Fróðskaparrit - 01.01.1998, Blaðsíða 164

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LATE HOLOCENE CLIMATIC FORCING OF GEOMORPHIC ACTIVITY
IN THE FAROEISLANDS; NORTH ATLANTIC OCEAN
gions, especially oceanic, have cooled. Re-
search on global climate change indicates
that, in general, land surfaces will heat or
cool more rapidly than oceans and that tem-
perature variations within especially high-
latitudinal regions will be pronounced
(Houghton et al., 1996), mainly due to the
operation of various, interrelated climatic
feedback mechanisms (Kellogg, 1973).
Instrumentally recorded surface tempe-
rature observations indicate the North At-
lantic region including Greenland and Ice-
land to have cooled significantly in the lat-
ter half of the 20th century (Jones and Brif-
fa, 1992; Houghton et al., 1996), which
makes this an important area for global
change research, past and present. Oceanic
circulation in the North Atlantic plays a
major role in determining poleward energy
transfer in the northern hemisphere, and is
thought to be a key factor regulating global
climate change (e.g., Ruddiman and Mcln-
tyre, 1981; Broecker et al., 1985; Rind et
ai, 1986; Bard et al., 1987; Broecker and
Denton, 1990; Lehman and Keigwin, 1992;
K09 et al, 1993; Bigg, 1996; Bjorck et al.,
1996; Rasmussen et al., 1997).
Within the North Atlantic region the
Faroe Islands are situated in a uniquely sen-
sitive part of the North Atlantic Ocean for
registering the timing and severity of late
Quaternary climatic changes (Humlum et
ai, 1996; Humlum, 1998). Warm and
saline Atlantic surface water presently
flows around the Faroe Islands into the
Norwegian and Greenland Seas, where
evaporation and cooling during winter pro-
duces a gradually higher water density.
This dense water then overtums, probably
in very localised regions up to a few tens of
kilometres in diameter, resulting in deep
convection (Bigg, 1996). The sinking cold
water represents a major constituent of
North Atlantic Deep Water, part of the
global thermohaline circulation, and is con-
sidered of global importance (Broecker,
1991). In comparatively warm periods,
when generally strong, or northward-dis-
placed, circulation occurs in the atmos-
phere and ocean, the Faroe Islands lie con-
tinually in the main arm of the North At-
lantic Drift. In colder periods, when the
North Atlantic Drift weakens or its main
branch takes a more southerly position, a
tongue of polar water from the East Iceland
branch of the East Greenland Current ap-
proaches the Faroe Islands from the north-
west. As a consequence, the Faroe Islands
are well placed to register terrestrial geo-
morphic imprints of any large amplitude
shifts of the water current boundary in the
North Atlantic, both past and present.
Topography and geology
The Faroe Islands have a total area of 1397
km2 and are situated between 61°20’N -
62°24’N and 6°15’W and 7°41’W. The
highlands rise gradually from about 400-
600 m a.s.l. in the southern part of the is-
lands to almost 900 m a.s.l. in the northern
and northeastern areas (Fig. 1). The aver-
age altitude is about 300 m a.s.l. The north-
eastern part of the Faroe Islands is domi-
nated by alpine topography, while rolling
highland plateaus delimited by steep head-
walls characterise the remaining regions.
The bedrock is Tertiary-age plateau basalts,
about 50-60 million years old, gently đip-