Oceansat-3 spots falling marine productivity as El Niño builds in Pacific

Isro's Oceansat-3 satellite has detected a marked fall in marine productivity across the equatorial Pacific Ocean, even as the current El Niño remains short of full strength, according to observations analysed by the space agency's National Remote Sensing Centre (NRSC) in Hyderabad.

El Niño refers to abnormal warming of sea-surface temperatures along the equatorial Pacific. This excess heat reshapes atmospheric winds and ocean circulation, with the potential to influence weather worldwide. The phenomenon is associated with extreme weather, heatwaves, high temperatures and deficient rainfall.

Launched in 2022, Oceansat-3 — also called the Earth Observation System EOS-06 — is built to monitor the atmosphere globally and to track the biological and physical properties of the ocean. Its data come from multiple sensors, including the Ocean Colour Monitor-3 (OCM-3) and a scatterometer.

Using these sensors, NRSC scientists examined chlorophyll-a — the green pigment that supports photosynthesis in plants — across the tropical Pacific for April, May and June of 2023, 2024, 2025 and 2026. Satellite readings for June 2024 and June 2025 matched neutral ENSO conditions.

However, observations for June 2026, under a developing El Niño, showed a clear reduction in surface chlorophyll-a. The decline coincided with a reversal of ocean-surface winds from easterlies to westerlies, a shift typical of El Niño years. The weakening and reversal of prevailing winds, along with the contracted westward spread of the chlorophyll-rich region during April–June 2026, further point to a developing El Niño event.

A fall in marine productivity, particularly in chlorophyll, can indirectly mean less food for marine life, potentially threatening its survival.

During El Niño, weakened equatorial trade winds and sharp sea-surface temperature contrasts curb the upward movement of cooler, nutrient-rich water from the subsurface that sustains phytoplankton. When nutrient-poor water reaches the sunlit upper ocean, phytoplankton growth is suppressed or confined to a smaller area. The result is lower surface chlorophyll-a concentrations and reduced marine productivity, NRSC experts said.

With several global weather agencies warning of a 'very strong' El Niño during September–November this year and the event expected to persist until February 2027, Isro cautioned that the low-chlorophyll zone in the Pacific could become more pronounced in the months ahead.