Perspective on ice age Terminations from absolute chronologies provided by global speleothem records

Abstract

Abstract. Glacial Terminations represent the largest amplitude climate changes of the last several million years. Several possible orbital-insolation triggers have been described to initiate and sustain glacial Terminations. Because of the availability of radiocarbon dating, the most recent Termination (TI) has been extensively characterized. Yet, it is widely discussed whether the sequence of feedbacks, millennial events and rates of change seen in TI is recurrent over previous Terminations. Beyond the limit of radiocarbon dating, records from the speleothem archive provide absolute age control through uranium-thorium dating and high-resolution proxy measurements. The PAGES SISALv3 global speleothem database allows us to synthesize the available speleothem records covering Terminations. However, speleothem climate signals are encoded in a number of proxies, and unlike proxies in other archives like ice or marine cores, the climatic interpretation of a given proxy can vary quite significantly among different regions. In this study, we synthesize the available speleothem records providing climate information for Terminations: TII, TIIIA,TIII, TIV and TV, present the records based on the aspect of climate encoded in the available records, examine the effects of different ice volume corrections on the final climate proxy record, evaluate whether there are leads and lags in the manifestation of Terminations across different aspects of the climate systems and different regions, we suggest directions for future speleothem research covering Terminations, speculate on suitable tuning targets among marine and ice core proxies, and discuss what model outputs maybe most suitable for comparison. We find that TII has the greatest number of globally distributed records followed by TIIA and TIII. The records covering TIV and TV are largely restricted to the East Asian and Southeast Asian monsoon regions. Modelling and data-model comparison studies have greatly increased our understanding of the interpretation of oxygen isotope records across Terminations. Ice volume corrections have the most significant impact on European speleothem records with moisture sourced directly from the North Atlantic region. Within each Termination, a sequence of events can be established between a sub-set of events and this sequence stays largely consistent across Terminations. However, improvements in dating and age-model uncertainties, higher resolution records and multi-proxy approaches are required to establish sequences within each sub-set of events. Beyond further research on targeted speleothem records, our recommendations for future directions include focusing on TII as a useful next target to understand climate dynamics, isotope-enabled transient simulations for better characterization of the other Terminations, and development of marine proxy records with signals common to speleothems to further improve the chronology of Terminations.