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

A recent study suggests that the precipitation records of the western 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) precipitation intensified and penetrated farther 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 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 suggest 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 mainly by eccentricity-scale (∼ 100–125 kyr) variability rather than the previously reported precession-dominated pattern during 3.25–2.95 Ma, which may reflect 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 influencing the westward penetration of summer moisture into the western Qaidam Basin were also different, and that the 20 kyr precessional signal and eccentricity-scale variability mainly reflect these differences in forcing response. In addition, the broad correspondence between these precipitation records and the benthic δ 18 O stack at the 40 kyr band suggests that high-latitude ice-volume variability, potentially including Antarctic ice-sheet variability, may also have modulated precipitation variations in the basin during ∼ 3.6–3.3 Ma. These findings provide new insight into how background climate conditions may shape orbital-scale hydroclimatic responses in the Asian interior during the Late Pliocene.