the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 May 2023
Air-Sea fluxes of dimethyl sulphide and methanethiol in the South-West Pacific
Abstract. Air-sea fluxes of dimethyl sulphide (DMS) and methanethiol (MeSH) from surface seawater in the remote Southern Pacific Ocean were measured in three Air-Sea Interface Tank (ASIT) experiments during the Sea2Cloud voyage in March 2020. The measured fluxes of 0.78 ± 0.44 ng m-2 s-1 and 0.05 ± 0.03 ng m-2 s-1 for DMS and MeSH, respectively, varied between experiments reflecting the different water mass types investigated, with lowest fluxes with subtropical water and highest with biologically-active water with sub-Tropical water and highest from the sub-Tropical Front. Measured DMS fluxes were consistent with calculated fluxes from a two-layer model using DMS concentration in the ASIT seawater. The experiments also determined the influence of elevated ozone, with one ASIT headspace amended with 10 ppbv ozone while the other provided an unamended control. Elevated ozone resulted in a decrease in DMS flux, corresponding to decreased conversion of dimethylsulfoniopropionate (DMSP) to DMS in the seawater. The MeSH:DMS flux range was 11–18 % across experiments, in line with previous observations, indicating that MeSH represents a significant contribution to the atmospheric sulfur budget. Using the ASIT results in combination with ambient seawater concentrations during Sea2Cloud, significant linear correlations were identified for both DMS and MeSH fluxes with nanophytoplankton cell abundance (rDMS= 0.73 and rMeSH= 0.86), indicating an important role for this phytoplankton size class, and also its potential as a proxy for estimating DMS and MeSH emissions in chemistry-climate models.
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CC1: 'Comment on egusphere-2023-516', Yuanxu Dong, 21 May 2023
Hi authors,
I have a question about the DMS flux.
I am wondering if the turbulence in the tank is the same as it in the air-sea interface. For example, high wind speed typically represents a strong turbulence and thus a quick gas exchange rate (i.e., larger K), but how to reproduce this turbulence in the tank?cheers,
Yuanxu.
Citation: https://doi.org/10.5194/egusphere-2023-516-CC1 -
CC2: 'Reply on CC1', Karine Sellegri, 21 May 2023
Dear Yanxu,
Thanks for your question! Yes the turbulence is lower in our tanks than in the real atmosphere in general. From the theoretical rate exchange approach (equations 4) that includes turbulence effect on the gaz exchange coefficient (eq 6), we calculate that our system operates at an equivalent wind speed of 0.59 m s-1, which is indeed lower than average wind speed in the open, free atmosphere. Changing the turbulence inside the tanks would need to increase the sheath air flowrate, however our goal is not so much to check the validity of equation 6 but to study how DMS concentrations and fluxes are a function of the seawater biogeochemistry so we kept this variable constant. With our system we cheked that DMS fluxes were well correlated to DMS concentrations in the seawater and therefore DMS fluxes variability is due to biogeochemical facors and not physical ones.
best,
Karine
Citation: https://doi.org/10.5194/egusphere-2023-516-CC2
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CC2: 'Reply on CC1', Karine Sellegri, 21 May 2023
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RC1: 'Comment on egusphere-2023-516', Anonymous Referee #1, 04 Jul 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-516/egusphere-2023-516-RC1-supplement.pdf
- AC1: 'Reply on RC1', Manon Rocco, 17 Oct 2023
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EC1: 'Comment on egusphere-2023-516', Maria Kanakidou, 04 Sep 2023
After careful reading of the manuscript, I agree with the reviewer that the manuscript requires drastic improvement in order to meet the quality for publication in ACP.
The authors need to properly cite earlier works both with regard to the understanding of the processes of DMS production in the sea water as well as to the DMS observations in the marine environment as already suggested by the reviewer. They also need to clearly demonstrate and spell out (also in the abstract) the originality and the added value of the work compared to earlier studies.
In addition, they have to thoroughly discuss the uncertainties introduced by the contamination and losses inside the ASITs. For instance, they mention that the O3 levels inside the ASIT are lower than the ambient levels in the control experiment due to losses on the walls and the pipeline. This means that the control experiment is not representative of the ambient atmosphere – so the derived fluxes are not representative either. In addition, if O3 is lost in the system why not having also artifacts for the other studied species? However, I cannot find an evaluation of how the errors induced by this artifact propagate to the main findings of the study. I would also like to see a more critical presentation of the results of the ASIT experiments since only 3 pairs of them have been performed. Even though these experiments are logistically heavy to be performed, it is difficult to draw a firm conclusion from a such small number of experimental results and thus the way the results are presented has to be appropriate.
Furthermore, the authors erroneously mention a lifetime of DMS for its reaction with O3 at 15 days with reference to Vrekoussis et al., 2004, who do not mention any relevant to that result since that study investigated OH and NO3 radicals atmospheric levels. To my knowledge there is only a very low upper limit rate for reactivity against O3. For a thorough review of DMS chemistry – although a bit old now -but very comprehensive the authors are directed to the Barnes et al Chemical Reviews paper Chem. Rev. 106, 940-975, 2006.and recent updates by Veres et al. 2021 https://doi.org/10.1073/pnas.1919344117
There are also inconsistencies between the numbers provided in the text and the figures as in Figures 4 and 5 pointed out by the reviewer. Although the color scale in Figure 4 does not allow to see the exact value of the concentrations, the high levels of DMS provided in the manuscript, for instance the 1285 ppt of DMS in line 269. In addition, alteration between ppt and ppb for DMS concentration in the text and the figures is rather confusing for the reader.
Furthermore, key references. like Sellegri et al 2923 and Rocco et al. 2021, are provided in the text and are missing from the ref list. The first one, I imagine, should be the Sea2Cloud description published in https://journals.ametsoc.org/view/journals/bams/104/5/BAMS-D-21-0063.1.xml and the second should be the paper in Nature Communications E&E https://www.nature.com/articles/s43247-021-00253-0 where ASIT results are also presented for organics.
The manuscript will also benefit from a careful re-reading and English correction.
Overall, I consider this manuscript requires a very careful examination of all its statements, the statements need to be supported by observations and statistical analysis (including p-values for all correlations), and needs to demonstrate its added value compared to earlier studies from different or even the same campaign. In addition, the content should reflect on the title. As is now, focused on the ASIT experiments, the title in the supplementary material seems closer to the content of the manuscript than the original title. After the requested major changes, the manuscript must be reviewed again.
Citation: https://doi.org/10.5194/egusphere-2023-516-EC1 - AC2: 'Reply on EC1', Manon Rocco, 17 Oct 2023
Status: closed
-
CC1: 'Comment on egusphere-2023-516', Yuanxu Dong, 21 May 2023
Hi authors,
I have a question about the DMS flux.
I am wondering if the turbulence in the tank is the same as it in the air-sea interface. For example, high wind speed typically represents a strong turbulence and thus a quick gas exchange rate (i.e., larger K), but how to reproduce this turbulence in the tank?cheers,
Yuanxu.
Citation: https://doi.org/10.5194/egusphere-2023-516-CC1 -
CC2: 'Reply on CC1', Karine Sellegri, 21 May 2023
Dear Yanxu,
Thanks for your question! Yes the turbulence is lower in our tanks than in the real atmosphere in general. From the theoretical rate exchange approach (equations 4) that includes turbulence effect on the gaz exchange coefficient (eq 6), we calculate that our system operates at an equivalent wind speed of 0.59 m s-1, which is indeed lower than average wind speed in the open, free atmosphere. Changing the turbulence inside the tanks would need to increase the sheath air flowrate, however our goal is not so much to check the validity of equation 6 but to study how DMS concentrations and fluxes are a function of the seawater biogeochemistry so we kept this variable constant. With our system we cheked that DMS fluxes were well correlated to DMS concentrations in the seawater and therefore DMS fluxes variability is due to biogeochemical facors and not physical ones.
best,
Karine
Citation: https://doi.org/10.5194/egusphere-2023-516-CC2
-
CC2: 'Reply on CC1', Karine Sellegri, 21 May 2023
-
RC1: 'Comment on egusphere-2023-516', Anonymous Referee #1, 04 Jul 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-516/egusphere-2023-516-RC1-supplement.pdf
- AC1: 'Reply on RC1', Manon Rocco, 17 Oct 2023
-
EC1: 'Comment on egusphere-2023-516', Maria Kanakidou, 04 Sep 2023
After careful reading of the manuscript, I agree with the reviewer that the manuscript requires drastic improvement in order to meet the quality for publication in ACP.
The authors need to properly cite earlier works both with regard to the understanding of the processes of DMS production in the sea water as well as to the DMS observations in the marine environment as already suggested by the reviewer. They also need to clearly demonstrate and spell out (also in the abstract) the originality and the added value of the work compared to earlier studies.
In addition, they have to thoroughly discuss the uncertainties introduced by the contamination and losses inside the ASITs. For instance, they mention that the O3 levels inside the ASIT are lower than the ambient levels in the control experiment due to losses on the walls and the pipeline. This means that the control experiment is not representative of the ambient atmosphere – so the derived fluxes are not representative either. In addition, if O3 is lost in the system why not having also artifacts for the other studied species? However, I cannot find an evaluation of how the errors induced by this artifact propagate to the main findings of the study. I would also like to see a more critical presentation of the results of the ASIT experiments since only 3 pairs of them have been performed. Even though these experiments are logistically heavy to be performed, it is difficult to draw a firm conclusion from a such small number of experimental results and thus the way the results are presented has to be appropriate.
Furthermore, the authors erroneously mention a lifetime of DMS for its reaction with O3 at 15 days with reference to Vrekoussis et al., 2004, who do not mention any relevant to that result since that study investigated OH and NO3 radicals atmospheric levels. To my knowledge there is only a very low upper limit rate for reactivity against O3. For a thorough review of DMS chemistry – although a bit old now -but very comprehensive the authors are directed to the Barnes et al Chemical Reviews paper Chem. Rev. 106, 940-975, 2006.and recent updates by Veres et al. 2021 https://doi.org/10.1073/pnas.1919344117
There are also inconsistencies between the numbers provided in the text and the figures as in Figures 4 and 5 pointed out by the reviewer. Although the color scale in Figure 4 does not allow to see the exact value of the concentrations, the high levels of DMS provided in the manuscript, for instance the 1285 ppt of DMS in line 269. In addition, alteration between ppt and ppb for DMS concentration in the text and the figures is rather confusing for the reader.
Furthermore, key references. like Sellegri et al 2923 and Rocco et al. 2021, are provided in the text and are missing from the ref list. The first one, I imagine, should be the Sea2Cloud description published in https://journals.ametsoc.org/view/journals/bams/104/5/BAMS-D-21-0063.1.xml and the second should be the paper in Nature Communications E&E https://www.nature.com/articles/s43247-021-00253-0 where ASIT results are also presented for organics.
The manuscript will also benefit from a careful re-reading and English correction.
Overall, I consider this manuscript requires a very careful examination of all its statements, the statements need to be supported by observations and statistical analysis (including p-values for all correlations), and needs to demonstrate its added value compared to earlier studies from different or even the same campaign. In addition, the content should reflect on the title. As is now, focused on the ASIT experiments, the title in the supplementary material seems closer to the content of the manuscript than the original title. After the requested major changes, the manuscript must be reviewed again.
Citation: https://doi.org/10.5194/egusphere-2023-516-EC1 - AC2: 'Reply on EC1', Manon Rocco, 17 Oct 2023
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