15
Descriptive Oceanography
The geographic distribution of density for the Atlantic in a north- south section is shown
in Figure 1.20. The upper layers tend to be concave upward, showing an increase from the
equator to the pole. Below 2000 m, the values of σ T range from 27.6 to 27.9 for most deep
waters. It should be pointed out that the flow of ocean waters tends to follow constantdensity surfaces. One can frequently trace the origin of deep waters to the region of formation at the surface.
Although the densities of water masses can be arrived at by a number of possible
combinations of S and T, one finds that only a limited number occur in different regions.
Thus, it is possible to recognize a water mass by its characteristic combination of water
properties. By plotting temperature against salinity (T- S plots) for individual oceanographic stations, it is possible to develop a characteristic diagram. The T- S relation for
the major ocean waters is shown in Figure 1.21. It is not necessary to plot density on this
Latitude
–60
–40
–20
0
20
40
60
80
SIGMA - T
20
22
24
26
28
30
Temp
S
σ T
Tropic
Equator
Tropic
Temperature (°C)
Salinity
–20
20
0
10
–10
38
32
35
Figure 1.19
Comparison of sigma- T to temperature and salinity for surface waters.
28
Potential Density Anomaly σ 0 [kg/m
3 ]
27.5
27
26.5
26
25.5
25
Ocean Data View
60°N
40°N
20°N
EQ
20°S
40°S
60°S
6000
5000
Depth [M]
4000
3000
2000
1000
27
27.8
27.85
27.2
27.4
27.6
26
25
0
Figure 1.20
North- south section of sigma- T in the Atlantic Ocean.