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

Submitted as: research article 16 Oct 2019

Submitted as: research article | 16 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Methanethiol, dimethyl sulfide and acetone over biologically productive waters in the SW Pacific Ocean

Sarah J. Lawson1, Cliff S. Law2,3, Mike J. Harvey2, Tom G. Bell4, Carolyn F. Walker2, Warren J. De Bruyn5, and Eric S. Saltzman6 Sarah J. Lawson et al.
  • 1Commonwealth Scientific and Industrial Research Organisation, Oceans and A tmosphere, Aspendale, Australia
  • 2National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 3Dept. Chemistry, University of Otago, Dunedin, New Zealand
  • 4Plymouth Marine Laboratory, Plymouth, UK
  • 5Schmidt College of Science and Technology, Chapman University, Orange, California, CA, USA
  • 6Earth System Science, University of California, Irvine, California, USA

Abstract. Atmospheric methanethiol (MeSHa), dimethyl sulfide (DMSa) and acetone (acetonea) were measured over biologically productive frontal waters in the remote South West Pacific Ocean in summertime 2012 during the Surface Ocean Aerosol Production (SOAP) voyage. MeSHa mixing ratios varied from below detection limit (< 10 ppt) up to 65 ppt and were 3–36 % of parallel DMSa mixing ratios. MeSHa and DMSa were correlated over the voyage (R2 = 0.3, slope = 0.07) with a stronger correlation over a coccolithophore-dominated phytoplankton bloom (R2 = 0.5, slope 0.13). The diurnal cycle for MeSHa shows similar behaviour to DMSa with mixing ratios varying by a factor of ~ 2 according to time of day with the minimum levels of both MeSHa and DMSa occurring at around 16:00 hrs. A positive flux of MeSH was calculated for 3 different nights and ranged from 3.5–5.8 µmol m−2 day−1 corresponding to 14–24 % of the DMS flux (MeSH / (MeSH + DMS). Spearman rank correlations with ocean biogeochemical parameters showed a moderate to strong positive and highly significant relationship between both MeSHa and DMSa with seawater DMS (DMSsw), and a moderate correlation with total dimethylsulfoniopropionate (total DMSP). A positive correlation of acetonea with water temperature and negative correlation with nutrient concentrations is consistent with reports of acetone production in warmer subtropical waters. Positive correlations of acetonea with cryptophyte and eukaryotic phytoplankton numbers, and high molecular weight sugars and Chromophoric Dissolved Organic Matter (CDOM), suggest an organic source. This work points to a significant ocean source of MeSH, highlighting the need for further studies into the distribution and fate of MeSH, and suggests links between atmospheric acetone levels and biogeochemistry over the mid-latitude ocean.

In addition, an intercalibration of DMSa at ambient levels using three independently calibrated instruments showed ~ 15–25 % higher mixing ratios from an Atmospheric Pressure Ionisation-Chemical Ionisation Mass Spectrometer (mesoCIMS) compared to a Gas Chromatograph with Sulfur Chemiluminescence Detector (GC-SCD) and proton transfer reaction mass spectrometer (PTR-MS). PTR-MS and mesoCIMS showed similar temporal behaviour with differences in ambient mixing ratios likely influenced by the DMSa gradient above the sea surface.

Sarah J. Lawson et al.
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Status: open (until 11 Dec 2019)
Status: open (until 11 Dec 2019)
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Sarah J. Lawson et al.
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DMS, acetone, methanethiol atmospheric data from SOAP voyage S. Lawson

Sarah J. Lawson et al.
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Short summary
Methanethiol (MeSH) is a reduced sulfur gas originating from phytoplankton, with a global ocean source ~ 17 % of dimethyl sulphide (DMS). It has been little studied, and is rarely observed over the ocean. In this work, MeSH was measured at much higher levels than previously observed (3–36 % of parallel DMS mixing ratios). MeSH could be a significant source of atmospheric sulfur over productive regions of the ocean, but its distribution, and its atmospheric impact requires more investigation.
Methanethiol (MeSH) is a reduced sulfur gas originating from phytoplankton, with a global ocean...