Expedition evidence reveals features of a unique deep-sea gas environment;
Return voyage planned for December for further exploration
Scripps Institution of Oceanography / University of California, San Diego:
During a recent oceanographic expedition off San Diego, graduate student researchers from Scripps Institution of Oceanography at UC San Diego discovered convincing evidence of a deep-sea site where methane is likely seeping out of the seafloor, the first such finding off San Diego County.
Such "methane seeps" are fascinating environments because of their extraordinary chemical features and often bizarre marine life. The area of interest, roughly 20 miles west of Del Mar, is centered on a fault zone known as the San Diego Trough Fault zone. Methane, a clear, highly combustible gas, exists in the earth's crust under the seafloor along many of the world's continental margins. Faults can provide a pathway for methane to "seep" upward toward the seafloor.
Ben Grupe (pointing), Blanka Lederer and Alexis Pasulka during the San Diego Coastal Expedition.
The Scripps graduate students made the discovery during the recent San Diego Coastal Expedition (bit.ly/sdcoastex), a multidisciplinary voyage conceived and executed by Scripps graduate students. The cruise was funded by the University of California Ship Funds Program, which supports student research at sea and provides seagoing leadership opportunities.
While conducting surveys in search of methane seeps aboard Scripps' research vessel Melville, the graduate students mapped a distinct mound on the seafloor at 1,036 meters depth (3,400 feet), spanning the size of a city block and rising to the height of a two-story building. The area had been recommended by Jamie Conrad, Holly Ryan (U.S. Geological Survey) and Charles Paull (Monterey Bay Aquarium Research Institute), who surveyed the faults in 2010.
A sediment core sample reveals black marks where sulfide is present, an indication of a methane seep environment.
"Below the mound," described Scripps geosciences graduate student Jillian Maloney, "we observed a disruption in subsurface sediment layers indicative of fluid seepage."
The Scripps researchers then deployed instruments to collect sediment cores, gathering further evidence such as seep-dwelling animals, sulfidic-smelling black mud and carbonate nodules. These samples are currently being analyzed in Scripps laboratories for chemical clues and other telling elements of the environment.
Organisms collected from the site include thread-like tubeworms called siboglinids and several clams. Siboglinids lack a mouth and digestive system and gain nutrition via a symbiotic relationship with bacteria living inside them%2