ISSN 1028334X, Doklady Earth Sciences, 2016, Vol. 468, Part 1, pp. 527–531. © Pleiades Publishing, Ltd., 2016. Original Russian Text © E.V. Bezrukova, A.A. Shchetnikov, M.I. Kuzmin, O.G. Sharova, N.V. Kulagina, P.P. Letunova, E.V. Ivanov, M.A. Kraynov, E.V. Kerber, I.A. Filinov, O.V. Levina, 2016, published in Doklady Akademii Nauk, 2016, Vol. 468, No. 3, pp. 323–327.
GEOGRAPHY
First Data on the Environment and Climate Change within the ZhomBolok Volcanic Field (Eastern Sayan Mountains) in the Middle–Late Holocene E. V. Bezrukovaa, b, A. A. Shchetnikovc, Academician M. I. Kuzmina, O. G. Sharovaa, b, N. V. Kulaginac, P. P. Letunovaa, b, E. V. Ivanova, M. A. Kraynova, E. V. Kerbera, I. A. Filinovc, and O. V. Levinaa Received November 18, 2015
Abstract—This paper considers the results of comprehensive lithological, biostratigraphic, and geochemical investigation of sediments in KharaNur 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 vol canic events did not exert a catastrophic impact on the regional landscape, but they caused dramatic changes in the local vegetation. The welldefined correlation of the regional events with the wellknown 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 ZhomBolok Region in the Middle– Late Holocene. DOI: 10.1134/S1028334X16050196
The lava flows and volcanoes in the ZhomBolok River valley (Fig. 1) in the Eastern Sayan Mountains are unique, because they are the largest manifestations of Holocene eruptions in the Central Asia Region [1]. The chronology of volcanic events is still poorly inves tigated. It is only known that lava outpourings were multiphase here, began in the postglacial time, and continued through the last millennium [2]. The volca nic events were accompanied by the formation of large dammed lakes. In the headwater of the ZhomBolok River valley, some such water reservoirs are observed even today. Mountain lakes are commonly undis turbed or slightly disturbed ecosystems readily responding to natural changes in their basins [3]. That is why the sediments of such lakes are used as valuable archives to reconstruct the paleoenvironmental condi tions. The main objective of our research was to study changes in the natural environment of the Zhom Bolok volcanic region (Fig. 1) recorded in the sedi ments of lavadammed KharaNur Lake (absolute altitude 1651 m) and to explain their causes. The lake
a Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033 Russia b Institute of Archeology and Ethnography, Siberian Branch, Russian Academy of Sciences, pr. Akad. Lavrentieva 17, Novosibirsk, 630090 Russia c Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033 Russia email:
[email protected]
sediments were drilled in summer of 2013 with a UWITEC cabletype gravitational sampler. A core of 130 cm in length was taken up from the water depth of 47 m. Only one AMS 14C date was obtained from the core bottom to estimate the sediment age (Poznan, Poland). The sediment age at the depth of 130 cm was estimated at 6035 ± 35 14C years (Poz58391) or 6881 ± 53 calibrated years [4]. The age model calcu lated by age extrapolation of the basal layer upwards with the assumption of a constant sedimentation rate was used to assess the likely age of paleogeographic events and their correlation with the known global environment records. The presentday vegetation of the area studied includes a lightconiferous taiga dom inated by larch Larix, sporadic Siberian pine Pinus sibirica, birch Betula sect. Albae, and spruce Picea obo vata. The ZhomBolok climate is extremely continen tal: the average annual total precipitation does not exceed 400 mm. The reconstruction was based on the results of palynological (Fig. 2) and Xray fluores cence analyses, and the study of physical and magnetic sediment properties carried out with an interval of 1– 0.5 cm and calculated environment and climate change indexes (Fig. 3). The forest vegetation density index (FVDI)—the ratio of total pollen of wood plants and that of shrubs and terrestrial herbs—makes it pos sible to estimate the relative proximity of a forest and/or its density near the drill point [5]. The CIA chemical weathering intensity index is used to assess the climate control over the chemical changes in vari ous natural sedimentation environments [6]. DC/LC is the ratio of darkconiferous and lightconiferous trees. Due to different requirements of these trees to ecolog
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6 km Fig. 1. Location of the ZhomBolok volcanic region based on a Landsat 7 2000 satellite image. The lava flow direction is indicated with an arrow. The drill point localization in the center of KharaNur Lake is shown with a black circle. The investigation area is shown with a rectangle in the inset.
ical–edaphic and climatic factors, this ratio can be regarded as an index of relative changes in the climate continentality. Loss on ignition (LOI) characterizes the organic matter volume, the concentration of bio genic silica SiO2 bio is indicative of the relative produc tion of a water reservoir, and the sediment magnetic susceptibility (MS) gives an idea of variations in the terrigenous material volume. Principal component analysis (PCA) was applied to the palynological anal ysis results to detect rearrangements in the composi tion of the spore–pollen spectra (SPS) and producing them vegetation. Three pollen zones are distinguished on a spore–pollen diagram (Fig. 2). Khrn3 (131–102 cm; 6900–6000/5500 years ago). SPS is characterized by a maximum pollen and spore concentration and predominance of arboreal pollen such as Picea, Abius, and Pinus sylvestris. The vegeta tion cover density index (VCDI) and DC/LC are high, while the PCA1 axis has negative values (Fig. 3). Khrn2 (102–48 cm; 6000/5500–2500 years ago). SPS is characterized by a lower arboreal pollen and spore concentration and a higher content of shrub pol len, in particular, Betula nanatype. VCDI values also got lower, while PCA1 data have positive values. Khrn1 (48–0 cm; 2500 years ago–to date). The palynomorph concentration remains low, abundant pollen of trees becomes sporadic. Meanwhile, the pol len content of Larix and herbs such as Poaceae, Arte misia, and Cyperaceae increased. The PCA1 results have negative values.
The core top 94 cm is composed of river silts with a high organic content underlain by a 36centimeter sequence of clay river sands and peat layers. Figure 3 demonstrates three zones with environment develop ment stages in the studied area. The Khrn3 zone is characterized by maximum concentration of palyno morphs, tree pollen, the highest VCDI and MS, and minimum SiO2 bio. The PCA1 axis corresponding to 54% of the total variations in the SPS compositions is indicative of rearrangement in the spore–pollen spec tra at the core depth of 102–100 cm (5500 years ago). According to the total core data, the basal layer forma tion was characterized by river (occasionally bog) sed imentation in the center of KharaNur Lake. Dark coniferous forests were suggested to grow near the cor ing point, because their pollen was deposited under the forest canopy [7]. The climate was moderately cold and humid, with an average annual rainfall of over 600 mm required for domination of dark coniferous forests. The MS index reflects a large amount of terrig enous material supplied from the lake catchment to the drilling point, which was much closer to the river bank than currently to the lake shore. Based on the comparison of changes in the environment in this area with those of the global stratotypes (Fig. 3), changes in the climatic system of the ZhomBolok River valley 5500 years ago were consistent with termination of the Holocene optimum 6000–5000 years ago, weakening of the Asian summer monsoon, lowering of summer insolation, and enhancement of the westerlies. The pollen concentration, VCDI, and MS multiply falls in the Khrn2 sediments. The tree pollen concen DOKLADY EARTH SCIENCES
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S po hru lle b n H po erb ll . Sp en or es Ab ies s Pi ibir ica ce a o Pi bov nu a s s ta ib iri ca Pi nu ss ylv es tri La s rix Be tu la Al alba na Be ste type tu r fr la ut na ico na sa ty Po pe ac e Ar ae tem C isia yp er a Sp cea e ha Ly gnu co m po di ac ea Po e zo lle ne n s
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Fig. 2. Simplified spore–pollen diagram for the sediment core of KharaNur Lake. (1) Lake silt; (2) river sand; (3) peat with veg etation residues; and (4) peaty soil layers.
tration, CIA, and LOI gradually decrease to the upper boundary of the zone. As follows from variations in indexes, the forest vegetation withdrew from the drill ing point later than 6000 years ago, biogenic sedimen tation was activated due to changes in the sedimenta tion conditions (lake formation), and magnetic min erals supplied from the lake catchment area were diluted. Accordingly, KharaNur Lake was formed in dimensions similar to the current ones not earlier than 6000 years ago. Deep restructuring of the natural envi ronment about 5500 years ago is also confirmed by a dramatic change in the PCA1 values (Fig. 3). Reorga nization took about 150–200 years, was not cata strophic, and led to a reduction in darkconiferous forests, but generally did not affect the forest vegeta tion near the lake (Fig. 3, tree pollen scale). The restructuring rate was calculated by the average tem poral resolution of pollen records (about 100 years). The darkconiferous taiga reduction later than about 6000 years ago is consistent with the reconstructions of the Baikal Region [8]; it was due to a decrease in the atmospheric moisture and increase in the climate con tinentality in parallel with enhancement of the westre lies and reduction in the summer insolation (Fig. 3). The Khrn1 sedimentation was accompanied by an ongoing decrease in tree pollen (Fig. 3). MS values remained low. Maximum values of SiO2 bio, LOI, and CIA were noted in the range of 31–8 cm (1500– 500 years ago). The PCA1 axis shows dramatic DOKLADY EARTH SCIENCES
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changes 3000–2500 years ago (Fig. 3). They are con sistent with the expansion of larch forests around KharaNur Lake likely in response to climatic deteri oration in the Northern Hemisphere (Fig. 3, isotopic and insolation scales) corresponding to event 2 in the North Atlantic Region [9] and its manifestation in the Baikal Region [10, 11]. Other indexes confirm inten sification of erosion processes in that time in the ZhomBolok River valley under colder and arid con ditions. High concentrations of charcoal microparti cles later than 2700 years ago induced intensification of fires in the KharaNur Lake basin without contra dicting the climate aridity trend. Their maximum peak about 800–700 years ago was in agreement with the dated volcano eruption in the ZhomBolok River val ley [2]. The increase in SiO2 bio and LOI and the decrease in MS at a depth of 25–7 cm (about 1000– 500 years ago) in compliance with the darkconiferous forest expansion in the ZhomBolok River valley could be a response of the local natural environment to improvement of the Medieval climate anomaly 1100–900 years ago [12]. Reduction in the environ mental indicators in the ZhomBolok River valley later than 500 years ago was probably due to climatic deterioration in the Little Ice Age. According to the total analytical data, the past almost 7000 years were marked by considerable changes in the natural and climatic conditions in the ZhomBolok Region. Based on our data, floodplain
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Fig. 3. Summary chart of the environment and climate indexes for the KharaNur Lake sediments relative to the NGRIP δ18O recording for the Greenland Ice Cores [13] as an air temperature index in the Northern Hemisphere and relative to δ18O for China stalagmites [14] as an intensity indicator of the summer Asian monsoon and summer insolation [15]. Thick lines in the CIA and LOI scales indicate a moving average at seven points; straight vertical lines in Tree Pollen, NGRIP δ18O, and Dongge Cave δ18O scales demonstrate a general trend toward an decrease in these indexes. (1) Lake silt; (2) river sand; (3) peat with vegetation residues; and (4) peaty soil layers.
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n tio rt a n en tio nc ra o t c t n le en ce nt t c n i e o m en rt dim c a e i n re ed nm s . op se ,‰ Ju N ) e , % .un ro tage cr 3 of po of s i s , v i 8 O n s ° t % v 1 l a n 0 i le 4 m e d 3 n s y ,% δ rs un oal cm ol tio2 ), 6 al e ion (5 , r , % an cm eC ‰ io og yea P a l p g l b l 1 n C I % t % I r i e o 2 , R /L D llen in so /m ng18 O, , C arc I, A tu tera re iO th e, A n o C S i a G I h g I C O o C S T l D L D δ N a N P P С V L A C M (W 0 0 rix a L 500 1000 1 1 1500 2000 2 2500 3000 3 3500 2 4000 4 4500 5000 5 5500 60 65 70 25 6000 6 3 6500 7000 7 4
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formation along the paleoflow banks with the develop ment of peat interlayers began about 7000 years ago coinciding with the eruption about 7130 years ago [2]. The last age was also obtained by the AMS 14C method by shrub twigs identified between ash layers. Yet, as follows from our reconstructions, this lava flow did not cause the development of KharaNur Lake in its cur rent form. This lake was formed later than 6000 years ago. Identified volcanic events of the Middle Holocene did not exert a catastrophic impact on the regional landscape, but they led to river damming, the appearance of KharaNur Lake, and changes in the local vegetation. The identified correlation of regional events with the wellknown records of the natural environment in the Northern Hemisphere is indica tive of the decisive influence of the global atmospheric circulation on restructuring of the landscape and the climate system in the ZhomBolok Region in the Middle–Late Holocene. The fact that KharaNur Lake was formed about 1500 years later than the dated volcanic eruption [2] points to incompleteness of the available results and to the need for a detailed chrono logical scale of paleoevents. In general, this investiga tion emphasizes the importance of and the need for comprehensive study of dammed lake sediments and volcanic eruption products from these unique areas to determine the chronology and intensity of eruptions and their impact on the Central Asia environment. ACKNOWLEDGMENTS This work was supported by the Russian Science Foundation (project no. 145000036) and the Rus sian Foundation for Basic Research (projects nos. 15 0501644 and 140500779).
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REFERENCES 1. V. V. Yarmolyuk, A. V. Nikiforov, and V. G. Ivanov, Vul kanol. Seismol., No. 5, 41–59 (2003). 2. A. V. Ivanov, S. G. Arzhannikov, E. I. Demonterova, et al., Bull. Volcanol. 73, 1279–1294 (2011). 3. R. Pienitz and A. F. Lotter, PAGES News, Adv. Pale olimnol. 17 (3), 92–93 (2009). 4. U. Danzeglocke, O. Jöris, and B. Weninger, CalPal 2007 Online, 2008. http://www.calpalonline.de. Accessed Dec. 17, 2014. 5. M. C. Cheung, Y. Zong, Z. Zheng, et al., Quat. Int. 333, 40–48 (2014). 6. G. RomanRoss, P. J. Depetris, M. A. Arribere, et al., J. Soc. Am. Earth Sci. 15, 657–667 (2002). 7. E. V. Bezrukova, A. A. Abzaeva, P. P. Letunova, et al., Quat. Int. 136, 18–32 (2005). 8. P. Tarasov, E. Bezrukova, E. Karabanov, et al., Palaeo geogr., Palaeoclimatol., Palaeoecol. 252, 440–457 (2007). 9. G. Bond, B. Kromer, J. Beer, et al., Science 294, 2130– 2136 (2001). 10. A. W. Mackay, E. V. Bezrukova, M. J. Leng, et al., Quat. Sci. Rev. 41, 119–131 (2012). 11. S. S. Kostrova, H. Meyer, B. Chapligin, E. V. Bezruk ova, P. E. Tarasov, and M. I. Kuzmin, Dokl. Earth Sci. 451 (1), 732–736 (2013). 12. M. E. Mann, Z. H. Zhang, S. Rutherford, et al., Sci ence 326, 1256–1260 (2009). 13. A. Svensson, K. K. Andersen, M. Bigler, et al., Clim. Past 4, 47–57 (2008). 14. D. X. Yuan, H. Cheng, R. L. Edwards, et al., Science 304, 575–578 (2004). 15. A. Berger and M. F. Loutre, Quat. Sci. Rev. 10, 297– 317 (1991).
Translated by E. Maslennikova
