Rit (Vísindafélag Íslendinga) - 01.06.1976, Side 97

11. 8D _ 8o18 RELATION IN ICELANDIC WATERS
Craig et al. (1956) first discussed the possibility of using com-
bined 8D and 8018 measurements on thermal waters to determine
whether such water is of meteoric origin and whether the water
was undergone any isotopic changes during its underground pas-
sage.
As mentioned previously, precipitation and surface water, not
affected hy other separation processes than evaporation and con-
densation in the atmosphere, should have a linear relationship be-
tween 8D and 8018 (Epstein et al. 1953, Friedman 1953, Craig
1961 a, Dansgaard 1964). This linear relationship, the meteoric
line, may vary somewhat from one place on the earth to another,
but for the North Atlantic region it is given by the expression
8d = 88018 4- 10. Consequently Craig et al. suggested that all
groundwater of meteoric origin which has not undergone isotopic
exchange with rocks during its underground passage should have
8d- and 8018-values which follow the meteoric line closely.
In order to study this relationship for thermal waters, 8D- and
8018-values of several hundred samples from various parts of the
world were measured (Craig et al. 1956, Craig 1963). The samples
were collected from both alkaline and acid springs; some of the
samples were taken from thermal areas in Iceland. The authors
came to the following conclusion: Since the alkaline springs have
about the same 8D-value as their associated surface waters and show
slight variable enrichment in O18 with respect to these waters, the
alkaline springs are deep circulating meteoric waters, which have
undergone variable amounts of oxygen isotope exchange with the
rocks but have not changed their hydrogen isotopes. Acidic springs
did not follow the meteoric line with a slope of 8, but all springs
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