WHAT CAN WE LEARN FROM ISOTOPES? - Chemical Fundamentals of Geology and Environmental Geoscience - page 195

16 O
99.76%

14 N
99.63%

12 C
98.9%

1 H
99.985%

18 O
0.20%

17 O
0.04%

15 N
0.37%

13 C
1. 10%

2 H
0.015%

34 S
4.21%

32 S
95.02%

33 S
0.75%

36 S
0.02%

Figure 10.9 The light-element stable isotope systems of interest to geochemists, superimposed on the relevant part of the
nuclide chart (cf. Figure 10.1.1); the histograms illustrate the average relative abundances of the minor isotopes.

'per mil' by analogy with 'per cent' - stands for parts-
per-thousand. The δ notation is used for all stable iso-
tope systems. The standards used, on the other hand,
vary from one isotope system to another (see
Table 10.3).

is then expressed in terms of its ' δ -value'. Using oxy-
gen isotopes as an example:

18

−

18

O
O

O
O

16 16

sample standard

δ 18

O = 1000 × ‰

(10.8)

18
16

O
O

Hydrogen and oxygen isotopes - keys to
past climates

standard

represents the measured atomic abundance
ratio of the heaviest oxygen isotope to the lightest
(and most abundant) one. 9 The symbol ‰ - pronounced

18

O
O

Hydrogen and oxygen are the elements that make up
water. Each has more than one stable isotope, and nat-
ural variations in the isotopic composition of these two
elements provide a means of tracing the origins of nat-
ural water samples, and of studying rock-water and
mineral-water interactions.

Here

16

17 O, the least abundant oxygen isotope, is not usually reported.

9