Part III: Antarctica and Academe - Scott Polar Research Institute

Chapter 11
Great waters: The Southern Ocean
T
he vast Southern Ocean encircles the Antarctic in a continuous ring of, mainly,
eastward- flowing water, which is the major connecting link between the three
ocean basins that lie to the north of it, and has also isolated the continent from
their warmer waters since the opening of the Drake Passage. The arrangement of the
continents and oceans, and the climate, have all changed continually throughout the
Earth's history. At the same time Gondwana fragmented, a process beginning about
180 million years ago (l80Ma), and following the opening of the Drake Passage 25-
30Ma ago the present oceanic circulation pattern was established.
This Antarctic Circumpolar Current (ACC) is also the only truly global current and
very large - an endless 24,000 km, ranging from 200 to l000 km wide its only
constriction being the Drake Passage. Enormous quantities of water are transported
at a rate of flow of about 7-l2 m/second, so that at the Drake Passage, on average l30
million m 3 flow through each second. That estimate is based on an array of 91 current
meters moored at different depths 50 km apart, recording over a year. Later records
showed that there were large differences from year to year and unexpected decreases
and increases in the flow over periods of a few weeks. Between l977 and l982 the
flow fluctuated between ll0 million m 3 /second and l45 million m 3 /second, a notable
degree of variation that is unexplained. The average transport is four times that of
the Gulf Stream or 400 times that of the Mississippi River. The flow extends to the
bottom; however the surface flow is unexceptional, averaging about [l] knots
compared with the Gulf Stream's 5 knots.
An important feature of the Southern Ocean and one which has great importance for
the distribution of living organisms, is the Antarctic Polar Front (also known as the
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