High-resolution geochemical and micropalaeontological profiling of the most recent eastern Mediterranean sapropel

A combined geochemical and micropalaeontological study of the most recently-deposited sapropel (S1) from the eastern Mediterranean Sea is reported from two cores in which the S1 sapropel units were rapidly deposited (15 and 20 cm ky−1). Such rapid accumulation rates have largely protected the two S1 units from post-depositional oxidation effects and allow a high-resolution investigation of conditions before, during and after S1 formation. The cores are from the Adriatic and Aegean Seas, and both record a simultaneous diminution in intensity of sapropel development at 7500 conventional radiocarbon years that divides both visual S1 units into two approximately equal lobes. Detailed foraminiferal analysis of the Aegean core reveals fluctuations in benthic foraminifera species that indicate anoxic or near-anoxic bottom water conditions during formation of the upper and lower lobes. The central S1 section shows a temporary repopulation by an opportunistic benthic species (G. orbicularis) indicative of improved bottom water oxygen levels. The appearance and disappearance of this species in the central section, and its reappearance just before the end of S1 times, also coincides with increases in abundance of pelagic foraminifera characteristic of cooler surface water conditions, and with local Mn peaks in the sapropel. These features are interpreted as indications of increased deep-water ventilation and bottom water O2 levels centred during S1 time. Although the S1 Corg contents are low at 1–2 wt.% because of dilution by high detrital fluxes, a set of elements (Ba, Cr, Cu, Mo, Ni, S, Se, U, V and Zn) generally present in other S1 units, older sapropels and black shales is clearly present at enhanced levels. Sulfur enrichment is well correlated with the Corg content throughout S1, and FeS2 formation accounts for the bulk of the observed S enrichment.