Change in dominant orbital cycles led to warm excursions during the middle–late Eocene cooling

ABSTRACT Orbital-scale hydroclimatic variability in terrestrial environments during the middle–late Eocene warmhouse is important to the understanding of climate dynamics of rhythmic cycles. Here, we report two continuous cyclostratigraphic records derived from shallow to deep lake deposits in East Asia to unravel orbital-scale hydroclimatic fluctuations between 43.22 Ma and 37.48 Ma. Our results show that 40 k.y. obliquity cycles paced hydroclimate dominantly during 43.22–41.57 Ma and 40.20–37.48 Ma, with periods of wetter and warmer climate in obliquity maxima. Obliquity may have forced hydroclimatic fluctuations by modulating the intensity of the East Asian Summer Monsoon, possibly through intricate feedback mechanisms involving high-latitude ice sheets within the climate system. Between 41.57 Ma and 40.20 Ma, 405 k.y. and ~100 k.y. eccentricity cycles became prominent. We observed transient warming events at the conjunctions of long and short eccentricity maxima. These findings suggest that the switch in the dominant orbital parameter may have disturbed the global carbon cycle, which subsequently led to continental hydroclimatic change. Our study highlights the role of obliquity and eccentricity cycles in influencing climate dynamics and underscores the importance of considering changes in dominant cycles when investigating continental hydroclimatic change.