Rit (Vísindafélag Íslendinga) - 01.06.1976, Page 60

the annual mean deuterium content of the precipitation on the
glaciers.
As discussed in the previous chapter, Icelandic glaciers can he
classified as soaked zones. Only a part of the annual precipitation
is accumulated; a part of it escapes as runoff during the following
summer. When the runoff percolates through the winter layer it
causes an extensive isotopic exchange between water and solid ice
leaving the remaining firn appreciably enriched in deuterium,
relative to its original value. Therefore a profile taken through a
glacier’s accumulation usually gives no reliable information about
the deuterium content of the past precipitation. This is in contrast
to high polar glaciers where the total annual precipitation is ac-
cumulated and profiles taken through the accumulation of those
glaciers provide a direct measure of the isotopic content of the pre-
cipitation.
The most precise method of obtaining information about the
deuterium content of the precipitation of Icelandic glaciers would
be to collect samples of the winter layers before the melting season
starts and then to place rain gauges on the glaciers during the
summer and collect monthly samples in the same way as at mete-
orological stations. The cost of such sampling has ruled out the use
of this method.
Tahle 6 shows the mean annual deuterium concentration and the
mean deuterium concentration for the periods October — April and
May — September for the three meteorological stations Rjúpna-
hæð, Hveravellir and Vegatunga. The amount of precipitation (in
mm) is also given as mean value for the corresponding period.
The period October — April or even October — May is the part of
the year when the precipitation on Icelandic glaciers usually falls
as snow, no melting occurs, and conditions are similar to those on
polar glaciers. Consequently, samples of the winter layer may be
taken as representative for the precipitation in this period. The
table shows that in spite of a slight annual periodicity in the deu-
terium concentration with a low deuterium in winter and high in
summer, the mean annual deuterium concentration is only slightly
higher than the mean concentration for the period October — April.
In all cases the difference is less than 1%0.
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