Disconnected from the energy of the sun, the permanently ice-covered Arctic deep sea receives miniscule amounts of organic matter that sustains life. Bacteria which can harvest the energy released from submarine hydrothermal sources could thus have an advantage. On research missions with the research vessel Polarstern, scientists from Germany found bacteria uniquely adapted to this geo-energy floating in deep-sea waters. They describe the role of these bacteria for biogeochemical cycling in the ocean.