A revised calendar age for the last reconnection of the Black Sea to the global ocean

During the last decade, a debate arose regarding the timing and pattern of the last reconnection of the Black Sea Lake with the global ocean. On a geochemical basis, the radiocarbon age of Black Sea Lake surface water, during the time of reconnection, was determined to be similar to 8400 C-14 a. BP. Despite the potential bias induced by the hard water effect in lakes, the reconnection age was calibrated without any reservoir age correction, which led to an estimate of similar to 9400 cal a. BR Since knowledge for the actual calendar age has important hydrologic implications that would provide new insights regarding the mechanism of reconnection, determining the actual calendar age for the last reconnection remains important. Based upon modeling experiments and micropaleontological reconstructions, the Black Sea Lake reconnection occurred in two steps, as follows: 1) Initial Marine Inflow (IMI) followed by 2) a period of increasing basin salinity that led to the Disappearance of Lacustrine Species (DLS). In order to better define the actual calendar age for the last reconnection, a review of the sedimentary expressions of the IMI and DLS boundaries was performed in order to correlate them throughout the Black Sea sedimentary environments. This correlation reconciles the apparent inconsistency in the published radiocarbon dataset, and provides the atmospheric radiocarbon age of the last reconnection, which represents the reference for reservoir age calculations and which can be directly calibrated. We determine reservoir ages for the water column, as well as the reconnection calendar age to be similar to 9000 cal a. BP. At the reconnection with the global ocean, Black Sea Lake reservoir ages were non-negligible and water-depth-dependent, consistent with a weak water column stratification during the Early Holocene. The calibrated age of Initial Marine Inflow (9000 cal a. BP) implies that the former Bosphorus sill was shallower by similar to 10 m than is commonly assumed in the literature. Compared to the sedimentary context of the Sakarya coastal plain, this result suggests that the level of the isolated Black Sea was below the former Bosphorus sill depth at the time of the last reconnection. Furthermore, a lag of 900 yr between Initial Marine Inflow and the Disappearance of Lacustrine Species indicates that approximately ten centuries were needed to establish the currently observed two-way flow exchange with the global ocean. (C) 2011 Elsevier Ltd. All rights reserved.