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April 28th, 2003; Leg 5, Day #8

Success! The Raman project made an important transition today toward evolving the laser Raman spectrometer (LRS) into an expeditionary tool when it completed the first in situ measurements of a natural sample on the seafloor. MBARI’s LRS made its debut last year as the first-ever deep-sea system, and those experiments analyzed known lab samples to verify system function. Today the LRS successfully measured spectra of hydrocarbon gas venting from the seafloor at a site 1580 meters deep in the Guaymas Basin. The research team of Peter Brewer, Sheri White, Bill Kirkwood, and Ed Peltzer are very excited by the results. They learned what manipulations were required to conduct the experiment and what sensitivities to expect in the measurements. The ROV Tiburon system delivered the data flawlessly, and the pilots displayed their skill in performing the unusual handling protocols required. The dominant spectral peaks in the data correspond to a methane signature, the main constituent of the vent gas. 

0428_01_56_19_16.jpg (104210 bytes)Tiburon was launched into the water early this morning after the LRS and heated funnel instrument were placed into its benthic drawer. The ROV descended to a gas vent site that we have been studying, now dubbed “Pinky’s Gas Vent” for the plastic flamingo lawn ornament that adorns the site (see right). Sheri and Bill

monitored the LRS software system in the dry lab. Peter and Ed were in the control room noting the ROV data, videotapes, and coordinating the ROV movements. All communicated across the ship’s phone system, with bantering back and forth between the two areas throughout the day. There was a moment of suspense when Tiburon unexpectedly reset its control system. All functions turned off and the cameras went black. The pilots quickly responded to the situation and soon had everything under control. The LRS was powered on again with no ill effect. 


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Pinky's gas vent site. ROV Tiburon's manipulator arm is ready to grasp the heated gas funnel instrument to begin collecting gas from the vent. The laser light glows green in the sample box. The skin of methane hydrate within the box did not contaminate the sample as no water signatures were seen in the spectra.

 

 

The experiment involved a series of painstaking steps that each required waiting time. The overall procedure included making background measurements with the LRS, using the heated funnel to collect a gas sample from the vent, maneuvering the funnel to a sample box at the end of the LRS, tipping it delicately to transfer the gas into the box, and acquiring data about the sample from the LRS. The added step of emptying the gas funnel sample into the LRS box was a difficult maneuver. On only the second try, ROV pilot Buzz Scott successfully transferred the sample to the box. Sheri called “We've got some gas!” from the lab as the LRS data showed a methane peak. Each measurement step took several minutes during the data acquisition, with the final phase lasting nearly 2.5 hours. The glowing green laser light of the LRS system was all that could be seen for those long stretches as the vehicle's lights had to be turned off for the experiment. 

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Sheri White studies the spectral peaks as the LRS system acquires data. Bill Kirkwood looks on.

 

 

Tiburon was recovered in mid-afternoon, and the ship moved to a new location. The purpose of this dive was to search for another gas vent. Charlie Paull studied the muddy and nearly featureless seafloor as Tiburon flew over it. He found no evidence of vent activity on the seafloor or on the scanning sonar. There was much discussion in the control room after the dive about where to look next. 

0428-sunset.jpg (33265 bytes)The day ended with a beautiful sunset that we watched from the ship's bow. Sheri and Bill are busy preparing the LRS for deployment tomorrow, and the others continue to work on lab samples and data.

  Debbie Meyer 

 

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