Southern Ocean

Why in news?

Recently,   a study on Southern ocean “Closing the loops on Southern Ocean dynamics: From the circumpolar current to ice shelves and from bottom mixing to surface waves “ revealed more details on the dynamic nature of Southern Ocean.

What are the characteristics of Southern Ocean?

• It is also known as the Antarctic Ocean, comprises the southernmost waters of the world ocean.
• It used to be part of the Pacific Ocean and it is separated from other Oceans by currents, not Continents.
• Location – It is generally taken to be south of 60° S latitude and encircling Antarctica.
• Size - It is the second-smallest of the five oceans.

• Characteristics – It experiences Earth’s strongest winds and largest waves.
• It is home to city-sized icebergs.
  • Antarctic Ice Sheet is the largest ice mass on Earth, equivalent to 58 metres of the global sea level.
  • The ice sheet flows onto the Southern Ocean surface in the form of giant ice shelves.
• It acts as an ocean hub as waters from the Atlantic, Pacific and Indian basins converge and mix in Southern ocean.
• It experiences dramatic seasonal changes and cold temperatures.
  • During winter, Southern Ocean freezes into a fringe of sea ice, almost doubling the size of Antarctica.
• It encompasses the biggest ocean current on the globe, as well as tiny turbulent flows that fit inside a teacup.
  • Antarctic Circumpolar Current (ACC)
  • Antarctic Slope Current
  • Sub-polar gyres
  • The meridional overturning circulation.

Antarctic Circumpolar Current (ACC) is the longest, strongest, deepest-reaching current on earth and circulates clockwise around the continent, carrying more water around the globe than any other current.

Why Southern Ocean is called as a global engine room?

• It is crucial to Earth’s natural systems.
• Creates masses of Ice - Much of the sea ice is produced in small regions of open water, called “polynyas”, formed by strong and cold winds blowing off Antarctica.
• Contributes to Ocean volume - As the ice forms, it ejects salt into the ocean surface and this extra salt, in addition to cooling effects from the atmosphere, makes the surface seawater heavier/ dense.
• The dense water sinks into the deep ocean.
  • The resulting dense water mass produced here accounts for 40% of the global ocean volume.
• It is ultimately lifted back to the ocean surface by centimeter-scale turbulent eddies.

Sothern Ocean acts as a time capsule as it takes hundred year for the ocean water from the surface to sink and return to surface. Water returning to the surface today reflects the cooler, pre-industrial climate when it first sank to the ocean depths.

• Forms Ice shelves – Antarctic ice sheets flows onto the Southern Ocean surface in the form of giant ice shelves.
• Solar reflector - Millions of square kilometers of a layer of sea ice acts as a giant solar reflector.

• Heat sink – It stores excess heat generated due to global warming.
• Carbon Sink – Excess carbon generated by anthropogenic greenhouse gas emission activities are absorbed by them.
• Regulates sea level – It controls the flux of heat to the huge ice sheet of Antarctica, the greatest threat to runaway global sea-level rise.
• It shields ice shelves from powerful Southern Ocean waves.

• Productive ecosystem - Powerful currents, cold temperatures and nutrient and oxygen-rich waters make the Southern Ocean one of the most productive marine ecosystems on Earth.

• In summer billions of microscopic algae (phytoplankton) proliferate, spreading into blooms large enough to be seen from space.

2021-2030 is adopted as UN Decade of Ocean Science for Sustainable Development.

• Recent Challenges - Southern Ocean’s sea ice has dramatically declined in recent years due to global warming.
• Lowest ever recorded sea ice minima in the past two Austral summers.
• Warmer, less salty and more buoyant water is less prone to sinking.
• Thus affecting the ocean current system.

What lies ahead?

• Advance Southern Ocean science by bringing in the scientific and broader community together to protect this vital natural asset.
• Promote technological innovation to develop more cost-effective observing systems such as drones and drifting robotic instruments.
• Governments need to make long-term commitments to scientific study of Antarctica and the Southern Ocean.
• Enhance national and international collaboration to make the best use of available resources.
• Take a multidisciplinary effort to model the Southern Ocean's response to anthropogenic forcing as a key priority.

SWOT satellite is a joint project of the European Union and United States to measure the ocean surface at unprecedented resolution

References

1. ASOC | Southern Ocean
2. Down To Earth | Giant waves, monster winds and Earth’s strongest current
3. PhyOrg | Mysterious Southern Ocean