Historical reconstruction of ocean acidification in the Australian  region

Lenton, Andrew; Tilbrook, Bronte; Matear, Richard J.; Sasse, Tristan P.; Nojiri, Yukihiro

doi:https://doi.org/10.5194/bg-13-1753-2016

Articles | Volume 13, issue 6

https://doi.org/10.5194/bg-13-1753-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-13-1753-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 6

Research article

|

21 Mar 2016

Research article |

| 21 Mar 2016

Historical reconstruction of ocean acidification in the Australian region

Andrew Lenton, Bronte Tilbrook, Richard J. Matear, Tristan P. Sasse, and Yukihiro Nojiri

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Final revised paper (published on 21 Mar 2016)
Preprint (discussion started on 03 Jun 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC C3388: 'Review of Lenton et al: Historical reconstruction of ocean acidification in the Australian region', Anonymous Referee #1, 07 Jul 2015
RC C3983: 'Comments to Lenton et al. "Historical reconstruction of Ocean Acidification in the Australian region"', Anonymous Referee #2, 31 Jul 2015
AC C5197: 'Response to Reviewers', andrew lenton, 11 Sep 2015
AC C5215: 'Comment on updated Alkalinity-Salinity Relationship', andrew lenton, 11 Sep 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (28 Sep 2015) by Christine Klaas

AR by andrew lenton on behalf of the Authors (30 Sep 2015)

ED: Referee Nomination & Report Request started (19 Oct 2015) by Christine Klaas

RR by Anonymous Referee #1 (02 Nov 2015)

Suggestions for revision or reasons for rejection

Review of Lenton et al: Historical reconstruction of ocean acidification in the Australian region

Lenton et al. have improved the manuscript considerably. They have addressed most comments of both reviewers. Yet, I’d like to ask the authors to work on their draft and uploaded files more thoroughly, there are still a number of typos, the abstract in the manuscript has not been updated as indicated in the answer to the reviewers and Figure 10 is still missing. See specific comments. The authors have to address these issues before publication of the manuscript.

Specific comments:

1) a)The abstract has been updated in the author comment response to reviewers. Yet, the abstract has not been updated in the main manuscript.

b) Please reconsider the use of the wording: "increase in ocean acidity levels"
(see: http://www.imber.info/News/News/A-plea-to-ocean-acidification-scientists:
It is unfortunate that the terminology used in some papers, presentations and media interviews is misleading. The definition of “acidic” in the Oxford English dictionary is “having the properties of an acid; having a pH of less than 7”. Despite the process of ocean acidification (the acidity of seawater, or hydrogen ion concentration, has increased by 28% since preindustrial time), the oceans are alkaline (pH higher than 7) and will not become acidic in the foreseeable future in most regions of the oceans. Hence, while it is accurate to refer to an “increase in acidity” or to “ocean acidification”, the terms “acid” or “acidic” should not be used when referring to seawater. Note that there are few exceptions, seawater can be acidic in some near-shore environments such as estuaries, in the immediate vicinity of CO2 vents, or in purposeful perturbation experiments.)

c) In the last sentence of the abstract it says: “… an important to link biological observations…”. This is grammatically incorrect and Reviewer 1 has mentioned this already in the first round of reviews. At least three of the five authors are native speakers and should be able to proofread their manuscript before submission.

2) Response to reviewers, C5199 (“What about SOCAT data”/ method of Sasse et al): The authors state that SOCAT data is not used and refer to the next comment. In the answer to the next comment, they explain the method of Sasse et al., but not what the input data is. Are these pCO2 data from SOCAT or from another source? Please indicate, what data is used in the main manuscript.

3) p. 12, lines 349-353: These two sentences are opposing each other. Which stations are you referring to for “larger changes in the north” and “largest changes occur in the Tasman Sea and along the southern coast”.

4) p. 12, line 354: Figure 10 is still missing.

5) p. 14, line 427ff: both reviewers have asked for a clear statement of the uncertainty for the assumption that Delta pCO2 does not change. The authors have written more text and have clearly stated that Delta pCO2 is assumed to be constant in time. They do, however, not discuss, how large the error is and what the implications are. Reviewer 2 wrote: “When combining this assumption with the atmospheric CO2 record, this will give the upper limit of DIC increase and thereby the upper limits of aragonite saturation state decrease and pH decrease associated with the atmospheric CO2 rise.“ This is the type of explicit statement that I still miss in the text.
The authors focus on pointing out that effects of primary production on pCO2 will be small, which is probably true, however, biological effects are only one driver of Delta pCO2. The other drivers should be addressed too, either explicitly or with a summarizing statement as the sentence from reviewer 2.

6) Figures 5,6,7: The figures have been improved (x and y-axis labels and tick marks in Figures 5,6,7). The tick marks on the color scale are still hard to read, particularly in a BG type-set version of the figures which are generally very small. You can take out every other tick mark, but increase their size, that will enhance readability. The same holds true for new Figure 8. It looks great on a full page, but it won’t be published in that size. Please also increase x-and y-tick label marks in Figure 9. Main and minor ticks are not distinguishable in Figure 9. Please also increase font size of ticks and labels in Figure 2.
Figures 5+6 don’t use the same color scale (5a: 1.8-4.2, but 6a: 1.5-4.2, 5b: 8.02-8.15, but 6b: 8.01-8.15)

Further technical comments:
p.2, line 53; than the preindustrial period → than in the preindustrial period or relative to the preindustrial period.
p.3, line 85: here and at a number of places: e.g. (Shaw et al., 2012) → (e.g., Shaw et al., 2012)
p.4, line 105: dissolved inorganic carbon dioxide (DIC) → dissolved inorganic carbon (DIC)
p.4, line 114: mixed layer this region → mixed layer in this region
throughout the manuscript: be consistent in using pCO2 or pCO2
p. 7, line 220: HadiSST represent → HadiSST represents
line 222: local process → local processes
p. 9, line 273: parenthesis around citation
p. 10, line 310: “we can only compare our results T14 away from these regions” → compare our results TO T14…
p. 11, line 327: T14 the product → the T14 product
p. 14, please check your style of citations on the whole page.
p. 14, 416/7: freshwater water changes → freshwater changes
p. 14, line 429: … products the existing products… → the existing products
p. 15, line 449: an new estimate –-> a new estimate
p. 16, line 487: impacts are likely vary → impacts likely vary

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RR by Anonymous Referee #3 (09 Dec 2015)

Suggestions for revision or reasons for rejection

In this manuscript by Lenton and colleagues, the authors reconstructed the evolution of pH and aragonite saturation state changes for the period between 1870-2013, using the present day ocean carbonate data in conjunction with atmospheric pCO2 records for the same period.

The paper clearly and thoroughly describes the methods and the data used and the results obtained from analysis. I trust their honest efforts put into this work and thus I sincerely hope their efforts will finally come to fruition.

The manuscript consists of two parts. The first part is the production of present-day maps of pCO2 and total alkalinity (TA), which were then used to calculate the similar maps of total carbon (DIC) and pH (or aragonite saturation state). I do not have any problem with this part. Certainly, the resulting products of pCO2 and TA distribution are more accurate than the same maps produced by Takahashi et al., because the authors used a lot more data than did Takahashi et al.

However, I have great disquiet with the second part of this manuscript. In this part of the manuscript, the authors transformed the present-day yearly cycle of pCO2 to yearly cycles for other years (years including all the way back to 1870) with the help of atmospheric pCO2 records for 1870-2013. The underlying assumption in this analysis was that the present-day pattern of pCO2 cycle in waters near Australia has remained unchanged for the analysis period (1870-2013). My wild guess is that their assumption may not be terribly wrong, but, at the same time, they may not be able to present convincing lines of evidence supporting that their assumption is reasonable. Therefore, I feel that this type of analysis is too much of a stretch of their present-day carbon observations to the past. I do find the second part of this manuscript (about the evolution of ocean acidification between 1870-2013), neither useful nor interesting.

I feel that the first part of this paper can stand by itself and thus still merit for publication. If the authors decide to do so, I have several technical comments. I also feel that the authors should greatly down play the second part of this paper.

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ED: Publish subject to minor revisions (Editor review) (11 Dec 2015) by Christine Klaas

AR by andrew lenton on behalf of the Authors (22 Feb 2016) Author's response Manuscript

ED: Publish as is (26 Feb 2016) by Christine Klaas

Dear Authors,
I am pleased to accept your manuscript for publication. Below please find some minor suggestions (typos) that you might consider when submitting for your final version.
Sincerely,
Christine Klaas.

Lines 23-24: "The observed changes in atmospheric CO2 and SST and
climatological salinity are then used reconstruct pH and aragonite saturation state"
should be "The observed changes in atmospheric CO2 and SST and
climatological salinity are then used to reconstruct pH and aragonite saturation state".

Line 27: "...shelf around Australia shows both the mean state, and seasonality in the present day is well represented..." should be "...shelf around Australia shows that both the mean state, and seasonality in the present day are well represented..."

Line 67: "slow to such levels that coral reefs may start to dissolve 67 (Silverman et al., 2009)." should be " slow to levels such that coral reefs may start to dissolve (Silverman et al., 2009)".

Lines 72-73: " The impact of these changes on the marine environment is fundamental for the management of future marine resources" shouldn't it be
"Understanding the impact of these changes on the marine environment is fundamental for the management of future marine resources" or "The impact of these changes on the marine environment is of fundamental importance for the management of future marine resources".

Lines 74-75: "An historical record" should be "A historical record".

Lines 166-168: "as no long-term high spatial and temporal resolution observations of ocean surface salinity at present exist around Australia (nor globally)" should be "as, at present, no long-term high spatial and temporal resolution observations of ocean surface salinity exist around Australia (nor globally)".

Lines 283-284: "This spatial pattern of this seasonality is quite heterogeneous" should be "This spatial pattern of seasonality is quite heterogeneous".

Lines 385-387: "This is perhaps not surprising given that freshwater water changes act as a dilution flux i.e. acting equally on DIC and total alkalinity (Lenton et al., 2012)." should be "This is perhaps not surprising given that changes in freshwater water input act as a dilution flux i.e. acting equally on DIC and total alkalinity (Lenton et al., 2012)."

Line 408-409: "From this study we can see that for an equivalent increase in (future) atmospheric CO2 levels, that the error introduced into our calculation of pH and aragonite saturation.." should be "From this study we can see that for an equivalent increase in (future) atmospheric CO2 levels, the error introduced into our calculation of pH and aragonite saturation..."

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AR by andrew lenton on behalf of the Authors (29 Feb 2016) Manuscript

Short summary

We reconstruct the observed variability and mean state in pH and aragonite saturation state around Australia at high spatial resolution and reconstruct the changes that have occurred in the Australian region over the last 140 years. We find that large changes in aragonite saturation state and pH have very different spatial patterns, which suggests that the biological responses to ocean acidification are likely to be non-uniform and dependent on the relative sensitivity of organisms to change.