'Methane Seep' Ecosystem Discovered off San Diego

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 centred 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" upwards toward the seafloor.

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 metres 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.

The Scripps researchers 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 analysed 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, while many clams at seeps get some of their food from sulfide-loving bacteria living on their gills.

A follow-up cruise is scheduled in December 2012, revisiting the seep to collect additional samples and learn more about this ecosystem. The team of graduate students hopes to raise funds to employ technologies such as video-driven coring instruments and towed video cameras that will give them an up-close look at the methane seep.

The search for local seeps was one focus area of the multidisciplinary San Diego Coastal Expedition, which included teams of students investigating the oceanography and marine ecosystems off San Diego and led by chief scientist Christina Frieder. In addition to Grupe, Pasulka and Maloney, other members of the seep team included geophysics graduate students Valerie Sahakian and Rachel Marcuson.

R/V Melville, the oldest ship in the U.S. academic fleet, is owned by the U.S. Navy and has been operated by Scripps Oceanography for all of its 41 years.