On the pathways of the equatorial subsurface currents in the eastern equatorial Pacific and their contributions to the Peru-Chile Undercurrent

The connections between the Equatorial Current System and the Peru Current System in the eastern tropical Pacific (ETP) are examined with a primitive equations eddy-resolving regional model. The quasi-equilibrium solutions reproduce three eastward equatorial subsurface currents of interest: the Equatorial Undercurrent (EUC, located between 1 degrees N and 1 degrees S), the primary Southern Subsurface Countercurrent (pSSCC, between 3 degrees and 4 degrees S) and, farther south the secondary Southern Subsurface Countercurrent (sSSCC, between 7 degrees and 8 degrees S). Using a Lagrangian tracking procedure, the fate of these currents in the ETP and their contribution to the Peru-Chile Undercurrent (PCUC) are studied. Lagrangian diagnostics show that for the most part the EUC water contributes to westward flows, including the South Equatorial Current and deeper flows below it, and strikingly only a very little fraction feeds the PCUC, while a significant part of both SSCCs contribute substantially. Mesoscale eddies are shown to exert an effect on these connections. In addition, about 30% of the PCUC is fed by the three subsurface equatorial flows (EUC, pSSCC, sSSCC). The remaining part of the PCUC comes from an alongshore recirculation associated with flows below it, and from the southern part of the domain (south of similar to 9 degrees S).