New challenges, new solutions
Several new measurement technologies come with this vehicle
Being a long-term endeavor means that there have been new challenges for the design, durability and reliability of the technology to be used. These challenges include:- sustaining great pressures at depths~ 200 bar, withstanding low temperatures, variable current conditions.
A wire telemetry and cable network system is used as there will be substantial power usage and the storage of data is impractical and inappropriate.
The system consists of one central station with internet/power connections to land and several small, multipurpose tele-operated robots that will reside and move along the seafloor and recharge at nodes. All crawlers will be connected to one central instrument system (Lander), which is located up to 100 meters from the node.
The Lander is a huge tripod consisting of an upper instrument cage with additional sensors and three large footpads. The MBARI Remotely Operated Vehicle (ROV) system Ventana will descend to the sediment from the service vessel and install the Lander and the crawlers. The Lander transfers the data of the robots to the land based data center via the internet. The network will provide real-time information and command-and-control capabilities to shore-based users.
One central Lander...
Transfers the data of the
robots via internet to the data center
The central Lander will be equipped with a CTD, a conductivity, temperature, and density profiler. A downward looking profiling Acoustic Doppler Current Profiler (ADCP) for hydrodynamics will be installed.
The ADCP is designed to send a pulsed sound signal into the water column and derive information about the water current velocities by analysis of the return echoes from particles in suspension in the water and this is done at different angles. An up-looking current meter, in situ filtration with 21 filters for particle measurements, a sediment trap with settling tube, a sonar to detect gas bubbles and a pan/tilt/zoom web cam for monitoring and video mosaicking will all be attached to the central Lander.
...and three mobile crawlers
The three crawlers will be equipped with sensor systems and experimental devices; a CTD, two methane sensors, a newly developed Schlieren optic application for the detection and quantification of fluid flow, 8 oxygen micro profilers, a benthic flow simulation chamber to determine particle dynamics, 3 shear-stress sensors, 3-4 pan/tilt/zoom web cams for controlled tele-operated crawler movement, a sonar to detect gas bubbles and a newly developed parametric echo sounder system to image mineral deposits in the upper sediment column at the decimeter scale and to detect pathways of fluid flow in high resolution.
Several new measurement
technologies come with this vehicle
Long term observations of Gas Hydrate and Venting Barkley Canyon (CA) within the joint venture Neptune Canada http://www.neptunecanada.ca/
Gas and fluid flux measurements by mobile underwater robots. Focused methane emission and its sources and sinks must be investigated in order to constrain the methane cycle and its potential as a climate regulator. Important processes needing quantification are the global distribution of hydrates, environmental changes causing (dissolution) dissociation or formation of gas hydrates, the quantification of free gas and methane-oversaturated pore water fluids, the subsurface transport of methane-bearing fluids, emission of gas bubbles and dissolved methane, and the microbial oxidation of methane to carbonate and sulfide.
Scientific progress in this field requires investigations of the entire methane cycle, from subsurface sediments to the atmosphere. The gas hydrate experimental site at Barkley Canyon will allow us to study the temporal and spatial fluxes of methane (fluid and gas) into the water column. Our hypothesis is that at this study site the emission of methane as bubbles must be taken into account besides the flow of dissolved methane through the sediment water interface, because most of the dissolved methane is consumed in the sediments by methanotrophic communities. This process is described for other gas hydrate sites like Hydrate Ridge. Four different geobiological settings are distinguished:
(1) areas of discrete gas discharge;
(2) areas of extensive bacterial mats;
(3) areas with clam fields of a few to a few tens of square meters ; and
(4) background sediments which may contain the chemosynthetic sulfideoxidizing clam Acharax at depths below 5-30 cm depending on the distance from the vent sites. These different settings have fluid flow rates varying over six orders of magnitude and are often no more than a few meters apart and delineated by sharp horizontal and vertical gradients of chemical and biological species.
Hence it is crucial to quantify these fluxes with the help of mobile underwater robots, capable to determine both, the diffusive methane emission and irregular gas release of methane through bubble formation.
The crawler will be equipped with CTD, Methane sensor, Schlieren optic application, bubble analyser and possibly with microsensors. Via teleoperated movements along the seafloor, the crawler will be directed to bubble sites. It will also detect fluids within the benthic boundary layer with its schlieren optic application. By moving among the four expected different geobiological settings described above, the crawler will enable us to quantify both fluid and gas flow into the water column under different hydrodynamic conditions. It is expected that these studies allow very exact estimates of the temporal and spatial variations of methane emissions.
Please go to our Science section to obtain more detailed information.