Paleoclimatic and paleoceanographic conditions leading to development of sapropel layer S1 in the Aegean Sea

Sapropel S1 occurs as 25–35 cm-thick black, weakly laminated muds in Aegean Sea cores. S1 was deposited between 9600 and 6400 yr B.P., during a period of isotopically depleted and relatively cool surface waters. Micro-faunal and -floral data indicate a major reduction in surface waters salinity during the deposition of S1, and oxygen isotopic data show a northerly fresh water source. Relatively light δ13Corg and high pollen-spore concentrations in S1 suggest increased influx of terrestrial organic carbon, probably supplied by major rivers draining into the northern Aegean Sea. Benthic foraminifera indicate high-nutrient, low oxygen bottom waters for S1, and together with silt-sized hematite and manganese coatings suggest that during the deposition of S1 surface sediments were oxic. Visual and XRD evidence of pyrite in S1, together with enrichments in S, Cu, Zn, As, Ni, Cr and Fe suggest that subsurface conditions were sufficiently reducing for SO42− reduction to occur, probably by diffusion from surface oxic into subsurface anoxic sediments. morphs in S1 show large increases in terrestrial pollen and spores, with the floral assemblage indicating significant influx from northern European rivers, and minor African components associated with increased summer monsoonal rain. Abundance of dinoflagellates and amorphogen suggests some increase in primary productivity in response to increased influx of humic compounds, however, there is no evidence of upwelling. The clay fraction in S1 shows notable decreases in smectite and kaolinite and reciprocal increases in illite and chlorite. The combined data suggested that the evolution of S1 in the Aegean Sea largely resulted from stagnation of the surface waters during the final disintegration of the continental ice sheets, rather than an increase in primary productivity and higher preservation of organic carbon on the sea floor.