168 ISSN 0145-8752, Moscow University Geology Bulletin, 2020, Vol. 75, No. 2, pp. 168–176. © Allerton Press, Inc., 2020. Russian Text © The Author(s), 2020, published in Vestnik Moskovskogo Universiteta, Seriya 4: Geologiya, 2020, No. 1, pp. 60–68. The Distribution of Elements in the Vertical Section of Bottom Sediments in the Black Sea E. I. Nemchenko a, *, O. A. Lipatnikova a, **, L. L. Demina b, ***, M. D. Kravchishina b, ****, and T. N. Lubkova a, ***** a Department of Geology, Moscow State University, Moscow, 119991 Russia b Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, 117997 Russia *e-mail: zhenya2008.ru@mail.ru **e-mail: lipatnikova_oa@mail.ru ***e-mail: l_demina@mail.ru ****e-mail: kravchishina@ocean.ru *****e-mail: tanya_lubkova@mail.ru Received April 25, 2019; revised October 16, 2019; accepted October 16, 2019 Abstract—The microelement composition of the vertical section of bottom sediments in the Black Sea has been studied. The analysis of the calculated enrichment factors relative to the mean composition of the Earth’s crust has shown that the lithogenic source dominates for most microelements. We revealed a signifi- cant enrichment with Ca and Sr (due to bioaccumulation) and with S, As, and Mo (as a result of hydrogen sulfide contamination and the effect of mud volcanoes). The calculated indicator ratios of elements allow evaluation of the presence of exhalation components in sediments (Fe + Mn/Ti) and of the transportation distance of terrigenous material (Ti/Zr). Paleoreconstruction of salinity (C org /S) and oxidation-reduction conditions in the bottom water layer (Mn/Fe, Mo/Mn, V/(V + Ni), and V/Mn) was performed. Keywords: Black Sea, bottom sediments, microelements, enrichment factors, indicator ratios DOI: 10.3103/S0145875220020064 INTRODUCTION Toxic metals are accumulated in bottom sediments (BSs) as a result of sedimentation of suspended sub- stances (gravitational precipitation), sorption pro- cesses at the water–sediment boundary, and biogenic sedimentation. Thus, BSs reflect processes that develop in the water column (Ovsyany et al., 2009). The aim of our study was to assess the distribution of microelements in a vertical section of bottom sedi- ments in the coastal zone of the Black Sea under oxi- dative conditions and in deep water under the condi- tions of hydrogen sulfide contamination. STUDY AREA The Black Sea is surrounded by land from all sides and is a sea of the basin type. The catchment area is 1 864000 km 2 ; the mean absolute sedimentation rate is 48.4 g/cm 2 over 1000 years. The Black Sea basin is among young geosynclinal rises: it is located mainly in the Alpine orogenic zone and only its northern part belongs to the southern edge of the Scythian Platform. The Black Sea water area is clearly divided into three parts: the shelf (to a depth of 200 m, which occupies 28% of the area), the continental slope (200–2000 m, 30%), and the deep-water basin (2000–2200 m, 42%) (Mitropol’skii et al., 1982). Hydrogen sulfide contamination of the water column deeper than 90–160 m, as revealed by N.I. Andrusov, is the main hydrochemical feature of the Black Sea. The anaerobic zone occupies approxi- mately 87% of the sea volume (Neretin, 1996; Volkov, 1984). According to some scientists, the main source of hydrogen sulfide is related to the bacterial process of sulfate reduction as a result of microbial activity (Iva- nov, 1964). A hydrothermal hypothesis exists that hydrogen sulfide flows from cracks on the sea floor as a result of volcanic activity (Kharchenko and Dolgii, 2014). The first comprehensive study of the lithology and stratigraphy of bottom sediments in the Black Sea was performed in the 1930s by A.D. Arkhangel’skii and N.M. Strakhov (Arkhangel’skii and Strakhov, 1938). These scientists identified three horizons: modern (Late Black Sea), ancient Black Sea, and Novoeuxin- ian strata, each of which is characterized by a number of specific lithological features, which were used for their identification in combination with microfossils. Modern Black Sea sediments are represented by low-