Millennial climate variability and organic matter accumulation under icehouse conditions

Abstract

Millennial climate variability (MCV) is a prominent feature of the Pleistocene high-resolution climate records and is closely linked to orbital-scale climate variability and glacial-interglacial cycles. However, the origin and internal climate feedback of pre-Quaternary MCV remain poorly constrained. To better understand the nature and evolution of MCV under icehouse conditions, we quantitatively analyzed four sets of paleoclimatic proxies (including natural gamma ray emissions, uranium, and total organic carbon) from mid-latitude lakes (Lucaogou Formation for Early Permian icehouse and Lakes Ohrid and Van for Quaternary icehouse) using amplitude modulation and bi-coherence spectral analysis. Our results suggest that MCV (with periods of 4–8 kyr) is modulated by eccentricity, obliquity, and precession cycles and can be directly generated by the harmonization between fundamental orbital cycles (e.g., obliquity and precession cycles). In both the Early Permian and Quaternary icehouses, the changes in the amplitude of the MCV were more pronounced within an intermediate climate (e.g., glacial-interglacial transition). In addition, robust petrographic evidence and in-phase relationships between total organic carbon and natural gamma ray emissions in millennial-scale cycles suggest that MCV affects mid-latitude organic matter accumulation by modulating hydrological cycles, primary productivity, and redox conditions. Our study highlights a common origin of MCV in two Phanerozoic icehouses and the complex nonlinear response to external orbital forcing of the Earth’s climate system.