Monterey Bay Aquarium Research Institute
2010 SouthernExpedition


Day 7 – The seafloor blizzard
July 15, 2010

1900 hours – On top of one of the Santa Monica mounds
Latitude 33 degrees 47.9622 minutes N
Longitude 118 degrees 38.7918 W

The day started with a visit to the site of an ongoing MBARI experiment, where it looked like there had been a blizzard on the seafloor. In January, MBARI researchers placed a seismometer, a current meter, and a homer beacon on this Santa Monica mound to gather data about this methane vent. Now those instruments appeared to be covered in several inches of snow and ice. But the white covering was actually a dense covering of filamentous bacteria that feed on the methane venting in the area. These instruments will be recovered next week, when another MBARI science team comes to this site on the second leg of the Southern Expedition.


instruments on Santa Monica mounds
MBARI instruments left on the top of one of the Santa Monica mounds just six months ago are now covered with chemosynthetic bacteria. Photos show the instruments the day they were deployed (top) and today (bottom).

Our MBARI colleagues helped steer this expedition toward this specific site because the active methane vents they discovered here make it a good place to prove the value of the laser Raman spectrometer’s pore-water probe. The methane at such sites has been underestimated for years, as the reading they usually get is limited to methane at equilibrium with one atmosphere of pressure. The rich chemosynthetic communities at such gas vents imply a much stronger presence of methane than has previously been measured. The 30-centimeter titanium probe allows the interrogation of the waters 30 centimeters into the sediment, something that has not been done before. The spectrometer can give much more accurate readings of the methane than traditional methods of taking push cores and analyzing them back at the lab because they do not suffer decompression losses. The Raman pore-water probe allows for measuring gases in situ under the pressure and temperature in the sediment. Today’s methane signals were often significantly higher than have been measured before.

The remotely operated vehicle flew over the mound, covered with carbonate chimneys and thick bacterial mats and expansive fields of chemosynthetic clams (V.elongata). The science crew scouted around for areas with significant populations of chemically dependent life, but also with sediment deep enough to insert the probe some 30 centimeters. It was important to avoid pushing the valuable Raman probe into the hard carbonate outcroppings, so the ROV pilots often first inserted a “dip stick” to test out the suitability of inserting the probe. If the dipstick slid easily into the mud, they knew it would be okay to insert the probe to test the pore waters there. Some of the methane signals recorded today were the highest the group has seen so far.

Clams as far as the ROV’s eye can see.

We also tried to do an in situ measurement of the gas bubbling from the seafloor. Using the ROV’s manipulator arm, the pilot held a push core over the bubbles. As they collected in the tube, they quickly formed hydrate skins, almost filling the tube. The plan was to take the tube to a shallower depth, to the point where the hydrate would turn to gas, then insert the LRS probe to measure the methane. A problem with the tube leaking gas prevented the completion of this measurement, but it was certainly interesting to watch how quickly the hydrate formed and to see the solid chunks of ice slough off the tube when we were done.

The laser Raman spectrometer probe is used to read the methane signal inside this carbonate chimney.

Tomorrow we will continue to map the methane signal in the area and will use a new method. A very long sediment core will be extracted using the MBARI vibracore, then laid on the seafloor and interrogated with the pore-water probe, which will be the first time the pore waters within such a deep sediment sample has been measured at depth, avoiding the problem of degassing that occurs if the sample is brought to the surface.

—Nancy Barr

Methane bubbles quickly filled a tube held over a active vent.
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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.