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May 8th, 2003; Leg 5, Day #18

Today’s dives were structured in the same way as yesterday’s: sediment coring and exploration around Pinkie’s Vent and laser Raman spectroscopy in the afternoon.  

Rendy Keaten started her day at 6:00 a.m. in the control room and saw more squid today during ROV Tiburon’s descent into the abyss. On our way down, we saw squid again at about 300 meters—this being the fourth day we’ve seen them at about this depth. The first day they just flashed by. The second day several followed us two or three hundred meters downward before they gave up, probably thankful Tiburon didn’t eat them. Yesterday three hung out in the lights for 50 meters or so, and the same occurred today. 

Steve Hallam, one of the microbiologists on board, has contributed the following narrative about today’s dives: 

Several types of bacterial mat were sampled in the vicinity of Pinkie’s Garden in an area dominated by rolling carbonate structures. In one patch, the mats were a rich white color with jelly-like consistency that was revealed when the push core touched their surface. In another area, the bacterial mats resembled Thioploca mats found in chemosynthetic clam communities in Monterey Canyon. These mat structures tended to be off-white in color in the center and were surrounded by nearly black sediments. In two instances, dense chemosynthetic communities consisting of crabs, clams, and lamellibrachian tubeworms were

observed intermingled with mat structures. Tubeworms appeared to be anchored to carbonates substrates beneath the topmost sediment layers. Juvenile tubeworms and clams were also observed in the mix. Unfortunately, attempts to collect sediments containing juvenile fauna were unsuccessful. However, several adult tubeworms and clams were collected, in addition to numerous sulfide-rich push cores. Once the Tiburon was back on deck, the most active cores were processed first in the squeezer lab to preserve their chemical identity. Two cores showed signs of active bubbling and a strong odor of hydrogen sulfide. Microbiological examination of these cores back at MBARI promises to be very interesting. Pinkie’s Garden should prove to be a veritable oasis on both the macro and microbiological scales. Tomorrow we’ll search for new vent sites to sample and characterize. 

The Tiburon was back on board by noon today to off-load the sediment cores and to reinstall the laser Raman probe, in preparation for the afternoon dive. Rendy Keaten has this to say about what happens to the cores once they go into the wet lab:  

When we started processing cores in the lab at noon today, we had eight cores for pore water chemistry, eight cores for micropaleontology, and eight more companion cores just in case one of the primary cores wasn’t in good shape. After three days of sediment core processing we have it down to a dance—with Charlie Paull being the choreographer. First we select the squeezer bodies. Typically, we use three small ones for the first three 2-centimeter depth intervals and three or four large ones for the 4-centimeter intervals, which we take deeper in the core. Lynne Christianson holds a squeezer body while Charlie fills them. Lynne places a dental dam on top of the squeeze body, and places it in the squeezer rack. Patrick and I attach syringes to the bottom of the squeezer body to collect the pore waters that flow out of the sediment when gas pressure is applied. When the syringes are full, we take them off for analysis by Bill in the chemistry van located on the back deck. Then we scrape out the cake of mud left in the squeezer, subsample it for DNA and percent carbonate analyses, then wash, dry, and reassemble the squeezer body for the next core. Today we had some lively music and good stories to help the afternoon along. 

Jill Pasteris, who is collaborating with us on the laser Raman project, has contributed these impressions for today’s update: 

Today was our third afternoon to carry out Raman spectroscopic analyses on the sea floor. One of many strange things about scientists is that, as soon as they get a procedure so well worked out that it becomes routine, they change it! So, after two days of work on the sea floor using our large Raman probe head and two special sampling funnels, we completely changed the probe head for today’s dive. Instead, we used our insertion probe, which has to be placed directly into the water or gas that is being analyzed. The whole assembly, with its long thin probe projecting into a small cube-shaped collection box, could barely fit into the special drawer in the bottom of the ROV. The ROV’s pilot skillfully used the robotic arm to lift the assembly and hold it over one of the vents in Pinkie’s Garden. This action allowed the gas that rose up to collect in the bottomless box. (Picture a metal anteater hovering over an anthill, but with bubbles pouring out instead of ants.) Our goal was to take Raman spectra of all the chemical components in the gas, which we immediately could tell was composed mostly of methane (so-called “natural gas”). Even as we watched the gas-collection box, white, fluffy, methane clathrate hydrate (an ice-like material that captures methane molecules within it) formed on its clear window. The probe head projected the green laser beam into the center in the box, where the gas was. When we take Raman spectra of samples, all the lights on the ROV are turned off. During the analysis, we therefore were treated to the image of what looked like a green-glowing gas lantern covered with frost. 

We decided to take advantage of the fact that we could make Raman analyses all the way back up to the surface as the ROV returned to the ship. So, the pilot carefully placed the whole Raman assembly, with the box still filled with gas and frosted with hydrate, back into the drawer of the ROV. As we rose up toward the surface, still making our analyses, the Raman peak for the methane gas slowly changed its position because the gas was decompressing (getting less dense). The analysis also showed when the methane clathrate hydrate melted and released its methane into the big bubble of gas that already was trapped in the box. As the ROV reached the surface and the last gas analysis was taken, the Raman team happily called it a day. 

It’s another late night for me, pulling together the daily update, after a full day in the lab. Much of what occupies my time shipboard is the chemical analysis of the pore water that the coring crew extracts from the sediment cores using the squeezers. This evening’s guest contributors, Steve Hallam, Rendy Keaten, and Jill Pasteris made my task much easier.   

Bill Ussler, reporting

 

 

With the assistance of Steve Hallam (left) and Lynne Christianson (right), Charlie Paull is sectioning a sediment push core in the wet lab. Steve is collecting a small dollop of sediment for microbiological analysis. Note the stylish colors of lab gloves.

 

 

 

The Tiburon is ready for launch through the moonpool doors. The laser Raman spectrometer is mounted vertically above the trapezoidal pyramid on the front porch of the Tiburon.

 

 

 

 

 

After a long dive day, Jill Pasteris, Sheri White, and Lynne Christianson enjoy a light moment on the lido deck of the R/V Western Flyer.

 

 

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