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

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.