the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jul 2022
Long-term and short-term inorganic carbon reservoirs in Aegean seawater – an experimental study
Abstract. The relevant literature does not explicitly address the fact that there are two fundamentally different inorganic carbon (DIC) reservoirs in seawater; (1) a long-term "background" DIC reservoir that is not in net-transfer equilibrium with the atmosphere, and (2) a short-term "atmospheric" DIC reservoir that is fed by atmospheric pCO2. In addition, we may define a third "anthropogenic" DIC reservoir that quantifies the increase in DIC since industrialization.
We perform experiments to quantify these reservoirs. We equilibrate Aegean seawater with N2-O2 (79:21) gases with variable pCO2 from < 10 to 100,000 µatm, and pure CO2 gas. We quantify electrochemically the changes in pH and, by titration and IR spectroscopy, total alkalinity (TA) and dissolved inorganic carbon (DIC) that occur with variations in pCO2. About 78 % of the Aegean DIC is “background“, introduced into the Aegean sea by the long-term carbon cycle, i.e. riverine input, remineralization of organic carbon, and hydrothermal CO2. In terms of concentration and in the short term, this reservoir is independent of atmospheric pCO2. About 22 % of DIC is atmospheric in origin and is in exchange equilibrium with atmospheric pCO2. The anthropogenic contribution to the atmospheric DIC reservoir is derived by measuring the increase in DIC between 280 (pre-industrial) and 410 µatm (present-day) pCO2 and quantified at around 26 %.
Our experiments also allow projections into the future. It has been suspected that increasing atmospheric pCO2 lowers the CO2 absorption capacity of ocean surface water. Our data confirm this assessment. When the pCO2 increases, the pH and the CO32--concentration fall, and with them the ability of seawater to hydrolyze CO2. Without measures to limit anthropogenic CO2 emissions, the absorption capacity of Aegean seawater in the year 2100 will be only about one half of the absorption capacity of today.
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Interactive discussion
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RC1: 'Comment on egusphere-2022-564', Anonymous Referee #1, 28 Aug 2022
General comment
The paper by Gäb et al., quantified the fraction of DIC that entered the Aegean Sea since the beginning of industrialisation. With their experimental approach, they quantify the percentages of different DIC reservoirs in the Aegean Sea and they subsequently discussed the buffering capacity of the analysed geographical area in the near future.
I enjoyed reading the paper that is lean and intuitive. The aim of the paper is clear.
However, I found in the text several unnecessary repetitions (introduction and discussion). I think that the discussion could be better developed and in some cases (see below) it’s not a very discussion but a repetition of what is already known or written in the results.
I was also very surprised by the paragraph in the conclusion that talks about the eventual beneficial effect of variations in carbonate chemistry (and nano-nuclei formations) for calcifiers. This final - and therefore important- statement comes out of the blue and without any previous discussion/introduction of the topic and good references.More comments down here:
Discussion: the two chapters 4.1 e 4.2 could go together.
Moreover, Line 264-270 are indeed the descriptions of the results. What do the authors want to say here? This part should be moved to the results and eventually, they can discuss here the difference DIC reservoir and what they mean in this part.I suggest changing the title of 4.3 with something that relates the study’s results to the application for future predictions.
Lines 315-318 It’s a kind of repetition of what was previously said as a global rule/condition (lines 297-303) but here for the Aegean Sea. Almost the same words are used and it seems that the reader is reading the same thing twice. This part should be reformulated.
Conclusion:
Every author has his/her personal style while writing a manuscript. I personally, for example, don’t write long conclusions and I leave more room for discussion. But I try here to follow the author’s style. So, said so, Lines 320-328 are another repetition of something that I read several times already. It’s unnecessary.What surprised me a lot was the paragraph from Line 335 since out of the blue the authors mentioned the consequences (maybe beneficial) of the formation of nano-nuclei on calcifiers.
I think that if the authors want to say something about this topic they should dig more: (i.e. a new discussion chapter on this topic). Only a few studies are cited and for example, it is not even clear what they mean with calcifiers: nannoplankton (e.g. coccolithophores), zooplankton like foraminifera?
What the authors are saying here about the consequences of this kind of carbonate chemistry perturbation on marine calcifiers is interesting. But the author has two choices: just mentioned it briefly (more briefly that in the text) or dig more into the topic. I suggest the latter since it would also make the paper much more appealing.Small comments:
Introduction:
Lines 35-40: split into two sentences because it’s too long. Maybe after Doney et al., 2009).
Line 40: more recent references? These are quite old.Methods:
Line 100: that is? DeleteResults:
Line 150 Mackenzie 1990
Line 153: ?? Respectively so low??? Can you rephrase and maybe delete the brackets?Discussion:
Line 253: don’t alter
Line 282: delete see below. Unnecessary
Line 294: e.g.â¨References:
The journals are not available for all papers. Is that a choice?
The author’s list, the title, the pages/volumes number and the year are available but the journals are never mentioned.
Moreover, the authors should add more doi to the list.Citation: https://doi.org/10.5194/egusphere-2022-564-RC1 -
AC1: 'Reply on RC1', Fabian Gäb, 08 Dec 2022
We thank the reviewer for his comments and found them very helpful. We can see how the reviewer has found some parts of the manuscript repetitive. In a revised version of the manuscript we will take that into account and make the mentioned paragraphs more concise. To address the most severe point of this review, we find after rereading, that indeed the paragraph about nano-sized prenucleation clusters feels coming out of the blue. We will rework the manuscript here in a revised version, since the topic deserves extra attention. The appreciation of a „lean and intuitive“ style with a „clear aim of the paper“ by the reviewer encourages us to pursuit a publication of the manuscript, although there are two quite negative reviews, which, among other things, criticize style and aim of the paper.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC1
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AC1: 'Reply on RC1', Fabian Gäb, 08 Dec 2022
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RC2: 'Comment on egusphere-2022-564', Anonymous Referee #2, 12 Sep 2022
Very clear paper, methodologies outlined in detailed and systematic fashion leading to clear suite of defensible conclusions.
Citation: https://doi.org/10.5194/egusphere-2022-564-RC2 -
AC2: 'Reply on RC2', Fabian Gäb, 08 Dec 2022
Thank you for this comment. It adds to the feeling we have about the fashion of the manuscript at least in the question of style of writing and the way our findings are presented.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC2
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AC2: 'Reply on RC2', Fabian Gäb, 08 Dec 2022
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RC3: 'Comment on egusphere-2022-564', Anonymous Referee #3, 15 Nov 2022
This manuscript by Gab et al. propose a new classification of seawater dissolved inorganic carbon (DIC) in two reservoirs (background and atmospheric) following a case study on seawater samples from the Aegean Sea. To do so, they proceed to an equilibration of seawater samples with 11 different gas mixtures of CO2 partial pressure (pCO2) ranging from near 0 uatm to pure CO2. The authors propose also an approach to quantify the proportion of anthropogenic DIC in seawater DIC.
The overall manuscript is poorly designed: multiple missing definitions in the introduction, incomplete methodology, discussion with references found in the Result section, results found in the discussion section, misuse and misunderstanding of published literature, inadequate listing of reference. There is also room for improvement regarding to the scientific writing.
That being said, the study merits to be published because the method seems sound and the attempt to quantify the anthropogenic carbon experimentally is welcome considering the numerous indirect methodology applied for this aim. Thus, considering my serious concerns regarding the quality of this submitted manuscript, I request major revisions.
General comments
I did not grasp the scientific interest of identifying and quantifying in seawater, in constant exposure to zero CO2 artificial atmosphere, the pool of DIC not equilibrating with the atmosphere. What are the interest and perspective of such discovery?
The authors emphasize in the manuscript that their results are valid only for the Aegean seawater. I suggest adding in the introduction specificities related to Mediterranean and Aegean seawater so that the reader can understand the context of the study samples.
The literature review provided in the introduction about estimates of ocean anthropogenic carbon quantification is largely incomplete and shows a misunderstanding of the literature. This serious lack of understanding is very problematic and also appear in the discussion section. I would expect in the introduction a quick review of other previously-published famous methods developed to achieve this aim (Delta C star, TTD, eMLR). Sabine et al. (2004), Tanhua et al. (2007) and Gruber et al. (2019) do not use mass balance calculation as a way to quantify the ocean anthropogenic carbon inventory, contrary to what is stated by the authors. Same for Freidlingstein et al. (2020) that use global ocean biogeochemistry models and observation-based data products to estimate the ocean anthropogenic carbon sink.
The authors find that, for Aegean seawater, the anthropogenic DIC is 26 % of the DIC equilibrating with the atmosphere. In section 4.3, they compare this estimate with estimates from the literature of the percentage of anthropogenic carbon emissions absorbed by the global ocean. It does not make any sense in comparing these estimates with an estimate of the proportion of anthropogenic DIC in seawater.
The reference section is not following Biogeosciences standards, including systematic omission of journal names and intermittent use of DOI.
Specific comments
Abstract:
line 12: The two proposed background DIC and atmospheric DIC reservoirs are not fundamentally different. According to the current knowledge, both are composed of DIC with similar composition, unless otherwise proven.
line 12: Please remove all unnecessary quotes for background, atmospheric and anthropogenic.
line 12: Please replace ; by :
line 14: Please define pCO2 in the abstract and in its first instance in line 70.
line 16: What is the interest of knowing the N2-O2 gas composition in the abstract? If there is not any, I suggest:
“We equilibrate the pCO2 of Aegean seawater samples using (idealized?) gas mixtures with pCO2 from < 10 to 100,000 µatm, as well as pure CO2 gas.”
Line 18: IR is not defined.
Intro:
line 36: In Biogeosciences, references are separated with “;” and a comma is placed before the reference year. Please proceed to the change systematically throughout the manuscript.
line 38: Please define CaCO3
line 43: I have never seen the notation CO2(aq) with a “o” such as CO2o(aq). Please remove this “o”.
line 44-45: No need to use the aqueous notation (aq) for CO32- and HCO3-.
line 45: replace CO2(atm) by CO2gas as usually annotated in seawater carbonate chemistry, e.g.:
Middelburg, J.J. (2019). Biogeochemical Processes and Inorganic Carbon Dynamics. In: Marine Carbon Biogeochemistry . SpringerBriefs in Earth System Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-10822-9_5
line 46: Ph and Alkalinity are not defined.
line 50,67,155,169,178,284,301,334,: Biogeosciences use the abbreviation Eq. (x) for equation, not “eqn. (x)”.
line 70: Missing reference for the pCO2 of around 280 uatm in the 1860s.
Methods:
line 74-75: Missing details regarding to the seawater sampling. The presence of microorganisms and detritus in the seawater could affect the seawater carbonate chemistry and influence CO2 parameters during the storage and the experiments (30 to 50 hours to reach equilibrium). Please give the geographical coordinates and the depth of the sampling, and any treatments applied during/after sampling such as filtration.
line 75: Practical salinity should be provided and the later is unitless. See Unesco (1981). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. Tech. Pap. Mar. Sci., 36
line 75: Please remove aq from Ca2+aq
line 76, 77, 78, 83, 123, 145, 164, 170, 209 222, 256, 267 : Please remove the dot between mmol and kg-1 (and other units). No special need of a “x”, “*” or a dot before the 10^x as well. More information: https://www.bipm.org/en/publications/si-brochure/
Line 76: TA already defined line 46-47.
line 77: Please add an explanation why you choose 400 uatm for equilibration. Was it the current surface atmospheric pCO2 at the sampling date and location? Is it coming from a reference or did you measure it? If measured, how?
line 77: I suggest to rephrase: “The total DIC after equilibrium with a pCO2 of 400 µatm is determined…”.
line 75-78: Please precise the seawater temperature when these measurements have been performed and if these measurements are all performed directly after sampling or just before the laboratory experiment with gas exposures.
line 80: A partial pressure is not a concentration…
line 80: Please remove “CO2”.
line 81: ”Uncertainties in the gas mixtures’ pCO2”
line 82: Please develop the abbreviation “vol.”. Missing unit of 1. If I understand correctly, I suggest “below 1 % of relative volume.”
line 84: Missing space after +- and before the unit.
line 85: The seawater carbonate system is highly sensitive to temperature (Weiss, 1974). The values measured from this seawater sample in equilibrium with near-zero CO2 gas at 17 °C should not be used with values from samples at 25 °C.
Weiss, R. F.: Carbon dioxide in water and seawater: the solubility of a non-ideal gas, Marine Chemistry, 2, 203–215, https://doi.org/10.1016/0304-4203(74)90015-2, 1974.
Table 1: Table titles should be above the table, not below.
line 97: Considering my comment on line 85, I have serious doubts that such calculation is valid using seawater samples at different temperatures (25°C and 17°C). Temperature changes CO2 solubility.
line 97-99: This belongs to the text body in the methods section, not to a table title.
line 98: What does “(*)” refer to? I suggest removing it.
line 98-99: Please use sentences such as : “Carbon speciations are calculated […]. Abbreviations are included for not analyzed (n/a) and not calculated (n/c).”
line 99: By the way, the abbreviation "n/a" is not used. Why is it needed to introduce it?
line 100: TA already defined line 46-47.
line 119: IR has been defined previously so you could use IR instead of infrared.
line 122: Please replace ”µmol DIC per kg water” by “umol DIC kg-1”.
line 121: 410 utam is defined here as ambient pCO2. I am curious of what the 400 uatm refers to line 77.
Results
line 130: The mention "dashed line in Fig. 1)" is not needed and already mentioned in the caption’s figure.
Figure 1: Please introduce in the captions the abbreviation “arg prec.”.
Figure 1: The dashed line/arrow that drops vertically at low pCO2 is not from PHREEQC. I suggest using another line type.
Figure 1: You put 25°C in the figure for log CO2 uatm >2. Please add “17°C” on the grey shaded area.
Figure 1, 2 and 3: Theses figures are copyrighted, coming from Gäb et al. (2017) but they have been slightly modified so I don't know if the following is valid: Please keep in mind that you might have to obtain a license through Elsevier/ScienceDirect Copyright Clearance Center's RightsLink® service to publish this preprint even if the original article is the same first author. If so, you might have to include an acknowledgement to the copyright. Or not?
Gäb, F., Ballhaus, C., Siemens, J., Heuser, A., Lissner, M., Geisler, T., and Garbe-Schönberg, D.: Siderite cannot be used as CO2 sensor for Archaean atmospheres, 214, 209–225, http://dx.doi.org/10.1016/j.gca.2017.07.027, 2017
line 142: TA abbreviation is already defined.
line 143: I would expect comparison with the literature in the discussion section.
Figure 2: Please introduce in the captions the abbreviation “extr. by arg”.
Figure 2 and 3: The pH isolines and the line from PHREEQC (or freshwater for Fig.3) are both dashed lines. Please use different line types to avoid confusion.
line 146: Please write sentences such as “”blue symbols represents…” or “Experimental data are depicted as blue symbols”, “The dashed line illustrates…”.
line 148: I suggest “Dashed isolines are depicting pH values calculated from PHREEQC (Parkhurst, 1995)”. One could remove the pH label in the middle of the figure.
line 147-148, 150-151, 159-160: Gäb et al’s statements stating that Zeebe and Wolf-Gladrow (2001) consider TA as independent of pCO2 are wrong. The Figure 1.1.3 page 7 of Zeebe and Wolf-Gladrow (2001) disqualifies these statements (copyright figure so I don’t dare to include it here). The figure clearly shows a dependency of Alkalinity to dissolved CO2. According to Zeebe and Wolf-Gladrow (2001), alkalinity is only independent to the invasion or release of CO2 from/to the atmosphere, but not to the physical dissolution of CO2. I do not have the book of Morse and Mackenzie (1990) to verify the statements but I am expecting the same misunderstanding from Gäb et al.
line 147-148, 150-151, 159-160: If it happens that these statements are kept, I suggest to move them to the discussion section.
line 165: Please move the freshwater and dashed line description to the figure 3 caption.
line 168-170: This is a copy-paste from the text body. Please remove it from the figure caption.
line 164, 170: If pure water is freshwater, please be consistent and use only pure water or fresh water throughout the manuscript.
line 163-165: These lines are not useful. They are only repeating the figure captions. I suggest removing them and begin line 172 with “In Fig. 2,”.
line 175-176: Here it is hypothesized that this fraction is not extractable by changing pCO2 on a 30-50 hours duration (daily timescale). I would expect such statement in the discussion with some explanation on what is preventing it to be extracted on monthly or yearly time scales, considering that DICback has fundamentally the same composition as DICatmo.
line 176-177: See my comment for line 85.
line 189: Please describe XRD and SEM in the methods section.
line 192-194: The whole sentence “”This is not to say…” is a bit out of scope. Please remove it.
line 204: metastable
line 202-203: See comment line 85.
line 207: Please remove “One such time series is shown in Fig. 5. “
line 208-209: I would expect an equation here rather than a wordy explanation of it.
line 210: Please add “”In Fig. 5, as expected, …”
line 212: semiquantify
line 214: No need to repeat what is explained in the text.
line 220: Missing space after the +- sign.
line 225: I am not sure if intuition has its place in science. Please remove or change the wording.
line 227-231: This should belong to the discussion section.
Discussion
line 242: You stated line 71 that “all our data and interpretations are valid only for Aegean seawater.” and here, you state for seawater in general?
line 257: Please define SO2.
line 255-260: I am not convinced by the sulfate analogy. The authors just compare a preindustrial atmospheric [SO2] concentration with, I guess, a contemporary seawater [SO42-] concentration (global average?) to support the fact that a supposed background DIC reservoir is not reacting to the atmosphere. The speculation done in line 258 (“probably”) does not help.
line 264-270: This should belong to the result section. This is not a discussion but only a presentation of results.
line 275-277: I f you refer to the estimate of 30 % of the anthropogenic carbon absorbed by the global ocean (and not only northern and tropical Atlantic waters) that Gruber et al. (1996) refers in their first introduction sentence, the 30 % comes from Schimel et al. (1994), not Gruber et al. (1996) itself.
line 277-278: This is a very vague, if not incorrect, descripition of the Delta C star methodology.
line 279: Sabine et al. (2004) do not use mass balance calculation but Delta C star.
line 282: Gruber et al. (2019) do not use mass balance calculation but eMLR.
line 282-284: The 34 PgC found by Gruber et al. (2019) relates to an increase of anthropogenic carbon inventory during a recent ˜14 year period, not a share. It cannot be compared to your estimate that is supposed to encompass a period beginning from preindustrial conditions. Freidlingstein et al. (2020) uses global ocean biogeochemistry models and observation-based data products to deduce the ocean anthropogenic carbon sink.
This section 4.2 does not make sense at all. The authors are misunderstanding all the literature cited. Comparing their anthropogenic carbon quantification in Aegean seawater with estimates of proportion of anthropogenic carbon emissions absorbed by the global ocean does not make sense.
line 297-298: This is neglecting the Atlantic deep water formation and the Southern Ocean subduction permitting to transport large amount of anthropogenic carbon to the deep ocean (Sabine et al., 2004).
line 306-309: I would expect an introduction to the Revelle factor in the introduction or in the method section, including the Revelle equation (please write it as a proper equation). I would expect the Figure 6 in the result section.
line 311: Please give the function used for extrapolation. This is highly speculative. Please see my suggestion below.
line 314: Why not using atmospheric pCO2 in 2100 from the literature? Such as the northern hemisphere value of SSP5-8.5:
Meinshausen et al.: The shared socio-economic pathway (SSP) greenhouse gas concentrations and their extensions to 2500, Geosci. Model Dev., 13, 3571–3605, https://doi.org/10.5194/gmd-13-3571-2020, 2020.
line 345-348: There is high speculation without reference on line 343-343 discrediting the entire paragraph.
Code availability
You might have to provide a Code availability section providing the link to download the PHREEQC software.
Reference
Numbers before each references are not needed.
line 411-414, 467-472: References are repeated.
Citation: https://doi.org/10.5194/egusphere-2022-564-RC3 -
AC3: 'Reply on RC3', Fabian Gäb, 08 Dec 2022
We thank the reviewer for this very detailed review and the intensive work he or she has put into our manuscript. Nevertheless we have to make a case in favor of our paper. The criticism regarding the design and writing style is not shared by the authors of the three other reviewers/comments. We take the liberty of following the suggestions made by the other reviewers regarding these points and focus on the scientific critique voiced by this reviewer. That being said, we agree with many of the scientific points raised in this review. Indeed our point of view from an outsider of the field, that enabled us to come up with these novel experiments, is hindering us from the comprehensive synthesis of the literature. Here a revised version of the manuscript will be carefully improved by us, since we agree with the critique made by the reviewer in this point: a complete reference of the previously published literature is needed.
After reading many of the detailed points posted by this reviewer, we feel they are valid. We thank him or her for pointing them out, so a revised manuscript can be updated to a much better version of a scientific paper. We will include the suggestions made here. Last but not least we would like to thank the reviewer for the observation that these kind of equilibrium experiments are indeed new and can add to the literature published before. Since we share this feeling, a revised manuscript will be prepared very carefully by us, if we are given the chance to do so.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC3
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AC3: 'Reply on RC3', Fabian Gäb, 08 Dec 2022
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CC1: 'Comment on egusphere-2022-564', Siv K Lauvset, 21 Nov 2022
I stumbled upon this manuscript after a discussion with a colleague and was intrigued. I quite like the concept, but I was disappointed at the authors failure to relate their results properly to the real world. It would have been great to see a proper motivation for the study, and a discussion about the applicability of these equilibrium experiments to a world that is currently far from being in equilibrium. The manuscript is reasonably well-written, but throughout the authors’ unfamiliarity with this scientific discipline is apparent. There are several cases where previous work is misunderstood, and these misunderstandings used to support conclusions. Unlike another reviewer I do not find the conclusions to be defendable. This work does merit publication, but only after major revisions. The authors also need to do a proper literature review about anthropogenic carbon and the methods used to estimate this (there are several with varying assumptions associated). Below I've listed the most serious issues I've identified.
Section 3.2
The authors claim that previous work and textbooks state that TA is independent of pCO2. This is incorrect. TA is in textbooks claimed to be independent of air-sea gas exchange. Meaning that increasing pCO2 in the ocean as a result of increasing pCO2 in the atmosphere does not change TA. The authors show that when pCO2 becomes very low aragonite precipitates and this changes TA. But what changes TA in this case is the precipitation of calcium carbonate, not gas exchange. The authors need to change their wording in this section.
Section 3.3
Here the authors make some quite wild speculation regarding the formation of aragonite ooides observed at the Bahama banks. It could very well be correct, but some more context would be useful here.
Section 4.1
The authors quantify the anthropogenic content by equilibrating their sample with atmospheres of 280 uatm (pre-industrial) and 410 uatm (present day) respectively. However, the present day atmospheric level is a result of the ocean and land sinks already removing ~50% of the emissions. So it is inappropriate to equilibrate with the current atmospheric level to quantify anthropogenic carbon in the ocean given that the current atmospheric level is a result of the ocean absorbing large amounts of emitted carbon. In addition, the authors are treating this as an equilibration problem while the real world is not in equilibrium. The thinking behind the method is flawed, and I am uncertain how relevant the results are to the real world. The authors offer no discussion for context here. A better motivation and justification on how these results relate to the real world is necessary.
Section 4.2 (and parts of the introduction)
Here the authors have fundamentally misunderstood the studies they cite, and the methods used by those studies. The authors, unfortunately, seem to be very unfamiliar with this field (ocean anthropogenic carbon) of research. This is a major flaw and the manuscript should not be published before it has been fixed. Gruber et al (2019) does not use mass balance to calculate the anthropogenic DIC changes in the ocean. Friedlingstein et al (2020) does not estimate anthropogenic DIC in the ocean at all, but rather the net flux of CO2 into the ocean, and does not use mass balance to do this. Equation 1 in Friedlingstein et al (2020) shows how the budget imbalance is estimated as a residual when all terms on the right-hand side of the equation are estimated/calculated independently. This is clearly explained in the Friedlingstein et al. (2020) paper. In the introduction the authors also claim that anthropogenic DIC is usually calculated using mass balance. This is incorrect. None of the studies they cite, nor any other as far as I am aware, use mass balance for this. Neither do anyone use “comparative analysis of DIC of deep ocean water that has not yet seen ingression of anthropogenic CO2 and other anthropogenic gas species”. Sabine et al (2004) and Gruber et al (1996) both use a method called DC*, but the authors seem to think these studies use different methods (mass balance in the former and comparative analysis of deep ocean and surface in the latter). Friedlingstein et al (2020) and Na et al (2022) do not estimate anthropogenic DIC at all, so it is very strange to include these studies here. Since the authors in section 4.2 goes on to draw conclusions about their own work based on their flawed understanding of previous work this is a major flaw in the paper.
Citation: https://doi.org/10.5194/egusphere-2022-564-CC1 -
AC4: 'Reply on CC1', Fabian Gäb, 08 Dec 2022
We thank the commenter for his remarks on our study. In many things said here, the commentary is similar to the content of Review #3. We concur with the call for a revision of the literature review, as this point was made by both reviewers. To repeat what was being said in our previous comment: We feel that it is, the outsiders point of view, that enabled us to come up with the idea of these experiments that, as other reviewers confirmed, are new in the field. That does of course not mean, that there is no need for proper scientific writing and literature connection.
The point raised about section 3.2 is valid, we will update our manuscript accordingly. The critique about section 3.3 is probably due to a misleading wording by our side. Speculating about the origin of whitenings was not our aim. We will rephrase. Concerning the rather fundamental critiques about the methodology we think that the author of the comment raised a very good point here. The disequilibrium between atmosphere and the different sinks has not been taken into the calculation by us. Here we will dig deep and revise our calculations fundamentally.
Finally, we want to thank the author for his feel that, despite the flaws mentioned above, our work merits publication.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC4
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AC4: 'Reply on CC1', Fabian Gäb, 08 Dec 2022
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-564', Anonymous Referee #1, 28 Aug 2022
General comment
The paper by Gäb et al., quantified the fraction of DIC that entered the Aegean Sea since the beginning of industrialisation. With their experimental approach, they quantify the percentages of different DIC reservoirs in the Aegean Sea and they subsequently discussed the buffering capacity of the analysed geographical area in the near future.
I enjoyed reading the paper that is lean and intuitive. The aim of the paper is clear.
However, I found in the text several unnecessary repetitions (introduction and discussion). I think that the discussion could be better developed and in some cases (see below) it’s not a very discussion but a repetition of what is already known or written in the results.
I was also very surprised by the paragraph in the conclusion that talks about the eventual beneficial effect of variations in carbonate chemistry (and nano-nuclei formations) for calcifiers. This final - and therefore important- statement comes out of the blue and without any previous discussion/introduction of the topic and good references.More comments down here:
Discussion: the two chapters 4.1 e 4.2 could go together.
Moreover, Line 264-270 are indeed the descriptions of the results. What do the authors want to say here? This part should be moved to the results and eventually, they can discuss here the difference DIC reservoir and what they mean in this part.I suggest changing the title of 4.3 with something that relates the study’s results to the application for future predictions.
Lines 315-318 It’s a kind of repetition of what was previously said as a global rule/condition (lines 297-303) but here for the Aegean Sea. Almost the same words are used and it seems that the reader is reading the same thing twice. This part should be reformulated.
Conclusion:
Every author has his/her personal style while writing a manuscript. I personally, for example, don’t write long conclusions and I leave more room for discussion. But I try here to follow the author’s style. So, said so, Lines 320-328 are another repetition of something that I read several times already. It’s unnecessary.What surprised me a lot was the paragraph from Line 335 since out of the blue the authors mentioned the consequences (maybe beneficial) of the formation of nano-nuclei on calcifiers.
I think that if the authors want to say something about this topic they should dig more: (i.e. a new discussion chapter on this topic). Only a few studies are cited and for example, it is not even clear what they mean with calcifiers: nannoplankton (e.g. coccolithophores), zooplankton like foraminifera?
What the authors are saying here about the consequences of this kind of carbonate chemistry perturbation on marine calcifiers is interesting. But the author has two choices: just mentioned it briefly (more briefly that in the text) or dig more into the topic. I suggest the latter since it would also make the paper much more appealing.Small comments:
Introduction:
Lines 35-40: split into two sentences because it’s too long. Maybe after Doney et al., 2009).
Line 40: more recent references? These are quite old.Methods:
Line 100: that is? DeleteResults:
Line 150 Mackenzie 1990
Line 153: ?? Respectively so low??? Can you rephrase and maybe delete the brackets?Discussion:
Line 253: don’t alter
Line 282: delete see below. Unnecessary
Line 294: e.g.â¨References:
The journals are not available for all papers. Is that a choice?
The author’s list, the title, the pages/volumes number and the year are available but the journals are never mentioned.
Moreover, the authors should add more doi to the list.Citation: https://doi.org/10.5194/egusphere-2022-564-RC1 -
AC1: 'Reply on RC1', Fabian Gäb, 08 Dec 2022
We thank the reviewer for his comments and found them very helpful. We can see how the reviewer has found some parts of the manuscript repetitive. In a revised version of the manuscript we will take that into account and make the mentioned paragraphs more concise. To address the most severe point of this review, we find after rereading, that indeed the paragraph about nano-sized prenucleation clusters feels coming out of the blue. We will rework the manuscript here in a revised version, since the topic deserves extra attention. The appreciation of a „lean and intuitive“ style with a „clear aim of the paper“ by the reviewer encourages us to pursuit a publication of the manuscript, although there are two quite negative reviews, which, among other things, criticize style and aim of the paper.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC1
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AC1: 'Reply on RC1', Fabian Gäb, 08 Dec 2022
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RC2: 'Comment on egusphere-2022-564', Anonymous Referee #2, 12 Sep 2022
Very clear paper, methodologies outlined in detailed and systematic fashion leading to clear suite of defensible conclusions.
Citation: https://doi.org/10.5194/egusphere-2022-564-RC2 -
AC2: 'Reply on RC2', Fabian Gäb, 08 Dec 2022
Thank you for this comment. It adds to the feeling we have about the fashion of the manuscript at least in the question of style of writing and the way our findings are presented.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC2
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AC2: 'Reply on RC2', Fabian Gäb, 08 Dec 2022
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RC3: 'Comment on egusphere-2022-564', Anonymous Referee #3, 15 Nov 2022
This manuscript by Gab et al. propose a new classification of seawater dissolved inorganic carbon (DIC) in two reservoirs (background and atmospheric) following a case study on seawater samples from the Aegean Sea. To do so, they proceed to an equilibration of seawater samples with 11 different gas mixtures of CO2 partial pressure (pCO2) ranging from near 0 uatm to pure CO2. The authors propose also an approach to quantify the proportion of anthropogenic DIC in seawater DIC.
The overall manuscript is poorly designed: multiple missing definitions in the introduction, incomplete methodology, discussion with references found in the Result section, results found in the discussion section, misuse and misunderstanding of published literature, inadequate listing of reference. There is also room for improvement regarding to the scientific writing.
That being said, the study merits to be published because the method seems sound and the attempt to quantify the anthropogenic carbon experimentally is welcome considering the numerous indirect methodology applied for this aim. Thus, considering my serious concerns regarding the quality of this submitted manuscript, I request major revisions.
General comments
I did not grasp the scientific interest of identifying and quantifying in seawater, in constant exposure to zero CO2 artificial atmosphere, the pool of DIC not equilibrating with the atmosphere. What are the interest and perspective of such discovery?
The authors emphasize in the manuscript that their results are valid only for the Aegean seawater. I suggest adding in the introduction specificities related to Mediterranean and Aegean seawater so that the reader can understand the context of the study samples.
The literature review provided in the introduction about estimates of ocean anthropogenic carbon quantification is largely incomplete and shows a misunderstanding of the literature. This serious lack of understanding is very problematic and also appear in the discussion section. I would expect in the introduction a quick review of other previously-published famous methods developed to achieve this aim (Delta C star, TTD, eMLR). Sabine et al. (2004), Tanhua et al. (2007) and Gruber et al. (2019) do not use mass balance calculation as a way to quantify the ocean anthropogenic carbon inventory, contrary to what is stated by the authors. Same for Freidlingstein et al. (2020) that use global ocean biogeochemistry models and observation-based data products to estimate the ocean anthropogenic carbon sink.
The authors find that, for Aegean seawater, the anthropogenic DIC is 26 % of the DIC equilibrating with the atmosphere. In section 4.3, they compare this estimate with estimates from the literature of the percentage of anthropogenic carbon emissions absorbed by the global ocean. It does not make any sense in comparing these estimates with an estimate of the proportion of anthropogenic DIC in seawater.
The reference section is not following Biogeosciences standards, including systematic omission of journal names and intermittent use of DOI.
Specific comments
Abstract:
line 12: The two proposed background DIC and atmospheric DIC reservoirs are not fundamentally different. According to the current knowledge, both are composed of DIC with similar composition, unless otherwise proven.
line 12: Please remove all unnecessary quotes for background, atmospheric and anthropogenic.
line 12: Please replace ; by :
line 14: Please define pCO2 in the abstract and in its first instance in line 70.
line 16: What is the interest of knowing the N2-O2 gas composition in the abstract? If there is not any, I suggest:
“We equilibrate the pCO2 of Aegean seawater samples using (idealized?) gas mixtures with pCO2 from < 10 to 100,000 µatm, as well as pure CO2 gas.”
Line 18: IR is not defined.
Intro:
line 36: In Biogeosciences, references are separated with “;” and a comma is placed before the reference year. Please proceed to the change systematically throughout the manuscript.
line 38: Please define CaCO3
line 43: I have never seen the notation CO2(aq) with a “o” such as CO2o(aq). Please remove this “o”.
line 44-45: No need to use the aqueous notation (aq) for CO32- and HCO3-.
line 45: replace CO2(atm) by CO2gas as usually annotated in seawater carbonate chemistry, e.g.:
Middelburg, J.J. (2019). Biogeochemical Processes and Inorganic Carbon Dynamics. In: Marine Carbon Biogeochemistry . SpringerBriefs in Earth System Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-10822-9_5
line 46: Ph and Alkalinity are not defined.
line 50,67,155,169,178,284,301,334,: Biogeosciences use the abbreviation Eq. (x) for equation, not “eqn. (x)”.
line 70: Missing reference for the pCO2 of around 280 uatm in the 1860s.
Methods:
line 74-75: Missing details regarding to the seawater sampling. The presence of microorganisms and detritus in the seawater could affect the seawater carbonate chemistry and influence CO2 parameters during the storage and the experiments (30 to 50 hours to reach equilibrium). Please give the geographical coordinates and the depth of the sampling, and any treatments applied during/after sampling such as filtration.
line 75: Practical salinity should be provided and the later is unitless. See Unesco (1981). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. Tech. Pap. Mar. Sci., 36
line 75: Please remove aq from Ca2+aq
line 76, 77, 78, 83, 123, 145, 164, 170, 209 222, 256, 267 : Please remove the dot between mmol and kg-1 (and other units). No special need of a “x”, “*” or a dot before the 10^x as well. More information: https://www.bipm.org/en/publications/si-brochure/
Line 76: TA already defined line 46-47.
line 77: Please add an explanation why you choose 400 uatm for equilibration. Was it the current surface atmospheric pCO2 at the sampling date and location? Is it coming from a reference or did you measure it? If measured, how?
line 77: I suggest to rephrase: “The total DIC after equilibrium with a pCO2 of 400 µatm is determined…”.
line 75-78: Please precise the seawater temperature when these measurements have been performed and if these measurements are all performed directly after sampling or just before the laboratory experiment with gas exposures.
line 80: A partial pressure is not a concentration…
line 80: Please remove “CO2”.
line 81: ”Uncertainties in the gas mixtures’ pCO2”
line 82: Please develop the abbreviation “vol.”. Missing unit of 1. If I understand correctly, I suggest “below 1 % of relative volume.”
line 84: Missing space after +- and before the unit.
line 85: The seawater carbonate system is highly sensitive to temperature (Weiss, 1974). The values measured from this seawater sample in equilibrium with near-zero CO2 gas at 17 °C should not be used with values from samples at 25 °C.
Weiss, R. F.: Carbon dioxide in water and seawater: the solubility of a non-ideal gas, Marine Chemistry, 2, 203–215, https://doi.org/10.1016/0304-4203(74)90015-2, 1974.
Table 1: Table titles should be above the table, not below.
line 97: Considering my comment on line 85, I have serious doubts that such calculation is valid using seawater samples at different temperatures (25°C and 17°C). Temperature changes CO2 solubility.
line 97-99: This belongs to the text body in the methods section, not to a table title.
line 98: What does “(*)” refer to? I suggest removing it.
line 98-99: Please use sentences such as : “Carbon speciations are calculated […]. Abbreviations are included for not analyzed (n/a) and not calculated (n/c).”
line 99: By the way, the abbreviation "n/a" is not used. Why is it needed to introduce it?
line 100: TA already defined line 46-47.
line 119: IR has been defined previously so you could use IR instead of infrared.
line 122: Please replace ”µmol DIC per kg water” by “umol DIC kg-1”.
line 121: 410 utam is defined here as ambient pCO2. I am curious of what the 400 uatm refers to line 77.
Results
line 130: The mention "dashed line in Fig. 1)" is not needed and already mentioned in the caption’s figure.
Figure 1: Please introduce in the captions the abbreviation “arg prec.”.
Figure 1: The dashed line/arrow that drops vertically at low pCO2 is not from PHREEQC. I suggest using another line type.
Figure 1: You put 25°C in the figure for log CO2 uatm >2. Please add “17°C” on the grey shaded area.
Figure 1, 2 and 3: Theses figures are copyrighted, coming from Gäb et al. (2017) but they have been slightly modified so I don't know if the following is valid: Please keep in mind that you might have to obtain a license through Elsevier/ScienceDirect Copyright Clearance Center's RightsLink® service to publish this preprint even if the original article is the same first author. If so, you might have to include an acknowledgement to the copyright. Or not?
Gäb, F., Ballhaus, C., Siemens, J., Heuser, A., Lissner, M., Geisler, T., and Garbe-Schönberg, D.: Siderite cannot be used as CO2 sensor for Archaean atmospheres, 214, 209–225, http://dx.doi.org/10.1016/j.gca.2017.07.027, 2017
line 142: TA abbreviation is already defined.
line 143: I would expect comparison with the literature in the discussion section.
Figure 2: Please introduce in the captions the abbreviation “extr. by arg”.
Figure 2 and 3: The pH isolines and the line from PHREEQC (or freshwater for Fig.3) are both dashed lines. Please use different line types to avoid confusion.
line 146: Please write sentences such as “”blue symbols represents…” or “Experimental data are depicted as blue symbols”, “The dashed line illustrates…”.
line 148: I suggest “Dashed isolines are depicting pH values calculated from PHREEQC (Parkhurst, 1995)”. One could remove the pH label in the middle of the figure.
line 147-148, 150-151, 159-160: Gäb et al’s statements stating that Zeebe and Wolf-Gladrow (2001) consider TA as independent of pCO2 are wrong. The Figure 1.1.3 page 7 of Zeebe and Wolf-Gladrow (2001) disqualifies these statements (copyright figure so I don’t dare to include it here). The figure clearly shows a dependency of Alkalinity to dissolved CO2. According to Zeebe and Wolf-Gladrow (2001), alkalinity is only independent to the invasion or release of CO2 from/to the atmosphere, but not to the physical dissolution of CO2. I do not have the book of Morse and Mackenzie (1990) to verify the statements but I am expecting the same misunderstanding from Gäb et al.
line 147-148, 150-151, 159-160: If it happens that these statements are kept, I suggest to move them to the discussion section.
line 165: Please move the freshwater and dashed line description to the figure 3 caption.
line 168-170: This is a copy-paste from the text body. Please remove it from the figure caption.
line 164, 170: If pure water is freshwater, please be consistent and use only pure water or fresh water throughout the manuscript.
line 163-165: These lines are not useful. They are only repeating the figure captions. I suggest removing them and begin line 172 with “In Fig. 2,”.
line 175-176: Here it is hypothesized that this fraction is not extractable by changing pCO2 on a 30-50 hours duration (daily timescale). I would expect such statement in the discussion with some explanation on what is preventing it to be extracted on monthly or yearly time scales, considering that DICback has fundamentally the same composition as DICatmo.
line 176-177: See my comment for line 85.
line 189: Please describe XRD and SEM in the methods section.
line 192-194: The whole sentence “”This is not to say…” is a bit out of scope. Please remove it.
line 204: metastable
line 202-203: See comment line 85.
line 207: Please remove “One such time series is shown in Fig. 5. “
line 208-209: I would expect an equation here rather than a wordy explanation of it.
line 210: Please add “”In Fig. 5, as expected, …”
line 212: semiquantify
line 214: No need to repeat what is explained in the text.
line 220: Missing space after the +- sign.
line 225: I am not sure if intuition has its place in science. Please remove or change the wording.
line 227-231: This should belong to the discussion section.
Discussion
line 242: You stated line 71 that “all our data and interpretations are valid only for Aegean seawater.” and here, you state for seawater in general?
line 257: Please define SO2.
line 255-260: I am not convinced by the sulfate analogy. The authors just compare a preindustrial atmospheric [SO2] concentration with, I guess, a contemporary seawater [SO42-] concentration (global average?) to support the fact that a supposed background DIC reservoir is not reacting to the atmosphere. The speculation done in line 258 (“probably”) does not help.
line 264-270: This should belong to the result section. This is not a discussion but only a presentation of results.
line 275-277: I f you refer to the estimate of 30 % of the anthropogenic carbon absorbed by the global ocean (and not only northern and tropical Atlantic waters) that Gruber et al. (1996) refers in their first introduction sentence, the 30 % comes from Schimel et al. (1994), not Gruber et al. (1996) itself.
line 277-278: This is a very vague, if not incorrect, descripition of the Delta C star methodology.
line 279: Sabine et al. (2004) do not use mass balance calculation but Delta C star.
line 282: Gruber et al. (2019) do not use mass balance calculation but eMLR.
line 282-284: The 34 PgC found by Gruber et al. (2019) relates to an increase of anthropogenic carbon inventory during a recent ˜14 year period, not a share. It cannot be compared to your estimate that is supposed to encompass a period beginning from preindustrial conditions. Freidlingstein et al. (2020) uses global ocean biogeochemistry models and observation-based data products to deduce the ocean anthropogenic carbon sink.
This section 4.2 does not make sense at all. The authors are misunderstanding all the literature cited. Comparing their anthropogenic carbon quantification in Aegean seawater with estimates of proportion of anthropogenic carbon emissions absorbed by the global ocean does not make sense.
line 297-298: This is neglecting the Atlantic deep water formation and the Southern Ocean subduction permitting to transport large amount of anthropogenic carbon to the deep ocean (Sabine et al., 2004).
line 306-309: I would expect an introduction to the Revelle factor in the introduction or in the method section, including the Revelle equation (please write it as a proper equation). I would expect the Figure 6 in the result section.
line 311: Please give the function used for extrapolation. This is highly speculative. Please see my suggestion below.
line 314: Why not using atmospheric pCO2 in 2100 from the literature? Such as the northern hemisphere value of SSP5-8.5:
Meinshausen et al.: The shared socio-economic pathway (SSP) greenhouse gas concentrations and their extensions to 2500, Geosci. Model Dev., 13, 3571–3605, https://doi.org/10.5194/gmd-13-3571-2020, 2020.
line 345-348: There is high speculation without reference on line 343-343 discrediting the entire paragraph.
Code availability
You might have to provide a Code availability section providing the link to download the PHREEQC software.
Reference
Numbers before each references are not needed.
line 411-414, 467-472: References are repeated.
Citation: https://doi.org/10.5194/egusphere-2022-564-RC3 -
AC3: 'Reply on RC3', Fabian Gäb, 08 Dec 2022
We thank the reviewer for this very detailed review and the intensive work he or she has put into our manuscript. Nevertheless we have to make a case in favor of our paper. The criticism regarding the design and writing style is not shared by the authors of the three other reviewers/comments. We take the liberty of following the suggestions made by the other reviewers regarding these points and focus on the scientific critique voiced by this reviewer. That being said, we agree with many of the scientific points raised in this review. Indeed our point of view from an outsider of the field, that enabled us to come up with these novel experiments, is hindering us from the comprehensive synthesis of the literature. Here a revised version of the manuscript will be carefully improved by us, since we agree with the critique made by the reviewer in this point: a complete reference of the previously published literature is needed.
After reading many of the detailed points posted by this reviewer, we feel they are valid. We thank him or her for pointing them out, so a revised manuscript can be updated to a much better version of a scientific paper. We will include the suggestions made here. Last but not least we would like to thank the reviewer for the observation that these kind of equilibrium experiments are indeed new and can add to the literature published before. Since we share this feeling, a revised manuscript will be prepared very carefully by us, if we are given the chance to do so.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC3
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AC3: 'Reply on RC3', Fabian Gäb, 08 Dec 2022
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CC1: 'Comment on egusphere-2022-564', Siv K Lauvset, 21 Nov 2022
I stumbled upon this manuscript after a discussion with a colleague and was intrigued. I quite like the concept, but I was disappointed at the authors failure to relate their results properly to the real world. It would have been great to see a proper motivation for the study, and a discussion about the applicability of these equilibrium experiments to a world that is currently far from being in equilibrium. The manuscript is reasonably well-written, but throughout the authors’ unfamiliarity with this scientific discipline is apparent. There are several cases where previous work is misunderstood, and these misunderstandings used to support conclusions. Unlike another reviewer I do not find the conclusions to be defendable. This work does merit publication, but only after major revisions. The authors also need to do a proper literature review about anthropogenic carbon and the methods used to estimate this (there are several with varying assumptions associated). Below I've listed the most serious issues I've identified.
Section 3.2
The authors claim that previous work and textbooks state that TA is independent of pCO2. This is incorrect. TA is in textbooks claimed to be independent of air-sea gas exchange. Meaning that increasing pCO2 in the ocean as a result of increasing pCO2 in the atmosphere does not change TA. The authors show that when pCO2 becomes very low aragonite precipitates and this changes TA. But what changes TA in this case is the precipitation of calcium carbonate, not gas exchange. The authors need to change their wording in this section.
Section 3.3
Here the authors make some quite wild speculation regarding the formation of aragonite ooides observed at the Bahama banks. It could very well be correct, but some more context would be useful here.
Section 4.1
The authors quantify the anthropogenic content by equilibrating their sample with atmospheres of 280 uatm (pre-industrial) and 410 uatm (present day) respectively. However, the present day atmospheric level is a result of the ocean and land sinks already removing ~50% of the emissions. So it is inappropriate to equilibrate with the current atmospheric level to quantify anthropogenic carbon in the ocean given that the current atmospheric level is a result of the ocean absorbing large amounts of emitted carbon. In addition, the authors are treating this as an equilibration problem while the real world is not in equilibrium. The thinking behind the method is flawed, and I am uncertain how relevant the results are to the real world. The authors offer no discussion for context here. A better motivation and justification on how these results relate to the real world is necessary.
Section 4.2 (and parts of the introduction)
Here the authors have fundamentally misunderstood the studies they cite, and the methods used by those studies. The authors, unfortunately, seem to be very unfamiliar with this field (ocean anthropogenic carbon) of research. This is a major flaw and the manuscript should not be published before it has been fixed. Gruber et al (2019) does not use mass balance to calculate the anthropogenic DIC changes in the ocean. Friedlingstein et al (2020) does not estimate anthropogenic DIC in the ocean at all, but rather the net flux of CO2 into the ocean, and does not use mass balance to do this. Equation 1 in Friedlingstein et al (2020) shows how the budget imbalance is estimated as a residual when all terms on the right-hand side of the equation are estimated/calculated independently. This is clearly explained in the Friedlingstein et al. (2020) paper. In the introduction the authors also claim that anthropogenic DIC is usually calculated using mass balance. This is incorrect. None of the studies they cite, nor any other as far as I am aware, use mass balance for this. Neither do anyone use “comparative analysis of DIC of deep ocean water that has not yet seen ingression of anthropogenic CO2 and other anthropogenic gas species”. Sabine et al (2004) and Gruber et al (1996) both use a method called DC*, but the authors seem to think these studies use different methods (mass balance in the former and comparative analysis of deep ocean and surface in the latter). Friedlingstein et al (2020) and Na et al (2022) do not estimate anthropogenic DIC at all, so it is very strange to include these studies here. Since the authors in section 4.2 goes on to draw conclusions about their own work based on their flawed understanding of previous work this is a major flaw in the paper.
Citation: https://doi.org/10.5194/egusphere-2022-564-CC1 -
AC4: 'Reply on CC1', Fabian Gäb, 08 Dec 2022
We thank the commenter for his remarks on our study. In many things said here, the commentary is similar to the content of Review #3. We concur with the call for a revision of the literature review, as this point was made by both reviewers. To repeat what was being said in our previous comment: We feel that it is, the outsiders point of view, that enabled us to come up with the idea of these experiments that, as other reviewers confirmed, are new in the field. That does of course not mean, that there is no need for proper scientific writing and literature connection.
The point raised about section 3.2 is valid, we will update our manuscript accordingly. The critique about section 3.3 is probably due to a misleading wording by our side. Speculating about the origin of whitenings was not our aim. We will rephrase. Concerning the rather fundamental critiques about the methodology we think that the author of the comment raised a very good point here. The disequilibrium between atmosphere and the different sinks has not been taken into the calculation by us. Here we will dig deep and revise our calculations fundamentally.
Finally, we want to thank the author for his feel that, despite the flaws mentioned above, our work merits publication.
Citation: https://doi.org/10.5194/egusphere-2022-564-AC4
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AC4: 'Reply on CC1', Fabian Gäb, 08 Dec 2022
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