Preprints
https://doi.org/10.5194/os-2021-13
https://doi.org/10.5194/os-2021-13

  02 Mar 2021

02 Mar 2021

Review status: this preprint is currently under review for the journal OS.

Interannual Variability in contributions of the Equatorial Undercurrent (EUC) to Peruvian Upwelling

Gandy Maria Rosales Quintana1, Robert Marsh2, and Luis Alfredo Icochea Salas3 Gandy Maria Rosales Quintana et al.
  • 1Tokyo University of Marine Science and Technology, Japan
  • 2University of Southampton, UK
  • 3Universidad Nacional Agraria La Molina, Peru

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.

Gandy Maria Rosales Quintana et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-13', David Webb, 16 Mar 2021
    • AC1: 'Reply on RC1', Gandy Rosales, 08 Jun 2021
  • EC1: 'Comment on os-2021-13', Neil Wells, 13 Apr 2021
    • AC2: 'Reply on EC1', Gandy Rosales, 08 Jun 2021
  • RC2: 'Comment on os-2021-13', Anonymous Referee #2, 15 Apr 2021
    • AC3: 'Reply on RC2', Gandy Rosales, 08 Jun 2021
  • RC3: 'Comment on os-2021-13', Anonymous Referee #3, 21 Apr 2021
    • AC4: 'Reply on RC3', Gandy Rosales, 08 Jun 2021

Gandy Maria Rosales Quintana et al.

Gandy Maria Rosales Quintana et al.

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Short summary
The Equatorial Undercurrent (EUC) plays a central role on the circulation and hydrography on tropical Pacific, with notable influence at the eastern boundary and coastal upwelling off Peru. By tracking virtual particles, we find that the EUC contribution to Peruvian upwelling is highly variable from year to year and related to El Niño Southern Oscillation (ENSO). The EUC contribution is more substantial during the cold and warm phases of ENSO, when a major shift in marine population occurred.