Late Glacial-early Holocene environmental changes in Charzykowskie Lake (northern Poland) based on oxygen and carbon isotopes and Cladocera data

Based on isotopic and cladoceran investigations of a 6-m-long sediment core, a reconstruction of paleoenvironmental dynamics in Charzykowskie Lake (northern Poland) is proposed. The sediments consist of sandy silts at the bottom, followed (in upward succession) by gyttja characterized by increasing CaCO3 content. The measured δ18O values oscillate from −9.3 to −5‰ and δ13C from - 5.7 to +0.4‰. We identify 24 taxa of subfossil Cladocera and six phases (CAZ) of faunal development. Isotopic and cladoceran data together with detrended correspondence analyses (DCA) allow reconstruction of the environmental conditions, particularly changes in water level, temperature, and trophic status, during the Late Glacial and early Holocene. The lowest water temperature, connected with the inflow of cold melt water, occurred in the Late Glacial and Preboreal period. Since the Boreal period, gradual warming is observed and expressed through a positive trend in both δ18O and δ13C values and changes in Cladocera species assemblages. The lake was deepest at the beginning of the Holocene as a result of dead ice melting (supply of melt water; lowering of lake bottom) and/or precipitation increase (change in atmospheric circulation). During the Boreal period, the fall in water level takes place despite the opposite trend observed at nearby sites. In addition, the cladoceran data indicate an initial decrease in trophic conditions from α-mesotrophic to oligotrophic and then an increase to the β-mesotrophic state.