title: Stable isotope evidence for the Bottom Convective Layer homogeneity in the Black Sea.
abstract: The Black Sea is the largest euxinic basin on the Earth. The anoxic zone consists of the upper part water mass stratified by density, and the lower water mass homogenized relative to density (depth >1750 m), named the Bottom Convective Layer. To assess homogeneity and possible exchange of matter across the upper and lower boundaries of the Bottom Convective Layer, new data on stable isotope composition of S, O and H were obtained. Samples were collected in August 2008 and March 2009 from two stations located in the eastern central part of the Black Sea. Distribution of δ(18)O and δD values of water for the entire water column did not vary seasonally. Appreciable differences were marked for δD value variation in the picnocline area (water depth 200-400 m) and in the BCL 5 m above the bottom that might be caused by penetration of intrusions with elevated portion of shelf modified Mediterranean Water. Observed linear relationship between δ(18)O (or δD) and salinity indicates that mixing water and salt occurs at the same time, and the deep water of the Black Sea has two end members: the high-salinity Mediterranean seawater and freshwater input. In the Bottom Convective Layer, the average δ(34)S (H2S) was -40.6 ± 0.5‰ and did not vary seasonally. At the bottom (depth > 2000 m), (34)S depletion down to -41.0‰ was observed. Our δ(34)S (SO4) data are by 2-3‰ higher than those measured previously for the Bottom Convective Layer. Sulfate from the aerobic zone with δ(34)S (SO4) = +21‰ corresponds to ocean water sulfate and that has not been subjected to sulfate reduction. Average δ(34)S (SO4) values for depths > 1250 m were found to be +23.0 ± 0.2‰ (1σ). Sulfur isotope composition of sulfate does not change in the Bottom Convective Layer and on its upper and lower boundaries, and does not depend on the season of observation.
authors.affiliation: PP Shirshov Institute of Oceanology, Russian Academy of Sciences, Nahimovskiy prospect, 36, Moscow 117997, Russia.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Dubinin
authors.affiliation: Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetniy per. 35, Moscow 119017, Russia ; University of Johannesburg, Auckland Park Kingsway Campus, P.O. Box 524, Johannesburg, Republic of South Africa.
authors.forename: Elena O
authors.initials: EO
authors.lastname: Dubinina
authors.affiliation: PP Shirshov Institute of Oceanology, Russian Academy of Sciences, Nahimovskiy prospect, 36, Moscow 117997, Russia.
authors.forename: Tatyana P
authors.initials: TP
authors.lastname: Demidova
authors.affiliation: Institute of Environmental Problems of the North, Russian Academy of Sciences, nab. Severnoy Dviny, 23, Arkhangelsk 163000, Russia.
authors.forename: Nataliya M
authors.initials: NM
authors.lastname: Kokryatskaya
authors.affiliation: PP Shirshov Institute of Oceanology, Russian Academy of Sciences, Nahimovskiy prospect, 36, Moscow 117997, Russia.
authors.forename: Maria N
authors.initials: MN
authors.lastname: Rimskaya-Korsakova
authors.affiliation: Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetniy per. 35, Moscow 119017, Russia.
authors.forename: Sofia A
authors.initials: SA
authors.lastname: Kosova
authors.affiliation: Norwegian Institute for Water Research, Gaustadalleen 21, Oslo No-0349, Norway.
authors.forename: Evgeniy V
authors.initials: EV
authors.lastname: Yakushev
keywords: Black Sea; Bottom Convective Layer; Hydrogen isotopes; Hydrogen sulfide; Oxygen isotopes; Sulfate; Sulfate reduction; Sulfur isotopes
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