 Leg 1 Logbook - Laser Raman Spectroscopy
Day 9 – Here a mound, there a mound, everywhere a mound, mound…
July 15, 2009 0900 hours – On-station at Barkley Canyon, west of Vancouver Island, Canada. Before the cruise, we asked Dave Caress to take a look at the high resolution topographic data he generated from the Mapping AUV survey during the 2006 Barkley Canyon Expedition to see if there were any more mounds besides the ones we had already located. At the time, we thought he might come up with maybe 6 or 8 new targets. Much to our surprise, Dave identified 40 suspected hydrate mounds from the topographic data. This is probably not an unreasonable number of targets for a geologist conducting a flyby survey; however, for ocean chemists who cannot resist stopping and poking a sensor into each and every mound we see, we knew that this was way more targets than we could possibly visit in a single dive day. So, before the dive we selected a subset of the targets and made a plan for visiting them in sequence. In order to help with our navigation locating the mound sites, we took down a homer beacon that we could place in the area and use as a guidepost. Once on the sea-floor, we quickly recognized a few landmarks that allowed us to transit to the Hyberg mound (where Pinkie is located) and placed our beacon on top of the mound. Using this beacon as a guidepost, we then navigated by dead reckoning to the various target mounds. Unlike the day before when we wandered aimlessly for the first hour or so, today we drove straight to our first target. And much to our delight, we found a small hydrate mound there. As it turned out, Dave Caress was quite good at looking at the topographic data and spotting hydrate mounds. Of the 16 sites we visited today, 15 were indeed hydrate mounds. Nice job, Dave! 
Homer beacon used for finding the range from and navigating back to a fixed point. 
One of the many hydrate mounds found by navigating to small topographic highs on a map prepared by Dave Caress from the mapping AUV data collected in 2006. Upon reaching our survey mound targets, the first thing we did was use our new “dip stick” probing tool. Before inserting the very valuable and very delicate laser Raman spectrometer pore-water probe, we wanted to “test” the site with an inexpensive probe or stick. Once again Peter Walz came to our rescue with a “dip stick” made from a piece of threaded rod (marked-off in 10 cm increments) and a rubber gripper handle. This way we could probe each mound to see if the sediment was soft enough to insert the pore-water probe, and upon withdrawing see if any oil, gas or hydrate leaked from the hole. We called this procedure “poke and hope”. In most cases, our hopes were rewarded as droplets of oil and gas bubbles leaked out of the hole when the dip stick was retracted. At one mound, the dip stick could hardly penetrate the sediment at all hitting a solid surface only 5-10 cm down. In this case, we reached into our box of tools on the ROV tool-sled tray and pulled out our benthic hoe. It took only a few shallow scrapes before the ROV pilot was releasing small chunks of oil saturated hydrate from the sea-floor. 
“Dip stick” used to poke into the new hydrate mounds to determine how deep we can insert the pore-water probe and to see if they contain gas or oil.
Using the benthic hoe to scrape off the sediment over-burden and expose gas hydrate at one of the hydrate mounds. We spent the day ranging northeast and south of the known hydrate field finding over a dozen new hydrate mounds. All on-board were impressed with the size of the field and the consistency of the finds in terms of mound size and the presence of oil and gas in every one but one of the targets. And when the sediment cover was thick enough, and no oil seemed to be present, then we inserted the LRS pore-water sampler in order to measure the gradient of methane in the sediment pore-water under in situ conditions and with minimal sediment disturbance. —Ed Peltzer 
Pore water probe inserted 24 cm into the sediment on top of a hydrate mound.
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Equipment
 R/V Western FlyerThe R/V Western Flyer is a small water-plane area twin hull (SWATH) oceanographic research vessel measuring 35.6 meters long and 16.2 meters wide. It was designed and constructed for MBARI to serve as the support vessel for ROV operations. Her missions include the Monterey Bay as well as extended cruises to Hawaii, Gulf of California and the Pacific Northwest.
ROV Doc Ricketts is MBARI's next generation ROV. The system breaks new ground in providing an integrated unmanned submersible research platform, with many powerful features providing efficient, reliable and precise sampling and data collection in a wide range of missions.
By bouncing a specially tuned laser beam off of almost any object or substance—solid, liquid, or gas—a laser Raman spectrometer can provide information about that object's chemical composition and molecular structure.
A push-core looks like a clear plastic tube with a rubber handle on one end. Just as its name implies, the push core is pushed down into loose sediment using ROV Tiburon's manipulator arm. As the sediment fills up the core, water exits out the top through one-way valves. When the core is pulled up again, these valves close, which (most of the time) keeps the sediment from sliding out of the core tube. When we bring these cores back to the surface, we typically look for living animals and organic material in the sediments.
Vibracoring is a common technique used to obtain samples from water-saturated sediment. These corers work by attaching a motor that induces high frequency vibrations in the core liner that in turn liquefies the sediment directly around the core cutter, enabling it to pass through the sediment with little resistance.
Carbon dioxide is a liquid at the temperatures and pressures on the seafloor where hydrates are known to occur. Because of this, one cannot simply take down a tank of gas and expect to be able to release it at depth. Instead, the CO2 piston accumulator is used to deliver precise volumes of liquid CO,2 to experiments on the seafloor. The valves are operated hydraulically by remote control and hydraulic pressure is used to expel the liquid CO2 and deliver it to the experiments.
MBARI's heat-flow probe is mounted on the side of the ROV Doc Ricketts inside the vertical stainless steel box. This both protects the delicate probe and provide the track so that the probe can be inserted into the sediment along a totally straight path. The probe contains five high precision platinum sensors which are used to measure the vertical temperature gradient in the sediments. This gradient along with some knowledge of the heat capacity of the sediment allows scientists to calculate the rate of heat loss from the sediments into the ocean. Research Team
Peter has taken part in more than 30 deep-sea cruises, and has served as chief scientist on major expeditions and on more than 90 ROV dives with MBARI ships and vehicles. His research interests include the ocean geochemistry of the greenhouse gases. He has devised novel techniques both for measurement and for extracting the oceanic signatures of global change. At MBARI his current interests include the geochemistry of gas hydrates, and the evolution of the oceanic fossil fuel CO2 signal. He has developed novel techniques for deep ocean laser Raman spectroscopy, and for testing the principles and impacts of deep ocean CO2 injection.
Ed is an ocean chemist who has been with MBARI since 1997. He has been involved in developing instrumentation and analytical techniques to study the composition of gases in gas hydrates and deep-sea vents. He has also collaborated on the development of new instrumentation for the measurement of temperature and pH from an ROV. As the group's project manager, Ed is also responsible for expedition planning and logistics.
Peter has worked as a research technician for a variety of scientists at MBARI. Most recently he has supported the research efforts of Dr. Peter Brewer and his interests in the ocean chemistry of greenhouse gases such as methane and carbon dioxide. Peter assists with the design, testing and deployment of the ocean going science hardware and works closely with the marine operations group to integrate new equipment to work with MBARI's ROV's.
Xin Zhang is a Ph.D. student from the Ocean University of China and is now studying at MBARI with Peter Brewer and Bill Kirkwood. He has been involved in the development of a Deep-Sea Raman Probe for the measurement of sediment pore water geochemistry. In this expedition, he will focus on obtaining the in situ pore water Raman spectra and the collection of pore water samples for subsequent shipboard analyses by ion and gas chromatography.
Keith is currently an associate engineer with ConocoPhillips focused on natural gas hydrates. Keith received his PhD in Chemical Engineering from the Colorado School of Mines in 2007. This was followed by a two-year postdoctoral fellowship at the Monterey Bay Aquarium Research Institute with Dr. Peter Brewer. His research interests include the use of carbon dioxide to replace methane in natural hydrates.
John has been a staff member at the NRC since 1974, first with the Division of Chemistry, then with the Steacie Institute for Molecular Sciences upon its establishment in 1991. His research focuses on the chemical applications of solid state nuclear magnetic resonance (NMR) spectroscopy, the development of multi-technique approaches to the characterization of materials, supramolecular chemistry, porous materials, clathrates, gas hydrates, and other guest-host materials. He has nearly 500 publications and six patents and is often an invited speaker at special events. |
