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Oceansat-3 shows El Niño weakening the ocean’s food supply

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First brief 11 Sep, 11:07 am IST Updated 11 Sep, 11:07 am IST 1 development 2 min read Latest ↓

Oceansat-3: June chlorophyll and wind comparisons — ISRO/NRSC · Used with attribution

Where it stands

ISRO’s Oceansat-3 observations show reduced surface chlorophyll in parts of the equatorial Pacific as El Niño developed in 2026. Chlorophyll is the light-capturing pigment in phytoplankton, microscopic organisms near the base of the marine food web. Weaker and reversed winds can reduce the rise of nutrient-rich water from below, limiting their growth. ISRO released the analysis on 10 September, using observations from April–June. This is a finding from an existing satellite, not a new launch. It points to stress on marine productivity; it does not measure a worldwide fall in fish catches.

Background

Sunlight alone cannot sustain the ocean’s microscopic producers. Phytoplankton also need nutrients, many of which come from deeper water. Winds help move surface water aside, allowing cooler, nutrient-rich water to rise. This process is called upwelling. During El Niño, changes in Pacific winds and the depth of the warm surface layer can weaken that supply. Less food for phytoplankton can then affect animals that feed on them and, further along the food web, fish and seabirds. The consequences differ between locations and seasons. Satellite measurements help track the first part of this chain, while measurements at sea help test the wider effects.

How it developed

Earlier context: Oceansat-3’s ocean instruments

How it started
Ocean colour and wind measurements can be read together

EOS-06, also called Oceansat-3, is an existing ocean-observation satellite. Its Ocean Colour Monitor measures reflected light in different bands, helping scientists estimate surface chlorophyll. A separate scatterometer provides ocean-surface wind information. Using both measurements allows researchers to examine how physical conditions and biological activity vary together. These measurements complement each other: changed winds may explain a change in nutrient supply and phytoplankton growth. The satellite does not directly count fish or measure every part of the marine ecosystem.

ISRO NOAA
10 September 2026: April–June observations analysed

New fact
June comparisons link lower chlorophyll with changed Pacific winds

NRSC compared June 2026 observations with June 2024 and June 2025, periods described as neutral ENSO conditions. Lower surface chlorophyll coincided with weakened or reversed winds in the western and central equatorial Pacific. The pattern supports reduced upwelling during the developing El Niño. ISRO says further interpretation should use measurements of temperature, sea level, thermocline depth and circulation. Conditions may become more pronounced if El Niño strengthens, but that is conditional. WMO’s seasonal outlook also stresses that regional effects vary; this observation is not a precise rainfall forecast for India.

ISRO / NRSC WMO NOAA

Why it matters for UPSC

GS1 · OceanographyGS3 · Environment and space technology

For GS1 and GS3, link ocean circulation, El Niño and marine ecology. Explain the wind–upwelling–nutrient–phytoplankton chain. Distinguish a satellite indicator from a direct fish-stock count, and observed changes from forecasts of what may happen next.

Key terms

El Niño and ENSOEl Niño is the warm phase of the El Niño–Southern Oscillation, a recurring interaction between the tropical Pacific Ocean and atmosphere. It involves changes in sea-surface temperatures, winds and rainfall. La Niña is the opposite cool phase; neutral conditions mean neither phase dominates.

Trade windsThe prevailing tropical winds that normally blow from east to west across the equatorial Pacific. Their strength helps shape surface currents and the distribution of warm water. When they weaken or reverse, the supply of deeper water to the surface can also change.

UpwellingThe rise of deeper water to replace surface water moved away by winds and currents. Deep water can carry nutrients into the sunlit layer, supporting microscopic life. Less upwelling can therefore reduce biological production even though sunlight remains available.

ThermoclineThe layer in which water temperature changes rapidly with depth, separating warmer surface water from colder water below. If it deepens, nutrient-rich deeper water can become less accessible to the surface. Its position helps explain why wind and temperature changes affect biological growth.

PhytoplanktonMicroscopic photosynthetic organisms that use sunlight and nutrients to grow in the upper ocean. They support many marine food webs because other organisms feed on them. Changes in their abundance can affect larger animals, but the effect is not identical across species or regions.

Chlorophyll-a as an indicatorA pigment involved in photosynthesis. Ocean-colour measurements can be used to estimate its concentration near the surface, helping track phytoplankton. It is an indicator of biological conditions, not a direct count of fish or a complete measurement of ocean health.

Ocean Colour Monitor and scatterometerTwo different satellite instruments. The colour monitor measures reflected light; the scatterometer uses radar observations to estimate ocean-surface winds. Combining their information helps researchers examine a possible physical explanation for a biological pattern, instead of viewing either pattern alone.

Marine productivity and food webMarine primary productivity concerns the production of organic matter by organisms such as phytoplankton. A food web describes how that material and energy support other life. Reduced productivity can put pressure on fisheries, but a claim about actual catches needs separate evidence.

Sources (5)

ISRO · official · EOS-06 mission and instruments
NOAA · official · How El Niño affects phytoplankton and marine food webs
ISRO / NRSC · official · Oceansat-3 observations of El Niño and marine productivity, 10 September 2026
WMO · official · El Niño outlook and regional uncertainty, 31 July 2026
NOAA · official · El Niño: winds, the thermocline and nutrient supply