Easter Microplate Expedition
March 23, 2005 Day 12
Please visit the ChEss website for additional information and translations in Español, Português, and Français.
Alvin dive# 4089, 38°S:
Joe and Dan were the observers - both first-timers - and Bruce was the pilot. By sheer coincidence, it's also Dan's birthday!
The dive started at "Pâle Etoile", but no additional mussel beds were seen; there were some shells of dead clams, but no live clams. So they motored to "Sebastian's Steamer", where they recovered the two crab traps deployed yesterday. The beef appeared to have been more attractive than the fish as bait. They collected some sulfide from the main vent, and watched as it vigorously vented black, mineral-rich "smoke" from the base, near where the science basket was parked. The quivers for the wax-corers fastened to the front of the basket became singed from the hot water, which was measured to be 326°C.
Quivers on the Alvin's science basket scorched by the 326oC water coming out of "Sebastian's Steamer".
The current was very strong, running south to north this time. The water was turbid, as if there was hydrothermal activity up-current somewhere. So they drove south, following the floc and using sightings of vent crabs as a bread-crumb trail. They zig-zagged along a series of tectonic fractures on the axis that were as much as 30m deep, and collected a glassy basalt pillow-bud along the way. They covered as much ground as they could, and ended the dive at a large collapse pit nearly two kilometers from their starting location. They found only diffuse venting and no more mussel beds or hydrothermal chimneys.
Left image: Fresh lava flow with abundant glassy pillow-buds. Right image: Tectonic fracture that broke large lava pillows, with a younger lava flow inside.
Both Joe and Dan had never dived in the Alvin before, so as they descended from the submersible they were treated to buckets of ice water thrown at them by those of us who had dived before.
Left image: The clear skies and light winds are deceptive: the long-period rollers are on the order of 13-14 feet, and today's recovery was a little wild. Right image: Joe's still grinning after the soaking! Maybe it was the four Snickers bars he confessed to eating for lunch.
Last night we made two dredges: on an eastward transect to the top of the small lava dome in the caldera of Foundation Seamount, then up the wall of the caldera. Both dredge hauls were full of large pillow lava wedges with glassy rinds. No signs of hydrothermal rocks or biology were present, so we have decided not to dive there.
Crabs, crabs, crabs!! That was the theme tonight! Yesterday Alvin put down two crab traps near Sebastian's Steamer. Today's
Alvin divers Bruce, Joe and Dan, retrieved the now swarming traps this afternoon. In the lab, we helped Michel sorted the crabs by sex and searched for eggs. Large mussel beds have yet to be found at 38°
south, but I have not given up hope the mussel pots we built will find a time to shine. Tomorrow Jessica is scheduled to dive, so I'm counting on her to bring back some mussels!
Shana, Ana, and Caren picking alvinellid worms from a sample. Right image:The head (4mm) of a hesionid worm. Photo by Greg Rouse, South Australian Museum.
All underwater photos were taken with the submersible Alvin, and are courtesy of Woods Hole Oceanographic Institution.