A developing El Nino is already leaving its mark on the Pacific Ocean, with an Isro satellite detecting a noticeable fall in surface chlorophyll-a levels during June 2026. The decline points to changes in marine productivity and offers an early glimpse of how the climate phenomenon is beginning to affect ocean conditions.
Observations from Isro’s Oceansat-3 satellite show that the drop in chlorophyll-a coincided with changes in surface winds across the equatorial Pacific. The findings suggest that the developing El Nino is not just an atmospheric event but is also triggering visible biological and physical changes in the ocean.
Satellite data reveals a shifting Pacific
Oceansat-3, also known as Earth Observation System EOS-06, was launched in 2022 to monitor ocean and atmospheric conditions. Its sensors track physical changes in the ocean as well as variations in marine biology.
Scientists at Isro’s National Remote Sensing Centre (NRSC) in Hyderabad analysed satellite data from the tropical Pacific for April, May and June across 2023, 2024, 2025 and 2026.
The comparison showed that June 2024 and June 2025 reflected neutral El Nino-Southern Oscillation (ENSO) conditions. However, June 2026 recorded a clear decline in surface chlorophyll-a levels as El Nino conditions began developing, The Tribune reports.
The satellite observations also showed that areas with higher chlorophyll concentrations had reduced in size and extended less towards the west during April-June 2026. At the same time, surface winds shifted from their usual easterly direction towards westerlies.
Together, these changes indicate that the Pacific Ocean is responding to the early stages of El Nino, giving scientists important clues about how the event may evolve in the coming months.
Why a fall in chlorophyll-a raises concern
Chlorophyll-a is present in phytoplankton, tiny marine organisms that form the foundation of much of the ocean food chain. A decline in chlorophyll-a levels can signal reduced marine productivity and may eventually affect species that depend on phytoplankton for survival.
During El Nino events, the normal trade winds along the equatorial Pacific weaken. This disrupts ocean circulation and reduces the upwelling of cold, nutrient-rich water from deeper layers.
With fewer nutrients reaching the sunlit surface, phytoplankton growth slows down or becomes limited to smaller regions. This leads to lower chlorophyll-a concentrations near the ocean surface.
The latest observations highlight how even small changes in ocean biology can reveal larger shifts in the climate system. Satellite monitoring is becoming increasingly important in understanding these changes before their wider effects are felt.
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El Nino may intensify in the months ahead
El Nino refers to unusual warming of sea-surface temperatures in the central and eastern equatorial Pacific. The phenomenon can disrupt atmospheric circulation and influence weather patterns across the world.
Its effects are often linked with heatwaves, extreme temperatures and changes in rainfall patterns in different regions.
Several global weather agencies have warned that El Nino could become stronger during September-November 2026 and may continue until February 2027.
The latest Isro satellite observations provide an early warning of the ocean’s changing state, showing that the impact of El Nino is already visible beneath the surface even before its full climatic effects emerge.
