Fate of the Equatorial Undercurrent in the Atlantic

The fate of water masses in the Equatorial Undercurrent (EUC) in the Atlantic is studied in a high-resolution ocean model. Lagrangian trajectory analysis is used to determine sites where water masses from the EUC upwell and downwell again. The use of Lagrangian mean transports to trace particles takes high temporal variability in the tropics into account. 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 Gulfstream. 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 does not recirculate but leaves the Atlantic basin at the southwestern side to participate in the global meridional overturning circulation. Most of that water has been transformed in the Atlantic to deep water.