In press: Journal of Physical Oceanography

A time-dependent trajectory algorithm is used to determine the sources of the Pacific Equatorial Undercurrent (EUC) in a global climate model with 1/4 degree (eddy-permitting) resolution and forced with realistic winds. The primary sources and pathways are identified and the transformation of properties in temperature/salinity space are explored. An estimate for the quantity of recirculation, a notoriously difficult property to estimate from observational data, is given. Over two-thirds of the water in the Pacific EUC at 140°W originates south of the equator. 70 % of the EUC is ventilated outside of the tropics (poleward of 13°S or 10°N): three quarters of these extratropical trajectories travel through the western boundary currents between their subduction and incorporation into the EUC and one fifth of the extratropical trajectories enter and leave the tropical band at least once before entering the EUC. 1