NONLINEAR VARIABILITY OF THE CLIMATIC SYSTEM FROM SINGULAR AND POWER SPECTRA OF LATE QUATERNARY RECORDS

Stable-isotope records from seven marine cores and one ice core provid e invaluable information on the intricate behavior of the climatic sys tem over time scales of 10(4) to 10(5) years. These records, in conjun ction with a simple coupled climate model, help us understand major me chanisms of paleoclimatic variability. The time intervals covered by t he records include the last glacial-interglacial cycle. In spite of th e difference in the nature of the records, common features are reveale d by advanced spectral-analysis tools. The dominant features are the p resence of orbital frequencies, on the one hand, and a low number of i nternal degrees of freedom, on the other. The climatic system appears therefore to act on the Quaternary time scales considered as a forced nonlinear oscillator. The internal mechanisms giving rise to the aperi odic oscillations include ice-albedo feedback, precipitation-temperatu re feedback, and interactions between the ice sheets and the bedrock.