Oxygen stable isotope composition of carbonate encrustations of two modern, widely distributed, morphologically different charophyte species

Abstract

Oxygen (δ18O) and carbon (δ13C) stable isotope analyses are among the standard methods applied in the studies of past environment, including climate. In lacustrine sediments, δ18O and δ13C values can be measured in various carbonates including charophyte encrustations. Application of the stable isotope record of lacustrine carbonates requires knowledge about the possibilities and limitations of the method. Thus, this study presents the oxygen stable isotope composition of carbonate encrustations precipitated by modern charophytes (δ18OCARB) and of ambient waters (δ18OWATER). The study objects were widely distributed and morphologically different charophyte species, large and branchy Chara tomentosa L. and small and slender Chara globularis Thuill. Each species was studied in five lakes located in western Poland, at three sites per lake. The study demonstrated that δ18OCARB values were similar for the two charophyte species and were lake-dependent. δ18OCARB and δ18OWATER relationships were also similar for the studied charophytes with carbonate encrustations 18O-depleted compared to ambient waters. The shift of mean δ18O values between C. tomentosa and C. globularis encrustations and ambient waters, 2‰ and 3.2‰, respectively, was evidenced in all studied lakes which may indicate potential applicability of δ18OCARB of the two species in paleolimnological studies.