The Gulf Stream is a oceanic current which takes its source between the Florida and the the Bahamas and is diluted in the Atlantic Ocean towards the Longitude of the Greenland. Its name is wrongly used to indicate the Atlantic northern Dérive, even the whole of the circulation of surface of the Northern Atlantic Ocean.

Discovered

It was probably known Indians Séminoles several centuries before the discovery of America. As of 1513, at the time of discovered Florida, the navigator Ponce of León notices that its Navire S is carried by important and fast running of hot Eau which comes from current the Caribbean Sea. It is only in 1770 that Benjamin Franklin, then person in charge of the administration of the Stations makes carry out a thorough study and a detailed cartography of the Gulf Stream to improve time of transport of the mail with the United Kingdom. It will take part itself in the studies and this work will have such a repercussion that it will give place to the legend according to which it is him which would have named it, even discovered. Actually, the existence of the current is largely known and accepted since 1519 and it is charted twice before the end of the 17th century.

Extended

The Gulf Stream is consisted of the fusion of the Courant of Florida, the Courant of Cuba and equatorial northern Running. Off Florida it is a true river, from 80 to 150 km broad and from 800 to 1200 m of depth, which runs out at a speed of 2 m/s, and whose edges are visible with the naked eye. It then skirts the coast towards north until the Cap Hatteras, then moves towards the east by forming meanders which end up being detached from the principal current in the form of swirls which attenuate in several days or a few weeks. These swirls are the principal mechanism of deceleration and dilution of the current.

The southern limit of the current is diluted quickly in the ocean from which the temperature and salinity are far from different. On the contrary the north-western limit also constitutes the south-eastern limit of the Running of Labrador, cold and running in opposite direction.

In the south of Greenland one continues to observe hotter pockets of water but the displacement of water is not done any more towards the east but statistically. A bottle thrown to the sea will be able to move during one day in about any direction, into one week it will have changed several times of direction but it is only at the end of several weeks which it will be clear that its average displacement is done towards the North-East.

Mechanism

This marine current is resulting from the difference in altitude between water surface of the Gulf of Mexico and that of the Atlantic. This difference in height is it even due to various causes: rotation of the ground, Circulation thermohaline, atmospheric circulation (Trade winds), configuration of the coast.

The engine of the Circulation thermohaline is the difference of Densité due to the salinity and the Température of water. Water Arctique S is denser because they colder and are salted. Atlantic water is less dense because they hotter and are salted. The first thus plunge under the seconds in direction of the the Antarctic, creating an aspiration of Atlantic water towards north.

Theories on the effects of the phenomenon

In 1855, a lieutenant of navy of the the United States, Matthew Fountain Maury, published The Physical Geography Of The Sea and its Meteorology , work which had a resounding success. it posed the assumption there that the Gulf Stream played an important role in the regulation of the winter temperatures of the West of Europe. Starting from observations made on both sides of the Atlantic, the author concluded that the Gulf Stream, only true local source of heat was responsible for the Climat winter European particularly soft. (15°C moreover on average than for the Canadian East ). But not having precise climatic statements of high-sea, the author did not distinguish the “maritime” climates from continental climates, actually basically different.

According to this theory, it is the Gulf Stream, heat, which would transfer in winter its thermal energy to the cold winds of west, stabilizing imbalance between the layers atmospheric and oceanic, due to a decreased solar radiation. The two layers would balance, reducing kind cooling of the temperatures. This old theory of more than one century was widely diffused until in the years 1990, of which by the handbooks of geography and the Encyclopédie S, without never scientifically to be however confirmed. One is unaware of still the exact importance of the impacts of the Gulf Stream on the continental or oceanic European climate, or on the formation of the clouds.

In fact, the Gulf Stream could play a part Climat ic, but more complex and perhaps indirect. It is not in any case alone to explain the relative softness of the European winters. Accumulated thermal energy the summer by the continent eurasiatic, but especially by the seas is to some extent restored the winter with the masses of air pushed by the winds in particular with the top of the Atlantic, without the latter knowing the disturbances that impose to them the North-South directed mountainous chains which border Amériques.
In addition, the oceanic current of jet , i.e. the deviation of the winds by the rotation of the Earth, or Force of Coriolis brings in winter on the continent, thanks to the dominant winds of West, of the oceanic air much softer than the continental air. However the dominant winds come from the west to Europe and rather from North for North America.

A study published in 2002 by Richard Seager (climatologist of the Columbia University) supports by models the assumption that the effect of the Gulf Stream is definitely less important than the effect of the atmospheric movements. Simulations of Richard Seager let think that the winter variation of average temperature observed between the East of the United States and the European West (except notable for Norway) is only not very related to the Gulf Stream, but rather with the directions of the dominant winds which differ: The presence of the Rocky Mountains and the geographical configuration would explain the variations in temperature best, the wind in the east of the United States coming from north, while the wind in the west of Europe comes from the west. The Gulf Stream would have in the various models tested by R. Seager an effect definitely weaker, and its stop would not change anything with the fact that North America would remain colder than Europe in winter. Its models suggest a cooling of about 4,5 to 6 °C with the average latitudes, and about 20°C in Norway, in the event of stop of the transport of oceanic heat, but also distributed on both sides of the Atlantic. This effect would not make then, with the average latitudes, that to compensate for the total warming.

If a contrast exists between Paris and Montreal, it is because of the rotation of the Earth which makes that with the moderated latitudes, the edges Is oceans profit from a oceanic climate: they are under the influence of the winds of West which are established between the subtropical anticyclones and the troughs of low pressure and which in their oceanic course draws heat and moisture.

Possibilities of disappearance of the GULF-stream

It was noted, thanks to taking away of Glace in the Antarctic, that the rate of CO₂ in the atmosphere varied with the temperatures. It oscillated indeed of 180 ppmv during the glaciations with 280 ppmv in interglacial periods ( 1 ppmv is a part per million in volume i.e. 1 cm ³ per m ³ of air ). The human activities recently carried the rate of CO₂ in the atmosphere to 370 ppmv, level ever reached since a million years. This rate increases in an accelerated way and becomes exponential, so that in 2050, it should reach 700 ppmv, and have thus doubled. Without forgetting the Methane, resulting from the Digestion of the Ruminant S and Marsh, estuaries and Rice ières, which is also powerful a Gaz with greenhouse effect, which increases also quickly. We know already that the temperature increased 0,6°C in 100 years, on the surface of the sphere; and that by Dilatation of warm water the level of the oceans goes up.

The cast iron of the continental Glacier S cannot induce of quantifiable rise of the oceans, but on the North Atlantic, the greenhouse effect is dissolving the immense glaciers of the Arctique and contributes to the increase in the pluviometry of the North Atlantic. These two joined together phenomena are at the origin of a fresh water contribution on this area. If ever this last had suddenly been too important, as that was the case at the beginning of the last glacial period (- 11 approximately 000 before our era: the glaciers found in North America, releasing water of immense lakes which cool the marine currents and produce a general cooling of the terrestrial climate), then the Gulf Stream could disappear. Indeed, an important fresh water contribution would decrease the differences in density of water between the Arctic Ocean and the sea of Norway. The place of diving of cool water and salted would be found on the level of the the Azores; and the Gulf Stream would be folded up on itself not going more beyond the Azores.

The Paléoclimatologie highlighted a strong coupling between average temperature of the northern hemisphere and intensity of the Atlantic currents. Remain to identify finely where are the causes and the consequences. The last climate knew brutal falls of about 5 °C in the Atlantic, 10 °C in Europe and 15 °C with the Greenland coupled to a deceleration of the currents (of which the fossil traces are observed by the sedimentology). These changes appear in only a few decades, suggest a very powerful loop of feedback. The last cooling of this type goes back to 8  approximately 200 years, and the study of the marine sediments lets think that it is well a massive fresh water contribution in the North Atlantic which would have stopped (or strongly slowed down) oceanic circulation.

However, for Martin Visbeck (Leibniz Institute of the marine science, physical Department of oceanography in Kiel, Germany), the currents of the North Atlantic could have lost 30% of their force from here 2100, allowing more cold winters the north of Europe, which would not mask however the warming in progress in Europe. (Without risk of a scenario as presented by the film the Day according to by Roland Emmerich, based on the brutal appearance of a Ice Age in the Northern hemisphere after the stop of the Gulf Stream)

Possible consequences

• Consequence on the winter cold. simulations of Richard Seager estimate that an interruption of the Gulf Stream (which could occur from here 20 or 200 years according to certain models) would induce only one nonsignificant or not very important change for the winter cooling of Western Europe compared to that of North America.

• Effects on the marine levels: the mean level of the sea is currently higher from approximately 1 meter in New York, than on the European coasts, partly because of the marine currents. A reduction of 30% of the currents of the western north of the Atlantic would imply a fall of the marine level in North America balanced by an increase in approximately 10 cm in Europe which it is necessary to add to the effect of dilation and the contributions of melt waters of the ices.

• boomerang Effect on the warming? the permanent diving of the current of North Atlantic Drift contributes to annually hiding a billion tons approximately of dissolved atmospheric CO₂ in surface water of the North Atlantic. This CO₂ which can be trapped in the deep layers for centuries.

If the marine currents slow down, the roadbases of the sea will be acidified more quickly and the sea could less absorb of CO₂, even salt out of them, and thus increase the atmospheric gas rates with greenhouse effect, which would increase the temperature of the northern hemisphere, as well as the cast iron of the glaciers, and thereafter the contributions of fresh water in the Atlantic, which would still slow down the currents by producing a self-sustained vicious circle.

Remain to study if the Gulf Stream has or not indirect impacts on the growth and distribution of the Plancton which can by its emissions indirectly influence the nucleation of the steam, i.e. on the formation of clouds, which have also an major importance in term of climatic regulation.

In addition, in addition to the phenomena of El Niño and Niña, other currents intervene. Thierry Delcroix (Laboratory of study in geophysics and space oceanography) note that the Programme of climatic Studies of the Pacific Ocean noted that the deep intermediate equatorial currents (which convey approximately 100 million m ³ of water a second) - 300 with - 1200 meters) had changed direction into 2000.

Concerning the Gulf Stream

• Érik Orsenna Portrait of the Gulf Stream, praise of the currents Threshold 2005.

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