Figure 3

Schematic of proposed carbon-microbe relationship in Lost City chimneys. Anoxic hydrothermal fluids transport ¹⁴C-free formate, methane, hydrogen, and sulfate through carbonate brucite chimneys. Sulfate reducers convert formate to ΣCO₂ that can then be utilized by autotrophs such as the Lost City Methanosarcinales. Depending on location, some seawater dissolved inorganic carbon is also incorporated into the DIC pool and is also available for microorganisms living in the chimneys. Due to the reversibility of the formate dehydrogenase enzyme, this modern carbon can be incorporated into the formate pool.