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April 26th, 2003; Leg 5, Day #6

0426w-funnel.jpg (52566 bytes)Peter Brewer danced a jig in the control room this morning after ROV Tiburon successfully found and collected gas from a hydrocarbon gas vent on the seafloor. His new instrument was positioned over the vent, the ice-like gas hydrate grew in the funnel, and the heated element inside melted the hydrate away to allow the gas to be suctioned into a special cylinder. Two different hydrocarbon gas vents were encountered during the dive as Tiburon explored along the ridge crest that we continue to study. Tiburon's camera recorded changes in terrain as it flew over rock outcrops and rubble alternating with areas of smooth sediment cover.

0426w-hydratepc.jpg (41289 bytes)After the dive, we found that one of the push core samples still had some pieces of ice-like gas hydrate entrained in the sediment. Once we had the sample in the laboratory, the gas hydrate dissolved rapidly and with great fizzing as it was exposed to ambient temperature and pressure. For sport, we lit the 

gases coming off the hydrate with a lighter to watch it burn and also to verify that the gases 0426w-fireice.jpg (31317 bytes)were methane and other hydrocarbons. It is rumored that one of our lead experts on gas hydrates can tell you how they taste!

The ship is transiting north tonight to a new location for tomorrow's dive. But we'll return to this Guaymas Basin ridge Monday morning--and hopefully to these gas vents--to deploy the laser Raman spectrometer (LRS) instrument. MBARI post-doc Sheri White has the following update on the LRS.

  Debbie Meyer


The laser Raman spectrometer (LRS) hasn't gone down on the ROV yet, but that doesn't mean we haven't been busy with it. The LRS illuminates a sample with green (532 nm) laser light and records the backscattered spectrum. While most of the light is reflected back at the same wavelength, a small amount (~1 out of every 100,000,000 photons) interacts with the molecules of the sample and is shifted in wavelength. The spectrum of the shifted backscattered light is like a finger print of the sample. The LRS can be used to study solids, liquids, and gases in situ. We are hoping to measure both natural gas venting from the seafloor and solid gas hydrates that form in the sediment.

We purchased our LRS from Kaiser Optical Systems and modified it for use in the deep ocean. Unfortunately, not all of its components are robust enough for work at sea. Unlike lab-based instruments, sea-going instruments are often subjected to shock and vibrations, and are dissembled and reassembled in pressure-tolerate housings on a regular basis. Modifications often need to be made at sea, where parts cannot be easily obtained.

0426w-sheribill2.jpg (59152 bytes)On arriving in La Paz a week ago, we unpacked our instrument and tested it. It seemed to have survived the transit well, so we assembled it into pressure housings to await its turn on the ROV. During the week, we had planned to calibrate the instrument, and perform a few experiments on deck in preparation for our dives. Unfortunately the shutter of the camera began misbehaving. Twice now, we have had to remove the spectrometer from the pressure housings and modify the shutter. Through the use of some wire used as a spacer, and a spring to help the failing motor open the shutter blades, we think we have fixed the problem. We are having a new shutter brought to La Paz so that we can replace it during our upcoming port stop. We just hope "Franken-shutter" can last until then.

  Sheri White

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