Reconnections of Marginal Basins to the World Ocean: New Data from the Marmara Sea

Sediment cores and reflection profiles acquired by the R/V Mediterranean Explorer in the summer of 2005 and from the R/V Urania in 2001 document that the transition from an ice-age lake to a marine sea was abrupt. Paleo-shorelines of the lake are present along the northern, eastern and southern shelves and lie well below the level of the Dardanelles outlet sill (-85m). Lacustrine strata were sub-aerially exposed on an erosion surface that extends across the shelf to beyond the -125m isobath. Radiocarbon dating, oxygen isotopes, mollusk, diatom and foraminifer assemblages, and sediment physical properties show that prior to 15.5 ka (age in calendar years) the lake was barren of fauna and its laminated sediments were indicative of climatically controlled deposition. Near 14.5 ka, oligohaline conditions with salinities of 1-5 parts per thousand were established as indicated by the Caspian mollusk assemblage Dreissena rostriformis, gastropods Theodoxus fluviatilis, and diatoms association delivered by Black Sea outflow. The flooding by marine waters at 14 ka submerged a coastal strip of gravelly sand. The desiccated condition of sediments beneath the flooding surface confirms that the lake surface was below its outlet at the time of reconnection with the Mediterranean indicating regional aridity. A complete replacement of fauna and flora occurs across the flooding surface. The variability in oxygen isotopes, foraminifer and mollusk content provide information on changing salinity, onset of anoxia, progressive deepening, warming and freshening of the Marmara Sea and output from the Black Sea at a millennial scale during the Holocene.