Holocene vegetation and climate history in Baikal Siberia reconstructed from pollen records and its implications for archaeology

Past research has greatly improved our understanding of palaeoenvironmental changes in the Lake Baikal Region, but at the same time has indicated intra-regional variations in this vast study area. Here we present a new AMS-dated late glacial-middle Holocene (ca. 13,500-4000 cal. yr BP) pollen record from Lake Ochaul (54 degrees 14'N, 106 degrees 28'E; altitude 641 m a.s.l.) situated in the less-studied area of Cis-Baikal and compare reconstructed vegetation and climate dynamics with the published environmental history of Trans-Baikal based on the pollen record from Lake Kotokel (52 degrees 47'N, 108 degrees 07'E; altitude 458 m a.s.l.). Although both records show comparable major long-term trends in vegetation, there are considerable differences. Around Ochaul the landscape was relatively open during the Younger Dryas stadial, but forest vegetation started to spread at the late glacial/Holocene transition (ca. 11,650 cal. yr BP), thus ca. 1000 years earlier than around Kotokel. While in both regions taiga forests spread during the early and middle Holocene, the marked increase in Scots pine pollen in the Kotokel record after ca. 6800 cal. yr BP is not seen in that from Ochaul, where birch and coniferous taxa, such as Siberian pine, larch, spruce and fir, dominate, indicating different environmental conditions and driving forces in both study regions. However, the pollen data from Ochaul emphasizes that the Cis-Baikal area also saw a continuous increase in forest cover and in the proportion of conifers over birch trees and shrubs during the early-middle Holocene, which may have contributed to a decrease in the number of large herbivores, the main food resource of the Early Neolithic hunter-gatherer groups. This and rather abrupt reorganization of atmospheric circulation, which affected atmospheric precipitation distribution resulting in thicker and longer-lasting snow cover, may have led to a collapse of Early Neolithic Kitoi populations ca. 6660 cal. yr BP followed by a cultural "hiatus" in the archaeological records during the Middle Neolithic phase (ca. 6660-6060 cal. yr BP). The results stress the importance of sub-regional palaeoenvironmental studies and the need for a representative network of well-dated, high-resolution sediment archives for a better understanding of environmental changes and their potential impacts on the hunter-gatherer populations in the archaeologically-defined micro-regions

Mercury loading within the Selenga River basin and Lake Baikal, Siberia

Mercury (Hg) loading in Lake Baikal, a UNESCO world heritage site, is growing and poses a serious health concern to the lake’s ecosystem due to the ability of Hg to transform into a toxic form, known as methylmercury (MeHg). Monitoring of Hg into Lake Baikal is spatially and temporally sparse, highlighting the need for insights into historic Hg loading. This study reports measurements of Hg concentrations from water collected in August 2013 and 2014 from across Lake Baikal and its main inflow, the Selenga River basin (Russia, Mongolia). We also report historic Hg contamination using sediment cores taken from the south and north basins of Lake Baikal, and a shallow lake in the Selenga Delta. Field measurements from August 2013 and 2014 show high Hg concentrations in the Selenga Delta and river waters, in comparison to pelagic lake waters. Sediment cores from Lake Baikal show that Hg enrichment commenced first in the south basin in the late-19th century, and then in the north basin in the mid-20th century. Hg flux was also 20-fold greater in the south basin compared to the north basin sediments. Hg enrichment was greatest in the Selenga Delta shallow lake (Enrichment Ratio (ER) = 2.3 in 1994 CE), with enrichment occurring in the mid- to late-20th century. Local sources of Hg are predominantly from gold mining along the Selenga River, which have been expanding over the last few decades. More recently, another source is atmospheric deposition from industrial activity in Asia, due to rapid economic growth across the region since the 1980s. As Hg can bioaccumulate and biomagnify through trophic levels to Baikal’s top consumer, the world’s only truly freshwater seal (Pusa sibirica), it is vital that Hg input at Lake Baikal and within its catchment is monitored and controlled

Sediment geochemistry of the section Tagay-1 at Olkhon Island (Lake Baikal, Eastern Siberia): a contribution to palaeoenvironmental interpretations

The Miocene Tagay section in the north-western part of Olkhon Island, Lake Baikal, provides a unique window into past life in northern Asia. To aid palaeoenvironmental reconstructions, we carried out whole-rock geochemical analyses of 17 sedimentary layers of this section. The aim of this geochemical approach is to examine the element variations as a response to climate change during formation of the Tagay section deposits with a focus on the hydrological regime of the catchment and in-lake processes. Our results establish that temperature and climate conditions during the formation of sediments of section Tagay-1 were fairly stable, no abrupt climatic changes occurred. The palaeoclimate was temperate, however, it had a cyclic nature: wet and semiarid epochs of different intensity and duration alternated. The basal part of the sediment sequence is dominated by terrigeneous material, mainly by surface runoff, so the sedimentation was fed by erosion products of the weathering crust. During sedimentation of this lower part (layers 17–9), the palaeo-lake level and salinity stayed practically unchanged. The drawdown of the palaeo-lake and increasing salinity started in the higher middle part (layer 8), and reached the minimum water level and maximum salinity in layers 7–6. Sediments of the layers 8–6 accumulated in an arid climate. After deposition of layer 5, the water level began to rise, and during formation of layer 3 it fell again. The highest sedimentation rate was in layers 12–5, these are also the layers with the highest enrichment of biogenic elements (layers 12, 7–5) and where carbonate deposition took place. The observed changes in element behaviour are related to hydrological changes in the catchment (precipitation), lake level status, and evaporation, and are ultimately driven by climate.The research presented here was supported via research grants from the Russian Foundation for Basic Research (No. 20-05-00247), the Russian Science Foundation (No. 19-17-00216, sedimentology and geochemistry), and the Government of the Russian Federation (No. 075-15-2021-631), and was carried out in accordance with a State Assignment of the Vinogradov Institute of Geochemistry SB RAS (No. 0284-2021-0003). Open access funding provided by Swedish Museum of Natural History</p

Arshan palaeoseismic feature of the Tunka fault (Baikal rift zone, Russia)

The traditional concept of the rift development of flank depressions in the Baikal rift zone is now doubted in view of some indicators for compression deformations identified by the seismogeological and geodetic methods. Besides, the paleoseismological investigations revealed seismogenic strike-slips and reverse faults in the Tunka fault zone that is a major structure-controlling element of the Tunka rift depression. However, a detailed study of the upslope-facing scarp in the Arshan paleoseismogenic structure zone has shown that its formation might be due to rift mechanism of basin formation. Age estimation has been made for the previously unknown pre-historic earthquake whose epicentral area coincides with the western flank of the Arshan paleoseismogenic structure. Judging from previously determined ages of paleoearthquakes, the mean recurrence period for faulting events on the central Tunka fault is 2780–3440 years

Late Quaternary geology of the Tunka rift basin (Lake Baikal region), Siberia, Russia

The objective of this research is to obtain a better understanding of the evolution of the Tunka rift basin, part of the Baikal rift zone, and how it relates to the overall geologic history of the region, particular for the Quaternary period. The tectonically active Baikal rift zone began forming over 50 million years ago and continues today. In the Tunka basin, during the Oligocene and Middle Pliocene, relatively weak tectonic disturbances took place and thick accumulations of organic-rich sands, silts, and clays were deposited in lacustrine–marshy subtropical environments. Tectonism increased between the Miocene and Pliocene and thick units of coarse alluvium and floodplain sediments were deposited. During the Late Pliocene–Quaternary, tectonism formed basins that are now filled with a variety of coarse clastic materials. Early and Middle Pleistocene sediments are poorly exposed, covered by widespread Late Pleistocene deposits. Three Late Pleistocene sedimentary facies dominate: boulder–pebble gravels (proluvial, glacial fluvial, and alluvial sediments), alluvial sand, and loess-like sediments with associated slope deposits altered by post-depositional wind erosion. The relationship between these complexes, including radiocarbon and other chronological data and fauna and flora remains, indicates that they began forming c. 70 000 yr ago. Paleosols, glacial deposits and cryogenic material indicate that at times the climate was cool or cold. During the early Late Pleistocene renewed tectonism took place causing increased deposition of coarse sediments. The middle Late Pleistocene deposits consist mostly of sandy, floodplain alluvium. By the end of the Late Pleistocene–Holocene, alluviation was reduced and replaced by a high degree of erosion and aeolian depositio

Late glacial and Holocene environmental change reconstructed from floodplain and aeolian sediments near Burdukovo, Lower Selenga River Valley (Lake Baikal region), Siberia

Floodplain and aeolian sediment snear Burdukovo reveal a detailed record of Holocene environmental change in the lower Selenga River Valley (Lak eBaikalregion, Siberia). During the late Pleistocene and early Holocene fine-grained alluvium accumulated on the floodplain followed by a period of increased landform stability and subsequent pedogenic formation. This part of the stratigraphical sequence yielded rich assemblages of terrestrial molluscs, which increase in species diversity from early pioneer communities with about ten taxa to levels containing over twice that number. The land snail assemblages also record an episode of relatively drier local habitats prior to ?9.2 ka BP with subsequent wetter conditions lasting until ?8.0 ka BP. This was followed by an abrupt and sustained change in floodplain deposition, shifting from overbank alluvium to aeolian sedimentation, within which a series of weakly developed soil horizons formed during the middle and lateHolocene periods. The onset of aeolian processes and relatively drier conditions in the middle Holocene at Burdukovo coincides with major changes observed both in other regional palaeoenvironmental proxy records and in local archaeological sequences, although it is still not clear how the two are linke

A Holocene molluscan succession from floodplain sediments of the upper Lena River (Lake Baikal region), Siberia

Floodplainsediments of the upperLenaRiver near Basovo in south-central Siberia have yielded the most detailed Holocenemolluscansuccession yet reported from the entire eastern Palaearctic. Over 72,500 shells from at least 28 species of terrestrial and 23 species of freshwater mollusc have been recovered, an abundance and diversity far higher than previously reported from the region. The molluscan assemblages are dominated by land snails, especially members of the genus Vallonia, represented by five species including Vallonia tenuilabris and two poorly known species Vallonia kamtschatica and Vallonia cf. chinensis. Other noteworthy species recovered include Gastrocopta theeli, Carychium pessimum, Vertigo extima (southernmost record), Vertigo microsphaera and the first Asian records of three other taxa (Vertigo geyeri, Vertigo genesii and Vertigo parcedentata). Illustrations are provided for the critical species, since opinions differ about the status of various taxa and the correct names that should be used. The molluscan assemblages show clear successional trends during the early to mid-Holocene, reflecting episodes of dryness/wetness on the floodplain. Drier conditions at ca 6350 14C yr BP coincide with major changes in the archaeological record seen at other sites in the region but it remains unclear whether the two are linked. A prominent charcoal-rich horizon dated to ca 2800 14C yr BP marks a burning event in the catchment, which resulted in a two-fold increase in sediment accumulation rate. Remains of small mammals occurred throughout the sequence including a tooth of Microtus cf. maximowiczii, possibly the first occurrence of Ungar vole west of LakeBaikal. The faunal analyses have been integrated with a detailed pedological study of the sedimentary profile and a chronology was obtained by means of 12 AMS radiocarbon dates. This study provides the first detailed palaeoecological information relating to Holocenemolluscan assemblages from the Cis-Baikalregion and lays the foundation for future work in the eastern Palaearcti

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 to 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

Not herbs and forbs alone: pollen‐based evidence for the presence of boreal trees and shrubs in Cis‐Baikal (Eastern Siberia) derived from the Last Glacial Maximum sediment of Lake Ochaul

A new accerator mass spectrometry (AMS)-dated sedimentary record from Lake Ochaul (54 degrees 14 ' N, 106 degrees 28 ' E; 641 m a.s.l.) in Eastern Siberia covers the interval from ca. 27 850 to 20 400 cal a bp at ca. 180-year resolution and contributes to a better understanding of the complex spatial vegetation pattern during the Last Glacial Maximum (LGM). Non-arboreal pollen taxa are abundant in the pollen assemblages (mean value ca. 92.6%), but boreal trees are represented by all major taxa that grow in the lake catchment today, including Betula sect. Albae (0.6-4.8%), Picea (0.6-2.8%), Pinus sibirica (Haploxylon type) (up to 1.5%), Pinus sylvestris (Diploxylon type) (up to 2%), Larix (up to 0.6%) and Abies (up to 0.6%). Betula sect. Nanae/Fruticosae (2-5.2%) and Salix (up to 3.2%) are the most representative boreal shrub taxa. Together with existing modern and fossil pollen data from the wider study region, the current record provides further evidence for the long-debated presence of boreal trees and shrubs in Eastern Siberia throughout the LGM. Our results show that the Upper Lena was a region in which refugia for arboreal taxa existed and that far-distant pollen transport can be ruled out as the source of the detected arboreal pollen