Isro satellite detects sharp drop in marine productivity as El Niño warms Pacific
2-minute summary
ISRO's Oceansat-3 (EOS-06) satellite has detected a significant decline in marine productivity and surface chlorophyll-a levels across the equatorial Pacific Ocean, linked to a developing El Niño phase in 2026. Data analyzed by the National Remote Sensing Centre (NRSC), Hyderabad, over the months of April, May, and June from 2023 to 2026, revealed a sharp drop in chlorophyll-a during June 2026. This ecological shift coincides with the weakening and reversal of equatorial trade winds from easterlies to westerlies. Under normal conditions, these winds drive the upwelling of cool, nutrient-rich subsurface waters that feed phytoplankton. During El Niño, the suppressed upwelling starves the sunlit upper ocean of nutrients, inhibiting phytoplankton growth (measured via chlorophyll-a). Because phytoplankton form the base of the marine food web, this decline threatens marine life and fisheries. With global agencies predicting a strong El Niño persisting into early 2027, this low-chlorophyll trend is expected to intensify.
Why it's in the news
ISRO's Oceansat-3 satellite has captured real-time empirical evidence of a sharp drop in marine chlorophyll-a in the equatorial Pacific, marking the biological onset and impact of a developing El Niño event in 2026.
Background and context
The El Niño Southern Oscillation (ENSO) is a major driver of global climate variability, characterized by periodic fluctuations in sea surface temperatures (SST) and atmospheric pressure across the equatorial Pacific. During El Niño (the warm phase), the weakening of easterly trade winds allows warm water to accumulate in the central and eastern Pacific. This suppresses the thermocline and halts the upwelling of nutrient-rich cold deep waters, which are vital for sustaining phytoplankton—the primary producers of the marine ecosystem. To monitor these critical oceanographic and atmospheric parameters, ISRO launched Oceansat-3 (EOS-06) in November 2022. Equipped with advanced payloads like the Ocean Colour Monitor-3 (OCM-3) and a Scatterometer, the satellite plays a vital role in tracking ocean health, chlorophyll concentrations, and wind vectors globally.
Committees and reports
- World Meteorological Organization (WMO) ENSO Update — Warned of a developing 'very strong' El Niño expected to last until February 2027, correlating with the biological anomalies observed by ISRO's Oceansat-3.
International organisations
- World Meteorological Organization (WMO) — The specialized agency of the United Nations responsible for monitoring global weather, climate, and water resources, which issued the warning on the 2026-2027 El Niño event.
Mains practice: Explain the biophysical mechanism through which El Niño impacts marine ecosystems and primary productivity. How do space-based remote sensing technologies aid in monitoring these changes?
El Niño, the warm phase of the El Niño Southern Oscillation (ENSO), is characterized by abnormal warming of sea surface temperatures (SSTs) in the equatorial Pacific. Beyond its well-known atmospheric impacts on global weather, El Niño profoundly disrupts marine ecosystems by suppressing primary ocean productivity.
• **Biophysical Mechanism of Impact**:
1. *Weakening of Trade Winds*: Under normal conditions, strong easterly trade winds push warm surface waters westward, allowing cold, nutrient-rich subsurface waters to rise (upwelling) in the eastern and central Pacific.
2. *Suppression of Upwelling*: During El Niño, these trade winds weaken or reverse to westerlies. This collapses the pressure gradient, deepens the thermocline, and blocks the upwelling of nutrient-dense deeper waters.
3. *Phytoplankton Decline*: Phytoplankton require nutrients (nitrates, phosphates) and sunlight to photosynthesize. The lack of upwelling starves the sunlit upper ocean of these nutrients, suppressing phytoplankton growth and sharply reducing chlorophyll-a levels.
4. *Marine Food Web Disruption*: As primary producers, a decline in phytoplankton directly reduces food availability for zooplankton, fish, and larger marine mammals, threatening marine biodiversity and commercial fisheries.
• **Role of Space-Based Remote Sensing (e.g., Oceansat-3)**:
1. *Chlorophyll-a Monitoring*: Satellites utilize specialized sensors like the Ocean Colour Monitor-3 (OCM-3) to detect green pigmentation (chlorophyll-a) on the ocean surface, mapping marine productivity in real-time.
2. *Wind Vector Analysis*: Scatterometers onboard these satellites measure ocean surface wind speed and direction, capturing the transition from easterly to westerly winds that signals El Niño.
3. *Sea Surface Temperature (SST) Mapping*: Thermal sensors track changes in ocean temperatures, helping scientists predict the onset and intensity of ENSO events.
In conclusion, space-based remote sensing acts as an indispensable tool for global climate monitoring. By linking atmospheric wind anomalies with biological declines in the ocean, satellites like Oceansat-3 enable proactive ecological management and disaster preparedness.
Prelims practice questions
Q1. With reference to ISRO's Oceansat-3 (EOS-06) satellite, consider the following statements: 1. It was launched to monitor both atmospheric and oceanographic physical and biological parameters. 2. It is equipped with an Ocean Colour Monitor (OCM-3) sensor to track surface chlorophyll-a levels. 3. It operates in a geostationary orbit to provide continuous real-time monitoring of the Indian Ocean region. Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: A. Oceansat-3 (EOS-06) is an Earth Observation satellite launched in 2022 into a Sun-synchronous polar orbit (not geostationary) to provide global coverage. It monitors ocean color, sea surface winds, and temperature using instruments like OCM-3 and a Scatterometer. Thus, statements 1 and 2 are correct, while statement 3 is incorrect.
Q2. During an El Niño event, which of the following oceanographic changes typically occur in the equatorial Pacific Ocean? 1. Reversal or weakening of equatorial trade winds from easterlies to westerlies. 2. Deepening of the thermocline in the eastern Pacific. 3. Enhanced upwelling of nutrient-rich cold waters off the coast of Peru. Select the correct answer using the code given below:
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: A. During El Niño, trade winds weaken or reverse (easterlies to westerlies), and the warm water pool moves eastward, deepening the thermocline in the eastern Pacific. This suppresses (rather than enhances) the upwelling of nutrient-rich cold waters. Therefore, statements 1 and 2 are correct, and statement 3 is incorrect.
Q3. Which of the following organizations/centers of ISRO is primarily responsible for receiving, processing, and distributing satellite data from Earth observation missions like Oceansat-3?
- National Remote Sensing Centre (NRSC), Hyderabad
- Liquid Propulsion Systems Centre (LPSC), Thiruvananthapuram
- Space Applications Centre (SAC), Ahmedabad
- Satish Dhawan Space Centre (SDSC), Sriharikota
Answer: A. The National Remote Sensing Centre (NRSC) in Hyderabad is the nodal agency under ISRO responsible for acquisition, processing, and dissemination of aerial and satellite remote sensing data (including Oceansat-3 data).
Revision flashcards
- What is Oceansat-3 (EOS-06) and when was it launched? It is an ISRO Earth Observation satellite launched in November 2022, designed to monitor ocean color, surface winds, and sea surface temperature globally.
- Which sensor on Oceansat-3 is specifically used to measure ocean chlorophyll-a concentrations? The Ocean Colour Monitor-3 (OCM-3) sensor.
- How does El Niño affect the prevailing trade winds in the equatorial Pacific? It causes the prevailing easterly trade winds to weaken or reverse into westerlies.
- Why does El Niño lead to a sharp drop in marine primary productivity? Weakened trade winds suppress the upwelling of cold, nutrient-rich subsurface waters, starving phytoplankton of the nutrients needed for photosynthesis.
- Which ISRO center processed the Oceansat-3 data showing the 2026 Pacific chlorophyll decline? The National Remote Sensing Centre (NRSC) located in Hyderabad.