The Subtropical Front

The northern boundary of the Southern Ocean is commonly defined through the Subtropical Front (STF). South of Australia its location is generally given as approximately 39 - 40°S, and closer to 47°S in the vicinity of Tasmania at 145°E (Figure 9).

In 1994 R/V Franklin completed two deep meridional sections south of Australia as part of the World Ocean Circulation Experiment (WOCE). The STF was found near 39°S in the west (at 120°E) but about 220 km further north in the east (at 132°E). Previous work (Tomczak and Godfrey, 1994; Kazmin and Rienecker, 1996) showed that its location south of Australia has large seasonal and interannual variability. The WOCE observations suggest that the front comes closer to Australia than previously thought (Figure 10) before it turns southward to connect to the Pacific Ocean south of Tasmania.

The STF of the southern hemisphere is characterised by positive meridional temperature and salinity gradients. The effect of the temperature change on density is usually larger than the effect of the salinity change. A pressure gradient is thus established across the front, which supports a geostrophic current. South of Australia the density compensation in the STF is nearly complete. The geostrophic current associated with the front, which attains 30 Sv near Africa and still carries 10 Sv as it approaches Australia (Stramma, 1992), virtually disappears south of the Great Australian Bight. This produces a situation where interleaving and double diffusion become important for the frontal dynamics (Figure 11).

(1 Sverdrup [Sv] = 1 million cubic metres per second)

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This page was created on 21/5/98

1998 M. Tomczak

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