Home – Home – Jornals – Contemporary Problems of Ecology 2017 number 4

We present a review of the modern information on palaeolimnological investigations in Russian part of Northern Eurasia. The results from the north-western part of the European Russia are presented in more details because this part of the country is better studied by palaeolimnological methods. Conditions of lacustrine sediment deposition around the Late Pleistocene/Holocene boundary are discussed together with the role of different external factors in formation of chemical composition of lake sediments, including such factors as volcanic activity and large meteorite impacts. Results of major paleoclimatic and paleoecological reconstructions across the northern Siberia are presented. A special attention is paid to the databases of biotic and abiotic parameters of the lakes as аn important basis for the reconstructions of climatic and ecological changes during the Late Pleistocene and Holocene

The macro-entomological method deals mostly with terrestrial species of insects that have hard exoskeleton (Coleoptera, some Hymenoptera and Homoptera, and sometimes other Orders). The method shows great potential in paleoenvironmental and paleoclimatic reconstructions of Quaternary in the world and in Siberia in particular. However the review of scientific publications shows that the fossil insects from Siberia are studied unevenly in different regions. The most studied sites are located in the north and in the middle parts of Western Siberia and in the northern-east of Eastern Siberia. The rest of Siberia is still almost unstudied. The main purpose of this paper is to present the macro-entomological method (sampling, laboratory treatment, applications) to a wide community of researches. In many cases insects enable more accurate paleoreconstructions than traditional paleobotanical methods. The macro-entomological method is especially effective in recognition of differences in superficially monotonous grassland communities which are typical for cold periods of Pleistocene.

We investigated chironomid fauna of surface sediments and a short sediment core (lake Bolshoy Kharbey) from Pechora river basin, Northern Russia. Twenty three investigated lakes have thermokarst, glacial or floodplain origin and are characterised by low mineralization, mostly hydrocarbon-calcium type of water and low concentration of biogenic elements. Most of the lakes have circumneutral pH around >7 and only two lakes are slightly more acidic with pH > 6. In the modern sediments we identified 96 chironomid taxa. Distribution of chironomids in the studied region is driven by continentality, mean T _July and рН. Chironomid communities from the core of the B. Kharbey lake demonstrate the highest similarity with the fauna of the deeper lakes of the glacial origin. The glacial lakes have the highest indices of continentality and the lowest winter temperatures within the investigated data set. The chironomid fauna of the glacial lakes is composed of the profundal, oligotrophic and cold-stenotherm taxa. The fauna of the floodplain and thermokarst lakes is more closely related to T _July and is composed of littoral and phytophilic taxa of meso- or eutrophic waters and moderate temperature conditions. The fauna of the acidic thermokarst lakes considerably differs from the other lakes. Chironomid communities here are represented by acidophilous taxa, and by the littoral and shallow water acid-tolerant taxa, that apparently, also can tolerate acidification. Studied sediment record covers ca last 250 years. The reconstructed T _July during the entire period remain slightly below the modern temperatures. From 1970 reconstructed T _July shows steady increase. The reconstructed water depths (WDs) of the lake are higher than today till 1980. The highest WDs are reconstructed for ca 1970. After that the WDs gradually decrease to the modern level. Changes of the WDs are most probably related to changes in the precipitation rate.

We studied a sediment core from the lake Khatanga-12 (Taimyr Peninsula, Krasnoyarsk region). The core is 131.5 cm long and covers ca of 7100 years of sedimentation. In this study we performed a chironomid analysis, made a qualitative reconstruction of the paleoenvironment in the region and quantitative reconstructions of mean-July air temperature and lake water depth using Russian regional statistical chironomid-based models [Nazarova et al., 2008, 2011, 2015]. The lake was formed during the mid-Holocene warming as a result of thermokarst processes. Development of the ecosystem of the lake Khatanga-12 was influenced by climatic factors and cryolithogenic processes. Mid-Holocene warming around 7100-6500 cal. yrs BP activated thermokarst processes and resulted in formation of the lake basin. Cooling was reconstructed between 6500 and 4500 cal. yrs BP. The sediments of the lake during this period have been formed by erosion processes of the lake banks. After 2500 cal. yrs BP reconstructed conditions are close to modern.

The article presents results of a comprehensive geochronological study of gyttja sediments from a profile located on a terrace above flood-plain on the right bank of the Ob River near Kolpashevo Town. The Th/U dating of the gittya yielded in ages in the range of 110-95 kyr. The results of the spore-pollen analysis suggest that the gyttja layer was formed in widespread middle taiga forest landscapes, with a dominance of spruce and that the climatic conditions were similar to modern. We assume that gyttja was formed in the interstadial time during MIS-5c or at the end of the Kazantsevo interglacial during the MIS-5e.

We present results of taxonomic and ecological investigation of diatoms from polygonal ponds and Quaternary permafrost deposits of the Bol’shoy Lyakhovsky Island and a reconstruction of climatic changes on the island during Late Pleistocene/Holocene transition using fossil diatom assemblages from the permafrost deposits. The taxonomic list of diatoms includes 159 species. Main ecological factors, driving the distribution of diatoms in the investigated area are mean July air temperature, рН, conductivity, water depth, and concentrations of Si⁴⁺ and Al³⁺. Rise of the water depth and formation of stable lacustrine conditions in the ancient thermokarst lake was related to climate amelioration and took place in the Late Pleistocene before 11860 ± 160 yrs BP and during the early Holocene between 11210 ± 160 and 7095 ± 60 yrs BP.

The paper presents the results of palynological analysis of fourty surface samples collected from the various geomorphological levels such as low and high floodplains, surfaces and slopes of terraces, tops of island remnants, etc. from different parts of the Lena River Delta. The obtained spore-pollen spectra (SPS) were compared to the modern vegetation. We studies the role of the long distance transported pollen and of the pollen from the local plant biocenosis in formation of the subrecent SPS. The modern vegetation is most adequately reflected in the SPS of the samples collected from the higher altitudes that range from 11 to 52 m above river level (a.r.l.). The SPS of the other samples contain up to 40 % of the long distance transported pollen (mostly Pinus s/g Haploxylon) . This results in a significant decrease in the share of the local pollen in the SPS. Our results will help to improve the reliability of palaeoclimatic reconstructions based on palaeopalynological data in Arctic regions.

Results of complex investigation of deposits from the dune massifs - tukulans Mahatta and Kysyl-Syr from the Vilyui river basin (Central Yakutia) are presented. On the basis of lithological and palynological data, and also on 17 radiocarbon dates, we reconstructed the structure of tukulans, performed a preliminary reconstruction of their development in the Vilyui river basin and of the environmental conditions during the chronological interval of their formation: Late Pleistocene - Holocene. We found that tukulans represent an aeolian type of deposits lying on sedimentary layers of a complex facial structure. Development of the vegetation during the last 40 thousand years can be divided into four stages; development of the tukulans is represented by three chronostratigraphical phases.

The paper presents results of the cladoceran analysis of a 382 cm long lake sediment core, collected from a pingo in the alas Khara Bulgunnyakh in Central Yakutia. According to the Cladocera analysis the formation of the lake coincided with the Holocene climatic optimum ~6600 cal. yrs BP. Using cluster analysis we identified four statistically significant ecological zones that are based on changes in species composition of the subfossil cladoceran communities. The period of optimal conditions for Cladoceran is characterized by complex community structures and numerous cladoceran remains in sediments, which accumulated between 6500 and 6000 cal. yrs BP. The development of the thermokarst water body was rapid and its existence was short, amounting at a total of ~800 years.

The article presents the first high resolution geochemical and pollen records from sediments of the Lake Baunt (55'11'15" N and 113'01'45" E), located within the continuous permafrost zone. Those records were used to obtain the first reconstructions of the environment and climate of the north Buryatia including the weathering conditions in the catchment area in the post-optimal time of Holocene. Over the last 7000 years the environment and climate on the north-east of Buryatia were heterogeneous. A relatively warm and dry climate was reconstructed for the end of the Holocene Climatic Optimum between 6900 and 6000 yrs BP. Later at about 6000-1500/1000 yrs BP the climate became colder that might have led to weakening of chemical weathering processes at more intense permafrost processes. The climate over the last 1500-1000 yrs BP was colder than today. The calculated environmental indices show different values in sediments of relatively warm and relatively cold intervals and reflect sedimentation conditions that have been controlled by climatic changes.

We reconstructed environmental changes that took place during the development of the Izyubrinye Solontsy Lake that belongs to the Solontsovskie (Shanduyskie) lake system located in the midlands of the Eastern Sikhote-Alin. Lakes were formed by landslides from the paleovolcano slopes. We performed a high resolution reconstruction of palaeoenvironmental changes using multi-proxy data (botanical, diatom, spore-pollen, radiocarbon analysis) from a peat section. We revealed high variability of the lake and the surrounding swamp palaeoenvironments in response to climate change in the late Holocene. Peat accumulation started ca 4000 ¹⁴С yrs BP. The main peat-forming plants were Sphagnum mosses and herbs, except for the period between 2330 and 1530 ¹⁴C yrs BP (2360-1480 cal. yrs BP) when the swamp was overgrown by larch forests and predominantly woody peat accumulated. Forest ecosystems on the lake coasts were quite stable. During the warm phases the role of fir and broadleaved trees increased in coniferous forests that include cedar; during the cooling intervals birch became more widespread. During the last millennium secondary forests occupied the lowlands. We determined ages of paleofires.