On the Nature of the Pliocene/Pleistocene ...

Although numerous endeavours have been undertaken to understand the nature of the 40-to-100 ka transition in the glacial cycle lengths that took place about 1.0-1.5 ma BP, this phenomenon remains a mystery up till now. A specially designed wavelet-based technique was used to treat paleoclimatic records related to those times in concepts of the mathematical dynamical system theory. The well known fact that the global climate system underwent a rhythmic behaviour of the ~41 ka period (the main period of the Earth’s axis obliquity) was interpreted during the Pliocene as an evidence of the limit cycle attractor in the climate system dynamics. Under the stress of gradual climate system cooling, the magnitude of this limit cycle attractor increased from the Early to Late Pliocene. But this increase was not monotonous because of the ~1.2 ma-long beat of obliquity. When this magnitude exceeded a certain level, the climatic limit cycle attractor lost its stability, and a new, more complex, attractor arose via the period doubling bifurcation that is well-known in the dynamical system theory. During the Pleistocene, the magnitude of the new-arisen attractor was essentially enhanced because of resonances with insolation variations that were induced by combinational tones of the Earth’s orbit eccentricity, and the attractor period trebled, doubled and trebled by turns depending on phase-locking to either of those tones. Keywords: Pliocene/Pleistocene Glacial Cycles; Orbital Insolation Variations; Climate Cooling Trend; Period Doubling/Trebling Bifurcation; Wavelet Analysis