Dear authors

I was pleased to see a new hydroclimate reconstruction with improved method being presented in this manuscript and I read it with much interest. The study marks a valuable contribution to the field. I had some issues with the validation of the reconstruction, see my comments in the attached PDF. I hope my inputs are helfpul for the revision.

Best regards, Raphael Neukom

This manuscript presents a new Common Era climate reconstruction of South America, generated via paleo data assimilation. The authors include speleothems in their methodology, a largely unused archive in paleo data reconstructions. The manuscript provides a detailed description of their DA methods, validation methods, and clearly discuss the methodological limitations. They use their climate reconstructions to examine climatological anomalies through time and compare their findings to existing DA products.

This manuscript was incredibly thorough and presents an exciting new advancement in the use of speleothem records in paleodata assimilation. I think the authors hit a good balance between interpreting their reconstruction and an honest discussion of the limitations/uncertainties. From my understanding of DA, the methodology and science seems sounds, and I believe the manuscript is nearly ready for publication. I focus my few comments here on organization and readability.

Appendix organization:  In my opinion, I think the Appendices are out of order (e.g. appendix D is reference before appendix C). This makes navigating through the very lengthy supplemental information a bit challenging. I would recommend reordering the appendices as follows (A, D, C, B). I ran into a similar issue with the supplemental figures within Appendix A. There were several times where figures were referenced out of order (e.g. AF9 and 10 were referenced before AF 5-8).

Supplemental figures: The number of supplemental figures in Appendix A makes the manuscript a bit cumbersome to read. I also find that the authors extensively discuss many of their supplemental figures in the text. This makes me wonder whether some should be moved to the main text? While I acknowledge that this may make the flow a bit less elegant, I think it would help guide the reader as the manuscript touches on quite a few different topics. I will not recommend any specific changes here and leave this decision up to the authors.

Line comments:

Line 65 – Missing some detail on the drivers of speleothem d18O. E.g. are there any studies specific to South America that should be cited here? What about upstream rainout, cloud effects. Etc… Dansgaard is a good reference, but some additional works should be cited here.

Line 75 – topic sentence is a bit confusing – perhaps say ‘are excluded’ instead of ‘may be excluded’

Line 399 – Unless I missed it, I couldn’t find the definition of the Southern Cone