Milankovitch band forcing of sub‐Milankovitch climate variability during the Pleistocene

Abstract

Climate variability at periods from 10 kyr to 12 kyr that originates from Milankovitch band forcing is quantified at three locations for the late Pleistocene (eastern equatorial Pacific Ocean Drilling Program site 846, eastern equatorial Atlantic ODP site 663, and northeastern Atlantic Deep Sea Drilling Project site 609). Variability at these periods is not present in the primary Milankovitch forcing, so no linear linkage to Milankovitch band variations is possible. However, these periods are equal to harmonics of precession band oscillations. The magnitude of interactions between processes that occur at different timescales can only be resolved in time series data through application of higher‐order statistics. Through such an application, we demonstrate that up to 75% of the variance in the 10‐ to 12‐kyr band in the sediment records is nonlinearly transferred from precession band (19–23 kyr) variations. Within the millennial to sub‐Milankovitch band, defined as the band of variance ranging from ∼15 to ∼2 kyr, approximately 1/3 of the variability in the records studied is consistent with a low‐frequency, Milankovitch band origin. This variability may derive from high sensitivity of the tropics to summertime insolation in both hemispheres relative to wintertime insolation. A mechanism having equatorial origin and related to low‐latitude precession variations appears consistent with the observations. Because the phase coupling between 10‐ to 12‐kyr oscillations and precession is resolved, this result has implications for development of models which seek to explain global climate variations on this timescale.