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Lake-level changes during the past 100,000 years at Lake Baikal, southern Siberia
Quaternary Research 62 (2004) 214 – 222 www.elsevier.com/locate/yqres
Short Paper
Lake-level changes during the past 100,000 years at Lake Baikal, southern Siberia Atsushi Urabea,*, Masaaki Tateishib, Yoshio Inouchic, Hirokazu Matsuokad, Takahiko Inouee, Alexsander Dmytrievf, Oleg M. Khlystovg a
Research Institute for Hazards in Snowy Areas, Niigata University, Niigata 950-2181, Japan b Faculty of Science, Niigata University, Niigata 950-2181, Japan c Center for Marine Environmental Studies, Ehime University, Matsuyama 790-8577, Japan d Kowa Consulting Office, Tokyo 202-0022, Japan e Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan f Faculty of Geology, Geological Data Processing and Geological Ecology, State Technical University, Irkutsk 664074, Russia g Limnological Institute, Siberian Branch of Russian Academy of Science, Irkutsk 664033, Russia Received 4 June 2003 Available online 3 August 2004
Abstract Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33–38 m; from MIS 3 through MIS 2, it fell an additional 11–15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages. D 2004 University of Washington. All rights reserved. Keywords: Seismic survey; Selenga Delta; Marine oxygen isotope stage; Lake-level change; Lake Baikal
Introduction Lake Baikal is a large lake in southern Siberia, where grass steppes to the south give way to Boreal forests. Recently, deep-water sediment cores have been extracted and analyzed to propose an interpretation of the late Pleistocene climate in the Baikal region. Colman et al. (1995) and Grachev et al. (1998) have analyzed variations of climatically sensitive diatom assemblages and biogenic silica from
* Corresponding author. Research Institute for Hazards in Snowy Areas, Niigata University, 8050 Ikarashi 2-cho Niigata 950-2181, Japan. Fax: +81 25 261 1699. E-mail address: [email protected] (A. Urabe).
the Lake Baikal cores and inferred correspondence to marine oxygen isotope stages (MIS). Lake levels also respond to climatic and other factors (e.g., Harrison, 1989, 1993; Harrison and Digerfeldt, 1993; Harrison and Tarasov, 1996; Kutzubach and Street-Perrott, 1985; Street and Grove, 1979). Dated sequences of lake levels can therefore be interpreted to constrain the timing and amplitude of effective precipitation and temperature fluctuations in the watershed (Street-Perrott and Harrison, 1985), provided other factors such as tectonic subsidence can be accounted for. Published estimates of water balance and the concentration of dissolved matter have disregarded lake-level fluctuation (Colman, 1998; Colman et al., 2003), and changes of 200 m inferred from the elevations of terraces around the lake (Mats, 1993; Mats et al., 2000) lack
0033-5894/$ - see front matter D 2004 University of Washington. All rights reserved. doi:10.1016/j.yqres.2004.06.002
A. Urabe et al. / Quaternary Research 62 (2004) 214–222 215
Figure 1. Maps of Lake Baikal and the Selenga delta. (a) Index map. Lake Baikal is located at the boundary of the Eurasian and Amurian plates. (b) The Selenga delta with seismic lines, coring sites, and lake bathymetry. The Selenga River is the largest river feeding Lake Baikal. Distribution and displacement of faults observed in the study area. The area is divided into northwestern and southeastern blocks by the faults AF7, AF8, and AF9. Seismic lines are indicated by bL.Q
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chronological constraints. Consequently, the relationship between fluctuations in the lake level and variations in regional climate has not been well defined. We have carried out a seismic survey and extracted sediment cores from the Selenga River delta in Lake Baikal (Fig. 1). This paper discusses the correlation between the seismic records and sediment samples, and provides age estimates for the buried sediment packets recorded by seismic reflectors. We used sequence stratigraphic analysis of the seismic record to estimate the lake-level changes in the Selenga delta during the last 100,000-yr glacial cycle.
Study area The Selenga delta lies between the Southern and Central basins in the southeastern part of Lake Baikal (Fig. 1a). The Selenga River, which originates in central Mongolia, provides about 50% of the water input into Lake Baikal, or ~30 km3 yr 1 (Shimaraev et al., 1994). Figure 1b shows the surveyed lake area, with bathymetry from depth records obtained during our seismic survey. There is a distinct depression in the northwestern part of the surveyed area, several kilometers from the coast of the delta. The depression is aligned northeast–southwest, parallel to the shoreline of the delta. Topographic highs with 30–80 m of relief border the depression. Posoliskaya Bank, which lies southwest of the delta, is an extension of one of these highs. The slope from the delta front to the depression averages b0.58; in contrast, the slope of the highs is ~38.
Table 1 Equipment and recording conditions Positioning Seismic survey Energy source Transducer Receiver Recorder Tape recorder
Recording condition Source: Uniboom Energy Shot interval Distance from the stern Receiver: single-channel streamer Elements Length Depth Distance from source to receiver Assumed speed of sound using depth conversions
GPS Receiver EG&G Uniboom System Seismic Energy Source MODEL 234 Uniboom MODEL 230 EG&G Hydrophones MODEL 265 Seismic Recorder MODEL 255 SONY DAT MODEL TCD–D8
200 or 300 J 0.6 s 30 m
8 4.6 m 0.2 m 5m
1500 ms
1
comparing core lengths and seismic records. Diatom analysis was performed by relative counting of Aulacoseira sp. and Cyclotella sp. at intervals of 10 cm in each core. Organic-rich sediment layers from depths of 300 cm in the st31 core and 200 cm in st33 were sampled for 14C dating (Table 2). Corrections for reservoir age were not attempted.
Approach Seismic survey
Results
Table 1 describes the equipment employed for the survey. Seismic profiles totaled ~500-km long and consisted of 33 lines oriented north–south or east–west lines (Fig. 1b).
Seismic profiles and stratigraphic interpretation
Bathymetry Water depths were measured by sounding as well as from the seismic profiles. These were used to generate the bathymetric contour map shown in Figure 1b. Sediment cores Gravity and piston sediment cores were extracted from two stations in water depths of 195 m (st31) and 125 m (st33) and analyzed for grain size, sediment bedding, and diatom content. Detailed lithofacies description was based on X-ray photographs. In estimating thicknesses of sediment packets, we accounted for sediment compaction by
Figure 2 shows a typical seismic section of the study area at profile L56, and identifies the distinct seismic reflectors that are traceable in the study area. We recognize three units in the seismic profiles, each subdivided into two or zones: baQ and bb.Q Zone a has a distinctive dense parallel reflected pattern, whereas Zone b has a sparse reflected pattern on seismic records. Figure 3 shows the interpretation of all the seismic records along the east–west track lines. Active faults In the frontal parts of the delta, escarpments were observed on the seismic profiles. Because they offset the recent lake sediments, we interpret these as scarps of active faults. The largest displacement observed for a normal fault at the delta
A. Urabe et al. / Quaternary Research 62 (2004) 214–222
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Table 2 Radiocarbon ages of core samples Sample No.
Conventional radiocarbon age (14C yr B.P.)
St31 (Bata-116650) St33 (Bata-116649)
13,160 F 110 13,060 F 120
d 13C (x) 27.3 27.8
Intercept of radiocarbon age (cal yr B.P.)
Calibrated age, 1r range: cal yr B.P. (probability)
15,820 15,705
16,225–15,410 (68%) 16,085–15,175 (68%)
Age calibration are carried out by INTCAL98 (Stuiver et al., 1998).
front was 135 m, cutting east–west profile L57 in 207 m of water (fault AF7 in Fig. 1b). The fault dips east at an apparent angle of 338. It also crosses the profiles L3 and L55, from which its northeast–southwest strike and true dip angle of 488
at L57 can be estimated. Displacements along the fault rapidly decrease toward both northeast and southwest. A total of 12 subparallel faults (AF1–12) are arranged in an echelon pattern (Fig. 1b). Most of them are southeast-
Figure 2. Seismic section (offshore side of L56) and division of the units. Classification of seismic stratigraphy of the Selenga delta. The blocks referred to (AF6–8) are identified in Figure 1b.
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Figure 3. Division and distribution of each unit on the seismic sections of the northwestern and southeastern block in an east–west direction (refer to Fig. 1b).
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dipping normal faults forming the northwestern wall of the topographic depression. In general, the southeastern block dips northwest. From the correlation of seismic reflectors across the fault, we suggest that fault AF7 already had moved when Unit IIIa was deposited, and remains active today. Figure 1b shows the inferred initiation age of each fault. The age of initiation increases toward the southwest. Core sediments Lithofacies of st31 and st33 are shown in Figure 4 and are summarized as follows (from top to bottom): clay with thinly laminated organic sediments, alternations of silt and clay, clay with thinly laminated organic sediments, clay, and clay with thinly laminated organic sediments. This laminated organic sediment consists of alternating thin layers of clay and silt, colored black to blackish gray, with high concentration of organic matter. Clay layers in the cores contain thin laminations of very fine to fine sand (Fig. 4). Sediments of st33 contain thicker silt layers and a greater number of thin sand layers of very fine to fine sand than sediments at st31, because the former is closer to delta front and at shallower depths. Judging from the record, cored sediment of st31 is correlated with Unit Ia and those of st33 correspond to Unit Ia and upper part of Unit Ib. Cored sediments of st33 are subdivided into Unit Ia, in which both
Figure 4. The stratigraphy of the surface area at coring stations 31 and 33.
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Aulacoseira sp. and Cyclotella sp. are abundant, and Unit Ib, in which both are absent (Fig. 4). Radiocarbon ages of organic sediments were 13,160 F 110 14C yr B.P. (~15,820 cal yr B.P.) 300 cm below the lake bottom at st31, and 13,060 F 120 14C yr B.P. (~15,710 cal yr B.P.) 200 cm below the lake bottom at st33. Both dated samples were taken from Unit Ia, but at st33 the transition to Unit Ib was only ~60 cm lower in the core (Fig. 4). At both st 31 and st33, the dated sediments were below the diatombarren zone.
Discussion Chronology of cores at stations In Lake Baikal, the productivity of diatoms is closely related to climate: high diatom productivities occur during warm stages, and low or barren productivities in cold stages (Grachev et al., 1998; Khursevich et al., 2001; Prokopenko et al., 2001b). The sediments from st33 show a drastic change from the lower diatom-barren zone (in Unit Ib) to an upper zone (in Unit Ia) in which both species, but especially Cyclotella sp., are abundant (Fig. 4). The recovery at st31 is less pronounced. The 14C dates from st31 and st33 indicate that deposition of Unit Ia began before ~15,700 cal yr B.P. and continued well after the diatom population recovered, during the Holocene (Grachev et al., 1998). The sediments from Unit Ia at both stations contain a 25–55 cm diatom-barren zone (Fig. 4), which resulted from a decrease in primary productivity. Although direct numerical dating of this zone was not done, the 14C ages did define a maximum age. This limiting age and the distinctive decrease of diatom productivity suggest that this barren zone is correlated to the Younger Dryas cooling period, which is well represented in Europe and is also recognized elsewhere in the world (e.g., Peteet, 1995), including Lake Baikal, where it has been recognized from profiles of biogenic silica content (Colman et al., 1995, 1999; Prokopenko et al., 2001a; Williams et al., 1997). The sediments of Unit Ia include numerous thin intercalations of very fine to fine sand in the clay and silt layers, suggesting that coarse materials were supplied into the lake during warm periods in the Holocene. The densely layered fine reflectors of Unit Ia (Fig. 2) imply the existence of thinly laminated coarse materials. On the other hand, the transparent reflecting horizons of Unit Ib and the direct evidence from the sediment core at st33 show it to be clay rich, lacking in intercalated thin sand layers. Unit Ib was most likely deposited during the cold period of MIS 2, before 15,700 cal yr B.P. Seismic records of Unit Ia and Unit Ib around the Selenga Delta have similar patterns, so the difference in seismic pattern is not simply due to changes in clastic supply routes (Fig. 3).
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Therefore, we interpret the densely layered pattern of seismic Units Ia, IIa, and IIIa as corresponding to warm periods. Age of units from sedimentation rates Average sedimentation rates at st31 and st33 of ~0.23 and ~0.15 mm/yr can be estimated from thickness and core shortening above the 14C-dated samples (300 and 200 cm, respectively; Fig. 4). Stations 31 and 33 are in water depths of 195 and 125 m, respectively. The sedimentation rate is greater at st31, where the water is deeper. Sedimentation rates at the surface of the Buguldeika saddle, away from the Selenga delta (Fig. 1b) and in 350 m of water, have been reported to be similar: 0.18–0.20 mm/yr (Colman et al., 1996, 1999). Station 33 was not suitable for age determination because it is located on the slope of delta front and may have been subjected to slumping and erosion (Fig. 2; L56). The age of each unit was therefore calculated from sedimentation rate at st31, where the seismic record shows the most stable patterns. At st31, the bases of Units Ia, Ib, IIa, IIb, and IIIa are 3.6, 8.6, 13.6, 20.0, and 30.0 m below the lake bottom, respectively. The corresponding age estimates were calculated assuming the sedimentation rate has been constant, which is probably not the case. The calculated ages for the bases of Units Ia, Ib, IIa, IIb, and IIIa were ~16,000, 38,000, 60,000, 88,000, and 132,000 yr, respectively. It is useful to note that these limiting age estimates do not exactly correspond to MIS boundaries. Comparison between the calculated unit ages and the biogenic silica profile shows a good correlation for densely laminated Units Ia, IIa, and IIIa and sediment layers with high silica content (Fig. 5), consistent with the inferred deposition of Units Ia, IIa, and IIIa under warm climatic conditions. The changes in the biogenic silica content correlate with the SPECMAP profile of d 18O (Colman et al., 1995; Prokopenko et al., 2001a). Hence, Units Ia, IIa, and IIIa may correspond in age to MIS 1, 3, and 5a (Fig. 5).
of Unit Ia through Unit IIIa. Because fault movements of the northwest block and the southeast block have been different (AF7, AF8, AF9: Fig. 1b), the depth of each reflector is described independently. From the reflection patterns, Units IIa and IIIa appear to comprise the topset and the foreset beds of the delta. They form progradational delta during stable lake level, and the elevations of the topset beds approximate the paleo-levels of the lake. In some areas, however, the seismic profiles show that the topset beds dip toward deeper water, and they appear to have been eroded. Consequently, the true lake level at the time of delta formation was probably a few meters higher than the level delineated from seismic records, although the discrepancy is difficult to quantify. Average values for the upper limits of Unit IIa and Unit IIIa in the northwestern block are determined to be 30 and 35 m, respectively, relative to the modern lake level (456 amsl), and 22 and 25 m, respectively, in the southeastern block. Erosional surfaces on Unit IIa inferred from the seismic records suggest that lake levels were stable during cold periods, and therefore the fluctuations must have occurred during climatic transitions. Unit Ib and Unit IIb appear to onlap the underlying units, and we consider them to have been deposited during such transitions from cold to warm periods. Lake levels then probably
Development of the delta Delta systems of Unit IIIa and Unit IIa show a pattern of aggradational conformities (Fig. 6). However, in the southern part of southeastern block (Fig. 1b; L57–L59), these units show a back-step pattern, which indicates a wave-cut terrace, developed over a considerable period of time. Subsidence along each fault has created topographic depressions, but it has not had a major effect on the delta system. Relative lake-level change The shallow sediment around the delta records the fluctuation of the lake level. Below, we discuss lake-level changes on the basis of the distribution patterns and depths
Figure 5. Correlation of the d 18O from the North Atlantic, biogenic silica content from Lake Baikal, and relative lake-level changes. (a) d 18O record is after Martinson et al. (1987). (b) Diatom content used by Grachev et al. (1997) (original data from Prof. M. Grachev, personal communication, 2003). (c) The relative lake-level fluctuations determined from the depth of seismic unit. Lake-level changes occur when the climate changes, approximately at MIS boundaries.
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Unit IIa Unit Ib Unit IIb
Unit IIIa
Unit IIa Unit Ib
Unit IIa
Unit IIb
Unit IIIa
Figure 6. Events in the delta development. MIS 5a: Formation of Unit IIIa. MIS 4: Lowering of the lake level and deposition of Unit IIb. MIS 3: Rise of the lakelevel and deposition of Unit IIa, which is aggradated to Unit IIIa. MIS 2: Lowering of the lake-level and deposition of Unit Ib. Formation of a back step or riser and a flat plane by wave cutting indicates that the lake-level was stabilized during the cold stage. The sediments of transgressive stage are not recognized. MIS 1: Deposition of Unit Ia, corresponding to the modern prograding delta.
corresponded to the upper limit of each unit plus the water depth. However, the upper limits of the units are commonly erosional surfaces, so the recovered levels may be minima (Fig. 3; L60). Average levels for the upper limits of Unit Ib and Unit IIb were determined at 45 and 73 m, respectively, in the northwestern block, and 33 and 58 m, respectively, in the southeastern block. Thus, the difference between the upper limits of Unit IIIa and Unit IIb in the northwestern block is 38 m in the northwestern block and 15 m in the southeastern block, and the respective differences between the upper limits of Unit IIa and Unit Ib are 33 and 11 m. These differences reflect the drop of lake level between Unit IIIa and IIb time. The present depths of the upper limits of the units (Fig. 5c) do not record absolute lake level because these depths have been affected by tectonic subsidence. However, the tectonic subsidence of 0.02 mm yr 1 in the northwestern block and 0.03 mm yr 1 in the southeastern block (assuming similar hydrological conditions during MIS1 and 5) accounts for only a small fraction (~2%) of the total inferred fluctuations in lake level, and we regard climatic change as the main cause of the lake-level changes. This is consistent with our correlation of sedimentation patterns and the marine climate record. If the warm and cold periods inferred from the sedimentary record do correspond to marine oxygen isotope stages, the lake level fell 33–38 m between MIS 5 and MIS 4 and 11–15 m between MIS 3 and MIS 2. Climatic inferences Temperature and precipitation in glacial periods at Lake Baikal have not been accurately estimated. However,
precipitation during the Last Glacial Maximum can be inferred to have decreased sharply, because pollen analysis shows that the region was cold and dry (tundra or barren arctic desert) then (Oda et al., 2000). Similar pollen records from France suggest that precipitation during glacial periods there decreased by 30% (Guiot et al., 1989). Significant lowering of temperature and decrease in precipitation are indicated in high-latitude regions. Present river influx at Lake Baikal is ~60 km3 yr 1, and evaporation is ~10 km3 yr 1 (Afanasyev, 1960; Shimaraev et al., 1994). The changing imbalance of river inflow and evaporation, and overflow down the Angara River, causes the observed lakelevel fluctuations. Although evaporation decreases in glacial periods, river inflow and precipitation on the lake surface also decrease, by about 15%, and lake level gradually falls then. Therefore, decreasing precipitation seems to be the phenomenon that controls lake level at Lake Baikal.
Summary This study analyzed of high-resolution seismic data in the shallow part of Selenga delta, calibrated by two 14C dates and correlated with analysis of sediment cores. It demonstrated that the water level in Lake Baikal decreased during the cold stages MIS 4 and 2. Lake level appears to respond to regional variations in temperature and precipitation, rising during warm periods and falling during cold periods, correlative with global climate changes. The fall in the lake level near the Selenga delta from MIS 5 through MIS 4 is estimated at 33–38 m, and from MIS 3 through MIS 2 at 11–15 m.
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Acknowledgments We are grateful to Professors Grachev and Mats of the Limnological Institute, Captains of the R/V Titov and R/V Vereshchagin, as well as the crews of the Titov and Vereshchagin for their assistance during the cruise. We thank Mrs. Yasukevich, and Mr. Reshetov, Mr. Kirill (translator) and Mrs. Naja (secretary of BICER), all of whom helped us in this study. References Afanasyev, A.N., 1960. The water budget of Lake Baikal: transactions of the Baikal Limnological Station. Academic Nark SSSR Vista, Siberia 18, 115 – 241. Colman, S.M., 1998. Water-level changes in Lake Baikal, Siberia: tectonism versus climate. Geology 26, 531 – 534. Colman, S.M., Peck, J.A., Karabanov, E.B., Carter, S.J., Bradbury, J.P., King, J.W., Williams, D.F., 1995. Continental climate response to orbital forcing from biogenic silica records in Lake Baikal, Siberia. Nature 378, 769 – 771. Colman, S.M., Jones, G.A., Rubin, M., King, J.W., Peck, J.A., Orem, W.H., 1996. AMS radiocarbon analyses from Lake Baikal, Siberia: challenges of dating sediments from a large, oligotrophic lake. Quaternary Science Reviews 15, 669 – 684. Colman, S.M., Peck, J.A., Hatton, J., Karabanov, E.B., King, J.W., 1999. Biogenic silica records from the BDP93 drill site and adjacent areas of the Selenga Delta, Lake Baikal, Siberia. Journal of Paleolimnology 21, 9 – 17. Colman, S.M., Karabanov, E.B., Nelson, C.H., 2003. Quaternary sedimentation and subsidence history of Lake Baikal, Siberia, based on seismic stratigraphy and coring. Journal of Sedimentary Geology 73, 941 – 956. Grachev, M.A., Likhoshway, Ye.V., Vorobyova, S.S., Khlystov, O.M., Bezrukova, E.V., Veinberg, E.V., Goldberg, E.L., Granina, L.Z., Koenakova, E.G., Lazo, F.I., Levina, O.V., Letunova, P.P., Otinov, P.V., Pirog, V.V., Fedotov, A.P., Yaskevich, S.A., Bobrov, V.A., Sukhorukov, F.V., Rezchikov, V.I., Fedorin, M.A., Zolotaryov, K.V., Kravchinsky, V.A., 1997. Signal of the paleoclimates of Upper Pleistocene in the sediments of Lake Baikal. Russian Geology and Geophysics 38, 957 – 980. Grachev, M.A., Vorobyova, S.S., Likhoshway, Y.V., Goldberg, E.L., Ziborova, G.A., Levina, O.V., Khlystov, O.M., 1998. A highresolution diatom record of the paleoclimates of east Siberia for the last 2.5 My from Lake Baikal. Quaternary Science Reviews 17, 1101 – 1106. Guiot, J., de Beaulieu, J.L., Pons, A., Reille, M., 1989. A 140,000-year continental climate reconstruction from two European pollen records. Nature 338, 309 – 313. Harrison, S.P., 1989. Lake-levels and climatic changes in eastern North America. Climate Dynamics 3, 157 – 167.
Harrison, S.P., 1993. Late Quaternary lake-level changes and climates of Australia. Quaternary Science Reviews 12, 211 – 231. Harrison, S.P., Digerfeldt, G., 1993. European lakes as palaeohydrological and palaeoclimatic indicators. Quaternary Science Reviews 12, 233 – 248. Harrison, S.P., Tarasov, P.E., 1996. Late Quaternary lake-level records from northern Eurasia. Quaternary Research 45, 138 – 159. Khursevich, G.K., Karabanov, E.B., Prokopenko, A.A., Williams, D.F., Kuzmin, M.I., Fedenya, S.A., Gvozdkov, A.A., 2001. Insolation regime in Siberia as a major factor controlling diatom production in Lake Baikal during the past 800,000 years. Quaternary International 80–81, 47 – 58. Kutzubach, J.E., Street-Perrott, A.F., 1985. Milankovitch forcing of fluctuations in the level of tropical lake from 18 to 0 kyr B.P. Nature 317, 130 – 134. Mats, V.D., 1993. The structure and development of the Baikal rift depression. Earth Science Review 34, 81 – 118. Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C., Shackleton, N.J., 1987. Age dating and the orbital theory of the ice ages—development of a high-resolution 0 to 300 000-year chronostratigraphy. Quaternary Research 27, 1 – 29. Mats, V.D., Fujii, S., Mashiko, K., Osipov, E.Yu., Yefrimova, I.M., Klimansky, A.V., 2000. Change in Lake Baikal water levels and runoff direction in the Quaternary Period. In: Minoura, K. (Ed.), Lake Baikal. Elsevier, Amsterdam, pp. 15 – 34. Oda, T., Minoura, K., Fujimura, C., Nakamura, T., Kawai, T., 2000. Vegetation history of the Baikal drainage basin during the last 250,000 years. Japanese Journal of Palynology 46, 81 – 92. Peteet, D.M., 1995. Global younger dryas? Quaternary International 28, 93 – 104. Prokopenko, A.A., Karabanov, E.B., Williams, D.F., Kuzmin, M.I., Shackleton, N.J., Crowhurst, S.J., Peck, J.A., Gvozdkov, A.A., King, J.W., 2001a. Biogenic silica record of the Lake Baikal response to climatic forcing during the Brunhes. Quaternary Research 55, 123 – 132. Prokopenko, A.A., Karabanov, E.B., Williams, D.F., Kuzmin, M.I., Khursevich, G.K., Gvozdkov, A.A., 2001b. The detailed record of climatic events during the past 75,000 yrs BP from the Lake Baikal drill core BDP-93-2. Quaternary International 80–81, 59 – 68. Shimaraev, M.N., Verbolov, V.I., Granin, N., Sherstayankin, P.P., 1994. Physical limnology of Lake Baikal: a review. BICER reprint, 2, Irkutsk, 80 pp. Street, F.A., Grove, A.T., 1979. Global maps of lake-level fluctuations since 30,000 yr BP. Quaternary Research 12, 83 – 118. Street-Perrott, F.A., Harrison, S.P., 1985. Lake levels and climate reconstruction. In: Hecht, A.D. (Ed.), Paleoclimate Analysis and Modeling. Wiley, New York, pp. 291 – 340. Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A., Kromer, B., McCormac, G., van der Plicht, J., Spurk, M., 1998. INTCAL98 radiocarbon age calibration, 24,000-0 cal BP. Radiocarbon 40, 1041 – 1083. Williams, D.F., Peck, J.A., Karabanov, E.B., Prokopenko, A.A., Kravchinsky, V., King, J., Kuzmin, M.I., 1997. Lake Baikal record of continental climate response to orbital insolation during the past 5 million years. Science 278, 1114 – 1117.
Short Paper
Lake-level changes during the past 100,000 years at Lake Baikal, southern Siberia Atsushi Urabea,*, Masaaki Tateishib, Yoshio Inouchic, Hirokazu Matsuokad, Takahiko Inouee, Alexsander Dmytrievf, Oleg M. Khlystovg a
Research Institute for Hazards in Snowy Areas, Niigata University, Niigata 950-2181, Japan b Faculty of Science, Niigata University, Niigata 950-2181, Japan c Center for Marine Environmental Studies, Ehime University, Matsuyama 790-8577, Japan d Kowa Consulting Office, Tokyo 202-0022, Japan e Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan f Faculty of Geology, Geological Data Processing and Geological Ecology, State Technical University, Irkutsk 664074, Russia g Limnological Institute, Siberian Branch of Russian Academy of Science, Irkutsk 664033, Russia Received 4 June 2003 Available online 3 August 2004
Abstract Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33–38 m; from MIS 3 through MIS 2, it fell an additional 11–15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages. D 2004 University of Washington. All rights reserved. Keywords: Seismic survey; Selenga Delta; Marine oxygen isotope stage; Lake-level change; Lake Baikal
Introduction Lake Baikal is a large lake in southern Siberia, where grass steppes to the south give way to Boreal forests. Recently, deep-water sediment cores have been extracted and analyzed to propose an interpretation of the late Pleistocene climate in the Baikal region. Colman et al. (1995) and Grachev et al. (1998) have analyzed variations of climatically sensitive diatom assemblages and biogenic silica from
* Corresponding author. Research Institute for Hazards in Snowy Areas, Niigata University, 8050 Ikarashi 2-cho Niigata 950-2181, Japan. Fax: +81 25 261 1699. E-mail address: [email protected] (A. Urabe).
the Lake Baikal cores and inferred correspondence to marine oxygen isotope stages (MIS). Lake levels also respond to climatic and other factors (e.g., Harrison, 1989, 1993; Harrison and Digerfeldt, 1993; Harrison and Tarasov, 1996; Kutzubach and Street-Perrott, 1985; Street and Grove, 1979). Dated sequences of lake levels can therefore be interpreted to constrain the timing and amplitude of effective precipitation and temperature fluctuations in the watershed (Street-Perrott and Harrison, 1985), provided other factors such as tectonic subsidence can be accounted for. Published estimates of water balance and the concentration of dissolved matter have disregarded lake-level fluctuation (Colman, 1998; Colman et al., 2003), and changes of 200 m inferred from the elevations of terraces around the lake (Mats, 1993; Mats et al., 2000) lack
0033-5894/$ - see front matter D 2004 University of Washington. All rights reserved. doi:10.1016/j.yqres.2004.06.002
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Figure 1. Maps of Lake Baikal and the Selenga delta. (a) Index map. Lake Baikal is located at the boundary of the Eurasian and Amurian plates. (b) The Selenga delta with seismic lines, coring sites, and lake bathymetry. The Selenga River is the largest river feeding Lake Baikal. Distribution and displacement of faults observed in the study area. The area is divided into northwestern and southeastern blocks by the faults AF7, AF8, and AF9. Seismic lines are indicated by bL.Q
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chronological constraints. Consequently, the relationship between fluctuations in the lake level and variations in regional climate has not been well defined. We have carried out a seismic survey and extracted sediment cores from the Selenga River delta in Lake Baikal (Fig. 1). This paper discusses the correlation between the seismic records and sediment samples, and provides age estimates for the buried sediment packets recorded by seismic reflectors. We used sequence stratigraphic analysis of the seismic record to estimate the lake-level changes in the Selenga delta during the last 100,000-yr glacial cycle.
Study area The Selenga delta lies between the Southern and Central basins in the southeastern part of Lake Baikal (Fig. 1a). The Selenga River, which originates in central Mongolia, provides about 50% of the water input into Lake Baikal, or ~30 km3 yr 1 (Shimaraev et al., 1994). Figure 1b shows the surveyed lake area, with bathymetry from depth records obtained during our seismic survey. There is a distinct depression in the northwestern part of the surveyed area, several kilometers from the coast of the delta. The depression is aligned northeast–southwest, parallel to the shoreline of the delta. Topographic highs with 30–80 m of relief border the depression. Posoliskaya Bank, which lies southwest of the delta, is an extension of one of these highs. The slope from the delta front to the depression averages b0.58; in contrast, the slope of the highs is ~38.
Table 1 Equipment and recording conditions Positioning Seismic survey Energy source Transducer Receiver Recorder Tape recorder
Recording condition Source: Uniboom Energy Shot interval Distance from the stern Receiver: single-channel streamer Elements Length Depth Distance from source to receiver Assumed speed of sound using depth conversions
GPS Receiver EG&G Uniboom System Seismic Energy Source MODEL 234 Uniboom MODEL 230 EG&G Hydrophones MODEL 265 Seismic Recorder MODEL 255 SONY DAT MODEL TCD–D8
200 or 300 J 0.6 s 30 m
8 4.6 m 0.2 m 5m
1500 ms
1
comparing core lengths and seismic records. Diatom analysis was performed by relative counting of Aulacoseira sp. and Cyclotella sp. at intervals of 10 cm in each core. Organic-rich sediment layers from depths of 300 cm in the st31 core and 200 cm in st33 were sampled for 14C dating (Table 2). Corrections for reservoir age were not attempted.
Approach Seismic survey
Results
Table 1 describes the equipment employed for the survey. Seismic profiles totaled ~500-km long and consisted of 33 lines oriented north–south or east–west lines (Fig. 1b).
Seismic profiles and stratigraphic interpretation
Bathymetry Water depths were measured by sounding as well as from the seismic profiles. These were used to generate the bathymetric contour map shown in Figure 1b. Sediment cores Gravity and piston sediment cores were extracted from two stations in water depths of 195 m (st31) and 125 m (st33) and analyzed for grain size, sediment bedding, and diatom content. Detailed lithofacies description was based on X-ray photographs. In estimating thicknesses of sediment packets, we accounted for sediment compaction by
Figure 2 shows a typical seismic section of the study area at profile L56, and identifies the distinct seismic reflectors that are traceable in the study area. We recognize three units in the seismic profiles, each subdivided into two or zones: baQ and bb.Q Zone a has a distinctive dense parallel reflected pattern, whereas Zone b has a sparse reflected pattern on seismic records. Figure 3 shows the interpretation of all the seismic records along the east–west track lines. Active faults In the frontal parts of the delta, escarpments were observed on the seismic profiles. Because they offset the recent lake sediments, we interpret these as scarps of active faults. The largest displacement observed for a normal fault at the delta
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Table 2 Radiocarbon ages of core samples Sample No.
Conventional radiocarbon age (14C yr B.P.)
St31 (Bata-116650) St33 (Bata-116649)
13,160 F 110 13,060 F 120
d 13C (x) 27.3 27.8
Intercept of radiocarbon age (cal yr B.P.)
Calibrated age, 1r range: cal yr B.P. (probability)
15,820 15,705
16,225–15,410 (68%) 16,085–15,175 (68%)
Age calibration are carried out by INTCAL98 (Stuiver et al., 1998).
front was 135 m, cutting east–west profile L57 in 207 m of water (fault AF7 in Fig. 1b). The fault dips east at an apparent angle of 338. It also crosses the profiles L3 and L55, from which its northeast–southwest strike and true dip angle of 488
at L57 can be estimated. Displacements along the fault rapidly decrease toward both northeast and southwest. A total of 12 subparallel faults (AF1–12) are arranged in an echelon pattern (Fig. 1b). Most of them are southeast-
Figure 2. Seismic section (offshore side of L56) and division of the units. Classification of seismic stratigraphy of the Selenga delta. The blocks referred to (AF6–8) are identified in Figure 1b.
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Figure 3. Division and distribution of each unit on the seismic sections of the northwestern and southeastern block in an east–west direction (refer to Fig. 1b).
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dipping normal faults forming the northwestern wall of the topographic depression. In general, the southeastern block dips northwest. From the correlation of seismic reflectors across the fault, we suggest that fault AF7 already had moved when Unit IIIa was deposited, and remains active today. Figure 1b shows the inferred initiation age of each fault. The age of initiation increases toward the southwest. Core sediments Lithofacies of st31 and st33 are shown in Figure 4 and are summarized as follows (from top to bottom): clay with thinly laminated organic sediments, alternations of silt and clay, clay with thinly laminated organic sediments, clay, and clay with thinly laminated organic sediments. This laminated organic sediment consists of alternating thin layers of clay and silt, colored black to blackish gray, with high concentration of organic matter. Clay layers in the cores contain thin laminations of very fine to fine sand (Fig. 4). Sediments of st33 contain thicker silt layers and a greater number of thin sand layers of very fine to fine sand than sediments at st31, because the former is closer to delta front and at shallower depths. Judging from the record, cored sediment of st31 is correlated with Unit Ia and those of st33 correspond to Unit Ia and upper part of Unit Ib. Cored sediments of st33 are subdivided into Unit Ia, in which both
Figure 4. The stratigraphy of the surface area at coring stations 31 and 33.
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Aulacoseira sp. and Cyclotella sp. are abundant, and Unit Ib, in which both are absent (Fig. 4). Radiocarbon ages of organic sediments were 13,160 F 110 14C yr B.P. (~15,820 cal yr B.P.) 300 cm below the lake bottom at st31, and 13,060 F 120 14C yr B.P. (~15,710 cal yr B.P.) 200 cm below the lake bottom at st33. Both dated samples were taken from Unit Ia, but at st33 the transition to Unit Ib was only ~60 cm lower in the core (Fig. 4). At both st 31 and st33, the dated sediments were below the diatombarren zone.
Discussion Chronology of cores at stations In Lake Baikal, the productivity of diatoms is closely related to climate: high diatom productivities occur during warm stages, and low or barren productivities in cold stages (Grachev et al., 1998; Khursevich et al., 2001; Prokopenko et al., 2001b). The sediments from st33 show a drastic change from the lower diatom-barren zone (in Unit Ib) to an upper zone (in Unit Ia) in which both species, but especially Cyclotella sp., are abundant (Fig. 4). The recovery at st31 is less pronounced. The 14C dates from st31 and st33 indicate that deposition of Unit Ia began before ~15,700 cal yr B.P. and continued well after the diatom population recovered, during the Holocene (Grachev et al., 1998). The sediments from Unit Ia at both stations contain a 25–55 cm diatom-barren zone (Fig. 4), which resulted from a decrease in primary productivity. Although direct numerical dating of this zone was not done, the 14C ages did define a maximum age. This limiting age and the distinctive decrease of diatom productivity suggest that this barren zone is correlated to the Younger Dryas cooling period, which is well represented in Europe and is also recognized elsewhere in the world (e.g., Peteet, 1995), including Lake Baikal, where it has been recognized from profiles of biogenic silica content (Colman et al., 1995, 1999; Prokopenko et al., 2001a; Williams et al., 1997). The sediments of Unit Ia include numerous thin intercalations of very fine to fine sand in the clay and silt layers, suggesting that coarse materials were supplied into the lake during warm periods in the Holocene. The densely layered fine reflectors of Unit Ia (Fig. 2) imply the existence of thinly laminated coarse materials. On the other hand, the transparent reflecting horizons of Unit Ib and the direct evidence from the sediment core at st33 show it to be clay rich, lacking in intercalated thin sand layers. Unit Ib was most likely deposited during the cold period of MIS 2, before 15,700 cal yr B.P. Seismic records of Unit Ia and Unit Ib around the Selenga Delta have similar patterns, so the difference in seismic pattern is not simply due to changes in clastic supply routes (Fig. 3).
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Therefore, we interpret the densely layered pattern of seismic Units Ia, IIa, and IIIa as corresponding to warm periods. Age of units from sedimentation rates Average sedimentation rates at st31 and st33 of ~0.23 and ~0.15 mm/yr can be estimated from thickness and core shortening above the 14C-dated samples (300 and 200 cm, respectively; Fig. 4). Stations 31 and 33 are in water depths of 195 and 125 m, respectively. The sedimentation rate is greater at st31, where the water is deeper. Sedimentation rates at the surface of the Buguldeika saddle, away from the Selenga delta (Fig. 1b) and in 350 m of water, have been reported to be similar: 0.18–0.20 mm/yr (Colman et al., 1996, 1999). Station 33 was not suitable for age determination because it is located on the slope of delta front and may have been subjected to slumping and erosion (Fig. 2; L56). The age of each unit was therefore calculated from sedimentation rate at st31, where the seismic record shows the most stable patterns. At st31, the bases of Units Ia, Ib, IIa, IIb, and IIIa are 3.6, 8.6, 13.6, 20.0, and 30.0 m below the lake bottom, respectively. The corresponding age estimates were calculated assuming the sedimentation rate has been constant, which is probably not the case. The calculated ages for the bases of Units Ia, Ib, IIa, IIb, and IIIa were ~16,000, 38,000, 60,000, 88,000, and 132,000 yr, respectively. It is useful to note that these limiting age estimates do not exactly correspond to MIS boundaries. Comparison between the calculated unit ages and the biogenic silica profile shows a good correlation for densely laminated Units Ia, IIa, and IIIa and sediment layers with high silica content (Fig. 5), consistent with the inferred deposition of Units Ia, IIa, and IIIa under warm climatic conditions. The changes in the biogenic silica content correlate with the SPECMAP profile of d 18O (Colman et al., 1995; Prokopenko et al., 2001a). Hence, Units Ia, IIa, and IIIa may correspond in age to MIS 1, 3, and 5a (Fig. 5).
of Unit Ia through Unit IIIa. Because fault movements of the northwest block and the southeast block have been different (AF7, AF8, AF9: Fig. 1b), the depth of each reflector is described independently. From the reflection patterns, Units IIa and IIIa appear to comprise the topset and the foreset beds of the delta. They form progradational delta during stable lake level, and the elevations of the topset beds approximate the paleo-levels of the lake. In some areas, however, the seismic profiles show that the topset beds dip toward deeper water, and they appear to have been eroded. Consequently, the true lake level at the time of delta formation was probably a few meters higher than the level delineated from seismic records, although the discrepancy is difficult to quantify. Average values for the upper limits of Unit IIa and Unit IIIa in the northwestern block are determined to be 30 and 35 m, respectively, relative to the modern lake level (456 amsl), and 22 and 25 m, respectively, in the southeastern block. Erosional surfaces on Unit IIa inferred from the seismic records suggest that lake levels were stable during cold periods, and therefore the fluctuations must have occurred during climatic transitions. Unit Ib and Unit IIb appear to onlap the underlying units, and we consider them to have been deposited during such transitions from cold to warm periods. Lake levels then probably
Development of the delta Delta systems of Unit IIIa and Unit IIa show a pattern of aggradational conformities (Fig. 6). However, in the southern part of southeastern block (Fig. 1b; L57–L59), these units show a back-step pattern, which indicates a wave-cut terrace, developed over a considerable period of time. Subsidence along each fault has created topographic depressions, but it has not had a major effect on the delta system. Relative lake-level change The shallow sediment around the delta records the fluctuation of the lake level. Below, we discuss lake-level changes on the basis of the distribution patterns and depths
Figure 5. Correlation of the d 18O from the North Atlantic, biogenic silica content from Lake Baikal, and relative lake-level changes. (a) d 18O record is after Martinson et al. (1987). (b) Diatom content used by Grachev et al. (1997) (original data from Prof. M. Grachev, personal communication, 2003). (c) The relative lake-level fluctuations determined from the depth of seismic unit. Lake-level changes occur when the climate changes, approximately at MIS boundaries.
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Unit IIa Unit Ib Unit IIb
Unit IIIa
Unit IIa Unit Ib
Unit IIa
Unit IIb
Unit IIIa
Figure 6. Events in the delta development. MIS 5a: Formation of Unit IIIa. MIS 4: Lowering of the lake level and deposition of Unit IIb. MIS 3: Rise of the lakelevel and deposition of Unit IIa, which is aggradated to Unit IIIa. MIS 2: Lowering of the lake-level and deposition of Unit Ib. Formation of a back step or riser and a flat plane by wave cutting indicates that the lake-level was stabilized during the cold stage. The sediments of transgressive stage are not recognized. MIS 1: Deposition of Unit Ia, corresponding to the modern prograding delta.
corresponded to the upper limit of each unit plus the water depth. However, the upper limits of the units are commonly erosional surfaces, so the recovered levels may be minima (Fig. 3; L60). Average levels for the upper limits of Unit Ib and Unit IIb were determined at 45 and 73 m, respectively, in the northwestern block, and 33 and 58 m, respectively, in the southeastern block. Thus, the difference between the upper limits of Unit IIIa and Unit IIb in the northwestern block is 38 m in the northwestern block and 15 m in the southeastern block, and the respective differences between the upper limits of Unit IIa and Unit Ib are 33 and 11 m. These differences reflect the drop of lake level between Unit IIIa and IIb time. The present depths of the upper limits of the units (Fig. 5c) do not record absolute lake level because these depths have been affected by tectonic subsidence. However, the tectonic subsidence of 0.02 mm yr 1 in the northwestern block and 0.03 mm yr 1 in the southeastern block (assuming similar hydrological conditions during MIS1 and 5) accounts for only a small fraction (~2%) of the total inferred fluctuations in lake level, and we regard climatic change as the main cause of the lake-level changes. This is consistent with our correlation of sedimentation patterns and the marine climate record. If the warm and cold periods inferred from the sedimentary record do correspond to marine oxygen isotope stages, the lake level fell 33–38 m between MIS 5 and MIS 4 and 11–15 m between MIS 3 and MIS 2. Climatic inferences Temperature and precipitation in glacial periods at Lake Baikal have not been accurately estimated. However,
precipitation during the Last Glacial Maximum can be inferred to have decreased sharply, because pollen analysis shows that the region was cold and dry (tundra or barren arctic desert) then (Oda et al., 2000). Similar pollen records from France suggest that precipitation during glacial periods there decreased by 30% (Guiot et al., 1989). Significant lowering of temperature and decrease in precipitation are indicated in high-latitude regions. Present river influx at Lake Baikal is ~60 km3 yr 1, and evaporation is ~10 km3 yr 1 (Afanasyev, 1960; Shimaraev et al., 1994). The changing imbalance of river inflow and evaporation, and overflow down the Angara River, causes the observed lakelevel fluctuations. Although evaporation decreases in glacial periods, river inflow and precipitation on the lake surface also decrease, by about 15%, and lake level gradually falls then. Therefore, decreasing precipitation seems to be the phenomenon that controls lake level at Lake Baikal.
Summary This study analyzed of high-resolution seismic data in the shallow part of Selenga delta, calibrated by two 14C dates and correlated with analysis of sediment cores. It demonstrated that the water level in Lake Baikal decreased during the cold stages MIS 4 and 2. Lake level appears to respond to regional variations in temperature and precipitation, rising during warm periods and falling during cold periods, correlative with global climate changes. The fall in the lake level near the Selenga delta from MIS 5 through MIS 4 is estimated at 33–38 m, and from MIS 3 through MIS 2 at 11–15 m.
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Acknowledgments We are grateful to Professors Grachev and Mats of the Limnological Institute, Captains of the R/V Titov and R/V Vereshchagin, as well as the crews of the Titov and Vereshchagin for their assistance during the cruise. We thank Mrs. Yasukevich, and Mr. Reshetov, Mr. Kirill (translator) and Mrs. Naja (secretary of BICER), all of whom helped us in this study. References Afanasyev, A.N., 1960. The water budget of Lake Baikal: transactions of the Baikal Limnological Station. Academic Nark SSSR Vista, Siberia 18, 115 – 241. Colman, S.M., 1998. Water-level changes in Lake Baikal, Siberia: tectonism versus climate. Geology 26, 531 – 534. Colman, S.M., Peck, J.A., Karabanov, E.B., Carter, S.J., Bradbury, J.P., King, J.W., Williams, D.F., 1995. Continental climate response to orbital forcing from biogenic silica records in Lake Baikal, Siberia. Nature 378, 769 – 771. Colman, S.M., Jones, G.A., Rubin, M., King, J.W., Peck, J.A., Orem, W.H., 1996. AMS radiocarbon analyses from Lake Baikal, Siberia: challenges of dating sediments from a large, oligotrophic lake. Quaternary Science Reviews 15, 669 – 684. Colman, S.M., Peck, J.A., Hatton, J., Karabanov, E.B., King, J.W., 1999. Biogenic silica records from the BDP93 drill site and adjacent areas of the Selenga Delta, Lake Baikal, Siberia. Journal of Paleolimnology 21, 9 – 17. Colman, S.M., Karabanov, E.B., Nelson, C.H., 2003. Quaternary sedimentation and subsidence history of Lake Baikal, Siberia, based on seismic stratigraphy and coring. Journal of Sedimentary Geology 73, 941 – 956. Grachev, M.A., Likhoshway, Ye.V., Vorobyova, S.S., Khlystov, O.M., Bezrukova, E.V., Veinberg, E.V., Goldberg, E.L., Granina, L.Z., Koenakova, E.G., Lazo, F.I., Levina, O.V., Letunova, P.P., Otinov, P.V., Pirog, V.V., Fedotov, A.P., Yaskevich, S.A., Bobrov, V.A., Sukhorukov, F.V., Rezchikov, V.I., Fedorin, M.A., Zolotaryov, K.V., Kravchinsky, V.A., 1997. Signal of the paleoclimates of Upper Pleistocene in the sediments of Lake Baikal. Russian Geology and Geophysics 38, 957 – 980. Grachev, M.A., Vorobyova, S.S., Likhoshway, Y.V., Goldberg, E.L., Ziborova, G.A., Levina, O.V., Khlystov, O.M., 1998. A highresolution diatom record of the paleoclimates of east Siberia for the last 2.5 My from Lake Baikal. Quaternary Science Reviews 17, 1101 – 1106. Guiot, J., de Beaulieu, J.L., Pons, A., Reille, M., 1989. A 140,000-year continental climate reconstruction from two European pollen records. Nature 338, 309 – 313. Harrison, S.P., 1989. Lake-levels and climatic changes in eastern North America. Climate Dynamics 3, 157 – 167.
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