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

Klintzsch, Thomas; Langer, Gerald; Nehrke, Gernot; Wieland, Anna; Lenhart, Katharina; Keppler, Frank

Methane (inline-formulaCH4) production within the oceanic mixed layer is a widespread phenomenon, but the underlying mechanisms are still under debate. Marine algae might contribute to the observed inline-formulaCH4 oversaturation in oxic waters, but so far direct evidence for inline-formulaCH4 production by marine algae has only been provided for the coccolithophore Emiliania huxleyi.

In the present study we investigated, next to E. huxleyi, other widespread haptophytes, i.e., Phaeocystis globosa and Chrysochromulina sp. We performed inline-formulaCH4 production and stable carbon isotope measurements and provide unambiguous evidence that all three investigated marine algae are involved in the production of inline-formulaCH4 under oxic conditions. Rates ranged from inline-formula1.9±0.6 to inline-formula3.1±0.4inline-formulaµg of inline-formulaCH4 per gram of POC (particulate organic carbon) per day, with Chrysochromulina sp. and E. huxleyi showing the lowest and highest rates, respectively. Cellular inline-formulaCH4 production rates ranged from inline-formula16.8±6.5 (P. globosa) to inline-formula62.3±6.4 ag inline-formulaCH4 cellinline-formula−1 dinline-formula−1 (E. huxleyi; ag inline-formula= 10inline-formula−18 g). In cultures that were treated with inline-formula13C-labeled hydrogen carbonate, inline-formulaδ13CH4 values increased with incubation time, resulting from the conversion of inline-formula13C–hydrogen carbonate to inline-formula13CH4. The addition of inline-formula13C-labeled dimethyl sulfide, dimethyl sulfoxide, and methionine sulfoxide – known algal metabolites that are ubiquitous in marine surface layers – resulted in the occurrence of inline-formula13C-enriched inline-formulaCH4 in cultures of E. huxleyi, clearly indicating that methylated sulfur compounds are also precursors of inline-formulaCH4. By comparing the algal inline-formulaCH4 production rates from our laboratory experiments with results previously reported in two field studies of the Pacific Ocean and the Baltic Sea, we might conclude that algae-mediated inline-formulaCH4 release is contributing to inline-formulaCH4 oversaturation in oxic waters. Therefore, we propose that haptophyte mediated inline-formulaCH4 production could be a common and important process in marine surface waters.

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Klintzsch, Thomas / Langer, Gerald / Nehrke, Gernot / et al: Methane production by three widespread marine phytoplankton species: release rates, precursor compounds, and potential relevance for the environment. 2019. Copernicus Publications.

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