[1] The extratropical sources of equatorial undercurrent (EUC) water have been identified for an ocean circulation model using Lagrangian trajectory analysis, lt has been found that the EUe waters emenate from a wide range of latitudes in the Pacific basin, with its densest constituent watennass being Subantarctic Mode Water (SAMW) from 50oS, Further analysis of the basin-scale circulation fields has revealed significant advective diapycnal mass fluxes associated with intergyre exchange, As a result of these diapycnal mass fluxes, the EUe transport as a function of density at 151°W (an Eulerian diagnostic) looks quite different from the original subduction rate as a function of density for the same collection of water particles, This implie...