Stormy and icy seas - Antarctica: Global Science from a Frozen Continent - page 148

Figure 5.9 Schematic representation of water

mass fronts of strong changes separating the
zone of little change in water mass properties.
(Credit: Eberhard Fahrbach, AWI)

warm

cold

North -Latitude- South

whales, seals and sea birds to feed at the fronts. Such intensive life at fronts can be
spotted from far away and the enhanced biological activity changes the water colour
from blue to greenish.
Due to their biological impact, fronts are visible not only at the sea surface
and from satellites but also in the sediments, since the increased production
enhances the amount of material sinking to the ocean bottom. From this sediment
record fronts can be located over geological time and since they are water mass
transition zones, ocean temperature and salinity distributions can be traced back.
However, since the processes are highly non-linear, the interpretation of the
evidence is normally not straightforward.
The Southern Ocean off the continental slope is normally structured by ve

major fronts:

￿

the Subtropical Front at about 40 S,

￿

the Subpolar or Subantarctic Front at about 45 S,

￿

the Polar Front at about 50 S,

￿

the Southern Antarctic Circumpolar Current Front at about 55 S, and

￿

the Southern Boundary of the Antarctic Circumpolar Current, which coincides in
the Atlantic sector to some extent with the Weddell Front, the northern limit of
the Weddell gyre (see Figure 5.6 ).

The fronts are subject to intense fluctuations due to meanders and eddies. Since

they are related to pressure gradients, which induce changes in sea surface height,
they can be detected and monitored by satellite altimetry. Quite frequently they
are also related to topographic structures on the sea floor such as ridges.

The Antarctic Circumpolar Current

The Antarctic Circumpolar Current forms a moving band around the Antarctic
Continent with flow from west to east and, with a water mass transport of about

140million m 3 s - 1 , it is the largest current system on Earth. It is split in different