Jökull - 01.12.1968, Side 24

S U M M A R Y
TRITIUM IN GROUND WATEli
AND GLACIERS IN ICELAND
Páll Theodórsson
Science Institute, University of Icelancl.
Since 1962 an extensive grouncl water in-
vestigation using the hydrogen isotopes has
been carried on at the Science Institute of the
University of Iceland. The main emphasis has
been on the geothermal ground water, study-
ing the geographical variation of the average
deuterium concentration in precipitation, sur-
face water and in ground water. Similar studies
have been made of the time variations of the
tritium concentration. As a part of this work
tlie deuterium and tritium concentration in
two of the largest glaciers have been studied.
The main results of the tritium measurements
in two boreholes in the glaciers Langjökull
and Vatnajökull are described in this article.
The holes were made with á thermal drill,
which is shown on Figs. 2 and 3. At the lower
end of a 1.2 m long tube 70 mm in diameter,
there is an annular electric heater, which melts
the ice, leaving a 45 mm diam. ice core. The
power in the heater was about 300 watts and
the drilling speed 1—2 meter per hour.
The first hole with the thermal drill was
made on Langjökull in May 1968. The depth
of the hole was 30 meters. The result of the
tritium measurements on this core is shown
on Fig. 5. This figure shows clearly that there
is an extensive isotopic exchange between the
rain and meltwater and the ice of the glacier.
At this altitude the accumulation of snow be-
gins probably in the beginning of October
and ends in April. It is further assumed that
the snow of March—April melts again. There-
fore the mean tritium concentration of the
wintermonths, October—February, is also shown
on Fig. 5, and the scale of the abscissa is
chosen to give the best fit to the tritium curve
of the glacier. It has generally been accepted
that there is only slight isotopic exchange be-
tween the ice and percolating meltwater in a
temperate glacier. Fig. 5 shows that this can-
not be the case. The same is also amply de-
monstrated by the deuterium measurements.
The tritium variations in the glacier must be
explained with the modifying influence of
summer rain and meltwater. The mean tri-
tium value of the precipitation of March—
September (at Rjupnahaed) is therefore shown
on Fig. 5. It is hoped that these results to-
gether with proper mathematical analysis will
give valuable information about the exchange
process.
In June 1968 another hole was drilled at
Bardarbunga in Vatnajökull, the largest gla-
cier in Iceland, at an altitucle of 1800 meters.
The deptli of this hole was 40 meters, but
then the drill got stuck and coulcl not be re-
covered.
The result of the tritium measurements of
the icecore is shown on Fig. 6. The monthly
mean value of the tritium concentration in
precipitation at Rjupnahaed is also shown on
Fig. 6, the scale of the abscissa being chosen
so as to give best fit.
The two curves are quite similar, indicating
that the glacier is arctic or at least very nearly
so. It should therefore be possible to obtain a
continuous record of the tritium concentration
in precipitation during the last decades by
drilling deep enough into the glacier at Bard-
arbunga. This would be of great value for
tritium measurements, as it is important to
know the tritium concentration in rain before
the atmosphere became contaminated with tri-
tium from hydrogen bombs. It is also anti-
cipated that deuterium measurements of such
an ice core could give interesting information.
An attempt will therefore be made to drill a
deeper hole into the glacier in the summer
1969. This work will be reported in greater
detail after further measurements have been
made.
358 JÖKULL 18. ÁR