Oxygen and carbon isotopes and trace-element/Ca ratios in Late Quaternary ostracods Loxoconcha lepida and Palmoconcha agilis from the Black Sea: Paleoclimatic and paleoceanographic implications

Oxygen and carbon isotopes and trace-element/Ca ratios are presented for the valves of benthic ostracods Palmoconcha agilis and Loxoconcha lepida extracted from two composite sediment cores from the Black Sea shelf. The two cores together provide a complete latest Pleistocene-Holocene sedimentary record, with 16 radio-carbon-dated shells in core M02-45 and 9 in core M05-50. Results reveal environmental changes and evolution of water chemistry associated with the last reconnection of the Black Sea to the global ocean. The delta O-18 values in composite cores M02-45 and M05-50 exhibit ranges of similar to 8.0 parts per thousand and similar to 3.0 parts per thousand, respectively; delta C-13 values show ranges of similar to 2.5 parts per thousand and similar to 2.0 parts per thousand. There are three isotopic substages: (a) substage 1c (12.1-9.4 cal ka) represents conditions in the Neoeuxine Lake with relatively high delta C-13 and low delta O-18, (b) substage 1b (9.4-6.3 cal ka) represents the transition from lacustrine to marine conditions with an increase in delta O-18 values as small amounts of Mediterranean water flowed into the Black Sea, and (c) substage 1a (6.3 cal ka to Present) represents the establishment of marine conditions like today with near-constant delta O-18 values and a trend of slowly increasing delta C-13. Trace-element/Ca ratios show downcore trends consistent with the three isotopic substages. At similar to 6.3 cal ka, isotopic data and trace-element/Ca ratios exhibit a major shift, with changes in the Mg/Ca ratio suggesting an increase in water temperature from 12-14 degrees C to 17-19 degrees C. These mid-Holocene changes in ostracod-valve composition and environmental conditions coincide with the weakening of Black Sea outflow and the proliferation of marine organisms.