April 16th, 2003; Leg 4, Day #13

Today was the last dive of leg 4. We targeted a site at the northernmost end of the East Pacific Rise, where the spreading center gives way to the Tamayo Fracture Zone. Again we had a dual purpose in this dive—to explore the geology of the spreading center and to search for new hydrothermal vents. We found no vents, but surely did not come away empty-handed. Dave Clague had a wonderful day looking at pillow basalts in a very unusual topographic setting. We climbed up two small seamounts on the axis of the Rise that were massive piles of pillow basalts. Dave collected some elegant glassy pillow buds that extended like stalactites from the large pillow basalts (see above). 

It's been a very profitable cruise. The weather cooperated, and we did not loose a single dive due to unsolvable equipment problems. The ROV Tiburon pilots and Western Flyer crew are remarkable. With the equivalent of bubblegum and bailing wire, and considerable ingenuity, they have you up and diving again in the morning. I have also been impressed with Tiburon. The ROV has performed admirably. It is very dexterous and capable of working in some tight situations. The dive at Hanging Gardens at 21˚ N on the East Pacific Rise is a good example. The terrain was very rough with collapsed lava pits, lava pillars, and sheer walls lining the walls of the axial caldera. The pilots had to negotiate their way through this dark maze and simultaneously manage the cable so that it would not be entangled or mangled by the sharp lavas or tall, hot hydrothermal chimneys. 

The biological observations made on this cruise were equally remarkable. I have visited the Guaymas Basin hydrothermal vents in the Gulf of California and 21˚ North on the East Pacific Rise before with the manned submersible Alvin. The Guaymas sites have changed very little since I visited them in 1990 and 1994. Robust hydrothermal chimneys still had luxurious colonies of the giant tubeworm Riftia pachyptila, and we saw large white vesicomyid clams in the vicinity of the vents. In contrast, the 21˚ North site has changed remarkably since I last saw it in 1990. The once luxurious vent communities at Clam Acres and nearby Hanging Gardens have almost died. Hanging Gardens had a few colonies of Riftia left at the base of a central smoker that was about 20 meters high. We found few living clams, Calyptogena magnifica, and large heaps of broken shells from dead clams. Clam Acres had also changed. Again, we found heaps of broken clamshells and few living individuals. Instead we saw many dispersed clumps of tubeworms that looked reasonably healthy. We also found some new little smokers that appeared to be growing on top of some sulfide mounds that were the remnants of earlier smokers that had crumbled (see Kaylynn's Korner on April 15). 

We have spent many long nights after Tiburon was recovered, sorting and dissecting specimens. We have a freezer full of tissue samples for our DNA studies, and boxes full of vials and bottles with preserved specimens. The science crew is cleaning the lab as we steam back to La Paz. This has been a very successful expedition. Having MBARI geologist Dave Clague along provided a novel perspective for the rest of us biologists. He was excited by the rocks and was very generous in explaining to us the stories they told. Shana Goffredi and Peter Girguis offered many insights regarding the physiology of vent animals and their associated microbes. Joe Jones and Josh Plant put in many long hours logging data, taking inventory, and performing chemical measurements. Mike Henry (from the Childress lab in Santa Barbara) was on constant crab patrol. His crab traps were very successful. Jean Marcus and Amanda Bates (from the Tunnicliffe lab in Victoria, BC) provided endless expertise in identifying the polychaete worms and gastropod mollusks. They also conducted some very fine-detailed video documentation of the animal communities living in the tubeworm clumps. It will take many months after we return to work up the data. I am indebted to all these individuals for the hard work and time they have devoted to this cruise. Thanks to all. 

Bob Vrijenhoek, Chief Scientist