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A sediment sequence was taken from a closed, high altitude lake (informal name Olive-backed Lake) in the central mountain range of Kamchatka, in the Russian Far East. The sequence was dated by radiocarbon and tephrochronology and used for multi-proxy analyses (chironomids, pollen, diatoms). Although the evolution of Beringian climate through the Holocene is primarily driven by global forcing mechanisms, regional controls, such as volcanic activity or vegetation dynamics, lead to a spatial heterogeneous response. This study aims to reconstruct past changes in the aquatic and terrestrial ecosystems and to separate the climate-driven response from a response to regional or localised environmental change. Radiocarbon dates from plant macrophytes gave a basal date of 7800 cal yr BP. Coring terminated in a tephra layer, so sedimentation at the lake started prior to this date, possibly in the early Holocene following local glacier retreat. Initially the catchment vegetation was dominated by Betula and Alnus woodland with a mosaic of open, wet, aquatic and semi-aquatic habitats. Between 7800 and 6000 cal yr BP the diatom-inferred lake water was pH 4.4–5.3 and chironomid and diatom assemblages in the lake were initially dominated by a small number of acidophilic/acid tolerant taxa. The frequency of Pinus pumila (Siberian dwarf pine) pollen increased from 5000 cal yr BP and threshold analysis indicates that P . pumila arrived in the catchment between 4200 and 3000 cal yr BP. Its range expansion was probably mediated by strengthening of the Aleutian Low pressure system and increased winter snowfall. The diatom-inferred pH reconstructions show that after an initial period of low pH, pH gradually increased from 5500 cal yr BP to pH 5.8 at 1500 cal yr BP. This trend of increasing pH through the Holocene is unusual in lake records, but the initially low pH may have resulted directly or indirectly from intense regional volcanic activity during the mid-Holocene. The chironomid-inferred July temperature reconstruction suggests cool periods between 3200–2800 cal yr BP and 1100–700 cal yr BP and a warmer period between 2800 and 1100 cal yr BP. Chironomid and diatom DCA scores decline from ca. 6000 cal yr BP, indicating compositional changes in these aquatic assemblages. In comparison declines in pollen PCA scores are delayed, starting ca. 5100 cal yr BP. The results suggest that while catchment vegetation was responding primarily to climate change, the biota within the lake and lake water chemistry were responding to localised environmental conditions. [ABSTRACT FROM AUTHOR]

High resolution palaeoenvironmental records in Far-Eastern Russia are rare, and the Kamchatka Peninsula is among the least studied areas of the region. This paper describes a record spanning the last ca. 11,000 yr, obtained from a bog in the southern part of Kamchatka. The radiocarbon dated core was analysed for pollen, testate amoebae, charcoal and loss-on-ignition (LOI). The vegetation during the early Holocene was dominated by grasses (Poaceae), birch ( Betula ) and heath (Ericaceae p. p.). Around 10,300 cal yr BP there was a substantial change in the vegetation cover to shrub alder ( Alnus viridis s.l.) stands with sedges and ferns (Polypodiophyta) as well as herbs such as meadow rue ( Thalictrum ) in the understory. In the surroundings of Utka peatlands started to form. The variations in the vegetation cover were most probably caused by climatic changes. At the beginning of sediment accumulation, before 10,300 cal yr BP, the composition of the vegetation points to cooler summers and/or decreased annual precipitation. Around 10,300 cal yr BP, changes in vegetation occurred due to rising temperatures and/or changed water regimes. Increased abundancies of dry indicating testate amoebae after 9100 cal yr BP point to intermediate to dry soil conditions. Between 8600 and 7700 cal yr BP tree alder ( Alnus incana ) was widely spread at the site which probably indicates optimal environmental conditions. The tephra layer at 381–384.5 cm (ca. 8500 cal yr BP) produces a strong impact on the testate amoebae assemblages. At 7700 cal yr BP there was a sudden drop of A. incana in the local vegetation. From this time on, A. incana and also A. viridis decrease continuously whereas Betula gradually increases. The upper part of the sequence (after 6300 cal yr BP) shows higher abundancies of meadowsweet ( Filipendula ) and sweet gale ( Myrica ) pollen. After 6300 cal yr BP, changes in testate amoebae demonstrate variable soil moisture conditions at the site. Between 3700 and 1800 cal yr BP, wet conditions dominate as dry indicating testate amoebae decrease. After 1800 cal yr BP soil conditions become more variable again but this time with dry dominating testate amoebae. In contrast to surrounding regions, there is no evidence of trees such as spruce or larch growing in the surroundings of the site even though those trees are characteristic of many eastern Siberian sites. This difference might be because of the maritime influence of the Okhotsk Sea. Even dwarf pine ( Pinus pumila ), which is currently widely dispersed in northern Kamchatka, became part of the local vegetation only during the last 700 yr. [ABSTRACT FROM AUTHOR]