Postglacial connection of the Black Sea to the Mediterranean and its relation to the timing of sapropel formation

Abstract

Abstract. The opening of the connection between the Mediterranean and Black Seas as sea level rose above the Bosporus sill has long been associated with the formation of the most recent, Holocene, sapropel deposit (S•) in the eastern Mediterranean, but the mechanism has remained elusive. We present a model for the opening of the Black Sea, based on hydraulics arguments, which demonstrates that increased freshwater flux out of the Black Sea began 500-1000 years after sea level reached sill depth and that the timescale for the increased freshwater flux that drained the freshwater reservoir of the Black Sea is about 2500-3500 years. We argue that the increased freshwater discharge out of the Black Sea would lead to decreased deep water formation and higher productivity in the surface waters in the eastern Mediterranean, two conditions generally associated with sapropel formation. The delay in increased freshwater flux after the opening of the Black Sea and the period of increased freshwater discharge appear to match the onset and duration of sapropel deposits in the eastern Mediterranean.

Why Early-Historical Radiocarbon Dates Downwind from the Mediterranean are Too Early

“…The paleoceanography is known to have been very different. During the last ice ages, the Black Sea was actually a freshwater lake (with no input from the Mediterranean; Lane-Serff et al 1997). As the ice ages ended, levels of the oceans, and thus the Mediterranean Sea, rose.…”

“…This caused a large reduction in the salinity, and hence density, of surface water in much of the eastern Mediterranean (Fontugne et al 1989;Aksu et al 1995;Kallel et al 1997;Lane-Serff et al 1997). Roughly concurrent with this was greater (freshwater) run-off from rivers discharging into the Mediterranean, most notably the Nile, and a substantial increase in the regional effective precipitation (Fontugne et al 1994;Gasse and Van Campo 1994;Kallel et al 1997;Martinez-Ruez et al 2000;Roberts et al 2001)-due to general climatic conditions, partially caused by orbital forcing (Rossignol-Strick 1983).…”

“…The Black freshwater was therefore forced up and out of the lake. It flowed over the incoming Mediterranean water, through the Bosporus Strait, and out into the eastern Mediterranean (Lane-Serff et al 1997;Aksu et al 1999). …”

The co-evolution of Black Sea level and composition through the last deglaciation and its paleoclimatic significance

“…Thus the Black Sea is well-situated to record climate changes in the continental interior. Prior studies have investigated the lithology and mineralogy of the glacial Black Sea lake sediments (Müller and Stoffers, 1974;Stoffers & Müller, 1978;Shopov et al, 1986;Major et al, 2002), but have focused primarily on the lake-to-marine transition (Wall & Dale, 1974;Deuser, 1972;Hay et al, 1991;Ryan et al, 1997;Lane-Serff et al, 1997).…”

Documenting the suboxic zone of the Black Sea via high-resolution real-time redox profiling

“…Natural barriers inhibiting vertical fluxes are established through density stratification of the water column (Sorokin, 1983;Anderson et al, 1988;Murray et al, 1995;Pers and Rahm, 2000;Scranton et al, 2001), caused by sharp increases in salinity (Anderson et al, 1988) and/or decreases in temperature (Scranton et al, 2001). In the case of the Black Sea, a vertical transition between oxic and anoxic waters is likely to have existed for over 7000 years (Arthur and Dean, 1998;Lane-Serff et al, 1997), since post-glacial saline Mediterranean waters broke through a land barrier and flooded the isolated freshwater Black Sea basin at a rate of 0.1-1 m per day, setting up a permanent pycnocline. The nature of the physical stratification and the subsequent steep chemical gradients make accurate sampling of these constituents around the redox transition problematic, yet crucial to understanding the overall redox budget of the Black Sea.…”