Fate of the Equatorial Undercurrent in the Atlantic

Abstract

The fate of water masses in the Equatorial Undercurrent (EUC) in the Atlantic is studied using a high-resolution ocean model. Lagrangian trajectory analysis is used to determine sites where water masses from the EUC upwell and later downwell. The use of Lagrangian mean transports to trace particles takes into account high-temporal variability in the tropics. Most EUC water upwells in the equatorial region. The pathways between the EUC core and the upwelling sites indicate that most particles upwell rather directly at the equator. Other upwelling sites are found close to the African contintent and along the Gulf Stream. After upwelling, particles subduct again in the tropical and subtropical Atlantic. The particles that recirculate back to the EUC experience, on average, five upwellings and downwellings. The sites where the particles subduct for the last time before returning to the EUC are found mainly along the South Equatorial Current. Most particles follow the western boundary back to the tropics. Two thirds of EUC transport at 20°W does not recirculate, but leaves the Atlantic basin at the southwestern side to participate in the global meridional overturning circulation. Most of this water has been transformed in the Atlantic to deep water.