High-resolution pollen records from Lake Baikal revealed considerable regional differences in the vegetation development and pronounced climate variability during the last glacial-interglacial transition and Holocene. Correlation between cores was successfully based on a chronology constructed from AMS 14 C dating of pollen concentrates. Comparison to other radiocarbon-dated pollen sequences from the Baikal region suggests that the chronology presented is very reliable and thus correlation to other dated events can easily be performed. Pollen indices, which reflect relative changes in major vegetation types and limitations of growing conditions by moisture availability and temperature, demonstrate near-synchronous vegetation changes, which suggest synchronous large-scale climate variation across the Baikal region. Due to the low level or even absence of human impact in the Lake Baikal region, the pollen data illustrate that in the continental interior of NE Eurasia Holocene climate variability was very pronounced. After initial warming and a strong increase in relative moisture (ca. 15-14.6 cal ka BP) the Bölling / Alleröd like event was punctuated by three cool and dry events. These events at approx. 14.2 ka BP, 13.8 ka BP and 13.2 cal ka BP can be compared to coolings as recorded in GISP 2 oxygen isotope records from Greenland ice cores. An expansion of Betula sect.Nane/Fruticosae, Artemisia and Chenopodiaceae marks the Younger Dryas-like cooling event (ca. 12.5-12 cal ka BP).
High temperatures and favourable moisture conditions during the first part ofHolocene favoured the optimum development of dark-coniferous taiga between 10-8 cal ka BP in the south and 9.0-7.5 cal ka in the northeast. A fir and spruce decline in the southern mountains (ca. 8-7 cal ka BP) can be related to the 8.2 cal ka BP cooling event. The pronounced mid-Holocene cooling event and a transition towards dry conditions (ca. 7.0-5.5 cal ka BP) preceded the nearly synchronous regional expansion of pine taiga.Maximum distribution of Scots pine forests marks the Holocene thermal optimum (ca. 6.5 -5.7 cal ka BP), which was followed by two subsequent cooling events (ca. 5.5-
ABSTRACT. This work focuses on the preparation and dating of sporomorph (pollen and spores) concentrates of high purity. Three sediment cores recovered from Lake Baikal within the EU-Project CONTINENT were subjected to palynological analyses and accelerator mass spectrometry (AMS) radiocarbon dating. Laboratory processing of concentrates was aimed at the removal of non-sporomorph organic matter by means of chemical treatment, micro-sieving, and heavy liquid separation. The obtained concentrates were checked under the microscope and sample purity was estimated on the basis of particle counts. The results of AMS 14 C dating show differences in the sedimentation rate among 3 sites of Lake Baikal.
METHODSLake Baikal is situated in southeast Siberia in the eastern part of the Russian Federation near the Mongolian border. It is the largest (20% of the total volume of surface freshwater), deepest (>1600 m), and probably oldest (about 25 million yr) lake on Earth.Radiocarbon dating of Lake Baikal sediments is a difficult challenge, as previous studies have proved (Coleman 1996). The main problem is the scarcity of material suitable for dating because the sediments are very poor in organic matter and carbonates. Our work focused on the preparation and dating of high-purity sporomorph concentrates.Three sediment cores recovered from Lake Baikal were subjected to palynological analyses and AMS 14 C dating. The cores come from 3 different locations: Posolskoe Bank, Vydrino Shoulder, and Continent Ridge (see Figure 1). The cores subjected to dating were collected with the use of a Kasten corer, which gives the best assurance of complete recovery of the sediment.The preliminary knowledge about sporomorph concentrations and sporomorph assemblages in Holocene and Late Glacial core sections, necessary for selecting appropriate subsampling levels, was gained during palynological analyses of these cores. Sample sizes ranged between 20 and 160 cm 3 (see Table 1), depending on available material, pollen concentrations, and a rough calculation of pollen mass and carbon content using data available from previous studies (Erdtman 1969;Brown et al. 1989). The volume of samples taken for preparation was adjusted to obtain a minimum carbon content of about 2-4 mg per sample.
Extraction of SporomorphsLaboratory processing of pollen and spore concentrates was aimed at achieving a high purity of the samples. The removal of inorganic and non-sporomorph organic matter was carried out using chemical treatment, micro-sieving, and heavy liquid separation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.