Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 171

been measured in the Húsavík water (see Table 14), the ratio
Öb/Öo18 seems to lie close to the meteoric line. This linear relation-
ship between ðo18 and 8D suggests that the water has not undergone
other changes in isotopic composition than can be ascribed to eva-
poration and condensation processes.
Thus we have no reason to believe that the deuterium concentra-
tion of the Húsavík and Hafralækur water has decreased during its
passage underground. The deuterium content of the groundwater
at Húsavík could have increased from that in the initial meteoric
water if we assume that the water has acquired its Cl~ by direct
mixing with sea water. The initial meteoric water would then have
been similar in deuterium content to that of the water recovered
from the well at Hafralækur.
Thus the only explanation which then remains for the low ðD-
value of the water recovered from the deepest well at Húsavík and
Hafralækur is that the water is very old and has been derived from
a precipitation somewhere in the interior of Iceland when the clim-
ate was considerably colder than it is to-day.
Deuterium studies on the 415 m long ice core from the glacier
Vatnajökull have shown that one degree centigrade lowering in
mean temperature results in an approximately 6%0 lower 8D-value
of the mean precipitation. Assume that the 8D-value decreases further
linearly with the air temperature and thus each 1°C lowering in
the temperature lowers the 8D-value of the precipitation by 6%0.
This means that even if the water at a depth of 1500 m in the
Húsavík wells and in the Hafralækur well originates as precipita-
tion deposited in the northem part of the glacier Vatnajökull, which
is the part of the country giving precipitation with the lowest ðD-
value, the water is a precipitation deposited when the mean air
temperature was approximately 5°C lower than to-day. Such a
low temperature has hardly existed since the time of the last gla-
ciation.
The 8018 — results obtained for the Camp Century ice core also
agree with this, since they indicate that the 8D-value of precipita-
tion deposited in the period 10 000 to 60 000 years ago, should have
been about 50%o — 100%o lower than to-day.
Consequently the deuterium studies support our previous sug-
gestion, that the thermal water at Húsavik and Hafralækur might
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