Isro satellite detects sharp drop in marine productivity as El Niño warms Pacific

El Niño is linked with extreme weather, heatwaves, high temperatures, and subdued rainfall. (Photo Credit: Wikimedia Commons)

Even before the ongoing El Niño becomes a full-blown event, Isro’s Oceansat-3 observations have captured a decline in marine productivity across the equatorial Pacific Ocean in recent months and linked it to the warming oceans.

El Niño is the abnormal warming in the sea surface temperatures recorded along the equatorial Pacific Ocean. This surplus warming alters the atmospheric wind and ocean wave flow patterns and carries the potential to alter global weather. El Niño is linked with extreme weather, heatwaves, high temperatures, and subdued rainfall.

Launched in 2022, Isro’s Oceansat-3 (also known as Earth Observation System EOS-06) is designed for global monitoring of the atmosphere along with observing the biological and physical parameters of the ocean. It has multi-sensor data gathering ability coming from the Ocean Colour Monitor-3 (OCM-3) and Scatterometer sensors.

The National Remote Sensing Centre (NRSC), Isro’s centre In Hyderabad, recorded observations of the chlorophyll-a (green pigmentation in plants meant to support photosynthesis) obtained using these sensors. These measurements and subsequent analysis were performed across the tropical Pacific Ocean for April, May and June of 2023, 2024, 2025 and 2026.

The satellite observations of June 2024 and June 2025 corroborated neutral ENSO conditions.

“But the observations for June 2026, under a developing El Niño scenario, revealed a notable reduction in surface chlorophyll-a. This decline coincides with a reversal of ocean-surface winds – from easterlies to westerlies as expected in El Niño years. This weakening and reversal of the prevailing winds, along with the shrunken westward extent of the chlorophyll region observed during April-June 2026, further supports the developing El Niño event,” they added.

Satellite images showing a reduction over the years in chlorophyll-a along the equatorial Pacific Ocean (Photo Credit: Isro)

Reduction in marine productivity, especially in the form of chlorophyll, could indirectly also mean reduced food for the marine life in the oceans, thus potentially threatening their existence.

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During an El Niño event, weakened equatorial trade winds and a steep variation in sea-surface temperatures tend to reduce the upward transportation of the cooler, nutrient-rich waters from the subsurface that feed the phytoplankton. As nutrient-deficit water reaches the sunlit upper ocean surface, phytoplankton growth gets suppressed or concentrated over a smaller region. As a result, there are lower concentrations of surface chlorophyll-a and thus reduced marine productivity, experts at NRSC said.

With multiple global weather agencies having warned of the development of a ‘very strong’ El Niño during September-November this year and the event forecast to prevail till February 2027, Isro warned that the low-chlorophyll region in the Pacific Ocean may become more pronounced in the coming months.