Satellites have recorded a clear drop in chlorophyll across the central Pacific as the 2026 El Niño strengthens. The change points to fewer phytoplankton at the base of the marine food web. NASA’s Earth Observatory tracked the decline against neutral conditions recorded in June 2025. ([1])
Early Signals From Orbit
Chlorophyll concentrations serve as a direct indicator of phytoplankton abundance. Lower readings mean less plant life near the surface. The observed reduction has already spread across a wide stretch of the equatorial Pacific. Scientists expect the pattern to expand as the event develops.
The timing aligns with the current strengthening phase of El Niño. Measurements show the shift began earlier than some models had projected. This provides a real-time view of how large-scale climate patterns affect ocean biology.
Why Nutrients Are Declining
Normal upwelling brings cold, nutrient-rich water from deeper layers to the surface. During El Niño, weakened trade winds allow the warm surface layer to thicken. That deeper warm layer blocks the usual rise of nutrients. Oceanographer Hyung-Gyu Lim noted that the reduced nutrient supply is a typical feature of developing El Niño events.
NASA researchers Matthew Kehrli and Graham Trolley explained the mechanism in detail. They described how the altered wind patterns suppress the vertical movement of water. As a result, phytoplankton receive fewer resources for growth. The process unfolds gradually but can affect large areas over several months.
Effects on the Food Web
Phytoplankton support zooplankton, which in turn feed fish, seabirds, and marine mammals. A sustained drop at the base reduces food availability throughout the chain. Past El Niño episodes produced measurable declines in fish catches, particularly in regions that rely on nutrient-driven productivity.
Peru’s anchovy fishery has shown sensitivity to these conditions in earlier events. Warmer surface waters and lower nutrient levels combine to limit the fish populations that support both commercial harvests and seabird colonies. Similar pressures could appear in other parts of the Pacific this year.
What Remains to Be Seen
The full geographic reach and duration of the chlorophyll decline are still unfolding. Satellite data will continue to track changes through the peak of the event. Researchers emphasize that not every El Niño produces identical biological responses.
Coastal communities and fisheries will watch for shifts in species distribution and abundance. The current observations offer an early warning rather than a final assessment. Continued monitoring will clarify how far the disruption extends and how long it persists.
