Statistical Constraints on the Relative Link Between Eccentricity Forcing and the 100,000-Year Glacial Cycle

The Milankovitch theory of orbital forcing fails to explain the 100-kyr pacing of the recent glacial cycles since the eccentricity cycle produces negligible changes in seasonal or mean annual insolation on this timescale. The 100-kyr periodicity has been proposed to arise from eccentricity pacing, obliquity pacing, or internal climate variability. A purely statistical test¹, based on cross-wavelet analysis between an untuned benthic isotope record (the LR04 stack) and insolation for the past 1.2 Myr, supports eccentricity pacing.

Here, we present a new version of this statistical test, which takes into consideration updated uncertainty estimates for the untuned LR04 age model. The new untuned age model is independent of orbital forcing but assumes a constant sediment rate between age control points, after adjustment for compaction. The age control points are provided by the radiometrically-dated magnetic reversals of the Quaternary geomagnetic instability time scale². Our approach to uncertainty quantification entails Monte-Carlo ensembles of possible realizations of the untuned age model, which takes into account the uncertainty in the age control tie points and the uncertainty in the compaction correction. We then apply cross-wavelet analysis on each Monte-Carlo record to investigate (1) the relative phase of eccentricity and glacial cycle and (2) the relative, time-dependent 100,000-year power of eccentricity and climate response over the past 1.2 Myr.

1 Lisiecki, L. Links between eccentricity forcing and the 100,000 year glacial cycle. Nature geoscience 3, 349-352, doi:10.1038/NGEO828 (2010).

2 Singer, B. S. A Quaternary geomagnetic instability time scale. Quaternary Geochronology 21, 29-52, doi:10.1016/j.quageo.2013.10.003 (2014).