Methane plume observations on Mars: Difference between revisions

Plants have values of from -10% or so down to -30% or less, clustering at around -13% and -28%<ref>O'Leary, Marion H. [http://sethnewsome.org/sethnewsome/EE_files/O%27Leary%201988.pdf "Carbon isotopes in photosynthesis."] Bioscience 38, no. 5 (1988): 328-336.</ref>. Algae have a similar range of values, from higher than -10% down to -30% or less. Coal and marine petroleum typically has values around -25%, terrestrial petroleum around -30%, and land plants average around -25%, but with a fair bit of variation around those figures. See figure 1 in this article.Park, Roderic, and Samuel Epstein. [https://authors.library.caltech.edu/62406/1/4259733.pdf "Metabolic fractionation of C13 & C12 in plants."] Plant Physiology 36, no. 2 (1961): 133.

 

 

The carbon 13 can be depleted by abiotic proceses. It can also be depleted in methane produced by heating organics (thermogenic methane) and meanwhile, sometimes methane produced by life is not depleted in carbon 13. It also depends on the isotopic composition of its precursor. Magmatic carbon, for instance, might be depleted in carbon 13. Also processes that alter the methane such as oxidation by hydrogen peroxide can deplete the carbon 12 turning a possible microbial signature into one that looks abiotic. Meanwhile diffusion through permeable rock can increase the carbon 12 levels to mimic a biogenic signature - this could be the dominant process if the methane has to pass through an almost impenetrable "cap" on its way to the surface.<ref name=nomadmethane>[https://meetingorganizer.copernicus.org/EPSC2018/EPSC2018-211-3.pdf NOMAD on ExoMars Trace Gas Orbiter: status and preliminary results] Ann C. Vandaele., Jose-Juan Lopez-Moreno, GiancarloBellucci, Manish R. Patel, FrankDaerden, IanR. Thomas,Eddy Neefs, BojanRistic, Sophie Berkenbosch, Bram Beeckman, Roland Clairquin, Claudio Queirolo and the NOMAD Team, EPSC Abstracts,Vol. 12, EPSC2018-211-3, 2018, European Planetary Science Congress 2018</ref>