Thursday 23rd March 2017 : First exploration dive

On Thursday morning, wind has strengthened to 30-35 knots. Nautile deployment for the first exploration dive is risky but successful, thanks to the cold-blooded and experienced deck crew. Julien, Guillaume and Ewan dive to about 4,500 m depth in an area located 5 km west of Snake Pit hydrothermal site (23°N).

After 2 hours of mandatory tests for the first submersible dive, the Nautile start the seafloor exploration for about 3 hours. The seabed geology is made of pillow lavas and lava tubes, covered by a layer of soft pelagic sediments, sometimes very thick.

Numerous red shrimps, holoturians, an octopus, sponges fixed on lava block, and a wonderful cerianthus were observed during this first exploration dive.

Sampled basalt fragments are now into the geology team hands for description, cutting, grinding and analysis for chemical and mineralogical compositions.

Then, the fluid/plume team lowered a CTD/rosette above Snake Pit active site. Sensors are recording 0.1°C temperature anomalies; no doubts, we are in the plume! Vivien and Jean-Pierre trigger the 16 bottles one by one to sample sea water from the hydrothermal plume that rises about 300 m above the seafloor before spreading horizontally over tens of kilometers.