Beyond the 100-kyr and 41-kyr dichotomy: ~76-kyr and ~52-kyr signals and forbidden periodicities

Takahito Mitsui 

While the Mid-Pleistocene Transition (MPT) is often described as a shift from 41-kyr to $\sim$100-kyr glacial cycles, this binary perspective fails to capture the nuanced spectral evolution of Quaternary climate. Applying wavelet-based spectral analysis to benthic d18O records, we identify previously underappreciated signals－~52 kyr before 1.2 Ma and ~76 kyr thereafter－marking the MPT's onset. Insolation analysis reveals these timescales primarily correspond to integer multiples (n) of the local-mean climatic precession period (T_p), with minor modulation by obliquity. We further find that when T_p falls within this intermediate range (20.5－22 kyr), high eccentricity triggers deglaciation, precluding the emergence of 60－65 kyr and 100－110 kyr cycles. These findings refine the conventional ``41-kyr to 100-kyr'' paradigm, revealing an evolution from a quasi-41-kyr regime including ~52-kyr cycles to a post-MPT regime of quantized ~76, ~95, and ~120~kyr cycles. This points to precession-based pacing as a persistent feature of Quaternary glacial dynamics.