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.
Fabian Matthias Gäb et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2022-564', Anonymous Referee #1, 28 Aug 2022
- AC1: 'Reply on RC1', Fabian Gäb, 08 Dec 2022
RC2: 'Comment on egusphere-2022-564', Anonymous Referee #2, 12 Sep 2022
- AC2: 'Reply on RC2', Fabian Gäb, 08 Dec 2022
RC3: 'Comment on egusphere-2022-564', Anonymous Referee #3, 15 Nov 2022
- AC3: 'Reply on RC3', Fabian Gäb, 08 Dec 2022
CC1: 'Comment on egusphere-2022-564', Siv K Lauvset, 21 Nov 2022
- AC4: 'Reply on CC1', Fabian Gäb, 08 Dec 2022
Fabian Matthias Gäb et al.
Fabian Matthias Gäb et al.
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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.
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.
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.
Line 100: that is? Delete
Line 150 Mackenzie 1990
Line 153: ?? Respectively so low??? Can you rephrase and maybe delete the brackets?
Line 253: don’t alter
Line 282: delete see below. Unnecessary
Line 294: e.g.â¨
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.