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

Abstract

[eng] 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 glacial terminations, an independent chronological control allows the relationships between orbital forcing and the climate response to be evaluated over multiple previous terminations. To assess this, we present geochemical records from the western Mediterranean, including two speleothems and one marine sediment core. The most notable speleothem, the so-called RAT, established a new long terrestrial climate record for this region, spanning Marine Isotope Stages from MIS 11 to MIS 7. 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. This is exemplified by new δ18O data of the Ocean Drilling Program (ODP) 977 site from the Alboran Sea, where the speleothem chronology was employed to adjust its age model. The new chronologies reveal an earlier onset of the deglacial melting for the TIV and TIII.a that is in contrast to the generally accepted marine chronologies and indicates that the duration of these deglaciations was variable, with TIV being particularly longer (∼ 20 kyr). This study also supports that the onset of deglacial melting always occurred during a declining precession index, while a nonunique relation occurred with the obliquity parameter.