Alexander A. Prokopenko

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.

RESPONSE OF LAKE BAIKAL ECOSYSTEM TO CLIMATE FORCING AND PCO2 CHANGE OVER THE LAST GLACIAL/INTERGLACIAL TRANSITION

Abstract The δ 13 C record of total organic carbon in the Lake Baikal core BDP-93-2 over the last glacial/interglacial transition shows remarkable correlation with atmospheric CO 2 fluctuations and the negative isotopic shift of 3.5–4‰ in response to the global increase in paleo- p CO 2 level. With rapid evolution of the Lake Baikal carbon cycle from full glacial to full interglacial modes, however, the p CO 2 signal in the Baikal δ 13 C sedimentary organic matter is inundated by the basin-wide productivity signal, in the Holocene. The Baikal diatom abundance record, as a paleotemperature proxy, lags behind the GISP2 ice core δ 18 O temperature proxy record by ca. 1 ka, possibly reflecting the response time of the Baikal ecosystem to major climatic transitions. There is no lag associated with the pronounced Younger Dryas cooling, however, suggesting a different forcing mechanism, with a short response time, for this abrupt climatic event in continental interior Asia. The phase difference observed between the diatom abundance and δ 13 C proxies in Lake Baikal core BDP-93-2 suggests their independent responses to different forcing mechanisms, further justifying their importance for paleoclimate reconstructions from Lake Baikal records.

Continental response to Heinrich events and Bond cycles in sedimentary record of Lake Baikal, Siberia

Abstract The sedimentary core BDP-93-2, Lake Baikal, southeast Siberia, provides a high-resolution record of the interval corresponding to marine oxygen isotope stage 3 (MIS 3). Sharp drops in fossil diatom abundance suggest the occurrence of short-term cooling episodes in Lake Baikal area during this time interval. AMS radiocarbon dates on core BDP-93-2 constrain the age of the upper three episodes (younger than 24 ka BP, younger than 30.5 ka BP, older than 34 ka BP) and therefore permit correlation of the Baikal diatom abundance record with records of iceberg discharge (Heinrich) events in the North Atlantic. Lithology of BDP-93-2 at the Selenga Delta indicates that cooling episodes are also associated with deposition of distinct layers of brownish mud enriched in terrestrial organic carbon. Thus, two types of signals associated with Heinrich events and Bond cooling cycles are observed in the sedimentary record from Lake Baikal. The lacustrine response to cooling episodes includes basin-wide decreases in diatom production, and the response of the catchment basin includes erosion of soils. These episodes of erosion, herein recognized as “Kuzmin events”, are likely related to dramatic changes in atmospheric precipitation regime that impacted the semi-arid provinces of Lake Baikal watershed over the short periods of time represented by these events.

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.

Deglacial methane emission signals in the carbon isotopic record of Lake Baikal

Changes in the concentrations of atmospheric greenhouse gases constitute an important part of global climate forcing. Here we present the first continental evidence for climatically caused changes in a methane gas hydrate reservoir. The organic carbon stable isotope record from Lake Baikal during the past 130 000 years registers regular emissions of isotopically light carbon by the occurrence of distinct negative shifts of 3–5‰ at every major orbitally forced cold-to-warm climatic transition during the past 130 000 years, including marine oxygen isotope stage boundaries 6/5e, 5d/5c, 5b/5a and 2/1. We conclude that these emissions were associated with decomposition of sedimentary clathrates, widespread in the Baikal basin. Among potential hypotheses to account for these methane episodes, the most probable appears to be hydrate dissociation due to deglacial warming of lake water. We estimate that as much as 12–33 Tg of methane could have been released with each episode. By recording the systematically recurring episodes of massive methane clathrate decomposition closely linked with the northern hemisphere temperatures during major orbital warmings, the new Baikal δ13C record provides further evidence for the potential involvement of clathrate reservoir in rapid deglacial rises of atmospheric methane levels.

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.

Depleted methane-derived carbon in waters of Lake Baikal, Siberia

Results of hydrochemical and stable isotope measurements during the ice-breaking period on Lake Baikal indicate an apparent lack of relationship between measured δ13C of dissolved inorganic carbon (DIC) and phytoplankton below the trophogenic layer. While planktonic values of −31.7 to −33.5‰ are within a typical lacustrine range, the δ13C values of DIC turned out to be very negative, from −28.9 to −35.6‰. These isotopic values of DIC appear to be associated with oxidation of methane that accumulated during winter ice cover period. At the time of sampling, however, the observed depletion did not affect the phytoplankton/DIC fractionation relationship, because the difference between phytoplankton and DIC (−20 to −22‰ in surface waters) lies within the expected range of the fractionation coefficient. By analogy with small lakes, we explain this lack of relationship by the time lag between peak productivity and peak methane oxidation. Our interpretation of the Baikal DIC isotopic signature is consistent with methanogenesis in bottom sediments and with the known presence of widespread unstable gas hydrates and active methane seeps on the lake floor. Our findings suggest that methane is an important component of the Baikal carbon cycle, that late winter concentrations of methane in Baikal under ice may be 3–4 orders of magnitude higher than previously reported values for summer, and that the lake may be emitting a significant amount of methane to the atmosphere.

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.

Glacial/Interglacial Changes in the Carbon Cycle of Lake Baikal

This chapter presents a conceptual framework for understanding the impact of glacial/interglacial climate changes on the carbon cycle of Lake Baikal. To do so, we bring together evidence from mass-balance estimates, from the carbon and nitrogen compositions of plankton, particulate organic matter and the surface layer of bottom sediments, and watershed soils and riverine sediments, as well as from Lake Baikal organic sedimentary records of the last glacial/interglacial transition and of the last climatic cycle to 130 Ka BP. The goal of this synthesis is to offer new ways of examining organic carbon paleoproductivity records.