Monterey Bay Aquarium Research Institute
2010 SouthernExpedition


Day 5 – Probing for a methane signal at the asphalt volcano
July 13, 2010

1500 hours – On station at asphalt volcano off the coast of Santa Barbara
Latitude 34 degrees 11.5423 minutes N
Longitude 119 degrees 36.9256 W

Scientists have long studied the gases in the seafloor by taking core samples of the sediment, then returning the sample to a laboratory and performing a chemical analysis of the pore waters in the sample. But gases that may be stable in the seafloor at depth may well bubble out and be lost with the change of pressure and temperature as the sample is brought to the surface. MBARI chemist Peter Brewer and his group set out today to see if an in situ measurement of gases in the sediment using their laser Raman spectrometer would yield more accurate data than the return of core samples to the surface.

To test this tool in the pore waters, we went to the site of an asphalt volcano described in a paper published earlier this year by a research group from U.C. Santa Barbara and Woods Hole Oceanographic Institution (D.A. Valentine, et al). Heavy oil seeping from the seafloor builds up mounds of tar deposits, like lava from a volcano. On the seafloor, it results in outcroppings that look like chunks of pavement torn from a highway, surrounded by a thick, black, sticky mud layer.

The new 30-centimeter titanium probe of the laser Raman spectrometer system is ready for insertion into the seafloor at the asphalt volcano. The reading came back with a strong methane signal at this location. Outcroppings of asphalt can be seen on the left behind the rockfish.

Brewer’s group installed their laser Raman spectrometer (LRS) on the ROV Doc Ricketts for the day’s dive. The LRS, one of the many tools the team has developed over the years to aid their studies of ocean chemistry, allows non-destructive chemical analysis simply by pointing a laser beam and looking at the changing color of the light that is scattered back. The color change is different for the different molecules, indicating what substances are present. We can even tell something about the environment the molecule is in, such as whether it is a gas or trapped in a solid because they all are slightly different.

The ROV dove to the asphalt volcano site at 200 meters depth where the LRS was deployed, using a new 30-centimeter long titanium probe. At one location, the probe was inserted into the sediment and returned a strong methane and sulfide signal – far higher than usually found in cores measured on the ship. The probe was inserted in several spots in the area, but before we were able to obtain another strong methane signal we had to cut the dive short. The wind had picked up to 35 knots, and the skipper determined it was no longer safe to keep the vehicle in the water. Brewer’s group had hoped to get a good push core sample at the same location to compare to the in situ LRS readings, but that was not to be on this mission.

Western Flyer engineers Lance Wardle and Shaun Summers prepare for the ROV launch.

With the day cut short, the debate was whether to stick around to dive in the same spot and continue this work tomorrow, or call it a “development day” – a chance to successfully test out the LRS and the new probe – and move on to the next site. We will be moving on to another location on the other side of Santa Cruz Island to begin a new dive tomorrow.

—Nancy Barr

Reference: Valentine, D.L., C.M. Reddy, C. Farwell, T. M. Hill, O. Pizarro, D.R. Yoerger, R. Camilli, R.K. Nelson, E.E. Peacock, S.C. Bagby, B.A. Clarke, C.N. Roman, and M. Soloway, (2010). Asphalt volcanoes as a potential source of methane to late Pleistocene coastal waters, Nature Geoscience 3: 345-348.

Second mate Pat Duffy, left, teaches the Western Flyer’s new chief mate, George Gunther, how to operate the crane for launching the ROV.
At one point a large pod of dolphins was swimming off the bow of the ship.
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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.


CTD Rosette

A CTD rosette is a cylindrical frame holding a group of plastic water-sampling tubes. Attached to this frame are instruments for measuring water temperature and conductivity (salinity) at various depths. Also attached to the rosette are instruments for measuring parameters such as chlorophyll, nutrients, and particulate matter in the water. As the frame is lowered over the side of a ship, water samples are taken automatically at various depths. Then the frame is raised to the surface again.


 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.

Andreas Hofmann
Postdoctoral Fellow, MBARI

Andreas is a MBARI Postdoctoral Fellow in the Brewer lab. He obtained a PhD in marine biogeochemistry in the Netherlands after his biology undergraduate and bioinformatics graduate studies in Germany. Andreas' specialty is pelagic and benthic biogeochemical modeling with a focus on pH and proton cycling. At MBARI, Andreas is working on the relation between pH and soundspeed, the characterization of marine "dead zones", the development of a sediment model to estimate biogeochemical rates from pore-water methane profiles obtained with the group's deep sea sediment Raman Probe, and on a few other related topics. On this cruise, Andreas will be involved in experiments using the mid-water CO2 and O2 control system and the sediment Raman probe, as well as in various data processing tasks.

Melissa Luna
Summer Intern, MBARI

Melissa is an MBARI 2010 Summer Intern working in the Brewer lab. She is a graduate of College of Charleston in Charleston, South Carolina with a BS in Chemistry. This summer Melissa will be working on using laser Raman techniques to examine hydrogen sulfide and bisulfide signals as a function of pH in marine pore waters in sea floor sediments.

Nancy Barr
Web/Print Project Manager, MBARI

Nancy manages the editing, design, and production of the MBARI annual report and participates in a variety of editorial and communication projects. She also oversees the institute website. Nancy has been to sea with several MBARI research groups, helping them to carefully remove worms from whale bones, annotate video, sift seafloor sediment, and collect and process water samples. For this expedition she will be in charge of the daily reports that will be posted to this website and will assist with other science crew tasks.

Xin Zhang
Seafloor Hydrothermal Activity Laboratory
Key Lab of Marine Geology and Environment
Institute of Oceanology, Chinese Academy of Sciences

Xin Zhang is a former MBARI student of Peter Brewer and Bill Kirkwood. He was involved in the development of a Deep-Sea Raman Probe for the measurement of sediment pore-water geochemistry.

Zeng Zhigang
Director, Seafloor Hydrothermal Activity Laboratory
Key Laboratory of Marine Geology and Environment
Institute of Oceanology, Chinese Academy of Sciences

Zeng Zhigang's research interests are in hydrothermal vents, geochemistry, economic geology, and the exploration of geology and mineral resources. He is on this expedition to learn more about MBARI's tools and methods for study ocean chemistry.