Dan Hammarlund

Late Weichselian and early Holocene climatic and environmental changes are inferred from stable carbon and oxygen isotope records obtained on bulk and biogenic carbonates from the sediment sequence of Lake Lednica, western Poland. Along with sediment and pollen stratigraphic data, a wide range of carbonate components occurring in the sediments was analysed for delta C-13 and delta O-18, including shells of several gastropod species and the bivalve genus Pisidium, carapaces of the ostracod subfamily Candoninae and oogonia of the aquatic macrophyte genus Chara. The development of catchment soils and the onset of authigenic carbonate production in response to the climatic amelioration during the Late Weichselian are clearly reflected by rising carbonate content, distinct isotopic shifts in bulk carbonates and decreasing delta C-13 values of bulk organic matter in the sediments. The GI-1/GS-1 (the Bolling-Allerod Interstadial complex/Younger Dryas Stadial) and the GS-1/Preboreal transitions are marked by significant shifts in delta O-18 values of 2-3 parts per thousand, as well as by distinct changes in carbonate content, indicative of a decrease and a subsequent increase in mean annual temperature. Corresponding delta C-13 records reflect primarily changes in aquatic productivity, with favourable conditions for phytoplankton and macrophytes during GI-1 and the Preboreal resulting in persistent C-13 enrichment. The Younger Dryas Stadial is characterised by depletions in C-13 and O-18, with indications of a climatic tripartition. Consistent offsets in delta C-13 and delta O-18 between records obtained on specific carbonate components reflect vital effects in combination with seasonal characteristics and habitat preferences of the respective carbonate-precipitating biota. Largely parallel first-order variations in delta C-13 and delta O-18 of the different carbonate components demonstrate that individual isotope records may provide important palaeoclimatic information, although more detailed reconstructions can be obtained from multi-component analysis. Copyright (C) 2009 John Wiley & Sons, Ltd.