Jökull - 01.12.1962, Page 56

Firstly, the ratio AD/AO18 is approximately
normal with the possible exception of sample
(12). This indicates in particular that the ther-
mal water is derived from the meteorological
cycle and contams practically no juvenile com-
ponents witli a different ratio AD/AO18.
The abnormal behaviour of sample (12) may
possibly be due to two factors. There may be
an error in the method of sampling as the
sample was taken from a well producing wet
steam. Furthermore, the ratio AD/AO18 is de-
pendent on the temperature and different
figures are obtained at 100°C than at the
temperatures prevailing in the meteorological
system.
Secondly, there is a considerable difference
between the isotopic concentrations in the
Reykjavík and the Akureyri areas. The pre-
cipitation in the Reykjavík area is generally of
an atlantic origin, wliereas the precipitation in
the Akureyri area is partially of a more arctic
origin.
Third, the data suggest that the rnain re-
charge area of the thermal springs (3) to (9)
does not lie in the region east and southeast
of the Reykjavík area. The tectonic lines in
the region liave a direction NE—SW and the
data are, therefore, indicative of a flow along
the lines rather than transverse to them.
Fourth, a comparison of the chemical and
isotopic data on sample (8) with the other
results suggests that this spring is independent
of the main hydrothermal systems in the area.
On the other hand, the clata on springs (3)
indicate that its water is derived from the same
system as (4) and (5) and possibly also (6) and
(7). The lower temperature is probably the
result of a cooling by conduction of heat from
the channeís of ascend.
The results on the tritium concentration are
no doubt influenced by the H-bomb test in
1954. Tliis is indicated by the high concentra-
tion in sample (10). The pre-bomb T/H ratio
was probably around 5xl0“18.
On the otlier hand, the tritium is quite low
in sample (4). The result indicates a subsurface
“age” of not less than 25 years which is re-
markable.
REFEREN CES:
Bodvarsson, G.: Physical Characteristics of Na-
tural Heat Resources in Iceland. Jökulll
11, 29-38, 1961.
Craig, H., Boato, G. and White, D. E.: Isotopic
Geochemistry of Thermal Waters. Proceed,-
i.ngs of the Second Conference on Nuclear
Processes in Geologic Sett.ings. Publ. 400,
Nat. Academy of Sciences, Nat. Research
Council, 1956.
Dansgaard, W.: The Isotopic Composition of
Natural Waters. Meddelelser om Grönlancl,
Bd. 165, Nr. 2, 1961.
54
JOKULL