New age constraints for glacial terminations IV, III, and III.a based on Western Mediterranean speleothem records

Abstract

Abstract. The full understanding of climate feedbacks responsible for the amplification of deglaciations requires robust chronologies for these climate transitions, but, in the case of marine records, radiocarbon chronologies are possible only for the last glacial termination. Although the assumed relationships between the marine isotopic record and the orbital parameters provide a first order chronology for the previous terminations, an independent chronological control allows the relationships between orbital forcing and the climate response to be assessed over multiple previous terminations. Here we present new geochemical records of Marine Isotope Stages 11 to 7 from a western Mediterranean speleothem, establishing a new long terrestrial climate record for this region. Its absolute U/Th dates provide an exceptional chronology for the glacial terminations IV, III, and III.a. The onset of these three glacial terminations was marked by rapid δ¹⁸O depletions, reflecting ocean freshening by ice melting, thus providing an excellent tie point for regional marine records also sensitive to such freshening. These new chronologies reveal an earlier onset of the deglacial melting for the TIV and TIII.a in contrast to the generally accepted marine chronologies and indicate that the duration of these deglaciations was variable, with TIV particularly longer (~20 kyr). This study also supports that the onset of deglacial melting always occurred during declining precession index while a nonunique relation occurred with the obliquity parameter.