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Fig. 5.11 Potential temperature on the sea floor in the Brazil Basin (Morris et al., 2001). See color plate section.

Shelf is the lightest among these four, at great depth it is the densest (Fig. 5.13). As a result, the Mediterranean outflow cannot sink to the sea floor of the world's oceans; instead, the cold water mass formed off the Filchner Ice Shelf is the water mass that covers the bottom layer in the world's oceans.

There are several reasons why the density of outflow is reordered: the thermobaric effect and mixing, which are controlled by the density difference between the outflow and the environment, plus the topographic slope. As discussed in Section 2.4.9, the thermobaric effect is due to the nonlinearity of the equation of state: the compressibility of seawater strongly depends on temperature. In particular, cold seawater is more compressible than warm seawater. The effect of mixing during the descent of the overflow downstream of the sill will be discussed below.

The thermobaric effect can be seen clearly from Table 5.1 and Figure 5.13. Although the Mediterranean outflow is the heaviest near the sea surface, it is much warmer than other deep water from other sources. Since warm water is less compressible, when the in situ

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Fig. 5.11 Potential temperature on the sea floor in the Brazil Basin (Morris et al., 2001). See color plate section.

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