Where the equatorial current comes out from tne Gulf of Mexico between Florida and Cuba it begins to be known as the Gulf Stream. It is the strongest ocean current that we know of, the only one that moves like a great river. In the Straits of Florida it has a depth of 2000 to 3000 feet, a width of about 40 miles in the narrowest part, and a velocity of nearly five miles an hour. As it comes out into the main Atlantic, however, it quickly loses its river-like quality and spreads into a broad shallow sheet which moves more and more slowly until its rate is only half a mile an hour. Although it keeps away from the immediate coast of the United States, its influence can be felt as far north as Cape Cod. Because of its presence the water on the south side of that cape is distinctly warmer than on the north, as everyone knows who has bathed in both places. When vessels sail from New York to Europe the passengers can easily detect the time when the vessel enters the stream, for the air becomes warmer, the water changes color, and jelly-fish and other forms of life become more abundant.
How the Atlantic Drift Modifies the Climate of Europe.—As the Gulf Stream is driven eastward by the prevailing westerlies it spreads out to a breadth of hundreds of miles and becomes the Atlantic "Drift." On the eastern side of the Atlantic part turns south and finally rejoins the equatorial current, while part passes northeast ward to the Arctic Ocean past Norway. In the North Atlantic the Drift spreads over the ocean's surface so widely that the winds blowing from the Atlantic Ocean to Europe are warmed, for they absorb some of the heat brought by the current from equatorial regions. Hence the winds blowing from the Atlantic Ocean to Europe are warmer than those blowing from the Pacific to our own continent. This is one reason why the most progressive and populous parts of Europe are about or 700 miles, farther north than the corresponding parts of North America. It must be remembered, however, that the westerly winds from the North Atlantic would give western Europe a decidedly warmer climate than Labrador even though there were no warm ocean current in the Atlantic.
The Effect of the Cold Labrador Current.—Since the Gulf Drift pours part of its waters into the Arctic Ocean, a return current is caused. This cold Arctic current creeps along the eastern coast of Greenland to Labrador and thence to New England. The Labrador Current, as it is called, is of considerable influence in causing the east winds of New England to be cool and raw. Its pres ence explains why sea-bathing is so much less common at the summer resorts of Maine than on the south shore of Cape Cod, for example.
It also explains the fogs in which the fishermen on the Grand Banks of Newfoundland are sometimes lost and perish. When south winds reach the Labrador Current they are cooled so much that their mois ture condenses. This causes frequent fogs not only on the Grand Banks of Newfoundland, but along the coasts of Maine and Nova Scotia. The dangers of the Grand Banks are increased by the ice bergs which the Labrador Current brings southward from Davis Strait. Not only are the icebergs dangerous in themselves, but their low temperature increases the fog. Fig. 76 is the official sailing chart of the North Atlantic for August. Notice how many foggy days occur near the Grand Banks. The dangers there are so great that since the Titanic was sunk by hitting an iceberg in 1912, the great North Atlantic trade route has been lengthened a little to carry it south of the Banks, The Oceanic Whirls.—Each of the other oceans, like the Atlantic, has a series of currents which are kept circling around by the prevail ing winds. The equatorial part of the Pacific whirl, as it may be called, is deflected northward like that of the Atlantic, but not to so great an extent. Nevertheless, the equatorial waters flowing north ward along the west coast of Asia warm the winds sufficiently to make the east side of Japan distinctly warmer than the northwest side, just as the south of Cape Cod is warmer than the north. Even in Alaska the effect of the warming of the water in distant equatorial regions can be felt in the fact that on the south coast the harbors are free from ice in winter.
In the southern hemisphere the whirls of the ocean currents go in the opposite direction from those of the northern hemisphere, since the winds, as we have seen, are deflected to the right in the north and the left in the south. Beyond the southern limit of the whirls an almost unbroken current flows eastward encircling Antarctica. It adds its effect to that of the "roaring forties," as the westerlies are called, in making navigation difficult. Captains of sailing vessels who have to navigate in this region often prefer to go two or three thousand miles extra and travel around the world with the winds and currents rather than to take a shorter course against them.
In the Indian Ocean there are currents like those of the larger oceans. In that region, however, the monsoon winds blow in op posite directions in different seasons, and the currents are corre spondingly reversed.