How Cyclones Help Fix Carbon in the Sea
In News
Recent studies by the National Institute of Oceanography (NIO), Academy of Scientific and Innovative Research (AcSIR), and Indian National Centre for Ocean Information Services (INCOIS) have found that tropical cyclones in the Bay of Bengal can help absorb and fix atmospheric carbon dioxide (CO₂) in seawater.
Contrary to perception, not all cyclones are purely destructive — some have positive environmental impacts.
Key Findings
1. India’s Oceanic Carbon Absorption
The Indian Ocean absorbs ~190 million tonnes of carbon per year.
The northern Indian Ocean, especially the Bay of Bengal, plays a major role in the global carbon budget.
2. Mechanism — How Cyclones Fix Carbon
Process | Description |
Vertical Mixing | Cyclones churn seawater, bringing carbon-rich water from below to the surface and pushing oxygen-rich water down, enhancing CO₂ uptake. |
Nutrient Upwelling | The upwelling stimulates phytoplankton growth (microscopic marine plants), which absorb CO₂ for photosynthesis. |
Freshwater Stratification | In the Bay of Bengal, freshwater from major rivers (Ganga, Brahmaputra, Mahanadi) forms a layer that limits mixing, affecting CO₂ absorption. |
Post-Cyclone Effect | When strong winds break stratification, nutrient mixing boosts biological activity — leading to temporary CO₂ absorption. |
3. Impact on Carbon Flux
Cyclones like Hudhud (2014) and Michaung (2023) studied for CO₂ absorption effects.
The Bay of Bengal can absorb up to 190 million tonnes of CO₂ annually.
Cyclones can both increase or decrease CO₂ uptake, depending on:
Wind intensity
Duration
Temperature and salinity
Mixing depth of the water column
Regional Variations
Bay of Bengal: Strongly influenced by freshwater inflow and stratification; cyclones enhance CO₂ uptake temporarily.
Arabian Sea: Receives less freshwater inflow, hence higher salinity and better vertical mixing even without cyclones.
Positive and Negative Effects
Positive Effects | Negative Effects |
Increased CO₂ absorption due to enhanced mixing and phytoplankton growth. | Some cyclones can release stored CO₂ by mixing deep carbon-rich water with surface water. |
Plankton blooms enhance marine productivity and carbon fixation. | Ocean acidification can increase due to higher CO₂ absorption, threatening marine life. |
Acts as a temporary carbon sink, absorbing more CO₂ than it emits. | Over long periods, the absorbed CO₂ may return to the atmosphere through respiration or decomposition. |
Ocean Acidification Concern
The Bay of Bengal is becoming more acidic, with pH levels dropping to ~7.9–8.0 (normal ~8.2).
Continuous CO₂ absorption increases the formation of carbonic acid (H₂CO₃), which:
Reduces calcium carbonate availability.
Affects shell-forming organisms and corals.
Threatens overall marine biodiversity.
Study-Based Insights
Hudhud (2014) and Michaung (2023) — both caused increased nutrient mixing and enhanced biological productivity.
The Bay’s pH fell by about 0.1 unit post-cyclone, indicating increased CO₂ uptake and mild acidification.
On a global scale, cyclones contribute to short-term CO₂ drawdown but may have neutral or minor long-term effects.
Scientific Explanation (Simplified)
Cyclone winds stir the upper ocean, mixing surface water with deeper layers.
This brings up nutrients (nitrates, phosphates) → phytoplankton bloom.
Phytoplankton absorb CO₂ → temporary carbon sink formation.
When plankton die, carbon sinks to the seabed, sequestering it.
However, over time, decomposition may release CO₂ back to the atmosphere.
Long-term Implications
Net Carbon Sink Potential: The Indian Ocean acts as a moderate carbon sink, but not permanent.
Climate Feedbacks: If global warming intensifies cyclone frequency, CO₂ absorption patterns could shift.
Policy Relevance: Highlights the importance of blue carbon ecosystems (oceans, mangroves, seagrasses) in India’s climate mitigation plans.
Prelims Pointers
Term / Concept | Explanation |
Blue Carbon | Carbon captured by oceanic and coastal ecosystems (mangroves, seagrass, phytoplankton). |
Ocean Stratification | Formation of layers in the ocean due to temperature and salinity differences. |
Phytoplankton Bloom | Rapid increase in algae population due to nutrient upwelling. |
Ocean Acidification | Reduction in ocean pH due to absorption of atmospheric CO₂. |
Prelims Practice MCQs
Q. Consider the following statements about cyclones and carbon absorption in oceans:
Cyclones always decrease CO₂ absorption by causing mixing of deep carbon-rich water.
Phytoplankton blooms caused by cyclones can increase temporary carbon fixation.
Ocean acidification increases when seawater absorbs more CO₂.
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: B
Q2. Which of the following statements is/are correct about the Bay of Bengal?
Freshwater inflow from major rivers increases surface stratification.
Cyclones can help break stratification, increasing nutrient upwelling.
Ocean acidification is lower in the Bay of Bengal than in the Arabian Sea.
Select the correct answer using the code below:
A. 1 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2, and 3
✅ Answer: B
Mains Practice Question
Q. “Tropical cyclones, though destructive, can contribute to carbon cycling and ocean productivity.” Discuss with reference to the Bay of Bengal region.
Answer Pointers:
Mechanism of mixing and CO₂ absorption.
Role of freshwater stratification and nutrient upwelling.
Benefits (temporary carbon sink, plankton growth).
Risks (acidification, biodiversity loss).
Significance for India’s carbon budget and marine conservation policy.