El Niño, the naturally recurring phenomenon characterized by warmer-than-normal water temperatures in parts of the equatorial Pacific, is having a profound impact on marine life. This article delves into the ecological effects of El Niño, particularly its influence on the marine food web. The focus is on the changes in chlorophyll concentrations, an indicator of phytoplankton abundance, observed by the Ocean Color Instrument (OCI) on NASA's PACE satellite. The central Pacific, around the equator due north of New Zealand, is experiencing a significant reduction in chlorophyll concentrations in 2026, which is expected to have ripple effects through the marine food web. This phenomenon is primarily due to the weakening of easterly equatorial trade winds, the extension of the warm surface layer of the ocean, and the suppression of the upwelling of cool, nutrient-rich water that typically fuels phytoplankton growth. As the El Niño progresses, these differences in the central Pacific are anticipated to become more pronounced, potentially leading to a greater difference in values across the region. The reduction in phytoplankton abundance has severe implications for coastal regions, including Peru's anchovy fisheries, which have seen profound declines in catch during past El Niños. This has led to the suspension of fishing to safeguard the country's main fishing resource. The disruptions to marine life can be severe, but a post-El Niño "chlorophyll rebound" can occur, fueled by higher iron concentrations delivered in ocean currents and dust arriving from drier land in parts of Central and South America. The PACE mission, launched in February 2024, is providing new tools for studying these changes, offering the first complete El Niño event for which the satellite will gather global, near-daily hyperspectral measurements. From my perspective, the PACE mission is a crucial step forward in our understanding of the complex interactions between El Niño and marine life, and its data will be instrumental in predicting and mitigating the impacts of future El Niño events on our oceans.
