Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events

Morgan, Eric J.; Lavric, Jost V.; Arévalo-Martínez, Damian L.; Bange, Hermann W.; Steinhoff, Tobias; Seifert, Thomas; Heimann, Martin

doi:https://doi.org/10.5194/bg-16-4065-2019

Articles | Volume 16, issue 20

https://doi.org/10.5194/bg-16-4065-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-16-4065-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 16, issue 20

Research article

|

21 Oct 2019

Research article |

| 21 Oct 2019

Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events

Eric J. Morgan, Jost V. Lavric, Damian L. Arévalo-Martínez, Hermann W. Bange, Tobias Steinhoff, Thomas Seifert, and Martin Heimann

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Final revised paper (published on 21 Oct 2019)
Supplement to the final revised paper
Preprint (discussion started on 26 Mar 2019)
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Interactive discussion

Status: closed

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

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- Supplement

RC1: 'BG-2019-103 Air–Sea Fluxes of Greenhouse Gases and Oxygen in the Northern Benguela Current Region During Upwelling Events', Anonymous Referee #1, 26 May 2019
- AC1: 'Response to Anonymous Referee #1', Eric Morgan, 11 Jun 2019
RC2: 'Review of Air–Sea Fluxes of Greenhouse Gases and Oxygen in the Northern Benguela Current Region During Upwelling Events by Morgan et al. for Biogeosciences', Anonymous Referee #2, 28 May 2019
- AC2: 'Response to Anonymous Referee #2', Eric Morgan, 11 Jun 2019

Peer-review completion

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

ED: Reconsider after major revisions (22 Jun 2019) by S. Wajih A. Naqvi

AR by Eric Morgan on behalf of the Authors (23 Jul 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Jul 2019) by S. Wajih A. Naqvi

RR by Anonymous Referee #2 (22 Aug 2019)

Suggestions for revision or reasons for rejection

This is my second review of the manuscript by Morgan et al. As stated in my first review, this is a nice study with relevance for the Biogeosciences readership. I commend the Authors for the serious consideration that they gave to my and another Reviewer comments. As a result, several aspects of the study have improved, including the presentation of the model, the discussion of uncertainty, and the discussion of the results in a broader context, and the figures.

The fact that the top-down estimates still seem to overestimate fluxes compared to the ship-based estimate even after tuning is still somewhat puzzling, but is well discussed in the paper. (CO2 is better matched compared to O2 and especially N2O, see Fig. 8 and Table 2). The Authors could add a comment on this potential low bias in the abstract as well, since it is an issue that may need to be resolved in future studies (e.g. with comparison to more ship based data).

It's also somewhat puzzling in Fig. 6 that the land-based concentrations are often higher than the ship-based concentrations (especially for CH4), and more "spiky", since dilution during transport from upwelling regions should have reduced and smoothed them. A discussion of these discrepancies could be added to Section 3.3.

Other than that, I feel that the paper is now suitable for publication. As a final suggestion, I encourage the Authors to give a careful reading to the manuscript to catch some lingering typos and awkwardly phrased sentences. A few are listed in the following:

Page 1, line 16: “episodic” could be changed to “variable”, since it refers to both “occurrence” (which can be episodic), and “intensity” (which can be variable, rather than episodic). Or alternatively the sentence can be rephrased.

Page 2 , line 24: change “based” to “based on”

Page 5, line 10: perhaps use “applied” instead of “generated”?

Page 6, line 10: change “no flux the gas” to “no flux of the gas”

Page 9, line 15: change “21 of excluded events were filtered based on” to “Of these, 21 events were excluded based on”

Page 11. line 4: should the uncertainty be added to the average flux density of CH4?

Page 12, line 13: change “reasonably” to “reasonably well”

Page 12, line 33: change “input” to “parameter”

Page 13, line 6: “tune the model” : please clarify, e.g. use a value of q so that F matches the bottom up value.

Page 15, line 34: change “site” to “sites”

Table 1: maybe add a note to clarify the difference between the “non-tuned" values and the “tuned” values

Figure 9, at the end of the caption: “correspond to” instead of “correspond with”.

Figure 8, caption: “three” should now be “two”?

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ED: Publish subject to minor revisions (review by editor) (01 Sep 2019) by S. Wajih A. Naqvi

AR by Eric Morgan on behalf of the Authors (13 Sep 2019) Author's response Manuscript

ED: Publish as is (18 Sep 2019) by S. Wajih A. Naqvi

AR by Eric Morgan on behalf of the Authors (18 Sep 2019)

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Short summary

Taking a 2-year atmospheric record of atmospheric oxygen and the greenhouse gases N₂O, CO₂, and CH₄, made at a coastal site in the Namib Desert, we estimated the fluxes of these gases from upwelling events in the northern Benguela Current region. We compared these results with flux measurements made on a research vessel in the study area at the same time and found that the two approaches agreed well. The study region was a source of N₂O, CO₂, and CH₄ to the atmosphere during upwelling events.