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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. [Copyright &y& Elsevier]

Abstract: Chloride and δ 18O compositions of interstitial water extracted from a long sediment core retrieved from the NW coast of the Black Sea allowed us to constrain the main hydrologic changes of the Back Sea during the Late Pleistocene and Holocene. Prior to its reconnection with the Mediterranean Sea (through the Marmara Sea) at approximately 9000 calendar yr before present (9kacalBP), the Black Sea has evolved as a fresh to brackish water lake. At the time of reconnection, hydrologic changes were drastic. Bottom water salinities changed from a few psu (practical salinity unit) to ∼22psu. Since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters. In order to reconstruct these former concentrations, we used an advection/diffusion model. Different scenarios of bottom water chloride and δ 18O variations were accounted for in this model in order to simulate “present day” vertical profiles for concentrations of interstitial water in order to compare them to measured ones. The comparison suggests that the glacial Black Sea was a homogeneous freshwater lake (with a δ 18O of ∼−10‰ and a salinity of ∼1psu). Modern hydrologic conditions would only have been reached at ∼2kacalBP, concomitant with the onset of coccolith-rich thin layers that characterize modern basin sediments. Such delayed salinization (over ∼7000yr) in the basin may have been due to higher precipitation during the early Holocene. We also simulated the impact of a catastrophic reconnection and a smoother reconnection. Both salinity scenarios lead to undistinguishable modelled “present day” profiles, indicating that the precise impact of the last reconnection was lost due to the advection/diffusion processes. [Copyright &y& Elsevier]

Abstract: In their comment Hiscott and co-authors adhere rigidly to ages and sources for sedimentary units in the subsurface of the Marmara shelf that they have previously reported in their publications from 2002 through 2007. This adherence is in spite of a superior age-depth model from our 13 m-long sediment core that penetrated deeply into the deposits under consideration and in disregard to the results of subsequent more-detailed and full-coverage mapping of the region under scrutiny. The age revisions are dismissed by the authors of the comment as representing sediments severely disturbed during coring. We rebut this criticism. The Bosporus source attributed by them to the sedimentary units sampled and dated by us appears to be driven by their conception that the Black Sea had a persistent outflow prior to its two-way connection with Marmara. Irrespective of whether the outflow was persistent, our reply shows that the drawing of the isopachs of the sedimentary units by Hiscott and co-authors was accomplished in a fashion to promote the Bosporus source hypothesis regardless of the geographic limits of their survey. The ages assigned to the units are equally indeterminate because the cores used by them have missing core tops of unknown lengths that are not discussed in their publications. Furthermore, the sub-bottom reflectors at the sites where the reflectors were calibrated to their only core without a missing top are actually hidden by the finite width of the bottom reflecting wavelet. [Copyright &y& Elsevier]

Continental ice sheets are a key component of the Earth's climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate-lake-FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas.