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Aquatic Deoxygenation is overall decline in the oxygen content of oceanic and coastal waters (happens when oxygen consumption is greater than oxygen replenishment).
Status of AD
- Ocean: About 2% of oxygen content in ocean has been lost since 1960s.
- More than 500 low-oxygen sites have been identified in coastal waters.
- Other water bodies: Lakes and reservoirs have experienced oxygen losses of 5.5 and 18.6 % respectively since 1980.
Reasons underscoring AD
- Global Warming caused by GHG: Rise in temperatures decreases solubility of oxygen in water.
- Also, warm surface layers in ocean prevent oxygen from mixing deeper into ocean (leading to low oxygen level in deep sea waters)
- Eutrophication: Nutrient over enrichment from anthropogenic sources (e.g. agriculture) leads to algal blooms and increased consumption of oxygen.
Impact on Ecosystems
- Occurrences of dead zones and ocean hypoxia effect
- Habitat compression (reducing quality and quantity of suitable habitat) for fisheries leads to reduced biomass, species loss.
- Affects regulation and modulation of Earth's climate (due to production of GHGs by microbiotic processes in such regions)
- Changes in marine food web due to increased risk of predation, and other factors e.g. Ocean acidification
Planetary boundaries
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