Nonlinear coupling between 100 ka periodicity of the paleoclimate records in loess and periodicities of precession and semiprecession

Abstract

In this paper, we use the automatic orbital tuning method to establish the time scales of Lingtai and Jingchuan loess-soil section, China, and Chashmanigar loess-soil section, Tadzhiki-stan, analyse the evolution of the ∼100 ka cycles of the three paleoclimate records respectively and afterwards employ the auto-bicoherence method to detect the coupling between the ∼100 ka periodicity and periodicities of obliquity, precession and semiprecession. The results show that from 0.0 Ma to 0.8 Ma there exists a quadratic phase coupling between ∼100 ka period and the period components of precession (16 ka) and semiprecession (about 13.8 ka, 12.4 ka, 11.1 ka), while from 1.6 Ma to 2.6 Ma, between 128 ka period and the period components of precession (19.3 ka and 16.8 ka) and semiprecession (about 10 ka). Evidence from the above calculation suggests that nonlinear interaction between precession and semiprecession waves may be the cause to produce ∼100 ka cyclicity in loess records.