NORTH ATLANTIC CURRENTS
Against the flow
ARTIALLY RESPONSIBLE FOR THE MILD WEATHER CONDITIONS OF WESTERN EUROPE, THE GULF STREAM AND ASSOCIATED CURRENTS PROVIDE THE NORTH ATLANTIC WITH ITS GENUINE “CHARACTER” AND SHAPES THIS OCEAN’S COMPLEX DYNAMICS.
The Gulf Stream, like all major currents, is governed by wind-induced circulation on the North Atlantic scale, circulation which intensifies on the western edge due to the earth’s rotation. The Gulf Stream’s movement is generated by the friction of the winds (which affects water up to a depth of 1500 to 2000 metres), and the relatively high temperature of the Gulf Stream is due to the fact that the current carries waters originating from an area located between Florida and the Bahamas. Thermohaline circulation (which results from a difference in water densities – as cold and salty water dives under warmer and less salty waters) affects layers below 2000 metres of depth. It can influence the position of the Gulf Stream, but does not play any role in its dynamics. Currents on such a large scale as the Gulf Stream generate their own medium scale eddies – 50 km to 200 km in diameter – which can actually cause the current to deviate and change direction — giving an additional headache for navigators. Off the coast of Florida, the boundaries of the Gulf Stream are visible to the naked eye and its dimensions would 62
make the world’s mightiest rivers jealous – it can reach a width of more than 90 miles with a maximum depth of roughly 4,000 feet. In the Straits of Florida, the volume of water transported by the Gulf Stream is estimated at 30 million cubic metres per second and this figure rises to 80 millions m3/s at 35° N! By way of comparison, the combined flow of all rivers that empty into the Atlantic is approximately 0.6 millions m3/s. The Gulf Stream travels along the east coast of North American until reaching Cape Hatteras (North Carolina, 35° N, 75° W), at which point it separates from the cold Virginia flow circulating towards the south. Off Cape Hatteras, at around 37° N, it abruptly shifts to the northeast, then heads due east on the 40° N parallel until reaching longitude 45° W to the southeast of Newfoundland, where it moves north to 50° N. This is where the Gulf Stream turns into the North Atlantic Drift and flows northeastwards towards Scotland and Norway while a secondary current travels towards the Bay of Biscay and the Portuguese coast. The thermoregulating role of the Gulf Stream and its influence on western Europe’s climate was initially theorized by Lieutenant Matthew Fontaine Maury (US Navy), in a book entitled “The Physical Geography of the Sea and its Meteorology”, published in 1855. Although the Gulf Stream theory has been widely accepted, the past 20 years have seen the scientific community challenge the basic facts, suggesting that it is a bit too simplistic and ignores the crucial importance of air circulation when explaining the temperature difference between the North American continent and Western Europe. Submitted to a regime of winds coming predominantly from the north, Canada and the northern US states would logically be colder than occidental Europe, which benefits from oceanic air flows (carried by the Jet Stream). This does not mean that the influence of the Gulf Stream and the North Atlantic
©B.Stichelbaut/Akena
Officially acknowledged by scholars and sailors since the Spanish Conquistador, Juan Ponce de Leon, discovered Florida, the Gulf Stream’s existence was, according to numerous historians, already recognised by the Seminole Indians. Ponce de Leon, taking part in Colombus’s second voyage to the New World in 1513, noticed that the ships of his flotilla were under the influence of a strong current coming from the Caribbean and noted this observation in his logbook. However, a comprehensive study of this phenomenon by the scientific genius, Benjamin Franklin, would not be undertaken for two and a half centuries. On top of his revolutionary theories about electricity, Franklin was an outstanding humanist and founded the first American public library. While working for the Postal Administration, he initiated a comprehensive study of the Gulf Stream in 1770 in order to optimize the travel time of mail sent to Europe providing a catalyst for oceanographers and triggering further research into the phenomenon during the 19th century.