Hydrogen-based microbial life in Arctic hydrothermal vent plumes of the Gakkel Ridge

Hydrothermal vents transport hot fluids rich in potential microbial energy sources into the water column. Here, we describe two deep-sea mounds with hydrothermal venting on the Gakkel Ridge in the ice-covered Central Arctic Ocean. Both mounds showed fresh pillow basalts and mineralization of metal sulfides. Vent fauna were rare, but locally filter feeders and opportunists grazing microbial mats were abundant. The hydrothermal plumes rose up to 800 m into the deep Arctic Ocean, and in the non-buoyant plume phase, rates of microbial carbon fixation were up to 50 times higher than values for background seawater. In the Polaris plume, sulfide and hydrogen supported the growth of the chemoautotrophs SUP05 and Candidatus Sulfuriomonas pluma. At the Aurora vents, the hydrogen oxidizer Ca. S. pluma dominated, whereas metal sulfide precipitation reduced the bioavailability of sulfide in the plume. There was no evidence for methane consumption at either site. Our results demonstrate the dominance of hydrogen as an energy source in Arctic hydrothermal vents.