Monterey Bay Aquarium Research Institute
2009 Pacific Northwest Expedition


Leg 1 Logbook - Laser Raman Spectroscopy
Day 12 – The Great White Hope
July 18, 2009

Back on station at Barkley Canyon, 40 nautical miles southwest of Vancouver Island, Canada.
Latitude 48 degrees 18.6 minutes N
Longitude 126 degrees 3.9 minutes W

We are back on station at Barkley Canyon. The cable laying ship has completed its work and the ROV survey is complete, so we are able to work the site again today. The purpose of this dive is to find a sample of pure/white gas hydrate and obtain a laser Raman spectrum. With this information we will be able to determine both the chemical composition and the crystal structure of the hydrate. This is not as easy as it sounds. Most of the gas hydrate found at this site has been permeated by a naturally occurring petroleum oil that has the consistency and odor of diesel fuel. Unfortunately, this fluid is also very fluorescent. And this fluorescence swamps out the Raman signal, so we can only inspect samples of the much rarer white hydrate with the laser Raman system.

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In another two-fisted operation the ROV pilots scrape the sediment at the top of a hydrate mound to liberate small bits of hydrate. These are then collected by the second pilot who carefully positions the hydrate basket over the plume of slowly rising pieces. Great job guys!

Thus, the day begins with a search for white hydrate. Due to the fact that this form dissolves rapidly in seawater, it is rarely seen in outcrops. Our only hope is that we will find some buried under a thin layer of sediment, which means a lot of digging, scraping, and hoeing. We will be keeping the pilots busy (and probably break a lot of tools). It is a long tedious process. We visit several locations where the white hydrate was seen during previous dives. Success comes by a bit of luck and determined persistence. Finally, we stumble upon some white hydrate buried under a thin layer of sediment when we scrape the top of a hydrate mound with our now famous benthic hoe (above). As the pieces slowly rise, we catch them in our homemade hydrate basket. We then carefully place the basket on the seafloor so that none of the flakes escape (well not too many) and then interrogate the specimen with our laser (below). Once the laser position is adjusted to the right distance for focus, we turn off the lights on the ROV to avoid contaminating the Raman spectrum with the spectrum from the white lights. As there were more failures at this than successes, we spend most of the day staring at a bright green spot on a very dark monitor—but with persistence comes success.

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With a specimen of pure white gas hydrate securely trapped in our hydrate basket, the ROV pilot skillfully places the probe-head of the laser Raman spectrometer in very close proximity to the hydrate surface. Once in focus, we turn out the lights and collect our spectrum.

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Every once in a while we get lucky and there are small outcrops of the white hydrate in the face of the hydrate mounds. Here we attempt to obtain a spectrum of the gas hydrate but contamination with a light petroleum hydrocarbon oil spoils the analysis. Whether this oil had permeated the sample or was merely a surface coating is unknown.

Later in the day we happen upon some exposed white hydrate and close in with our spectrometer probe-head (above). Unfortunately, there is just enough oil in this sample to overwhelm the Raman effect, so we are disappointed. Undaunted, we press on with our next task: to collect some of the oil that is both ruining our spectra and that comes oozing out of the sediment almost everywhere when we land with the ROV. Naturally, now that we want oil, we find mostly gas hydrates buried in the sediment and very little oil. After trying several sites, we finally find one rich in oil but collecting it turns out to be another thing altogether. Finally, we decide to just grope around in the mud with our gas sampling funnel. On the fourth or fifth try (who is counting at this point) we hit a gusher (below). It takes more persistence but we fill most of the funnel with oil. Then with time running out on our dive, we open the sampling valve and suck the oil along with just a bit of seawater into our sampling cylinder capturing the sample. This time we will have to wait until we get home to find out what we’ve got.

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Our last task of the day was to collect a sample of the oil that seems to ooze out of the sediment almost everywhere we land. While it turns out to be easy to liberate the oil from the sediment, catching it is quite something else. Eventually, we place the gas collection funnel right in the sediment and root around with it. In just a few minutes we have more than enough oil for a sample. Here you can see quite a few oil droplets escaping from our efforts to capture them.

Our dive is done and so are most of our tasks planned for this leg of the expedition. Tomorrow we finish up here, then we must return to Hydrate Ridge to collect our elevator and finish the gas exchange experiment. Stay tuned…

—Ed Peltzer

 

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Leg 1
 Equipment

R/V Western Flyer

The 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

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.

Laser Raman spectrometer DORISS2

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.


Push cores

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.

Vibracores

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.


CO2 accumulator

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.


Heat-flow probe

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 Brewer
Senior Scientist, MBARI

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 Peltzer
Senior Research Specialist, MBARI

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 Walz
Senior Research Technician, MBARI

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
Graduate Student, Ocean University of China & Visiting Investigator, MBARI

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 Hester
Conoco Phillips

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 Ripmeester
Principal Research Officer, Materials Structure and Function Group
National Research Council Canada

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.