Late glacial and Holocene vegetation and regional climate variability evidenced in high-resolution pollen records from Lake Baikal

Abstract

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-

Clay-mineral record in Lake Baikal sediments: The Holocene and Late Glacial transition

“…Similar but less pronounced palynological assemblage changes are also recorded in the southern basin (P4a, Fig. 2A; Demske et al, 2005). The significant cooling during the Younger Dryas is also recorded in West Siberian palynological records (Khotinsky, 1984a;Velichko et al, 2002).…”

“…2A. The Younger Dryas/Preboreal transition derived from either the palynological zonation (Demske et al, 2005) or the 14 C age model (Piotrowska et al, 2004) are quite consistent with the geomagnetic age model (Fig. 2A).…”

“…The Younger Dryas is marked by a pronounced cooling and very dry conditions (Velichko et al, 2002). In the northern basin, palynological zone C-3b is marked by an arboreal pollen assemblage without dark taiga species but abundant sub-alpine shrubs: C-3b reflects a cold climate related to the Younger Dryas period (Demske et al, 2005). Similar but less pronounced palynological assemblage changes are also recorded in the southern basin (P4a, Fig.…”

“…According to the mean sedimentation rates, the centimeter-scale sampling step allows for a temporal resolution of the order of 100 years: the average time span between two consecutive samples is ~ 60 to 250 yr. Roberts (2002) (Demske et al, 2005) and radiocarbon age model (Piotrowska et al, 2004) . Note the consistency between the palynological zonation, the radiocarbon and palaeomagnetic (Demory et al, 2005) …”

“…On a local scale we will compare our clay results with biological proxies: i.e., the palynological reconstructions established on adjacent box cores in the southern and northern basins (Demske et al, 2005; cfr. Fig.…”