Antarctic Circumpolar Current
Daily Earth Science Hydrosphere Repost

The Antarctic Circumpolar Current: An Ouroboros

The only place in the world where an ocean current can circumnavigate the globe and return upon itself like a mythical ouroboros is in the southern hemisphere. There, unimpeded by continents and driven by westerly winds, the Antarctic Circumpolar Current (ACC) endlessly circles the globe flowing from west to east.

 The ACC extends from the sea surface to depths of 4000 meters, and the water flow measures approximately 175 million cubic meters per second. For scale, this is about 100 times greater than the combined flow of all the rivers on the planet. The circumpolar current travels at speeds over 3 km per hour, and water temperatures range from -1 to 5 degrees Celsius.

A nickname for the ACC is the “giant mixmaster” because it connects the Atlantic, Pacific, and Indian Oceans. When water from one of these oceans entrains in the ACC, it can be transported to either of the other two oceans.

The primary forces creating the ACC are strong westerly winds and changing ocean surface temperatures. Winds provide the power that moves the current along, but the current itself is constrained by physical barriers, temperature differentials, and salinity changes. Its narrowest constriction point is the 800 km stretch between South America and Antarctica. This is where the ACC flows through the Drake Passage.  

Keeping the chill in

The world’s oceans exert a powerful influence on climate, and the ACC is no exception. It encircles Antarctica in the same way that atmospheric currents, like the jet stream, circle the globe around a polar vortex. This deep, cold mass of circulating water provides a barrier to heat transfer, keeping the warmer northern waters at bay. This barrier helps keep Antarctica frozen. 

The ACC also plays a role in the Antarctic marine ecosystem. When nutrient-rich bottom waters flowing from the Atlantic, Pacific, and Indian oceans enter into the ACC, they then flow southeastward and upward. This process supports the upwelling necessary to sustain phytoplankton in the Antarctic ecosystem. So, when the summer sun returns each year to Antarctica, these primary producers thrive. Sunlight and nutrients are all they need to create an abundant food source. This is an energy source upon which the rest of the food chain depends.

How climate change will affect the ACC is unknown. We know the upper 2000 meters of the Southern Ocean have warmed with rising global temperatures, and salinity has decreased. There is also some evidence that deeper waters are warming. If there is an increase in the amount of heat being transferred from north to south across the ACC, then we can expect to see increased melting of Antarctic ice. Perhaps that is already happening. Antarctica’s rate of ice loss has increased from 40 gigatons per year in 1979 to 250 gigatons in 2017.


ArcheanWeb:

Acid and phytoplankton in the ocean’s food chain (Source: ArcheanWeb) – https://archeanweb.com/2020/01/28/acid-and-phytoplankton-the-oceans-food-chain/ Also:

Thermohaline circulation (Source: ArcheanWeb) – https://archeanweb.com/2020/04/03/thermohaline-circulation/ Also:

Riding the global conveyor belt (Source: ArcheanWeb) – https://archeanweb.com/2020/04/06/riding-the-global-conveyor-belt/ Also:


Sources:

Introduction: The Ocean’s Meridional Overturning Circulation (By Andreas Schmittner, John C.H. Chiang, and Sidney R. Hemming) – http://people.oregonstate.edu/~schmita2/pdf/S/schmittner07agu_intro.pdf Also:

Explainer: how the Antarctic Circumpolar Current helps keep Antarctica frozen. (By Helen Phillips, Benoit Legresy, and Nathan  Bindoff – The Conversation) – https://theconversation.com/explainer-how-the-antarctic-circumpolar-current-helps-keep-antarctica-frozen-106164 Also:

Deep waters spiral upward around Antarctica (By Lauren Hinkel | Oceans at MIT) – http://news.mit.edu/2017/research-explores-deep-waters-spiraling-upward-around-antarctica-0926 Also:

Antarctica’s Ocean Circulation (Polar Discovery Woods Hole Oceanographic Institution) – http://polardiscovery.whoi.edu/antarctica/circulation.html Also:

Feature Image: Antarctic Circumpolar Current (NASA) (Modified) – his file is in the public domain in the United States because it was solely created by NASA.

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.