GULF STREAM. The most important and best-known current in the Atlantic Ocean, de riving its name from the Gulf of Mexico. out of which it flows between the coast of Florida on the west and the Bahamas on the east. Its breadth in the narrowest portion is about 50 miles, and its depth about 2000 feet; the velocity averages between two and three miles per hour, reaching an extreme of five or six miles in some localities. This great mass of warm water, having a temperature several degrees higher than the neighboring ocean, flows northeastwardly along the American coast, but can no longer be distinguished from the rest of the ocean drift by either temperature, saltness, color, or motion, after it has passed latitude 40° N. and the meridian 60° W. As it passes the thirty:second parallel between the Bermudas and the coast of Carolina it is divided into several small streams of about 100 fathoms deep and aggregating 150 miles wide. North of this region the increasing westerly winds so break up the surface and mix the waters that it is improper to speak of the Gulf Stream as having any further existence; since it becomes the general drift of warm water from the southwestern Atlantic northeastward to Europe, which is a general phenomenon that has little or nothing to do with the special Gulf Stream, properly so called.
By means of floating derelicts, bottles, and buoys, the general drift of the ocean surface cur rents has been studied with great care. This drift is seen to depend wholly on the wind, and may trend to the northeast or southeast as the winds and storms vary. The majority of the der elicts in the Atlantic Ocean circulate around the Sea of Sargasso, but occasionally one penetrates directly through it. Very rarely does a derelict make its way from America to the European coast. Where the western edge of the so-called Gulf Stream passes by and intermingles with the cold northerly drift, close to the coasts of New foundland and New England, banks of fog are formed; but these are not the fogs that trouble navigation. The latter are due to the flow of warm southwest winds over the cold ocean water, and therefore depend for their existence on the wind rather than on the Gulf Stream. It is a common error to attribute the warmth of Europe, as compared with the cold in America in the same latitude, to the influence of the Gulf Stream; meteorology shows that the southwest winds of Europe, bringing moisture from the ocean, are not appreciably affected by the Gulf Stream. On the other hand, this deep layer of moist southwest wind contains far more latent heat than the same quantity of dry air at the same temperature; and it is the evolution of latent heat by this moist air in the formation of fog, cloud, and rain that raises the temperature of the atmosphere over Europe, and prevents loss of heat by radiation. Precisely the same phe
nomenon is found on the leeward side of each of the Great Lakes, and of the Mediterranean Sea, the Baltic, and probably every other large sheet of water.
The mechanical cause of the Gulf Stream has been clearly expounded by William Ferrel. It is not caused wholly by the winds. The steady northwest trade winds are not strong enough to raise any considerable mass of water in front of them. Hurricane winds may raise the level several feet temporarily, but the trade winds scarcely an inch. The accurate levelings of the Coast and Geodetic Survey have shown that there is no appreciable difference of level between the water in the Gulf of Mexico and that of the Atlantic on the opposite coast of Florida. The Gulf Stream is a result of the general vertical circulation of the ocean, bringing from the north cold water which sinks below, while the warm water of the equatorial region rises, and slides northward above the cold current; owing to the rotation of the earth, each of these currents de viates toward the right, so that the cold cur rent presses toward the southwest and the sur face current toward the northeast. These pres sures are very slight, but by acting for long ages they have given the upper layers of the ocean a slight general rotation. By thus being pushed against the shores or through narrow channels, the mass of water far below the influence of sur face winds is forced to seek its channel of easiest flow, and the cold water flowing through certain passages between the West Indian Islands into the Caribbean Sea flows thence into the Gulf of Mexico, and finally it rounds Cape Sable as warm water from the gulf. The Gulf Stream really has its origin in deep currents far east of the Windward and Leeward Islands, and is pressed northward beyond Cape Sable by the force of the water pushing behind it from the Atlantic Ocean into and through the Caribbean Sea. In other parts of the globe there are great ocean currents that depend wholly upon the winds, but this does not seem to be the case with the Gulf Stream.
BIBLIOGRAPHY. Ferrel, Winds of the Globe Bibliography. Ferrel, Winds of the Globe (New York, 1895) ; Agassiz, Three Cruises of the Blake (Boston, 1888) ; Pillsbury, in Annual Report, published by the United States Coast Survey (Washington, 1800) ; Thomson and Blake, Reports of the Scientific Results of 11. M. S. Challenger (London, 1880-95).