Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 59

meteorological data from several stations in Iceland for the period
1931—1960, it is found that at none of these stations does the pre-
cipitation in a single year exceed 1.5 times the mean value. If we
accordingly set 4500 mm as an upper limit for the year in ques-
tion at L-1 and use this in the balance equation together with
other availahle data, it would give an effective fractionation factor,
Ketf = 1.0190. Thus there is reason to believe that the effective
fractionation factor for deuterium exchange between ice and water
at L-l lies between the limits of 1.0208 and 1.0190.
Such simple methods as listed ahove are apparently valid in
special cases, i.e. where the seasonal variation is small and at alti-
tudes where the runoff ratio is high enough to cause extensive
homogenization. The previously mentioned exchange model deve-
loped hy Búason (1969) and tested hy Ámason et al. (1973)
should, in principle, be applicable to determine the runoff ratio for
every case on temperate glaciers, although its general validity must
be checked in more detail.
The validity of the stable isotope method for determining the
runoff ratio rests on the fact that it only requires information ahout
the isotope composition of the snowpack, after the homogenization
is completed, and information about the isotope content of the
total precipitation. The isotope composition of the snowpack can
easily be measured in the fim. The isotope composition of the total
precipitation is more difficult to measure directly at many places
on the glaciers. In regions with small seasonal variations, a suffi-
ciently accurate value can be obtained from information about the
isotope content of winter precipitation measured directly in the
snowpack hefore the summer melting hegins. In other places it
might be possible to measure the stable isotope content of the an-
nual precipitation at a meteorological station not far from the gla-
cier and then adjust this by an experimentally estimated altitude
effect.
•5. 4 Deuterium content of precipitation on Icelandic glaciers.
Approximately 10% of Iceland is covered by glaciers. Therefore
in order to draw a map showing the distribution of deuterium in
the precipitation throughout the country, it is important to know
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