The Late Pleistocene-Early Holocene palaeoenvironmental evolution in the SE Baltic region: a multi-proxy palaeolimnological approach based on the Kamyshovoe Lake record

The Kamyshovoe Lake (54 22 605` N, 22 ° 42 790` E, 189 m a.s.l.) sedimentary record in the southeastern Baltic Sea Region was studied to reconstruct climatic fluctuations and abiotic responses to them during Late Glacial and Early Holocene time. New results of geochemical, chironomid, isotopic, and palaeomagnetic data analysis were correlated with earlier evidence for lithological and palynological changes in the Kamyshovoe Lake record (Kublitsky et al., subm.). The fragment of the record studied encompassed an interval between ca. 16 000 and 6 500 cal. a BP. The results obtained have led the authors to the following conclusions: 1. Palaeoclimatic chironomid-inferred reconstruction reflects summer temperature fluctuations of approximately 5°C over the period of ca. 15 300 – 6 800 cal. a BP. Mean July temperature was shown to increase from ca. 15 300 to 14 370 cal. a BP with an exceptionally high reconstructed temperature (19.8°C). A decreasing trend for summer temperatures is observed between 14 370 and 12 000 cal. a BP, when a minimum temperature (11.5°C) was recorded. A steady but very smooth rising temperature trend with fluctuations between 12.5 and 14.0°C persisted until ca. 9 800 cal. a BP, when a warmer period (14.1 – 16.0°C) began. 2. The Kamyshovoe Lake sequence reflects clear environmental responses to short-term early Holocene climatic oscillations superimposed upon general warming: about 11 300 cal. a BP, 10 700 – 10 500 cal. a BP, and 10 000 – 9 800 cal. a BP. These cooling events are diagnosed by chironomid analysis and changes in the palynological spectrum, geochemical record and lithostratigraphy of the sediments. 3. Despite marked changes in the vegetation around Kamyshovoe Lake at the onset of the Holocene climatic warming dated at 11 700 cal. a BP, no clear sediment responses at that time have been detected. All available data, including recent geochemical, isotopic and palaeomagnetic evidence, prove that both the terrestrial and limnic environments remained unstable until ca. 11 500 cal. a BP, when the sedimentation environment began to transform markedly. The detailed study of bottom sediments from Kamyshovoe Lake has considerably expanded our knowledge of the climate and changes in the lake systems in the southeastern Baltic Sea Region at the Pleistocene-Holocene boundary. The results obtained show the significance of local factors and conditions which, together with global processes, could be responsible for differences in the response of natural systems to global trends. The study of Kamyshovoe Lake shows that in this case differences were indicated by the non-simultaneous and unequally distinct pattern of the response of individual natural components to global changes in climate.