Glacial hydrologic conditions in the Black Sea reconstructed using geochemical pore water profiles

Chloride and delta O-18 compositions of interstitial water extracted from a long sediment core retrieved from the NW coast of the Black Sea allowed us to constrain the main hydrologic changes of the Back Sea during the Late Pleistocene and Holocene. Prior to its reconnection with the Mediterranean Sea (through the Marmara Sea) at approximately 9000 calendar yr before present (9 ka cal BP), the Black Sea has evolved as a fresh to brackish water lake. At the time of reconnection, hydrologic changes were drastic. Bottom water salinities changed from a few psu (practical salinity unit) to similar to 22 psu. Since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters. In order to reconstruct these former concentrations, we used an advection/diffusion model. Different scenarios of bottom water chloride and delta O-18 variations were accounted for in this model in order to simulate "present day" vertical profiles for concentrations of interstitial water in order to compare them to measured ones. The comparison suggests that the glacial Black Sea was a homogeneous freshwater lake (with a delta O-18 of similar to - 10 parts per thousand M. and a salinity of similar to 1 psu). Modem hydrologic conditions would only have been reached at similar to 2 ka cal BP, concomitant with the onset of coccolith-rich thin layers that characterize modern basin sediments. Such delayed salinization (over similar to 7000 yr) in the basin may have been due to higher precipitation during the early Holocene. We also simulated the impact of a catastrophic reconnection and a smoother reconnection. Both salinity scenarios lead to undistinguishable modelled "present day" profiles, indicating that the precise impact of the last reconnection was lost due to the advection/diffusion processes. (C) 2010 Elsevier B.V. All rights reserved.