Submarine canyons are steep-sided valleys extending along the continental shelf and into the continental slopes. Some submarine canyons are extensions of rivers or continental faults. A continental shelf is the part of a continent that extends under the sea shore and into the deep-ocean floor. Even though continental shelves lie under water, they are part of a continent. The actual limit of a continent is not the coastline, but the edge of the continental shelf. A continental shelf average 65 km (40 miles) in width. Deep canyons and channels are found along the edges of continental shelves.
A continental shelf extends from the line along the coast to a point known as the shelf break, from where the continental shelf continues descending through a steeper slope and into the deep ocean floor in what is known as the continental slope. In most coastal regions, continental shelves extend for less than one km (0.62 miles), for instance the coast along the state of California; however, in other regions, continental shelves may extend for up to 1,000 km (620 miles), such as the Northern coast of Siberia. The average depth of a continental shelf is 60 m (197 ft.), allowing the penetration of sunlight, and the conditions for sea life to flourish.
Submarine canyons are steep-sided valleys lying on the sea floor of continental slopes, sometimes extending onto the deep ocean floor. Many submarine canyons may continue as submarine channels (abyssal channels) for hundreds of kilometers along the deep ocean sea floor. Little light penetrates submarine canyons. Often, submarine canyons are found as extensions to large river flows. Some others have been found to coincide with geologic faults, such as the Carmel Canyon, which is a tributary to the Monterrey Bay and coincides with the San Gregorio fault.
There are a number of theories about the formation of submarine canyons. One theory states that submarine canyons were shaped during glacial times when sea levels were below present sea level, and river streams reached the edges of the continental shelf; however, subaerial river erosion could not have been possible to water depths of up to 300 meters (984 ft.), where canyons have been mapped. Another theory suggests that they could have been carved by erosion and sediment transport of their overlying layers produced by landslides and water turbidity. Other potential triggers include tidal fluctuation, storms, earthquakes, and density water currents.
The landslides from submarine canyon walls deposit sediments on the canyon floor. The nutrients contained within the sediments provide nutrients for deep-ocean organisms. Most organisms found in submarine canyons are not unique to them, but are also found in other sea habitats. Because submarine canyons occupy extensions varying from shallow waters to the deep ocean waters, they host a diversity of ocean life. Rocky protrusions along canyon walls are inhabited by invertebrates, including corals, feather stars, and tunicates. Canyon walls provide habitat for a number of fish, clam, and worms. Soft sediments deposited in the canyon floor provide nutrients for a diverse community of invertebrates and fishes.
The Monterrey canyon in Monterrey bay, California is the largest submarine canyon along the West coast of North America, extending 153 km (95 miles) into the Pacific Ocean, and reaching depths of more than 3,600 meters (11,800 ft.). The Monterrey submarine canyon provides a perfect setting for scientific research on deep ocean marine life. The largest submarine canyon is the Zhemchug canyon in the middle of the Bering Sea. With a depth of 2.6 km (1.6 miles), the Zhemchug Canyon has a drainage area of 11,350 km2 (7,000 miles2) and a volume area of 5,800 km (3,600 miles2).
Submarine canyons are vulnerable to human activity. Organic pollutants, such as DDT and PCBs have been found in the fishes in Monterrey Submarine Canyon The risk of contaminant accumulation is greater in submarine canyons because the flow of sediments and pollutants tends to concentrate at the very depths of the canyon. Most of the sediment carried by long shore currents ends up in the depths of submarine canyons. According to jstor.org, canyons serve as sediment confinement for large concentrations of trace metals and organic compounds.