The northern European shelf as an increasing net sink for CO<sub>2</sub>

Becker, Meike; Olsen, Are; Landschützer, Peter; Omar, Abdirhaman; Rehder, Gregor; Rödenbeck, Christian; Skjelvan, Ingunn

doi:https://doi.org/10.5194/bg-18-1127-2021

Articles | Volume 18, issue 3

https://doi.org/10.5194/bg-18-1127-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-18-1127-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 3

Research article

|

15 Feb 2021

Research article |

| 15 Feb 2021

The northern European shelf as an increasing net sink for CO₂

Meike Becker, Are Olsen, Peter Landschützer, Abdirhaman Omar, Gregor Rehder, Christian Rödenbeck, and Ingunn Skjelvan

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Final revised paper (published on 15 Feb 2021)
Supplement to the final revised paper
Preprint (discussion started on 14 Jan 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'review', Anonymous Referee #1, 06 Feb 2020
- AC3: 'Answer to review 1', Meike Becker, 20 May 2020
RC2: 'Review', Anonymous Referee #2, 18 Mar 2020
- AC2: 'Answer to review 2', Meike Becker, 20 May 2020
AC1: 'Answer to review 1', Meike Becker, 20 May 2020

Peer-review completion

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

ED: Reconsider after major revisions (25 May 2020) by Jack Middelburg

AR by Meike Becker on behalf of the Authors (28 May 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Jun 2020) by Jack Middelburg

RR by Anonymous Referee #1 (04 Jun 2020)

RR by Anonymous Referee #2 (30 Jun 2020)

Suggestions for revision or reasons for rejection

Many of the issues raised in the first review have been well addressed but the authors have argued that they do not wish to address others.

The unwillingness to publish the actual MLR equation used remains a concern. The given reason is "We recommend strongly to develop a specific fit for any new application." What if the new application is to directly compare the result here with another MLR - to compare the directions and relative importance of the variables driving the fit - either developed for the same region with newer data or for a different region? Not showing the different terms also hinders assessment of whether the fit makes sense, whether terms with well-known relationships with pCO2 (e.g. temperature) are driving it in the expected direction, whether the relationships are meaningful and linked to underlying processes (and therefore probably more reliable for predicting beyond the input dataset) or simply spurious correlations for the specific training data used. Finally, keeping something so critical to the study as a secret "black box" seems to contradict the open access principles of this journal.

The comparison between previous results in Table 1 vs the signficance plot in Figure 9 has not been addressed. The authors may of course decide that discussing the actual drivers (e.g. NAO) of interannual variability is beyond the scope of this study. But even ignoring the drivers, the point remains that the new results here show that trends determined over the short periods that were the basis of previous studies are not significant. As things stand, a new result that implicitly casts doubt on earlier work is being presented here without comment.

The issue regarding the northern Baltic Sea containing only a single month of data was acknowledged in the author responses but it would be better to discuss this briefly in the manuscript itself. Looking back to the map on Figure 9 it's interesting to see that this region does not have black dots to indicate non-significant trends. The method therefore claims to identify a significant long-term trend for a region containing only one month from one year of training data. This makes me wonder whether significance is being assessed in a suitable way.

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ED: Reconsider after major revisions (17 Aug 2020) by Jack Middelburg

AR by Meike Becker on behalf of the Authors (09 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Oct 2020) by Jack Middelburg

RR by Anonymous Referee #1 (12 Oct 2020)

ED: Reconsider after major revisions (15 Oct 2020) by Jack Middelburg

AR by Meike Becker on behalf of the Authors (30 Oct 2020) Author's response Manuscript

ED: Publish subject to technical corrections (05 Nov 2020) by Jack Middelburg

AR by Meike Becker on behalf of the Authors (12 Nov 2020) Author's response Manuscript

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Short summary

We developed a simple method to refine existing open-ocean maps towards different coastal seas. Using a multi-linear regression, we produced monthly maps of surface ocean fCO₂ in the northern European coastal seas (the North Sea, the Baltic Sea, the Norwegian Coast and the Barents Sea) covering a time period from 1998 to 2016. Based on this fCO₂ map, we calculate trends in surface ocean fCO₂, pH and the air–sea gas exchange.

The northern European shelf as an increasing net sink for CO2

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Interactive discussion

Peer-review completion

The northern European shelf as an increasing net sink for CO₂