the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Apr 2026
Multi-proxy evidence for orbital-paced ISM variability in PT2 lacustrine sediment records from Southwest China
Abstract. The Indian summer monsoon (ISM) is strongly influenced by orbital forcing. However, the dominant cycles are different in various paleoclimate indicators. This has limited our understanding of the dynamics of the ISM. Here we present a high-resolution ISM record spanning ~184–25 ka by magnetic parameters (ARM, χ, SIRM, and χfd%) and geochemical indicators (Rb/Sr and Ti) from lacustrine sediments in the Heqing Basin, southwestern China. In the PT2 core, ARM shows the clearest precession-scale (~20 ka) variability, likely reflecting its strong sensitivity to precipitation-driven changes in fine magnetic particle input. In contrast, Rb/Sr is dominated by glacial-interglacial (~100 ka) variability, probably because it responds to slower catchment-scale processes, such as chemical weathering and sediment redistribution. During MIS 5, low detrital input and a relative enrichment of fine magnetic grains likely shifted ARM toward stronger grain-size control rather than concentration control. This may have allowed the precession-scale signal to be expressed more clearly. Reductive dissolution likely modulated the amplitude of magnetic parameters, but did not fundamentally erase their primary orbital-scale signals. Our results highlight the importance of proxy-specific interpretation and demonstrate the value of ARM for reconstructing precession-paced ISM variability in southwestern China.
- Preprint
(1704 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 18 Jun 2026)
- RC1: 'Comment on egusphere-2026-2154', Anonymous Referee #1, 14 May 2026 reply
-
CC1: 'Comment on egusphere-2026-2154', Kenji Matsuzaki, 21 May 2026
reply
Comment on Yang et al., EGUsphere
This study presents a comprehensive analysis of lake sediment paleomagnetic data, compared with geochemical proxies, and discusses their implications for paleoceanographic reconstructions. The authors argue that magnetic properties of lake sediments can be used to infer variations in the Indian Summer Monsoon (ISM), given their close relationship with precipitation and moisture transport associated with monsoonal dynamics. They further compare multiple proxy records and emphasize that different proxies respond to distinct orbital forcings for instance, magnetic data appear to be primarily influenced by precession, consistent with monsoonal variability, whereas Rb/Sr ratios show a dominant ~100 kyr cyclicity, potentially reflecting glacial–interglacial climate changes.
Overall, the results appear robust and the study is conducted with scientific rigor. However, my main concern relates to the novelty of the work. It remains unclear what fundamentally new insight this study brings to the existing body of literature. This aspect should be more clearly articulated in a revised manuscript. In addition, I outline below several major and specific concerns aimed at improving the clarity, interpretation, and overall readability of the manuscript.
Major Comment
1. Introduction and Discussion:
The authors present a wide range of paleo-proxies from southwestern China and note that different proxies exhibit distinct cyclicities. While the study is spatially focused, it is valuable that the authors explain what each proxy represents and acknowledge their respective limitations and biases. The discussion of lake sediment magnetism as a well-established proxy for paleoclimate and particularly for monsoon dynamics is appropriate and balanced.
However, the broader scientific motivation remains insufficiently developed. The importance of improving our understanding of ISM dynamics is not clearly articulated, nor is the strategic significance of southwestern China as a study region. This should be expanded to better justify the study.
Furthermore, the role of the East Asian Summer Monsoon (EASM) should be more explicitly considered, given the geographic setting and the known interactions between monsoon subsystems.
Finally, the need for high-resolution climatic records is not convincingly justified. Given the already extensive body of knowledge on ISM variability, the authors should more clearly define the specific knowledge gap their study addresses and the precise research question they aim to answer.
2. Geochemical Analysis
For interpretations based on elemental data, it is essential to provide at least a basic geological description of the surrounding lithologies, including rock types and dominant mineral phases. This information is necessary to constrain the potential sources of transported material (e.g., via erosion or aeolian input). While a detailed description is not required, the absence of such context currently limits the robustness of the geochemical interpretations.
3. Spectral (Frequency) Analysis
The spectral analysis indicates a clear ~20 kyr cycle in the ARM and SIRM records. On other proxies, such as a potential ~20 kyr signal, appear weak and fall below confidence thresholds. In contrast, the ~100 kyr cycle is robust and statistically significant.
In the discussion, the authors should more critically assess what the spectral analysis can reliably demonstrate. In particular, they should clarify the strengths and limitations of each proxy in resolving orbital-scale variability and avoid over-interpreting non-significant periodicities.
The identification of a time interval (~90–130 ka) during which precession forcing appears diminished is an interesting result. This observation should be more explicitly linked to the spectral analysis. The authors should clarify how proxy sensitivity may vary under reduced precessional forcing and whether this behavior is consistent with the expected climatic significance of the proxies used.
Specific Comments
L.22–26: This statement is incomplete. The ISM is part of the broader global monsoon system, which includes African and East Asian subsystems. Given their dynamical connections and the study region, the influence of the EASM should be acknowledged. Please revise and consider citing: An et al. (2015), Annual Review of Earth and Planetary Sciences.
L.30–33: The discussion should be better grounded in foundational studies (e.g., Hays et al., 1976; Berger and Loutre; Ruddiman, 2001). The current focus on recent literature is too narrow.
L.33–35: The interpretation is incomplete. Eccentricity mainly modulates precession amplitude rather than directly forcing climate. This indirect role should be better explained (see Ruddiman, 2001).
L.38: Please cite Figure 1. The figure would benefit from indicating ISM and EASM fronts to improve spatial understanding.
L.70: If basin altitude is not directly supported by your data, this section should be reconsidered or removed.
L.75: Please include (or cite) sedimentological descriptions and ideally a lithological column.
L.82–99: This section falls outside my expertise and should be carefully evaluated by a specialist reviewer.
L.108–114: Please clarify how the paleomagnetic age model is established (e.g., stratigraphy vs. orbital tuning). Are independent age constraints (¹⁴C, OSL) available? Without these, the chronology remains relative rather than absolute.
L.110: Please specify the software used for analyses.
L.118–199: Expand and justify the consistency between your results and previous studies.
L.120: Explain the significance of the 120° value.
L.121–123: Clarify the relationship between temperature and magnetic minerals (magnetite, hematite) with more precision.
L.125: An r = 0.47 indicates only moderate correlation; this should not be overstated. Please revise.
L.130: Inferring that geochemical proxies track ISM solely because they align with magnetic proxies is an oversimplification. Orbital-scale analysis is required.
L.148: Specify the cycle being discussed (e.g., 100 kyr).
L.181–182: Please elaborate on the interaction between ISM and EASM.
Citation: https://doi.org/10.5194/egusphere-2026-2154-CC1 -
RC2: 'Comment on egusphere-2026-2154', Kenji Matsuzaki, 21 May 2026
reply
Comment on Yang et al., EGUsphere
This study presents a comprehensive analysis of lake sediment paleomagnetic data, compared with geochemical proxies, and discusses their implications for paleoceanographic reconstructions. The authors argue that magnetic properties of lake sediments can be used to infer variations in the Indian Summer Monsoon (ISM), given their close relationship with precipitation and moisture transport associated with monsoonal dynamics. They further compare multiple proxy records and emphasize that different proxies respond to distinct orbital forcings for instance, magnetic data appear to be primarily influenced by precession, consistent with monsoonal variability, whereas Rb/Sr ratios show a dominant ~100 kyr cyclicity, potentially reflecting glacial–interglacial climate changes.
Overall, the results appear robust and the study is conducted with scientific rigor. However, my main concern relates to the novelty of the work. It remains unclear what fundamentally new insight this study brings to the existing body of literature. This aspect should be more clearly articulated in a revised manuscript. In addition, I outline below several major and specific concerns aimed at improving the clarity, interpretation, and overall readability of the manuscript.
Major Comment
1. Introduction and Discussion:
The authors present a wide range of paleo-proxies from southwestern China and note that different proxies exhibit distinct cyclicities. While the study is spatially focused, it is valuable that the authors explain what each proxy represents and acknowledge their respective limitations and biases. The discussion of lake sediment magnetism as a well-established proxy for paleoclimate and particularly for monsoon dynamics is appropriate and balanced.
However, the broader scientific motivation remains insufficiently developed. The importance of improving our understanding of ISM dynamics is not clearly articulated, nor is the strategic significance of southwestern China as a study region. This should be expanded to better justify the study.
Furthermore, the role of the East Asian Summer Monsoon (EASM) should be more explicitly considered, given the geographic setting and the known interactions between monsoon subsystems.
Finally, the need for high-resolution climatic records is not convincingly justified. Given the already extensive body of knowledge on ISM variability, the authors should more clearly define the specific knowledge gap their study addresses and the precise research question they aim to answer.
2. Geochemical Analysis
For interpretations based on elemental data, it is essential to provide at least a basic geological description of the surrounding lithologies, including rock types and dominant mineral phases. This information is necessary to constrain the potential sources of transported material (e.g., via erosion or aeolian input). While a detailed description is not required, the absence of such context currently limits the robustness of the geochemical interpretations.
3. Spectral (Frequency) Analysis
The spectral analysis indicates a clear ~20 kyr cycle in the ARM and SIRM records. On other proxies, such as a potential ~20 kyr signal, appear weak and fall below confidence thresholds. In contrast, the ~100 kyr cycle is robust and statistically significant.
In the discussion, the authors should more critically assess what the spectral analysis can reliably demonstrate. In particular, they should clarify the strengths and limitations of each proxy in resolving orbital-scale variability and avoid over-interpreting non-significant periodicities.
The identification of a time interval (~90–130 ka) during which precession forcing appears diminished is an interesting result. This observation should be more explicitly linked to the spectral analysis. The authors should clarify how proxy sensitivity may vary under reduced precessional forcing and whether this behavior is consistent with the expected climatic significance of the proxies used.
Specific Comments
L.22–26: This statement is incomplete. The ISM is part of the broader global monsoon system, which includes African and East Asian subsystems. Given their dynamical connections and the study region, the influence of the EASM should be acknowledged. Please revise and consider citing: An et al. (2015), Annual Review of Earth and Planetary Sciences.
L.30–33: The discussion should be better grounded in foundational studies (e.g., Hays et al., 1976; Berger and Loutre; Ruddiman, 2001). The current focus on recent literature is too narrow.
L.33–35: The interpretation is incomplete. Eccentricity mainly modulates precession amplitude rather than directly forcing climate. This indirect role should be better explained (see Ruddiman, 2001).
L.38: Please cite Figure 1. The figure would benefit from indicating ISM and EASM fronts to improve spatial understanding.
L.70: If basin altitude is not directly supported by your data, this section should be reconsidered or removed.
L.75: Please include (or cite) sedimentological descriptions and ideally a lithological column.
L.82–99: This section falls outside my expertise and should be carefully evaluated by a specialist reviewer.
L.108–114: Please clarify how the paleomagnetic age model is established (e.g., stratigraphy vs. orbital tuning). Are independent age constraints (¹⁴C, OSL) available? Without these, the chronology remains relative rather than absolute.
L.110: Please specify the software used for analyses.
L.118–199: Expand and justify the consistency between your results and previous studies.
L.120: Explain the significance of the 120° value.
L.121–123: Clarify the relationship between temperature and magnetic minerals (magnetite, hematite) with more precision.
L.125: An r = 0.47 indicates only moderate correlation; this should not be overstated. Please revise.
L.130: Inferring that geochemical proxies track ISM solely because they align with magnetic proxies is an oversimplification. Orbital-scale analysis is required.
L.148: Specify the cycle being discussed (e.g., 100 kyr).
L.181–182: Please elaborate on the interaction between ISM and EASM.
Citation: https://doi.org/10.5194/egusphere-2026-2154-RC2 -
RC3: 'Comment on egusphere-2026-2154', Anonymous Referee #3, 29 May 2026
reply
The authors show that ARM and the Rb/Sr ratio behave differently in the lacustrine sediment, meaning that these two parameters reflect different forcing mechanism.
Rb/Sr variations have clear 100 kyr variability, while ARM has marginal 20 kyr variability. It is thus desirable to reinforce the ARM interpretation. Unfortunately, other rock magnetic data do not give coherent picture, often due to contradictory presentations. Consequently, its scientific value is uncertain. I recommend major revision before further evaluation.
The major problem is around discussion about "SD grain signals", which is emphasized as a merit of ARM. At line 127, the authors say "strongly magnetic samples display pronounced SD grain signals". But at line 186, "these changes led to (...) reduced Ti, xi, ARM, and SIRM values. At the same time, the magnetic grain size distributions shifts toward finer fractions (...)." These are contradictory. The data are shown in Fig. 3. They are too small to be read, but besides it I'm not sure which figure shows "pronounced SD signals." The FORC diagrams look more or less the same.
Second major point is that, although the author try to explain the difference between ARM and Rb/Sr by speculating the effect of denudation on Rb/Sr, the explanation does not seem to explain 100 kyr variability in xi or ARM/IRM.
Other minor points are as follows:
Line 92: what is the "xi curves"?
Line 95-96: please give measurement parameters for FORCs.
Line 95-96: give references for FORC diagrams.
Line 119: "The consistency (...) support this interpretation." What is consistent with what? Why "consistency" support the sediment source model?
Line 120, Figure 3: I don't see 300-400 C decline.
Line 129: At this point we don't know if magnetism is driven by ISM, so the correspondence to geochemical proxies does not say anything about the mechanism.
Line 102 and 131: I don't unerstand the role of Ti. If the sediment source does not change much and Ti is immobile during weathering, why Ti concentration changes? Maybe Ti flux is more appropriate than Ti concentration?
Line 148, Figure 5: Does xi and SIRM show precessional variability? It does not align with ARM and outside the shaded band (though I am not sure about the meaning of the shading).Citation: https://doi.org/10.5194/egusphere-2026-2154-RC3
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 238 | 58 | 25 | 321 | 29 | 28 |
- HTML: 238
- PDF: 58
- XML: 25
- Total: 321
- BibTeX: 29
- EndNote: 28
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
The authors rely heavily on ARM as a primary indicator of precipitation-driven fine magnetic flux. However, in a lacustrine setting like the Heqing Basin, magnetic mineralogy can be significantly altered by post-depositional reductive diagenesis. High organic matter burial in lake sediments often leads to the dissolution of fine-grained magnetite (the primary carrier of the ARM signal). The authors must provide more robust evidence (e.g., S-ratio or hysteresis loops) to prove that the ARM fluctuations reflect primary environmental flux rather than selective preservation/dissolution under changing redox conditions.
The use of Rb/Sr as a weathering proxy and Ti as a runoff proxy assumes a constant sediment source. However, Southwest China is geologically complex. The authors should address whether shifts in these ratios could be influenced by changes in sediment provenance (e.g., changes in river catchment area) rather than purely reflecting the intensity of the Indian Summer Monsoon (ISM). Without a detailed provenance analysis, the monsoon intensity interpretation of these geochemical signals remains somewhat circumstantial.
The age model spans ~184–25 ka. While the authors use established markers, lacustrine records are potential for variable sedimentation rates and potential hiatuses that are difficult to detect without a dense network of absolute dates (e.g., AMS 14C or OSL).
If the age model relies on linear interpolation between sparse control points, the orbital cycles identified in the spectral analysis might be artifacts of the age-depth relationship. The authors need to perform a sensitivity test on their age model to demonstrate that the ~20 ka precession signal is robust even when chronological uncertainties (which can be several thousand years in this time range) are factored in.
The authors compare the PT2 record directly with the Sanbao and Hulu Cave records. However, speleothem is an integrated signal of moisture transport distance and upstream depletion, whereas magnetic/geochemical proxies in a lake reflect local effective precipitation.
Direct correlation without addressing potential phase lags is problematic. For example, if the PT2 record shows a precession peak that is offset by 2–3 kyr from the speleothem record, does this reflect a real physical lag in the climate system or an error in the PT2 age model?
Comparing a terrestrial record from Southwest China to the Bay of Bengal (BoB) marine records is standard, but the authors overlook the regional heterogeneity of the ISM. The drivers of precipitation in the Heqing Basin (influenced by Tibetan Plateau orography) may differ significantly from the open-ocean signals recorded in the BoB. The manuscript tends to force a global fit with marine isotopes stages rather than exploring why the PT2 record might legitimately deviate from marine trends due to local threshold effects or rain-shadow dynamics.
The study attributes almost all variability to the ISM. A more critical comparison should include records of the Westerlies, which also influence Southwest China. Failure to distinguish between ISM-driven moisture and Westerly-driven winter precipitation complicates the "monsoon" interpretation of the ARM and geochemical proxies.