Context:
Scientists caution that, in a scenario of high carbon emissions, the Atlantic Meridional Overturning Circulation (ACC) could decrease in speed by approximately 20 percent by the year 2050.
Atlantic Circumpolar Current (ACC)
- Also known as the West Wind Drift
- Strongest and largest wind-driven current on Earth
- Moves clockwise around Antarctica when viewed from the South Pole
- Only current in the global ocean to close upon itself in a circumpolar loop
- Driven by strong westerly winds
- Only current that goes all the way around the planet and connects the Atlantic, Pacific, and Indian Oceans
- Massive flow of water acting as a barrier, separating the Southern Ocean from more northern oceans
Functions of ACC:
- Cold current that acts as a barrier, preventing warmer waters from reaching Antarctica
- Moves warm water from the equator to the poles and cold water to the equator
- Absorbs carbon dioxide from the atmosphere and stores it deep in the ocean
- Brings nutrients from deep water to the surface, supporting marine ecosystems
- Reduces subtropical heat influx, thermally isolating Antarctica
- Maintains fresh, cold, stable waters for sea ice formation and limits the northern extent of seasonal sea ice fields
- Blocks invasive species (e.g., bull kelp, shrimp, mollusks) from other continents from reaching Antarctica
Reasons for Weakening ACC
- Changes in Ocean Salinity: Accelerated melting of ice shelves (global warming) around Antarctica results in weakening of Antarctic Bottom Water (AABW)
- AABW is a sinking process, a critical component of global ocean circulation tied to ACC circulation
- Changes in Wind Patterns: Climate change alters the pattern of westerly winds in the Southern Hemisphere
- Positive Feedback Loop: Reduced sea ice exacerbates warming and freshwater input, creating a feedback loop that further weakens ACC
Potential Impact of Weakening of ACC
- High climate variability with more extreme weather in certain regions
- Accelerated global warming due to reduced ocean capacity as a carbon sink
- Impact on the food web due to arrival of invasive species on the fragile Antarctic continent
- Impact on the global ocean current system due to weakening of the Antarctic Bottom Water (AABW)
Previous Year Question
Westerlies in southern hemisphere are stronger and persistent than in northern hemisphere. Why?
1. Southern hemisphere has less landmass as compared to northern hemisphere.
2. Coriolis force is higher in southern hemisphere as compared to northern hemisphere
Which of the statement(s) given above is/are correct?
[UPSC Civil Services Exam – 2011 Prelims]
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (a)
Explanation:
The Coriolis force is zero right at the equator. It is maximum at the poles. Hence, statement 2 is not correct.
