Jökull - 01.12.1990, Blaðsíða 94

ó,80 %o
-38.0 -38.0 -34.0 -32.0 -30.0 -28.0 %
Figure 5. The Figure shows all C-14 dated shells from
Iceland reported in the literature in relation to the
é180 profiles from Dye 3, SW-Greenland. —Myndin
sýnir aldur íslenskra skelja sem greindar hafa verið
með C-14 aðferðinni í Ijósi <5lsO sniðsins frá Dye 3,
SV-Grœnlandi.
from <5180 analyses of marine molluscs.
14C AGE DETERMINATIONS
The age of shell fragments in marine sediments
younger than ca 40.000 years can be determined by
the radiocarbon dating technique (Libby, 1955). This
method has become a standard dating tool in Quater-
nary geology as well as in Archaeology and Paleob-
otany (Mook,1980).
A number of Icelandic shells from several local-
ities have been radiocarbon dated. The datings have
been performed at the conventional radiocarbon labo-
ratories in Lund, Uppsala, Trondheim and at the AMS
laboratory in Aarhus. All shell-dates reported in the
literature (Hjartarson, 1989b) in addition to new un-
published AMS analyses, performed at the Institute of
Physics, University of Aarhus are plotted on Fig. 5.
The figure shows also the part of the isotopic curve
from the Dye-3 core, Greenland, that reflects the last
violent oscillation of the Late Weichselian glaciation
i.e. Bölling-Alleröd-Younger Dryas (13.000-10.000
BP).
On Fig. 5 a distinction is made between samples
from the Reykjavík region, South, West, and North
Iceland. The samples from North Iceland are all from
Melrakkaslétta and are of late Bölling, mid-Alleröd
and Preboreal age, so are the samples from West-
ern Iceland which all originate from Hvalfjörður and
Melasveit. Samples from Southern Iceland and the
Reykjavík region are of late Alleröd and Preboreal
age. This demonstrates that during those periods the
sea level has been higher than today. On the other hand
very few samples dated so far are of Younger Dryas
age, despite considerable search, indicating extensive
glaciation of the country at that time. This contra-
dicts the conventional view that during the Younger
Dryas stage the glaciation of Iceland was restricted to
the interior of the country (Einarsson, 1985; Einars-
son and Albertsson, 1988). However, in recent studies
this view has been doubted and with more extensive
explorations of the Quatemary geology of Iceland and
first and foremost with more systematic datings a new
picture of the Younger Dryas glaciation is emerging
supporting severe glaciation of the country at that time
(Ingólfsson, 1987b; Pétursson, 1987; Hjartarson and
Ingólfsson, 1988; Hjartarson, Í989a; Andersen et ai,
1989; Norðdahl and Hafliðason, 1990).
ó180/A' marine shells as paleoclimatic in-
DICATORS
The oxygen isotopic ratios of fossil shells can be
used as paleoclimatic indicators as the <5I80 of the shell
is dependent on temperature and <5180 of the water, as
described in the following equation (Epstein et al.,
1953; Craig, 1965);
t(°C) = 16.9 - 4.2(<518Oc - 518Ow) +
0.13(é18Oc — <518Ow)2 (1)
90 JÖKULL, No. 40, 1990