Monterey Bay Aquarium Research Institute
2009 Pacific Northwest Expedition


Leg 1 Logbook - Laser Raman Spectroscopy
Day 4 – If it is Friday, it is time to get to work ...
July 10, 2009

0900 hours – On Station at Hydrate Ridge, 50 nautical miles off the Oregon coast.
Latitude 44 degrees 34.2 minutes N
Longitude 125 degrees 8.9 minutes W

Last night, the R/V Western Flyer arrived on station at the southern summit of Hydrate Ridge. This site is well known among geochemists as an active deep water methane gas vent. The gas is more than 98 percent pure methane indicating that it is primarily biogenic in origin. This methane and the associated hydrogen sulfide support a local community of bacteria which form mats on the seafloor. Additionally, at these temperatures (approx 4 degrees C) and pressures (80 atmospheres), the methane reacts with seawater to form clathrate hydrates which are of great interest to the Brewer group and the subject of our expedition. Unfortunately, should the gas hydrates ever be exposed on the seafloor, they will quickly dissolve. It is only in the methane-rich sediments that they are stable. So our hunt begins by looking for either active gas vents (which we can see with the sonar on the ROV) or the bacteria mats on the seafloor.

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Randy Prickett, Peter Walz, and Dan Benvenutti prepare the elevator for a dawn launch at Hydrate Ridge.

This morning everyone was up before dawn so that we could launch the elevator at first light (above). The elevator will carry several glass chambers where we will place the clathrate hydrates for inspection with our laser Raman spectrometer. Once the elevator is hung over the side by the A-frame and gently lowered into the water, a release line is pulled (see below) and it is allowed to free-fall 800 meters to the seafloor. A homing beacon is attached so that we can track it from the ship, and then find it on the seafloor. Later the ROV will move it into position near a hydrate collection site for our experiments.

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MBARI’s vibra-core elevator is carefully lowered into the ocean from the A-frame on the stern of the R/V Western Flyer. When the release line is pulled, the elevator will free-fall to the seafloor 800 meters below. A homing beacon is attached so that we can track the elevator by sonar during its descent and then quickly locate it with the ROV on the seafloor.
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Once the elevator is released, the moon-pool area is a flurry of activity as the ROV pilots ready the vehicle for launch.

Once the elevator was released, all hands turned to making the ROV ready for launch. The pilots were moving so fast, that not even high speed digital photography could “catch them on film” (above). Within less than a half hour, the ROV was ready for launch and our day’s dive could begin. We dove directly for the elevator as everyone was anxious to see if it landed upright and if the glass chambers had survived the free descent to the sea-floor. Following the sonar beacon, we quickly located the elevator and to everyone’s delight it had landed upright and all the equipment was intact (see below).

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MBARI’s elevator has arrived safely and upright on the seafloor. Here it is located at 800 meters depth just slightly west of the southern summit of Hydrate Ridge. The orange color is the float pack made of syntactic foam that will allow the elevator to rise to the sea surface when the weights are released at the end of the experiment. One of the glass hydrate chambers is visible on the lower right of the elevator.

After exploring the seafloor for an hour, we located several bacteria mats which seemed likely candidates for harboring methane and hydrogen sulfide rich sediments below. Normally, core samples would be taken that would need to be carried to the sea surface and analyzed on-board. However, with our new pore-water attachment for our second generation deep-ocean Raman in situ spectrometer (DORISS2), we were hoping to conduct our analyses on the seafloor. So we quickly set-up the ROV relying on the skill of the pilots to carefully insert the probe straight-down into the sediment below the bacteria mats (see images below). Initial analysis of the spectra revealed the presence of methane and hydrogen sulfide just 20-30 centimeters below the seafloor. Encouraged by our early success we spent the day inspecting the sediments below the bacteria mats at a variety of sites near the southern summit of Hydrate Ridge.

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The pore-water probe is carefully inserted into the sediment below a bacteria mat (white) with skillful manipulation of the ROV arm by the ROV pilot. Visible at left is a conventional push-core which was collected for comparison with the in-situ analyses.

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A close-up view of the pore-water sediment probe. The scale on the side of the probe shows the depth of penetration (in this case 27.5 cm). A small rockfish lurks nearby keeping careful watch on our experiment.

Late in the day, we spotted several small gas vents on the ROV sonar and transited over to take a look. Unfortunately, before we could accomplish much, the wind had come up and with the sea surface getting rough we elected to recover the ROV and return another day.

—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.