the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Air-Sea fluxes of dimethyl sulphide and methanethiol in the South-West Pacific
Erin Dunne
Alexia Saint-Macary
Maija Peltola
Theresa Barthelmeß
Neill Barr
Karl Safi
Andrew Marriner
Stacy Deppeler
James Harnwell
Anja Engel
Aurélie Colomb
Alfonso Saiz-Lopez
Mike Harvey
Cliff S. Law
Karine Sellegri
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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Manon Rocco et al.
Status: open (until 20 Jun 2023)
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CC1: 'Comment on egusphere-2023-516', Yuanxu Dong, 21 May 2023
reply
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
reply
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
reply
Manon Rocco et al.
Manon Rocco et al.
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