Dynamics of Surface Chlorophyll and the Asymmetric Response of the High Productive Zone in the Peruvian Sea: Effects of El Niño and La Niña

Abstract

This study analyzes over 26 years of satellite data to explore the seasonal and interannual variability of surface chlorophyll-a from September 1997 to March 2024, focusing on the impacts of the El Niño-Southern Oscillation (ENSO). We investigate how these phases affect the High Productivity Zone (HPZ) during two seasonal periods: The Warm Season (December to April) and the Cold Season (June to September). From an ENSO-neutral perspective, the HPZ is more extensive and exhibits higher chlorophyll concentrations during the Warm Season. Conversely, in the Cold Season, low chlorophyll concentrations are found and the area of the HPZ is reduced by 88,000 km². Under El Niño conditions, chlorophyll-a concentrations decrease consistently along the near-offshore region, but a counter-intuitive increase is observed within the 25 km from shore. La Niña phase enhances chlorophyll in the near-offshore region while reducing it in the very nearshore waters. This study further highlights the asymmetric response of various physical drivers (such as upwelling strength and light) to different ENSO phases. This finding underscores the intricate interplay between ENSO and marine productivity, where the response can vary seasonally. These findings underscore a spatially complex response of the Peruvian coastal productivity to ENSO phases. Understanding these dynamics is vital for predicting future shifts in coastal productivity and for developing adaptive management strategies to mitigate the impacts of climate variability on marine resources.