The Gulf Stream

is the second largest ocean current, after the Antarctic Circumpolar Current. It has its source in the warm waters of the eastern part of the Gulf of Mexico. These waters pass through the Straits of Florida to become the Gulf Stream, which flows northeastward from approximately Cape Hatteras, North Carolina, across the Atlantic toward Europe. At its greatest the Gulf Stream is approximately 100 miles wide and several hundred feet deep -- far larger than any river on earth. It also flows faster than any known river, up to 138 miles (222 kilometers) a day. Measured in volume per second, the Gulf Stream moves about 1,000 times faster than does the Mississippi River.

After the Gulf Stream flows through the Straits of Florida, it passes the Little Bahama Bank, where it is joined by the Antilles Current. The combined current continues northward, widening and slowing as it goes. The Gulf Stream forms the northwest boundary of the Sargasso Sea, separating the warm waters of that sea from the chill waters of the North Atlantic. The stream, about 50 miles (80 kilometers) wide and 3,000 feet (910 meters) deep, then follows the Atlantic coast of North America. A narrow strip of cold water, called the "cold wall," separates the Gulf Stream from the coast. By the time the Gulf Stream reaches Charleston, South Carolina, it has slowed to about 40 miles (64 kilometers) a day. At the Newfoundland Banks it is only moving about 10 miles (16 kilometers) a day and is no longer a strong current. From there it spreads out and becomes a general drift of warm water that moves eastward toward Europe. This part of the stream is known as the North Atlantic Current.

The North Atlantic Current divides into three branches just east of the Grand Banks. The main branch flows generally northeastward towards the British Isles, one branch flows north towards Iceland, and the other flows east and then south along the western coast of Africa.

The Gulf Stream may be partly responsible for the warm southwesterly winds that make the climate of Great Britain and northwestern Europe much warmer than parts of North America that lie equally far north. These winds pick up heat and moisture from the Sargasso Sea and the Gulf Stream. The winds also greatly influence the climate of the countries they touch. For example, the average January temperature in northern Norway is about 45° F. (7° C), higher than normal for that latitude. The warm waters of the Gulf Stream keep many ports in northwestern Europe ice-free all winter. Hammerfest, Norway, for example, is an important sea-fishing center in winter, while Riga, Latvia, 800 miles (1,300 kilometers) south of Hammerfest, is icebound.

satellite view showing sea surface temperatures

In the sea surface temperature image at left, the warm waters (yellow) of the Gulf Stream snake from bottom left to top right, showing several deep bends in the path. In fact, the northernmost of the two deep bends actually loops back on itself, creating a closed-off eddy. On the northern side of the current, cold waters (blue) dip southward into the Gulf Stream's warmth.

Often chlorophyll, which indicates the presence of marine plant life, is higher (yellow) along boundaries between cool and warm waters, where currents are mixing up nutrient-rich water from deep in the ocean. Many of the temperature boundaries along the loops in the Gulf Stream are mirrored in the chlorophyll image at right with a stripe of lighter blue or yellow, indicating elevated chlorophyll.

satellite view showing chlorophyll concentration

Winds and currents are the main cause of the Gulf Stream. Trade winds cause a westerly flow of water where the Atlantic Ocean crosses the equator. These westerly currents are called the North and South Equatorial currents. The South Equatorial Current flows west to strike the north coast of Brazil, where two-fifths of its waters are directed into the Caribbean Sea. As it flows into the Caribbean, the South Equatorial Current reinforces the warm waters of the North Equatorial Current. The combined equatorial currents then flow through the narrow Yucatan Channel and through the Straits of Florida to become the Gulf Stream.