A multiproxy reconstruction of the Late Pleistocene-Holocene paleoenvironment: New insights from the NW Black Sea

We provide new data on the Black Sea evolution during the preconnection and reconnection stages with the Mediterranean, based on sedimentology, geochemistry, calcareous nannoplankton and ostracods analysis, in 13 cores placed between 141 m and 1315 m water depths. Unit 1 - The Coccolith Mud, Unit 2 - The Sapropel Mud and Unit 3 - The Lacustrine Lutite, including red-brownish depositional intervals, were identified in all studied deep-water cores. These units are not present in a shallow setting, i.e., above 166.7 m water depth, being replaced by sandy levels and shell debris. The red-brownish layers are interpreted as hyperpycnites, but some of the red successions show turbidite features, especially the ones situated on canyon sides, at a water depth below 600 m. In the oldest intercepted Unit 3 of the Neoeuxinian lake, CaCO3 values are constantly low, but towards the top of this unit they show two distinct peaks, interpreted as signals of Bulling-Allerud and Preboreal interstadials. In between, a significant decrease in CaCO3 values, linked to the setting of the Younger Dryas, is coincident in the deep cores with diatom blooms and high frequency of ostracods related to cooler waters. The scarce but continuous occurrence of Emiliania huxleyi nannoplankton species from the top of Unit 3 indicates that the salinity was at least 10-11 parts per thousand prior the Sapropel Mud deposition and increase at a least 17 parts per thousand within the lower part of Unit. 2. In the same interval, the Ponto-Caspian ostracods are still present. The Mediterranean ostracods consistently occur from the top of Unit 2, when bottom water salinity reached values for allowing their survival. The first bloom of E. huxleyi is placed at the base of Unit 2, where coccolith laminae occur, while the second bloom is placed in Unit 1 that contains exclusively Mediterranean ostracods and consistent assemblages of benthonic foraminifers, similar with the ones present today.