Discovery and Description of Giant Submarine Smectite Cones on the Seafloor in Eyjafjordur, Northern Iceland, and a Novel Thermal Microbial Habitat

Abstract

With the submersible JAGO and by scuba diving we discovered three remarkable geothermal cones, rising 33, 25, and 45 m from the seafloor at a depth of 65 m in Eyjafjordur, northern Iceland. The greatest geothermal activity was on the highest cone, which discharged up to 50 liters of freshwater per s at 72°C and pH 10.0. The cones were built up from precipitated smectite, formed by mixing of the hot SiO₂-rich geothermal fluid with the cold Mg-rich seawater. By connecting a rubber hose to one outflow, about 240 liters of pure geothermal fluids was concentrated through a 0.2-μm-pore-size filter. Among 50 thermophilic isolates, we found members of Bacillus and Thermonema and a new unidentified low-G+C gram-positive member of theBacteria as well as one member of theArchaea, Desulfurococcus mobilis. Analysis of small-subunit rRNA genes PCR amplified and cloned directly from environmental DNA showed that 41 out of 45Bacteria sequences belonged to members of theAquificales, whereas all of the 10Archaea sequences belonged to theKorarchaeota. The physiological characteristics of isolates from different parts of the cones indicate a completely freshwater habitat, supporting the possibility of subterranean transmittance of terrestrial organisms.