A review of Ostracoda stable isotopes in palaeoclimate reconstruction on the Tibetan Plateau

Ostracods in Tibetan Plateau (TP) waters have well-constrained ecological preferences, pronounced with favourable moult season and last-instar shell calcification in summer, their shell (biogenic carbonates) stable isotopes, therefore, have a great potential use as a palaeoclimate indicator, notably on seasonal basis. However, our understanding of the isotopic fractionations in a long record remains elusive, particularly as biocarbonates frequently precipitate out of thermodynamics-based isotopic equilibrium with ambient waters. The knowledge gap arises from the different roles of metabolic and kinetic effects in disequilibrium fractionations, in addition to the impacts of various surface processes in the lake catchment on the input and output of isotopic flux of a lake basin. In this review, we provide a comprehensive overview on multiple factors for value variation of biological carbonate isotopes in terms of ostracods from different lakes over the Tibetan Plateau, to reduce the knowledge gap for future study. We address (1) the ecological preferences of ostracod species used for stable isotope analysis on the TP and the analytical reproducibility error of an individual measurement on several genus/species; (2) multiple factors for different shell isotope values of modern ostracods including metabolic and kinetic effects in disequilibrium fractionations as well as the impacts of in-lake and catchment processes on isotopic signal change in ambient waters; (3) the differences and related indications of stable isotope values of nature and culture modern and fossil ostracods from the same species (Eucypris mareotica); (4) the spatial stable isotope distribution patterns of the reported ostracod populations and their controlling factors in one lake and/or between several lakes through time and (5) different temporal distribution patterns of stable isotopes and their relevant triggers in four selected TP lakes with comparable or incomparable hydrological conditions during a long period of the last 15,000 to 32,000 years. The successful use of difference transformation of stable isotope data from Nam Co Lake for further reconstruction of palaeotemperature anomaly in terms of various seasonal anomalies show a great potential of this tool in palaeoclimate reconstruction at interannual scale in the future.