An Improved Age Model for Late Pleistocene Benthic δ18O and Analysis of the Orbital Phases of Glacial Terminations

Abstract:

The relative influence of obliquity and precession phases on the pacing of glacial terminations during the Late Pleistocene “100-kyr world” may provide insight into the mechanisms that trigger these climate transitions. Characterizing the phase of glacial terminations relative to orbital cycles requires termination age estimates with small, well-defined uncertainties. Whereas age estimates for ocean sediment cores often have large uncertainties of several thousand years, 230Th and U-Pb dating techniques for speleothems yield higher resolution age models with greater age control. By correlating weak monsoon intervals (WMIs) from a high-resolution 230Th-dated speleothem δ18O composite record (Cheng et al., 2016) with ice-rafted debris (IRD) in six North Atlantic cores, we constructed a new North Atlantic δ18O stack with a well-constrained probabilistic age model for the past 640 kyr. Monte Carlo samples of age models for the δ18O record and a probabilistic change point algorithm are used to characterize uncertainty for the start age of each termination. These age estimates are used to evaluate the timing of glacial terminations with respect to obliquity and precession, and the observed phase variability for obliquity and precession is compared with the expected variability arising from age uncertainty. Finally, we assess the different phase characteristics of weak, or failed, terminations (e.g., TIIIa, TVIIa) versus strong terminations (e.g. TI, TII, TV).