GULF STREAM

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. The Gulf Stream influences the climate of the east coast of North America from Florida to Newfoundland, and the west coast of Europe.

Contents

The Gulf Stream proper and the North Atlantic Drift

Normal behavior of the Gulf Stream

Localized effects

North America

The effect of global warming

See also

References

Footnotes

The Gulf Stream proper and the North Atlantic Drift

First charted by Benjamin Franklin in 1786, the Gulf Stream proper is a western-intensified current, largely driven by wind stress.^[1] 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 European winters) 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.^[2] There is speculation that global warming might affect the thermohaline circulation, diminish the NAD, and perhaps lead to relative cooling in Western Europe.

Normal behavior of the Gulf Stream

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. 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, transporting about 1.4 petawatts of heat, equivalent to 100 times the world energy demand.^[3] 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. 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.
Typically, the Gulf Stream is 80–150 km wide and 800–1200 m deep. The current velocity is fastest near the surface, with the maximum speed typically about 2 m/s^[4] (approx. 3.9 knots).
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. The second process involves the formation of sea ice, which likewise increases the salinity of the brine solution, thereby decreasing its freezing point. These two processes produce water that is denser and colder (or, more exactly, water that is still liquid at a lower temperature). In the North Atlantic Ocean, the water becomes so cold and dense that it begins to sink down through warmer, 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.

Localized effects

North America

The Gulf Stream is influential on the climate of the east coast of Florida, especially southeast Florida, helping to keep temperatures warmer than in the rest of the southeastern United States during the winter. During the summer, the effect is opposite but small. 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.

The effect of global warming

Main articles: Shutdown of thermohaline circulation

There is some speculation that global warming could decrease or shutdown thermohaline circulation and therefore reduce the North Atlantic Drift. The timescale that this might happen in is unclear; perhaps a few decades or a few hundred years [1]. This could trigger localised cooling in the North Atlantic and lead to cooling (or lesser warming) in that region, particularly affecting areas that are warmed by the North Atlantic Drift, such as Scandinavia and Great Britain.^[5] The chances of this occurring are unclear.^[6]
At present, most available data show that Gulf Stream flow was stable over the past 40 years.^[7] One report, based on a snapshot survey, suggested that the deep return flow has weakened^[8] by 30% since 1957, which would imply a weakening in the North Atlantic Deep Water production.^[9] However, this should have caused a temperature drop of several degrees in northwest Europe, which has not been observed. It was later discovered, using the first cross-Atlantic array of moored current meters, that variations within one year were just as large.^[10] At least part of the apparent weakening of the Gulf Stream (if real) may be cyclical and connected to recent positive values of North Atlantic Oscillation.^[11] Recent research^[12] shows that Gulf Stream volume transport during the Little Ice Age was ten per cent weaker than today’s, implying that diminished oceanic heat transport may have contributed to the 16th- to the mid-19th-century cooling in the North Atlantic.

See also

★ Climate

★ Global warming

★ Ocean current

★ Oceanography

★ North Atlantic Drift

★ Rogue wave

References

★ Corona Magazine Issue 124: Science (German, Transported amount of power)

★ The North Atlantic Drift Current Barbie Bischof, Arthur J. Mariano, Edward H. Ryan

★ Could the Atlantic Current Switch Off?

★ Influence of the Atlantic Subpolar Gyre on the Thermohaline Circulation, Hátún ''et al.'', , , Science, (Increased temperature and salinity in the Nordic Seas.)

Footnotes

1. What Is the Thermohaline Circulation?, , Carl, Wunsch, Science, (see also Rahmstorf.)
2. The Source of Europe's Mild Climate, , Richard, Seager, American Scientist Online,
3. Scientists probing a dying current bring worst climate fears to the surface Jonathan Leake (Web archive)
4. The Gulf Stream
5. The Thermohaline Ocean Circulation
6. Abrupt climate changes: from the past to the future – a review, , T. F., Stocker, International Journal of Earth Sciences, 1999
7. Decrease in Atlantic circulation? Gavin Schmidt
8. Slowing of the Atlantic meridional overturning circulation at 25°N, , Harry L., Bryden, Nature, 2005
9. Ocean changes 'will cool Europe' Richard Black
10. False Alarm: Atlantic Conveyor Belt Hasn't Slowed Down After All, , Richard A., Kerr, Science,
11. Sixteen years of Florida Current transport at 27° N, , Molly O'Neil, Baringer, Geophysical Research Letters, 2001
12. Gulf Stream density structure and transport during the past millennium, , David C., Lund, Nature, 2006