The Santa Elena Ophiolite comprises 250 km2
of ultramafic rocks and mafic associations along the northwestern Pacific coast of Costa Rica. Uplifted ultramafic rocks originating from Earth’s mantle represent a reservoir of carbon and reducing power, which, during the process of serpentinization, are liberated into the surface environment, potentially supporting microbial growth.
The extremely variable weather conditions that occur on the Santa Elena Peninsula between the wet (May – October) and dry (November – April) seasons result in a unique hydrogeological environment. Contrary to other continental serpentinization environments (e.g., Tablelands, Canada; Western Coastal Range, USA; Gruppo di Voltri, Italy), in this tropical scenario, precipitation quantities and intensities are usually greater and occur during extended periods of time. This facilitates infiltration, accelerating water-rock interactions and liberating carbon and energy to the surface environment.
Such extreme seasonal events provide a unique opportunity to investigate the response of microbial metabolisms (at the interface of deep carbon and energy fluxes) under a dynamic subsurface hydrology setting. During an expedition in March 2013, we sampled a series of alkaline springs along the peninsula. Preliminary V4-V5 sequence data suggests these fluids have low diversity and indicates the presence of microorganisms involved in hydrogen, methane, and methanol metabolism, including bacteria from the genera Hydrogenophaga and Methylibium and from the family Methylophilaceae, as well as archaea from the orders Methanobacteriales, Methanocellales, and Methanomicrobiales. In this project we intend to demonstrate links between geochemistry, hydrology, and microbial activities related to subsurface processes at Santa Elena Ophiolite.