Cold seep

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Tubeworms, soft corals and chemosynthetic mussels at a seep located 3,000 metres down on the Florida Escarpment. Eelpouts, a Galatheid crab and an alvinocarid shrimp feed on mussels damaged during a sampling exercise.

A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs. Cold seeps are distinct from hydrothermal vents: the former's emissions are of the same temperature as the surrounding seawater, whereas the latter's emissions are super-heated. Cold seeps constitute a biome supporting several endemic species.

Entire communities of light independent organisms - known as extremophiles - develop in and around cold seeps, most relying on a symbiotic relationship with chemoautotrophic bacteria. These prokaryotes, both Archaea and Eubacteria, process sulfides and methane through chemosynthesis into chemical energy. Higher organisms, namely vesicomyid clams and siboglinid tube worms use this energy to power their own life processes, and in exchange provide both safety and a reliable source of food for the bacteria. Other bacteria form mats, blanketing sizable areas in the process.

Beggiatoal bacterial mat at a seep on Blake Ridge, off South Carolina. The red dots are range-finding laser beams.

Unlike hydrothermal vents, which are volatile and ephemeral environments, cold seeps emit at a slow and dependable rate. Likely owing to the differing temperatures and stability, cold seep organisms are much longer-lived than those inhabiting hydrothermal vents. Indeed, recent research has revealed that the seep tubeworm Lamellibrachia luymesi may be the longest living noncolonial invertebrate known, with a minimum lifespan of between 170 and 250 years.

Cold seeps were first discovered in 1984 by Dr. Charles Paull in the Gulf of Mexico at a depth of 3,200 metres. Since then, seeps have been discovered in other parts of the world's oceans, including the Monterey Canyon just off Monterey Bay, California, the Sea of Japan, off the Pacific coast of Costa Rica, in the Atlantic off of Africa, in waters off the coast of Alaska, and under an ice shelf in Antarctica [1]. The deepest seep community known is found in the Japan trench at a depth of 7326 m.

Cold seeps develop unique topography over time, where reactions between methane and seawater create carbonate rock formations and reefs. These reactions may also be dependent on bacterial activity. Ikaite, a hydrous calcium carbonate, can be associated with oxidizing methane at cold seeps.