Clumped Isotope Composition of Recent Ostracods from Lakes on the Northeastern Qinghai-Tibetan Plateau, China

In recent years, carbonate clumped isotopes (Δ₄₇, quantifying the excess abundance of CO₂ of mass 47 (¹³C¹⁸O¹⁶O) in carbonate relative to the theoretical random distribution) have been developed as a paleothermometer for reconstruction of surface paleoenvironments. This method is based on the temperature dependence of rare isotope 'clumping' into the same carbonate ion group in the carbonate mineral lattice. Because Δ₄₇ is referenced to the random distribution of clumped isotopes, calculated from the carbonate isotopic composition, the extent of clumping is independent of the isotope composition of the water from which carbonate precipitates, providing unique advantages over many other paleotemperature proxies. The clumped isotope composition of corals, foraminifera, brachiopods and land snail shells, have been used to elucidate the temperatures at which the carbonates precipitated, thus reflecting the environmental temperature or indicating paleohydrological changes in combination with the shell oxygen isotope composition. The oxygen isotopic composition of ostracod shells in paleo-lakes has provided understanding of the evolution of lacustrine systems in the context of changes in climate and hydrology. Despite the frequent use of oxygen isotope in ostracod-based palaeoenvironmental reconstruction, there have been no studies of carbonate clumped isotopes in ostracods and their paleoenvironmental implications until now. In this study, the Δ₄₇ values of recent ostracod shells form 9 lakes with different salinities on the Tibetan Plateau were measured to evaluate the potential of ostracod Δ₄₇ as a quantitative proxy of temperature. Our results showed that water temperature varies from 6 21℃ based on the calculation from ostracod Δ₄₇, and these temperature also relate to water depth and volumes of lakes. The calculated lake water δ¹⁸O in brackish lakes is very similar to the measured δ¹⁸O value of lake water, but the calculated lake water δ¹⁸O is higher than the measured value in freshwater lakes. These results suggest that ostracod Δ₄₇ is not affected by 'vital effects' in brackish lakes, and can be used to quantitatively reconstruct water temperature history, but the 'vital effects' on the δ¹⁸O values of ostracods cannot be neglected when freshwater species are used in paleoenvrionmental studies.