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This article presents first tephrochronological data on the volcanic activity in the valley of the Jom-Bolok River (East Sayan Mountains, Siberia), which is the largest manifestation of the Holocene eruptions in Central Asia. The data results from our study of the proglacial Kaskadnoe-1 Lake situated near the Jom-Bolok basalt field. The lake sediments include a series of tephra-rich layers. Radiocarbon dating of the lake sediments provided a robust age model which allowed us to build timing of eruptions formed the Jom-Bolok volcanic field. We recognize two large phases of volcanism separated by almost 5 thousand years dormant phase. The first phase is traced back to ca. 14.3 cal ka BP and lasted until 6.3 cal ka BP. Ten clusters of microtephra layers in the sediments of the first phase show 300-800 years recurrence of the volcanic events weakening upward. The event of 14.3-13.3 cal ka BP probably represents the strongest eruptions of the Jom-Bolok. The second phase started ca. 1.6 cal ka BP and highly likely continues in our days. Its strongest eruptions occurred between 1.6 and 0.8 cal ka BP with periodicity of 200 years. This tephrostratigraphy shows a multiplicity of the Jom-Bolok volcanic events and amplifies the earlier built scheme resulted from investigations of the stratified basalts, pyroclasts and lake damming events.

The first results of tephrochronological studies of Late Pleistocene–Holocene volcanic eruptions in the Zhom-Bolok River valley (Eastern Sayan) are reported. Based on the analysis of bottom sediments of the glacial lake Kaskadnoe-1, a detailed chronological scale of volcanic activity in this region has been worked out. It is established that the eruptions began at least 14 300 years ago and continued, gradually weakening, to 6280 years ago. In this period, ten groups of peaks of sediment enrichment in microtephra are registered for Kaskadnoe-1 Lake. The average interval between the stages of eruptions in this period was ~500–600 years. Between 14 300 and 13 400 years ago, the most large-scale volcanic events took place, eruptions were practically not interrupted, and the explosive activity was the most intense. The volcanic activity in the region in the period between 6280 and 2000 years ago is characterized by a relative rest. Later, eruptions resumed reaching peak values 1150 years ago and completing 800 years ago.

The first results of radiocarbon dating of the Gothenburg and Mono Lake paleomagnetic excursions identified in a sedimentary section of bottom sediments of Baunt Lake (Northern Transbaikalia) are presented. The exact geochronological positions of these excursions are 13.2 and 25.8 ka, respectively. The estimated time of existence of the paleomagnetic events of ~100 and 500 years for the Gothenburg and Mono Lake excursions, respectively, can serve as geochronological markers for understanding the real time over which such global changes in the Earth’s magnetic field can occur.

In March 2014, the Lake Baunt bottom sediments were drilled in the deepest part of the lake basin (33 m). The penetrated interval is 13.7 m thick, with the age of the base being evaluated at 28–30 ka. Lithological study of the penetrated sediments demonstrates the upper part of the section dominated by diatom ooze, whose concentration decreases gradually downward the section, up to the replacement of the ooze by silty clay. The obtained data on variations in petromagnetic parameters, concentration of biogenic silica, and sediment compaction indicate considerable variations of sedimentary environments during the Late Pleistocene and Holocene. Being compared with the previously reconstructed landscape and climate dynamics for the sedimentary succession of Lake Kotokel for this time interval, the above parameters reveal that the Lake Baunt bottom sediments reliably fix the regional paleoclimate signal. For the first time for lakes of the Baikal region, Gothenburg and Mono Lake magnetic excursions are identified in the paleomagnetic record of the Lake Baunt section.

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.

The method of detailed sampling of sediments from Lake Ilchir allowed obtaining a high-resolution record of changes in the natural environment, which meets the world modern standards of temporal resolution in the studies of the Holocene environment. The data on the palynological analysis of bottom sediments from Lake Ilchir (51°58’26.0” N and 100°59’29.0” E) enable us to reconstruct the composition of vegetation and the structure of landscapes in the lake basin as well as to understand the process of its change in Middle-Late Holocene. The lake is located in the Republic of Buryatia and is the source of the Irkut River, which flows into the Angara River. The results obtained are unique for the regional Holocene environment, since they allow us to clarify the nature of changes in regional vegetation with an average time interval of 125 years. A reliable age model provides for intra-and interregional correlations of environmental changes that helps to understand the possible causes of changes in regional vegetation. Palynological records from inland regions are important for reconstructing the processes of past changes in landscapes, assessing the sensitivity of ecosystems in these regions to future climatic variations that affect the composition of vegetation and its change in time.

Palaeoenvironmental changes including vegetation, chemical weathering intensity, lakes water level fluctuations, and climate dynamics, from the East Sayan Mountains were investigated using multiple proxies such as pollen, mineralogical, petromagnetic, X-ray fluorescence analyses and radiocarbon dating.

The study addressed seasonal and interannual variations in the components of the trophic status (organic carbon, nitrogen and phosphorus; silica; suspended matter; and chlorophyll-a) and ionic composition (bicarbonates, sulfates, chlorides, calcium, magnesium, sodium, and potassium) in the headwater streams of the Angara River since the 1950s. The results show that the concentrations and seasonal variations of these components and long-term trends of their mean annual concentrations resulted from the interplay of biological, hydrological, and anthropogenic processes operating in Lake Baikal and reflect the current ecological state of the lake.

A new experiment of the Hövsgöl Drilling Project was carried out in Lake Hövsgöl in 2004, as part of the international program of scientific drilling in the Baikal Rift. The reported data include a preliminary description of the recovered lake sediments (HDP-04 core), with their compositions and physical properties, and a tentative age-depth model based on the paleomagnetic polarity scale. This is the first evidence that the lithology of sediments deposited for the past ~1 Myr records periodic alternation of carbonate-free diatomaceous mud and carbonate-bearing silty clay. The diatom intervals in the record are interpreted as corresponding to interglacials by analogy with the periodicity known since the Last Glacial. The core bears signature of at least nine lithological change events. The sediment lithology records extremely low stand of Paleo-Hövsgöl (shallow-water facies produced by erosion of older sediments at the point where the today’s lake reaches a depth of 240 m). Correlation of the HDP-04 core data with reflection profiling evidence confirms the presence of quite a large gap in the Pleistocene sedimentary record from the Hövsgöl rift basin. The discovery of alternating carbonate-rich/carbonate-free cycles and evidence for sudden lake level changes impart special importance to the Hövsgöl archive: It can provide a deeper insight into the regional water budget and humidity history than it has been so far possible for the Middle and Late Pleistocene.

Sedimentary sections from Lake Baikal in Siberia and Lake Hovsgol in Mongolia show that during the Last Glacial Maximum (LGM), planktonic/benthic diatoms, chrysophyte cysts, sponge spicules and zooplankton remains did not accumulate in the lake sediments. The combined data suggest a drastic lowering of photosynthetic production and perhaps the collapse of the ecosystems of both lakes due to significant environmental changes during the LGM. Both lakes were almost uninhabited during the LGM. Starting from ∼12,000 to 13,000 14C years ago, the planktonic communities redeveloped and primary production increased in both lakes. As a result, Holocene sediments contain abundant and well-preserved planktonic/benthic diatoms, stomatocysts, sponge spicules and zooplankton remains. The ecosystem stress in Lake Baikal during glacial time appears to be due to a decrease in nutrient loading from the watershed, lowering of surface water temperature, and very low transparency of water and ice. We believe that endemic species in Baikal survived during glacial ecological catastrophes in refugia that could have been a source of species that invaded and repopulated Baikal after intense and long glacial winters. The ecosystem stress in Lake Hovsgol during glacial time appears to be due primarily to drastic lake level falls, and changes in water chemistry. At the beginning of the Holocene, Lake Hovsgol was reoccupied again by cosmopolitan species probably from surrounding small lakes and rivers. In addition to the LGM results, we also show that Lake Baikal planktonic diatom species diversity during the last 350 ka is closely related to solar insolation fluctuations caused by the 23 and 41 ka cycles of the Earth's precession and obliquity. Our results also indicate that Baikal's planktonic diatom species diversity, as measured by the Shannon–Weiner index, correlates with the oxygen isotope record that represents changes in global ice volume.

Five boreholes, drilled in different geological structures of Lake Baikal by the International Baikal Drilling Project, allowed us to obtain unique paleoclimatic records, which can be regarded as being representative of continental Asia. One of the most sensitive paleoclimate proxies in the sedimentary core is the number of diatoms, and correspondingly the amount of biogenic silica. The major and trace elements, the magnetic susceptibility, the clay mineral composition, and a number of other parameters also reflect changes in the environment and the climate.

Publisher Summary This chapter describes the paleoclimatic record over the period of 5 million years based on variations in diatom abundance in the sediments of a 200 m core obtained from Lake Baikal. The data represent a long, continuous continental record of climate changes in Central Asia during the Late Cenozoic. The record shows the climatic cooling trend that started in Pleistocene and is superimposed on the short-term cyclic climatic variations controlled by the Earth's orbital parameters. The record also reveals the presence of the two cold episodes (each about 300 Ka long) at the time intervals 2.82–2.48 Ma and 1.75–1.45 Ma characterized by glaciations at their maximum phases. These cooling periods in Lake Baikal record are also registered as global cooling in other paleoclimate records of the Northern Hemisphere. The continental record of Lake Baikal contains the majority of climatic events found in marine records and demonstrates that continental regions of Asia responded to all major changes in the Earth's climate recorded in the long oxygen isotopic records.