Matteo Selci, Martina Cascone, Timothy J Rogers, Alberto Vitale Brovarone, Carlos J Ramirez, Patrick Beaudry, Shuhei Ono, Mustafa Yucel, Gerdhard L. Jessen, Metthew O Schrenk, J. Maarten de Moor, Peter H Barry, Angelina Cordone, Karen G Lloyd, Donato Giovannelli

Convergent margins are gateways to Earth’s interior where volatile species are cycled between the planet's surface and interior. At these locations, carbon is recycled from deep reservoirs in two main forms: oxidized carbon, such as carbon dioxide, and reduced carbon, such as methane. While the former is quantitatively more important and its volcanic fluxes have been better constrained, the latter represents the most reduced form of carbon on Earth and greatly contributes to greenhouse effects and climate stability. Understanding the geological and biological processes underpinning the origin and fate of methane in convergent margins is thus pivotal to constraining carbon cycling and redox balance in convergent margins. Here, we present coupled geochemical and microbiological data from 47 geothermal deeply-sourced seeps spanning the Costa Rica and Panama convergent margin. By analyzing the presence and diversity of methane-cycling microorganisms and using clumped isotope data, we observed that biotic and abiotic processes are both involved in driving the quantity and isotopic signature of methane cycled to the surface, providing an unprecedented snapshot of the geobiological processes controlling methane cycling in convergent margins.