Jökull - 01.12.1979, Page 48

somewhat obscured by the arrival of Pacific mol-
luscs. In the Breidavík deposits on Tjörnes at least 4
glacial-interglacial cycles have been found. The
fauna in the marine sediments in Breidavik which
is of Lower Pleistocene age is similar to the present
one in the area, but the presence of Porllandia arctica
(Gray) in marine layers resting directly on tillites
shows, however, high-arctic conditions with low
water temperature, close to 0°C, at the beginning
of the interglacials. In Upper Pleistocene inter-
glacials the water temperature was apparently
similar to the present one, but slightly higher dur-
ing the last one, as revealed by the boreal molluscs
in the Fossvogur deposits.
During the retreat of the ice in Late Glacial time
some readvances occurred, the last ones being the
Álftanes readvance, 12.500—12.000 B.P., and Búdi
readvance, 11.000—10.000 B.P.
Holocene climate
Holocene climatic changes are mainly reflected
by changes in the vegetation, recorded in bog and
lake deposits. The dating of the changes is greatly
facilitated by numerous tephra layers that serve as
good time markers, as their chronology is fairly well
known.
In early Holocene, 10.000—9000 B.P., there was
a small Betula maximum in North Iceland, whereas
South Iceland seems to have been Betula-free. This
may support the theory that a part of the Icelandic
flora has survived the last glaciation in ice-free
refugia in northern Iceland. About 9000 B.P. Betula
immigrated rapidly into southern Iceland as indi-
cated by the first great Betula maximum in the
pollen diagrams. During this maximum, correlated
with the Boreal and Lower Atlantic in continental
Europe, annual mean temperature may have been
about 2°C higher than today and the precipitation
was somewhat lower. A Betula minimum equated
with the wet Atlantic of continental Europe started
about 6500 B.P. The Betula receded and bogs be-
came wide-spread as the precipitation increased.
The temperature must have been somewhat higher
than the present one, as this interval shows a dis-
tinct Sphagnum maximum, but this plant is not
spore-producing now in Iceland. Between 5000 and
2500 B.P. the second great Betula maximum occur-
red and Betula vegetation covered at least 50% of
the country. This time is correlated with the Sub-
boreal of continental Europe. The annual mean
temperature was probably 2—3°C higher than
today, the precipitation was somewhat lower and
the winters were rather mild. Deposits from the
Nucella transgression in Subboreal time, when
sea-level apparently rose about 3 m, are known
from Northwest Iceland. A climatic deterioration
took place about 2500 B.P. The Betula vegetation
declined somewhat and bogs became widespread
again.
After the beginning of settlement in Iceland, i.e.
about 870 A.D., the Betula vegetation decreased
rapidly. There is a sharp increase of grasses, and
cultural indicators appeared. A rapid soil erosion
began. This reflects the devastating influence of the
settlement on the vegetation of Iceland.
SELECTED REFERENCES
Akhmetiev, M.A., G.M. Brattseva, R.E. Giterman,
L.V. Golubeva and A.I. Moiseeva, 1978: [Late
Cenozoic stratigraphy and flora of Iceland].
Trans.Acad.Sci.USSR 316: 188 pp. (In
Russian).
Einarsson, Th., 1963: Pollen-analytical studies on
the vegetation and climate history of Iceland in
Late and Post-Glacial times. In Löve, A. &
Löve, D. (Ed.): North Atlantic Biota and their
History: 355 — 365. Pergamon Press Oxford.
Einarsson, Th., 1966: Þættir úr loftslagssögu Is-
lands [Chapters from the climatic history of
Iceland]. Vedrid 11 (2): 47-53.
Einarsson, Th., 1977: Um gródur á ísöld á Islandi.
[On the Pleistocene vegetation in Iceland]. In
(Ed.): Skógarmál: 56—72. Reykjavík.
Friedrich, W.L., 1966: Zur Geologie von Brjáns-
laekur (Nordwest-Island) unter besonderer
Berúcksichtigung der fossilen Flora. Sonder-
veröff. Geol. Inst. Univ. Köln. 10: 108 pp.
Schwarzbach, M., 1955: Beitráge zur Klimage-
schichte Islands I. Allgemeiner Uberblick der
Klimageschichte Islands. Neues Jb. Geol. Pal-
áontol. Mh. 3: 97—130.
Schwarzbach, M. & H.D. Pflug, 1957: Beitráge zur
Klimageschichte Islands VI. Das Klima des
jiingeren Tertiárs in Island. Neues Jb. Geol.
Paláontol. Abh. 104 (3): 279—298.
46 JÖKULL 29. ÁR