Easter Microplate Expedition
March 28, 2005 Day 17
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Alvin dive# 4093, 32°S
Greg and Jenny were the observers and Bruce was the pilot. We returned to the same area as yesterday's dive, with four mussel pot collections being the first goal. We immediately found the Saguaro Field of black smokers (see image on right). These edifices have developed flanges that precipitated from very hot, clear water that ponds underneath. The water then spills upward over the flanges like shimmering, upside-down waterfalls, which are visible to us because of the density difference with the surrounding seawater. The vents emanate from cracks in the sheet flows and broad, lobate pillows around the rim of two large, collapsed lava ponds. This stretch of the East Pacific Rise between the Easter and Juan Fernandez Microplates has the fastest spreading rate in the world, on the order of 15 cm/year. For about ten kilometers to the north and south of where we dove, the ridge axis is greatly inflated (a broad dome in profile) compared to nearby parts of the ridge, suggesting especially high magma supply right here. The lavas we observed were very fresh and glassy, and the sheet flows had the jumbled, "hackly" appearance of an effusive eruption of very fluid lava.
Greg and Jenny before and after the dive. Greg was a first-timer; Jenny's dive ten years ago entitled her to escape the icy shower.
"Changes in latitudes, changes in attitudes, nothing remains quite the same. With all of our running and all of our cunning, if we couldn't laugh we would all go insane!"–Buffett
Our recent latitudinal adjustment from the chilly 38° South to the more tropical 32° South definitely brought a change in attitude! Sweatshirts and jeans have been replaced with tank tops and shorts once again, even here in the air-conditioned lab. This girl is certainly happy! My favorite part of the day is watching the sub being recovered out on the fantail, where everybody takes a break and enjoys the sun (and the crew antics!) for a little while. I'm going to miss this!
Since I can't leave the mussel pots unloved in a log entry, I should mention that today's dive filled ALL FOUR of them very nicely! Bruce the pilot did a great job, without breaking anything or scraping off our William and Mary stickers! We processed animals until about 11pm, and now they're all set to provide us with lots of good data about mussel beds. The latest biological entertainment (especially when we're working late) has been the big red commensal scaleworms that live inside the mussel shells—almost always one worm per mussel. They are really disgusting. This where the END of the above song quote comes into play... we laugh a lot through the insanity of working out here. The fun never ends on Atlantis!
Left image: The tubeworm that got away. The giant plume of a Riftia tubeworm is sticking out horizontally from under a flange in a sulfide edifice (look below the red laser beam dot, above the black science equipment handle #9). It retracted the plume when it sensed us, and we couldn't reach in far enough to collect it. Right image: Sampling mussels and associated fauna with a mussel pot. The mussels are in patches where diffuse vent fluids emanate through the jumbled sheet flow.
Left: Nerida and Joe removing stalked barnacles from fishing float flotsam that was picked up today by the alert ship's crew. Right: Gooseneck barnacles attached to the fishing floats.
Sunset. Photo by Dan Layton-Matthews, University of Ottawa/Toronto.
All underwater photos were taken with the submersible Alvin, and are courtesy of Woods Hole Oceanographic Institution.