667 / 2024-09-18 21:22:15

Forcing of the millennial cycles in ice-free Cretaceous by eccentricity-modulated precession

Millennial cycles,Nonlinearity,Precession,Late Cretaceous,Songliao Basin

Session 42 - Deep-time ocean and climate changes: insights from models and proxies

Abrupt and millennial-scale climate variabilities (1–10 kyr; MCVs) characterized the last glacial period, but their origin remains debated, especially regarding ice-related and ice-dispensable mechanisms. Here, we estimate three centennial-resolution, continuous paleoclimate records (grayscale, log (Ca/Ti), and Rb/Sr), retrieved from the rhythmic deep-lacustrine successions deposited in the Songliao Basin (Northeast China) during the Late-Cretaceous Campanian, a period when the glaciations are not expected. All three datasets exhibit significant MCVs and are closely phase-coupled on this timescale, indicating humid/arid climate implications. Complex decomposition of MCVs and the nonlinear bicoherence spectra indicate that the millennial cycles are most likely derived from precession through its harmonics and the further nonlinear combination tones of these harmonics. These discoveries indicate that Pleistocene millennial events are not necessarily related to ice but rather strengthen the view that the North Atlantic MCVs were controlled by low-latitude climate changes induced by a nonlinear response to the precession.