13
Descriptive Oceanography
Equation of Seawater 2010 (TEOS-10) in Chapter 2. A typical sigma- T profile is shown in
Figure  1.18. The density normally increases with increasing depth. Minimum energy is
obtained when the less- dense water is at the surface. The density of surface waters shown
in Figure 1.19 is strongly affected by temperature, except in polar regions, where salinity
becomes important.
In coastal waters, fjords, and estuaries, salinity often controls the density at all depths.
It should be pointed out that a reasonable estimate of the density of rivers and lakes can
be made from the seawater equation of state at the same salinity (Millero, 2000b). Deep
waters in the oceans will have a higher density than the value calculated from the conductivity salinity because of the added nutrients and carbonate from the oxidation of
36
35.5
35
34.5
34
Ocean Data View
EQ
20°S
60°S
Indian Ocean I8
0
1000
2000
3000
I8
Depth [m]
4000
5000
Salinity [pss-78]
Figure 1.16
North- south section of salinity in Indian Ocean.
30
0
10
20
Temperature °C
30
35
Salinity
40
75%
99%
Melting (–2°)
Point
Figure 1.17
Temperature versus salinity for ocean waters.