 Leg 3 Logbook - Gas Hydrates
Day 6 — A Tale of Two Dives
August 7, 2009 Latitude 48 degrees 40.26 minutes N Today was another two-dive day, but the two dives were very different from one another. The first dive exemplified the repetitive, systematic, and sometimes tedious effort that goes into collecting scientific data—the kind of data that forms the basis for a respectable scientific paper. The second dive was full of excitement and dramatic discoveries. During the morning’s dive, Charlie collected a series of samples and measurements starting within Bullseye Vent and extending out into the surrounding flat, muddy seafloor. As in yesterday’s dives, we had plenty of time to watch brittle stars crawl around on the mud while we collected vibracores and heat-flow measurements. We only traveled about 50 meters between each measurement, and it was visually hard to tell one site from another. 
Craig and I have developed a new, more
efficient method for removing excess water from the vibracore tubes.
The goal of all this repetitive sampling was to find out if there were any differences in the sediment chemistry or heat flow between the “vent” and the surrounding area. If the sediments near the vent were very different from those farther away, it might imply that the vent was still active. Conversely, if there were very few differences between the vent and surrounding seafloor, it would imply that the Bullseye Vent site might have been active in the past, but is not currently active. We won’t know which of these alternatives are true until the samples are analyzed in the lab. But everything we have seen over the last two days suggests that not much is happening in Bullseye Vent currrently. 
No less than eight people swarm around ROV Doc Ricketts
during one of our quick “pit stops” between dives. Since the ROV can
only carry five vibracores (the vertical aluminum tubes on the right
side of the image), we often come up to the surface as soon as we have
used up all the cores on the vehicle. This allows us to collect up to 10
vibracores a day. We need these two-meter-long cores to obtain
samples of seafloor sediment at depths where methane in the sediment is
interacting with seawater.
After several hours of systematic sampling, we brought the ROV back to the surface for a quick “pit stop” and core removal. Then we headed back down, this time to explore an underwater slope a few hundred meters east of Bullseye vent. The excitement started during the long descent, when several large Humbolt squid followed us down through the water, hunting small fish that were attracted to our lights. These squid are typically found in tropical waters, but apparently followed a patch of warm water all the way north to Canadian waters. When we were about 150 meters above the bottom, the real excitement started. The sonar screen on the ROV (which is looks like a color version of the classic circular sonar screens in old submarine movies) started showing strange reflective patches in the water around us. Normally we don’t see anything on the sonar until we reach the seafloor. We flew over toward one of these patches and discovered that it was a stream of little bubbles rising up through the water. It felt as if the ROV had suddenly flown into a glass of champagne. However, instead of carbon dioxide, we knew that these bubbles probably contained methane, rising up from vents on the seafloor. We tried to follow the bubbles down to the seafloor to find an active methane vent, but they mysteriously disappeared. So we wandered the seafloor looking for the source of the bubbles. At first we were frustrated in our search, but then we made the second exciting discovery of the dive—we stumbled upon the bones of a dead whale. The whale’s vertebrae formed a neat line about eight meters (26 feet) long across the seafloor. They were coated with white bacteria like bread mold. The whale’s two-meter-wide skull loomed in the darkness nearby, creating a macabre but fascinating scene. 
We were fascinated to find this backbone of a dead whale
on the seafloor. From the size of the head and vertebrae, we figure it
was either a humpback or a blue whale.
Such “whalefalls” provide a huge banquet for deep-sea animals, which can last for years or even decades. They also support many amazing and unusual animals. For example, Bob Vrijenhoek, one of our fellow researchers at MBARI, discovered a family of worms that live almost entirely on the bones of whale bones. These worms have no eyes, legs, mouths, or stomachs, but they do have some internal bacteria that let them live off the fat in whale bones. We wanted to collect a piece of the dead whale’s backbone, but none of its vertebrae would fit in our sample boxes. So we collected dozens of high-resolution photographs, which we hope will provide hours of entertainment for Bob Vrijenhoek and his research team. After taking the photos, we reluctantly left the whale carcass behind and returned to our previous exercise—chasing bubbles. This led us to our next discovery—a patch of seafloor where huge, flat slabs of rock had buckled upward and cracked like a concrete driveway being forced upward by tree roots. Charlie jumped out of his chair in excitement and exclaimed, “This is exactly what I hoped to see!” The buckled rocks demonstrated that something related to the methane vents was forcing the seafloor up from underneath. Charlie believes that this same process created many of the mysterious seafloor features he has seen around methane vents. After taking yet more photographs, we left the buckled slabs and followed the sonar until we finally found what we had been looking for—an active methane vent. It was even marked by an “X” on the seafloor (the “X” had formed where two cracks crossed an outcrop of rocks and mud). From within a three centimeter wide crack in the seafloor, a continuous curtain of bubbles rose up into the water, creating an almost magical scene. 
A beautiful curtain of bubbles streamed out of this crack in
the seafloor—our first active methane vent!
After taking still more photographs, we finally got down to the first planned scientific task of the dive—installing Laura Lapham’s second osmosampler on the seafloor. Laura was elated to find a methane vent where she could place her chemical sample collector right next to the stream of bubbles. Of course, by placing the apparatus on the seafloor next to the vent, we improve the visual aesthetics of the site. But we consoled ourselves in the knowledge that this seafloor area was continually being reworked by the gas percolating up from underneath. After successfully installing Laura’s sampler, the rest of the dive was almost anticlimactic. We went back into “systematic fieldwork” mode, collecting a few more vibracores and heat-flow measurements before heading back to the surface. With no push cores and only a few vibracores to process, the wet lab was deserted by 6:30 p.m. Quite a change from previous evenings! Instead of processing cores, we sat around the dry lab talking for hours about the things we had seen during our dive (as well as everything else under the sun). Tomorrow (Saturday) will be our last day working around Bullseye Vent. On Sunday, a cable-laying ship will be laying an undersea research cable in this area and another scientific ROV will be diving nearby at the same time. But what we discovered today suggests that more discoveries have yet to be made in this part of the ocean. —Kim Fulton-Bennett
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Track the ship
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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