Table of Contents
Relevance: APPSC: Geography, Environment, Science and Technology.
- Prelims: EOS-06, Oceansat-3, NRSC, OCM-3, Scatterometer, Chlorophyll-a, Phytoplankton, Equatorial Upwelling, ENSO.
- Mains: Ocean–Atmosphere Interaction, Marine Productivity, Satellite-Based Climate Monitoring, Ecosystem Resilience.
Why in News?
- India’s EOS-06/Oceansat-3 satellite has detected changes in ocean winds and surface chlorophyll associated with the developing El Niño in the tropical Pacific.
- ISRO’s National Remote Sensing Centre (NRSC) analysed chlorophyll and wind observations for April, May and June during 2023–2026, helping connect physical ocean changes with biological responses.
What Did the Satellite Observe?
- Lower Chlorophyll-a: Surface concentrations declined markedly in June 2026, compared with neutral ENSO conditions.
- Changing Winds: Prevailing easterly winds weakened, with westerly reversals observed in the analysed region.
- Contracting Productive Zone: The area of elevated chlorophyll progressively contracted westward between April and June 2026, indicating reduced nutrient supply through equatorial upwelling.
How Does El Niño Affect Marine Productivity?
Understanding El Niño
- El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO), a recurring interaction between the tropical Pacific Ocean and the atmosphere. It involves unusually warm surface waters in the central and eastern equatorial Pacific, alongside changes in atmospheric circulation.
Normal Conditions: Winds Support Upwelling
- Under normal conditions, easterly trade winds help move warm surface water westward. Wind-driven movement also causes surface waters to diverge near the equator, allowing deeper water to rise.
- This process, called upwelling, brings relatively cold, nutrient-rich water towards the surface. These nutrients support phytoplankton, microscopic photosynthetic organisms that form the base of many marine food webs.
El Niño Conditions: Nutrient Supply Weakens
- During El Niño, weakened trade winds and changes in the ocean’s upper layers can reduce the supply of nutrient-rich water to the surface.
The resulting relationship is:
Weaker winds and altered ocean conditions → Reduced nutrient supply → Lower phytoplankton abundance → Potential decline in marine productivity.
Why is Chlorophyll-a Important?
- Chlorophyll-a is a pigment used in photosynthesis. Its concentration helps scientists estimate phytoplankton abundance.
- However, chlorophyll is an indicator, not a direct measurement of fish stocks or the total health of a marine ecosystem. Its interpretation requires supporting information on ocean conditions.
About EOS-06/Oceansat-3
EOS-06, also called Oceansat-3, is India’s third-generation Oceansat satellite. It was launched on November 26, 2022, aboard PSLV-C54 from Sriharikota, into a polar sun-synchronous orbit.
Its instruments support complementary observations:
- Ocean Colour Monitor-3 (OCM-3): Measures ocean colour, enabling estimates of chlorophyll and other ocean parameters.
- Ku-Band Scatterometer (SCAT-3): Provides information on ocean-surface wind speed and direction.
- Sea Surface Temperature Monitor (SSTM): Measures ocean-surface temperature.
- ARGOS Payload: Supports satellite-based data collection.
For the reported El Niño study, scientists combined OCM-3 chlorophyll estimates with scatterometer wind observations.
Conclusion
Oceansat-3 demonstrates how satellite observations can connect changing winds with biological responses in the ocean. Combining ocean colour, wind and temperature data strengthens understanding of El Niño, marine productivity and climate variability.
CARE MCQ
Q. Consider the following statements:
- Chlorophyll-a concentration is used as an indicator of phytoplankton abundance.
- A scatterometer provides information on ocean-surface winds.
- El Niño generally strengthens nutrient-rich upwelling in the central and eastern equatorial Pacific.
Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a) 1 and 2 only
Statement-wise Explanation
- Statement 1 is correct: Chlorophyll-a is a photosynthetic pigment used to estimate phytoplankton abundance.
- Statement 2 is correct: Scatterometer observations help determine ocean-surface wind speed and direction.
- Statement 3 is incorrect: El Niño generally reduces nutrient supply to surface waters through weakened upwelling and changes in upper-ocean conditions.
FAQs
1. What is Oceansat-3?
It is EOS-06, an Indian satellite designed for ocean observation.
2. Which organisation conducted the reported analysis?
The National Remote Sensing Centre (NRSC) of ISRO.
3. What is upwelling?
It is the upward movement of deeper, generally nutrient-rich water towards the ocean surface.
4. Why do scientists measure chlorophyll-a?
It helps estimate phytoplankton abundance and assess changes in marine biological conditions.
5. Which two instruments were combined in this study?
The Ocean Colour Monitor-3 and the EOS-06 Scatterometer.
