Rit (Vísindafélag Íslendinga) - 01.06.1976, Blaðsíða 56

the Alps, where the difference between the winter and summer
precipitation is of the order A8o18 = 14%0 (Deutsch et al. 1966),
higher 018 content can sometimes be found in the runoff than in
the remaining firn, although the reverse might he expected from
isotopic exchange. Similar results were found in studies carried out
at the Weissfluhjoch sampling point, where drainage samples col-
lected from the snowpack sometimes showed 8D-value higher than
the mean 8D-value of the snowpack left. The results obtained for
Weissfluhjoch, however, fitted satisfactorily into Búason’s theore-
tical model (Árnason et al. 1973).
In regions with low seasonal difference between the mean isotope
content of the winter and summer precipitation the exchange effect
appears more pronounced. Such is the case on the Icelandic glaciers
which seem especially well-suited for studying these phenomena,
not only because of the low seasonal amplitude, hut also because
the extent of such an exchange can he studied continuously from
zones where the runoff ratio approaches unity, to zones where the
runoff ratio is so small that it has practically no effect on the
8-variations in the accumulation.
5. 3 Determination of the runoff ratio on temperate
glaciers by the stable isotope method.
One of the most important parameters for the study of the mass
budget of glaciers is the accumulation rate. On temperate glaciers
only a part of the total annual precipitation is accumulated; a part
of it escapes as runoff during the warm season. Therefore on tem-
perate glaciers determination of the nmoff ratio is of a great im-
portance. The runoff ratio is that part of the precipitation which
escapes as meltwater or rain during the summer thaw.
Several methods have been applied for determination of the
accumulation rate. Such methods are, for instance, snow stake
measurements, classical stratigraphic methods (Schytt 1958), mea-
surements of |3-activity profiles to identify reference horizons (Pic-
ciotto et al. 1963, Wilgain et al. 1965, Crozas et al. 1966, Ambach
et al. 1967, 1969, 1970 a and 1971), and measurements of tritium
profiles (Ambach et al. 1969 a and 1970 b, Theodórsson 1972 and
Merlivat et al 1973).
52
1