A new deep-sea probe for in situ pH measurement in the environment of hydrothermal vent biological communities

In situ measurements have been shown to be the most relevant means to characterise the chemical properties of the highly dynamic medium surrounding hydrothermal vent organisms. However, few instrumental devices can perform such measurements at great depth, and there is great need to extend the range of chemical parameters that can be determined in situ. To investigate the spatial and temporal variations of pH within the habitats of vent organisms, a deep-sea probe was developed and successfully tested during the HOPE’99 diving cruise (13°N, East Pacific Rise). In situ measurements allowed us to quantify the pH range over different biological communities, highlighting differences between the habitats, as well as micro-scale variations. As pH is expected to play a significant role in major biogeochemical processes occurring in the seawater/fluid-mixing zone, this probe should be of great utility for the study of interactions between vent communities and their environment.