M. I. Kuzmin

Muted climate variations in continental Siberia during the mid-Pleistocene epoch

The large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 (MIS 12) and MIS 11, spanning the interval between about 480 and 380 kyr ago, has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period, with consequences for global ice volume, sea level and the global carbon cycle. The extent of the change is intriguing, because orbital forcing is predicted to have been relatively weak at that time. Here we analyse a continuous sediment record from Lake Baikal, Siberia, which reveals a virtually continuous interglacial diatom assemblage, a stable littoral benthic diatom assemblage and lithogenic sediments with ‘interglacial’ characteristics for the period from MIS 15a to MIS 11 (from about 580 to 380 kyr ago). From these data, we infer significantly weaker climate contrasts between MIS 12 and 11 than during more recent glacial–interglacial transitions in the late Pleistocene epoch (about 130 to 10 kyr ago). For the period from MIS 15a to MIS 11, we also infer an apparent lack of extensive mountain glaciation.

The Lake Baikal drilling project in the context of a global lake drilling initiative

Abstract Records of the tectonic and climatic evolution of continental interiors are important for understanding the dynamics of the Earths climate system, evolutionary processes within the terrestrial biosphere, and human origins. Sediment drill cores recovered from Lake Baikal provide essential records not only for comparison with oceanic records of marine processes, but also benchmarks which can be used to help interpret other continental records including other lake archives scheduled to be drilled in the near future. Drilling of Lake Baikal made it possible for the first time to have a continental archive with the same scientific and chronostratigraphic integrity as marine records to address critical questions of the Quaternary and Pliocene. The Lake Baikal drilling project (BDP) rapidly progressed from piston coring and seismic reflection studies to conducting the first scientific drilling in 4 short years and to very deep drilling in over 8 years. BDP has taken advantage of the harsh Siberian winters by using the frozen surface of Lake Baikal as a drilling platform. The positioning of the drill sites was selected using seismic and piston coring surveys. By continuously improving the drilling operations and technology, BDP has achieved new core recovery and depth records over the last ten years and become the worlds leader in pioneering the recovery of high-quality, extremely long lacustrine sediment sequences from deep water. The success of BDP came at a time of growing interest in lake drilling among members of the paleoclimate community with few recent large-scale coordination efforts to draw upon. At the organizational, technological and financial levels, some recent changes are favorable for the development of a global lake drilling initiative, which could become as successful and efficient as the ocean drilling program.

Magnetic record of Lake Baikal sediments: chronological and paleoclimatic implication for the last 6.7 Myr

Magnetic remanence vectors for 1472 samples taken from a 601 m core through Lake Baikal sediments are reported along with a complete magnetic susceptibility profile obtained from a pass-through system. Matching the stable remanence directions to the standard geomagnetic polarity time scale (GPTS) provides a robust chronology from the present back to V6.7 Ma and yields a remarkably constant sediment accumulation rate of 3.9 cm/kyr. For earlier times ^ represented by depths s 270 m ^ correlation to the GPTS is more problematic. Susceptibility fluctuations reflect climatic changes that can be matched to the marine oxygen isotope pattern for the last 6.7 Myr. Spectral analysis of the resulting susceptibility time series then indicates that, for the most part, the Milankovitch obliquity signal dominates. However, when the temporal evolution of the frequency content is investigated by analyzing sequences of time windows, a complex picture emerges in which eccentricity and precession power appear during some intervals. Furthermore, there is persistent evidence for significant power in a ‘non-Milankovitch’ band between 28 and 35 kyr. A 2003 Elsevier Science B.V. All rights reserved.

Biostratigraphic significance of new fossil species of the diatom genera Stephanodiscus and Cyclotella from upper Cenozoic deposits of Lake Baikal, Siberia

Three new extinct taxa of the genus Stephanodiscus Ehrenberg (S. williamsii sp. nov., S. princeps sp. nov., S. yukonensis var. antiquus var. nov.) and four new extinct species and two new extinct varieties of the genus Cyclotella (Kutzing) Brebisson (C. iris var. insueta var. nov., C. tempereiformica sp. nov., C. distincta sp. nov., C. comtaeformica sp. nov., C. comtaeformica var. spinata var. nov. and C. praeminuta sp. nov.) are described from Upper Cenozoic lacustrine sediments of Lake Baikal (boreholes BDP-96-1 and BDP-96-2). The narrow biostratigraphic ranges of the new taxa warrant their use as index-fossil species for defining a diatom zonation, for accurate correlation and age control of Lake Baikal sediments. The comparative morphological analysis of the newly described Cyclotella taxa allowed us to trace the evolution of morphological features in these diatoms through time. The short time intervals during which the Stephanodiscus taxa existed in ancient Baikal imply that these species were unable to adapt to rapidly changing paleoecological and paleolimnological conditions caused by abrupt Pleistocene climatic fluctuations.

Evolution of freshwater centric diatoms within the Baikal rift zone during the late Cenozoic

Publisher Summary The evolution of freshwater centric diatoms within the Baikal rift zone during the late Cenozoic is associated with processes of extinction and renewal and reflects global climatic changes. The Pliocene and Pleistocene history of centric diatoms is documented most completely in Lake Baikal sediments penetrated by two drill holes BDP-96-1 (200 m deep) and BDP-96-2 (100 m deep) at the top of the underwater Academician Ridge. A detailed Pliocene–Pleistocene record of diatom species and diatom biostatigraphy of a 200 m sedimentary section are presented. The record shows that intense speciation of diatoms corresponds to the time at 1.5 Ma (early Pleistocene) and appears to be related to the beginning of Siberian glaciations. The Middle and Late Miocene diatom community within the Baikal Rift Zone extends from the Tunka depression, located 60 km west of the southern edge of Lake Baikal. Re-examination of this diatom assemblage by SEM allowed more precise definition of the morphological features of certain centric diatoms, and identification of new extinct taxa, Lobodiscus sibericus , Actinocyclus tuncaensis, Alveolophora tscheremissinovae, Aulacoseira praegranulata var. tuncaica, Cyclotella tuncaica, and Stephanodiscus tuncaensus.

Polychlorinated biphenyls in surface soil in urban and background areas of Mongolia.

Polychlorinated biphenyls (PCBs) were measured in soil in some industrial towns (Ulaanbaatar, Suhbaatar, Erdenet, Darhan, Tsetserleg, Hovd, Ulaangom, Altay, Bayanhongor, Arvayheer, Saynshand, Choybalsan) and in background and rural areas of Mongolia. The average sum of all investigated PCB congeners in soil of Mongolia comes to 7.4 ng/g dry weight (DW) and varies from 0.53 ng/g DW till 114 ng/g DW. PCB levels in soil from towns are significantly higher than those in soil from background and rural areas. The PCB homological composition in soil sampled in highly-PCB-polluted sites is similar to the PCB homological pattern in Sovol and Aroclor 1254. Significant correlation between soil organic carbon and low chlorinated PCB both for towns and background sites was found. Significant differences in PCB means in soil in different natural zones were found.

Yb, Eu, and (Yb + Eu)-stabilized 3 × 1 and 3 × 2 reconstructions on Si(1 1 1)

The atomic arrangement of Si(1 1 1)3 × 1 and 3 × 2 surfaces stabilized by adsorption of divalent rare-earth metals (RE=ytterbium (Yb) and europium (Eu)) in the range of 0.1–0.33 monolayer (ML) has been studied by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The 3 × 2 surface is shown to have the metal coverage of 1/6 ML and possess the atomic arrangement which is independent on the nature of adsorbed RE atoms. Based on the analysis of empty and filled-state STM images, the honeycomb-chain-channel structure is proposed for Yb and Eu-induced 3 × 2 reconstructions, with the adsorption sites of metal atoms being strongly shifted from T4 or H3. A poor ordering of RE atoms in this structure results in 1/2-order LEED streaks in narrow energy range (60–80 eV). The origin of 3 × 1 reconstruction is discussed in terms of present results as well as previously published data.

High‐Resolution Mis 11 Record from the Continental Sedimentary Archive of Lake Baikal

The sedimentary record of Lake Baikal reveals details about the climatic response of continental Asia during the interval 423-362 Ka BP, corresponding to marine oxygen isotope stage MIS 11. The MIS 11 record in Lake Baikal is marked by two plateaus of high biogenic silica content corresponding to MIS 11.3 and 11.2. The middle part of MIS 11 (substage 11.2) exhibits the highest biogenic silica accumulation, reflecting the warmest regional climate, of the last 450 Ka. These interglacial conditions in continental Asia were uninterrupted for about 32 Ka, making MIS 11 the longest interglacial in Siberia, greatly exceeding the duration of interglacial conditions during MIS 5e, 7e and 9e. This extremely long and warm interglacial period of MIS 11.3-11.2 in Siberia ended abruptly with dramatic cooling at 394-390 Ka BP. This cooling resulted in brief mountain glaciation in Siberia due to the amplified response of continental Asia to insolation forcing. The cooling during MIS 11 produced irreversible change in the climate of continental Asia as suggested by diatom succession and by biogenic silica accumulation. Diatom species composition further reveals more complex structure of MIS 11 and makes a strong case for insolation control of diatom production in Lake Baikal.

Glaciations of central asia in the late cenozoic according to the sedimentary record from lake baikal

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

Formation of an ordered pattern of Bi nanolines on InAs(100) by self-assembly

Self-assembly of uniform patterns of nanolines over large surface areas has been proven to be difficult. The authors report that bismuth (Bi) adsorbate self-assembles into an ordered pattern of Bi nanolines separated by 4.3nm on the Bi-stabilized InAs(100)(2×1). The resulted nanoline surface is studied by scanning tunneling microscopy (STM) and low-energy electron diffraction. The plausible atomic models for the Bi nanolines are proposed on the basis of the STM results. The Bi lines are suggested to consist of two chains of adjacent Bi dimers positioned parallel to the chain and parallel to the Bi dimers of the (2×1) substrate.