Gulf Stream 

The Gulf Stream is orange and yellow in this representation of water temperatures of the Atlantic. Source: NASA.
For other uses, see Gulf Stream (disambiguation).

The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. At about 30°W, 40°N, it splits in two, with the northern stream crossing to northern Europe and the southern stream recirculating off West Africa. It is part of the North Atlantic Subtropical Gyre. The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe. Its presence has led to the development of strong cyclones of all types, both within the atmosphere and within the ocean. The Gulf Stream is also a significant potential source of renewable power generation.

Thanks to the Gulf Stream, the climate of Western Europe (and especially Northern Europe) is much warmer than it would otherwise be.

Contents

Discovery and properties

Benjamin Franklin's map of the Gulf Stream

European discovery of the Gulf Stream dates to the 1513 expedition of Juan Ponce de León, after which it became widely used by Spanish ships sailing from the Caribbean to Spain.1 In 1786 Benjamin Franklin studied and mapped the current in detail.2 The Gulf Stream proper is a western-intensified current, largely driven by wind stress.3 The North Atlantic Drift, in contrast, is largely thermohaline circulation driven. By carrying warm water northeast across the Atlantic, it makes Western Europe (and especially Northern Europe) warmer than they otherwise would be. However, the extent of its contribution to the actual temperature differential between North America and Europe is a matter of dispute.4clarification needed

Behavior

A river of sea water, called the Atlantic North Equatorial Current, flows westward off the coast of northern Africa. When this current interacts with the northeastern coast of South America, the current forks into two branches. One passes into the Caribbean Sea, while a second, the Antilles Current, flows north and east of the West Indies.citation needed These two branches rejoin north of the Straits of Florida, as shown on the accompanying map.

Consequently, the resulting Gulf Stream is a strong ocean current. It transports water at a rate of 30 million cubic meters per second (30 sverdrups) through the Florida Straits. After it passes Cape Hatteras, this rate increases to 80 million cubic meters per second.citation needed The volume of the Gulf Stream dwarfs all rivers that empty into the Atlantic combined, which barely total 0.6 million cubic meters per second. It is weaker, however, than the Antarctic Circumpolar Current.citation needed

Typically, the Gulf Stream is 80 kilometres (50 mi) to 150 kilometres (93 mi) wide and 800 metres (2,600 ft) to 1,200 metres (3,900 ft) deep. The current velocity is fastest near the surface, with the maximum speed typically about 2.5 metres per second (5.6 mph).5

As it travels north, the warm water transported by the Gulf Stream undergoes evaporative cooling and brine exclusion. The cooling is wind driven: wind moving over the water cools it and also causes evaporation, leaving a saltier brine. In this process, the water increases in salinity and density, and decreases in temperature.citation needed These two processes produce water that is denser and colder (or, more precisely, water that is still liquid at a lower temperature). In the North Atlantic Ocean, the water becomes so dense that it begins to sink down through less salty and less dense water. (The convective action is not unlike that of a lava lamp.) This downdraft of heavy, cold and dense water becomes a part of the North Atlantic Deep Water, a southgoing stream.citation needed

Schematic of the world's ocean currents. Click for larger image.

Localized effects

See also: Climate of Florida

The Gulf Stream is influential on the climate of the Florida peninsula, as east winds during most months of the year move warmer air from over the Gulf Stream inland,6 helping to keep temperatures milder across the state than elsewhere across the Southeast during the winter. The Gulf Stream makes the climate of offshore islands of Massachusetts, Martha's Vineyard, and Nantucket milder than that of Massachusetts Bay, which is isolated from Gulf Stream effects by Cape Cod.7

The North Atlantic Current of the Gulf Stream, along with similar warm air currents, helps keep Ireland and the western coast of Great Britain a couple of degrees warmer than the east. However, the difference is most dramatic in the western coastal islands of Scotland.8 Parts of Ireland and the west coast of Scotland have a mild enough climate to support palm-like cabbage trees even though they are a degree further north than Moscow.9

A noticable effect of the Gulf Stream and the strong westerly winds (driven by the warm water of the Gulf Stream) on Europe occurs along the Norwegian coast.10 Northern parts of Norway lie close to the Arctic zone, most of which is covered with ice and snow in winter. However, almost all of Norway's coast remains free of ice and snow throughout the year.11

Hurricane Alex formed and moved along the axis of the Gulf Stream in 2004.

Effect on cyclone formation

The warm water and temperature contrast along the edge of the Gulf Stream often increases the intensity of cyclones, tropical or otherwise. Tropical cyclone generation normally requires water temperatures in excess of 26.5 °C (79.7 °F).12 Tropical cyclone formation is common over the Gulf Stream, especially in the month of July. Storms travel westward through the Caribbean and then, either move in a northerly direction and curve towards the eastern coast of the United States, or stay on a north-westward track and enter the Gulf of Mexico.13 Such storms have the potential to create strong winds and extensive damage to the United States' Southeast Coastal Areas. Strong extratropical cyclones have been shown to deepen significantly along a shallow frontal zone, forced by the Gulf Stream itself during the cold season.14 Subtropical cyclones also tend to generate near the Gulf Stream. 75 percent of such systems documented between 1951 and 2000, formed near this warm water current, with two annual peaks of activity occurring during the months of May and October.15 Cyclones within the ocean form under the Gulf Stream, extending as deep as 3,500 metres (11,000 ft) beneath the ocean's surface.16

Possible renewable power source

The Gulf Stream transports about 1.4 petawatts of heat, equivalent to 100 times the world energy demand.17 and research is underway to tap this power in a couple of different ways. One idea, which would supply the equivalent power of several nuclear power plants, would deploy a field of underwater turbines placed 1,000 feet (300 m) under the center of the core of the Gulf Stream. Ocean thermal energy could also be harnessed to produce electricity, utilizing the temperature difference between cold deep water and warm surface water.18

See also

Sister project Wikimedia Commons has media related to: Gulf stream

References

Footnotes

  1. ^ Fernandez-Armesto, Felipe (2006). Pathfinders: A Global History of Exploration, W.W. Norton & Company. pp. p. 194. ISBN 0-393-06259-7. 
  2. ^ 1785: Benjamin Franklin's Sundry Maritime Observations, NOAA Ocean Explorer
  3. ^ Wunsch, Carl (November 8, 2002). "What Is the Thermohaline Circulation?". Science 298 (5596): 1179–1181. doi:10.1126/science.1079329. PMID 12424356, http://www.sciencemag.org/cgi/content/summary/298/5596/1179.  (see also Rahmstorf.)
  4. ^ Seager, Richard (July–August, 2006). "The Source of Europe's Mild Climate". American Scientist Online, http://www.americanscientist.org/issues/feature/2006/4/the-source-of-europes-mild-climate. Retrieved on 23 September 2008. 
  5. ^ Phillips, Pamela. "The Gulf Stream". USNA/Johns Hopkins. Retrieved on 2007-08-02.
  6. ^ National Climatic Data Center. Climatic Wind Data for the United States. Retrieved on 2007-06-02.
  7. ^ Captain John Lacouture (1995). "The Gulf Stream Charts of Benjamin Franklin and Timothy Folger". Nantucket Historical Society. Retrieved on 2008-09-10.
  8. ^ "Satellites Record Weakening North Atlantic Current Impact". NASA. Retrieved on 2008-09-10.
  9. ^ "Cordyline australis Cabbage Palm". The Garden Flora of Northern Ireland. Retrieved on 2007-07-20.
  10. ^ Barbie Bischof, Arthur J. Mariano, Edward H. Ryan (2003). "The North Atlantic Drift Current". The National Oceanographic Partnership Program. Retrieved on 2008-09-10.
  11. ^ Erik A. Rasmussen, John Turner (2003). Polar Lows, Cambridge University Press. p. p. 68. 
  12. ^ Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. "Frequently Asked Questions: How do tropical cyclones form?". NOAA. Retrieved on 2006-07-26.
  13. ^ National Hurricane Center.Atlantic Hurricane Database. Retrieved on 2008-06-10.
  14. ^ S. Businger, T. M. Graziano, M. L. Kaplan, and R. A. Rozumalski. Cold-air cyclogenesis along the Gulf-Stream front: investigation of diabatic impacts on cyclone development, frontal structure, and track. Retrieved on 2008-09-21.
  15. ^ David M. Roth. P 1.43 A FIFTY YEAR HISTORY OF SUBTROPICAL CYCLONES. Retrieved on 208-09-21.
  16. ^ D. K. Savidge and J. M. Bane. Cyclogenesis in the deep ocean beneath the Gulf Stream. 1. Description. Retrieved on 2008-09-21.
  17. ^dead linkLeake, Jonathan (December 5, 2005). "Scientists probing a dying current bring worst climate fears to the surface", The Australian.  (Web archive)
  18. ^ Jeremy Elton Jacquot. Gulf Stream's Tidal Energy Could Provide Up to a Third of Florida's Power. Retrieved on 2008-09-21.

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