40
Chemical Oceanography, 4th Edition
in oceanography and other fields. The slow mixing of 14 C over its lifetime with normal
carbon will lead to lower concentrations in the older ocean waters. Thus, the atmosphere
will have the highest ratios of 14 C/ C, and the deep North Pacific will have the lowest ratios
of 14 C/ C. Sections of the Δ 14 C = ( 14 C/ C – 1) 1000 (‰) in the Atlantic and Pacific Oceans are
shown in Figure 1.45.
1.5.2 Tritium and Helium-3
Tritium ( 3 H or T) is a radioactive isotope of hydrogen. It has a half-life of 12.4 yr. It is introduced into the surface of the oceans as water (HTO) from both natural input and nuclear
weapons tests in the late 1950s and early 1960s. One of the reactions that leads to tritium
in the atmosphere is
14 N + n ⇒ 3 H + 12 C
(1.3)
The radioactive decay of tritium is by the reaction
3 H ⇒ 3 He + e –
(1.4)
0
2000
4000
–120
100
–80
–110
<–100
–100
–80
100
–40
–20
–60
0
–100
–110
–120
–100
–110
–140
–120
<–160
>–160
–160
–180
–150
–220
–240
–230
–90
0
90
–210
–160 to –180
–90
0
90
–160
6000
50S
40
30
20
10
EQ
Latitude
∆ 14 C in the Atlantic Ocean
10
20
30
40
50
60
70N
60S
50
40
30
20
Latitude
∆
14 C in the Pacific Ocean
10
EQ
10
20
30
40 50N
Depth (m)
0
2000
4000
6000
Depth (m)
Figure 1.45
Section of Δ 14 C in the Atlantic Ocean and the Pacific Ocean.