale.