Náttúrufræðingurinn - 2012, Side 84

Náttúrufræðingurinn
84
Summary
Deglaciation of Iceland and
Relative Sea-level Changes
At the Last Glacial Maximum (c. 25,000 cal.
years BP (calibrated years before present
(AD 1950)), Iceland was covered by an
ice sheet that extended towards the
shelf break (Fig. 1). This has been veri-
fied by a number of marine geological
and seismostratigraphical studies. Its
thickness over the central highlands is
not well known, but geomorphologi-
cal, volcanological and modelling data
suggest maximum thicknesses of
1500±500 m. Nunataks occurred in
coastal areas, primarily in North and
East Iceland. The ice sheet was drained
by large ice streams entering major
fjords and bays around the island.
Available data suggest a relatively
late onset of deglaciation: It started
18,500–16,700 cal. years BP off North
Iceland but later than 15,500 cal. years
BP off West Iceland. The deglaciation
after 15,500 cal. years BP was extremely
rapid, and probably controlled by rap-
idly rising global sea level causing the
marine-based part of the ice sheet to
destabilize and eventually collapse. By
13,900 cal. years BP the ice fronts were
within the present coastline around
Iceland. Relative sea level stood at the
marine limit in West Iceland, at 150 m
a.s.l., c. 14,600 cal. years BP (Figs. 2 and
9). Subsequently, there was a rapid re-
gression as Iceland’s oceanic crust re-
bounded quickly in response to de-
creased glacial loading. Once inside the
coast and because of climate deteriora-
tion, the ice sheet started growing again,
culminating in a significant Younger
Dryas advance. The growth of the ice
sheet was accompanied by a transgres-
sion of relative sea-level which culmi-
nated at c. 12,000 cal. years BP. After a
brief early Preboreal (c. 11,200 cal years
BP) glacial advance, accompanied by a
relative sea-level transgression in the
coastal areas, the ice sheet disintegrated
rapidly and glaciers were at or within
present glacier limits prior to 8,800 cal.
years BP.
11. mynd. Samantekt á niðurstöðum um stærð jökla á Íslandi á síðari hluta síðasta jökul-
skeiðs og afstæðar sjávarstöðubreytingar á síðjökultíma og í upphafi nútíma á Vestur- og
Suðvesturlandi.2 Eftirfarandi ferlar eru á þessari mynd: North GRIP, sem sýnir breyti-
legan styrk 18O samsætunnar í Grænlandsjökli.84 Hlutfall Borealtegunda götunga í kjarna
úr Jökuldjúpi.67 Fjöldi ísborinna korna og afstæður styrkur Irmingerstraumsins fyrir
Norðurlandi.27 Áætlaður lofthiti á strandsvæðum Norður- og Vesturlands.54 – Summary
of the late Weichselian and early Holocene extent of the Icelandic ice sheet and relative sea-
level changes compared with (1) The NorthGRIP 18O. (2) Proportional changes in number
of Boreal foraminifera off West Iceland. (3) Number of ice-rafted debris and relative
strength of the Irminger current off North Iceland. (4) Assumed coastal air temperature in
North and West Iceland.