Easter Microplate Expedition
March 31, 2005 Day 20
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Alvin dive# 4095, 23.5°S
Bob and Nerida were the observers and Gavin was the pilot. This site was the strangest place Bob has ever seen: a series of narrow ridges separated by deep 30-50m deep crevasses with hydrothermal chimneys down inside.
The sub would follow a ridge until it pinched out to a point, then hop over to the next, which eventually pinched out also. The sulfide chimneys were immense, but did not stick up above the walls of the crevasses. Many of the tops were no longer venting, but the bases sometimes were. It was hard to maneuver
down inside the crevasses, like being in a tight parking lot, Bob said. Some chimneys were stone dead, while nearby ones vented vigorously. They found lots of bacterial mats and shimmering water, with temperatures to
296.6°C, but none of the usual vent fauna: no clams, tubeworms or mussels, and very few crabs. There used to be tubeworms here: some smokers had fossilized
Riftia and Alvinella tubes encrusted with sulfide tufts, with some of the fossil tubes now acting as conduits for venting hot water. There weren't the usual critters whose increasing densities help lead you to the vents (the brachyuran crabs and serpulid worms), but serpulids were found on some of the dead chimneys. The anemones were larger than
Alvin's science basket, and there were many octopus, snails, large starfish, and amazing sponges.
Just as the sub reached the surface after the dive, the skies opened and it poured. Rather than flood the inside of the sphere, they trundled the sub back into its hanger before they popped the hatch for the divers to disembark. Nerida received her
first-timer's water treatment out in the rain.
Nicole and Jenny placing a lava pillar into a pair of milk crates fastened end-to-end, kindly provided by the
Alvin pilots. The pillar is fractured and extremely fragile. We need to immobilize and protect it further before we disembark next week. It was collected from the floor of a drained lava lake on the ridge axis near Nolan's Nook. It was standing vertically and has glass "bathtub ring" marks on the outside that were left when the lake level dropped, and it is hollow inside. Its formation is under debate, which we hope geochemical analyses of the lava will resolve.
Tubes of Oasisia and Tevnia catalogued in the lab.
All underwater photos were taken with the submersible Alvin, and are courtesy of Woods Hole Oceanographic Institution.