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the water being more dense and heavier than the surrounding ocean water has the
tendency to “fall down,” i.e., to stream vertically down to the ocean bottom. At depths
near the bottom, the Gulf Stream merely changes its direction and fl ows to the south
even though there is no slope of water level related to its new direction of fl ow. A
similar occurrence of ocean water fl owing downward is observed when the salinity
of water increases and provides a second reason why the Gulf Stream changes its
direction. As the warmer water of the Gulf Stream compared with that of the sur-
rounding ocean moves to the north, evaporation is higher and none of its salts evapo-
rate with water molecules. During its long trip from the Equatorial region to the
Arctic Ocean, the salinity of the Gulf Stream increases. Prevailing winds blowing to
the East also infl uence the direction of the Gulf Stream (Fig. 9.1 ).
Knowing that the fl ow of water in the ocean on a megascale is infl uenced by
several acting factors, or forces, we shall merely add them together and analytically
transform them into potentials. The difference of potentials between two locations,
or better expressed as a potential gradient, determines the direction of fl ow.
Moreover, the higher magnitude of this gradient, the greater is the velocity or the
rate of water fl ow. The potential gradient for an ocean current or stream on a global
Fig. 9.1 Gulf Stream is a part of global ocean circulation - thermohaline circulation. It starts in
the Mexican Gulf and fl ows to the north and to the northeast. It is warming up the parts of North
America and of the Western Europe. Far on the north the waters cool and increase their salinity.
Several branches of the stream fl ow therefore down to the ocean bottom and fl ow as bottom stream
to the south
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