Jökull - 01.12.1999, Side 3

A summary of the environmental history of the Skagi peninsula,
northern Iceland, 11,300-7800 BP
Mats Rundgren
Department of Quaternary Geology, Lund University, Tornavagen 13, S-223 63 Lund, Sweden
Abstract - A summary is presented ofthe Late Weichselian and early Holocene changes ofvege-
tation, climate and sea level on the Skagi peninsula, northern lceland, as reflected in bio- and
lithostratigraphic data from five sediment sequences. The period 11,300-10,900 BP was charac-
terized by grass-tundra vegetation and low lake productivity, indicating cold climatic conditions.
Milder conditions after 10,900 BP are reflected by an expansion of dwatf shrubs and increased
limnic productivity. The Younger Dryas cold event began with an abrupt cooling at 10,600 BP
that caused a return to grass-tundra vegetation and low limnic productivity. A marine transgres-
sion occurred in the later part ofthis cold event. Abrupt warming associated with the opening of
the Holocene at 9900 BP resulted in a change to herb-tundra vegetation and high lake productiv-
ity. Rapid regression after 9900 BP was followed by a minor transgression in the period 9800-
9700 BP, coincident with a short-lived cooling event on Skagi (the Preboreal oscillation). A
dwarf-shrub expansion and raised limnic productivity at 9600 BP indicate milder conditions. Rel-
ative sea levelfell below present sea level at 9000 BP. A rapid change in the composition ofthe
dwarf-shrub and shrub vegetation at 8800 BP may reflect a temperature rise and a change to
drier summer conditions. Another rapid vegetational succession at 8000 BP resulted in a domi-
nant slirub and dwarf-shrub tundra vegetation in the period 8000-7800 BP. The Late Weichselian
and early Holocene climatic reconstruction for Skagi fits well with palaeoclimatic data from
other parts of the North Atlantic region, indicating a close connection between deglacial ocean
circulation changes and climatic conditions on Iceland. In addition, the recording of transgres-
sions on Skagi during cold events implies that the Icelandic lithosphere is extremely sensitive to
changes in volume of glacial ice.
INTRODUCTION
The North Atlantic region experienced a series of
abrupt climatic changes during the Pleistocene—
Holocene transition, as shown by palaeoclimatic
proxy data from ice cores, marine sediments and ter-
restrial sequences, and the dynamic climatic history
of this region has to a large extent been attributed to
displacements of the North Atlantic oceanic polar
front (Ruddiman and Mclntyre, 1981; K05 et al.,
1993; NASP Members: Executive Group, 1994; Fig.
1), i.e. the southern limit of cold, prevalently sea-ice
covered polar waters (Mclntyre et al., 1972). Deep-
sea records from the North Atlantic Ocean suggest a
rapid northward shift of the polar front around 13,000
BP from a position at the latitude of northern Portugal
to the vicinity of Iceland (throughout this paper, BP
refers to uncalibrated 14C years). The beginning of the
Younger Dryas cold event at c. 11,000 BP was associ-
ated with a return of polar waters to the latitude of
southwestern Ireland. This event ended at c. 10,000
BP with a rapid retreat of the polar front to a position
between Iceland and Greenland, and this northward
retreat continued during the Early Holocene.
The climatic record from Greenland ice-cores
(Dansgaard et al, 1989, 1993; Johnsen et al., 1992;
Alley et al., 1993; Mayewski et al., 1993; Johnsen et
al, 1995) is concordant with the marine record from
JÖKULL, No. 47, 1999
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