The paleoenvironmental evolution of the Black Sea is closely linked to the ingression of Mediterranean seawater over the Bosporus sill after the Last Glacial Maximum. We have reconstructed the temporal and spatial development of the Black Sea suboxic chemocline, which divides oxic surface water from anoxic, sulfi dic (euxinic) deep water. By combining high-resolution geochemical records of bulk parameters (carbonate, total organic carbon, sulfur), trace metals (Cu, Mo, V), and an isotopic proxy (δ 56 Fe) from seven sediment cores in the Black Sea, we generated a single composite geochemical core log that serves as a reference archive for the entire basin. Our proxy records refl ect the changing depositional and redox conditions of the Black Sea and permit us to estimate the infl ow budget of Mediterranean seawater throughout the Holocene. Our data indicate a gradual rise of the chemocline until ca. 5.3 ka, when suboxic waters fl ooded the shelf for the fi rst time. Trace metal and isotopic inventories document one major descent of the chemocline since the onset of brackish/ marine conditions before the present stable situation was established. INTRODUCTION The Black Sea is an enclosed marine basin where the ingression of Mediterranean seawater over the shallow Bosporus sill is causing stratifi cation of the water column. The stable pycnocline coincides with the chemocline, and stagnant sulfi dic deep water favors the deposition of organic-rich sediments (sapropels). There is an ongoing debate whether the seawater ingression into the basin during the Holocene sea-level rise occurred catastrophically in one single step (the Great Flood; Ryan et al., 1997), or more gradually over a longer time period (Aksu et al., 2002; Degens and Ross, 1974; Yanko-Hombach et al., 2007). The suboxic chemocline, separating oxic surface from sulfi dic deep water, is currently at ~150 m water depth (Huang et al., 2000). Its vertical migration ultimately governs the redox development in the Black Sea. Using metal abundances (Fe and Mo) and Fe isotopes (δ 56 Fe), we unravel the Holocene history of the chemocline and provide evidence for the temporal and spatial development of euxinic conditions in this type location of a restricted basin (Brumsack, 2006; Calvert and Pedersen, 1993). Sedimentary enrichment of Fe has been observed in sapropels from the Black Sea and other restricted basins (e.g., Anderson and Raiswell, 2004). The most widely accepted explanation for these characteristic enrichments implies the lateral transfer of reactive Fe from suboxic shelf sediments to the sulfi dic water column of euxinic basins, where it is sequestered into syngenetic pyrite (Canfi eld et al., 1996; Wijsman et al., 2001; Wilkin et al., 1997). In this model, microbially induced diagenetic reactions within the suboxic shelf sediments cause mobilization of reactive Fe with a light Fe isotope composition, which is laterally conveyed in the suboxic chemocline. Strong support for this Fe shuttle model comes from the covariation between bulk sedimentary Fe/...
