Southern Hydrate Ridge, in the central Cascadia accretionary complex, is one of the best-studied gas hydrate deposits. Vigorous seafloor venting and formation of gas rich hydrate deposits near the seafloor have been documented here through ODP drilling during Legs 146 and 204 (Trehu et al., 2004, 2006) and through a series of seafloor studies using submersibles and ROV’s (Levin, 2005; Suess et al., 1999; 2001). These studies have provided a good understanding of how gas hydrate is distributed in marine sediments and the processes that lead to heterogeneity in this distribution. The subsurface has been imaged with 3D seismic data (Trehu et al., 2004), which define a focused plumbing system beneath the summit of Hydrate Ridge and bottom simulating reflectors at only 120-150 m beneath the seafloor (Bangs et al., 2005; 2011).
Follow-on high resolution mapping and digital still mosaicking by the RSN team utilizing the ROV’s Jason 2 and ROPOS and autonomous vehicle Sentry in 2010 and 2011, show that the most intense methane venting and mat development is currently confined to a 300 X 300 m circular shaped area defined by extremely hummocky terrain. There is a general tendency for venting to be localized at the summit of the hummocks. Venting of methane and hydrogen sulfide-rich fluids support extensive bacterial mats and clam beds. The area is highly dynamic with numerous extinct and active venting sites and extensive carbonate deposits marking past upflow zones.
Southern Hydrate Ridge is an important observatory site to define the temporal evolution of methane hydrate systems in response to seismic events. It is also an important area to quantify material fluxes from the seafloor and the impacts of methane release on overlying ocean chemistry. It provides an excellent opportunity to understand biogeochemical coupling associated with gas hydrate formation and destruction. To meet these needs, the RSN will install a localized cabled array of instruments in 2013 that includes geophysical, chemical, and physical, and biological sensors.
The real-time interactive capabilities of the cabled observatory are critical to studying gas-hydrate systems because many of the key processes may occur over short time scales. Events such as bubble plume formation, the creation of collapse zones, and increased seepage in response to earthquakes will require adaptive response and sampling capabilities that include full resolution sampling by upward-looking sonars, fluid and gas sampling, long-term duration collection of plume and seep imagery from cameras, and in situ manipulation of chemical sensors, which coupled with flow meters, provide estimates of transient and more stable chemical flux. Future infrastructure ideally would include response capabilities by instrumented autonomous vehicles conducting nested surveys within a fence of cabled instrumented moorings (Gas-Hydrate Observatories Workshop, 2007). Such capabilities would provide full water column chemical measurements and quantification of methane flux through the water column.
Location: 44.6ºN 125.1ºW Water Depth: 780-771 meters
- 1 Low-Voltage Node
- 1 Medium-Power Junction Box
- 1 Low-Power Junction Box
- Instruments (pdf above)