Elemental geochemistry of freshwater snail shells: palaeolimnology of a Holsteinian (MIS 11) deposit from eastern Poland

The elemental shell chemistry of two freshwater snails, Viviparus diluvianus (Kunth) and Valvata piscinalis (Müller) was studied for palaeoenvironmental purposes. The shells were collected from lake sediments from five Holsteinian (Marine Isotope Stage 11) sites in eastern Poland (Ossówka, Hrud II, Roskosz, Ortel Królewski and Szymanowo) and analysed for Ca, Mg, Sr, Mn and Fe. The Fe/Mn molar ratio was used as a redox indicator, with lower values (and high Mn concentrations) pointing to suboxic conditions. These occurred in the beginning of the Taxus zone and during the transition between the Taxus and Pinus‐Larix zones at Ortel Królewski, and in the Holsteinian thermal maximum (Carpinus‐Abies zone) at Roskosz Lake. Strongly reducing conditions, indicated by increased Fe and Fe/Mn values, prevailed at Ortel Królewski palaeolake in the middle of the Taxus zone, in the Pinus‐Larix zone and in the upper part of the Roskosz sequence. Indicators of anoxia correlate with eutrophic conditions, enhanced productivity and oxygen consumption due to organic matter decay. The most distinct environmental changes in the records are comparable to other central and northern European records and to the main climatic oscillations during the Holsteinian, inferred from palynological, malacological and isotopic data.     

Stable 18O and 13C isotope records of Viviparus diluvianus (Kunth, 1865) shells from Holsteinian (MIS 11) lakes of eastern Poland as palaeoenvironmental and palaeoclimatic proxies

The oxygen and carbon stable isotope composition of Viviparus diluvianus shells was determined in the palaeolakes of the Holsteinian interglacial (MIS 11) in eastern Poland: the Ortel Królewski, Hrud, Ossówka, Roskosz and Szymanowo lakes. The occurrence of V. diluvianus covers the Taxus zone, the so‐called intra‐interglacial cooling period (Pinus‐Larix zone), the climatic optimum (Carpinus‐Abies zone) and the post‐optimal period with an undefined pollen zone. The isotope record of V. diluvianus shells allowed palaeoclimate and palaeoenvironmental reconstructions. δ¹⁸O and δ¹³C vary from −8.7‰ in the post‐optimal period to −4.8‰ in the optimal period, and from −10.6‰ at the beginning of the Taxus zone to −4.2‰ at the climatic optimum, respectively. A positive correlation of the isotope curves indicates closed‐water bodies, and only at Roskosz was some occasional overflow inferred. Higher oxygen isotopes correspond to an increase in temperature and/or enhanced evaporation, which is well marked in the Carpinus‐Abies zone, whereas samples enriched in ¹³C are correlated with periods demonstrating a lower water level and higher productivity in the lakes. Episodes of lake shallowing and dense aquatic vegetation occurred in the Pinus‐Larix zone and during the climatic optimum. The isotope ratios for the climatic optimum significantly exceed those of the other periods, thus pointing to warmer conditions. An estimation of relative changes of average summer temperatures using the δ¹⁸O/temperature gradient yielded variation of 1–2 °C within the lakes. Absolute temperature reconstructions indicate the effects of specific local conditions. Hence, V. diluvianus shells offer a reliable proxy in qualitative studies of interglacial lake records.