Spatiotemporal variability and ENSO modulation of subsurface anticyclonic eddies（Puddies）in the Peru-Chile eastern boundary upwelling system

ROSALES QUINTANA G.M.; NAGAI T.; ICOCHEA SALAS L.A. · La Mer (2025) · DOI: 10.32211/lamer.63.3-4_95

Resumen

In eastern boundary upwelling systems(EBUSs), eddies are crucial for offshore transport of biogeochemical tracers and their vertical exchanges. We investigate the spatial and temporal variability of subsurface-intensified anticyclonic eddies(Puddies)in the Peruvian EBUS using high-resolution reanalysis and observations. Results show that subsurface intensified anticyclonic eddies dominate the subsurface layer, accounting for 54% of the total number of subsurface eddies. They exhibit a marked seasonal cycle, peaking in austral autumn closely aligned with eddy kinetic energy and Peru-Chile Undercurrent(PCUC)variability. The number of subsurface intensified anticyclonic eddies increases during El Niño events(1997–1998, 2015-2016), and moderately warm years(2008, 2012 and 2014), coinciding with a deepening of the σθ= 26-isopycnal near the coast, as the equatorial warm pool propagates poleward as the coastal trapped waves. This propagating deepening of the isopycnal intensifies the PCUC and fosters greater subsurface eddy generation. Several methods were used to estimate the phase speed of the propagation. For the reanalysis data, the poleward phase speeds of the first baroclinic mode internal Kelvin wave obtained by solving the vertical modal equation range from 0.8 to 1.7 m s-1 with higher values in higher latitude, that are consistent very well with the direct estimation of the propagation speeds using the first order polynomial fit to the peaks of isopycnal displacement. Using the coherence spectral analysis, the mean propagation speed of 40-85-m bandpassed σθ observation data between Chicama and Callao was estimated to be 0.87 m s-1, consistent with those estimated using reanalysis. These findings underscore how large-scale climate variability, through coastal-trapped-Kelvin waves propagation and subsequent PCUC intensification, significantly modulates the subsurface eddy activity in the Peruvian EBUS. © (2025), (Societe Franco-Japonaise d’Oceanographie). All rights reserved.

Instituciones: Universidad Nacional Agraria La Molina