Continental shelf: verschil tussen versies

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Regel 7: Regel 7:
 
The continental shelf is a shallow, near horizontal seafloor extension from the [[shoreline]] to the upper '''continental slope'''. This shelf forms the shallow margin of each deep-ocean basin. At the ocean side it is terminated by a pronounced change in bottom gradient (degree of slope). This is called the '''shelf break'''. The continental shelf is characterized by a very gentle slope less than 1 degree. The average depth is about 150 m and it has an average width of 70 km. But local variations are common, ranging from more than 1000 km in the Arctic Ocean to a few kilometers along the Pacific coast of North and South America. The water above the continental shelf is called '''neritic water'''. Below the shelf break is the continental slope. This zone is much steeper than the continental shelf. At the base of this steep slope is the '''continental rise''' which finally merges into the deep ocean floor, the '''abyssal plain'''. The continental shelf, slope and rise are part of the '''continental margin'''. This is the transition zone between the continental and the oceanic crust.
 
The continental shelf is a shallow, near horizontal seafloor extension from the [[shoreline]] to the upper '''continental slope'''. This shelf forms the shallow margin of each deep-ocean basin. At the ocean side it is terminated by a pronounced change in bottom gradient (degree of slope). This is called the '''shelf break'''. The continental shelf is characterized by a very gentle slope less than 1 degree. The average depth is about 150 m and it has an average width of 70 km. But local variations are common, ranging from more than 1000 km in the Arctic Ocean to a few kilometers along the Pacific coast of North and South America. The water above the continental shelf is called '''neritic water'''. Below the shelf break is the continental slope. This zone is much steeper than the continental shelf. At the base of this steep slope is the '''continental rise''' which finally merges into the deep ocean floor, the '''abyssal plain'''. The continental shelf, slope and rise are part of the '''continental margin'''. This is the transition zone between the continental and the oceanic crust.
  
[[image:Continental_shelf.jpg|center|thumb|400px|caption|Basic composition of the continental margins <ref>http://www.onr.navy.mil/Focus/ocean/regions/oceanfloor2.htm</ref>]]
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[[image:Continental_shelf.png|center|thumb|400px|caption|Basic composition of the continental margins <ref>http://www.onr.navy.mil/Focus/ocean/regions/oceanfloor2.htm</ref>]]
  
 
Generally it is one of the most productive parts of the ocean. Many benthic, coastal animals have evolved larval stages which swim for a time in the water. These larvae are also abundant in the neritic water. Although the continental shelf zones comprise only 7.6% of the surface area of the world oceans, they provide 15-30% of the oceanic [[biological productivity|primary production]]. <ref>Yool A. Fashman M.J.R. 2001. An examination of the ‘continental shelf pump’ in an open ocean general circulation model. Global Biogeochemical Cycles 15(4):831-844</ref>
 
Generally it is one of the most productive parts of the ocean. Many benthic, coastal animals have evolved larval stages which swim for a time in the water. These larvae are also abundant in the neritic water. Although the continental shelf zones comprise only 7.6% of the surface area of the world oceans, they provide 15-30% of the oceanic [[biological productivity|primary production]]. <ref>Yool A. Fashman M.J.R. 2001. An examination of the ‘continental shelf pump’ in an open ocean general circulation model. Global Biogeochemical Cycles 15(4):831-844</ref>
Regel 18: Regel 18:
 
==Shelf sedimentation==
 
==Shelf sedimentation==
  
Energy for eroding and transporting sediment grains is provided by the tides and wind-generated [[waves]] and [[currents]]. In general, waves seem to be the dominant process affecting the sea bottom. Because the continental shelf is shallow, the waves have a large impact on the bottom in comparison to the open ocean. Water becomes increasingly calmer with depth, so the deeper you go, the more your bottom is unaffected by waves. Breaking waves affect the shoreline and remove and suspend all the fine sediment into the water. Only medium and coarse sand and gravel can be deposited on the [[beach]] and in the [[nearshore zone]]. More seaward the bottom energy induced by waves decreases with depth. This causes a decreasing grain size with distance [[offshore]]. Sedimentation under different depositional conditions in the past indicate the past [[sea level rise|sea level]] changes and are known as '''relict sediments'''. This shows the importance of sea level fluctuations for the sediment composition.
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Energy for eroding and transporting sediment grains is provided by the tides and wind-generated [[waves]] and [[currents]]. In general, waves seem to be the dominant process affecting the sea bottom. Because the continental shelf is shallow, the waves have a large impact on the bottom in comparison to the open ocean. Water becomes increasingly calmer with depth, so the deeper you go, the more your bottom is unaffected by waves. Breaking waves affect the shoreline and remove and suspend all the fine sediment into the water. Only medium and coarse sand and gravel can be deposited on the [[beach]] and in the [[nearshore zone]]. More seaward the bottom energy induced by waves decreases with depth. This causes a decreasing grain size with distance offshore. Sedimentation under different depositional conditions in the past indicate the past [[sea level rise|sea level]] changes and are known as '''relict sediments'''. This shows the importance of sea level fluctuations for the sediment composition.

Versie van 14 jul 2008 om 15:44

This article describes the habitat of the continental shelf. It is one of the sub-categories within the section dealing with biodiversity of marine habitats and ecosystems. It gives an overview about the characteristics, processes such as sedimentation and biota. A short section about legal aspects is also added.


Introduction

The continental shelf is a shallow, near horizontal seafloor extension from the shoreline to the upper continental slope. This shelf forms the shallow margin of each deep-ocean basin. At the ocean side it is terminated by a pronounced change in bottom gradient (degree of slope). This is called the shelf break. The continental shelf is characterized by a very gentle slope less than 1 degree. The average depth is about 150 m and it has an average width of 70 km. But local variations are common, ranging from more than 1000 km in the Arctic Ocean to a few kilometers along the Pacific coast of North and South America. The water above the continental shelf is called neritic water. Below the shelf break is the continental slope. This zone is much steeper than the continental shelf. At the base of this steep slope is the continental rise which finally merges into the deep ocean floor, the abyssal plain. The continental shelf, slope and rise are part of the continental margin. This is the transition zone between the continental and the oceanic crust.

Basic composition of the continental margins [1]

Generally it is one of the most productive parts of the ocean. Many benthic, coastal animals have evolved larval stages which swim for a time in the water. These larvae are also abundant in the neritic water. Although the continental shelf zones comprise only 7.6% of the surface area of the world oceans, they provide 15-30% of the oceanic primary production. [2]

Examples of these shelf seas are the Baltic an North Sea, Yellow and East China, Hudson Bay, Bering Sea,…

The global continental shelf (marked in turquoise) [3]


Shelf sedimentation

Energy for eroding and transporting sediment grains is provided by the tides and wind-generated waves and currents. In general, waves seem to be the dominant process affecting the sea bottom. Because the continental shelf is shallow, the waves have a large impact on the bottom in comparison to the open ocean. Water becomes increasingly calmer with depth, so the deeper you go, the more your bottom is unaffected by waves. Breaking waves affect the shoreline and remove and suspend all the fine sediment into the water. Only medium and coarse sand and gravel can be deposited on the beach and in the nearshore zone. More seaward the bottom energy induced by waves decreases with depth. This causes a decreasing grain size with distance offshore. Sedimentation under different depositional conditions in the past indicate the past sea level changes and are known as relict sediments. This shows the importance of sea level fluctuations for the sediment composition.
  1. http://www.onr.navy.mil/Focus/ocean/regions/oceanfloor2.htm
  2. Yool A. Fashman M.J.R. 2001. An examination of the ‘continental shelf pump’ in an open ocean general circulation model. Global Biogeochemical Cycles 15(4):831-844
  3. http://en.wikipedia.org/wiki/Continental_shelf