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April 14th, 2003; Leg 4, Day #11

Today's update is provided by Jean Marcus, from the University of Victoria.

Area of Study: 21º N, East Pacific Rise 

Site: Hanging Gardens 

Our day got off to a bit of a slow start. Our usual 6:30 a.m. launch was delayed as the ROV Tiburon’s robotic arm was misbehaving. The ROV had to come back on deck for some last-minute repairs, but the ROV pilots fixed it quickly, and we were back in the water by 9 a.m. It is no small task to keep such a complex and sophisticated piece of machinery operating smoothly! Even with daily maintenance, trouble-shooting is a major part of successfully operating a deep-sea submersible.

Apr14_golfball_sponge.jpg (82343 bytes)Our destination today was Hanging Gardens, a small vent field about 1.5 kilometers south of Clam Acres (our dive site yesterday). When we reached the seafloor, we spent a few hours trying to locate the site—when you’re >2 kilometers under water, there are no

signposts to point you in the right direction! There are, however, telltale signs that you’re getting near: typical deep-sea species such as sponges and surpulid worms tend to increase in density near vent sites to take advantage of the localized productivity. During our search, we stumbled across a beautiful “golf-ball” sponge (Chondrocladia sp.) perched on the edge of a wall. To me, this animal looks like something right out of the 1970s! The biology of this particular species is unknown, but it may be a carnivorous sponge that feeds on living prey like other species of the Cladorhizidae. After admiring the sponge for several minutes, our search for Hanging Gardens continued… 

Apr14_clam_shells.jpg (81529 bytes)When our chief scientist Bob Vrijenhoek last visited Hanging Gardens thirteen years ago, it was a lush field of thriving tubeworms and clams. We were therefore surprised when we starting seeing patches and patches of dead, empty clamshells scattered throughout the lava crevices (see left). Apr14_crabs.jpg (76307 bytes)A few small clumps of tubeworms also appeared as we entered the field, but they too looked unhealthy. The only live critters of any notable size seemed to be the hundreds of crabs crawling all over the basalt, presumably feeding on the dead and dying clams and tubeworms (see right). If this site was Hanging Gardens, it had dramatically changed since Bob was last here! 

Apr14_black_smoker.jpg (55536 bytes)When we saw a few markers left behind by other scientists and a huge black smoker chimney in the distance (see left), we knew we were at the right site. Although most of the diffuse vents in the field had shut down, fluid was still vigorously pumping out of the chimney at temperatures >300º C. Apart from a clump of Alvinella pompejana (“Pompeii worm,” a polychaete species famoApr14_alvinella.jpg (86693 bytes)us for living in the hottest microhabitat at vents clustered around the chimney orifice, see right), the chimney was oddly devoid of animals. It was interesting to see, first hand, evidence of the ephemeral nature of hydrothermal vent habitats.

 

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