The high concentrations of methane in the vent fluids of the Lost City Hydrothermal Field represent the sum of abiotic and biological sources and sinks. Stable isotopes of carbon are of limited value in discriminating between the various sources of methane because the isotope effects associated with the multiple processes forming and consuming methane are each poorly constrained, and the products of these processes are pooled. Furthermore, reservoir effects complicate interpretation: the near quantitative reduction of inorganic carbon to methane under highly reducing conditions limits the isotope effects associated with methanogenesis. However, the carbon isotope compositions of lipids derived from anaerobic methanotrophs suggest that more than one isotopically distinct pool of methane exists at Lost City. In this analysis we integrate multiple lines of evidence to constrain the relative contribution of various processes at Lost City. The processes that we consider here include i) Fischer-Tropsch-type (FTT) abiotic synthesis of methane and other hydrocarbons, ii) the Sabatier process for the abiotic synthesis of methane alone, iii) biological methane production by Methanosarcinales, and iv) biological methane consumption by anaerobic and aerobic methanotrophs. This analysis suggests that abiotic processes, particularly the Sabatier reaction, are likely to be the dominant source of methane at Lost City. Biological methane is present in the vent fluids, but does not compose a high fraction of the total methane pool. These observations imply that ultramafic systems could have supplied abundant reduced carbon to the early Earth, even without biological catalysis.

Original languageEnglish
Pages (from-to)34-41
Number of pages8
JournalEarth and Planetary Science Letters
Issue number1-2
StatePublished - Aug 2010


  • Carbon isotopes
  • Hydrogen isotopes
  • Lost City Hydrothermal Field
  • Methane


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