Fig. 1: Bathymetric map of the Lucky Strike hydrothermal field and images of the sampled iron-rich microbial mats, modified from Chavagnac et al.60 and Astorch-Cardona et al.29.

The studied mats and their associated active hydrothermal vents are shown. No hydrothermal vent was detected at LL site. Chlorinity increases from CAP to LL sites. Scale bars: 5 cm. [Capelinhos (CAP); North Tour Eiffel (NTE); South Isabel (SI); West Sintra (WS); Lava Lake (LL)].