Hydrothermal activity in the Lau Basin: First results from the NAUTILAU Cruise

The Lau Basin, a back arc spreading center, is one of the most active hydrothermal areas in the ocean. A scientific team from France, Germany, and Tonga investigated the southern Lau Basin near Tonga in 1989 to study the processes of seafloor ore-mineral formation associated with hydrothermal circulation along the volcanic Valu Fa ridge (Ride de Valu Fa in Figure 1), which lies in back of the Tonga-Kermadec trench. Between April 17 and May 10 scientists on the R/V Nadir used the submersible Nautile to make 22 dives in the southern Lau Basin. The cruise was called NAUTILAU, for Nautile in Lau Basin. In addition to the standard equipment of the submersible (video and photo cameras, and temperature probe), a CTD (conductivity-temperature-depth) instrument was integrated with a “mini rosette” water sampling device used for the first time on the Nautile to obtain correlations between the geological observations and the physical and chemical anomalies measured in the seawater.