Rit (Vísindafélag Íslendinga) - 01.06.1976, Blaðsíða 65

found to be from volcanic eruptions occurring in 1934 and 1922
respectively. The total ice core recovered was found to span back
to the year 1917. A complete deuterium record of the entire ice
core is given by Árnason (1970), but the deuterium results ob-
tained for the uppermost 40 m of the core are shown in Fig. 9.
It appears from Fig. 9 that the ðD-variations of the snowpack and
the fim are only slightly affected by percolating meltwater. The
same appears from P. Theodórsson’s tritium studies of the core. At
a depth of 20 m, corresponding to 6 years’ accumulation, the varia-
tions begin to smooth out, but without any appreciable change in
the mean 8D-value of the ice. This smoothing-out process is appar-
ently associated with the transformation of firn to clear ice, which
has already begun at a depth of 20 m, and is almost completed at
35 m.
When compared with meteorological data, the 8D-record shows
that although the mean air temperature of a single year is not re-
flected in the record, the variations of longer periods obviously are.
The periods 1966—1968, 1948—1954 and the years before 1920,
which have relatively low mean air temperature, all result in low
Ón-values in the core.
The deuterium profile from V—18 suggests that, although 8D-
variations of periods shorter than one year are obliterated in the
firn within a few years, the mean annual 8D-value of the precipi-
tations may be preserved in the ice.
Because of lack of a seasonal 8D-amplitude in the ice, it is not
possible to date the ice by counting the summer maxima down-
wards to the core, as is the case at some places on the Greenland
1Ce cap (Dansgaard et al. 1973). Tephrachronology, however, ap-
Parently offers a special opportunity for dating the ice in Iceland,
since tephra layers from recorded eruptions were found to be pre-
served in the ice and are easily detectable.
In 1972, a continuous ice core was obtained by drilling a 415 m
^eep hole into the Vatnajökull ice-cap. The hole, V—21, was lo-
cated at an altitude of 1800 m; the location is shown in Fig. 11.
^ detailed description of the mechanical drill, especially constructed
^0r this purpose, is given elsewhere (Árnason et al. 1974). The
core recovery was better than 99%.
In the uppermost part of the ice core, covering the last ten years,
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