[A-OS13] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS13-06] Interannual Variability in contributions of the Equatorial Undercurrent (EUC) to Peruvian Upwelling

*Gandy Maria Rosales Quintana¹、Robert Marsh²、Luis Alfredo Icochea Salas³ (1.Course of Applied Marine Environmental Studies, Tokyo University of Marine Science and Technology、2.University of Southampton, UK、3.Universidad Nacional Agraria La Molina, Peru)

キーワード：Peruvian Upwelling, Equatorial Undercurrent, Particle tracking

Time-varying sources of upwelling waters off the coast of northern Peruvian are analysed in a Lagrangian frame- work, tracking virtual particles backwards in time. Particle trajectories are calculated with temperature, salinity and velocity fields from a hindcast spanning 1988-2007, obtained with an eddy-resolving (1/12o) global configuration of the NEMO ocean model. At 30 and 100 m, where late-December coastal upwelling rates exceed 50 m per month, particles are seeded in proportion to the upwelling rate. Ensemble maps of particle concentration, age, depth, temperature, salinity and density reveal that a substantial but variable fraction of the particles upwelling off Peru arrive via the Equatorial Undercurrent (EUC). Particles follow the EUC core at around 250 m, characterized by temperatures of around 15-17oC, salinities in the range 34.9-35.2, and densities of = 25.5-26.5 . Additional inflows are via two slightly deeper branches further south from the main system, at around 3oS and 8o. The annual percentage of particles recruited by the EUC (17.5-47% and 16.5-54.6%, from 30 and 100 m respectively) reveal that more of the Peruvian upwelling can be tracked back to the EUC during El Niño and weak La Niña events. In contrast, upwelling waters are of more local origin during a strong La Niña,. Annually averaging EUC transport at specific longitudes, notable anomalies are evident during the major El Niño /La Niña transition of 1997-99. On short timescales, a degree of longitudinal coherence is evident in EUC transport, with transport anomalies at 160oW evident at the Galapagos Is- lands (92oW) around 30-35 days later. We conclude that the Peruvian upwelling system is subject to a variable EUC influence, on a wide range of timescales, most notably the interannual timescale of El Niño Southern Oscillation (ENSO).