Continental shelf
From Palaeos
Contents |
[edit] Introduction
The continental shelf refers to the shallow sea bottom just offshore of most continents between the water's edge and the point of increasing slope, a sharp drop-off where the bottom plunges steeply, known as the continental slope.
The continental shelf is submerged during periods of higher sea level, when it is covered by shallow seas (shelf seas) and gulfs. During glacial periods the sea level drops and the shelf becomes dry land, such as happened during the Pleistocene glaciations. Conversely, during warmer periods where the polar ice melts, the sea transgresses over the land, submerging the continental shelf further and creating inland seas.
[edit] Sediments
The continental shelves are covered by terrigenous sediments; that is, those derived from erosion of the continents.
Today, little of the sediment is from current rivers; some 60-70% of the sediment on the world's shelves is relict sediment, deposited during the last ice age, when sea level was 100-120 m lower than it is now.
Sediments usually become increasingly fine with distance from the coast; sand is limited to shallow, wave-agitated waters, while silt and clays are deposited in quieter, deep water far offshore. These shelf sediments accumulate at an average rate of 30 cm/1000 years, with a range from 15-40 cm, which is much faster than that for deep-sea pelagic sediments.
[edit] Biota
Because of the sunlight available in shallow waters, the continental shelves teem with life compared to deeper waters. The pelagic (water column) environment of the continental shelf constitutes the neritic zone, and the benthic (sea floor) province of the shelf is the sublittoral zone.
[edit] References
- Gross, Grant M. Oceanography: A View of the Earth. Englewood Cliffs: Prentice-Hall, Inc., 1972. ISBN 0-13-629659-9
- Pinet, Paul R. (1996) Invitation to Oceanography. St. Paul, MN: West Publishing Co., 1996. ISBN 0-7637-2136-0 (3rd ed.)
