Antilles Current and east of the Grand Banks is known as the Gulf Stream
The part of the Gulf Stream System between the meeting place of the Florida and Antilles Current and east of the Grand Banks is known as the Gulf Stream.
It follows the continental slope between the Florida Strait and Cape Haterras and then continues in a narrow band towards the east. The Gulf Stream appears like a river in the ocean. It transports huge quantity of water i.e. about 55 x 106m3 per second.
The width of the main current is about 50 km. According to Stommel, the Gulf Stream is a narrow band of high velocity water which forms the boundary between the two entirely different water masses.
Because of the presence of this current the warm water in the Sargasso Sea is not allowed to flow over the cool and dense coastal water. There is a great difference between the surface temperature of this current and that of the marginal seas of the continent.
For example, the temperature recorded on the southern portion of the Gulf Stream is about 20°C during winter, whereas the temperature of the coastal waters is only 14°C.
A sea traveler named Lescarbot observed that in a vertical cross-section the Gulf Stream can be divided into three distinct layers: (i) The surface layer is a few meters thick and is marked by the seasonal variation of temperature, (ii) Below the surface layer there is another layer in which there is a rapid decrease of temperature with increasing depth.
This layer is called the main thermo-cline. (iii) Under the third layer there is a very thick layer of cold water below 1500 meters. Let us remember that the high velocity movement of water in the Gulf Stream is confined to its surface layers only.
Generally the surface waters of the Gulf Stream are characterized by a very rapid movement. On the basis of measurements made by Iselin the Gulf Stream flows with a velocity of 120- 140cm. per second.
According to Dietrich and Iselin, the total transport of water amounts to about 75 to 93 million cubic meters per second near the Chesapeake Bay. To the east and west of the Stream distinctive water masses are present.
The influence of the bottom relief of the ocean on the path of motion of the Gulf Stream is clearly discernible. Up to 33°N latitude it flows along the Blake Plateau at about 800 meter depth, but beyond this the depth of the ocean varies from 4000 to 5000 meters.
It is interesting to note that since its movement below 1500 meters is rather slow, the bottom relief does not affect its position, and its influence is negligible.
The limits of the Gulf Stream are determined by the characteristics of its surface waters like the colour change and the lines of Sargassum seaweed.
However, the inner edge or the western boundary of the current is defined by the pressure gradient between the warm, saline water to the south-east, and the fresh and cold water to the north-west.
The warm core of the Gulf Stream has been defined as that part of the Stream in which water is warmer than that at the same depth to the east. Usually it is at 300 to 400 meters. At the left side of the warm core there are sudden changes in the surface temperature, colour of water, and other features.
Another characteristic feature of the Gulf Stream is that there are large eddies and meanders in it. However, these meanders, eddies and filaments are not permanent; they appear and disappear.
The wave length of some of these meanders may be as much as 200 km. When the Gulf Stream merges into the North Atlantic Drift near 40″N latitude, the meanders break up into several eddies.
An additional peculiarity connected with the Gulf Stream is the gradual rising of the water level along the coast of the United States of America. The direction of the increasing sea-level is from south to north.
The difference between the sea levels at Florida and Halifax is about 35cm. Because of the difference in the sea level a down-slope current is produced which flows along the coast and continental shelf from north to south.
It is possible due to the piling-up of water in the north-western part of the North Atlantic Ocean brought about by the south-west wind. This coastal current carries very cold water towards the south.
Thus, the left side boundary of the Gulf Stream becomes more distinct due to the greater difference in the temperature of the stream and the adjacent coastal water. The coastal water being very cold, this boundary is called the cold wall.
The presence of cold water between the Gulf Stream and the U.S. coast has involved various arguments. Some think that enormous quantity of water brought by the rivers with low temperature flows towards the south along the coast.
Besides the inflow of various rivers, the water of the Gulf of St. Lawrence is an additional factor in increasing the cold water mass, while there is another school of oceanographers in whose opinion the extreme cold of the interior of the landmass exercises its influence on the coastal waters.
But a number of oceanographers believe that the westerlies, the off-shore winds, drive the warm water away from the coast, and to compensate the loss of water in the coastal sea, there is an upwelling of deeper cold water towards the surface.
Besides, the cold Labrador Current brings the cold water mass with it up to the Cape Haterras. As stated earlier, the Gulf Stream proper is confined between the Cape Haterras and the Grand Banks, and in this region the Gulf Stream flows along the east coast of the United States of America.
After crossing 40°N latitude, the Gulf Stream under the influence of the prevailing westerles changes its direction of flow towards the east. In addition to the influence of the westerlies, the Coriolis force is an important factor in changing the direction of this current.
On its onward journey the Gulf Stream loses its identity and is bifurcated into various branches. Numerous eddies and counter currents originate between these branches.
This northerly extension of the Gulf Stream is known as the North Atlantic Drift which consists of several broader bands or filaments of current.
It is worth while to remember that besides carrying an enormous quantity of water northwards, the Gulf Stream carries with it a considerable amount of heat as well. According to Defant, the amount of salt carried north is about 1,210,000 tons per second.
The North Atlantic Drift conveys the warm water in the high latitudes, and it is clear in the distribution of sea-surface isotherms. There is a distinct zonal contrast in the waters between Norway and Greenland.
It is a well-known fact that the coastal waters and fiords of Norway are open to shipping throughout the year, even beyond the Arctic Circle.
On the contrary, the coast of eastern Greenland is not accessible to shipping for most of the year. The difference between the average temperature for a particular place and the average for the latitude is as much as 27°C.