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E.V. Bezrukova1, A.A. Abzaeva1, P.P. Letunova1, N.V. Kulagina2, and L.A. Orlova3 EVIDENCE of ENVIRONMENTAL INSTABILITY of the LA

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E.V. Bezrukova1, A.A. Abzaeva1, P.P. Letunova1, N.V. Kulagina2, and L.A. Orlova3 EVIDENCE of ENVIRONMENTAL INSTABILITY of the LA PALEOENVIRONMENT. THE STONE AGE 17 E.V. Bezrukova1, A.A. Abzaeva1, P.P. Letunova1, N.V. Kulagina2, and L.A. Orlova3 1Laboratory of Archaeology and Paleoecology, Irkutsk State University, K. Marxa 1, Irkutsk, 664003, Russia E-mail: [email protected] 2Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, Lermontova 128, Irkutsk, 664033, Russia E-mail: [email protected] 3Laboratory of Cenozoic Geology and Paleoclimatology, Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Akademika Koptyuga 3, Novosibirsk, 630090, Russia E-mail: [email protected] EVIDENCE OF ENVIRONMENTAL INSTABILITY OF THE LAKE BAIKAL AREA AFTER THE LAST GLACIATION (BASED ON POLLEN RECORDS FROM PEATLANDS)* Pollen analysis of two dated sedimentary cores from lacustrine-boggy sediments in various parts of the Lake Baikal area yielded the fi rst complete record of deep changes in the lake catchment area during the Late Glacial and Early Holocene. The Early Middle Holocene record shows an optimum – a humid and mild climate with warm winters between ca 10,000 and 7000 BP. During the Late Holocene, the climate grew more and more continental, and dark coniferous forests were replaced by light coniferous ones. Comparison of variation ranges of paleogeographic events in the Late Pleistocene and Holocene recorded in our samples with previously known records for the Lake Baikal area and other regions of Eurasia indicated that major changes of vegetation and climate mostly correlate with the global ice retreat, solar radiation level, and the concentration of carbon dioxide in the atmosphere. Less signifi cant short-term fl uctuations of vegetation and climate recorded in our archives can be regarded as regional ecosystem responses to solar activity changes of a quasi-millenary scale. Regional pollen records demonstrate a distinct relationship with the climate of the Northern Hemisphere as a whole. The amplitude of these changes is higher in the northeastern Lake Baikal area than in its southern part. Key words: Pollen analysis, paleoclimate, paleoecology, Late Glacial, Holocene, Lake Baikal catchment area. Introduction evolution of the climate during the Late Glacial and in the Holocene (Rind, Overpeek, 1993). Before the natural To evaluate the anthropogenic climatic changes and dynamics of the recent past, i.e. of Termination 1 and their relationship with natural environmental changes, of the Holocene, universally represented by sediments, one must first of all assess the directionality of the has been adequately described and interpreted, it will be impossible to evaluate the magnitude of the *This study was supported by the Russian Foundation anthropogenic impact on the environment and climate. for Basic Research (Project 09-05-00123-а) and the Baikal Our knowledge of the recent geological past is limited. Archaeological Project. Currently, the most reliable oxygen-isotopic record Archaeology, Ethnology & Anthropology of Eurasia 37 (3) 2009 E-mail: [email protected] © 2009, E.V. Bezrukova, A.A. Abzaeva, P.P. Letunova, N.V. Kulagina, and L.A. Orlova 17 18 of temperature changes in the Late Glacial and in the thousand years (Kataoka et al., 2003; Bezrukova, Holocene, based on the ice core from Greenland, contains Krivonogov, Abzaeva et al., 2005; Bezrukova, Belov, signals of sharp short-lived climatic fl uctuations during Abzaeva et al., 2006; Bezrukova, Belov, Letunova et al., the Late Glacial and evidences a relatively stable climate 2008; Bezrukova, Krivonogov, Takahara et al., 2008). in the Holocene (GRIP Members, 1995). However, data As the study of these records has demonstrated, climatic concerning the geochemical admixture in the same core fl uctuations in the Holocene had a larger amplitude and attest to climatic instability and the irregularity of the higher frequency than previously believed, although the Holocene characteristics at least in Greenland (Mayewski range was lower than during the Late Glacial. et al., 1997). Climatic fluctuations in the Holocene The objective of the present article is to develop have been demonstrated in many regions (Enzel et al., a high-resolution reconstruction of Late Glacial and 1999; Wurster, Patterson, 2001; Zhao et al., 2007), and Holocene environmental changes in the Lake Baikal various mechanisms explaining these fl uctuations have area using dated pollen records from marsh systems, been suggested (Bond et al., 2001; Visbeek, 2002). It which today are situated in areas with different biological is impossible to reconstruct the temporal and spatial and climatic parameters – those in the southern and variation of the Late Glacial and Holocene climate and the northeastern shores of the lake. Before the mid- environment without information from various regions 17th century, neither area was subjected to a signifi cant of the planet, especially those where the environment is anthropogenic impact. Therefore the sedimentation particularly sensitive to climatic changes. Earlier studies records from these ecosystems will hopefully refl ect the have shown that geochemical and diatom records from the natural environmental changes. bottom sediments of Lake Baikal meet this requirement (Uchastniki..., 1998; Khursevich et al., 2001; BDP-99..., 2005; and others). However, earlier reconstructions of Study areas climate in these studies are based on averaged signals from deep-water cores. Meanwhile, the Lake Baikal basin Duguldzera. The core was taken at the eastern Baikal spans nearly four degrees of latitude and, because its shore (Fig. 1), in the forest ecosystem of the middle southern and northern parts display climatic differences mountain zone. Larch, Scots and Siberian pines dominate at the present, such differences must have existed in the this ecosystem. Forests composed of larch, Siberian pine, past as well. The relevant information can be obtained and spruce occupy more elevated areas on mountain from peatland ecosystems, where a thick layer of organic slopes and in valleys. Open Siberian pine and fi r forests sediments contains a continuous record of environmental of a primarily valley type grow higher. This region changes with a high time resolution over the last 15 is characterized by an extreme continental climate. According to data of the nearest weather station at Davsha, mean January and July temperatures are –22 ºС and +14 ºС, respectively; the mean annual temperature equals –3.3 ºС. Mean annual precipitation ranges from 350 to 400 mm. Insular permafrost occurs in this region (Baikal..., 1993). Dulikha. The peat bog is located on the southern 1 shore of Baikal (Fig. 1), where southern Siberian taiga composed of Siberian pine and fi r predominates. Larch trees are rare in marshlands. Birches form secondary forests, replacing dark coniferous forests in felling areas and fi re-sites. The climate is moderate continental (Ibid.). Mean July, January, and annual temperatures are +14.4, – 17.7, and –0.7 oC, respectively. Mean annual precipitation is 600–650 mm. Thus, the temperatures in the two areas differ by 4–5 oC in January, by 2 oC in July, and by approx. 2.5 oC on average, whereas the difference between mean 3 annual precipitation levels is nearly 250 mm. 2 Materials and methods Fig. 1. Map showing the location of the core sites. 1 – Duguldzera; 2 – Dulikha; 3 – VER93-2 bottom sediments, station The Duguldzera core is 400 cm long. The upper 330 24 GC. cm are represented by peat of various composition; 19 the lower 70 cm are formed by lacustrine gyttja with of the present article, the diagrams themselves are less an admixture of clay mineral particles. Every fourth important than the indices of environmental changes centimeter was subjected to pollen analysis; therefore based on these diagrams. Duguldzera is designated Dz the temporal resolution of the record is 150–200 years. and Dulikha is labeled Dl. The chronological model of the section is based on seven radiocarbon dates. The depth of Late Glacial and Holocene peat sediments Results and interpretation in the Dulikha core is 500 cm (Bezrukova, Krivonogov, Abzaeva et al., 2005). Every fourth centimeter of the Four zones have been recognized in the Duguldzera pollen core was treated with pollen analysis. The average diagram (Fig. 2). They are described from bottom to top. temporal resolution of the record is 100–150 years. The The zones are characterized by the most signifi cant pollen chronological model of this core is based on three dates taxa for paleoenvironmental reconstructions. (Table). Dz4: Artemisia – Betula alba-type – Picea; > 16,000 Chronological limits of pollen zones were estimated BP; depth 400–385 cm. Sediments are represented by by linear interpolation between the dates. To evaluate mineralized gyttja. Spore-pollen spectra (hereafter, SPS) the possible mechanisms behind the vegetation changes evidence the first maxima of pollen of spruce (Picea and to correlate the temporal limits of these changes with obovata) and birches of both sections (Betula sect. those for the Northern Hemisphere, radiocarbon dates Albae and Betula sect. Nanae). The herbaceous group is were calibrated using CalPal software (Danzeglocke, dominated by Artemisia pollen. Jöris, Weninger, 2008). Age estimates in pollen diagrams Dz3д: Artemisia – Salix – Betula alba-type; meadow- are calibrated. steppe motley grassland; ~16,000–14,700 BP; depth 385– The classifi cation of pollen taxa used for the calculation 355 cm. SPS formed in lacustrine gyttja. Tall birch pollen of pollen indices of temperature and moisture corresponds prevails along with pollen of shrub birch, willow, and to the taxa grouping applied in the biome reconstruction mesoxerophytic herbs. method (Prentice et al., 1996; Tarasov et al., 2000; Dz3г: Betula alba-type – Cyperaceae – Salix; Demske et al., 2005). ~14,700–14,000 BP; depth 355–345 cm. Birch and Pollen diagrams are presented here in the most general willow pollen dominate SPS; sedge pollen occurs in large form for several reasons: (1) the complete diagram quantities. of the Dulikha section has already been published Dz3в: Duschekia – Picea – Larix – Betula alba-type – (Bezrukova et al., 2005), although dates were given Equisetum; ~14,000–13,200 BP; depth 345–325 cm.
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