See attached file

The manuscript submitted by Kost et al deals with the characterization of the atmosphere-karst vadose zone-cave system at a cave located in the Northwest Iberian Peninsula. The characterisation is based on a cave monitoring programme including measurements of cave air, bedrock chemistry, and drip water δ¹³C DIC, δ¹⁸O and δD as well as 16 trace elements with irregular measurements for about 16 months. The study finds sensitivities of drip rates to climatic seasonality but relatively low variations of the stable water isotopes which they attribute to a well-mixed reservoir in the vadose zone above the cave. δ¹³C DIC indicates the influence of seasonal vegetation dynamics and related microbial activity. Their measurements further indicate limited the extent of the seasonal variation of degassing and prior calcite precipitation (PCP). They also indicate that stalagmite growth is limited to the summer and winter seasons.

The study is well-written and concise. The simultaneous monitoring of multiple variable permits in-depth analysis of the processes controlling cave drip water composition and stalagmite growth in the observed cave. There are only few minor points that should be addressed:

• The results section already includes a lot of interpretation and link to other references, which should be moved to the discussion section.
• Assumption of P-PET equals available water for downward percolation from the surface. I do not completely agree with this assumption as it assumes that AET equals PET, which is often not the case and which may explain why the drips are also active in summer.
• AET and PET depend on factors like land cover type, soil thicknesses, and rooting depth. Consequently, they affect what is left for feeding the drips below and also how fast a drip reacts to rainfall events (see for instance Berthelin and Hartmann, 2020; Carrière et al., 2020; Sarrazin et al., 2018).
• The authors mention the 7-day antecedent cumulative rainfall method by Baker et al (2020, 2021) did not work but did they also try the simple bucket model used in the same studies? This may help resolving the question about PET being a goof proxy for AET and allow to estimate vertical percolation in the preceding years.
• The authors state that the spatial variability of drip waters suggest that they are not feed by the same reservoir but multiple reservoirs with varying dominance of diffuse and preferential flow routes. However, different contributions of diffuse and preferential flow would not affect the time, volume weighted averages of the drips. More preferential flow would only result in stronger visibility of the seasonal isotopic signal of the rain, which the authors did not find. The obvious differences in average δ¹⁸O and δD must originate from different processes than mixing alone. Maybe, the processes found by Treble et al. (2022) can support the interpretation.
• When discussing the effect of evaporation on stable water isotopes, it is not clear whether the authors mean evaporation and/or transpiration because only the former results in fractionation.
• Generally, the discussion section seems to be quite long, especially when considering that it already starts in the results section (see my previous comment). It would be helpful, if the authors could tailor it a bit more to the main outcomes of the paper.

I am convinced that these points can be implemented within the frame of minor revisions.

References

Berthelin, R. and Hartmann, A.: The Shallow Subsurface of Karst Systems : Review and Directions, in: Advances in Karst Science, edited by: Bertrand, C., Denimal, S., Steinmann, M., and Renard, P., Springer International Publishing, Cham, 61–68, https://doi.org/10.1007/978-3-030-14015-1_7, 2020.

Carrière, S. D., Martin-StPaul, N. K., Cakpo, C. B., Patris, N., Gillon, M., Chalikakis, K., Doussan, C., Olioso, A., Babic, M., Jouineau, A., Simioni, G., and Davi, H.: The role of deep vadose zone water in tree transpiration during drought periods in karst settings – Insights from isotopic tracing and leaf water potential, Science of the Total Environment, 699, 134332, https://doi.org/10.1016/j.scitotenv.2019.134332, 2020.

Sarrazin, F., Hartmann, A., Pianosi, F., Rosolem, R., and Wagener, T.: V2Karst V1.1: A parsimonious large-scale integrated vegetation-recharge model to simulate the impact of climate and land cover change in karst regions, Geosci Model Dev, 11, https://doi.org/10.5194/gmd-11-4933-2018, 2018.

Treble, P. C., Baker, A., Abram, N. J., Hellstrom, J. C., Abram, N. J., Crawford, J., Gagan, M. K., Borsato, A., Griffiths, A., Bajo, P., Markowska, M., Priestley, S., Hankin, S., and Paterson, D.: Ubiquitous karst hydrological control on speleothem oxygen isotope variability in a global study, Commun Earth Environ, https://doi.org/10.1038/s43247-022-00347-3, 2022.