Monday 25th February
By 0115h we had completed our final dive task at the Beebe Vent Field: collecting Valerie and Alain's high-temperature loggers that placed on vent chimneys during an earlier dive. The loggers have been recording the temperature of the fluids jetting from the vents every minute for the past few days, and their records should reveal how that flow varies.
We expect the flow to vary with tides, even 5 km deep on the ocean. There are tides in the very gentle bottom currents across the vents, and also "Earth tides": the dilation and contraction of the rock matrix of the vents themselves. So it is good to have all the loggers back, even though collecting one that slipped down between two vent spires was a challenge for the skills of the ROV pilots.
At 0421h the ROV was secured on deck, and at the ship began to glide over the moon-brushed sea towards the island of Monserrat. That moment marked the official end of Voyage 82 of the RRS James Cook. The ship and ROV will now carry out an investigation of sediments around Monserrat, which should reveal the history of the currently active volcano on the island. That project is led by Peter Talling of the National Oceanography Centre in Southampton, to whom I have now handed over as Principal Scientist aboard ship.
This will therefore be my final entry for this voyage; I have swapped the Principal Scientist's quarters for a very comfortable cabin on Boat Deck, but in doing so I no longer have direct internet access. Our task now, during the four days that it will take to reach Monserrat, is to compile our expedition report, which summarises all our activities with the ship, and details of all the samples and data that we collected.
We spent a total of 17.9 days working in the Cayman Trough. During that period, we had equipment deployed from the ship 76 percent of the time (e.g. the CTD probe and the Isis ROV). We spent 13 percent of our time undertaking "deck work" (e.g. preparing equipment for deployment). The ship spent 11 percent of the time in transit between our different study locations. I am pleased to report that there was only 0.4 percent of time logged as "idle".
But perhaps the figure of which I am most proud is the amount of "bottom time" achieved by the Isis ROV: more than 196 hours. To put that another way, Isis was at work on the ocean floor for more than 45 percent of our time out here. We made 11 dives in total, and our averge bottom time per dive was 17 hours; maximum was 35 hours and minimum was 10 hours. We also took the ROV on some of the deepest dives in its career so far.
Given that our science plan included some activities other than ROV dives, and that the ROV has to return at least occasionlly to deliver samples, receive routine maintenance, and be reconfigured for different tasks, I am very pleased by that amount of time on the ocean floor. Those figures reinforce my view of ROVs as highly efficient tools for deep-sea science - and the Isis ROV in particular, with its 24h operations and support for long dive times with minimal turnaround between.
Achieving the objectives for this expedition has been the result of a superb team effort; there are perhaps few areas of science that depend so much on the concerted activity of a diverse group of people. We could not do our science at sea without the hard work of the ship's officers, engineers, deck crew, domestic team, and expedition technicians. It has been a pleasure, yet again, to work with the world-class facility of the RRS James Cook and Isis ROV - and yet again, I am struck by how the excellence of this facility comes from its people.
I am also grateful to all the science team aboard for their support and patience during my first major stint in the "big chair" as Principal Scientist. We have collected the samples and data to address our key questions, about the geological processes that form and drive the vents here, the reactions of vent fluids with the wider ocean, and how species disperse and evolve in the ocean depths.
The deep ocean remains a vast open frontier for science, but the research papers that we will produce from this expedition should advance our understanding of it here. We have also collected samples and data for the research projects of the PhD students and early career researchers aboard, who will in time lead the further exploration and investigation of the ocean depths in new areas.
There is still plenty out there for us to explore and investigate, and I hope plenty more voyages to come. During this expedition, we have been able to share what we are doing more widely than before, via several blogs, social media, live video links to schools, and live coverage by traditional media. I hope that we can do even more in future to involve all those who are interested in exploring the hidden face of our world, and the challenges and opportunities that it has to offer.