Origin and fate of methane in the Central American convergent margin

Convergent margins are gateways through which volatile species such as carbon, water, hydrogen, and sulfur are exchanged between Earth’s surface and its interior. In these subduction zone settings, carbon is fluxed from depth in two main forms: oxidized carbon as carbon dioxide and reduced carbon in the form of methane. While the former is quantitatively more important and its volcanic fluxes have been better constrained, the latter can serve as carbon and energy sources to microbiological communities and may contribute to greenhouse effects and climate stability. Constraining the geological and biological processes that govern the production, transformation, and fate of methane at convergent margins is therefore crucial for understanding the deep carbon cycle and the redox balance. Here, we present data from 47 deeply-sourced geothermal seeps spanning the Costa Rican and Panamanian convergent margins. By integrating the diversity of methane-cycling prokaryotes (5.2 % of the total community) with clumped methane isotope data (Δ13CH3D: -0.59 to 8.32), we provide an unprecedented view of the geobiological processes controlling methane cycling in these systems. Our results indicate that host rock lithology and geological setting strongly influence both the abundance and isotopic signature of the methane cycled to the surface. These findings suggest that different geological settings promote either methane production, methane oxidation, or biological overprinting. We therefore propose the geological setting as the principal control on how secondary geological and biological processes modify deep-sourced methane signals and ultimately affect the fate of methane within convergent margins.