Stará Jímka a Late Pleistocene glacial lake (Czech, Hercynicum, central Europe). Climatic and vegetation changes based on pollen, paleozoology, and abiotic proxies
Abstrakt
Two glacial cirques Stará Jímka (49.068° N, 13.403° E, 1 110 m a. s. l.) and Prášilské jezero Lake creating a step-like system occurred on the eastern slope of Poledník Mountain (1 315 m a. s. l.) (Bohemian Forest). Profile of Stará Jímka demonstrates paleoenvironment changes in the glacial lake and its catchment area during the Alleroed and Younger Dryas periods.
The limnic sediment of 5 m thickness was investigated by combining pollen and paleozoology (chironomids, cladocerans) analysis with macro-climate settings (Bryson model), and abiotic proxies. Laacher See Tephra (LST) layer was discovered by phosphorus enrichment (XRF element scanning) and by volcanic glass shards for the first time in the Czech Republic beyond the respected SW-NE transect through central Northern Europe.
LST had a position just above ASM 14C date 10970+-50 BP (Beta-366540). The Bayesian modeled age is 12820+-70 cal BP with a 95% probability range of 12970 to 12715 cal BP.
That corresponds to the age range of the Laacher See eruption (LSE), (Eiffel, W Germany). The Late Glacial vegetation development of Stará Jímka was divided into four phases (STJ 1-4).
The sedimentation (STJ 1) started in cooling interval in the Late-Glacial interstadial with vegetation cover of dwarf shrub steppe (wild grasses and heliophytes; Artemisia, Thalictrum) of willow, which grew here before the expansion of birch woodland. In the Late-Glacial interstadial Juniperus expanded into the previous herbaceous vegetation (STJ 2).
The forest withBetula domination suppressed heliophytic plants. Pinus pollen was in lower proportions than Betula which suggested reduced pine in the forests.
LSE induced short-term cooling; some vegetation taxa decreased (Betula nana, Betula, Cyperaceae) while Dryas octopetala and Pinus increased. Then the restoration of Betula forest was rather quick.
Water table was rather low, for example only Hydrocotyle colonized the bottom of the lake. Last two phases were dedicated to the Younger Dryas stadial with climatic deterioration.
The older phase (STJ 3) outlines not only preference to Pinus, Salix, Betula humilis and Alnus viridis, but also to arto-alpine herbal species. Such as period was reflected by frequent wildfires (quantitative charcoal analysis) and by the great change in paleolake ecosystem combined with the LSE and the onset of the Younger Dryas.
The younger part (STJ 4) is characterized with occurrence of Corylus, Pinus cembra and Betula nana.