The OMZ and nutrients features as a signature of interannual and low frequency variability off the peruvian upwelling system

Abstract

The last years, the Humboldt Current Upwelling Ecosystem and particularly the Northern component off Peru, was a natural scenario for several studies and a "hot spot" for scientists around the world because of their unique characteristics: (1) one of the bigger catch productivity, (2) one of the shallowest, intense and acidic Oxygen Minimum Zone (OMZ), (3) one of the intense nitrogen lost areas and anammox activity, and (4) one of the strongest interannual variability associated with the Equatorial remote forcing. In this context, we examined the oceanographic and biogeochemical variability associated with the OMZ off central Peru, from a monthly time-series (1996–2009) recorded off Callao (12°02' S). Both, physical and chemical time series exhibit a significant temporal variability, with intense interannual El Niño effects in the deepening of the OMZ distribution and nutrients dynamic but also intraseasonal activity by the influence of the Equatorial Kelvin Wave (IEKW). The chemical time series indicate after 2002 year higher frequency variability in phase with the increase of the IEKW, particularly with the second mode activity. We present evidences that the IEKW appear to modulate the distribution and intensity of the OMZ in the area and in consequence an impact on the chemical structure and biogeochemical activity. The data suggest that the remote forcing could be strongest not only at interannual but also at lower temporal frequencies changing the seasonal signature of upwelling systems.