Can the atmosphere influence the location and intensity of ocean currents?  Sylvain Watelet, PhD student of oceanography at the University of Liege, studied the links between the North Atlantic Oscillation, an atmospheric phenomena that is happening above the Atlantic, and the Gulf Stream, that originates along the coast of Florida. His research - which has focused on observation of the Gulf Stream for over a century! - shows that there is indeed a correlation between the two under certain circumstances (1). The characteristics of the atmosphere may be used to predict the behaviour of the ocean current.

Legend has it that Juan Ponce de Léon was hoping to lay his hands on the famed fountain of youth somewhere on the Bimini islands, an archipelago of the Bahamas. Instead of eternal youth the Spanish explorer discovered the Gulf Stream, this marine current which rises along the coast of Florida.  In any case, he was the first to describe it in his ship’s log dating back to 1513. The story goes that just as they were drawing up alongside it, the three expedition ships were pulled away by the current. Hot and swift, he wrote, with blue water side by side with the greener water of the Atlantic. The Conquistador wrote of his surprise at not being able to navigate against it despite favourable winds.

More than two centuries later, Benjamin Franklin, one of the founding forefathers of the United States, undertook extensive mapping of the Gulf Stream with the aim of reducing the sailing time for American mail going to Great Britain.  In 1870, Jules Verne contributed to its legend by devoting a chapter to it in Twenty Thousand Leagues Under the Sea, calling it the “king of tempests” and describing it as the “largest river in the sea, which has its banks, its fish and its own temperature”.     

Since then, the Gulf Stream has become the ocean current that is best known by the public at large. It influences temperatures in Western Europe, having followed the eastern coastlines of the United States before crossing the Atlantic Ocean and heating the North Atlantic Drift, an ocean current which is an extension of it.  Although we know quite a lot about its characteristics proper, scientific research to date has shed little light on the relationship between the Gulf Stream and the atmosphere. It is this subject that Sylvain Watelet, PhD student in the Oceanography Department of the University of Liege has chosen to explore.

“I did a Masters in climatology, he explains. When I graduated I was offered work in oceanography, developing a software package called Diva, while I was working on my thesis. This software is a means of interpolating occasional and discreet measurements (temperature, salinity etc.) on the ocean to reconstruct continuous fields.   “In order to keep a link to his initial training, he chose to make a parallel with the atmosphere and picked the Gulf Stream for its power – several million cubic metres per second – which makes it quite easy to detect. “The idea was to determine whether the direction of the winds on the Atlantic has an influence on the intensity and the location of the Gulf Stream”, he sums up.

Where high and low pressure meet

So, Sylvain Watelet undertook the task of comparing the ocean current to the North Atlantic Oscillation (NAO in short), an atmospheric phenomena that is happening above the Atlantic, and which is influenced by interferences between the Icelandic depression and Azores anticyclone. In other words, in a high pressure area (which turns clockwise) and a low pressure area (which turns anti-clockwise). This is what is known in our jargon as a dipole.  When this is clearly defined, it can give rise to a very strong current from the west.  On the other hand, when it is not well formed, the winds become more dispersed or “meridional” (north-south or south-north), leading to cold shifts southward and warm ones northward, etc.  

(1) Reconstruction of the Gulf Stream since 1900 and correlation with the North Atlantic Oscillation, Geophysical Research Abstracts, Vol. 17, EGU2015-2577, 2015, EGU General Assembly 2015