Continental shelf
Submerged edge of a continent, rich in life and resources.
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island is known as an 'insular shelf.' The continental margin, between the continental shelf and the abyssal plain, comprises a steep continental slope, surrounded by the flatter continental rise, in which sediment from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope. The shelf usually ends at a point of increasing slope called the shelf break, below which is the continental slope, then the continental rise, merging into the abyssal plain. Continental shelves cover about 27 million km², equal to about 7% of the ocean surface, and are the best understood part of the ocean floor due to their relative accessibility.
- area
- about 27 million km² (10 million sq mi)
- average_width
- about 80 km (50 mi)
- average_slope
- about 0.5°
- sediment_accumulation_rate
- 15–40 cm per millennium
- global_primary_productivity_support
- 15–20%
Lore & Background
The continental shelf is a physiographic province of the ocean, but it is not part of the deep ocean basin proper; it is the flooded margin of the continent. The shelf area is commonly subdivided into inner, mid, and outer continental shelf, each with specific geomorphology and marine biology. The character of the shelf changes dramatically at the shelf break, where the continental slope begins. The continental slope is much steeper, with an average angle of 3°, and is often cut with submarine canyons, whose formation mechanisms were not well understood until the 1960s.
Reader's Guide
Continental shelves are of great significance because they support a disproportionate share of marine life and human economic activity. Despite covering only about 8% of Earth's ocean surface area, shelf seas support 15–20% of global primary productivity, due to sunlight in shallow waters and mixing from tides and currents. Most commercial exploitation of the sea, such as offshore drilling for hydrocarbons and extraction of metallic and non-metallic ore, takes place on the continental shelf. This legal definition differs significantly from the geological one, granting sovereign rights even to volcanic islands that have no actual continental shelf. The shelves are covered by terrigenous sediments, with 60–70% being relict sediment from the last ice age. Their economic and ecological importance makes them a focus of ongoing research, including studies of changing wind, rainfall, and ocean currents in a warming climate.
Did You Know?
- About 60–70% of sediment on the world's shelves is relict sediment deposited during the last ice age.
- Shelf seas support 15–20% of global primary productivity despite covering only about 8% of the ocean surface.
Frequently Asked Questions
Who is Continental shelf?
A continental shelf is the submerged, gently sloping extension of a continent that lies beneath a shallow body of water called a shelf sea. It typically stretches about 80 km from the coastline and remains shallower than 100 m across most of its surface.
What are Continental shelf's powers/role?
The shelf serves as a biological and economic powerhouse, supporting dense marine ecosystems and harboring significant mineral and energy deposits. Its gentle gradient of roughly 0.5° lets sunlight reach the seafloor, driving productivity that the deep ocean simply cannot match.
Why is Continental shelf important?
Spanning roughly 27 million km², the shelf is one of the most biologically and economically productive zones on the planet, hosting major fisheries and hydrocarbon reserves. During glacial periods, falling sea levels exposed much of this area as dry land, dramatically reshaping coastlines and habitats.
What are Continental shelf's key stats?
The shelf averages about 80 km in width, stays under 100 m deep, and accumulates sediment at a rate of 15 to 40 cm per millennium. Where an island sits on a shelf, that surrounding zone is specifically called an insular shelf.
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