Prelims (GS I) - Indian and World Geography-Physical, Social, Economic Geography of India and the World.
Mains (GS I) – Geographical features and their location-changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.
Why in news?
A recent study published in the journal Nature Geoscience has revealed how monsoon patterns significantly impact marine productivity in the Bay of Bengal.
Despite covering less than 1% of the world's ocean area, the Bay of Bengal it provides nearly 8% of global fishery production.
Key Findings of the study
- Extreme Monsson conditions – The study found that both abnormally strong and weak monsoons throughout history caused major disruptions in ocean mixing.
- This mixing play important role in climate, marine life, and cycles carbon and oxygen in the ocean.
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Ocean mixing
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- Ocean mixing - It is the process of warm, sun-filled surface water mixing with cold, nutrient-rich water near the bottom of the ocean.
- Winds, ocean currents, and tides are responsible for most ocean mixing.
Types of Ocean Mixing
- Vertical Mixing – It occurs when water from different depths mixes, often driven by Wind, Turbulence, Convection.
- Horizontal/Lateral Mixing – Driven by ocean currents.
- Diapycnal Mixing – Mixing across density surfaces, often due to turbulence or internal wave breaking.
- Tidal Mixing – Tides interacting with seafloor features (e.g., seamounts, continental shelves) generate internal waves and turbulence.
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- Reduced food availability – Up to 50% reduction in food availability for marine life in surface waters.
- Historical trend – Significant declines happened in certain period when extreme monsoon weather was observed.
- Heinrich Stadial 1 (a cold phase between 17,500 and 15,500 years ago).
- Early Holocene (about 10,500 to 9,500 years ago).
- Impact on plankton growth – The ability of the ocean to support plankton growth is reduced which forms the base of the marine food chain.
- Impact on food security – The decline in ocean productivity reduces fish stocks and impacts food security for coastal communities.
Reasons for Disruption
- During strong monsoons – Increased rainfall leads to greater river runoff into the Bay and this excess freshwater creates a buoyant surface layer which prevents nutrient mixing from deeper waters.
Buoyant surface layer formed as a result of difference in density of water where warm, less dense water floats on top of cooler, denser water.
- During weak monsoons – Due to reduced wind-driven mixing that limits the upwelling of nutrient-rich deep waters.
- Surface waters become starved of essential nutrients.
Reference
The Hindu| Changes in monsoon affect marine productivity
