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Investigations of glacier history at the Late Weichselian/early Holocene transition in Northern Iceland as a basis for palaeoclimatic reconstructions

Flateyjardalur
Funding agency German Research Council (Projects VE 89/13-1, VE 89/13-3)
Duration 07/1999 - 06/2001, 04/2002 - 03/2003
Project leader Prof. Dr. Jörg-Friedhelm Venzke, Institute of Geography, University of Bremen
Project team Mag. Maria Grießer, Mag. Edith Hessenberger, Mag. Stephan Jenewein, Michael Kasper, Mag. Andrew Moran, Mag. Ronald Schmidt, Dipl.-Geogr. Friedrun Sorms, Dr. Maria Wastl (contact for further information)
Cooperation Prof. Dr. John Andrews, INSTAAR, University of Colorado at Boulder
Prof. Dr. Peter Mirwald, Institute of Mineralogy and Petrography, University of Innsbruck
Dr. Hreggviður Norðdahl, Science Institute, University of Iceland, Reykjavík
Dr. Halldór Pétursson, The Icelandic Institute of Natural History, Akureyri
Prof. Dr. Johann Stötter, Institute of Geography, University of Innsbruck
Project aim
The Late Weichselian/early Holocene transition with its rapid and extreme climatic variations is of great importance for understanding global-scale changes in the climatic system. This is reflected in international research programmes (e.g. PAGES, IGCP, INTIMATE). The aim of this reseach project was the reconstruction of palaeoclimatic conditions in Iceland at the Late Weichselian/early Holocene transition by comparing the behaviour of the outlet glaciers of the inland ice with that of the local glaciation in Northern Iceland.
The climatic conditions in Iceland are characterized by a marked contrast between humid and maritime conditions in the south and dry, more continental conditions in the north. This is a consequence of the different origin of the air masses governed by the position of the polar front. The contrast in precipitation conditions is reflected in the mass balance and the resulting size of the glaciers. While Southern and Central Iceland are characterized by large ice caps, the mountains on the Tröllaskagi and Flateyjarskagi peninsulas of Northern Iceland carry only small corrie and valley glaciers. These ca. 250 glaciers with present surface areas from less than 1 km² to few km² react very rapidly (within years) to changes in temperature and precipitation conditions.
Methods
moraines in Torfdalur The reconstruction of glacier extents is based on mapping the moraine remnants and ice-marginal sediments both of the local glaciers on the Tröllaskagi and Flateyjarskagi peninsulas in Northern Iceland and of the outlet glacier of the South Icelandic ice sheet in Eyjafjörður. For the local glaciers, this provided the basis to reconstruct the surface areas and the equilibrium line altitudes (= ELAs) for different stages of the glaciation. The spatial comparison of reconstructed equilibrium line altitude depressions relative to the maximum glacier extent during the Little Ice Age was used to establish a temporal pattern of the local glacier advances based on classes of similar ELA depressions. The spatial and temporal connection between the reconstructed extents of the local glaciers and the position of the outlet glacier in Eyjafjörður is based on geomorphological and stratigraphical evidence such as moraines and traces of marine abrasion as well as sediments of ice-dammed lakes and tephra layers. The tephras also provide chronohorizons for the absolute dating of the findings.
The corresponding climatic conditions were inferred by means of a climate (temperature, precipitation) - glacier model. Assuming that Late Weichselian/early Holocene temperature variations in the North Atlantic region were more or less uniform over wider areas, the comparison of the behaviour of the inland ice of Southern Iceland and the local glaciers in Northern Iceland allows inferences on precipitation distribution during this period of thermal instability. The palaeoclimatic reconstructions on the basis of the glacier history thus provide an important source of additional information both for comparison with the isotope temperature record of the Greenland ice cores and with palaeoclimatic reconstructions from marine cores in the northern North Atlantic.
Results
Present evidence allows the identification of four stages of local glacier extents in Northern Iceland during the Late Weichselian/early Holocene transition. These stages are geomorphologically and stratigraphically compared with corresponding extents of the outlet glacier in Eyjafjörður. A basic age model for these findings is provided by tephrochronology. During stage I the glaciers on Tröllaskagi and Flateyjarskagi showed ELA depressions around 500 m. At the same time the outlet glacier from the ice sheet of Southern and Central Iceland terminated just north of Grenivík in the middle part of Eyjafjörður (Grenivík I stage). Stage I was reached at ca. 10300 BP (uncalibrated radiocarbon years) or later. During stage II, which was reached later than ca. 10300 BP, the ELA depressions of the local glaciers were around 200 m while the Eyjafjörður outlet glacier terminated just south of Grenivík (Grenivík II stage). The reconstructed ELA depressions for Preboreal advances of the local glaciers are less than 100 m. At this time the outlet glacier in Eyjafjörður terminated near Hólar, ca. 35 km inside the present coastline. Since ca. 9200 BP, the local glaciers in Northern Iceland have never been much larger than they were during their Little Ice Age maximum extent.
For the palaeoclimatic interpretation of the reconstructed glacier history, the generally limited extent of the local corrie and valley glaciers in Northern Iceland during the Younger Dryas can be noted. These glaciers terminated in the middle or inner parts of the main tributary valleys of Eyjafjörður (e.g. Svarfaðardalur, Hörgárdalur, Glerárdalur). Only in valleys close to the sea (Karlsárdalur, Brettingsstaðadalur) they extended beyond the present coast. At the same time the outlet glacier of the ice sheet of Southern and Central Iceland still reached to the outer part of Eyjafjörður. This may provide an indication that the present precipitation gradient between Southern and Northern Iceland was even more pronounced under Late Weichselian conditions.
Publications
Stötter, J., Wastl, M. and Venzke, J.-F. (2000). The local glaciation of central Northern Iceland during the late Weichselian/early Holocene transition. In: Russell, A.J. and Marren, P.M. (eds.), Iceland 2000: Modern Processes and Past Environments, Keele University, Department of Geography Occasional Papers Series, 21, 106-108. Abstract
Wastl, M., Stötter, J. and Venzke, J.-F. (2001). Gletschergeschichtliche Untersuchungen zum Übergang Spätglazial/Postglazial in Nordisland. Norden, 14, 127-144. Abstract
Wastl, M., Stötter, J. and Venzke, J.-F. (2003). Neue Beiträge zur spätglazialen und holozänen Gletschergeschichte in Nordisland. Norden, 15, 137-150. Abstract
Wastl, M., Stötter, J., Geitner, C. and Venzke, J.-F. (2004). Gletschergeschichtliche Untersuchungen zum Übergang Spätglazial/Postglazial in Nordisland als Grundlage paläoklimatischer Rekonstruktionen. Mitteilungen der Österreichischen Geographischen Gesellschaft, 146, 165-192. Abstract
Wastl, M. and Stötter, J. (2005). Holocene glacier history. In: Caseldine, C., Russel, A., Harðardóttir, J. and Knudsen, Ó. (eds.), Iceland - Modern Processes and Past Environments (Developments in Quaternary Science, 5), pp. 221-240. Elsevier, Amsterdam.
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