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May 19th, 2003; Leg 6, Day #5

After two successful instrument recovery dives yesterday, we returned overnight to the submarine canyons on the eastern margin of Peninsula Concepcion. This morning we dove in 850 meters of water and explored a major bifurcation of the same canyon we visited on May 17th. This canyon is cut into the continental margin and is oriented approximately east-west.

Submarine canyons have the same general anatomy as rivers do on land and in some cases act as conduits for the movement of terrestrially derived material into the deep sea. At the bifurcation, the main, active channel turned to the southwest and a subsidiary channel went off towards the northwest. The floor of this subsidiary channel is at a higher elevation than the main channel axis, creating what would be called a hanging valley on land. The seafloor of the subsidiary channel comprised very loosely consolidated fine-grained sediments and a small chemosynthetic clam community was located near the deepest part of the channel. These features suggest that this channel is presently inactive. Because chemosynthetic clams have a life-span on the order of 10 to 30 years, it is reasonable to conclude that little sediment transport activity has occurred during this timeframe. In contrast, sediment push cores from the main channel contained coarser material, and some dead rhodoliths. Because rhodoliths are photosynthetic and live in shallow water, the presence of these dead rhodoliths at 850 meters water depth indicates that material is actively moving down the canyon from shallow water (10s of meters depth) into the deep sea. 

 

 

Alexandra Chee and Jorge Ledesma-Vasquez measuring and describing rock samples.

 

 

 

After every dive, the samples that we have collected are processed in the wet lab during the evening. Rock samples are cleaned, photographed, measured, and described. Sediment push cores are extruded and subsampled for pore water analysis and sediment chemistry. The vibracores are split, photographed, measured, and described. Biological specimens are cleaned, catalogued, and frozen. Today’s collection of photos illustrates some of the activities that occur in the lab. 

 

 

Dave Caress and Charlie Paull cutting the aluminum core tube of a vibracore using
an electric sheet-metal shear.

 

 

 

 

 

 

Charlie Paull and Gary Greene splitting a vibracore. After
the core tube has been cut with the shear, they insert thin, stainless steel sheets to cut the sediment into equal halves.

 

 

 

 

 

This is the result of splitting a vibracore.

 

 

 

Tonight we had a spectacular display of bioluminescence at the bow of the R/V Western Flyer. Dolphins like to swim in front of the two pontoons that form the submerged part of the ship’s hull (the Western Flyer is a twin-hulled, SWATH vessel). As the boat moves through the water, a small bow wake is generated, and this creates a hydrodynamic wave that the dolphins seem to enjoy riding. At night, bioluminescent streamlines outline the shape of the dolphins, and these persist as a trail of bioluminescence 10 or more feet behind the dolphins. Whenever the dolphins arched out of the water for a breath of air, each droplet of water that splashed onto to sea surface generated sparks of light. Occasional flying fish leapt out of the water, and, as they bounced across the water, they generated a bright flash of white light each time they hit the sea surface. After a few hours, the bottle-nose dolphins began to peel off one by one, and finally, this natural fireworks display was over for the night.  

Here is the explanation for Friday’s mystery photo. I took this frame grab as the ROV Tiburon was nearing the sea surface during a dive. The black line running vertically through the center of the photo is the clump weight cable that is used to orient and guide the ROV upward into the moon pool. During the final stages of recovery of the ROV, a hydraulically actuated clamp (black structure at the top of the photo) grabs the cable, and the vehicle slides up the wire to the sea surface. Without this guide wire, there is a greater risk that the ROV would miss the moon pool and smash upward into the hull. Having this guide wire becomes especially important during rough seas. 

And, for the fans of Pinkie, our gal has had a relaxing day on the Western Flyer—a little exercise and sunning herself on the lido deck. Tomorrow is the big day—the LAST dive of the Gulf of California Expedition. Will she take another ride on the Tiburon? Will she find Boss? Answers tomorrow. 

 

 

 

 

 

 

Bill Ussler, reporting

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