Water-Isotope Proxies in Lake Sediments: Calibrations, Uncertainties, and New Directions

Paleoclimatologists have long recognized that H and O isotopes of materials in lake sediments can help reconstruct past climate and environmental change. Here, a global synthesis of O isotopes in lab-cultured or core-top carbonates and organic macrofossils and of H isotopes in core-top sedimentary plant waxes confirms their strong correlations with source water isotopes. New proxies, such as H isotopes of microbial lipids, are also emerging. Given the prevalence of lakes around the world, these methods show immense promise for generating networks of water-isotope reconstructions needed to characterize past climates. This review summarizes current knowledge of these proxies, their relationships to modern water isotopes, and challenges in their interpretation. Future progress in applying water-isotope proxies would benefit from collecting relevant site environmental and ecological data, generating calibrated water-isotope reconstructions for direct comparison with observational data, and cross-validating reconstructions across multiple proxies or sites. ▪ Reconstructions of past water isotopes promise rich insight into paleoclimate dynamics and have support from a range of modern calibration studies. ▪ Multiple water-isotope proxies, including carbonate minerals, aquatic organism remains, and leaf waxes, reliably track meteoric water isotopes. ▪ Newly emerging water-isotope proxies, such as archaeal and bacterial glycerol dialkyl glycerol tetraethers, promise to expand the range of settings and questions available for investigation. ▪ Expanding modern calibration datasets can clarify the limitations on water-isotope reconstructions while enhancing interpretations.