Fróðskaparrit - 01.01.1998, Síða 163

169
Late Holocene climatic Forcing of
Geomorphic Activity
in the Faroe Islands
Seinholosena veðurlagið elvdi til jarðformandi virksemi í Føroyum
Ole Humlum and Hanne H. Christiansen
Institute of Geography, University of Copenhagen, Øster Voldgade 10, DK 1350 Copenhagen K., Denmark
Phone: +45 35 32 2500, fax: +45 35 32 2501, e-mail: oh@geogr.ku.dk and hhc@geogr.ku.dk.
Úrtak
Veðurlagið í Føroyum er óstøðugt.Tí ber til at skráseta,
nær og hvussu ógvisligar seinholosenar veðurlagsbroyt-
ingar eru, sum endurspegla broytingar í termohalinu
ringrásini. Hædd millum 250-450 m yvir sjóvarmálan-
um er nútíðar lágmarkið fyri periglasialum virksemi; tað
svarar til ein árligan miðallufttemperatur upp á 5-3,5°C.
Oman fyri hesa hædđina eru virkin periglasial drøg
vanlig, og gróðurin lítil. Periglasiala økið røkkur til
hægsta hálendi (mesta hædd er 882 m yvir sjóvarmálan-
um). Veðurlagið í Føroyum seint í 20. øld er merkt av
sera nógvari vætu og nógvum vindi heldur enn av ógv-
isligum kulda. Nútíðar træmarkið er nær sjóvarmálan-
um, og í dag er tann møguliga ósamanhangandi perma-
frosthæddin 300-500 m oman fyri tey hægstu fjøllini. A
sama hátt man tann møguliga glasiatiónshæddin í dag
bert vera 150-250 m oman fyri tey hægstu fjøllini. Með-
an køld millumbil vóru í teirri lítlu ístíðini, kann tað
lægra markið fyri periglasialum virksemi bráðfeingis
hava nærkað seg sjóvarmálanum, samstundis sum
permafrost fór at taka seg upp her og har í hálendinum,
og tá vóru nøkur støð á teimum hægstu fjøllunum óivað
nær endurglasiatión.
Abstract
The location of the Faroe Islands in a climatically
uniquely sensitive part of the North Atlantic region pro-
vides opportunities to register timing and severity of late
Holocene climatic changes reflecting variations in ther-
mohaline circulation. An altitudinal range of 250-450 m
a.s.l. represents the modern lower limit for periglacial
activity, corresponding to a mean annual air temperature
of 5-3.5°C. Above this range, active periglacial features
are widespread and plant growth restricted. The
periglacial zone extends to the top of the highlands
(maximum altitude 882 m a.s.l.). The late 20th century
climate in the Faroe Islands is characterised by extreme
humidity and strong winds, rather than extreme cold.
The present treeline is close to sea level, and the poten-
tial present discontinuous permafrost level is situated
300-500 m above the highest mountains. Likewise, the
modern potential glaciation level is presumably situated
only 150-250 m above the highest mountains. During
cold intervals of the Little Ice Age the lower limit for
periglacial activity may temporarily have approached
sea level, simultaneous with incipient establishment of
sporadic permafrost in the highlands, and a number of
sites in the highest mountains then were presumably
close to reglaciation.
Introduction
Analysis of meteorological land and ma-
rine temperatures indicate that the planet
surface has heated about 0.5°C since the
late 19th century (Jones and Briffa, 1992).
The observed warming, however, has not
been equal everywhere, nor equal through-
out the seasons. Some of the greatest warm-
ing has occurred over continental areas of
the Northem Hemisphere, while other re-
Fróðskaparrit 46. bók 1998: 169-189