 Leg 3 Logbook - Gas Hydrates
Day 2 — An eventful first dive
August 3, 2009 Latitude 44 degrees 34.079 minutes N The day started out like most days on the Oregon coast—calm and foggy. At 9:00 a.m. sharp, we left the dock and steamed out the entrance channel, passing underneath the picturesque span of the Yaquina Bay Bridge. Both ship’s crew and science crew took photos, talking of past and future journeys, and thinking of our friends and family on shore. The ship’s crew has been at sea (with short breaks) since the beginning of July. 
Second Mate Pat Duffy takes souvenir photos of Jim Boedecker and Dan Benvenuti as we leave Yaquina Bay.
Although the skies remained overcast, the winds stayed relatively light. We passed pairs of murres—adults and young swimming side by side—while albatrosses wheeled over the swells. According to the crew, the water has been unusually warm (up to 60 degrees Fahrenheit), and albacore tuna have been biting just offshore. On the way out, we had our required security and safety briefing, which included donning bright red survival suits (and waving at the camera). It’s one of those little rituals that are part of going out to sea on a research cruise. 
Tess, Craig, and Yirang model their survival suits during the security and safety meeting.
Around 2:00 in the afternoon, we reached our day’s dive spot, about 64 kilometers (40 miles) offshore. As we prepared to lower the ROV into the water, a pod of dolphins swam by, splashing and eyeing our strange looking craft. In addition to its usual cameras and manipulator arms, the ROV carried about 32 push cores and five long, aluminum vibracore tubes that we hoped to use to collect samples of seafloor sediment. It also carried four Niskin bottles for collecting seawater. 
Brian Schaefer helps launch ROV Doc Ricketts during our first dive of the cruise. On the far right you can see the seven-foot-long aluminum core tubes on the side of the ROV that are used to collect samples of deep-sea sediment. Today’s dive was in the southern portion of an area called Hydrate Ridge, but we didn’t see any methane hydrates during the dive. What we did see, at least on the sonar maps, was a strange, oval depression in the seafloor, several hundred meters across, with a 30-meter-high mound in the middle. In the exaggerated vertical scale of the sonar maps, this feature looked to me like the ruins of a medieval castle, complete with a surrounding moat. We reached bottom on the flat seafloor outside the “moat.” Although the seafloor was covered with mud, we weren’t able to insert our core tubes more than half a meter, presumably because of some very hard layers within the mud. When we later examined a little of this mud in the lab, it was very hard, as if it had been buried a few tens of meters below the seafloor, then somehow ended up back near the sea surface again. We descended into the “moat” and then began to climb up the central mound. Soon we came upon huge slabs of very hard, light-colored rock. Looming out of the darkness, these outcrops again reminded me of the ancient ruins of some massive fortress. They were split by large cracks, some of which were half a meter across and several meters deep. These slabs are most likely a type of rock known as carbonate. Carbonate rocks often form where methane from beneath the seafloor comes in contact with chemicals such as sulfate in seawater. Some geologists who have studied Hydrate Ridge believe that the carbonate mounds in this area formed above the seafloor, growing upward around groundwater seeps like the weird tufa towers at Mono Lake. Charlie Paull has an alternative hypothesis. He believes that these carbonates formed below the seafloor, within the mud, and were later lifted up by pressures from below. They could also have been exposed when the softer sediments around them were eroded away by currents. Charlie has studied similar carbonate structures off Southern California and in the Gulf of California, where he has seen similar evidence of uplift and erosion. One of his goals on this expedition is to find evidence for his hypothesis in the heavily studied areas of Hydrate Ridge and Barkley Canyon. Unfortunately, not only were we unable to collect any deep core samples during our dive, but we had a significant equipment failure. A few hours into the dive, a rack that we used to carry the seven-foot-long vibracore tubes broke off the ROV and fell to the seafloor. It took us a few minutes to realize what had happened, but at that point there wasn’t much we could do. 
This photo, taken by ROV Doc Ricketts, shows the massive slabs of rock that lie cracked and broken on the slopes of southern Hydrate Ridge. For scale, you can see the seven-foot-long vibracore tubes and the core rack that fell off the ROV during our dive. Since we still had some time left to dive, we decided to collect video instead of cores. We spent the next hour or two flying slowly up the sides of the mound, videotaping the rugged slabs of carbonate rock. As Charlie pointed out, the cracks in the slabs looked a lot like the cracks that form on the crust of a loaf of bread, as it rises in the oven. This and other observations added support for his hypothesis that the rocks on Hydrate Ridge were pushed up from underneath. In the end, the ROV pilots were able to bring the core rack back to the surface, but not the vibracores we had collected. After preserving the remaining push cores and water samples, most of the science team headed to bed. The captain has turned the boat northward and is presently heading toward the hydrate outcrops off Vancouver Island. We will be steaming north all night and most of tomorrow. While we’re underway, the ROV pilots will repair the core rack and the science crew will figure out how to get the sediment samples that Charlie needs to understand some of these strange and impressive seafloor features. 
Michael Riedel, from the Canadian Geological Survey, examines some of the short sediment cores that we collected during our dive.
—Kim Fulton-Bennett
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Equipment
 R/V Western FlyerThe 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 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.
R/V Zephyr is the primary support vessel for MBARI's autonomous underwater vehicle (AUV) program. This 26-meter vessel is also used to maintain environmental moorings, collect time-series data along the California Current, and support scuba divers as they study near-shore habitats.
The MBARI Mapping AUV is a torpedo-shaped vehicle equipped with four mapping sonars that operate simultaneously during a mission. The multibeam sonar produces high-resolution bathymetry (analogous to topography on land), the sidescan sonars produce imagery based on the intensity of the sound energy's reflections, and the subbottom profiler penetrates sediments on the seafloor, allowing the detection of layers within the sediments, faults, and depth to the basement rock.
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.
The benthic elevator allows us to carry more than the ROV itself can carry. Loaded with sediment enrichers, it is deployed from the ship before the dive and free-falls to the bottom where the ROV pulls the equipment from the elevator for use. After the ROV is recovered, the elevator anchor's acoustic release is triggered from the ship, and the elevator freely ascends to the surface and is recovered.
Niskin bottles are used to collect water samples as well as the tiny bacteria and plankton in the water. The caps at both ends are open until the bottles are tripped, when the caps snap closed.
Held by the ROV's manipulator, the wire on the right is placed into the fluid emitted from a hydrothermal vent to record the temperature. Research Team
Charlie Paull has been a marine geologist and geochemical stratigrapher at MBARI since January 1999. The central theme of Charlie's work involves investigating the fluxes of fluids and gases through continental margins. Over the past decade his primary focus has been gas hydrate research on the Blake Ridge gas hydrate field on the continental rise off of southeastern North America. Assessing the global distribution of gas hydrate and interstitial gas is a continuing interest as well as the development of new techniques to detect the presence of gas hydrate in marine sediments. Charlie's other ongoing work is focused on the geology associated with seafloor seepage sites, including investigating the deposits associated with chemosynthetic communities, determining the processes that occur at the methane-sulfate boundary, and understanding the origin of pockmarks and other potential seafloor fluid venting sites.
During expeditions, Bill Ussler is primarily responsibility for the operation of the custom-built, portable chemistry lab van which contains a complete analytical laboratory for the analysis of the fluids and gases contained in marine sediments. Along with colleague Charlie Paull, Bill studies how methane (natural gas) forms and moves within seafloor sediments.
Michael Riedel was part of an international team of scientists supported by the Integrated Ocean Drilling Program (IODP) which completed a unique research expedition in 2005 aimed at recovering samples of gas hydrate, an ice-like substance hidden beneath the seafloor off Canada's western coast. As IODP Expedition 311's co-chief scientist, Michael explored his interest in gas hydrate; he believes such deposits have played an important role in ancient global climate change.
Ross's research interests are in seismo-acoustic propagation, with specific application to the study of marine gas hydrates, and development and application of acoustic inverse methods for estimation of geophysical properties of the ocean bottom and for source localization. (Note: At the last minute Ross was unable to participate in the cruise, although he did attend the initial science meeting before the ship left the dock.)
As a member of the USGS Coastal and Marine Geology Program, Mary McGann's professional interests include: foraminiferal and pollen biostratigraphy, paleoecology and biogeography; sedimentary paleoenvironment mapping, quaternary paleoclimatology; and AMS C-14 chronostratigraphy.
Laura's research is concentrated on studying methane cycling at cold seeps, biogeochemcial cycling of methane and sulfer in deep sea sediments, development of deep sea instrumentation to collect novel samples, stable isotope geochemistry, modeling of biogeochemical processes and temporal variability of dissolved methane concentrations. The focus of her research has been mainly on gas hydrate environments, but she is also interested in other systems that relate to the carbon cycle. Her research seeks to understand how methane is distributed between different pools, e.g. dissolved or hydrate phases, and also to understand how local biogeochemical processes affect this methane, mostly through anaerobic methane oxidation.
Kim helps people outside of the institute to understand MBARI's research and development efforts. He does this by writing news releases and articles about MBARI research, as well as by helping members of the press who want to write their own articles or create video stories about MBARI. His academic background is in marine geology, environmental planning, and science writing.
Yirang is an undergraduate at UC Davis in Environmental Studies and Ecological Engineering. She is an exchange student from Korea University who is interested in methane hydrates as an alternative energy source and in the ecological communities around methane seeps. She is very happy to have the opportunity to go on this cruise.
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