STABLE AND RADIOGENIC ISOTOPE CONSTRAINTS ON THE DEGLACIAL HISTORY OF THE BLACK AND MARMARA SEAS

The history of hydrologic exchange along the Black Sea-Mediterranean corridor has been the subject of much recent debate, with implications not only for the regional hydrologic balance but also for the response of continental climate to glacial periodicity and for the history of civilization in the region. The direction and timing of water flow between the basins is determined by two factors—1) change in global sea level relative to the depths of the sills dividing the basins from one another; and 2) climatic changes controlling inflow from the vast drainage areas and local evaporation. Sill depth, continental runoff and evaporation all remain controversial, and the record of water exchange provides crucial tests of competing models. Since there are consequences for the sensitivity of continental regions to climate change and tests of the controversial theory of a catastrophic flooding of the Black Sea basin the problem is by no means only of local interest.

New cores spanning the last deglaciation in both the Black and Marmara seas provide the basis for high resolution cross-study of connection and separation between the two basins. The sediments record the transformation of the Black and Marmara seas from fresh/brackish to brackish/marine as rising global sea level topped their dividing sills. This study focuses on isotopic measurements (d¹⁸O, d¹³C, and ⁸⁷Sr/⁸⁶Sr) of biogenic carbonates from the last 20,000 years. Use of traditional paleoceanographic proxies, such as d¹⁸O and d¹³C, is complicated in these intercontinental basins because of fractionation processes including evaporation and temperature, as well as significant changes in source inputs. The combined stable and radiogenic isotopic records allows comparison of non-conservative processes with conservative mixing of waters between the two basins. The first marine influx is seen clearly as a pronounced and progressive shift to marine values in all proxies. Outflow from the Black Sea to the Sea of Marmara prior to marine influence in either basin is seen by covariation in the isotopic records. Periods of basin isolation are inferred from independently evolving isotopic compositions. Placement of these periods in the context of a more refined age model will constrain models and theories of recent Black Sea history and its relation to paleoclimate.