Fig. 4
Evidence of hydrothermally active seafloor documented during the OFOBS survey. (a) Sidescan sonar image acquired along the OFOBS trackline. Circular features (red arrows) and elongated, spiky shadows (white arrows) suggests the presence of hydrothermal chimneys located just beyond the visual range of the OFOBS cameras. Also note the relatively smooth, sedimented seafloor. (b) Seafloor photograph taken at the site where the sidescan sonar depicted chimney structures, as shown in (a). (c, d) Traces of (focused) venting, including massive sulfide deposits exhibiting rust-orange weathering and remnants of extinct hydrothermal chimneys. (e, f) Dense hydrothermalism-associated fauna observed in a region exhibiting pronounced anomalies in ORP, optical backscatter, and temperature near the seafloor (cf. Fig. 2a, c). Panel (e) highlights amphipods (arrow), tubeworms, and red anemones within a pocket of presumed diffuse hydrothermal discharge. The white fibrous organisms in (e) and (f) are likely tubeworms covered in chemosynthetic bacteria, resembling siboglinid tube worms and microbial filaments found at the nearby Jøtul site40. A close-up is shown in Supplementary Fig. S6; note, however, that we did not collect physical specimens of the fauna to validate the seafloor images. Also note the moderately sedimented seafloor with localized exposures of bedrock, likely consisting of variably serpentinized ultramafic rocks. Refer to Fig. 2a for image locations.
