| 13 May 2026
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.
This manuscript presents new magnetic-parameter and median grain-size records from the Gansen section in the western Qaidam Basin and integrates them with previously published records to reconstruct hydroclimate variations during the Late Pliocene to Early Pleistocene. The study addresses an important question: whether the precession-dominated precipitation pattern previously identified during the mPWP was persistent throughout the Late Pliocene or restricted to a specific warm interval.
The manuscript is clearly structured, the scientific question is relevant, and the new data provide useful information for understanding orbital-scale hydroclimate variability in the Asian interior. The comparison between the 3.6–3.3 Ma interval and the previously published 3.25–2.95 Ma interval is particularly interesting. The finding that precipitation variability may have shifted from a 100-kyr-dominated pattern to a precession-dominated pattern under different background climate states is potentially significant.
Overall, I find the manuscript suitable for publication after minor revision. The main conclusions are generally reasonable, but several points require clarification, especially regarding the age model, spectral-analysis procedures, proxy interpretation, and the wording of the forcing mechanisms.
Specific comments
1. The chronology is based on the previously published paleomagnetic framework. Because the manuscript focuses on orbital-scale variability, the age model should be described in slightly more detail. I suggest that the authors add a short summary of the main magnetostratigraphic tie points, interpolation approach, and sedimentation-rate changes. It would also be helpful to briefly mention how chronological uncertainty may affect the identification of 20-kyr, 40-kyr, and 100-kyr cycles. This does not require a new age model, but the current manuscript would benefit from a clearer statement of the chronological basis of the orbital interpretation.
2. The spectral results are important for the main conclusion, but the methods are not described in sufficient detail. Please specify the spectral-analysis method used, the interpolation step, detrending method, red-noise background, confidence-level calculation, and filtering procedure. The figure captions should also include enough information for readers to understand how the spectral peaks and filtered curves were obtained. The authors may also consider adding a short statement on the robustness of the 100-kyr peak during 3.6–3.3 Ma, given that this interval contains only a limited number of eccentricity-scale cycles.
3. The interpretation that the 100-kyr cyclicity reflects a nonlinear response to insolation forcing is interesting and reasonable. However, eccentricity itself has a weak direct effect on insolation, so the mechanism should be described more cautiously. I suggest using wording such as “may reflect” or “is consistent with” rather than stronger statements implying a direct causal relationship. The possible roles of Antarctic ice-sheet variability and annual insolation are worth discussing, but they should be presented as plausible hypotheses rather than fully demonstrated mechanisms.
4. The use of χfd/HIRM as a precipitation-sensitive proxy is appropriate and is supported by previous work in the Qaidam Basin. However, it would be helpful to briefly summarize why this ratio can be used in the GS section. In particular, the authors should clarify whether post-depositional dissolution, evaporite dilution, or changes in sediment source are unlikely to dominate the magnetic signal.
5. The interpretation of coarser median grain size as reflecting stronger precipitation is plausible in a closed shallow-lake setting. However, hydrodynamic conditions should be considered. The grain size of fluvial, delta or nearshore lacustrine sediment is correlated with hydrodynamic conditions, which, in turn, are closely linked to precipitation variability. Therefore, it can indirectly indicate changes in precipitation patterns.
6. The phase relationship between the GS records and the benthic oxygen isotope stack at the 40-kyr band is interesting. However, the benthic δ18O stack reflects both global ice volume and deep-water temperature, and it should not be treated as a pure Antarctic ice-sheet record. I suggest revising the relevant sentences to “high-latitude ice-volume and/or deep-ocean temperature changes” or “Antarctic ice-sheet variability may have contributed to the observed 40-kyr signal.” This would make the interpretation more cautious and scientifically precise.
Technical corrections
1. The title says “Late Pliocene,” but the record extends to 1.8 Ma. Please consider using “Late Pliocene to Early Pleistocene” where appropriate.
2. Please distinguish clearly between the formal mPWP interval, 3.264–3.025 Ma, and the broader 3.25–2.95 Ma interval used in the analysis.
3. Line 38, “Precipitation variations during 3.6–3.3 Ma was characterized” should be revised to “precipitation variations during 3.6–3.3 Ma were characterized.”
4. Lines 135-136 “major moisture source” should be “major moisture sources.”
5. Line 211, “high-frequent fluctuations” should be changed to “high-frequency fluctuations.”
6. Lines 382-383, “seasonable insolation variations” should be “seasonal insolation variations.”
7. Line 384 “Lasker et al.” should be corrected to “Laskar et al.”
8. The sample numbers should be clarified. The manuscript states that 149 samples were measured, but the numbers given for different intervals should be made consistent.
9. Figure 4 should include more methodological information in the caption, including the spectral method and confidence level.