Oxidation pathways for formic acid under low temperature hydrothermal conditions: Implications for the chemical and isotopic evolution of organics on Mars

δ13C values of residual formic acid in the homogeneous H2O2(aq)-HCOOH(aq)-H2O system are consistent with previous studies. However, magnetite-bearing experiments produce a negative shift in δ13C of residual formic acid, perhaps specific to OH-imposed oxidation of organic compounds. This would indicate that isotopic fractionations by this oxidation pathway are opposite to kinetic fractionation effects expected in biologically driven oxidation processes. This could have important implications for putative H2O2(aq)-bearing Martian subsurface environments and the evolution of organics at low-temperature hydrothermal conditions.