Reversal in circulation and rising surface salinit

Reversal in circulation and rising surface salinity in Sourthen Ocean

Why in news?
Recent studies reveal dramatic changes in the Southern Ocean, including a reversal in circulation and rising surface salinity since 2016, contrary to prior expectations of freshening waters.

Reasons Behind the Change

Circulation Reversal (SMOC):
- The Southern Meridional Overturning Circulation (SMOC) has reversed. Instead of surface waters sinking, deep waters are now rising to the surface, bringing heat and carbon dioxide long stored in the abyss.
Sea Ice Decline:
- Since 2015, Antarctica has lost sea ice equal to the size of Greenland. Less ice means less freshwater input, contributing to higher salinity at the surface.
Atmospheric & Climate Drivers:
- Stronger winds and shifting storm tracks around Antarctica are altering ocean mixing.
- Warming atmosphere reduces snowfall and ice formation, further cutting freshwater supply.
Feedback Loops:
- Rising deep waters release heat and COâ‚‚, accelerating warming and ice melt.
- Saltier waters reduce buoyancy, reinforcing circulation changes.

Implications for Climate and Ecosystems
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Implication	Details
Carbon Cycle	Deep waters release stored COâ‚‚, weakening the ocean’s role as a carbon sink.
Heat Release	Rising deep waters bring trapped heat to the surface, intensifying Antarctic ice melt.
Sea Ice Loss	Salinity rise reduces freezing potential, accelerating sea ice decline.
Global Climate Feedbacks	Changes in Southern Ocean circulation affect the entire Earth system, including monsoons and Atlantic circulation.
Marine Ecosystems	Altered nutrient distribution impacts phytoplankton, krill, and higher food chains.

Risks and Challenges

Acceleration of Climate Change: The Southern Ocean has been a buffer, absorbing ~40% of human COâ‚‚ emissions. Its weakening role could speed up atmospheric warming.
Unpredictable Weather Patterns: Disruption of global circulation may affect rainfall and storm systems worldwide.
Ecosystem Collapse: Antarctic marine life, dependent on stable ice and nutrient flows, faces existential threats.

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