Precession-induced millennial climate cycles in greenhouse Cretaceous.

Millennial-scale climate cycles persist throughout greenhouse climates, yet the mechanisms remain unclear. Here, using proxy reconstructions, we present centennial-resolution geological records from early Campanian greenhouse deposits in both mid-latitude East Asia and low-latitude Southern Atlantic. These records document pronounced millennial ( ~ 1-6 kyr) wet-dry climate cycles. The amplitude modulation relationship between the most prominent ~4-5-kyr cycles (corresponding to the ¼ precession cycle) and eccentricity aligns perfectly with the theoretically calculated equatorial insolation cycles, demonstrating the climate effect of this predicted insolation forcing on global climate. Other millennial cycles primarily emerge from these ~4-5-kyr cycles via nonlinear amplitude modulation and combination tones. Proxy reconstructions and theoretical calculation thus converge to demonstrate that during this warm greenhouse period, precession can directly and indirectly stimulate millennial climate cycles. The deterministic link between astronomical parameters and millennial climate cycles implies that high-frequency climate oscillations may be predictable in future greenhouse-like climates, particularly under anthropogenic warming.