Jökull - 01.12.1990, Side 119

below. The lower layer in core 1 is more depleted in
salts, and the pH is higher, than the one in core 2.
The accumulation of a seasonal snowpack and the
subsequent spring melt can cause acid episodes in
streams and lakes. It is therefore of interest to analyse
the effect of the degree of partial melting of snow upon
the pH of meltwater. This pH can be derived from the
measured pH of snow and residual snow samples. The
melting of about 10% of the original mass of a snow,
using constraints from the Vatnajökull glacier, pro-
duces a meltwater with a pH that is more than 1 pH
unit lower than that of the original snow. This lower-
ing of pH in the meltwater is similar to the one reported
during episodic acidification in North America, Scan-
dinavia and upland Britain, but fortunately in this case
pH lowering starts at pH 5.4 in the Vatnajökull glacier
in Iceland but in the other cases the original pH is often
around 4.5 so that the acidification brings the pH down
to about 3.5. The model described here simulates the
melting caused by the sun and can be used to simulate
fractional melting, that is to say, melting where the
meltwater is continuously drained from of the system.
However, some experimental or field data is needed
m order to constrain fractional melting.
If precipitation in Iceland ever gets severely pol-
luted by acids like H2S04 or HN03 the highlands and
the northern part of the island will be sensitive because
°f the accumulation of snow in the wintertime and the
preferential release of the protons and pollutants in the
early meltwaters. Hazardous pollution of the snow-
Pack can for example be brought about by volcanic
eruptions.
The lowering of the pH of meltwaters can happen
by a partial melting of unpolluted snow. That is to say,
snow that consists of pure water and sea salts but no
strong acids. This is caused by the preferential release
°f anions relative to cations balanced by the release
°f protons. The higher the concentration of immobile
relative to mobile cations in the pristine snow, the
greater is the lowering of the pH of the meltwater.
ACKNOWLEDGEMENTS
I am grateful to friends and colleagues at the Uni-
versity of Iceland and from The Iceland Glaciological
Society, who contributedassistance with field- and an-
alytical work. In particular I would like to thank Helgi
Bjömsson, Anna María Agústsdóttir, Finnur Pálsson,
Ægir Þór Jónsson, Svanbjörg H. Haraldsdóttir, Mikael
Marlies, Margrét ísdal, Theodór Theodórsson, Jón
Þórðarson and Níels Óskarsson. Reviews of an earlier
version of this paper by Halldór Armannsson, Stefán
Amórsson, Bryndís Brandsdóttir, Jón Ólafsson and
Leó Kristjánsson are deeply appreciated.
This study was supported by the Icelandic Science
Foundation, The Research Fund of The University of
Iceland and The Iceland Glaciological Society.
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