the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Apr 2025
Late Holocene Wetland Environmental Changes and Their Climatic Drivers in the Marginal Regions of the Tibetan Plateau
Abstract. This study investigates the dynamics and driving mechanisms of wetland environment changes in the northeastern Tibetan Plateau, focusing on the expansion and contraction of wetlands in Maqin County, on the northeastern edge of the Tibetan Plateau during the late Holocene. By analyzing sediment samples from three borehole profiles through spore-pollen extraction and identification, OSL dating, and other methods, we reconstructed the spatiotemporal dynamics of wetland expansion and contraction. The results of pollen analysis show that changes in the proportion of Cyperaceae and Asteraceae pollen reflect the dynamic transition between wetland and grassland ecosystems. In the early period (approximately 7000–4000 BP), Cyperaceae dominated, indicating a more humid wetland environment; however, in the middle and late periods (from about 4000 BP onwards), the proportion of Cyperaceae gradually decreased, and Asteraceae increased significantly, reflecting a trend of increasing aridification and grassland expansion. Further analysis suggests that the primary drivers of wetland degradation may be related to the weakening of the Asian monsoon, rising temperatures, and regional aridification. A comparison with global climate models (CMIP6) reveals that wetland changes in the northeastern Tibetan Plateau are somewhat synchronized with global climate patterns during both wet and dry periods. This study reveals the spatiotemporal characteristics of the dynamic transition between wetland and grassland ecosystems in the northeastern Tibetan Plateau and explores the influence of climate change, monsoon fluctuations, and other factors on wetland evolution, providing new perspectives and theoretical foundations for understanding the response of plateau ecosystems to global climate change and for wetland conservation.
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RC1: 'Comment on egusphere-2025-1321', Anonymous Referee #1, 28 May 2025
General Assessment:
This manuscript explores the paleoenvironmental and paleoclimatic drivers of wetland development on the Tibetan Plateau, focusing on three boreholes within an unnamed wetland in Maqin County, China. The research questions raised are relevant and of potential interest to the paleoclimate community. However, the current version of the manuscript falls short of the standards expected for publication in Climate of the Past.
Major methodological weaknesses, particularly in the statistical analyses, undermine the credibility of the findings. Issues include: the use of inappropriate or incorrect statistical methods (e.g., flawed fractional abundance calculations and correlation matrices), insufficient sample sizes due to overly broad time windows (up to 2000 years), and inadequate documentation of key elements such as the age-depth model, full pollen data, and site description. Additionally, several interpretations are unsubstantiated, important references are missing, and the figures lack clarity and informativeness.
In its current form, the manuscript is not suitable for publication. I encourage the authors to undertake substantial revisions before considering resubmission to another journal.
Major Comments:
1. Age-Depth Model
The manuscript introduces OSL dating, yet an age-depth model is neither shown nor discussed. Given the temporal focus of the study, this is a critical omission and must be addressed.2. Wetland Site Description
The manuscript lacks a basic description of the wetland. What type of wetland is being studied? What is the dominant vegetation and hydrology? This is particularly important given the reliance on Cyperaceae and Asteraceae pollen. A clear description of the current vegetation distribution is also needed.
Section 2.1 could be divided into "Regional Setting" and "Local Study Area" to better structure this information. Figure 2 could support this section.3. Pollen Taxonomy and Interpretation
The text refers to “Tree pollen…” (lines 164–166), suggesting a full pollen diagram should be included, but none is provided.
Figures 3–5 are inconsistent in how fractional abundances are calculated. In Fig. 3, Cyperaceae and Asteraceae are normalized to 100%, whereas this is not the case in later figures.
The focus on only two taxa (Cyperaceae and Asteraceae) is overly reductive. A more robust approach would involve using pollen influx data or justified indices.
The manuscript lacks references validating the use of Cyperaceae as a wetland index or Asteraceae as a drought indicator. The use of these taxa as proxies must be clearly justified or supported by calibration studies.
Fig. 5b labels “Asteraceae ratio (drought index)” — it is unclear whether this refers to a ratio or a fractional abundance. Clarification is needed.4. Figure 4 – Methodological and Interpretive Issues
This figure is unclear. Is it a composite of all three cores? How were the values binned by depth and time? This must be explicitly described in the methods.
The curves do not sum to 100%, which contradicts earlier figures. This inconsistency should be resolved.
Several statements about trends in Fig. 4 are incorrect (e.g., lines 270 and 275 misrepresent the actual data trends "Cyperaceae increases with depth" or "Over time, Cyperaceae decreases..."). Moreover, panel axes are reversed, making the figure difficult to interpret.
Finnaly, it is very unlikely to have a perfect linearity between pollen abundances and depth...5. Time Window Selection
The choice to aggregate data into 2000-year time windows is problematic, especially given the apparent depth resolution of the pollen data. For Holocene studies, windows of 100–500 years are more appropriate. This decision dramatically reduces the number of data points and statistical power, and the aggregation is too important to record any temporal trend.6. Statistical Analysis
The current statistical approach is fundamentally flawed. Constructing indices as Cy/(Cy+Ast) and Ast/(Cy+Ast) will always yield a perfect negative correlation (r = -1). Therefore, statements like line 342–344 are mathematically trivial and meaningless.
Additionally, drawing conclusions from correlation matrices with only 7 time windows lacks statistical validity. A complete rethinking of the statistical methods is necessary.7. References
The reference list needs thorough checking. For example, Tiner (2017) is listed but not cited. Ensure all listed references are cited in the text and all citations are listed in the references.Minor Comments
Line 20: Consider using “Mid-Holocene” instead of “early period.”
Line 51: Add a supporting reference.
Line 61: Why focus solely on the Late Holocene (ca. 4200 yr cal BP) if your archive records older timespan?
Line 69: Mention that wetlands may also be influenced by local hydrology, slope, and surrounding vegetation—not just climate and human activity.
Line 73: Same comment as line 61.
Lines 104–105: Needs reformulation for clarity.Figure 1: The first panel is distorted. Use standard terminology: replace “west wind circulation” with “westerlies” and “East Asian Monsoon” with “East Asian Summer Monsoon.” Remove the last sentence from the caption. Include the source of the cartographic data (e.g., elevation model, satellite imagery).
Line 161–162: Include a reference for the use of Lycopodium tablets.
Section 2.4: Repetitive writting of “Use…” at the beginning of sentences sounds awkward. Reword for fluency.
Line 213: The term “interpolation” may not be accurate. If the data are stacked and binned, please describe it as such.
Lines 242–244: The assumption mentioned here must be supported by evidence or references.
Line 263: Time cannot be expressed in centimeters. Clarify the axis label or unit.
Figure 5: The temperature scales in panel B vary too widely, making the comparison ineffective. Standardize the scale or present the data separately for clarity.
Citation: https://doi.org/10.5194/egusphere-2025-1321-RC1 -
CC1: 'Comment on egusphere-2025-1321', Xiaozhong Huang, 15 Jun 2025
The manuscript has done new records in the eastern part of Tibet Plateau, which would help us to understand past wetland and vegetation dynamics and related climate change during the past several thousand years. The data are valuable to be published. While, I have to point out some confusion points in this MS.
1) the chronology should be present on the lithological diagram to show the location of the OSL samples and age results.
2) for the data description, it is really confusion for the pollen data. For the Figure 3 and Figure 4a, it is very clear that the Cyperaceae is higher in the upper part of the core Y (after 4ka), while, the context Line 270-271 says that "Cyperaceae pollen increases with depth, particularly around 2.0 meters...", Cyperaceae was low in the lower section!!! So, the two profiles results are quite different in Figure 4... Please correct it, although it does not influence your interpretation. It also need to clarify that the pollen species has different environmental significance for different location of your sites. This may help your interpretations.
3) For the Figure 2, you had better add a red dot to show your profile location on the picture.
4) For the climate background, I can recommend some new references showing late Holocene warming in present cold regions (Huang Cong et al., 2024 GPC, https://doi.org/10.1016/j.gloplacha.2024.104577).
Citation: https://doi.org/10.5194/egusphere-2025-1321-CC1 -
RC2: 'Comment on egusphere-2025-1321', Anonymous Referee #2, 18 Jun 2025
I've reviewed the existing comments and fully agree with them. Let me add a few additional points of my own.
I couldn't find any description of the vegetation around the sampling points. This is important because Cyperaceae can also be indicators of arid high-altitude cobresian communities, not just wetlands.
Why wasn’t the radiocarbon method used for control, given that organic remains are present in the profiles?
Unusual age models – there's no zero centimeter anywhere. Is the topmost cm not contemporary/modern?
Lines 270-272: I observe that Cyperaceae pollen decreases with depth—the deeper the layer, the less it is present, rather than increasing.
Lines 282-283: while Asteraceae begins rising around 3000 years ago and reaches its highest levels near the present. - I might be misunderstanding something, but Figure 3 shows a completely different pattern - Asteraceae peak in the mid-Holocene and then decline, except in core T where there are no modern deposits at all.
I fail to see the merit in this discussion section as it reiterates claims about Asteraceae increasing in the late Holocene and Cyperaceae being abundant during 7-4 kyr BP, while the actual data (Fig. 3) clearly show the opposite pattern. I strongly recommend that the authors:
- Re-examine their age-depth model,
- Provide proper documentation of the pollen data,
- Include complete pollen diagrams,
- Re-evaluate all their hypotheses.
In its current form, the study's conclusions appear completely unsubstantiated.
Citation: https://doi.org/10.5194/egusphere-2025-1321-RC2
Status: closed (peer review stopped)
-
RC1: 'Comment on egusphere-2025-1321', Anonymous Referee #1, 28 May 2025
General Assessment:
This manuscript explores the paleoenvironmental and paleoclimatic drivers of wetland development on the Tibetan Plateau, focusing on three boreholes within an unnamed wetland in Maqin County, China. The research questions raised are relevant and of potential interest to the paleoclimate community. However, the current version of the manuscript falls short of the standards expected for publication in Climate of the Past.
Major methodological weaknesses, particularly in the statistical analyses, undermine the credibility of the findings. Issues include: the use of inappropriate or incorrect statistical methods (e.g., flawed fractional abundance calculations and correlation matrices), insufficient sample sizes due to overly broad time windows (up to 2000 years), and inadequate documentation of key elements such as the age-depth model, full pollen data, and site description. Additionally, several interpretations are unsubstantiated, important references are missing, and the figures lack clarity and informativeness.
In its current form, the manuscript is not suitable for publication. I encourage the authors to undertake substantial revisions before considering resubmission to another journal.
Major Comments:
1. Age-Depth Model
The manuscript introduces OSL dating, yet an age-depth model is neither shown nor discussed. Given the temporal focus of the study, this is a critical omission and must be addressed.2. Wetland Site Description
The manuscript lacks a basic description of the wetland. What type of wetland is being studied? What is the dominant vegetation and hydrology? This is particularly important given the reliance on Cyperaceae and Asteraceae pollen. A clear description of the current vegetation distribution is also needed.
Section 2.1 could be divided into "Regional Setting" and "Local Study Area" to better structure this information. Figure 2 could support this section.3. Pollen Taxonomy and Interpretation
The text refers to “Tree pollen…” (lines 164–166), suggesting a full pollen diagram should be included, but none is provided.
Figures 3–5 are inconsistent in how fractional abundances are calculated. In Fig. 3, Cyperaceae and Asteraceae are normalized to 100%, whereas this is not the case in later figures.
The focus on only two taxa (Cyperaceae and Asteraceae) is overly reductive. A more robust approach would involve using pollen influx data or justified indices.
The manuscript lacks references validating the use of Cyperaceae as a wetland index or Asteraceae as a drought indicator. The use of these taxa as proxies must be clearly justified or supported by calibration studies.
Fig. 5b labels “Asteraceae ratio (drought index)” — it is unclear whether this refers to a ratio or a fractional abundance. Clarification is needed.4. Figure 4 – Methodological and Interpretive Issues
This figure is unclear. Is it a composite of all three cores? How were the values binned by depth and time? This must be explicitly described in the methods.
The curves do not sum to 100%, which contradicts earlier figures. This inconsistency should be resolved.
Several statements about trends in Fig. 4 are incorrect (e.g., lines 270 and 275 misrepresent the actual data trends "Cyperaceae increases with depth" or "Over time, Cyperaceae decreases..."). Moreover, panel axes are reversed, making the figure difficult to interpret.
Finnaly, it is very unlikely to have a perfect linearity between pollen abundances and depth...5. Time Window Selection
The choice to aggregate data into 2000-year time windows is problematic, especially given the apparent depth resolution of the pollen data. For Holocene studies, windows of 100–500 years are more appropriate. This decision dramatically reduces the number of data points and statistical power, and the aggregation is too important to record any temporal trend.6. Statistical Analysis
The current statistical approach is fundamentally flawed. Constructing indices as Cy/(Cy+Ast) and Ast/(Cy+Ast) will always yield a perfect negative correlation (r = -1). Therefore, statements like line 342–344 are mathematically trivial and meaningless.
Additionally, drawing conclusions from correlation matrices with only 7 time windows lacks statistical validity. A complete rethinking of the statistical methods is necessary.7. References
The reference list needs thorough checking. For example, Tiner (2017) is listed but not cited. Ensure all listed references are cited in the text and all citations are listed in the references.Minor Comments
Line 20: Consider using “Mid-Holocene” instead of “early period.”
Line 51: Add a supporting reference.
Line 61: Why focus solely on the Late Holocene (ca. 4200 yr cal BP) if your archive records older timespan?
Line 69: Mention that wetlands may also be influenced by local hydrology, slope, and surrounding vegetation—not just climate and human activity.
Line 73: Same comment as line 61.
Lines 104–105: Needs reformulation for clarity.Figure 1: The first panel is distorted. Use standard terminology: replace “west wind circulation” with “westerlies” and “East Asian Monsoon” with “East Asian Summer Monsoon.” Remove the last sentence from the caption. Include the source of the cartographic data (e.g., elevation model, satellite imagery).
Line 161–162: Include a reference for the use of Lycopodium tablets.
Section 2.4: Repetitive writting of “Use…” at the beginning of sentences sounds awkward. Reword for fluency.
Line 213: The term “interpolation” may not be accurate. If the data are stacked and binned, please describe it as such.
Lines 242–244: The assumption mentioned here must be supported by evidence or references.
Line 263: Time cannot be expressed in centimeters. Clarify the axis label or unit.
Figure 5: The temperature scales in panel B vary too widely, making the comparison ineffective. Standardize the scale or present the data separately for clarity.
Citation: https://doi.org/10.5194/egusphere-2025-1321-RC1 -
CC1: 'Comment on egusphere-2025-1321', Xiaozhong Huang, 15 Jun 2025
The manuscript has done new records in the eastern part of Tibet Plateau, which would help us to understand past wetland and vegetation dynamics and related climate change during the past several thousand years. The data are valuable to be published. While, I have to point out some confusion points in this MS.
1) the chronology should be present on the lithological diagram to show the location of the OSL samples and age results.
2) for the data description, it is really confusion for the pollen data. For the Figure 3 and Figure 4a, it is very clear that the Cyperaceae is higher in the upper part of the core Y (after 4ka), while, the context Line 270-271 says that "Cyperaceae pollen increases with depth, particularly around 2.0 meters...", Cyperaceae was low in the lower section!!! So, the two profiles results are quite different in Figure 4... Please correct it, although it does not influence your interpretation. It also need to clarify that the pollen species has different environmental significance for different location of your sites. This may help your interpretations.
3) For the Figure 2, you had better add a red dot to show your profile location on the picture.
4) For the climate background, I can recommend some new references showing late Holocene warming in present cold regions (Huang Cong et al., 2024 GPC, https://doi.org/10.1016/j.gloplacha.2024.104577).
Citation: https://doi.org/10.5194/egusphere-2025-1321-CC1 -
RC2: 'Comment on egusphere-2025-1321', Anonymous Referee #2, 18 Jun 2025
I've reviewed the existing comments and fully agree with them. Let me add a few additional points of my own.
I couldn't find any description of the vegetation around the sampling points. This is important because Cyperaceae can also be indicators of arid high-altitude cobresian communities, not just wetlands.
Why wasn’t the radiocarbon method used for control, given that organic remains are present in the profiles?
Unusual age models – there's no zero centimeter anywhere. Is the topmost cm not contemporary/modern?
Lines 270-272: I observe that Cyperaceae pollen decreases with depth—the deeper the layer, the less it is present, rather than increasing.
Lines 282-283: while Asteraceae begins rising around 3000 years ago and reaches its highest levels near the present. - I might be misunderstanding something, but Figure 3 shows a completely different pattern - Asteraceae peak in the mid-Holocene and then decline, except in core T where there are no modern deposits at all.
I fail to see the merit in this discussion section as it reiterates claims about Asteraceae increasing in the late Holocene and Cyperaceae being abundant during 7-4 kyr BP, while the actual data (Fig. 3) clearly show the opposite pattern. I strongly recommend that the authors:
- Re-examine their age-depth model,
- Provide proper documentation of the pollen data,
- Include complete pollen diagrams,
- Re-evaluate all their hypotheses.
In its current form, the study's conclusions appear completely unsubstantiated.
Citation: https://doi.org/10.5194/egusphere-2025-1321-RC2
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