The Late Quaternary Glaciations as the Response of a Three-Component Feedback System to Earth-Orbital Forcing

Barry Saltzman Department of Geology and Geophysics, Yale University, New Haven, CT 06511

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Anthony R. Hansen Department of Geology and Geophysics, Yale University, New Haven, CT 06511

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Kirk A. Maasch Department of Geology and Geophysics, Yale University, New Haven, CT 06511

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Abstract

A climatic feedback system previously described, consisting of three prognostic nonlinear equations governing the mass of ice sheets ζ, the mass of marine and continental marginal ice χ, and the mean ocean temperature θ is forced by a representation of the effects of external earth-orbital variations. With reasonable amplitudes for the eccentricity, obliquity, and precession forcing, the free oscillatory solutions of major period near 100 kyr can be modified in a way that substantially agrees with the δ18O-derived observations of ice mass evolution. In particular, a proper structure, variance spectrum, and “phase lock” of the major variations are obtained over the last 400 kyr. An analysis of the sensitivity of these results to variations in the model parameters and to random perturbations shows that the solution is robust for small changes in all but a few of the equation coefficients. Concomitant variability in the marine ice mass, ocean temperature and net radiation at the top of the atmosphere are predicted, the signatures of which must be sought in the geological records to check the validity of the model. An independent estimate of the variations of ocean temperature θ, derived with plausible assumptions from the difference between the solution for ζ and the δ18O record, is shown to be compatible with the solution obtained for θ.

Abstract

A climatic feedback system previously described, consisting of three prognostic nonlinear equations governing the mass of ice sheets ζ, the mass of marine and continental marginal ice χ, and the mean ocean temperature θ is forced by a representation of the effects of external earth-orbital variations. With reasonable amplitudes for the eccentricity, obliquity, and precession forcing, the free oscillatory solutions of major period near 100 kyr can be modified in a way that substantially agrees with the δ18O-derived observations of ice mass evolution. In particular, a proper structure, variance spectrum, and “phase lock” of the major variations are obtained over the last 400 kyr. An analysis of the sensitivity of these results to variations in the model parameters and to random perturbations shows that the solution is robust for small changes in all but a few of the equation coefficients. Concomitant variability in the marine ice mass, ocean temperature and net radiation at the top of the atmosphere are predicted, the signatures of which must be sought in the geological records to check the validity of the model. An independent estimate of the variations of ocean temperature θ, derived with plausible assumptions from the difference between the solution for ζ and the δ18O record, is shown to be compatible with the solution obtained for θ.

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