EXPLORING THE STRUCTURE OF THE MIDPLEISTOCENE REVOLUTION WITH ADVANCED METHODS OF TIME-SERIES ANALYSIS

The mid-Pleistocene climate transition is a complex global change lead ing to Late Pleistocene ice ages with increased mean ice volume and do minant 100-ka cycle. A thorough understanding of this transition deman ds quantitative investigations in the time and frequency domains, and in the ''stochastic domain''. Three methods of time-series analysis ar e presented which have been adapted for this purpose. They are tested by means of predefined, artificial time series and applied to benthic oxygen isotope (delta(18)O) records which serve as ice volume indicato r. Results are as follows: (a) The time-dependent mean shows an increa se of 0.35 parts per thousand, vs PDB from 942 to 892 ka. (b) Evolutio nary spectral analysis reveals an abrupt increase of 100-ka cycle ampl itude at approximately 650 ka. (c) Probability density function exhibi ts a bifurcation behavior at approximately 725 ka. These findings poin t to a multiple transition from a more linear climate system to a stro ng nonlinear system. The significant lead of the transition in mean, i n relation to the 100-ka amplitude change and bifurcation is left open for explanation.