Selci, Matteo Microbial influences on subduction zone volatiles cycling. [Tesi di dottorato]

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Abstract

Convergent margins are gateways to Earth’s interior where volatile species such as carbon, water, hydrogen, and sulfur are cycled between the surface and the interior of the planet. Among these elements, carbon is the main element in terms of contribution to the wellbeing and sustainability of life on Earth. Unlike surface environments where carbon cycling is well constrained, its role in the subsurface environment remains still not well understood. To date, numerous studies have focused on the fate of carbon through the deep layers of our planet, looking at the subsurface microbiota as a key player in carbon sequestration. In subduction zones, the two main forms of carbon available for microorganisms are CO2 and CH4, while organic carbon and CO are less abundant. Here, a number of chemolithoautotrophic microorganisms work as carbon sinks, utilizing CO2 and CO as electron acceptors, donors and as carbon sources. This thesis aims to increase our knowledge of the interactions between biosphere and geosphere with a first focus on the microbial overprint on the volatiles that are cycled at convergent margins. Central American convergent margin hot springs and other secondary geothermal manifestations, broadly referred to as deeply-sourced seeps, were investigated with a multidisciplinary approach that include geochemistry and microbiology analyses, essential for linking geology and biology underlying this thesis. Besides their use as a window to the subsurface, hot springs have been used for centuries for leisure as well as religious rituals by human populations. Given the large number of samples collected in this work, one of the secondary aims has been to investigate the anthropic use of the springs and its link to the potential presence of pathogens.

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