Leg 3 (which was completed on 6 September) was a mix of highs and lows. We started with rough weather conditions that delayed our departure by a day and made our transit out to Axial Seamount… less than ideal (see student blogs for more details). Even once we were onsite, we were on weather hold for another 12 hours. When the weather cleared and just as it seemed like we were going to get into a rhythm, we ran into technical issues on our first dive. The Jason ROV and the instrument it was recovering were brought aboard safely, but fixing the tether (which allows the vehicle to be controlled from the ship) set us back another six hours – a remarkably quick turnaround for such a challenging repair. These setbacks on an already short leg with lots to do certainly adds stress to already challenging operations, but the team onboard rose to the occasion.
After the Jason team’s record-setting tether repair, the RCA team reprioritized the tasks for Leg 3 and prepared a number of instruments to be deployed in the shortened period of time remaining. All in all we managed five dives on Leg 3, deploying six pieces of equipment and instruments, collecting two Isobaric Gas Tight (IGT) hydrothermal fluid samples, and three Niskin samples for instrument verification and PI projects, as well as communicating with the three FETCH tripods – a task originally scheduled for Leg 4. While we have one CTD stand and some further samples to collect, we will be back at Axial Seamount on Leg 4 to complete those tasks.
Two of our Leg 3 dives took place at International District, surrounded by the beautiful hydrothermal vents and chemosynthetic animal communities. We deployed a RAS/PPS sampler which collects fluid and DNA samples from the vents, specifically a vent known as “Tiny Towers”. This same vent, and the cap that the RAS/PPS samples from, is observed year-round by a digital still camera. The third instrument deployed at International District (the Hydrothermal Vent Fluid Temperature and Resistivity sensor) samples the temperature and chemical properties of the hydrothermal vent fluid. Vent fluid is extremely acidic (low pH), and resistivity is an analogue for chlorinity, a way of measuring how salty the fluid is compared to background seawater. There is already one of these instruments, known as the TRHPH, deployed at the “Escargot” vent. Since that TRHPH is working well, we deployed a new TRHPH at the vent known as “Diva”.
Even though it seems like it would be simple to insert a probe into a vent, they are not always perfectly hollow, and the temperature disparity between the 300 ºC vent fluid and the 2 ºC deep-sea background water can destroy the sensitive probes, so they have to be inserted slowly and carefully. Because we can get real-time feedback via the seafloor electro-optical cable, we could monitor the temperature and insert the probe in a slow and safe manner, and we immediately knew that the probe was in 340 ºC water and still getting valid resistivity readings. These vents are spectacular structures which host fantastic animals, and it’s a joy every year for the students, researchers, and engineers to visit these sites and get a chance to marvel at this “other world” – definitely ending on a high note.