On the Timing and Forcing Mechanisms of Late Pleistocene Glacial Terminations: Insights from a New High-Resolution Benthic Stable Oxygen Isotope Record of the Eastern Mediterranean

Abstract:

We present the first long (~1.2 Ma) benthic oxygen isotope record from the eastern Mediterranean, based on ODP Sites 967 and 968, which clearly reflects the behavior of global climate on a glacial-interglacial scale. The age model for our record is based on tuning the elemental ratio of titanium versus aluminum (Ti/Al) against insolation. The Ti/Al record is dominated by the precession-related changes in northern African climate, i.e. monsoonal forcing, and hence largely independent of glacial-interglacial variability. We found the largest offset between our chronology and that of the widely applied, open ocean stacked record LR04 (Lisiecki and Raymo, 2005) for T_VII (~624 ka), which occurred ~9 kyr earlier according to our estimates, though in agreement with the AICC2012 δD_ice chronology of EPICA Dome C (Bazin et al., 2013). Spectral cross-correlation analysis between our benthic δ¹⁸O record and 65°N summer insolation reveals significant amounts of power in the obliquity and precession range, with an average lag of 5.5±0.8 kyr for obliquity, and 6.0±1.0 kyr for precession. In addition, our results show that the obliquity-related time lag was smaller (3.0±3.3 kyr) prior to ~900 ka than after (5.7±1.1 kyr), suggesting that on average the glacial response time to obliquity forcing increased during the mid-Pleistocene transition, much later than assumed by Lisiecki and Raymo (2005). Finally, we found that almost all glacial terminations have a consistent phase relationship of ~45±45 degrees with respect to the precession and obliquity-driven increases in 65°N summer insolation, consistent with the general consensus that both obliquity and precession are important for deglaciation during the Late Pleistocene. Exceptions are glacial terminations T_IIIb, T₃₆ and potentially T₃₂ (and T_VII T₂₄ and T₃₄), which show this consistent phase relationship only with precession (only with obliquity). Our findings point towards an early (>1200 ka) onset of the Mid Pleistocene Transition. Vice versa, the timing of T_VII, which can only be explained as a response to obliquity forcing, indicates that the transition lasted until at least after MIS 15.