Rit (Vísindafélag Íslendinga) - 01.06.1976, Side 57

In the polar regions, where the seasonal 8-oscillations survive in
the fim and ice, they offer an excellent opportunity to measure
the accumulation rate. Several authors have applied this method
to determine the accumulation rates in the polar regions and com-
pared these results with results obtained by other methods. (Gon-
fiantini et al. 1963, Epstein et al. 1965, Picciotto et al. 1966 and
1968, Lorius et al. 1968, Johnsen et al. 1972). In most cases, the
stable isotope method seems to give satisfactory results.
On temperate glaciers, where the seasonal variations in stable
isotope content are small, as in Iceland (Árnason 1970), or where
they are strongly modified by percolation of meltwater, the stable
ísotope method for determination of the accumulation rate does not
work unless the conditions are quite favourable (Deutsch et al.
1966). Stable isotope studies on fim profiles in temperate regions
are, however, of great importance since they can be used, together
with density measurements, to estimate the ranoff ratio.
Because of the small seasonal 8-variations and very extensive
isotopic homogenization, Árnason (1969) was abie to determine
the runoff ratio at four localities on Icelandic glaciers; at two loca-
lities on the Langjökull glacier at an altitude of 1230 and 1300 m
respectively and at two localities on the Vatnajökull glacier at an
altitude of 1300 and 1540 m respectively. (These places are shown
on Fig. 11 and Fig. 12 as V—1, V—15, L-1 and L-4, together with
the date of sampling).
As a first step it is possible to set up a simple balance equation
where q:
8,:
8P:
8i (1 — q) + 8W • q = 8P
the runoff ratio
the mean 8D-value of the fim that remains after the
summer thaw
the mean 8D-value of the water which escapes during
the summer.
the mean 8D-value of the annual precipitation.
can be obtained by measuring the deuterium content of the firn be-
low the uppermost winter layer. 8W may be derived from the equation
= 1 + (Si/lOOO)
efr 1 + (8W/100Ö)
where Ketf is the effective fractionation factor.
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