Hydrogeochemistry and Strontium Isotopic Signatures of Mineral Waters from Furnas and Fogo Volcanoes (São Miguel, Azores)
, Fatima Viveiros 1,2, Nuno Durães 3, Rui Coutinho 1,2, César Andrade 1,4, José Francisco Santos 3 and Maria Helena Acciaioli 3Round 1
Reviewer 1 Report
The reviewed paper presents some new hydrogeochemical, isotopic hydrogeochemical (including δ18O, δ2H, δ13C and δ34S) and Strontium isotopic data (87Sr/86Sr) from mineral waters from Furnas and Fogo, two active volcanoes at Sao Miguel (Azores). Provided data allows to characterize the two systems and to differentiate the Furnas and Fogo Strontium isotopic signature.
It is a good paper and provided data are of interest in other volcanic hydrogeological systems, but it must be improved in some aspects, as figures. Some conceptual aspects should be considered. The general data from the springs should be described or included in a table, as altitude, mean yields, geologic position, type of springs, etc. The suggested changes are detailed below:
- Line 145: Change Table 2 for Table 1.
Table 1 I think this table is not relevant for the paper objective. It would be better to include a table with rock geochemical data from the two studied volcanoes, if necessary.
- Lines 215-217: I would delete this sentence if marine intrusion is not present in the studied springs. If this sentence is included, it must be explained why it is relevant.
- Line 257: Check the Furnas thermal waters numeration. Attending to the temperature, I think the sentence must be “The thermal waters (Fu2, Fu4 and Fu5)”.
- Line 266: Change “dissolution” to “hydrolysis”.
- Line 268-269: Revise this sentence because in these volcanic aquifers with endogenous gas contribution, bicarbonate enrichment originates also from volcanic gases. Sometimes, depending on the climate, an important fraction of bicarbonate come from endogenous CO2, as δ13C of CITD shows.
Table 2 Indicate the type of water for the springs: Thermal or Cold spring. It is easily deductible from the temperature, but it would improve the reading.
- Line 17 (second part): Indicate the origin of the LMWL (reference) and the deuterium excess. I can deduce from Figure 4 that some springs from Fogo and Furnas (cold or thermal) are displaced to the left, so they show a little δ18O lightening. It has been observed in other volcanic aquifers with endogenous gas contribution. It could be discussed.
- Lines 38-39 (second part): I think it is a conceptual error. S come from volcanic gases, but not from volcanic rocks. If not, indicate what volcanic rocks are you referring to (Line 42, second part).
- Line 46 (second part): Where are the stromatolites? Have they been described?
- Line 51 (second part): Fig. 5B. You can change the figure or the numeration in Line 51 and Line 59.
- Lines 74-78 (second part): The areas where the samples were collected have not been well described, so this discussion is very weak. Please, consider to change or to remove it.
- Lines 82-94 (second part): This paragraph is repeated.
- Line 142 (second part): “amphiboles hydrolysis” instead of dissolution. Consider to include geochemistry of rocks instead of mineralogy if possible.
- Line 148-149 (second part): Consider if juvenile sulfur come from endogenous gases.
Revise all the subscripts and superscripts of the dissolved compounds, please. I think this is an edition mistake.
Figures
Figure 1: It must be deeply improved. Please, indicate in (A) the location of (B) and (C). I think it is not necessary to indicate in (A) the location of all the volcanic units of Sao Miguel, but only the two included in the paper. Fig. S2 can include all these locations. I think this orthophotos (or satellite photos) are flashy, but traditional maps offers more information. As an example: At what altitude are the springs located? It is not explained in the text and the maps could be more informative.
In this figure 1, the springs are located in (A), (B) and (C). Please, remove from (A) because they are not visible. The green points in (B) and (C) are difficult to see also, so I suggest changing the colors to better visible: red, yellow, orange is ok.
The legend must be included in this figure.
Figure 2: A legend must be included. This Piper plot should be better explained (or used) in the text or over drawn with some indications.
Figure 4: Change the axis titles (δ instead of d).
Figure 5: Change A for B or change the text as indicated in Line 51 (second part).
Figure 6: The two vertical scales should be the same. Consider to show all data in the same graphic, differentiated by triangles (Furnas) or circles (Fogo).
Figure 7: I think it would be indicated to include also this type of graphic for Furnas samples to substantiate the isotopic equilibrium for Furnas (Lines 103-104, second part).
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments
Point 1: Line 145: Change Table 2 for Table 1. / Table 1 I think this table is not relevant for the paper objective. It would be better to include a table with rock geochemical data from the two studied volcanoes, if necessary.
Response 1: The table was removed, and the data was converted to text format. The papers that we looked at didn’t present the geochemical data (values of the components) instead, they combined it with the mineralogy. We are using mineralogy to gain insight into geochemistry. We recognize the importance of rock geochemistry for this and future work, and we are conducting research on the geochemistry of the sampling locations as a result.
Point 2: Lines 215-217: I would delete this sentence if marine intrusion is not present in the studied springs. If this sentence is included, it must be explained why it is relevant.
Response 2: This is a pertinent observation since all the samples discharge from pearched-water bodies. The sentence was deleted.
Point 3: Line 257: Check the Furnas thermal waters numeration. Attending to the temperature, I think the sentence must be “The thermal waters (Fu2, Fu4 and Fu5)”.
Response 3: Thank you for pointing this out. The numeration was corrected once the thermal waters from Furnas are Fu1, Fu2, Fu4.
Point 4: Line 266: Change “dissolution” to “hydrolysis”.
Response 4: We changed the term as a result of your suggestion.
Point 5: Line 268-269: Revise this sentence because in these volcanic aquifers with endogenous gas contribution, bicarbonate enrichment originates also from volcanic gases. Sometimes, depending on the climate, an important fraction of bicarbonate come from endogenous CO2, as δ13C of CITD shows.
Response 5: We revised the sentence as you suggested.
Point 6: Table 2 Indicate the type of water for the springs: Thermal or Cold spring. It is easily deductible from the temperature, but it would improve the reading.
Response 6: In order to improve the reading experience, information regarding the type of spring was added to the table.
Point 7: Line 17 (second part): Indicate the origin of the LMWL (reference) and the deuterium excess. I can deduce from Figure 4 that some springs from Fogo and Furnas (cold or thermal) are displaced to the left, so they show a little δ18O lightening. It has been observed in other volcanic aquifers with endogenous gas contribution. It could be discussed.
Response 7: The origin of the LMWL and the corresponding reference were added to the text. The observed improvement was attributed to evaporation processes, as previously observed in other papers.
Point 8: Lines 38-39 (second part): I think it is a conceptual error. S come from volcanic gases, but not from volcanic rocks. If not, indicate what volcanic rocks are you referring to (Line 42, second part).
Response 8: Thank you for pointing this out; the S comes from the volcanic gases. The sentence has been altered.
Point 9: Line 46 (second part): Where are the stromatolites? Have they been described?
Response 9: Woitischeck et al. (2017) discovered stromatolites in thin sections of precipitates, and this information was incorporated into the text. They did not, however, describe them.
Point 10: Line 51 (second part): Fig. 5B. You can change the figure or the numeration in Line 51 and Line 59.
Response 10: There was an error in the text's formatting. Figure numeration and positioning were corrected.
Point 11: Lines 74-78 (second part): The areas where the samples were collected have not been well described, so this discussion is very weak. Please, consider to change or to remove it.
Response 11: The sentence was unclear so we changed it.
Point 12: Lines 82-94 (second part): This paragraph is repeated.
Response 12: Thank you for your observation. The extra paragraph has been removed.
Point 13: Line 142 (second part): “amphiboles hydrolysis” instead of dissolution. Consider to include geochemistry of rocks instead of mineralogy if possible.
Response 13: As a result of your suggestions, we modified the term. In our responses to reviews 1 and 2, we clarified the question about the geochemistry of the rocks.
Point 14: Line 148-149 (second part): Consider if juvenile sulfur come from endogenous gases.
Response 14: We took your suggestions into account and made the necessary changes.
Point 15: Revise all the subscripts and superscripts of the dissolved compounds, please. I think this is an edition mistake.
Response 15: There was an error in the edition. The document has been revised.
Point 16: Figure 1: It must be deeply improved. Please, indicate in (A) the location of (B) and (C). I think it is not necessary to indicate in (A) the location of all the volcanic units of Sao Miguel, but only the two included in the paper. Fig. S2 can include all these locations. I think this orthophotos (or satellite photos) are flashy, but traditional maps offers more information. As an example: At what altitude are the springs located? It is not explained in the text and the maps could be more informative.
Response 16: We decided to improve the figures and respective legends in response to your comments. The altitude will be added to the table.
Point 17: In this figure 1, the springs are located in (A), (B) and (C). Please, remove from (A) because they are not visible. The green points in (B) and (C) are difficult to see also, so I suggest changing the colors to better visible: red, yellow, orange is ok.
Response 17: Based on your feedback, we decided to change the colors of the springs to improve visibility.
Point 18: The legend must be included in this figure. / Figure 2: A legend must be included. This Piper plot should be better explained (or used) in the text or over drawn with some indications.
Response 18: Thank you for noticing. There was a formatting error in the document, but everything is now properly formatted.
Point 19: Figure 4: Change the axis titles (δ instead of d).
Response 19: Thank you for your observation. The axis titles have been updated.
Point 20: Figure 5: Change A for B or change the text as indicated in Line 51 (second part).
Response 20: The document had a formatting error, and the images were switched. Everything is now formatted correctly.
Point 21: Figure 6: The two vertical scales should be the same. Consider to show all data in the same graphic, differentiated by triangles (Furnas) or circles (Fogo).
Response 21: Thank you for your suggestions. As a result, we decided to display the data in the same graphic.
Point 22: Figure 7: I think it would be indicated to include also this type of graphic for Furnas samples to substantiate the isotopic equilibrium for Furnas (Lines 103-104, second part).
Response 22: We decided to include the graphic for Furnas samples after some thought. Thank you for your contributions for the improvement of this paper.R
Author Response File: Author Response.pdf
Reviewer 2 Report
I request the authors to make the following corrections in the paper:
- please use the same figure numbering style - start with S1 and S2 then switch to 1, 2 ...Please number with 1, 2, 3 etc. starting with the first figure
- please provide clearer figures for figure S2 and figure 1 (a). in figure 1 (a) the legend is not understood
- figure 2 has no legend
- reference 61 is missing from the text
Author Response
Response to Reviewer 2 Comments
Point 1: Please use the same figure numbering style - start with S1 and S2 then switch to 1, 2 ...Please number with 1, 2, 3 etc. starting with the first figure
Response 1: There was an error in the text's formatting. The first two figures should have been included in the supplemental materials section. The document has been revised and properly formatted.
Point 2: Please provide clearer figures for figure S2 and figure 1 (a). in figure 1 (a) the legend is not understood
Response 2: We decided to improve the figures and respective legends in response to your comments.
Point 3: Figure 2 has no legend
Response 3: Thank you for noticing. There was a formatting error in the document, but everything is now properly formatted.
Point 4: Reference 61 is missing from the text
Response 4: Thank you for pointing this out. The reference was inserted in the text.
Author Response File: Author Response.pdf
