Southern Ocean sea ice. Photo: Isa Rosso

Voyager: Is There Really a Southern Ocean?

Asked by Michigan Center Junior High School 7th Grade class, Michigan Center, Mich.

Yes and no! To scientists, the broad ocean region surrounding Antarctica is the Southern Ocean. It roughly includes all ocean regions south of about 30 degrees South latitude, which is more or less where the southern tip of Africa is, down to the coast of Antarctica. It includes the Antarctic Circumpolar Current (ACC), the world’s strongest current which circulates around Antarctica in a clockwise fashion.

We oceanographers define the Southern Ocean by its physical characteristics but government entities define oceans differently. In 2000, the International Hydrographic Organization, which oversees the charting of the world’s oceans, defined the Southern Ocean as all the ocean regions found south of 60 degrees South, which is more or less where sea ice is found, but has yet to endorse that definition because of disagreement whether that is the best way to define it. There’s been little progress since. That definition does not include most of the ACC or the Drake Passage, which is the narrow space between South America and Antarctica through which the ACC squeezes. Both the ACC and Drake Passage are crucial to the dynamics of the Southern Ocean. There is also an agreement called the International Antarctic Treaty that sets aside all of the Southern Ocean south of 60 degrees South and Antarctica itself for cooperative scientific investigation.

So, officially the jury is still out whether there really is a Southern Ocean but we scientists have our own working definition that guides our research. 

  • Lynne Talley, physical oceanographer, Scripps Institution of Oceanography, UC San Diego, author of Descriptive Physical Oceanography, a textbook considered the standard for introductory physical oceanography courses

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