Left is a picture of a black smoker taken on the Rainbow field during the MoMARDREAM-Naut cruise in 2007 by the Nautile camera. Right is the bathymetric map of the Rainbow hydrothermal field: modified after Charlou et al. . The map was established during the FLORES cruise, but the smokers were sampled again during the EXOMAR, MoMARDREAM-Naut and MOMAR08-Leg2 cruises. The box roughly marks the boundary of the active zone of the site, which can be described by 3 main active sub-areas: south-west (around A and B), central (Thermitière, dot) and north-east (around C). Sampling locations have been marked by crosses and have been referred in the text to A, B and C. The Twister® # that was used for extraction of the fluid sample stands next to each cross (to be related to Table 2).