March 7, 2003: Leg 2, Day #6

This was our last dive for Leg 2 of the Gulf of California Expedition. Today we needed to deploy all the instruments and then do the most critical operation of our entire experiment—collect one of the thermocouple arrays embedded in new fragile chimney growth. The vehicle problems and late hours of last night resulted in a mid-morning launch. We needed to have the ROV back on board by 9 p.m. to arrive in La Paz before dark on Saturday. The pressure of the time limit was with us the entire day. We hurried to Toadstool only to discover that the Homer did not respond, and it required extra survey time to find our study site. The osmosampler  and thermocouple array were efficiently placed into the prepared sites on the edge of the large carbonate mound structure (see above and left). Then we completed the sampling of the structure, including a small chimney that had grown back overnight. Next we headed north as quickly as possible to the thermocouple array on Busted Mushroom. We were shocked to see a new chimney almost 1 meter tall that had grown over the tops of the instruments in only 48 hours (see right). We used the scoop to try to get a sample from the top of the chimney, but it was too delicate. 

The moment of truth arrived. The crux of the experiment was to recover (in one piece) the sulfide structure grown around the thermocouple array (see deployment). We needed to compare the measured temperatures from the thermocouples with the minerals and microbes in the solid sulfides. Questions plagued us—will it work, or will the newly grown chimney fall to pieces en route to the white plastic biobox waiting in the drawer? Meg Tivey started to explain to Chief Pilot Buck Reynolds what needed to be done. Buck reminded her that we had been through this in multiple planning sessions. The only thing left to do was to make it work. 

Everyone in the control room went silent and held their breath in as the ROV manipulator gently tugged the thermocouple array from the chimney. Amazingly, a melon-sized piece of sulfide came with the thermocouple. We all cheered then fell silent as we watched the thermocouple and its cargo as they were slowly carried to the drawer and carefully placed into the biobox (see left). Once the package was safe, the real cheering began and as well as promises of free beers for all. We completed the remaining work in high spirits and headed for port. 

Once the ROV was on the ship, celebrating had to be put on hold again. The sulfide needed to be sampled for microbes immediately. The entire biobox (see below left) was carried into the lab and the array removed (see below right). The sulfide  was examined, mapped out, and then subsampled by Stakes, Tivey and Reysenbach. 

The cruise was a great success for all the scientists. Stakes, Tivey, and Reysenbach’s grad student, Page, look forward to collecting the final arrays in two months at the end of the GOC expedition.

 - Debra Stakes

From left: Wheat, Koski, Reysenbach, Page, Preston, and Osorio