Satellite observations by the Indian Space Research Organisation (ISRO) have detected a decline in marine productivity across parts of the tropical Pacific Ocean, providing fresh evidence of the evolving El Niño–Southern Oscillation (ENSO) and its impact on ocean conditions.
ISRO's National Remote Sensing Centre (NRSC) analysed chlorophyll-a observations from the Ocean Colour Monitor-3 (OCM-3) and ocean-surface wind data from the EOS-06 Scatterometer for April, May and June during 2023–2026.
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A comparison of June 2024 and June 2025, when ENSO conditions were neutral, with June 2026 observations during the developing El Niño showed a marked decline in surface chlorophyll-a. Chlorophyll-a is an indicator of phytoplankton abundance.
The decline coincided with a shift in equatorial winds from their usual easterly direction to westerlies, weakening the ocean's normal upwelling process across parts of the western and central equatorial Pacific. This reduces the movement of cool, nutrient-rich subsurface water towards the surface, limiting phytoplankton growth and lowering marine productivity.
ISRO said the apparent contraction of the westward extent of areas with elevated chlorophyll levels between April and June 2026 further supports evidence of weakening equatorial upwelling as El Niño developed.
The combined observations from OCM-3 and the EOS-06 Scatterometer highlight the strong biophysical coupling between ocean winds and marine productivity during the developing climate event. If El Niño intensifies, the low-chlorophyll region could become more pronounced, researchers said.
The satellite findings are consistent with the World Meteorological Organisation's (WMO) outlook, which in June estimated an approximately 80% probability of El Niño conditions developing during June-August 2026. By late July, the WMO said the event was intensifying and expected to strengthen during August-October.
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ISRO said further assessment will require observations of equatorial winds, sea-surface temperatures, sea-level height, thermocline depth and ocean circulation to track the event's evolution and its wider environmental impacts.
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