Beginning in the Caribbean and ending in the northern North Atlantic, the Gulf Stream System is one of the world’s most powerful and intensely studied current systems. The Stream is the fastest ocean current in the world.  Off the Atlantic seaboard of the United States, the Gulf Stream flows at a rate nearly 300 times faster than the typical flow of the Amazon River. The velocity of the current is fastest near the surface, with the maximum speed typically about 5.6 miles per hour (nine kilometers per hour). The average speed of the Gulf Stream, however, is four miles per hour (6.4 kilometers per hour). The current slows to a speed of about one mile per hour (1.6 kilometers per hour) as it widens to the north.

The Gulf Stream transports nearly four billion cubic feet of water per second, an amount greater than that carried by all of the world's rivers combined. The current plays an important role in the poleward transfer of heat and salt, and in warming the European subcontinent, although recent research suggests that winds carry much of the heat that warms northern Europe. The average annual temperature of northwest Europe is about 9°C above the average for its latitude.

The combination of the Trade Winds (10° to 25°N) blowing to the west and the Westerlies (35° to 55°N) blowing to the east cause the North Atlantic to rotate clockwise. These patterns of trade winds drive the North Equatorial Current to the west. As the current approaches the Caribbean Sea, water moves through the multiple channels of the Antilles and Caribbean Islands, and eventually loops into the Gulf of Mexico before exiting through the Straits of Florida.

Along the east coast of Florida the current is joined by the Antilles Current, and the current, now called the Gulf Stream, runs parallel to the coast until reaching Cape Hatteras, North Carolina, where it leaves the coast and enters deeper water. While flowing in deep water the Stream often forms large meanders or fluctuations in its path. At approximately 50°W, the Gulf Stream splits into several currents the largest being the North Atlantic Current. The North Atlantic Current then feeds both the Norwegian Current that transports water northward along the west coast of Europe, and the Canary Current that flows south towards the on the eastern side of the Atlantic.

The Gulf Stream transports a staggering amount of water and heat. The volume of water transport is measured in Sverdrups (Sv), in honor of the pioneering oceanographer Harald Sverdrup. One Sverdrup is one million cubic meters of water per second! The Gulf Stream transports approximately 31 Sv of water and 1.3 x 10¹⁵ W of heat into the North Atlantic Ocean. The transport of the Gulf Stream then increases to about 85 Sv near Cape Hatteras, peaks at 150 Sv near 65°W, then decreases eastward of 65°W. To put this in perspective, the entire global input of freshwater from rivers to the ocean is equal to about 1 Sv.

Just as the atmosphere circulates heat by storms–the largest being hurricanes, the oceans also circulate heat by “storms” called eddies. The largest and most energetic eddies in the ocean are rings that shed off the Gulf Stream. These eddies or “rings” form when Gulf Stream meanders break off the Stream creating independent circulatory systems. These rings are the only way that warm tropical water located south of the Gulf Stream can be moved north of the Gulf Stream, and the only way cold nutrient rich shelf water located north of the Gulf Stream can be moved south of the Gulf Stream. Thus, rings in the Gulf Stream are a very important way for the ocean to distribute heat and energy. During an average year 10 to 15 rings are formed. The warm rings are usually between 150-300 km in diameter, can have rotational velocities over 1 m/s, and last for a few months or a year.

In addition to its well-known warming influence on places like Iceland and Scotland, the Gulf Stream directly affects weather and climate patterns over the entire Northern Hemisphere, and perhaps even world wide. The Gulf Stream affects the entire lower atmosphere in the form of air and cloud temperatures, rain bands, pressure fields and wind convergence. For example, the Gulf Stream supports a precipitation band with upward motions and cloud formations that reach 7 miles high and penetrate the upper troposphere. The troposphere, extending between eight and 16 kilometers (five to 10 miles) above the Earth's surface, is the lowest and densest part of Earth's atmosphere and also accounts for almost all of its water vapor and rainfall. It is likely that these direct effects ripple through the entire climate system, via teleconnections, i.e. linkages between changes in atmospheric circulation occurring in distant weather events.

The Stream had a decided impact on the development of the American colonies, and on maritime transportation in general. Most colonization south of Virginia arrived via southern route across the Atlantic even though it was 2,000-3,000 miles farther. Throughout the colonial era, the Gulf Stream remained the principal ocean route along the southern coast of North America. Trade in rum, sugar and spices nourished the young colonies and was vital to the economic needs of the growing markets. Return voyages to Europe almost always used at least part of the Gulf Stream. American whaling captains knew that whales could be found along the Stream’s plankton-rich boundaries. They also knew travel back to New England whaling ports was faster when the route tracked north of the powerful force of the current.

Spanish galleons, laden with the treasure of the New World, used the current as an expressway as they made their trip back to Europe. Many ships of which wrecked upon its reefs, which soon led to an industry known as “wrecking,” or salvaging goods from wrecked ships. The Bahamians excelled at such salvaging, and when Florida became a U.S. territory, Key West and Indian Key became the Keys’ primary headquarters for this industry.

The Gulf Stream may have been known to Ponce de Leon, who sailed to Florida in 1513.  However, Benjamin Franklin is credited with popularizing its importance to From 10 August 1753 through 31 January 1774, Benjamin Franklin deputy postmaster general of North America from 1753 to 1774. Observing that American postal ships could make the journey from England to the colonies days, if not weeks, faster than the English merchant ships, English postal authorities summoned Franklin to London for an explanation. Franklin consulted his cousin, Timothy Folger, a whaling ship captain from Nantucket and together they created a chart illustrating its affect on ships (Figure 1).  Their map did an excellent job of representing what we know now to be the actual average position of the Stream.

FIGURE 1.  Benjamin Franklin Map of Gulf Stream  Source: NOAA.

Sources

• Coastal Carolina University, Department of Marine Science, A Gulf Stream Tutorial.
• Minobe, S., A. Kuwano-Yoshida, N. Komori, S.-P. Xie, and R.J. Small, 2008. Influence of the Gulf Stream on the troposphere. Nature 452, 206-209 (13 March 2008).
• National Oceanic and Atmospheric Administration, Benjamin Franklin’s ‘Sundry Maritime Observations.
• Wilkinson, Jerry, History of the Gulf Stream at KeyHistory.org.

Resources on the Web

• Joanna Gyory, Arthur J. Mariano, Edward H. Ryan, The Gulf Stream, Ocean Surface Currents, Miami University
• Path of the Gulf Stream, Coastal Carolina University
• Gulf Stream Weakened in 'Little Ice Age,' Nature