CO₂ Dynamics and Transport Mechanisms Across Atmosphere–Soil–Cave Interfaces in Karst Critical Zones

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is a thorough and well-designed study.

The one major weakness I would cite is the lack of discussion of the implications of this topic on paleoclimate research. Speleothem isotopes are a major paleoclimate proxy, and this work has important implications for how these proxies are analyzed. This manuscript only mentions paleoclimate very briefly in the Conclusions and not at all in the Discussion or Introduction.

My other major complaint is the lack of attention to the bedrock. The studied cave is in a dolomite terrain, so water entering the cave whether through fissures or as drip water, has contact with the dolomite. Some dissolution must occur, which impacts the isotopic composition of CO2 degassed within the cave. Even if this contribution is negligible compared to the other sources, it needs to be considered and discussed.

Minor comments

Lines 39-40. Start by explicitly defining the terms you use. Not everyone may be familiar with the concept of the critical zone or understand “complex surface-subsurface dual permeability structures.”

Lines 45-46. It would be helpful to explain how these systems are synergistic instead just saying that they are.

Line 62. Is the “high in summer, low in winter” trend for caves global or regional? That is, does this generalization apply mainly to regions with monsoonal climates?

Lines 124-125. This might be a good place to point out the differences in vegetation type, the C4 crop plants vs, mainly C3 natural vegetation.

Line 148. The soil CO2 was measured only once a month? Do you mean a single reading, or an average of multiple readings over a set time period?

Line 155. What does “Approximately residual gas” mean?

Line 230. This is where (apparently) you assume that degassing of drip water does not contribute to the cave air. Is this assumption valid?

Line 316-317. How much difference is there in plant and root spatial density between the sites? I would assume croplands are low and grasslands are high.

Lines 402-403. “…and the CO2 released is low; on the contrary, it is high.” Something is missing here.

Lines 409-410. “…and the correlation slightly increased with increasing soil depth.” Could that be because Ts is more stable at greater depth?

Lines 460-463. Make it clear that enrichment and depletion are relative terms, in this case to atmospheric carbon.

Lines 541-543. “… that they may be negatively correlated with cave CO2 variability, however, have a slight contribution to PC1.”  Not a sentence as written.

Line 583. “geological carbon fluxes.” Is this drip water CO2 degassing, or gaseous flux from hydrothermal or magmatic processes?

Line 635. Along with root respiration, include microbial respiration.

Line 739. So here you finally mention the formation of carbonic acid which dissolved carbonate. So how important is the dissolution of soil and bedrock carbonate and the degassing of the water when it reaches the cave?

Line 789. You mention the implications for paleoclimate studies in the Conclusions, but never discussed this in the Discussion.

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a multi-year monitoring study (2019–2023) of CO₂ dynamics and transport mechanisms across the atmosphere–soil–cave continuum in Mahuang Cave, a dolomite cave in southwestern China. The dataset is valuable, the methodological framework is comprehensive, and the results are of clear significance for understanding carbon cycling in karst critical zones. However, several aspects require substantial revision before the manuscript can be considered for publication.

1. The authors should highlight how long-term monitoring in a dolomite cave, the explicit identification of nonlinear soil thresholds, and multi-scale coupling analyses contribute beyond existing studies.
2. The manuscript focuses exclusively on dolomite caves without explicit comparison to limestone caves, which dominate global karst research. To broaden the relevance of the findings, the authors should integrate a comparative discussion with results from typical limestone caves (e.g., Caves in Guilin).
3. The conclusion section repeats too many detailed results and lacks conciseness.
4. Present the full loading matrix in a table, not only in the figure, to allow quantitative assessment of variable contributions.
5. Language should be streamlined: avoid repeated formulations such as “high in rainy season – low in dry season.” Furthermore, readability should be enhanced by clarifying whether "3 m" and "2–3 m" in lines 182 and 186 refer to distance or time.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf