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Late Quaternary ice sheet history and dynamics in central and southern Scandinavia
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK). (Quaternary Geology)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recent work suggests an emerging new paradigm for the Scandinavian ice sheet (SIS); one of a dynamically fluctuating ice sheet. This doctoral research project explicitly examines the history and dynamics of the SIS at four sites within Sweden and Norway, and provides results covering different time periods of glacial history. Two relatively new dating techniques are used to constrain the ice sheet history: the optically stimulated luminescence (OSL) dating technique and the terrestrial cosmogenic nuclide (TCN) exposure dating technique.

OSL dating of interstadial sediments in central Sweden and central Norway indicate ice-free conditions during times when it was previously inferred the sites were occupied by the SIS. Specifically, the SIS was absent or restricted to the mountains for at least part of Marine Isotope Stage 3 around 52 to 36 kyr ago. Inland portions of Norway were ice-free during part of the Last Glacial Maximum around 25 to 20 kyr ago.

Consistent TCN exposure ages of boulders from the Vimmerby moraine in southern Sweden, and their compatibility with previous estimates for the timing of deglaciation based on radiocarbon dating and varve chronology, indicate that the southern margin of the SIS was at the Vimmerby moraine ~14 kyr ago.

In central Sweden, consistent TCN ages for boulders on the summit of Mt. Åreskutan and for the earlier deglaciated highest elevation moraine related to the SIS in Sweden agree with previous estimates for the timing of deglaciation around 10 ka ago. These results indicate rapid decay of the SIS during deglaciation. Unusually old radiocarbon ages of tree remains previously studied from Mt. Åreskutan are rejected on the basis of incompatibility with consistent TCN ages for deglaciation, and incompatibility with established paleoecological and paleoglaciological reconstructions.

Altogether this research conducted in different areas, covering different time periods, and using comparative geochronological methods demonstrates that the SIS was highly dynamic and sensitive to environmental change.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University , 2010. , 32 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 22
Keyword [en]
Scandinavian ice sheet, ice sheet dynamics, luminescence dating, cosmogenic exposure dating, geochronology, moraine, interstadial, deglaciation, nunatak
National Category
Geology
Research subject
Quarternary Geology
Identifiers
URN: urn:nbn:se:su:diva-38611ISBN: 978-91-7447-068-0 (print)OAI: oai:DiVA.org:su-38611DiVA: diva2:311283
Public defence
2010-06-04, De Geersalensalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.Available from: 2010-05-11 Created: 2010-04-21 Last updated: 2010-12-30Bibliographically approved
List of papers
1. New 10Be cosmogenic ages from the Vimmerby moraine confirm the timing of Scandinavian Ice Sheet deglaciation in southern Sweden
Open this publication in new window or tab >>New 10Be cosmogenic ages from the Vimmerby moraine confirm the timing of Scandinavian Ice Sheet deglaciation in southern Sweden
2009 (English)In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 91A, no 2, 113-120 p.Article in journal (Refereed) Published
Abstract [en]

The overall pattern of deglaciation of the southern part of the Scandinavian Ice Sheet has been considered established, although details of the chronology and ice sheet dynamics are less well known. Even less is known for the south Swedish Upland because the area was deglaciated mostly by stagnation. Within this area lies the conspicuous Vimmerby moraine, for which we have used the terrestrial cosmogenic nuclide (10Be) exposure dating technique to derive the exposure age of six glacially transported boulders. The six 10Be cosmogenic ages are internally consistent, ranging from 14.9 ± 1.5 to 12.4 ± 1.3 ka with a mean of 13.6 ±0.9 ka. Adjusting for the effects of surface erosion, snow burial and glacio-isostatic rebound causes the mean age to increase only by c. 6% to c. 14.4± 0.9 ka. The 10Be derived age for the Vimmerby moraine is in agreement with previous estimates forthe timing of deglaciation based on radiocarbon dating and varve chronology. This result shows promise for further terrestrial cosmogenic nuclide exposure studies in southern Sweden.

Place, publisher, year, edition, pages
Blackwell Publishing / Swedish Society for Anthropology and Geography, 2009
National Category
Geology
Identifiers
urn:nbn:se:su:diva-31406 (URN)10.1111/j.1468-0459.2009.00358.x (DOI)000266700400005 ()
Available from: 2010-04-30 Created: 2009-11-12 Last updated: 2017-12-12Bibliographically approved
2. Re-dating the Pilgrimstad Interstadial with OSL: a warmer climate and a smaller ice sheet during the Swedish Middle Weichselian (MIS 3)?
Open this publication in new window or tab >>Re-dating the Pilgrimstad Interstadial with OSL: a warmer climate and a smaller ice sheet during the Swedish Middle Weichselian (MIS 3)?
2010 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 39, no 2, 367-376 p.Article in journal (Refereed) Published
Abstract [en]

Pilgrimstad in central Sweden is an important locality for reconstructing environmental changes during the last glacial period (the Weichselian). Its central location has implications for the Scandinavian Ice Sheet as a whole. The site has been assigned an Early Weichselian age (marine isotope stage (MIS) 5 a/c; >74 ka), based on pollen stratigraphic correlations with type sections in continental Europe, but the few absolute dating attempts so far have given uncertain results. We re-excavated the site and collected 10 samples for optically stimulated luminescence (OSL) dating from mineral- and organic-rich sediments within the new Pilgrimstad section. Single aliquots of quartz were analysed using a post-IR blue single aliquot regenerative-dose (SAR) protocol. Dose recovery tests were satisfactory and OSL ages are internally consistent. All, except one from an underlying unit that is older, lie in the range 52–36 ka, which places the interstadial sediments in the Middle Weichselian (MIS 3); this is compatible with existing radiocarbon ages, including two measured with accelerator mass spectrometry (AMS). The mean of the OSL ages is 44±6 ka (n=9). The OSL ages cannot be assigned to the Early Weichselian for all reasonable adjustments to water content estimates and other parameters. The new ages suggest that climate was relatively mild and that the Scandinavian Ice Sheet was absent or restricted to the mountains for at least parts of MIS 3. These results are supported by other recent studies completed in Fennoscandia.

National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-38853 (URN)10.1111/j.1502-3885.2009.00130.x (DOI)
Available from: 2010-05-21 Created: 2010-04-30 Last updated: 2017-12-12Bibliographically approved
3. OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet
Open this publication in new window or tab >>OSL ages in central Norway confirm a MIS 2 interstadial (25-20 ka) and a dynamic Scandinavian ice sheet
(English)In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457XArticle in journal (Other academic) Submitted
Abstract [en]

Recent work has suggested that the Scandinavian ice sheet was much more dynamic than previously believed, and its western marine-based margin can provide an analogue to the rapid-paced fluctuations and deglaciation observed at the margins of the Antarctic and Greenland ice sheets.

In this study we used a complimentary dating technique, OSL (Optically Stimulated Luminescence dating), to confirm the existence of the Trofors interstadial in central Norway; an ice-free period that existed from ~25 to 20 ka recorded at multiple sites throughout Norway (cf. Andøya interstadial) and that divides the Last Glacial Maximum (LGM) into two stadials. OSL signal component analysis was used to optimize data analysis, and internal (methodological) tests show the results to be of good quality. Both large and small aliquots gave consistent OSL ages (22.3 ±1.7 ka, n = 7) for sub-till glaciofluvial/fluvial sediments at the Langsmoen stratigraphic site, and an apparent old age (~100 ka) for a poorly bleached sample of glaciolacustrine sediment at the nearby stratigraphically-related Flora site. Eight radiocarbon ages of sediment from the Flora site gave consistent ages (20.9 ±1.6 cal. ka BP) that overlap within 1σ with OSL ages from the nearby Langsmoen site. The similarity in age within and between these stratigraphically-related sites and using different geochronological techniques strongly suggests that this area was ice-free around ~21 or 22 ka. The existence of the Trofors interstadial along with other interstadials during the Middle and Late Weichselian (MIS 3 and MIS 2) indicates that not only the western margin, but the whole western part of the Scandinavian ice sheet, from the ice divide to the ice margin was very dynamic. These large changes in the ice margin and accompanying drawdown of the ice surface would have affected the eastern part of the ice sheet as well.

Keyword
Optically stimulated luminescence (OSL) dating, Scandinavian ice sheet, Trofors interstadial, MIS 2, LGM, Norway
National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-38796 (URN)
Available from: 2010-04-30 Created: 2010-04-29 Last updated: 2017-12-12Bibliographically approved
4. High-elevation cosmogenic nuclide dating of the last deglaciation in the central Swedish mountains: implications for the timing of tree establishment
Open this publication in new window or tab >>High-elevation cosmogenic nuclide dating of the last deglaciation in the central Swedish mountains: implications for the timing of tree establishment
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We use cosmogenic exposure ages to determine the timing of deglaciation of the Scandinavian ice sheet (SIS) at summit elevation in the central Swedish mountains. Mean exposure ages for boulders on the summit of Mt. Åreskutan (10.6 ±0.6 ka, n = 3, 1420 m a.s.l.) and from the highest-elevation moraine related to SIS deglaciation in Sweden (12.0 ±0.6 ka, n = 3, 1135 m a.s.l.) are consistent with previous lower-elevation radiocarbon age estimates for the timing of deglaciation. Summit areas in this region deglaciated ~12.0-10.6 ka, coinciding approximately with the termination of the Younger Dryas cold interval (11.7 ka). Unusually old radiocarbon ages of tree remains previously studied from the summit-area of Mt. Åreskutan are rejected on the basis of incompatibility with consistent TCN ages for deglaciation, and incompatibility with established paleoecological and paleoglaciological reconstructions. Analysis of the new exposure ages against radiocarbon ages from lower elevation indicates that the SIS decayed rapidly during final deglaciation.

Keyword
cosmogenic exposure dating, radiocarbon dating, moraine, deglaciation, nunatak
National Category
Geology
Research subject
Quarternary Geology
Identifiers
urn:nbn:se:su:diva-38797 (URN)
Available from: 2010-04-30 Created: 2010-04-29 Last updated: 2010-12-29Bibliographically approved

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