Geology Reference
In-Depth Information
Figure 4 The surface circulation in the ocean
(Adapted from Stowe, 1979.
4
)
maintain the superimposed flow fields. This process is called upwelling
and is of considerable importance in that biochemical respiration of
organic material at depth ensures that the ascending water is nutrient-
rich. Upwelling occurs notably in the eastern oceanic boundaries where
longshore winds result in the offshore transport of the surface water.
Examples are found off the coasts of Peru and West Africa. Similar
processes cause upwelling in the Arabian Sea, but this is seasonal due to
the monsoon effect. A divergence is a zone in which the flow fields
separate. In such a case, upwelling may result as observed in the equa-
torial Pacific. It should be noted that a region in which the streamlines
come together is known as a convergence, and the water sinks in this zone.
The density of the water controls the deepwater circulation. If the
density of a water body increases, it has a tendency to sink. Subsequently,
it will spread out over a horizon of uniform s
y
. As the density can be
raised due to either an increase in the salinity or a decrease in the
temperature, the deepwater circulatory system is also known as thermoh-
aline circulation. As shown in Figure 5 of the ocean conveyor belt, the
densest oceanic waters are formed in Polar Regions due to the relatively
low temperatures and the salinity increase that results from ice formation.
Antarctic Bottom Water (ABW) is generated in the Weddell Sea and flows
northward into the South Atlantic. North Atlantic Deep Water (NADW)
