The continental shelf is the part of each continent that is sometimes called the coastal plain and was a dry part of the continent during the glacial periods, but is undersea between glacial periods. The continental shelf is covered by relatively shallow seas and gulfs. Though the continental shelf is treated as a physical part of the ocean, it is not part of the deep ocean basin proper, but the flooded margins of the continent. In order to determine territorial waters, under the United Nations Convention on the Law of the Sea, the name continental shelf was given a legal definition as the stretch of the seabed adjacent to the shores of a particular country to which it belongs.
The size of the continental shelf varies greatly. It is not uncommon for some areas of the world to have virtually no continental shelf at all. This happens, in particular, where the forward edge of an advancing oceanic tectonic plate dives beneath continental crust in an offshore subduction zone like off the coast of Chile. The Siberian Shelf, in the Arctic Ocean, is the largest continental shelf. This continental shelf stretches to 1500 kilometers in width. The South China Sea lies over another extensive area of continental shelf, Called the Sunda Shelf, which joins Borneo, Sumatra, and Java to the Asian mainland. The North Sea and the Persian Gulf are two other bodies of water that overlay large continental shelves.
The continental shelf usually ends at a point of decreasing slope which is called the shelf break. The sea floor below the break is known as the continental slope. Below the slope is the continental rise, which finally merges into the deep ocean floor. The continental shelf and the slope are part of the continental margin. The continental shelf area is commonly subdivided into three areas: the inner continental shelf, mid continental shelf, and the outer continental shelf, each with their specific geology and marine life. The character of the shelf changes dramatically at the shelf break, where the continental slope begins. With very few exceptions, the shelf break is located at a uniform depth of roughly 140 m. This is probably related to the extent of the flow of past glaciers. The continental shelf is covered by terrigenous sediments which means they are derived from the erosion of the continents, but very little of the sediment is from current rivers; some 60-70% of the sediment on the world’s continental shelves was deposited during the last ice age, when sea level was 100-120 m lower than it is now.
There is a good article about the continental shelf here. We have a great article about the seven continents of Earth here on Universe Today. Astronomy Cast offers a good episode about the many aspects of the planet Earth.
Sources:
http://www.earthfacts.net/earth-dynamics/continentalshelf/
http://www.eoearth.org/article/Coastal_zone?topic=58074
Comments on this entry are closed.