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May 16th, 2003; Leg 6, Day #2

We conducted four shallow dives in close proximity to the coastline near Isla Coronado. These dives continued our efforts to determine if rhodoliths are transported from the shallow waters where they live to greater depths. Today’s dive locations were selected because rhodoliths are abundant in the shallow water along this part of the coast. The first dive landed on a muddy seafloor at 894 meters. As we explored the seafloor in this area, we found some outcrops of hard slabs of rock and collected samples for later study and identification. After a few hours of exploration and the collection of sediment cores, ROV Tiburon was brought back on deck. Our subsequent dive sites were nearby, in 200, 120, and 165 meters water depth, respectively. During each of these dives, we maintained a constant depth while we explored the seafloor. We did not find any rhodoliths on the seafloor, nor in any of the sediment push cores or vibracores we collected today. Near the end of the last dive today, we encountered a large expanse of encrusting corals on a hard seafloor in 165 meters of water (see above). This seafloor is comprised of large, rounded pebbles and cobbles cemented by what looks like calcium

carbonate. This conglomerate pavement on the seafloor may have been a beach face at one time, and once this pavement subsided, the corals grew on the hard surface.  

During the past two evenings, we have processed the sediment cores in the wet lab. The push cores are extruded onto towels, cut longitudinally, and measured and described. The push cores are cleaned in water and placed back on the Tiburon for use the next day. Because the vibracore tubes are made of aluminum and typically contain up to one meter of sediment, we cut the cores longitudinally using an electric sheet-metal shear. Nearly all the cores comprised greenish to brown silts and clays, and some cores displayed a thinly laminated structure caused by alternation between the silty material and light-colored, calcareous sand of a biological origin. These layers of sandy biogenic material were derived from calcareous (calcium carbonate-bearing) organisms, such as rhodoliths and molluscs, and are indicative of high-energy storm events. 

Here is the answer to yesterday’s mystery photo. Doug Alexander, Darrel Palmer, and Paul Ban are deflating large air cushions that are hung between the R/V Western Flyer and the dock to protect the ship’s hull while it is in port. There isn’t much deck space on the Western Flyer, so these cushion are deflated and stowed after every departure. 



Another mystery photo has crossed my desk today—the answer will appear on Monday, May 19th. 



And, for the fans of Pinkie, Pinkie has returned to the Western Flyer! She appeared this morning in the wet lab, anxious to catch up on shipboard news and to have a look at a map of our dive areas (see left). Although she missed the fire and boat drill held a few days ago, she wasn’t able to slip by without some review of safety on the boat. Our staff photographer caught her reading the posting about how to use an immersion suit. “B-b-b-but…,” she asked. “Do you have my size?” 


Bill Ussler, reporting, with assistance from Jorge Ledesma-Vasquez.


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