EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2023-516 Air-Sea fluxes of dimethyl sulphide and methanethiol in the South-West Pacific Rocco Manon https://orcid.org/0000-0002-4575-0185 1 8 Dunne Erin 2 Saint-Macary Alexia https://orcid.org/0000-0002-6958-6359 3 7 Peltola Maija https://orcid.org/0000-0002-7046-3057 1 Barthelmeß Theresa https://orcid.org/0000-0001-7573-4621 5 Barr Neill 3 Safi Karl 4 Marriner Andrew 3 Deppeler Stacy https://orcid.org/0000-0003-2213-2656 3 Harnwell James 2 Engel Anja https://orcid.org/0000-0002-1042-1955 5 Colomb Aurélie 1 Saiz-Lopez Alfonso https://orcid.org/0000-0002-0060-1581 6 Harvey Mike 3 9 Law Cliff S. https://orcid.org/0000-0002-7669-2475 3 7 Sellegri Karine 1 Université Clermont Auvergne, CNRS, Laboratoire de Météorologie Physique (LaMP), 63000, Clermont-Ferrand, France CSIRO Ocean & Atmosphere, Aspendale, Australia National Institute of Water and Atmospheric Research, Wellington, New Zealand National Institute of Water and Atmospheric Research, Hamilton, New Zealand GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany National Center for Atmospheric Research, NCAR, Boulder, USA Department of Marine Science, University of Otago, New Zealand now at: Instituto de Astronomia, Geofísica e Ciências Atmosféricas/IAG - Universidade de São Paulo - Laboratório de Estudos Ambientais/IPA, São Paulo, Brazil Deceased European Research Council 771369 08 05 2023 2023 1 31 Copyright: © 2023 Manon Rocco et al. 2023 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2023/egusphere-2023-516/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2023/egusphere-2023-516/egusphere-2023-516.pdf

<p>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 &plusmn; 0.44 ng m<sup>-2</sup> s<sup>-1</sup> and 0.05 &plusmn; 0.03 ng m<sup>-2</sup> s<sup>-1</sup> 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&ndash;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 (r<sub>DMS</sub>= 0.73 and r<sub>MeSH</sub>= 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.</p>