Volume 13, issue 10 | Copyright
Biogeosciences, 13, 3163-3174, 2016
https://doi.org/10.5194/bg-13-3163-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Jun 2016

Research article | 01 Jun 2016

Evidence for methane production by the marine algae Emiliania huxleyi

Katharina Lenhart1,2,3, Thomas Klintzsch2,4,5, Gerald Langer6, Gernot Nehrke7, Michael Bunge5, Sylvia Schnell5, and Frank Keppler3,4 Katharina Lenhart et al.
  • 1Center for Organismal Studies, University of Heidelberg, Im Neuenheimer Feld 360, 69120 Heidelberg, Germany
  • 2Department of Plant Ecology (IFZ), Heinrich-Buff-Ring 26–32, 35320 Gießen, Germany
  • 3Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
  • 4Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 234–236, 69120 Heidelberg, Germany
  • 5Department of Applied Microbiology (IFZ), Heinrich-Buff-Ring 26–32, 35320 Gießen, Germany
  • 6The Marine Biological Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth, Devon, PL1 2PB, UK
  • 7Alfred Wegener Institute (AWI), Am Handelshafen 12, 27570 Bremerhaven, Germany

Abstract. Methane (CH4), an important greenhouse gas that affects radiation balance and consequently the earth's climate, still has uncertainties in its sinks and sources. The world's oceans are considered to be a source of CH4 to the atmosphere, although the biogeochemical processes involved in its formation are not fully understood. Several recent studies provided strong evidence of CH4 production in oxic marine and freshwaters, but its source is still a topic of debate. Studies of CH4 dynamics in surface waters of oceans and large lakes have concluded that pelagic CH4 supersaturation cannot be sustained either by lateral inputs from littoral or benthic inputs alone. However, regional and temporal oversaturation of surface waters occurs frequently. This comprises the observation of a CH4 oversaturating state within the surface mixed layer, sometimes also termed the "oceanic methane paradox". In this study we considered marine algae as a possible direct source of CH4. Therefore, the coccolithophore Emiliania huxleyi was grown under controlled laboratory conditions and supplemented with two 13C-labeled carbon substrates, namely bicarbonate and a position-specific 13C-labeled methionine (R-S-13CH3). The CH4 production was 0.7µg particular organic carbon (POC) g−1d−1, or 30ngg−1POCh−1. After supplementation of the cultures with the 13C-labeled substrate, the isotope label was observed in headspace CH4. Moreover, the absence of methanogenic archaea within the algal culture and the oxic conditions during CH4 formation suggest that the widespread marine algae Emiliania huxleyi might contribute to the observed spatially and temporally restricted CH4 oversaturation in ocean surface waters.

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In this study we investigated marine algae as a source of CH4 in oxic surface waters of oceans. Algae-derived CH4 may explain the CH4 oversaturating state within the surface mixed layer, sometimes also termed the "oceanic methane paradox". This finding of an overlooked source of CH4 in marine environments will be of considerable importance to scientists in many disciplines because algae play a crucial role in organic matter cycling in marine and freshwater ecosystems.
In this study we investigated marine algae as a source of CH4 in oxic surface waters of oceans....
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