Orbital-scale hydroclimate variations in the western Qaidam Basin during the Late Pliocene: evidence from magnetic parameters and median grain size

Abstract. A recent study suggests that the precipitation records of the Qaidam Basin during the middle Piacenzian warm period (mPWP, 3.264–3.025 Ma) are broadly consistent with those of the monsoon influenced regions, and are highly sensitive to 20-kyr precessional cycles, implying that the East Asian summer monsoon (EASM) intensified and migrated westward into the Asian interior during this warm interval. However, it remains unclear whether such a precession-dominated pattern persisted throughout the Late Pliocene or was restricted to specific intervals. To address this question, we present new magnetic parameter and median grain size records from the Gansen (GS) section for 3.6–3.25 Ma and 2.95–1.8 Ma, and integrate them with the previously published records for 3.25–2.95 Ma to assess orbital-scale precipitation variations in the western Qaidam Basin during the Late Pliocene. The results show that EASM-related summer moisture reached the western Qaidam Basin during 3.6–3.25 Ma, although the associated precipitation was weaker than during 3.25–2.95 Ma. Spectral analysis further reveals that precipitation variations during 3.6–3.3 Ma were characterized by dominant 100–kyr cyclicity rather than the previously reported precession-dominated pattern during 3.25–2.95 Ma, suggesting a nonlinear response to insolation forcing. This contrast indicates that the precession-dominated pattern was not a persistent feature throughout the Late Pliocene in the western Qaidam Basin. Instead, our results suggest that under different climatic background states, the dominant processes controlling the westward penetration of summer moisture into the western Qaidam Basin were also different, and that the 20-kyr and 100-kyr periodicities mainly reflect these differences in forcing response. In addition, the similar phase variations between these precipitation records and the benthic oxygen isotope stack at the 40-kyr band imply that Antarctic ice sheets may have modulated hydroclimatic variations in the basin. These findings provide new insight into how background climate conditions may shape the orbital-scale response of precipitation, and more broadly hydroclimatic variations, in the Asian interior during warm periods.