Difference between revisions of "Template:This weeks featured article"

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(Coastal Hydrodynamics And Transport Processes)
(Marine Plankton)
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==Coastal Hydrodynamics And Transport Processes==
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==Marine Plankton==
  
[[Image:tombolo2.jpg|thumb|300px|right|Tombolo formation behind coastal breakwater, an example of the result of coastal transport processes]]
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[[Image:coscinodiscuswailesii_pnw.jpg|thumb|left|250px|''The diatom'' Coscinodiscus wailesii. ''The two ‘valves’ of the cell can be seen in the top left image. Image taken by M. Hoppenrath, provided courtesy of Plankton*Net (image # 12641) <ref name = "Plankton Net"> Plankton Net; Data Provider at the Alfred Wegener Insitute for Polar and Marine Research: http://planktonnet.awi.de/</ref>.'']]
  
The hydrodynamic conditions or processes, that come about from [[Tidal wave|waves]] transforming over a coastal profile and generating wave set up and [[Longshore current|longshore currents]], will result in movement and transport of the sediments (e.g. sand) present in the profile. This is referred to as ''littoral transport processes'' and is the main subject of this article. However, transport of fine sediments will also be discussed, but only very briefly.
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[[Plankton]] consists of a diverse range of living organisms that spend at least a part of their life cycle suspended in water. The term [[plankton]] is actually a Greek word, meaning ''that which is made to wander or drift''. This term is further divided into the [[phytoplankton]] and [[zooplankton]], meaning plant- (Gk. ''phyto'') and animal- (Gk. ''zoön'') drifters respectively.  
  
The sediment on the seabed is transported when it is exposed to large enough forces, or ''shear stresses'', by the water movements. These movements can be caused by the current or by the wave orbital velocities or a combination of both, the latter being the most important situation. The relevant parameters for the description of the sediment transport along a shoreline or in a coastal area are therefore the following:
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Planktonic organisms may have a limited ability to control their fine-scale distribution in the water column, but are otherwise at the mercy of oceanic currents and water movements. Holoplantkon refers to those organisms that spend their entire life in the plankton, as opposed to the meroplantkon, which are only planktonic for a part of their lives. Organisms that are capable of resisting the powers of currents, such as fish and squid, are referred to as neckton.
  
*The wave conditions at the site and the possible variations over the site plus the adjoining areas
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Planktonic organisms are typically classified into broad size categories according to the ''' ‘Sieburth-scale’ ''', originally proposed in 1978. Viruses and jelly fish sit at opposite ends of this scale, which runs from fractions of a millimetre to metres.
*The current conditions as well as the variations of these over the area
 
*The water-level conditions, i.e. tide, storm surge and wave set-up
 
*The [[bathymetry]] (the depth variations) in the area
 
*The [[sediment]] characteristics over the area
 
*The sources and sinks of sediment, such as rivers, eroding coasts or tidal inlets
 

Revision as of 08:47, 6 October 2009

Marine Plankton

The diatom Coscinodiscus wailesii. The two ‘valves’ of the cell can be seen in the top left image. Image taken by M. Hoppenrath, provided courtesy of Plankton*Net (image # 12641) [1].

Plankton consists of a diverse range of living organisms that spend at least a part of their life cycle suspended in water. The term plankton is actually a Greek word, meaning that which is made to wander or drift. This term is further divided into the phytoplankton and zooplankton, meaning plant- (Gk. phyto) and animal- (Gk. zoön) drifters respectively.

Planktonic organisms may have a limited ability to control their fine-scale distribution in the water column, but are otherwise at the mercy of oceanic currents and water movements. Holoplantkon refers to those organisms that spend their entire life in the plankton, as opposed to the meroplantkon, which are only planktonic for a part of their lives. Organisms that are capable of resisting the powers of currents, such as fish and squid, are referred to as neckton.

Planktonic organisms are typically classified into broad size categories according to the ‘Sieburth-scale’ , originally proposed in 1978. Viruses and jelly fish sit at opposite ends of this scale, which runs from fractions of a millimetre to metres.
  1. Plankton Net; Data Provider at the Alfred Wegener Insitute for Polar and Marine Research: http://planktonnet.awi.de/