Tropical Control of the Gulf Stream Path

The path of the Gulf Stream as it leaves the continental shelf near Cape Hatteras is marked by a sharp gradient in ocean temperature known as the North Wall. Fluctuations in the position of the North Wall have large impacts in the distribution of heat in the North Atlantic and on plankton populations. There is consensus among researchers that processes in the North Atlantic impacted by the North Atlantic Oscillation trigger displacements of North Wall position. This paper presents evidence of tropical control on the Gulf Stream path in the variations of the Atlantic Meridional Mode (AMM) which is characterized by an interhemispheric gradient in sea surface temperatures and oscillations in the strength of surface winds across the equator. Evidence suggests two time scales for this interaction. Anomalous Ekman suction induced by AMM cools the tropical Atlantic. The cold water in the western tropical Atlantic is entrained into the currents feeding the Gulf Stream and this cooling signal reaches North Wall within a year. The cold anomalies in the central tropical Atlantic propagate westward—likely as baroclinic Rossby waves—reaching the Gulf Stream and resulting in a southward shift in the North Wall position after a delay of approximately one year.