24
Chemical Oceanography, 4th Edition
has a half- life t 1/2 of 12 yr and entered the North Atlantic waters after the 1960 atomic bomb
tests. The TTO measurement made about 10 yr after the GEOSECS work shows the further
movement of North Atlantic deep waters.
A summary of the balance of water masses for the South Atlantic is shown in Figure 1.31.
The southward flow consists of 17 Sv of surface waters and 18 Sv of deep waters. The northward flow consists of 23 Sv of upper gyre waters, 9 Sv of Antarctic intermediate waters,
and 3 Sv of Antarctic bottom waters.
Another feature of the circulation of the Atlantic waters that should be mentioned is
the vertical circulation in the equatorial regions (shown in Figure 1.32). There is a general
upwelling that is revealed in the profiles of salinity and temperature described previously.
These features bring cold, nutrient- rich waters near the surface and support primary productivity near the equator. Studies have also examined the countercurrents near the equatorial regions. More will be said about this when discussing the Pacific Ocean waters.
20S
100
200
W
W
W
E
W
W
10
0
10
20N
Figure 1.32
Vertical circulation in the Equatorial Atlantic.
S. America
To South
Brazil
Gyre
Benguela
Gyre
10
18
35 Sv
7
16
7
17
23
Deep
9
3
35 Sv
Intermed.
Bottom
To North
S
Upper
Intermed.
Deep
S
S
Bottom
N
N
N
S
Africa
Figure 1.31
The balance of water masses in the South Atlantic.