The Lost City hydrothermal field (LCHF) and associated microbial communities are fueled by reactions between mantle rocks and seawater, a process referred to as serpentinization that releases abundant molecular hydrogen. Mixing of serpentinization fluids with seawater can provide the energy and raw materials needed to support a biosphere that may extend deep into the subseafloor. Despite considerable interest in such systems, the linkages between biological communities and geological processes remain poorly explored.
The present study seeks to examine hydrothermal ‘brucite-calcite’ veins we recently identified in altered mantle rocks recovered from the Iberia Margin. This assemblage is otherwise exclusively found in chimneys of the LCHF and forms when alkaline hydrothermal fluids mix with seawater. By analogy we take these findings as a first indication that equivalent mixing processes took place in the subseafloor of the Iberia Margin, most likely during the Cretaceous. Preliminary spectroscopic data and DNA extraction attempts suggest that microbial biomass including nucleic acids entrapped during mineral growth has been preserved. In order to gain deeper insights into subsurface mixing and microbiological processes at the Iberia margin, we propose to conduct an interdisciplinary petrological and biological study of drill cores recovered during the Ocean Drilling Program (Leg 149). To this end we will use a combination of leading edge metagenomic tools and state-of-the-art spectroscopic techniques. The results will not only represent a first step toward a direct comparison of mid-ocean ridge and passive margin ‘Lost-City’-type hydrothermal systems, we will leverage the metagenomic data to investigate microbial biogeography and dispersal (mechanisms) between these geotectonic settings.
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