Palaeoenvironmental Changes

A sedimentary core recovered from the cirque basin of Labský důl valley (1039 m a.s.l.) in the Krkonoše Mountains reflects the environmental history for approximately the last 30 000 years. Analyses of magnetic susceptibility, carbon content, pollen assemblages and macrofossil data in a 15 m thick sediment sequence provide the first continuous record of Lateglacial and Holocene vegetation history in Sudetes region of the Czech Republic. The succession of sedimentary units in the lower part of the core suggests that the cirque was ice-free before the onset of the last glaciation at the beginning of marine isotope stage 2. Highly variable climate prevailed during this period with cold conditions culminating about 18 cal ka BP. Cold climates persisted until the Lateglacial period, evidenced by an identified warming and subsequent cooling event correlated with the Younger Dryas period. Sparse, treeless vegetation dominated in the catchment area at that time. The sequence of interrupted thinly laminated silts reflects the retreat and temporary readvance of a local glacier in the cirque during 12.5–10.8 cal ka BP. Subsequently, the alpine treeline ecotone gradually shifted above the cirque floor. Palaeoclimatic conditions in the early Holocene fluctuated strongly, whereas since 5.1 cal ka BP conditions have been more stable. Pollen-based climate reconstructions suggest significant cooling at around 9.8–9.3, 7.7–7.5 and 4.0–3.3 cal ka BP. Spruce forests have dominated the site since 5.0 cal ka BP when the vegetation became similar to the modern one. Two phases of increased sedimentation were identified within the Holocene culminating about 9.2–7.5 cal ka BP and 5.8–5.5 cal ka BP. Sediment yield was as high as 2.4 mm·yr–1 during the period reflecting environmental changes during the Atlantic/Sub-Boreal transition.

In order to obtain information about landscape activity and stability during the Late Quaternary in the Transcaucasian region, fluvial sediments of the lower Algeti River in SE-Georgia were studied by means of geomorphologic, sedimentologic and geochronologic methods. These investigations show that sediments aggraded by the Late Pleistocene braided Algeti River were strongly incised around the Pleistocene/Holocene transition, and subsequently a small-scale pattern of diachronous fluvial terraces deposited by the now meandering river developed in the new valley during the Holocene. Prior to ca. 3 cal. ka BP, active phases of river channel aggradation and overbank sedimentation about 6 cal. ka BP and 3.4–3.2 cal. ka BP can be linked with climate-driven vegetation changes, i.e. stronger fluvial dynamics with sedimentation occurred during more arid and colder periods whereas the Caucasian Holocene climate optimum between 6 and 3.4 cal. ka BP was characterized by stable geomorphologic conditions. After 3 cal. ka BP, strongly increased human impact documented by former pollen studies is reflected by the fluvial dynamics as well, i.e. an activity phase of strong overbank sedimentation 2.7– 2.1 cal. ka BP occurred during a period when forests in the Lesser Caucasus were burnt down. Two subsequent activity phases with fluvial sedimentation can be linked with historic events that probably both influenced vegetation distribution of the region, i.e. a period of flourishing of Georgia during the Middle Age and a time of large scale destruction of the country due to a Persian invasion at the end of the 18th century AD, respectively. Thus, whereas no influence of tectonic events or fluctuations of the Caspian Sea level on the fluvial dynamics could be detected, SE-Georgia shows its fragile character with respect to climate- and human driven vegetation-changes similar to other semi-arid landscapes of the Mediterranean region.

A sedimentary core recovered from the cirque basin of Labsk y dů l valley (1039 m a.s.l.) in the Krkonoše Mountains reflects the environmental history for approximately the last 30,000 years. Analyses of magnetic susceptibility, carbon content, pollen assemblages and macrofossil data in a 15 m thick sediment sequence provide the first continuous record of Lateglacial and Holocene vegetation history in Sudetes region of the Czech Republic. The succession of sedimentary units in the lower part of the core suggests that the cirque was ice-free before the onset of the last glaciation at the beginning of marine isotope stage 2. Highly variable climate prevailed during this period with cold conditions culminating about 18 cal ka BP. Cold climates persisted until the Lateglacial period, evidenced by an identified warming and subsequent cooling event correlated with the Younger Dryas period. Sparse, treeless vegetation dominated in the catchment area at that time. The sequence of interrupted thinly laminated silts reflects the retreat and temporary readvance of a local glacier in the cirque during 12.5-10.8 calka BP. Subsequently, the alpine treeline ecotone gradually shifted above the cirque floor. Palaeoclimatic conditions in the early Holocene fluctuated strongly, whereas since 5.1 cal ka BP conditions have been more stable. Pollen-based climate reconstructions suggest significant cooling at around 9.8-9.3, 7.7-7.5 and 4.0-3.3 cal ka BP. Spruce forests have dominated the site since 5.0 cal ka BP when the vegetation became similar to the modern one. Two phases of increased sedimentation were identified within the Holocene culminating about 9.2-7.5 cal ka BP and 5.8-5.5 cal ka BP. Sediment yield was as high as 2.4 mm yr À1 during the period, reflecting environmental changes during the Atlantic/Sub-Boreal transition.