Monterey Bay Aquarium Research Institute
2010 SouthernExpedition


Day 8 – Well, that explains all these clams!
July 16, 2010

1830 hours – Santa Monica mounds   
Latitude 33 degrees 48.1162 minutes N
Longitude 118 degrees 39.3908 W

Another first today – the successful pairing of two MBARI research tools to collect more accurate ocean geochemistry data.  While Peter Brewer’s group has been using laser Raman spectroscopy for several years to read the chemical signal in-situ, geologist Charlie Paull’s group has been using a vibracoring system to collect two-meter-long sediment cores that provide clues to stratigraphy and the structure of geologic features. Today the two systems were used in concert for the first time in an exciting adventure.

The two-meter long aluminum vibracore tubes were pre-drilled with small holes which were then covered with tape; the tape would keep the mud inside the core, but be easy enough to poke through with the pore water probe. The ROV pilots installed the vibracore system on the vehicle before the 835-meter dive. The ROV was set down on the seafloor in areas with chemosynthetic clams and bacterial mats (signs of methane venting). The long tubes were inserted into the seafloor; it can be next to impossible to push a core deep into the sediment, which is why the vibracoring system provides vibration to help work the tube into the sediment. The long tubes were inserted into the seafloor; it can be next to impossible to push a core deep into the sediment, which is why the vibracoring system provides vibration to help work the tube into the sediment.

vibracore
The laser Raman spectrometer pore-water probe is inserted into a hole in the two-meter-long vibracore tube resting on the seafloor. The mud at the that section of the core came from approximately one meter deep into the seafloor, and the Raman system returned a clear methane signal higher than what has been ever measured for the depth.

The first core was filled about two-thirds of the way, then pulled out of the mud and laid on the seafloor. The laser Raman pore-water probe was pulled out of the ROV tray and inserted into one of those holes in the core; a sample of the pore water was drawn into the probe and passed in front of the internal laser beam. It was a new low for the geochemists—an in situ reading of the chemistry of water from more than a meter deep in the muddy seafloor. As I’ve explained in previous logs, this will give a much more accurate reading than bringing the same sediment to the surface, as the gases will tend toward equilibrium on the transit to the surface.

When the first Raman spectra reading showed a significant methane signal, Brewer jumped out of his seat in excitement and did a dance of joy, sharing a “high five” with his former student Xin Zhang. The methane signal was present in the next two holes (representing shallower depths in the sediment) then petered out in the higher sections of the core, showing the methane signal was stronger at greater depth, dissipating closer to the seafloor. The full strength of this methane never would have been detected had the core sample been brought to the surface.

It was the test of a new technique which could prove useful to geochemists and microbiologists who are interested in methane vent sites. Scientists long suspected there must be more methane at these vent sites than they were able to measure because there had to be a substantial source of energy for the thriving chemosynthetic communities of clams and bacteria found there. 

Knute Brekke working on ROV
The ROV pilots spent many hours preparing the vehicle for this dive, which involved installing a vibracore system onto the vehicle. When the two-meter-long cores were perched on the front of the vehicle, they interfered with one of the cameras, so Chief Pilot Knute Brekke climbed onto the Doc Ricketts and removed the camera. Pilots Buzz Scott, left, and Mark Talkovic, right, along with Bryan Schaefer and D.J. Osborne also prepared the vehicle and took turns in the pilots’ seats to perform the exacting tasks needed to make today’s experiment a success.

Now, note that I make a lot of the steps along the way sound easy, but the tasks put to the ROV pilots are often quite challenging. The pilots rotate shifts throughout the day, and as one pilot handed off to the other, he would warn his colleague that what he was about to do would be exacting and tedious. Manipulating the various tools attached to the vehicle and inserting the probe into small holes in the vibracore tube, all while working remotely via a video monitor aboard the ship, is takes skill and practice. The science crew and the pilots work closely during the entire dive, and the science crew is very appreciative of MBARI’s expert ROV crew, which makes the experiments possible.

—Nancy Barr

Andreas at work Melissa at work Zhang at work in the lab

Andreas Hofmann, Melissa Luna, and Xin Zhang processed the pore waters from the push cores taken earlier in the cruise and prepare the samples for gas analysis back at the lab.

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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.