A revised calendar age for the last reconnection of the Black Sea to the global ocean |
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| Authors: | G Soulet G Ménot G Lericolais E Bard |
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| Institution: | 1. Siberian Research Institute of Geology, Geophysics and Mineral Resources, Krasnyi pr. 67, Novosibirsk, 630091, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. Centro de Investigación Mariña, Universidade de Vigo, Edificio Filomena Dato, Campus Marcosende s/n, 36310 Vigo, Spain;2. Dept. Bioloxía Vexetal Ciencias do Solo, Facultade de Ciencias, Universidade de Vigo, Campus Marcosende s/n, 36310 Vigo, Spain;3. School of Earth and Environment, University of Leeds, Woodhouse, Leeds LS2 9JT, United Kingdom;4. Dept. Xeociencias Mariñas, Facultade de Ciencias, Universidade de Vigo, Campus Marcosende s/n, 36310 Vigo, Spain;5. Gl-1934-TB, Laboratorio de Botánica e Bioxeografía, IBADER, Universidade de Santiago de Compostela, Campus Universitario s/n, 27002 Lugo, Spain |
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| Abstract: | 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 ～8400 14C 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 ～9400 cal a. BP. 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 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 ～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. |
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