Tags:Science & TechUPSC
For Prelims: Dissolved Oxygen (DO), Thermohaline Circulation, Southern Ocean, Oxygen Minimum Zone (OMZ), Nodal Body, Study Period, Oxygen Level Change (2011-2025), Max Increase Depth
For Mains: Ocean deoxygenation, climate change impact on oceans, Southern Ocean circulation, marine ecosystem health, NCPOR research
Source:
Dainik Bhaskar
5 facts for one-day exams
SSC, railway, police and teaching exams ask direct questions like these.
- NCPOR study found oxygen rise in the Indian sector of the Southern Ocean.
- Dissolved oxygen increased from 4.5 to 5.5 ml/L between 2011 and 2025.
- Maximum oxygen increase was at 300 to 2,000 metres depth.
- Global ocean oxygen has declined by about 2% since the mid-20th century.
- NCPOR is headquartered in Goa and works under the Ministry of Earth Sciences.
Why in the news?
A study by the National Centre for Polar and Ocean Research (NCPOR), Goa, found that dissolved oxygen levels in the Indian sector of the Southern Ocean have increased from 4.5 to 5.5 ml/L between 2011 and 2025, contrary to the global trend of declining ocean oxygen. This rise, driven by changes in temperature and salinity that improved vertical mixing, benefits marine flora and fauna.
Summary
- The study covers the period 1993 to 2025 and shows an increase in dissolved oxygen in the Indian sector of the Southern Ocean.
- The maximum increase was observed at 300-2,000 m depth, with oxygen rising at 2.37 micromol/kg/year in the Antarctic zone and 1.41 micromol/kg/year in the polar zone.
- Globally, ocean oxygen has declined by about 2% since the mid-20th century, making this regional increase a positive anomaly.
Highlights
Oxygen Rise in Southern Ocean
Dissolved oxygen in the Indian sector of the Southern Ocean increased from 4.5 to 5.5 ml/L (2011-2025), reversing the global trend of deoxygenation.
NCPOR Study Findings
The study by Goa-based NCPOR found oxygen rising at 2.37 micromol/kg/year in the Antarctic zone at 300-2,000 m depth.
Cause: Temperature and Salinity
Increased temperature and salinity reduced water layer stratification, allowing oxygen-rich surface water to mix better into deeper layers.
Background
Oceans absorb about 30% of human-caused CO₂, leading to warming and deoxygenation. Globally, ocean oxygen has declined by ~2% since the mid-20th century, harming marine life and ecosystems. However, the Indian sector of the Southern Ocean, a region crucial for global ocean circulation, shows an opposite trend.
Key Analysis and Impact
The rise in dissolved oxygen (4.5 to 5.5 ml/L) is attributed to changes in water column structure: increased temperature and salinity reduced the density difference between layers, enabling better vertical mixing of oxygen-rich surface water. This has boosted marine flora and is beneficial for fish and other marine organisms. The findings are significant because the Southern Ocean drives global thermohaline circulation.
Way Forward
This study provides a baseline for monitoring regional ocean health. Further research is needed to understand if this trend is temporary or long-lasting, and to model its impact on fisheries and carbon cycling in the Indian Ocean region.
Oxygen trends: Southern Ocean vs Global
| Region | Trend | Key Data |
|---|---|---|
| Southern Ocean (Indian sector) | Increase | 4.5 to 5.5 ml/L (2011-2025) |
| Global oceans | Decline | ~2% since mid-20th century |
Background GK
Textbook concepts you need to understand this news
- Dissolved Oxygen (DO)
- The amount of gaseous oxygen (O₂) dissolved in water. It is a key indicator of water quality and essential for the survival of aquatic organisms.
- Thermohaline Circulation
- A large-scale ocean circulation driven by global density gradients created by surface heat and freshwater fluxes. It plays a key role in distributing heat and nutrients around the planet.
- Southern Ocean
- The ocean surrounding Antarctica, extending from the Antarctic coastline to 60°S latitude. It connects the Atlantic, Pacific, and Indian Oceans and is critical for global climate regulation.
- Oxygen Minimum Zone (OMZ)
- A layer in the water column (typically 100-1,500 m depth) where oxygen saturation is at its lowest, often due to high biological activity and limited mixing.
Facts to remember
Tap a card to see the answer. Try to recall it first.
How exams will ask this
- Data: Oxygen increased from 4.5 to 5.5 ml/L (2011-2025) in the Indian sector of the Southern Ocean.
- Data: Global ocean oxygen declined by ~2% since mid-20th century.
Don't make this mistake!
They may swap the region (e.g., 'Indian Ocean' instead of 'Southern Ocean's Indian sector') or confuse the direction of change (decline vs. increase). They may also state that the study was done by the Ministry of Earth Sciences directly, not by NCPOR, or mix up the depth ranges.
Write these in mains answers
- Ocean deoxygenation, climate change impact on oceans, Southern Ocean circulation, marine ecosystem health, NCPOR research
Stuck? Get it in one tap
Dissolved oxygen is the oxygen gas mixed into seawater, which marine animals need to breathe. A new study by NCPOR shows that in the Indian part of the Southern Ocean, this oxygen level rose from 4.5 to 5.5 ml/L over 14 years. This happened because warmer and saltier water mixed better, carrying oxygen deeper. Globally, oceans are losing oxygen, so this is a positive sign for marine life in that region.
- NCPOR study found oxygen rise in the Indian sector of the Southern Ocean.
- Dissolved oxygen increased from 4.5 to 5.5 ml/L between 2011 and 2025.
- Maximum oxygen increase was at 300 to 2,000 metres depth.
- Global ocean oxygen has declined by about 2% since the mid-20th century.
- NCPOR is headquartered in Goa and works under the Ministry of Earth Sciences.
- Geography: Oceanography: Temperature, salinity, and ocean currents
- Environment: Climate change impacts on oceans
Related concepts: Dissolved Oxygen (DO), Thermohaline Circulation, Southern Ocean, Oxygen Minimum Zone (OMZ)
Practice questions
Pick an answer, then read the explanation.
- Q1Easy
Which institute conducted the study that found rising oxygen levels in the Indian sector of the Southern Ocean?
Explanation: The study was conducted by the Goa-based National Centre for Polar and Ocean Research (NCPOR). NIO, IITM, and INCOIS are other ocean/atmosphere research bodies under the Ministry of Earth Sciences, but this specific study is by NCPOR.
- Q2Hard
Consider the following statements:
- 1.Dissolved oxygen in the Indian sector of the Southern Ocean increased from 4.5 to 5.5 ml/L between 2011 and 2025.
- 2.Globally, ocean oxygen levels have increased by about 2% since the mid-20th century.
- 3.The maximum increase in oxygen was observed at depths between 300 and 2,000 metres.
Which of the statements given above is/are correct?
Explanation: Statement 1 is correct: the study found oxygen rose from 4.5 to 5.5 ml/L. Statement 2 is incorrect: global ocean oxygen has declined by about 2%, not increased. Statement 3 is correct: the maximum rise was at 300-2,000 m depth. Hence option C is correct.
- Q3Medium
At what rate did dissolved oxygen increase annually in the Antarctic zone of the Southern Ocean's Indian sector, according to the NCPOR study?
Explanation: The study found oxygen increased at 2.37 micromol per kg per year in the Antarctic zone. 1.41 micromol is the rate for the polar zone. 4.5 and 5.5 are the oxygen levels in ml/L, not the annual rate.
- Q4Medium
What is the primary reason cited for the increase in dissolved oxygen in the Indian sector of the Southern Ocean?
Explanation: The study attributes the oxygen rise to increased temperature and salinity, which reduced the density difference between water layers, allowing better vertical mixing of oxygen-rich surface water to depth. The other options are not supported by the news.
Frequently asked questions
1. What did the NCPOR study find about oxygen in the Southern Ocean?
The study found that dissolved oxygen in the Indian sector of the Southern Ocean increased from 4.5 to 5.5 ml/L between 2011 and 2025, with the maximum rise at 300-2,000 metres depth.
2. What is the cause of the oxygen increase in the Southern Ocean?
Increased temperature and salinity reduced water layer stratification, allowing oxygen-rich surface water to mix more effectively into deeper layers.
3. What is the global trend in ocean oxygen levels?
Globally, ocean oxygen has declined by about 2% since the mid-20th century, unlike the increase observed in the Indian sector of the Southern Ocean.
4. Where is the National Centre for Polar and Ocean Research located?
The National Centre for Polar and Ocean Research (NCPOR) is headquartered in Goa, India.
All sources
- Original10 November 2026 · Read story
