Rit (Vísindafélag Íslendinga) - 01.06.1976, Blaðsíða 17

Botii deuterium and oxygen-18 measurements are based on mass-
spectrometric methods using the improved mass-spectrometer initi-
ally designed by Nier (1947).
In deuterium determinations the hydrogen is released from the
water and the measurement is carried out by comparing the two
hydrogen components HD (mass 3) and H2 (mass 2).
In the oxygen isotope work excess of water is isotopically equi-
librated with carbon dioxide. After the equilibration the oxygen-18
content of C02 is equal to that of the water multiplied by a frac-
tionation factor. The measurement is carried out by comparing the
components CO*6 (mass 44) and C016018 (mass 46).
In his pioneering work, Friedman (1953) was able to show that
different waters differ in their deuterium content according to their
origin and history. Later, a more extensive work by Friedman et al.
(1964) illustrated well how such deuterium measurements can be
used in a study of the hydrologic cycle.
In much the same way as for deuterium, the pioneering work on
oxygen-18 was in subsequent years followed by more extensive stu-
dies by Dansgaard (1961, 1964).
Craig et al. (1956) demonstrated well how simultaneous deu-
terium and oxygen-18 measurements can be useful in studying the
origin and history of thermal water. They analysed several hundred
samples of thermal waters from many places in the world, includ-
ing some samples from Iceland. Their conclusion was that the ther-
mal water must be almost entirely of meteoric origin. In some cases
they found that the water was somewhat enriched in oxygen-18
due to isotopic exchange with silicate rocks. Regarding the hydrogen
isotopes, however, they found no evidence for isotopic exchange.
This is understandable from the fact that the rocks are about 50%
oxygen by weight but contain only minute amounts of hydrogen.
Already in 1954 some water samples from hot and cold springs
and rivers in Iceland were collected by G. Böðvarsson and sent to
the University of Chicago, where they were analysed by H. Craig
for deuteriiun and oxygen-18 content in the years following. Al-
though the results were first published in 1962 (Böðvarsson 1962),
the authors seem, already in 1957, to have been aware of how use-
ful such measurements might be for study of geothermal systems
in Iceland (Böðvarsson, private communication).
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