Jökull - 01.12.1990, Blaðsíða 87

The late glacial history of Iceland. Comparison with isotopic
data from Greenland and Europe, and deep sea sediments
Árný Erla Sveinbjömsdóttir and Sigfús J. Johnsen
Science Institute, University oflceland
Dunhagi 3, IS107 Reykjavík, Iceland.
abstract
Paleoclimatic research on deep ice cores from
Greenland has revealed that the late Weichselian
glaciation in the North Atlantic region was charac-
terized by a long series of climatic oscillations. The
same climatic variations during the Bölling - Alleröd
- Younger Dryas period have also been observed in
iake sediments in Switzerland suggesting the same cli-
matic evolution in Northern Europe during that time.
0 has been suggested that the reason for this simi-
larity is major shifts ofthe North Atlantic polarfront
associated with similar changes in the North Atlantic
current. A.v expected the geological record in Iceland
also reflects these climatic variations during the last
3000 years ofthe last glaciation; the warm Bölling -
Alleröd periods and the cold Younger Dryas period,
where a severe glaciation ofthe country is suggested.
A good correlation is observed between paleotemper-
atures calculated from <5180 measurements of shells
from marine sediments ofknown age in Southern and
Western Iceland and the paleotemperatures revealed
by the Greenland Ice.
INTRODUCTION
The end of the last glacial period in Iceland
(Late Weichselian) was a time of swift and profound
changes. The ice sheet contracted rapidly, sea level
rose submerging the present lowlands and then re-
ceded to expose them again. This was, however, not
a time of simple warming and unidirectional change
but a complicated interplay of warming and cooling,
changing oceanic currents and weather pattems and
coastline changes due to increasing sea volume and
isostatic readjustments.
Changes in climate of this magnitude are not lo-
cal and will therefore correlate with general climatic
changes at this latitude or even world wide. Local ef-
fects may significantly delay or enhance those overall
changes due to special local conditions. The purpose
of the present account is to explore what changes have
been observed and dated in the North Atlantic region
and compare with what has been measured and dated
in Iceland sofar.
The late glacial history of Iceland has been studied
by geologists by mapping moraines, till units, glacial
striations and raised beaches. These studies have
revealed the climatic changes in Iceland during the
Bölling - Older Dryas - Alleröd - Younger Dryas oscil-
lations (Late Weichselian) some 13.000-10.000 years
BP (BP designates conventional radiocarbon years be-
fore present=1950). Further information about the
climate at that time can be obtained by calculating pa-
leotemperatures from <5180 in marine shells from late
glacial time. The first attempt to do so is reported
here.
Raised beaches are often suggestive of warm cli-
mate in particular when associated with strong silt for-
mation due to retreating glaciers. Glacial sediments
however indicate cold phases and advancing glaciers.
Raised shoreline features are common in Iceland, and
for example in the Borgarfjörðurregion, there are indi-
cations that during the Older Dryas stage the sea level
has been > 60 m above present sea level and 90 m
JÖKULL, No. 40,1990 83