Fróðskaparrit - 01.01.1998, Síða 180

186
LATE HOLOCENE CLIMATIC FORCING OF GEOMORPHIC ACTIVITY
IN THE FAROE ISLANDS; NORTH ATLANTIC OCEAN
and seasonal 20th century global tempera-
ture variations, Jones and Briffa (1992)
concluded that oceanic regions of the world
vary more coherently than terrestrial re-
gions, and that data obtained from oceanic
regions therefore are likely to be more in-
dicative of any global change than observa-
tions obtained from other regions.
As demonstrated by Briffa and Jones
(1993), summer season air temperatures
are the most atypical of all the various sea-
sonal averages, especially in the Northern
Hemisphere, where most of the global sur-
face warming observed since the middle of
the 19th century has occurred in winter,
spring and autumn, but only little in sum-
mer. Inferring climate change on the basis
of observations biased toward summer con-
ditions is therefore questionable regardless
of spatial scale, and winter responsive data,
in general, represent a much more powerful
source of information. Therefore, in an
overall global change context, the occur-
rence of geomorphic cold-climate pheno-
mena such as those discussed above should
be considered with special interest, because
they are controlled mainly by winter season
climate. In short, winter-sensitive geomor-
phic phenomena in oceanic land areas such
as the Faroe Islands are therefore expected
to yield extraordinarily important informa-
tion on climate change, past as well as pre-
sent.
Conclusions
The Faroe Islands is close to the 20th cen-
tury southem limit for the northern hemi-
sphere polar periglacial zone. According to
the treeline, the modern periglacial envi-
ronment on the Faroe Islands extends al-
most to sea level. The occurrence of active
periglacial features such as patterned
ground and sorted stripes, however, suggest
the modern lower periglacial boundary to
be located within a range from 250 to 450
m a.s.l. This altitudinal range is controlled
by temperatures as well as exposure to
wind and insolation. Above the periglacial
boundary the vegetation rapidly becomes
patchy and periglacial activity widespread.
The modern limit of periglacial activity on
the Faroe Islands corresponds to a MAAT
of about 3.5-5°C.
From a geomorphological point of view
the land areas above the periglacial bound-
ary (about 50% of the total land area) rep-
resent a typical cold-climate, arctic envi-
ronment. The present MAAT is only slight-
ly above 0°C at the highest mountains on
the Faroe Islands, but the modem potential
discontinuous permafrost level is most like-
ly situated 300-500 m higher. During cold
intervals of the LIA the lower limit for
periglacial activity may temporarily have
approached sea level, contemporary with
beginning establishment of sporadic per-
mafrost in the highlands. Presumably, a few
sites in the highest mountains were then
close to reglaciation. By this, the present
Faroese landscape is highly sensitive to-
wards any climatic change; a situation
which is enhanced by the location in a
uniquely sensitive region of the North At-
lantic Ocean for registering Holocene cli-
matic changes, as is documented by proxy
data, historical records and modern obser-
vations on climate and geomorphic pro-
cesses.