Multi-Proxy Responses to Orbital-Scale Climate Change in East Asia during the Early Eocene Climatic Optimum (EECO)

: The Early Eocene Climatic Optimum (EECO) is one of the best geological analogs for future global warming scenarios. Exploring the climatic evolution of East Asia during this interval is of great significance for understanding regional climate trends under future greenhouse conditions. However, orbital-scale studies—especially those integrating multiple paleoclimatic proxies—remain scarce, limiting comprehensive and in-depth understanding of climate variability in East Asia during the EECO. The Milai section from the central Gonjo Basin in Tibet, located in East Asia, preserves a continuous, long-duration terrestrial succession with a well-established chronological framework, making it an ideal archive for studying climate evolution of East Asia during the EECO. This study focuses on the Milai section and builds upon an established astronomical timescale. Utilizing multiple high-resolution paleoclimate proxies (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr, Fe/Ca, Fe/Mn, Ti/Ca, and a*), we integrate sedimentology, principal component analysis, spectral analysis, evolutionary fast Fourier transform spectrogram and power decomposition methods to investigate the responses of multiple paleoclimate proxies to orbital-scale climate changes in the Gonjo Basin across the EECO. Results indicate that different paleoclimate proxies exhibit similar responses to astronomical cycles. Compared to contemporaneous astronomical theoretical solutions, these proxies generally exhibit stronger power in the eccentricity band and weaker power in the obliquity and precession bands. Orbital-scale climate changes in the Gonjo Basin during the EECO were jointly forced by eccentricity and obliquity cycles: eccentricity likely exerted influence by modulating low-latitude insolation, while obliquity may have acted by regulating meridional insolation gradient variations between the equator and the pole. This study offers new evidence for understanding climate variability in East Asia during the EECO, and provides important insights for understanding future regional climate change under greenhouse conditions.