Rocco, M., Dunne, E., Salignat, R., Saint‐Macary, A., Peltola, M., Barthelmeß, Theresa, Chamba, G., Barr, N., Safi, K., Marriner, A., Deppeler, S., Rose, C., Uitz, J., Harnwell, J., Engel, Anja , Colomb, A., Saiz‐Lopez, A., Harvey, M. J., Law, C. S. and Sellegri, K. (2025) Relating Dimethyl Sulphide and Methanethiol Fluxes to Surface Biota in the South‐West Pacific Using Shipboard Air‐Sea Interface Tanks. Journal of Geophysical Research: Atmospheres, 130 (1). e2024JD041072. DOI 10.1029/2024JD041072.

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Abstract

Dimethyl sulphide (DMS) and methanethiol (MeSH) emissions from South Pacific surface seawater were determined in deck board Air‐Sea Interface Tanks during the Sea2Cloud voyage in March 2020. The measured fluxes from water to headspace (F) varied with water mass type, with lowest fluxes observed with Subtropical and Subantarctic waters and highest fluxes from Frontal waters. Measured DMS fluxes were consistent with fluxes calculated using a two‐layer model and seawater DMS concentrations. The MeSH:DMS flux ratio was 11%–18% across the three water mass types, confirming that MeSH may represent a significant unaccounted contribution to the atmospheric sulfur budget, with potentially important implications for marine aerosol formation and growth in models. Combining data from the ASITs and ambient surface seawater identified significant Spearman rank correlations for both dissolved DMS and MeSH with nanophytoplankton cell abundance ( p value < 0.012), suggesting an important role for this phytoplankton size class in determining regional DMS and MeSH emissions. Applying a nanophytoplankton‐based parameterization to estimate DMS w provided good agreement with a recent DMS climatology. Consequently, the observed relationship between DMS w , MeSH w and nanophytoplankton cell abundances may be applicable for modeling atmospheric fluxes.

Plain Language Summary

In March 2020, researchers conducted experiments during the Sea2Cloud voyage east of New Zealand in which they measured the emissions of the climate relevant gases dimethyl sulphide (DMS) and methanethiol (MeSH). These sulfur gases are produced by marine microorganisms and their emissions were measured in tanks containing different sea water types. Lowest emissions were observed in Subtropical and Subantarctic waters while the highest were in Frontal waters where Subantarctic and Subtropical seawaters meet and support large phytoplankton blooms. While DMS has been extensively studied, there are far fewer measurements of MeSH which this study confirmed be a significant, relatively constantly scaled to DMS and previously underestimated contributor to atmospheric sulfur levels with potential implications for climate. The study established significant correlations between DMS and MeSH fluxes and nanophytoplankton cell abundance, highlighting the importance of this phytoplankton size class in marine emissions to the atmosphere. The results presented here can help constrain emissions of these sulfur gases in climate models.

Key Points

Ratio of methanethiol (MeSH) to dimethyl sulphide (DMS) fluxes of 11%–18% is consistent across different water types in Southern Ocean waters
Significant correlations between DMS w and MeSH w and nanophytoplankton were observed, enabling development of parameterizations for models

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