the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Feb 2025
Technical note: Acidification methodology impacts sediment decarbonation as revealed by bulk and serial oxidation measurements
Abstract. Acidification is frequently adopted to remove carbonates preceding particulate organic carbon (POC) measurements. In practice, acid rinsing and acid fumigation are two typical and well-established acidification methods eliminating inorganic carbon. However, detailed protocols therein are most likely adopted based on conventional laboratory practices, assuming that the measurement precision is unaffected by experiment conditions. In fact, acidification can cause mineral dissolution and leaching of organic components, and therefore impacts the quantity and composition of residual POC considerably. Nonetheless, the effect of acidification on POC properties and the underlying mechanisms are ambiguous when relying solely on bulk measurements. In this study, we investigated POC properties following acidification using ramped temperature pyrolysis/oxidation (RPO) technique, in combination with bulk carbon analyses, to assess the impact of different decarbonation pretreatments on the sedimentary organic carbon (OC) measurements. Our results reveal that both acidification method (rinsing or fumigation) and HCl concentrations under acid rinsing are main factors dictating OC properties measured. Notably, despite negligible differences in bulk measurements, RPO results show distinct variations between these two acidification methods. In combination with other evidence, our study suggests that the alteration of organic-inorganic associations, which is ubiquitous during acidification, drives the behaviour of POC properties that measured. Furthermore, we demonstrate that the characteristics of residual POC in acid-rinsed samples are more proximal to pristine, natural states of the raw materials, whereas the strikingly discrepant differences between two acidification methods can be attributed mainly to the perturbation caused by calcium chlorides after acid fumigation.
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Status: closed
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RC1: 'Comment on egusphere-2025-701', Anonymous Referee #1, 16 Apr 2025
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AC1: 'Reply on RC1', Xingqian Cui, 11 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-701/egusphere-2025-701-AC1-supplement.pdf
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AC1: 'Reply on RC1', Xingqian Cui, 11 Jul 2025
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RC2: 'Comment on egusphere-2025-701', Anonymous Referee #2, 26 Jun 2025
I think this is a good study but could do with more information such as C/N, FTIR etc. And I would have liked to see the results of what was lost (since you did talk about the supernant)
The paper is very long and hard to follow. I would suggest reducing and making concise, and bringing the RPO and acid experiment together instead of dealing with them separately that makes it hard to evaluate. R1's suggestion of 2 papers seems like a good idea to me. There are good results here but I think the paper itself is confusing and hard to read due to sample codes, jumping back and forward for different methods, and the lack of linkage between the acid/RPO experiments.
I have commented on the attached pre-print.
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AC2: 'Reply on RC2', Xingqian Cui, 11 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-701/egusphere-2025-701-AC2-supplement.pdf
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AC2: 'Reply on RC2', Xingqian Cui, 11 Jul 2025
Status: closed
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RC1: 'Comment on egusphere-2025-701', Anonymous Referee #1, 16 Apr 2025
Review of Songfan He et al. “Technical note: Acidification methodology impacts sediment decarbonation as revealed by bulk and serial oxidation measurements”
This article discusses various methods of acidification of sediment samples to remove carbonates and the effects of these acidification methods on the residual organic carbon. The range of acidification methods used are liquid acid of various acid concentrations (hot or room temp, various time intervals) followed by rinsing, fumigation with strong acid followed either no rinse or rinse and the dried by either oven drying or freeze drying. They then evaluate the remaining carbon by total carbon measurements and stable carbon measurements. They then discuss a relatively new ramped temperature pyrolysis/oxidation (RPO) technique where they test the various acidified samples by heating and provide data and interpretation of CO2 evolution versus temperature.
The information in the paper is worthy of publication. But significant editorial changes and clarifications are needed. I include a scan of the MS with rough suggestions/comments.
My most major comment is that it seems that this MS could be broken into two different papers. One with the the acidification portion and TOC and d13C study. One with the RPO study. The two parts of the paper are not well joined. The conclusion section is nearly all (or all but the last sentence) about the acidification portion.
Much of the language throughout needs cleaning up. Examples of odd word choices and potential changes:
“more proximal to pristine” – “more similar to pristine”
“strikingly discrepant” – “Strikingly different”
“Current instrument advancing allows” - “Current instruments allows”
“superposition of myriad signals” - “addition of several signals”
“we carefully instilled several drops” - “we carefully added several drops”
“13C-enriched moieties” – Maybe “13C-enriched compounds”
“To reconcile and depict coincident” – “To illustrate”?
“exhibit constant gradation” ?
“Besides, our study” - “Finally, our study”
Specific comments below - see also the scan MS with handwritten comments
Four samples are used for the various treatments. Each of the samples is abbreviated but the abbreviates are far too complex. For example, one sedimentary rock is abbreviated “1207-GR-11”. Another sedimentary rock is “MS05-135”. Why not just call them Sed1 and Sed2. No need for complex abbreviation that confuses the reader and makes the reader must refer back each time the sample is named.
In section 2.2 the different acidification methods are termed EC1 through EC12. Define EC – it might be “experimental condition” but the reader is unclear why “EC” is used.
In section 2.2 EC11 and EC12 are also named “fume I” and “fume II” – this is confusing.
Table 1 needs work. What is “Mark*”. Maybe add an additional column that shows that EC-1 is the control. And that EC11 and EC12 are also named “fume I” and “fume II”
Line 104 - Air drying – the reviewer thinks that this is room temperature drying. “Oven drying” is also air drying. Need clarification.
Line 107 – This is a reviewer’s pet peeve. “… to remove acid vapors completely” – Oven drying or freeze drying of fumigated samples might remove acid vapors but any acid vapors that settled on the sample remain. In fact, as water is evaporated remaining HCl simply becomes more concentrated until no more water can evaporate. The HCl remains on the sample and in the silver capsule. Just a note.
Table 2. Carbonate % needs work. First, what is this carbonate? In the original sample? In the acidified sample (hard to believe – if this much carbonate remained in the sample post acidification, then EC1 through EC11 all completely fail)? How was it measured? No mention of method. What are some N.A. Is EC12 the only method that removed all carbonate or is it the only method that carbonate was not measured?
Section 4 RPO. In general, RPO should be spelled out a few more times. Maybe at the start of the various sections.
A drawing of the RPO system would be great. It would help to understand the upper and lower sections.
Are the RPO catalytic wires designed to be consumables and replace often? What material?
Line 134 “whereas” is the wrong word.
Figure 1 – the names for the various treatments on the x-axes are confusing. They are not the “EC” names. They should be consistent. Also they are not in the same numerical order as the “EC” names.
Again, using both “EC12” and “fume II” is confusing
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AC1: 'Reply on RC1', Xingqian Cui, 11 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-701/egusphere-2025-701-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Xingqian Cui, 11 Jul 2025
-
RC2: 'Comment on egusphere-2025-701', Anonymous Referee #2, 26 Jun 2025
I think this is a good study but could do with more information such as C/N, FTIR etc. And I would have liked to see the results of what was lost (since you did talk about the supernant)
The paper is very long and hard to follow. I would suggest reducing and making concise, and bringing the RPO and acid experiment together instead of dealing with them separately that makes it hard to evaluate. R1's suggestion of 2 papers seems like a good idea to me. There are good results here but I think the paper itself is confusing and hard to read due to sample codes, jumping back and forward for different methods, and the lack of linkage between the acid/RPO experiments.
I have commented on the attached pre-print.
-
AC2: 'Reply on RC2', Xingqian Cui, 11 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-701/egusphere-2025-701-AC2-supplement.pdf
-
AC2: 'Reply on RC2', Xingqian Cui, 11 Jul 2025
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Review of Songfan He et al. “Technical note: Acidification methodology impacts sediment decarbonation as revealed by bulk and serial oxidation measurements”
This article discusses various methods of acidification of sediment samples to remove carbonates and the effects of these acidification methods on the residual organic carbon. The range of acidification methods used are liquid acid of various acid concentrations (hot or room temp, various time intervals) followed by rinsing, fumigation with strong acid followed either no rinse or rinse and the dried by either oven drying or freeze drying. They then evaluate the remaining carbon by total carbon measurements and stable carbon measurements. They then discuss a relatively new ramped temperature pyrolysis/oxidation (RPO) technique where they test the various acidified samples by heating and provide data and interpretation of CO2 evolution versus temperature.
The information in the paper is worthy of publication. But significant editorial changes and clarifications are needed. I include a scan of the MS with rough suggestions/comments.
My most major comment is that it seems that this MS could be broken into two different papers. One with the the acidification portion and TOC and d13C study. One with the RPO study. The two parts of the paper are not well joined. The conclusion section is nearly all (or all but the last sentence) about the acidification portion.
Much of the language throughout needs cleaning up. Examples of odd word choices and potential changes:
“more proximal to pristine” – “more similar to pristine”
“strikingly discrepant” – “Strikingly different”
“Current instrument advancing allows” - “Current instruments allows”
“superposition of myriad signals” - “addition of several signals”
“we carefully instilled several drops” - “we carefully added several drops”
“13C-enriched moieties” – Maybe “13C-enriched compounds”
“To reconcile and depict coincident” – “To illustrate”?
“exhibit constant gradation” ?
“Besides, our study” - “Finally, our study”
Specific comments below - see also the scan MS with handwritten comments
Four samples are used for the various treatments. Each of the samples is abbreviated but the abbreviates are far too complex. For example, one sedimentary rock is abbreviated “1207-GR-11”. Another sedimentary rock is “MS05-135”. Why not just call them Sed1 and Sed2. No need for complex abbreviation that confuses the reader and makes the reader must refer back each time the sample is named.
In section 2.2 the different acidification methods are termed EC1 through EC12. Define EC – it might be “experimental condition” but the reader is unclear why “EC” is used.
In section 2.2 EC11 and EC12 are also named “fume I” and “fume II” – this is confusing.
Table 1 needs work. What is “Mark*”. Maybe add an additional column that shows that EC-1 is the control. And that EC11 and EC12 are also named “fume I” and “fume II”
Line 104 - Air drying – the reviewer thinks that this is room temperature drying. “Oven drying” is also air drying. Need clarification.
Line 107 – This is a reviewer’s pet peeve. “… to remove acid vapors completely” – Oven drying or freeze drying of fumigated samples might remove acid vapors but any acid vapors that settled on the sample remain. In fact, as water is evaporated remaining HCl simply becomes more concentrated until no more water can evaporate. The HCl remains on the sample and in the silver capsule. Just a note.
Table 2. Carbonate % needs work. First, what is this carbonate? In the original sample? In the acidified sample (hard to believe – if this much carbonate remained in the sample post acidification, then EC1 through EC11 all completely fail)? How was it measured? No mention of method. What are some N.A. Is EC12 the only method that removed all carbonate or is it the only method that carbonate was not measured?
Section 4 RPO. In general, RPO should be spelled out a few more times. Maybe at the start of the various sections.
A drawing of the RPO system would be great. It would help to understand the upper and lower sections.
Are the RPO catalytic wires designed to be consumables and replace often? What material?
Line 134 “whereas” is the wrong word.
Figure 1 – the names for the various treatments on the x-axes are confusing. They are not the “EC” names. They should be consistent. Also they are not in the same numerical order as the “EC” names.
Again, using both “EC12” and “fume II” is confusing