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https://doi.org/10.5194/bg-2020-2
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-2
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Feb 2020

Submitted as: research article | 03 Feb 2020

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This preprint is currently under review for the journal BG.

Underway seawater and atmospheric measurements of volatile organic compounds in the Southern Ocean

Charel Wohl1,2,3, Ian Brown1, Vassilis Kitidis1, Anna E. Jones3, William T. Sturges2, Philip D. Nightingale1,2,4, and Mingxi Yang1 Charel Wohl et al.
  • 1Plymouth Marine Laboratory, Plymouth, PL1 3DH, UK
  • 2Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
  • 3British Antarctic Survey, Cambridge, High Cross, Madingley Road, CB3 0ET, UK
  • 4Sustainable Agriculture Systems, Rothamsted Research, North Wyke, Devon, EX20 2SB, UK

Abstract. Dimethyl sulfide and volatile organic compounds and are important for atmospheric chemistry. The oceanic emissions of biogenically derived gases, including dimethyl sulfide and especially isoprene, are not well constrained. The role of the ocean in the global budgets of atmospheric methanol, acetone and acetaldehyde is even more poorly known. In order to quantify the air-sea fluxes of these gases we measured their seawater concentrations and air mixing ratios in the Atlantic sector of the Southern Ocean, along a ~ 11 000 km long transect at approximately 60° S in Feb–Apr 2019. Concentrations, oceanic saturations and estimated fluxes of several simultaneously sampled volatile organic compounds (methanol, acetone, acetaldehyde, dimethyl sulfide and isoprene) are presented here. Campaign mean (± 1σ) surface water concentrations of dimethyl sulfide, isoprene, methanol, acetone and acetaldehyde were 2.60 (± 3.94), 0.0133 (± 0.0063), 67 (± 35), 5.5 (± 2.5) and 2.6 (± 2.7) nmol dm−3 respectively. In this dataset, seawater isoprene and methanol concentrations correlated positively. Furthermore, seawater acetone, methanol and isoprene concentrations were found to correlate negatively with the fugacity of carbon dioxide, possibly due to a common biological origin. Campaign mean (± 1σ) air mixing ratios of methanol, acetone and acetaldehyde were relatively low at 0.17 (± 0.08), 0.081 (± 0.031) and 0.049 (± 0.040) ppbv. We observed diel changes in averaged acetaldehyde concentrations in seawater and ambient air (and to a lesser degree also for acetone and isoprene), which suggest light-driven productions. Campaign mean (± 1σ) fluxes of 4.3 (± 7.4) µmol m−2 d−1 DMS and 0.028 (± 0.021) µmol m−2 d−1 isoprene are determined where a positive flux indicates from the ocean to the atmosphere. Methanol was largely undersaturated in the surface ocean with a mean (± 1σ) net flux of −2.4 (± 4.7) µmol m−2 d−1, but also had a few occasional episodes of outgassing This section of the Southern Ocean was found to be both a source and a sink for acetone and acetaldehyde this time of the year, depending on location, resulting in a mean flux of −0.55 (± 1.15) µmol m−2 d−1 for acetone and −0.28 (± 1.22) µmol m−2 d−1 for acetaldehyde. The data collected here will be important for constraining the oceanic source/sink of these gases and potentially help to elucidate the presence of common sources/sinks for these compounds.

Charel Wohl et al.

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Charel Wohl et al.

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Latest update: 25 Feb 2020
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Short summary
The oceans represent a poorly understood source of organic carbon to the atmosphere. In this paper, we present ship based measurements of specific compounds in ambient air and seawater of the Southern Ocean. We present fluxes of these gases between air and sea at very high resolution. The data also contains evidence for day and night variations of some of these compounds. These measurements can be used to better understand the role of the Southern Ocean in the cycling of these compounds.
The oceans represent a poorly understood source of organic carbon to the atmosphere. In this...
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