Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth’s climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration.We acknowledge financial support from Australian Research Council Discovery Project grants 0664621 (to J.D.W.), 110102185 (to R.N.D., J.D.W., J.C.H., E.W., A.E.F., and S.F.), and 160102969 (to R.N.D., J.D.W., G.Z., E.W., and P.F.). We thank the Gruppo Speleologico Lucchese and the Federazione Speleologica Toscana for logistic and funding support. The SUERC contribution to this study falls within the framework of the Scottish Alliance for Geoscience, Environment and Society (SAGES). P.B. was the recipient of a University of Melbourne International Postgraduate Research Scholarship and Postgraduate Writing-Up Award supported by the Albert Shimmins Fund. J.C.H. was the recipient of an Australian Research Council Future Fellowship (FT130100801). P.F. acknowledges support from the European Union through a Marie-Curie Reintegration grant (PERG-GA-2010-272134 - MILLEVARIABILI). D.H. acknowledges support from the UK Natural Environmental Research Council. E.W. is supported by a Royal Society Professorship. A.H.L.V. and T.R. received financial support from Fundação para a Ciência e a Tecnologia (FCT, Portugal) projects MOWCADYN (PTDC/MAR-PRO/3761/2012), WarmWorld (PTDC/CTA-GEO/29897/2017), and CCMAR (UID/ Multi/04326/2019). Samples from the marine sites were provided by the Integrated Ocean Drilling Program to D.H., A.H.L.V., and T.R.