Monterey Bay Aquarium Research Institute

 


Gas Hydrates - Background
Chief Scientist: Charlie Paull
22 August - 3 September 2011

Dr. Charlie Paull's research team will conduct both mapping AUV surveys and ROV dives to continue their on-going investigations of processes associated with seafloor gas venting and modern submarine canyons. In 2011, they plan to focus on one geographically restricted area surrounding Eel Canyon, offshore of Eureka, California, where both these themes can be addressed simultaneously. Mapping AUV surveys should be conducted from the R/V Zephyr before conducting ROV dives. This data will then be used to direct Doc Ricketts dives to ground truth the mapping surveys.

Eel River Margin – Submarine Gas Venting Plumes and Seeps
Several gas vent sites exist along the Eel River margin (see Figure 1 below). A group of persistent water column acoustic anomalies (referred to as plumes) were recently discovered during NOAA Ocean Exploration mapping cruises (Gardner et al., 2009). Methane gas bubbles rising from the seafloor are believed to be the cause of these acoustic anomalies. The originally discovered plume can be traced using multibeam sonar data from the seafloor (~1800 m water depth) into the water column for ~1,400 m (Gardner et al., 2009). A second mapping cruise passed over this area, confirmed the persistence of the original plume, and identified four similar plumes. The tops of all five plumes are in ~400 m water depth, which is above the top of pure methane hydrate stability in this area (~520 m water depth), suggesting that thermogenic gases may be present, which enhance gas hydrate stability. Four of these plumes emanate from Eel Canyon, and one is from a slide scar just south of the canyon. The existing ~10-m resolution surface ship multibeam bathymetry indicates that some of these plumes originate from sea floor topographic features like the Santa Monica and Barkley Canyon mounds, which are topics of on-going research by several groups at MBARI.

Other methane seep sites in shallower water depths (520 to 600 m) also occur in the Eel River area. A fortuitous discovery of gas hydrate in a piston core during the 1980’s resulted in Eel River becoming a classic seep research site (Brooks et al., 1999). Since then, many research groups have visited the same three gas vents largely because their locations are known. Very little is still known about the geologic context of these features and even a detailed basemap of the classic Eel River seep area does not exist. Existing seafloor images in this area reveal very rough, fine-scale topography. These sites are especially curious because they are at or near the top of methane hydrate stability in this area, and the present seafloor here could have been impacted and altered by multiple cycles of gas hydrate formation and decomposition.

Understanding the processes associated with seafloor gas venting and the impact of associated phenomena on seafloor morphology has been a long-term goal of the Paull group. These efforts include detailed work looking at the local biogeochemistry, sources of energy to support chemosynthetic biological communities, and the formation of authigenic carbonates. Recently collected AUV multibeam data, complemented by ROV observations and sampling have also revealed a remarkable amount of fine-scale geomorphology and seafloor structures associated with gas venting and/or near subsurface gas hydrate accumulations. These include previously unknown karst-like seafloor textures, seafloor depressions, and local topographic highs. These features clearly indicate dramatic modification of the seafloor, involving both localized excavation in some areas and the elevation of the seafloor in others. Apparently, these features are somehow related to gas venting, gas hydrate development and related phenomena. However, the processes that generate such features are poorly understood. MBARI’s AUV high-resolution seafloor surveys provide a unique and new dimension in seafloor vent studies. Application of MBARI’s combined assets now enable imaging and sampling the seafloor associated with these features in enough detail to begin to understand the geologic evolution and geochemical history of these morphologic features. Efforts will also be taken to utilize our AUV and ROV carried sensors to image these water column hydrocarbon plumes.

Eel Canyon - Sediment Transport and Hyperpycnal Flows
Sediments on the floor of Eel Canyon and its fan (Figure 1) are likely to reflect processes that are substantially different from those responsible for the most recent sediment deposition on the floor of Monterey Canyon or any of the other canyon systems we have investigated to date. A supply of sand appears to be necessary for generating the types of sediment transport ‘events’ we now know occur regularly within Monterey Canyon. Repeated AUV multibeam mapping has shown that these transport events alter the shape of the axial channel and leave behind the crescent-shaped bedforms that have attracted so much interest from the geologic community. Because Eel Canyon’s head is not connected to the shoreline, its does not receive a regular supply of sand. However, Eel Canyon may have experienced significant activity of a different kind. More specifically, floods from the Eel River are thought to be capable of generating periodic hyperpycnal flows, which presumably descend into the Eel Canyon carrying huge amounts of fine sediment (Mulder and Syvitski, 1995).

Figure 1 Part A shows bathymetry at 100 m contour interval of the continental margin offshore of Eureka California and locations of Eel River, Mendocino Fracture Zone (MFZ) and Eel Canyon. The location of the ‘classic Eel River seeps’ are indicated with an X. The area indicated with the red box is shown in more detail in Part B. Part B shows multibeam bathymetry of the area where six huge water column plumes were discovered (black dots; Gardner et al., 2009). Two emanate from a slide scars to the south of Eel Canyon, and four emanate from the seafloor and northern flanks of Eel Canyon. Arrows indicate steps within the canyon floor. Part C is a detailed map of the slide scar area where a Santa Monica mound-like feature occurs (black arrow).

The continental shelf off the Eel River was the site of the STRATAFORM project, an intensive study of sediment transport from a river onto a continental shelf (e.g., Nittouer, 1999). This project benefited from the fortuitous occurrence of huge floods on the Eel River in 1995 and 1997. These were 25- to 100-year flood events and had sediment loads capable of generating hyperpycnal flows. These flooding events temporarily dumped an appreciable blanket of sediment on the continental shelf. However, only 25% of the discharged sediment could be accounted for and the fate of the majority of the sediment carried in these flooding events has never been established (Imran and Syvitski, 2000). Whether or not any of the historical floods generated hyperpycnal flows that descended into Eel Canyon, the axis of Eel Canyon is a place where periodic hyperpycnal flows are likely to have occurred in recent times.

Lamb et al. (2008) have shown using 10-m resolution surface ship multibeam data that huge repetitive bedforms with wavelengths of ~1 km and amplitudes over 10 m occur on the flanks of Eel Canyon. They suggest these bedforms were formed by gigantic hyperpycnal flows, which is further evidence for the occurrence of hyperpycnal flows in Eel Canyon. Moreover, the existing surface ship multibeam data indicate that a series of curious topographic steps occur along the canyon axis, which are not clearly resolved (Figure 1). Our previous experience has shown that the much more detailed data provided by AUV multibeam surveys are critical for conducting an intelligent sampling program and provide dramatically more understanding and constraints on the nature of the processes that occur within submarine canyons.

While hyperpycnal flows are believed to be among the major sediment transport processes on earth, surprisingly little is know about them, especially as suspended sediments move away from the river mouths and flow downslope. For example, no substantial documentation exists about the nature of the sedimentary deposits within Eel Canyon below ~600 m water depth. In fact, remarkably little is known about the deposits that hyperpycnal flows produce. Most of the putative hyperpycnal flow deposits have been identified within terrestrial outcrops. However, it is simply an inference that any of the deposits in Eel Canyon were actually deposited by hyperpycnal flows (Mulder and Syvitski, 1995). Obviously, this is an area that needs calibration with a modern process study of the type we have pioneered using our combined AUV multibeam mapping and ROV-deployed vibracoring systems and propose to conduct in Eel Canyon.

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Leg 4
 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.

R/V Zephyr

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.

AUV D.Allan.B.

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.

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 the ROV'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.

Niskin bottles

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.


Heat flow probe

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.


Biobox

The box fits in a partition in the sample drawer. It is shown open, with an animal being placed into it by the ROV's manipulator. When the lid is closed, the box will hold water to protect the animals inside.


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.


 Crew

R/V Western Flyer

Ian Young
Master


 

George Gunther
First Mate


 

Matt Noyes
Chief Engineer


 

Andrew McKee
Second Mate


 

Lance Wardle
First Engineer


 

Olin Jordan
Oiler


 

Paul Tucker
Second Engineer


 

Vincent Nunes
Bosun


 

Dan Chamberlain
Electronics Officer


 

Patrick Mitts
Steward


 

ROV Doc Ricketts

Knute Brekke
Chief ROV Pilot


 

Mark Talkovic
Senior ROV Pilot


 

Randy Prickett
Senior ROV Pilot


 

Bryan Schaefer
ROV Pilot/Technician


 

Eric Martin
ROV Pilot/Technician


 

 Research Team

Charlie Paull
Chief Scientist
MBARI

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. 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.

Bill Ussler
Senior Research Specialist
MBARI

During expeditions, Bill Ussler is primarily responsible 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.

Eve Lundsten
Research Technician
MBARI

Eve Lundsten works with Charlie Paull in the Continental Margins Lab. Eve's background is in hydrology but she uses her mapping skills, and some of her technical skills to help Charlie Paull understand the processes that are creating the features we see on the sea floor. One of her main responsibilities on this expedition will be running the GIS system. We use Arc GIS and our high resolution, AUV collected bathymetric maps to help direct our research to the precise location of interest on the sea floor. Eve will also help out with processing and cataloguing sediment samples and vibracores. Eve is very excited to participate in this cruise and is looking forward to many exciting discoveries.

Roberto Gwiazda
Research Specialist
MBARI

Roberto is a geochemist by training, and his interests lie at the intersection of marine geology and sediment and water chemistry. On this expedition, Roberto will be responsible for collection and analytical measurements of pore water chemistry on samples taken from sediment cores, and will participate in the collection and analysis of methane from gas vents on the seafloor.

Krystle Anderson
Research Assistant
MBARI

Krystle Anderson is a research assistant working for Charlie Paull in the Continental Margins Lab. Krystle's background is primarily in the acquisition and processing of seafloor mapping data. She came from CSUMB Seafloor Mapping Lab where she obtained her data processing and GIS skills. Krystle spends a majority of her time processing and creating high-resolution maps of multibeam data collected from the mapping AUV. The high-resolution maps Krystle helps create will then be used to aid navigation for the ROV to explore particular areas of interest. On this expedition Krystle will assist with running the GIS system, processing and cataloguing sediment samples and vibracores. This is Krystle's first research expedition with MBARI and she is very excited to be involved in this deep sea excursion.

Philip Barnes
Marine Geologist
National Institute of Water & Atmospheric Research
New Zealand

Philip's specialist interests are in active margin plate boundary processes, including submarine neotectonics, sedimentary basins and sequences, and geohazards. He has undertaken research on subduction, thrust, strike-slip, and rift tectonic systems, sequence stratigraphy and sedimentation processes, submarine landslides, canyon systems, and fluid seepage. Recent initiatives have included the development of on-fault submarine paleoseismic techniques, earthquake source characterisation for national seismic hazard assessment, fluid seepage along the Hikurangi subduction margin, slip rate assessment on the offshore Alpine fault, and submarine canyon development in central and eastern New Zealand. Since the devastating February 2011 earthquakes in Christchurch City, he has been leading seismic reflection studies of active faulting as part of an urgent earthquake risk and recovery work program.

Mary McGann
U.S. Geological Survey
Pacific Coastal and Marine Science Center

Mary is a micropaleontologist/ biologist with the USGS Pacific Coastal and Marine Science Center. Her interests focus on using microbiota (primarily foraminifera but also pollen) in climate, geohazards, sediment transport, and paleotsunami investigations, as well as in biomonitoring marine pollution sites and for AMS C-14 chronostratigraphy.

Brian Edwards
U.S. Geological Survey
Pacific Coastal and Marine Science Center

Brian Edwards, a sedimentologist with the USGS Pacific Coastal and Marine Science Center, has more than 30 years of sea-going experience on 60-plus coring and geophysical cruises along the west coast of the United States and in high-latitude environments (the Ross Sea [Antarctica], the North Pacific Ocean, the Bering Sea, and the Arctic Ocean). Brian specializes in sedimentary processes and stratigraphy, integrating insights gleaned from seafloor rock and sediment samples with information from remote-mapping products, such as close-up photographs of the seafloor, high-resolution bathymetric maps, and seismic-reflection profiles. His recent studies have focused on how sediment moves from the land to the deep sea, processes controlling submarine landslides, saltwater intrusion into coastal aquifer systems, marine pollution, seafloor habitats, and the Cenozoic history of the Arctic Ocean.

Andreia Afonso
Task Group for Maritime Affairs
Portugal

Andreia Afonso has a degree in Marine Sciences from the Lusofona University where she has specialized in the field of Physical Oceanography. Since 2008, Andreia has been working within the former EMEPC (Task Group for the Extension of the Continental Shelf), now called EMAM (Task Group for the Maritime Affairs), where she received ROV pilot and engineer training and has integrated the 6000m rated ROV LUSO technical team. She has participated in five multidisciplinary missions, dominantly in the scope of the Continental Shelf Extension Project involving deep sea research. Andreia is very interested and motivated by the conceptualization, development and implementation of new sea technologies and tools. Apart from EMAM's ROV Team related tasks, she is now project coordinator at EMAM for the development of a modular buoy as a ground for the development of a near shore marine environmental monitoring observatory.

Saulwood Lin
Sediment Biogeochemist
Institute of Oceanography
National Taiwan University

Saulwood Lin is interested in diagenesis in sediments. He has been working on biogeochemical processes associated with gas hydrate and chemical weathering of small river drainage basins. In one ROV cruise he participated, he found a unique cold seep environment in the passive margin off Taiwan. To better understand gas seeps and chemosynthesis community, he joins the MBARI cruise for the purposes of learning ROV instrumentations, sampling and operation of ROV and AUV to facilitate Taiwan's gas hydrate research.