5,000 5,500

Figure 2.2 Annual mean Atlantic Ocean zonal average (by 1° squares) of temperature (° C) as a function of depth. Note the break in the depth scale at 1000 m (Levitus, 1982).

2.2.2 Salinity distribution

The distribution of salinity at the surface of the ocean is shown in Figure 2.3, and notable features have been summarized by Levitus (1982). Specifically, subtropical salinity maxima associated with the excess of evaporation (E) over precipitation (P) appear in all the individual oceans (regions where E — P > 0). Subpolar regions exhibit low salinities associated with the excess of precipitation over evaporation (regions where E — P < 0). Low-salinity tongues associated with runoff from major river systems, such as the Amazon, are also apparent.

Unlike the temperature fields, salinity does not exhibit a consistent stratification with depth, as for example in the Atlantic Ocean (Figure 2.4). These patterns reflect the complex movements of water throughout the oceans.

2.2.3 Water masses

Using the concept of water masses facilitates descriptions of sea-water characteristics and motions. This concept is analogous to that employed by meteorologists to describe air masses in weather patterns. Air masses are

Figure 2.3 Annual mean salinity (ppt) at the sea surface (Levitus, 1982).

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