Jökull - 01.12.1990, Blaðsíða 82

with varying snow cover are inhospitable for any tree
vegetation.
CONCLUDING REMARKS
A pollen diagram for the period 9650 B.P. to 6900
B.P. at Krosshólsmýri, Flateyjardalur in central North
Iceland, is presented. Three Local Pollen Assemblage
Zones are described. The first one, a Salix-Ericales-
herb assemblage, is so far unique for North Iceland.
Following that there is aBetula-Junipei'us-herb assem-
blage, and lastly a tree birch assemblage indicating a
woodland vegetation about 7000 B.P. Size measure-
ments on all Betula pollen grains are given in size fre-
quency diagrams, thus giving some idea about Betula
nana and B. pubescens proportions in the landscape
of the early Holocene. All age estimates are based
on the two radiocarbon dates available and are shown
graphically by means of a time/depth curve.
Fluctuations in the Juniperus pollen curve are as-
sumed to derive from climatic changes resulting in
paludification and expanding mires. As a reason for
this, changes in the ocean current pattem north of Ice-
land are suggested.
The pollen diagram from Krosshólsmýri has the
best time resolution of all the pollen localities pub-
lished up to now, with about one sample per century.
Therefore we may expect to see some fluctuations
there in more detail than elsewhere. Such fluctuations
can be masked out at the other sites, because of larger
time spans between samples due to slower sedimenta-
tion rate or fewer samples per equivalent time spans
as the sampling interval is too great. Consequently a
more comprehensive vegetational history is obtained,
which gives a basis for more decisive interpretations
than elsewhere in Iceland, although the general picture
seems to be similar. Last but not least Krosshólsmýri
predates the previously investigated localities and adds
about 800 14C years to the Holocene vegetational his-
tory of Iceland.
ACKNOWLEDGEMENTS
This work was supported by grants from the Ice-
landic Science Fund and the Science Fund of the Uni-
versity of Iceland. The Science Institute, University
of Iceland, contributed work facilities. I am indebted
to my colleague Dr. Hreggviður Norðdahl for mak-
ing the Krosshólsmýri sediment core available to me
and allowing me to use his 14C-dates, to Dr. Bent
Fredskild, docent Leifur A. Símonarson and Professor
Þorleifur Einarsson who all made helpful comments
on an earlier draft of the manuscript, to Dr. Jón Eiríks-
son for help with the drawings and Kristinn Einarsson
for correcting my English.
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78 JÖKULL, No. 40, 1990