Náttúrufræðingurinn - 1957, Blaðsíða 37

MÓRINN í SELTJÖRN
193
peninsula Seltjarnarnes near Reykjavík. Fig. 1 shows the location o£ the peat, and
of the sections A and B shown on figs 4 and 5. Fig. 4 shows the peat layer in
Seltjörn in relation to the high water and low water level.
In 1954 the present writer sent a sample of mud peat constituting the bot-
tom layer of the Seltjörn peat (cf Fig. 4) to the Geochronometric Laboratory in
Yale for radiocarbon dating. He expresses his gratitude to Director J. S. Deevey
J:r and Acting Director Henry L. Kraybill for their readiness to run the
sample. The sample was found to be 9030±280 years. This led to a closer in-
vestigation o£ the Seltjörn peat in cooperation with two other Icelandic geo-
logists, Jón Jónsson, who carried out a cliatom analysis of a peat section and
Thorleifur Einarsson, who made a pollendiagram of the same section. They
publish their results in the accompanying papers.
The present writer discusses the consequenses the radiocarbon dating of
the Seltjörn peat has for the conception of the shore line development and
the postglacial climate history of SW-Iceland. The dating of the peat sample
proves that already 9000 years ago the isostatic rising of SW-Iceland had ad-
vanced so far that the sea-level at Seltjörn was somewhat lower, probably 3—4
m lower, than at present. In a paper published in 1952 G. Kjartansson proved
that at Raudhóll near Flafnarfjördur (10 km S of Seltjörn) a transgression has
occurred raising the sea level to c. 50% of its highest postglacial limit at a time
when the sea temperature at the shore was about the same as now. From the oc-
currence of species such as Nucella (Purpura) Lapillus and Litorina obtusata tlie
present writer concludes that tlie July airtemperature and the niain annual air-
temperature in the area at the transgression maximum can hardly liave been
more than 1.5° C lower than at present (1901—1930), and the difference may
well have been less or even none. The transgression must liave occurred either
just after the Younger Dryas Time (dotted line of fig. 6) or during the Alleröd
oscillation (dash line on fig. 6). Presupposing that the shore line development
at Raudhóll is not influenced by any local disturbances the latter alternative
seems more probable. A consequence would be that in Iceland the Alleröd climate
was warmer, compared with the present climate, than it was in Great Britain and
continental NW Europe. This might be due to the rest of the great inland ice in
NW Europe having affected the air- and ocean- currents in adjacent areas much
more effectively than did the rest of thc ice cap in Iceland.
The present writer leaves open the question whether the Seltjarnarnes penin-
sula is still sinking or not, but maintains that the sea level has risen at least some
few metres since 3000 years ago and that this must be due to an isostatic sink-
ing of the land. He emphasizes the necessity of a comprehensive systematic
study of the lateglacial and postglacial shore line development in Iceland.