Ocean deoxygenation
Topic: Oceans: Hydrological Cycle, Relief of the Ocean Floor, Temperature and Salinity · NCERT: Beyond NCERT
Meaning
Ocean deoxygenation means the ocean is losing the oxygen dissolved in its water. One cause is warming, because warm water holds less oxygen than cold water. A second cause is fertiliser that rivers wash into the sea. It feeds algal blooms (fast growth of algae), and when the algae die and rot they use up oxygen. The ocean has lost about 2% of its oxygen since 1960. Fish and other sea life cannot live in water with too little oxygen, so fisheries and coastal livelihoods suffer.
Example
The Arabian Sea, west of India, has an oxygen minimum zone, a layer of water with very little oxygen. It is one of the largest such zones in the world, and it is spreading.
Don't confuse with
- Ocean acidification: here the ocean takes in CO₂ and its water becomes more acidic, with surface pH falling from about 8.2 to about 8.1. The problem is acidity, not a loss of oxygen.
Related concepts
- Ocean acidification
- Marine heatwave
- Microplastics
- Great Pacific Garbage Patch
- Atlantic Meridional Overturning Circulation
- BBNJ Agreement