Figure 4.

Multitaper spectral analysis of glacial-Holocene petrologic events from cores VM 29–191 and VM 23–81 (reproduced from ref. 2, Fig. 7), compared with periodicities in tidal forcing. Overlain in red are the averages (calculated from 0 to 31.1 kyr BP) of the 1,800- and 5,000-year tidal periods (A) and times of peak forcing of the former cycle (B). Tidal timing and periodicity assume invariant orbital parameters, except for the 5,800-year period that is based on assuming secular variability of climatic precession, as described in the “Secular Variations in Tidal Forcing” section of the text.