Abstract. Time-varying sources of upwelling waters off the coast of northern Peruvian are analysed in a Lagrangian framework, tracking virtual particles backwards in time for 12 months. 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, characterised by temperatures of around 15–17 ºC, salinities in the range 34.9–35.2, and densities of σ = 25.5–26.5. Additional inflows are via two slightly deeper branches further south from the main system, at around 3º S 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, a notable negative-to-positive transition is evident during the major El Niño/La Niña events of 1997–99. On short timescales, a degree of longitudinal coherence is evident in EUC transport, with transport anomalies at 160º W evident at the Galapagos Islands (92º W) around 30–35 days later. It is concluded 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). Identifying this variability as a driver of shifts in population and catch data for several key species, during the study period, these new findings may inform sustainable management of commercially-important fisheries off northern Peru.
Bacterial Community Composition in a Semi-Intensive Shrimp Culture of L. vannamei during El Niño 1997-98 and La Niña 1999
