Holocene glacier fluctuations and variations in winter
precipitation:
Svein Olaf Dahl1
and Atle Nesje2
1 Department of
Geography, University of Bergen
2 Department of
Geology, University of Bergen
A close
exponential relationship between mean ablation-season temperature (1 May - 30
September) and winter precipitation (1 October - 30 April) has been
demonstrated at the equilibrium-line altitude (ELA) of Norwegian glaciers
existing in continental to maritime climatic regimes. This relationship implies
that, if either the winter precipitation or the ablation-season temperature at
the ELA is known, the other factor can be calculated. It also implies that if
the former ELA is known, it is possible to calculate how the winter
precipitation has varied backwards in time if an independent record of
summer-temperature variations is used in the calculation.
At
Hardangerjøkulen, detailed knowledge of the number, age and magnitude of
Holocene glacier fluctuations based on 4 sites has been used to reconstruct ELA
variations for the last 10,000 cal yr BP. A summer (July) temperature curve
(adjusted for land uplift) based on chironomids from a small lake at Finse has
been used to quantify variations in Holocene winter precipitation. If the
modern winter precipitation is equal to 100% for the meteorological normal
period 1961-90, winter precipitation has varied from ca. 50 to more than 200%
at Hardangerjøkulen during the last 10,000 cal yr BP.
The history of
Holocene glacier variations and corresponding ELA fluctuations of
Jostedalsbreen have been reconstructed from proglacial lacustrine sediments and
terrestrial sites. By using the same approach as described for Hardangerjøkulen
including the independent summer temperature record based on chironomids from
Finse, the general pattern of Holocene winter-precipitation variations in the
Jostedalsbreen region is similar to that quantified for Hardangerjøkulen.
Periods of low winter precipitation during the Holocene at Hardangerjøkulen and
in the Jostedalsbreen region correlate with periods of enhanced ice-rafting in
the North Atlantic. Mass balance data from maritime glaciers in southern Norway
show that years with high NAO index correspond to years of high winter balance.
The Holocene winter precipitation curves for Hardangerjøkulen and
Jostedalsbreen may therefore reflect periods during the Holocene with
prevailing mild and wet winter conditions (positive NAO index) and periods with
prevailing cold and dry winters (negative NAO index), and thus large-scale
Holocene variability in the atmospheric circulation over NW Europe.
Holocene
glacier fluctuations in southern Norway based on pro-glacial lakes and
terrestrial sites
Svein Olaf Dahl1
and Atle Nesje2
1 Department of
Geography, University of Bergen
2 Department of
Geology, University of Bergen
Preliminary
results or results submitted for publication will be presented from Folgefonna,
Dyrafonn in inner Hardanger, Grovabreen in Sunnfjord, Jostedalsbreen,
Bukkehamarbreen, Bøverbreen and Leirbreen in Jotunheimen, and from small cirque
glaciers at Snøhetta, Dovre.
The maximum
vertical extent of the Late Weichselian Scandinavian ice sheet in Norway:
Preliminary results along transects in Nordland/Troms (Senja to inner Troms,
Andøya to Skånland) and from Oslo to Trondheim
Svein Olaf Dahl1
and Atle Nesje2
1 Department of
Geography, University of Bergen
2 Department of
Geology, University of Bergen
Preliminary
results based on in situ weathered blockfields, clay-mineral analyses,
exposure datings and radiocarbon dates will be presented for 3 transects:
A W-E transect
from Senja to inner Troms including a N-S transect on Senja.
A NW-SE transect
from northern Andøya across the islands of Grytøya and Rolla to Skånland in
southern Troms.
A N-S transect
from Trondheim to Oslo between Dovre and the Swedish border.
The preliminary
results indicate a low gradient and poly-centric Late Weichselian Scandinavian
ice sheet.