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Ice sheet growth under dirty conditions: implications of debris cover for early glaciation advances
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
2002 (English)In: Quaternary International, ISSN 1040-6182, Vol. 95-96, 35-42 p.Article in journal (Refereed) Published
Abstract [en]

Debris-covered glaciers respond differently to any given set of climatic conditions than clean glaciers. This difference stems from change in ablation rate caused by a debris cover, approaching zero ablation with sufficiently thick protective cover, a mechanism not yet considered in the context of ice sheet growth. Critical to applying the mechanism to ice sheets is supply of debris. We postulate that periods after major interglacials offer the best conditions for dirty advances. This is because the volume of debris, previously deposited and weathered in interglacial time, the latter a function of exposure length, should be at a maximum. Advances of dirty ice sheets generate landforms and in positions deviating from clean-ice advances under similar climatic conditions. Hence, inferences of both ice sheet properties inferred from such dirty ice advances and the climate conditions related to such advances must be cautious. Furthermore, modeling of past ice sheets must consider the effect of debris cover whenever indications exist for such a cover.

Place, publisher, year, edition, pages
2002. Vol. 95-96, 35-42 p.
National Category
Physical Geography Geology
URN: urn:nbn:se:su:diva-22973DOI: 10.1016/S1040-6182(02)00025-3OAI: diva2:189837
Available from: 2004-05-05 Created: 2004-05-05 Last updated: 2011-06-20Bibliographically approved
In thesis
1. Mountain centered icefields in northern Scandinavia
Open this publication in new window or tab >>Mountain centered icefields in northern Scandinavia
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. These have persisted in the Scandinavian mountains for about 65% of the Quaternary. Mountain based glaciers thus had a profound impact on large-scale geomorphology, which is manifested in large-scale glacial landforms such as fjords, glacial lakes and U-shaped valleys in and close to the mountain range.

Through a mapping of glacial landforms in the northern Scandinavian mountain range, in particular a striking set of lateral moraines, this thesis offers new insights into Weichselian stages predating the last glacial maximum. The aerial photograph mapping and field evidence yield evidence that these lateral moraines were overridden by glacier ice subsequent to their formation. The lateral moraines were dated using terrestrial cosmogenic nuclide techniques. Although the terrestrial cosmogenic nuclide signature of the moraines is inconclusive, an early Weichselian age is tentatively suggested through correlations with other landforms and stratigraphical archives in the region. The abundance and coherent spatial pattern of the lateral moraines also allow a spatial reconstruction of this ice field. The ice field was controlled by topography and had nunataks protruding also where it was thickest close to the elevation axis of the Scandinavian mountain range. Outlet glaciers discharged into the Norwegian fjords and major valleys in Sweden.

The process by which mountain based glaciers grow into an ice sheet is a matter of debate. In this thesis, a feedback mechanism between debris on the ice surface and ice sheet growth is presented. In essence, the growth of glaciers and ice sheets may be accelerated by an abundance of debris in their ablation areas. This may occur when the debris cover on the glacier surface inhibits ablation, effectively increasing the glaciers mass balance. It is thus possible that a dirty ablation area may cause the glacier to advance further than a clean glacier under similar conditions. An ice free period of significant length allows soil production through weathering, frost shattering, and slope processes. As glaciers advance through this assemblage of sediments, significant amounts of debris end up on the surface due to both mass wastage and subglacial entrainment. Evidence that this chain of events may occur, is given by large expanses of hummocky moraine (local name Veiki moraine) in the northern Swedish lowlands. Because the Veiki moraine has been correlated with the first Weichselian advance following the Eemian, it implies a heavily debris charged ice sheet emanating from the mountain range and terminating in a stagnant fashion in the lowlands.

Place, publisher, year, edition, pages
Stockholm: Institutionen för naturgeografi och kvartärgeologi, 2004. 77 p.
Avhandling i geografi med naturgeografisk inriktning, ISSN 1650-4992 ; 29
Scandinavia, Quaternary, Weichselian, mountain, icefield, ice sheet
National Category
Physical Geography
urn:nbn:se:su:diva-131 (URN)91-7265-877-0 (ISBN)
Public defence
2004-05-26, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 13:00
Available from: 2004-05-05 Created: 2004-05-05Bibliographically approved

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