Reconstructions of the early and middle Holocene climate and environment based on δ13C and δ18O records in biogenic carbonates; Lake Niepruszewskie, western Poland

Abstract

The present study investigates environmental conditions during sediment accumulation in Lake Niepruszewskie, western Poland. Palaeolimnological reconstructions are based on stable isotope composition (δ¹³C and δ¹⁸O) of a wide range of biogenic carbonates occurring in the sediments, including shells of several gastropod species and the bivalve genus Pisidium, carapaces of ostracods belonging to the subfamily Candoninae and encrustations and oogonia of the aquatic macrophyte genus Chara. According to the radiocarbon dates obtained, accumulation of the sediment sequence began in the early Atlantic and terminated in the early Subboreal. Both δ¹³C and δ¹⁸O records reveal significant and frequent fluctuations that are attributed to repeated changes in the Lake Niepruszewskie water balance. However, conditions of prevailing long water residence time, accompanied by high productivity within the lake, are reflected in a ¹³C-enriched carbon-isotope record.Minimum δ¹³C and δ¹⁸O values were recorded for the earliest Atlantic and maximum values characterize the interglacial optimum during the middle and late Atlantic. Discrepancies observed between isotope records of particular taxa reflect the specific season and subhabitat of each carbonate secretion. ¹³C-enriched Chara encrustations and oogonia are consistent with their precipitation within the photic zone, which is commonly ¹³C-enriched due to the photosynthetic activity of macrophytes and phytoplankton. The carbon isotope composition of Lymnaea auricularia shells indicates that breathing behaviour leaves its imprint on δ¹³C in snail shells. In aquatic air-breathing pulmonate gastropods this results in ¹³C-depletion in shells. Isotope records of individual shells of two snail species, Valvata piscinalis and Gyraulus laevis, indicate that in order to obtain mean δ¹³C and δ¹⁸O values that are representative of a 5 cm thick sampling interval, stable isotope signatures of more than five shells must be obtained.