Today we plan to recover all the equipment
that was left during Leg 2 as part of the Guaymas Instrumented Vent
Experiment (GIVE). Today our thoughts are more like, “GIVE ME BACK MY
INSTRUMENTS!” There are nine different instrument packages distributed
at four vent sites. These packages include three thermocouple
arrays, hopefully with some quantity of attached sulfide. Each thermocouple
array has its own datalogger with a detachable ICL
that connects it to the array. There are also three OsmoSamplers with an
attached HOBO temperature recorder and long inlet snorkel. Each of the
four vent sites is marked with an acoustic beacon that must also be
recovered. The four sites are separated by less than 700 meters of mud,
vents, and animal communities. The acoustic beacons will guide us to the
general area, but we will need to review the framegrabs from last March to
remind ourselves of the landmarks. The most-northern site is a new,
hydrocarbon-rich, low-temperature site found and named by us because it
looked like a hydrothermal “Theme Park.”
The most-southern site, Toadstool, is similarly venting clear, diffusive
fluid. However, the two sites in the middle, Rebecca’s
Roost and Busted Mushroom, are large, high-temperature structures.
The big unknown, of course, is how much the chimneys at Rebecca’s Roost and Busted Mushroom have over-grown the instruments. The other two sites, Toadstool and Theme Park, were less active, and we only expect small chimneys (if any at all) from those two locations. When we left the array at
Theme Park, there was only a stream of
diffusive flow through the frame (see above). At Toadstool, a small
chimney re-grew overnight at the array site and had to be removed before
deploying the array (see 3/7 image).
The OsmoSampler was placed nearby (see
3/7 image). At Rebecca’s Roost, the OsmoSampler was left with the
inlet hanging precariously from a rapidly growing chimney (see
3/6 image). We may have to be clever to pull it loose. The Busted
Mushroom site may prove to be the most challenging, however, since we saw
the chimney re-grow by over a meter during a few days (see 3/3,
3/4, and 3/7
updates). When the site was
visited a week later, the change was amazing.
Over the past month, Meg Tivey and I have discussed many different possible recovery strategies. We have worked out a plan to accumulate the items and fill the ROV drawer and front porch twice, on two separate short dives during our one dive day. On the first dive, T590, we visited Toadstool and then Theme Park. Toadstool surprised us with a thermocouple array completely cemented into place by a carbonate pavement. Only with great effort did the Schilling manipulator finally break free—a very important sample (see right). By the time we had recovered the empty array at Theme Park and the two acoustic beacons, we had the drawer and the front porch full of gear (see left). Rebecca’s Roost proved to be the big heart breaker. The chimney had grown over a meter and a half taller and had gotten wider, too. The HOBO temperature recorder that we had left draped down the side was now embedded into the wall of the chimney (below left)! The recorder broke into pieces when we tried to grab it and the OsmoSampler hose inlet was completely melted (below right).
Busted Mushroom was the last site that we visited. We saved it for last because we were fearful of needing hours to break apart some massive structure to extricate our instruments. What a surprise awaited us. The mushroom family had indeed grown taller and wider, but our instruments were safely beneath most of the growth. In fact, the narrow trunk made it easy to knock over the entire structure, so all we needed to do was pick up everything and go home. The sample from Busted Mushroom provided us with a complete transect of the chimney wall and had beautiful crystals encrusting the frame.
Data from the Busted Mushroom site is