7.7 Continental Shelf Flow
235
The continental shelves are also used as a final destination for various types
of anthropogenic materials, and all types of pollutants, such as sewage, heavy
metals, petroleum compounds and toxic pesticides. The efficiency of removing
these waste contaminants from their source is dependent on the mixing and
dispersion due to wave and tidal action. These processes are discussed in
detail in the next chapter. However, it should be noted that the capacity of
the ocean to disperse anthropogenic contaminants is not boundless. There
are cases, where due to alterations in water quality, the food web has been
interrupted and local fisheries have collapsed.
At present, the tendency to consider the continental shelves as systems with
interactive living and non-living elements prevails. There are various attempts
to categorize continental shelves, depending on the factors which shape them.
As far as water flows on the continental shelves are concerned, the most important factors are the location of the shelf on the ocean boundary (eastern
or western boundary), presence or absence of large rivers, and shelf width. In
the next section we illustrate the influence of these factors by some specific
examples. We start with flows at western boundaries.
7.7.2 Western Boundary Currents
As was shown in Fig. 7.6, western boundary currents are part of the main ocean
gyres in the Pacific, Atlantic and Indian Ocean. In the Northern Hemisphere,
these currents flow north along the western boundaries of the ocean basins,
while in the Southern Hemisphere they flow south. All western boundary currents have a number of common features. They form narrow streams along
the western continental rise of ocean basins and they extend to great depths,
well below the thermocline. Usually at some point they separate from the basin
boundary and continue to flow into the open ocean as narrow jets. This jet-like
flows create many instabilities along their paths. However, due to variations in
bottom topography, each current possesses its own individual characteristics.
The magnitude of some western boundary currents are: 50 Sv for the Kuroshio,
30 Sv for the Gulf Stream and the Brazil current, 25 Sv for the East Australian
Current, and 70 Sv for the Agulhas Current. Let us note that, for example,
a discharge of 50 Sv means that 4000 cubic kilometres of water is transported
per day (Tomczak and Godfrey, 1994).
Probably the most studied western boundary currents are the Gulf Stream
in the Atlantic Ocean and the Kuroshio in the Pacific. There is extended
professional literature on these currents, for example Stommel (1965), Pickard
and Emery (1982), Tomczak and Godfrey (1994), Stommel and Yoshida (1972),
Mizuno and White (1983), and others. Therefore, in this section we describe
two other western boundary currents flowing in the Southern Hemisphere, i. e.
the East Australian Current in the Pacific, and Agulhas Current in the Indian
Ocean.
East Australian Current. This current is one of the weakest western boundary currents. Its low transport volume results from the fact that part of the
235
The continental shelves are also used as a final destination for various types
of anthropogenic materials, and all types of pollutants, such as sewage, heavy
metals, petroleum compounds and toxic pesticides. The efficiency of removing
these waste contaminants from their source is dependent on the mixing and
dispersion due to wave and tidal action. These processes are discussed in
detail in the next chapter. However, it should be noted that the capacity of
the ocean to disperse anthropogenic contaminants is not boundless. There
are cases, where due to alterations in water quality, the food web has been
interrupted and local fisheries have collapsed.
At present, the tendency to consider the continental shelves as systems with
interactive living and non-living elements prevails. There are various attempts
to categorize continental shelves, depending on the factors which shape them.
As far as water flows on the continental shelves are concerned, the most important factors are the location of the shelf on the ocean boundary (eastern
or western boundary), presence or absence of large rivers, and shelf width. In
the next section we illustrate the influence of these factors by some specific
examples. We start with flows at western boundaries.
7.7.2 Western Boundary Currents
As was shown in Fig. 7.6, western boundary currents are part of the main ocean
gyres in the Pacific, Atlantic and Indian Ocean. In the Northern Hemisphere,
these currents flow north along the western boundaries of the ocean basins,
while in the Southern Hemisphere they flow south. All western boundary currents have a number of common features. They form narrow streams along
the western continental rise of ocean basins and they extend to great depths,
well below the thermocline. Usually at some point they separate from the basin
boundary and continue to flow into the open ocean as narrow jets. This jet-like
flows create many instabilities along their paths. However, due to variations in
bottom topography, each current possesses its own individual characteristics.
The magnitude of some western boundary currents are: 50 Sv for the Kuroshio,
30 Sv for the Gulf Stream and the Brazil current, 25 Sv for the East Australian
Current, and 70 Sv for the Agulhas Current. Let us note that, for example,
a discharge of 50 Sv means that 4000 cubic kilometres of water is transported
per day (Tomczak and Godfrey, 1994).
Probably the most studied western boundary currents are the Gulf Stream
in the Atlantic Ocean and the Kuroshio in the Pacific. There is extended
professional literature on these currents, for example Stommel (1965), Pickard
and Emery (1982), Tomczak and Godfrey (1994), Stommel and Yoshida (1972),
Mizuno and White (1983), and others. Therefore, in this section we describe
two other western boundary currents flowing in the Southern Hemisphere, i. e.
the East Australian Current in the Pacific, and Agulhas Current in the Indian
Ocean.
East Australian Current. This current is one of the weakest western boundary currents. Its low transport volume results from the fact that part of the