The Southern Ocean is the fourth largest of the five world oceans, yet it is the one that the fewest mariners will ever sail through. Circling the Antarctic continent, its current forms a virtual moat isolating and keeping Antarctica frozen.
Other oceans are bounded by continental landmasses, but the Southern Ocean is defined by the Antarctic Convergence, a subtle band of sea surface temperature changes. This is an irregular boundary varying from 48- to 60-degrees south latitude, where sea surface temperature drops from five to ten degrees Fahrenheit over a distance of 20 to 30 miles. While this may not seem like a big change, it is a very significant gradient within the oceans.
Ship operations are impossible year-round, as sea ice covers roughly 80 percent of the Southern Ocean for the Austral winter and some of the spring and fall. In the summer, roughly 11 percent of the surface remains permanently ice-covered.
Driven by strong prevailing westerly winds, the Antarctic Circumpolar Current (ACC), or West Wind Drift, creates a clockwise circulation around the continent. The volume of water movement is equivalent to 1,000 Amazon Rivers, or four Gulf Streams. Not impeded by landmasses, the Southern Ocean has the highest average sea states in the world.
The nearshore East Wind Drift, or Antarctic Coastal Current, has one-tenth the flow of the ACC and is propelled by cold, dense air from the high interior of the continent as it flows downslope to the coastlines. Descending from altitudes as great as 9,200 feet near the South Pole plateau, the airflow can reach sustained nearshore velocities greater than 180 miles per hour.
As the West Wind Drift squeezes through the narrow and shallow Drake Passage, it creates a dynamic upwelling condition. This upwelling is the vertical turbulent movement of water that brings up nutrients from the depths into shallow surface waters. To the east (downstream) of the Passage, this creates optimum conditions for high biological productivity.
The Antarctic Convergence is an eco-boundary with different species of bird and marine life on each side. The most abundant animal here is the Antarctic krill, a macro-zooplankton roughly two inches long. Estimates of the amount of krill on the planet are as high as 500 million tons. Considering that the average world fish catch is approximately 90 million tons per year, krill could have potential as a food source.
Mother Nature does not make this easy, however. Krill are fished in the roughest and most remote ocean in the world; their shells are high in toxic fluoride; and they spoil rapidly if not processed immediately. Norway, Poland, Japan, and Korea currently fish this resource, with current annual harvests in the realm of 100,000 tons. While krill may not be a major commercial fishery for human consumption, these animals are a critical food source for marine mammals, seabirds, and millions of penguins.
In the future, one of the Southern Ocean’s greatest resources may be ice. While there are few places in the Northern Hemisphere where icebergs occur, in the Antarctic, huge tabular icebergs are launched into the Southern Ocean from coastal glaciers and ice shelves. The Ross Ice Shelf in the West Antarctic is the size of France. In 2017, an iceberg the size of Delaware broke off the Larsen Ice Shelf into the Weddell Sea. The keel depth of the iceberg was nearly 700 feet.
Propelled by both the East and West Wind Drifts, these giant icebergs slowly circle the continent, breaking into smaller bergs until they melt in warmer waters. Some are carried away by currents into the Pacific, Atlantic, and Indian oceans, and could become valuable sources of freshwater if captured. The technical and operational problems would be formidable, but with 91 percent of the world’s freshwater sitting on the Antarctic Continent, it is worth considering—especially when nearly one half of the people on our planet are existing without safe or certain water supplies.
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