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

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 spe ctral analysis of delta(18)O proxy climate records have cast doubt on the t heory [Muller and MacDonald, 1997a, b]. The spectral signature of the "100 kyr" component, which dominates the climate record over the past 0.6-0.5 My r 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 re lative to the invariant plane of the solar system. Here we show that the sp ectral signature of delta(18)O records are entirely consistent with Milanko vitch mechanisms in which deglaciations are triggered every fourth or fifth precessional cycle. Such mechanisms may involve the buildup of "excess" ic e due to low summertime insolation at the previous precessional "high."