Alexander A. Shchetnikov

Analytical approaches for determination of bromine in sediment core samples by X-ray fluorescence spectrometry

Bromine has been recognized as a valuable indicator for paleoclimatic studies. Wavelength dispersive X-ray fluorescence (WDXRF) and total reflection X-ray fluorescence (TXRF) methods were applied to study the bromine distributions in lake sediment cores. Conventional WDXRF technique usually requires relatively large mass of a sediment sample and a set of calibration samples. Some analytical approaches were developed to apply WDXRF to small sediment core samples in the absence of adequate calibration samples with a known Br content. The mass of a sample to be analyzed was reduced up to 200-300mg and the internal standard method with correction using fundamental parameters was developed for Br quantification. TXRF technique based on the direct analysis of a solid suspension using 20mg of sediment sample by internal standard method was additionally tested. The accuracy of the WDXRF and TXRF techniques was assessed by the comparative analysis of reference materials of sediments, soil and biological samples. In general, good agreement was achieved between the reference values and the measured values. The detection limits of Br were 1mg/kg and 0.4mg/kg for WDXRF and TXRF respectively. The results of the Br determination obtained with different XRF techniques were comparable to each other and used for paleoclimatic reconstructions.

First data on the environment and climate change within the Zhom-Bolok volcanic field (Eastern Sayan Mountains) in the Middle–Late Holocene

This paper considers the results of comprehensive lithological, biostratigraphic, and geochemical investigation of sediments in Khara-Nur Lake (Eastern Sayan Mountains) situated in the area of the greatest Holocene eruptions in the Central Asia Region. The age of the basal sediment layer is estimated at 6881 ± 53 years. The local natural environment and climate have undergone great changes since that time. The Holocene volcanic events did not exert a catastrophic impact on the regional landscape, but they caused dramatic changes in the local vegetation. The well-defined correlation of the regional events with the well-known records of the natural environment in the Northern Hemisphere is indicative of the decisive influence of global atmospheric circulation on restructuring the landscape and climate system in the Zhom-Bolok Region in the Middle–Late Holocene.

New data on the age of neopleistocene sediments in the Tunka rift valley (Southwestern Baikal Region) derived from 14C dating of large mammal fossils

293 The Tunka rift has served and continues to serve as one of the main test areas for investigating basin terres trial Pleistocene sediments of the Baikal rift zone. This area hosts several stratotypes of Cenozoic sedimentary formations of the Baikal region [1, 2]. In recent years, detailed lithological–stratigraphic investigations of Quaternary sediments have been carried out in natural outcrops of Cenozoic sections in the Tunka rift [3, 4] with revision of known sections and thorough exami nation of new sections. These investigations provided a representative collection of fossil organic remains, which were dated by the radiocarbon method. This allowed age limits of key representatives of the large mammal fauna used for paleontological substantiation of Pleistocene reference sections of the Baikal region to be specified for southern East Siberia. The main bone bearing sections of the Tunka rift are located in the following localities: Slavin Yar, Sha bartai, Elovka, Belyi Yar, Zaktui, and Bol’shoi Zang isan (Fig. 1). The Slavin Yar section is located on the left side of the Zun Murin River mouth in the southwestern mar gin of the Torskaya depression inversely uplifted and incised up to a depth of 30 m. In this area, crystalline bedrocks are overlain by Neogene ocherous conglom erates [3]. Their eroded surface is, in turn, overlain with an angular unconformity by unconsolidated flu vial sediments. The mammal remains were found in buried soil layers located at different depth levels of this section: bones of Mammuthus primigenius, Coelo donta antiquitatis, Cervus elaphus, and Capreolus sp. at 8 and 11 m, a horn of Procarpa gutturosa at 13 m, and bones of Ursus sp. and Equus sp. at 19–20 m. The 14C dates of 45 810 ± 4070 and 37 790 ± 310 years ago were obtained for the bone bearing sediments cropping out at 11 and 8 m, respectively (table). The Shabartai section is located on the right side of the Irkut River in the area of its crossing the Elovka interdepression saddle (Fig. 1). In this area, fluvial sediments grading into winnowed varieties at the sec tion top envelop a high inversely uplifted tectonic step representing the right bank segment of the Elovskii Spur. The spur is 115–120 m high relative to the Irkut River channel. At its summit, Neopleistocene sedi ments are exposed in the near road excavation to a depth of 10 m. The section is largely composed of light brown wavy laminated silty sands. The thicknesses of separate laminae are usually up to 10 cm. In the upper part of the section, the sediments are winnowed. The lower part of the section is largely composed of yellow ish to brownish gray fine grained sands with intercala tions of gravelly sands enriched with limonite. The sediments are characterized by parallel lamination with the general southwestward incline of bedding sur faces at angles of 20°–25°. The sands at a depth of 10 m yielded a radiothermoluminescence age of 50 400 ± 3000 years ago [5], and the maxilla fragment of M. primigenius found slightly above the level of 9 m (Fig. 2) was dated back to 46 600 ± 900 years ago (table).

Lake sediment records of persistent organic pollutants and polycyclic aromatic hydrocarbons in southern Siberia mirror the changing fortunes of the Russian economy over the past 70 years

Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) have previously been detected in the surface sediments, water, and endemic organisms of Lake Baikal, a UNESCO World Heritage Site. The Selenga River is the primary source of freshwater to Lake Baikal, and transports pollutants accumulating in the Selenga River basin to the lake. Sources of POPs and PAHs in the Selenga River basin grew through the 20th century. In the present study, temporal changes in the concentrations of PAHs and POPs were reconstructed from two lakes in the Selenga River basin over the past 150 years using paleolimnological techniques. Increased concentrations in PAHs and PCBs were recorded initially in the 1930s. The 1940s-1980s was the period of greatest exposure to organic contamination, and concentrations of dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs) and many PAHs peaked between the 1960s and 1980s in the two lakes. Declines in concentrations and fluxes were recorded for most PAHs and POPs in the 1980s and 1990s. Temporal trends in concentrations of total and individual compounds/congeners of PAH, PCBs, and polybrominated diphenyl ethers (PBDEs) indicate the contribution of both local and regional sources of contamination in the 20th and 21st centuries. Temporal variations in contaminants can be linked to economic and industrial growth in the former USSR after World War II and the economic decline of Russia in the late-1980s and early-1990s, as well as global trends in industrialization and development during the mid-20th century.