Surface temperatures in the western North Atlantic: Most of the North American landmass is black and dark blue (cold), while the Gulf Stream is red (warm). Source:NASA
TheGulf Stream is a warm and swiftAtlanticocean current that originates in theGulf of Mexico and flows through theStraits of Florida and up the eastern coastline of the United States, then veers east near 36°N latitude (North Carolina) and moves toward Northwest Europe as theNorth Atlantic Current. The process ofwestern intensification causes the Gulf Stream to be a northward-accelerating current off the east coast of North America. Around40°0′N30°0′W / 40.000°N 30.000°W /40.000; -30.000, it splits in two, with the northern stream, the North Atlantic Drift, crossing to Northern Europe and the southern stream, theCanary Current, recirculating off West Africa.
The Gulf Stream influences the climate of the coastal areas of the East Coast of the United States from Florida to southeast Virginia (near 36°N latitude), and to a greater degree, the climate of Northwest Europe. A consensus exists that the climate of Northwest Europe is warmer than other areas of similar latitude at least partially because of the strong North Atlantic Current.[1][2][3] It is part of theNorth Atlantic Gyre. Its presence has led to the development of strongcyclones of all types, both within theatmosphere and within the ocean.
Benjamin Franklin's chart of the Gulf Stream printed in London in 1769
European discovery of the Gulf Stream dates to the 1512 expedition ofJuan Ponce de León, after which it became widely used by Spanish ships sailing from theCaribbean to Spain.[4] A summary of Ponce de León's voyage log on April 22, 1513, noted, "A current such that, although they had great wind, they could not proceed forwards, but backwards and it seems that they were proceeding well; at the end, it was known that the current was more powerful than the wind."[5]
Benjamin Franklin became interested in theNorth Atlantic Ocean circulation patterns. In 1768, while in England, Franklin heard a curious complaint from the ColonialBoard of Customs: "Why did it take British packets several weeks longer to reach New York from England than it took an average American merchant ship to reachNewport, Rhode Island, despite the merchant ships leaving from London and having to sail down theRiver Thames and then the length of theEnglish Channel before they sailed across the Atlantic, while the packets left fromFalmouth in Cornwall?"[6]
Franklin asked his cousin Timothy Folger, aNantucket Island whaling captain, for an answer. Folger explained that merchant ships routinely crossed the current—which was identified by whale behaviour, measurement of the water's temperature, and changes in the water's colour—while the mail packet captains ran against it.[6] Franklin had Folger sketch the path of the current on a chart of the Atlantic and add notes on how to avoid the current when sailing from England to America. Franklin then forwarded the chart to Anthony Todd, secretary of the British Post Office.[6] Franklin's Gulf Stream chart was printed in 1769 in London, but it was mostly ignored by British sea captains.[7] A copy of the chart was printed in Paris circa 1770–1773, and a third version was published by Franklin in Philadelphia in 1786.[8][9]
The Gulf Stream proper is awestern-intensified current, driven largely bywind stress.[10] In 1958, oceanographerHenry Stommel noted, "very little water from the Gulf of Mexico is actually in the stream".[11] TheNorth Atlantic Current, in contrast, is largely driven bythermohaline circulation. Its carrying warm water northeast across the Atlantic makes Western Europe and especially Northern Europe warmer and milder than it otherwise would be.[12]
The specific location of the Gulf Stream changes seasonally, being closer to the coast of North America in the summer and further away in the winter.[13]
Evolution of the Gulf Stream to the west of Ireland continuing as theNorth Atlantic Current
A river of sea water, called theAtlantic North Equatorial Current, flows westwards off the coast of Central Africa. When this current interacts with the northeastern coast of South America, the current forks into two branches. One passes into theCaribbean Sea, while a second, theAntilles Current, flows north and east of theWest Indies.[14] These two branches rejoin north of the Straits of Florida.
Thetrade winds blow westwards in the tropics,[15] and thewesterlies blow eastwards at mid-latitudes.[16] This wind pattern applies astress to the subtropical ocean surface with negativecurl across the north Atlantic Ocean.[17] The resultingSverdrup transport is equatorward.[18]
Because of the conservation ofpotential vorticity caused by the northward-moving winds on thesubtropical ridge's western periphery and the increased relative vorticity of northward-moving water, transport is balanced by a narrow, accelerating poleward current. This flows along the western boundary of the ocean basin, outweighing the effects of friction with the western boundary current, and is known as theLabrador Current.[19] The conservation of potential vorticity also causes bends along the Gulf Stream, which occasionally break off as the Gulf Stream's position shifts, forming separate warm and cold eddies.[20] This overall process, known as western intensification, causes currents on the western boundary of an ocean basin, such as the Gulf Stream, to be stronger than those on the eastern boundary.[21]
As a consequence, the resulting Gulf Stream is a strong ocean current. It transports water at a rate of 30 million cubic metres per second (30sverdrups) through the Florida Straits. As it passes south of Newfoundland, this rate increases to 150 sverdrups.[22] The volume of the Gulf Stream dwarfs all rivers that empty into the Atlantic combined, which total 0.6 sverdrups. It is weaker, however, than theAntarctic Circumpolar Current.[23] Given the strength and proximity of the Gulf Stream, beaches along the East Coast of the United States may be more vulnerable to large sea-level anomalies, which significantly impact rates ofcoastal erosion.[24]
The Gulf Stream is typically 100 km (62 mi) wide and 800 to 1,200 m (2,600 to 3,900 ft) deep. The current velocity is fastest near the surface, with the maximum speed typically about 2.5 m/s (5.6 mph).[25] As it travels north, the warm water transported by the Gulf Stream undergoes evaporative cooling. The cooling is wind-driven; wind moving over the water causesevaporation, cooling the water and increasing itssalinity and density. When sea ice forms, salts are left out of the ice, a process known as brine exclusion.[26] 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. (Theconvective action is similar to alava lamp.) This downdraft of cold, dense water becomes a part of theNorth Atlantic Deep Water, a southgoing stream.[27] Very littleseaweed lies within the current, although seaweed lies in clusters to its east.[28]
In April 2018, two studies published in the British scientific journalNature[29][30] found the Gulf Stream to be at its weakest for at least 1,600 years.[31]
The Gulf Stream is influential on theclimate of the Florida peninsula. The portion off the Florida coast, referred to as theFlorida Current, maintains an average water temperature of at least 24 °C (75 °F) during the winter, and often 29 °C (84 °F) in summer and fall.[32] East winds moving over this warm water move warm air from over the Gulf Stream inland,[33] helping to keep temperatures milder across the state than elsewhere across the Southeastern United States during the winter.
The Gulf Stream carries a wide variety of tropical fish and organisms northward along the East Coast fromFlorida to extreme southeastMassachusetts in spring and summer. Following the warm waters of the Gulf Stream, tropical fish are often encountered off the East Coast as they search for food, including several species ofBatoidea,Dolphin,Barracuda, andTriggerfish. The Gulf Stream's proximity toNantucket,Massachusetts, adds to itsbiodiversity, because it is the northern limit for southern varieties of plant life, and the southern limit for northern plant species, Nantucket being warmer during winter than the mainland in winter[34] just 30 miles to the north.[35] North of Nantucket Island along the New England coast northward to the eastern Canadian coast the coldLabrador Current is found.
The North Atlantic Current of the Gulf Stream, along with similar warm air currents, helps keepIreland and the western coast ofGreat Britain a few degrees warmer than the east.[36] However, the difference is most dramatic in thewestern coastal islands of Scotland.[37][failed verification] A noticeable effect of the Gulf Stream and the strong westerly winds on Europe occurs along theNorwegian coast.[12] Northern parts ofNorway lie close to theArctic 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.[38] The warming effect provided by the Gulf Stream has allowed fairly large settlements to be developed and maintained on the coast ofNorthern Norway, includingTromsø, the third-largest city north of the Arctic Circle. Weather systems warmed by the Gulf Stream drift into Northern Europe, also warming the climate behind theScandinavian Mountains.
The possibility of a Gulf Stream collapse has been covered by some news publications.[39][40][41][42][43] TheIPCC Sixth Assessment Report addressed this issue specifically, and found that based on model projections and theoretical understanding, the Gulf Stream will not shut down in a warming climate.[44] While the Gulf Stream is expected to slow down as theAtlantic meridional overturning circulation (AMOC) weakens, it will not collapse, even if the AMOC were to collapse.[44] Nevertheless, this slowing down will have significant effects, including a rise in sea level along the North American coast, reduced precipitation in the midlatitudes, changing patterns of strong precipitation around Europe and the tropics, and stronger storms in the North Atlantic.[44]
Hurricane Sandy intensified as it tracked northward along the axis of the Gulf Stream in 2012
The warm water and temperature contrast along the edge of the Gulf Stream often increase the intensity of cyclones,tropical or otherwise.Tropical cyclone generation normally requires water temperatures in excess of 26.5 °C (79.7 °F).[45] Tropical cyclone formation is common over the Gulf Stream, especially in July. Storms travel westward through the Caribbean and then either move in a northward direction and curve towards the eastern coast of the United States or stay on a north-westward track and enter theGulf of Mexico.[46] Such storms have the potential to create strong winds and extensive damage to theUnited States' Southeast coastal areas.Hurricane Sandy in 2012 was a recent example of a hurricane tracking along the Gulf Stream and gaining strength.[47]
Strongextratropical cyclones have been shown to deepen significantly along a shallowfrontal zone, forced by the Gulf Stream, during thecold season.[48]Subtropical cyclones also tend to be generated near the Gulf Stream. About 75% of such systems documented between 1951 and 2000 formed near this warm-water current, with two annual peaks of activity occurring during May and October.[49] Cyclones within the ocean itself form under the Gulf Stream, extending as deep as 3,500 m (11,500 ft) beneath the ocean's surface.[50]
The Gulf Stream periodically forms rings resulting from a meander of the Gulf Stream being closed off from an alternate route distinctive from that meander, creating an independent eddy. These eddies have two types: cold-core rings, which rotatecyclonically (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere), and warm-core rings, which rotate anticyclonically. These rings have the capacity to transport the distinct biological, chemical, and physical properties of their originating waters to the new waters into which they travel.
^Elizabeth Rowe; Arthur J. Mariano; Edward H. Ryan."The Antilles Current". Cooperative Institute for Marine and Atmospheric Studies. Retrieved2009-01-06.
^Glossary of Meteorology (2009)."trade winds".Glossary of Meteorology. American Meteorological Society. Archived fromthe original on 2008-12-11. Retrieved2008-09-08.
^Joanna Gyory; Arthur J. Mariano; Edward H. Ryan."The Gulf Stream". Cooperative Institute for Marine and Atmospheric Studies. Retrieved2009-01-06.
^Ryan Smith; Melicie Desflots; Sean White; Arthur J. Mariano; Edward H. Ryan."The Antarctic CP Current". Cooperative Institute for Marine and Atmospheric Studies. Retrieved2009-01-06.
^abcFox-Kemper, B.;Hewitt, H.T.; Xiao, C.; Aðalgeirsdóttir, G.; Drijfhout, S.S.; Edwards, T.L.; Golledge, N.R.; Hemer, M.; Kopp, R.E.; Krinner, G.; Mix, A. (2021). Masson-Delmotte, V.; Zhai, P.; Pirani, A.; Connors, S.L.; Péan, C.; Berger, S.; Caud, N.; Chen, Y.; Goldfarb, L. (eds.)."Ocean, Cryosphere and Sea Level Change"(PDF).Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.2021. Cambridge University Press, Cambridge, UK and New York, NY, USA: 1321.doi:10.1017/9781009157896.011.ISBN9781009157896.
