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Stable isotope composition ([delta^18]O and [delta^13]C) of biogenic carbonates derived from the Lake Lednica sediments at Rybitwy, western Poland, was applied to obtain data on climatic changes during the Late Glacial and early Holocene. A wide range of carbonates occurring in the sediments was analysed for [delta^18]O and [delta^13]C records, including shells of several gastropod species, the bivalve genus Pisidium and carapaces of ostracods belonging to the subfamily Candoninae. The [delta^18]O and [delta^13]C records reveal changes commonly observed for the Late Glacial and early Holocene with the exception of the low oxygen isotope values of the Bolling and Allerod Interstadials. The latter is interpreted as a consequence of [^18]O-depletion of the lake water resulting from gradual melting of the dead ice that still filled the deepest parts of the Lake Lednica valley during the period described. The Younger Dryas Stadial begins with the isotopically lightest values in the sequence; however, due to the [^18]O-depleted values of the Allerod Interstadial the Allerod/Younger Dryas boundary is poorly marked. The Younger Dryas/Preboreal transition is documented by a significant shift in [delta^18]O values of about 2-3[per mil], resulting from an increase in the mean annual temperature. The [delta^13]C record reflects the productivity level in the lake, with [^13]C-enriched carbonates during the Bolling and Allerod Interstadials, and the Preboreal and Boreal, when photosynthetic activity of phytoplankton and macrophytes was the most intensive. Differences in [delta^18]O and [delta^13]C values between mollusc shells and ostracod carapaces reflect the specific season and subhabitat of each carbonate secretion.
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