|I’d like to reiterate from my previous review that I think the authors have done an excellent job examining the processes controlling Hell’s Bells formation over a series of manuscripts. I’m looking forward to reading the additional manuscripts they mention are in preparation. |
I have only a few general criticisms and hope to see the paper published in due course. First, the paper is now entirely too long. Second, and related to the first, at least some of the length of the manuscript can be reduced by removing the detailed descriptions of all of the different ways that the halocline can oscillate (see comments related to Page 26). I briefly expand on these points in my line-by-line comments, below.
Page 1, Line 30 – I recommend adding annual tidal variability to the list of possible causes for halocline oscillation. The authors mention this in their rebuttal, but do not include it in the manuscript.
Page 2, Line 5 – Stalactites, by definition, only form by dripping water. They cannot form underwater. Please change to “speleothems” or “secondary precipitates.”
Page 2, line 12 – meter should be plural.
Page 2, line 15 – if they are above the anoxic/sulfidic zone, how is the environment “toxic”?
Page 3, line 4 – there is no plausible method of estimating unmapped cave lengths. I recommend removing the suggestion that there is more than 7,000 km of possible cave.
Page 3, line 6 – Karst cave is probably redundant in this context.
Page 3, line 10 – recommend changing “seawater” to “saline water” as the geochemical composition of some of this water is distinct from seawater.
Page 3, line 11-14 – the halocline has been proposed to be an area of carbonate mineral undersaturation on the basis of numerical models and geomorphology, however, geochemical studies rarely find undersaturation due to mixing (which is the point of the Gulley et al. 2016 paper that is cited here as evidence of undersaturation in haloclines).
Page 6, line 10 – change to tourist.
Page 6 – line 23. The hysteresis observed in pH is clearly shown in the graphs, but I hesitate to conclude that the authors can interpret those results to indicate pH values should be lower in the saline water. Their pH profiles show pH values of ~6.8. Lower pH values of 6.6 seem unlikely considering the buffering capacity of seawater (Ben-Yaakov, 1973)
Page 6 – line 33-34 – how were the glass vials used to sample water underwater? Were the vials empty and then opened (pressure makes this unlikely). Were the vials pre-filled with water and then purged with breathing gas? If so, how many purges were used?
Page 23 – Fig 9 - DOC appears to spike in the turbid layer and no3 concentrations are high in freshwater above the halocline. Oxidation of organic material in sediments is important, but the data in figure 3 suggest that organic matter accumulation at the density interface in the turbid zone is also important. Is there any way to include these processes in Fig 9 and in the text referencing Fig 9?
Page 25, line 21 – replace “wide vertical zone” with “thick vertical zone” to make it more clear that the reference is to the vertical dimension.
Page 26, entire section on oscillation of the halocline - I think the authors can reduce the length of this entire section by simply stating that the elevation of the halocline oscillates over multiple timescales in response to droughts, hurricanes, and annual tidal fluctuations that are superimposed upon on a longer term increase in sea level. This would allow them to dodge the complicated (and not particularly well-explained) hydraulics associated with recharge elevation of the halocline (which really doesn’t add much besides length to this paper). If the authors feel this is super important, they should follow it up with a second paper with the data they mention having collected.
Page 30, Section 4.4 – In the rebuttal, the authors indicate that Hell’s Bells are also found in caves with light, so the requirement for a lightless environment here is confusing. Further, I think the authors should specifically mention the requirement for a thick mixing zone. I would then go on to explain how other mixing zones that have been studied in the Yucatan differ from these requirements.
Ben‐Yaakov, S., 1973. pH BUFFERING OF PORE WATER OF RECENT ANOXIC MARINE SEDIMENTS 1. Limnology and Oceanography, 18(1), pp.86-94.