Is the spectral signature of the 100 kyr glacial cycle consistent with a Milankovitch origin?

Abstract

Milankovitch theory seeks to explain the Quaternary glaciations via changes in seasonal insolation caused by periodic changes in the Earth's obliquity, orbital precession, and eccentricity. However, recent high-resolution spectral analysis of δ18O proxy climate records have cast doubt on the theory [Muller and MacDonald, 1997a, b]. The spectral signature of the '100 kyr' component, which dominates the climate record over the past 0.6-0.8 Myr does not match the frequencies of the eccentricity variation. Muller and MacDonald [1997b, c] have therefore argued that a more likely pacemaker for the climate cycles is the variation in inclination of the Earth's orbit relative to the invariant plane of the solar system. Here we show that the spectral signature of δ18O records are entirely consistent with Milankovitch mechanisms in which deglaciations are triggered every fourth or fifth precessional cycle. Such mechanisms may involve the buildup of 'excess' ice due to low summertime insolation at the previous precessional 'high'.