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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-245
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-245
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 01 Jul 2019

Submitted as: research article | 01 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Methane production by three widespread marine phytoplankton species: release rates, precursor compounds, and relevance for the environment

Thomas Klintzsch1, Gerald Langer2, Gernot Nehrke3, Anna Wieland1, Katharina Lenhart1,4, and Frank Keppler1,5 Thomas Klintzsch et al.
  • 1Institute of Earth Sciences, University Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
  • 2The Marine Biological Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth, Devon, PL12PB, UK
  • 3Alfred Wegener Institute (AWI), Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 4University of Applied Sciences, Berlinstr. 109, Bingen 55411, Germany
  • 5Heidelberg Center for the Environment HCE, Heidelberg University, D-69120 Heidelberg, Germany

Abstract. The world’s oceans are considered to be a minor source of methane (CH4) to the atmosphere although the magnitude of total net emissions is highly uncertain. In recent years the origin of the frequently observed in situ CH4 production in the ocean mixed layer has received much attention. Marine algae might contribute to the observed CH4 oversaturation in oxic waters, but so far direct evidence for CH4 production by marine algae has only been provided for the coccolithophore Emiliania huxleyi. In the present study we investigated, next to Emiliania huxleyi, other widespread haptophytes, i.e. Phaeocystis globosa and Chrysochromulina sp. for CH4 formation. Our results of CH4 production and stable carbon isotope measurements provide unambiguous evidence that all three investigated marine algae produce CH4 per se under oxic conditions and at rates ranging from 1.6 ± 0.5 to 2.7 ± 0.7 µg CH4 per g POC (particulate organic carbon) d−1 at a temperature of 20 °C with Chrysochromulina sp. and E. huxleyi showing the lowest and highest rates, respectively. In cultures that were treated with 13C-labelled hydrogen carbonate δ13CH4 values increased with incubation time, clearly resulting from the conversion of 13C-hydrogen carbonate to 13CH4. The addition of 13C labelled dimethyl sulfide, dimethyl sulfoxide and methionine sulfoxide – known algal metabolites that are ubiquitous in marine surface layers - enabled us to clearly monitor the occurrence of 13C-enriched CH4 in cultures of Emiliania huxleyi clearly indicating that methylated sulphur compounds are also precursors of CH4. We propose that CH4 production could be a common process among marine haptophytes likely contributing to CH4 oversaturation in oxic waters.

Thomas Klintzsch et al.
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Thomas Klintzsch et al.
Thomas Klintzsch et al.
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Short summary
Marine algae might contribute to the observed methane oversaturation in oxic waters, but so far direct evidence for methane production by marine algae is limited. We investigated three widespread haptophytes for methane formation. Our results provide unambiguous evidence that all investigated marine algae produce methane per se and at substantial rates. We conclude that each of the three algae studied here could substantially account for the methane production observed in field studies.
Marine algae might contribute to the observed methane oversaturation in oxic waters, but so far...
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