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| 2. |
- Briner, Jason P., et al.
(författare)
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Configuration of the Scandinavian Ice Sheet in southwestern Norway during the Younger Dryas
- 2023
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Ingår i: Norwegian Journal of Geology. - 2387-5844. ; 103
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Tidskriftsartikel (refereegranskat)abstract
- The extent of the Scandinavian Ice Sheet in southwestern Norway is precisely located during the well-characterized Younger Dryas re-advance. However, the thickness of the ice sheet is less well constrained inland from the terminal position. Some exceptions include lateral moraines traced inland and up to 1000 m a.s.l. along Hardangerfjorden. Here, we apply 10Be dating in two areas: (1) bedrock and boulders in the high-relief landscapes near the Younger Dryas margin around the Bergen urban area, and (2) boulders from an upland 1600 m a.s.l. much farther (120 km) inland. We find that coastal summits ranging from ~400 to ~680 m a.s.l. and located only ~10–15 km up-flow from the ice margin, were covered by the Scandinavian Ice Sheet during the Younger Dryas. The scatter in the 10Be age population of 22 boulder samples is best explained by isotopic inheritance owing to inefficient subglacial erosion during the foregoing glaciation. Most of the 11 bedrock samples also exhibit inheritance, pointing to the source of inheritance in boulders and implying inefficient subglacial erosion during the last glaciation even in valley-bottoms near Bergen. Regional glacial striae compilations suggest that ice flow during maximum Younger Dryas ice-sheet configurations was for the most part cross-valley, with potentially low basal slip rates. Five new 10Be ages from the inland site help to constrain ice height far inland. We combine these new results with prior information to generate a cross profile of the Younger Dryas ice sheet in southern Norway.
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| 3. |
- Henriksen, Mona, et al.
(författare)
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Dynamics and retreat of the Late Weichselian Kongsfjorden ice stream, NW Svalbard
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 92, s. 235-245
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial cosmogenic nuclide dating in combination with detailed landform mapping in the Kongsf-jordhallet area, NW Svalbard, have provided new insight on configuration, dynamics, and deglaciation of the Late Weichselian Kongsfjorden ice stream. The minimum Late Weichselian ice surface elevation in Kongsfjorden was >449 m a.s.l. indicating considerably thicker ice and a steeper surface gradient than earlier suggested. For the adjacent inter-ice stream area an even steeper surface slope is reconstructed. The glacial landforms, as well as the surface exposure ages of erratic boulders at different elevations, suggest a gradual lowering of the ice surface. Deglaciation of the higher elevations was probably underway by 20.0 ka. At ca 16.6 ka a large moraine complex ('the Kongsfjorden moraine') was deposited close to the fjord mouth. The shape of the moraines, the steep ice surface gradient, as well as the correlation to fine laminated clay lacking ice rafted debris deposited in the trough beyond the moraine suggest that ice dynamics switched from ice-stream behaviour to a slower flowing outlet (tidewater) glacier. A Younger Dryas or Early Holocene advance of local valley glaciers is shown by moraine lobes cross-cutting the Late Weichselian lateral moraines. (C) 2013 Elsevier Ltd. All rights reserved.
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| 5. |
- Larsen, Nicolaj Krog, et al.
(författare)
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Investigating the last deglaciation of the Scandinavian Ice Sheet in southwest Sweden with Be-10 exposure dating
- 2012
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 27:2, s. 211-220
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Tidskriftsartikel (refereegranskat)abstract
- In this study we have obtained 17 cosmogenic exposure ages from three well-developed moraine systems - Halland Coastal Moraines (HCM), Goteborg Moraine (GM) and Levene Moraine (LM) - which were formed during the last deglaciation in southwest Sweden by the Scandinavian Ice Sheet (SIS). The inferred ages of the inner HCM, GM and LM are 16.7 +/- 1.6, 16.1 +/- 1.4 and 13.6 +/- 1.4 ka, respectively, which is slightly older than previous estimates of the deglaciation based on the minimum limiting radiocarbon ages and pollen stratigraphy. During this short interval from 16.7 +/- 1.6 to 13.6 +/- 1.4 ka a large part (100-125 km) of the marine-based sector of the SIS in southwest Sweden was deglaciated, giving an average ice margin retreat between 20 to 50 m a(-1). The inception of the deglaciation pre-dated the Bolling/Allerod warming, the rapid sea level rise at 14.6 cal. ka BP and the first inflow of warm Atlantic waters into Skagerrak. We suggest that ice retreat in southwest Sweden is mainly a dynamical response governed by the disintegration of the Norwegian Channel Ice Stream and not primarily driven by climatic changes. Copyright (c) 2011 John Wiley & Sons, Ltd.
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| 6. |
- Linge, Henriette, et al.
(författare)
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Assessing the use of U-Th methods to determine the age of cold-water calcareous algae
- 2008
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Ingår i: Quaternary Geochronology. - : Elsevier. - 1871-1014 .- 1878-0350. ; 3:1-2, s. 76-88
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Tidskriftsartikel (refereegranskat)abstract
- Calcitic crusts of calcareous red algae could be suitable material for age determination of raised marine deposits and palaeothermometry at annual to sub-annual resolution. We examined the potential of U-Th dating of cold-water calcareous algae by analysing fossil specimens (n = 10) from Kapp Ekholm (Svalbard) and recent specimens from Norway (n = 3) and Scotland (n = 1). After initial measurements using alpha-spectrometry, thermal ionisation mass spectrometry (TIMS) was used to study the material in more detail. Recent specimens contain 0.19-1.55 mu g g(-1) U, and the measured (U-234/U-231) activity ratios vary between 1.12 and 1.30. Fossil specimens contain 1-168 mu g g(-1) U, and display variable and highly elevated initial (U-234/U-238) activity ratios. In general, the TIMS results show increasing (U-234/U-238) activity ratios and concentrations of U and Th with increasing stratigraphic age. From this it is evident that marine calcareous red algae contain U in-vivo and they experience substantial post-mortem uptake of U. We conclude that direct U-Th dating of fossil calcareous algae from raised marine deposits is not viable without further geochemical understanding of the in-vivo uptake and post-depositional pathways of U and Th in such deposits. Despite the convincing open-system behaviour of the material, comparison with previously published chronostratigraphy from the site shows that the calcareous algae generally yield ages that are too old. This is in contrast to the expected result based on simple continuous post-mortem U accumulation and calls for a complex model comprising migration of U and multi-component addition of Th (detrital/colloidal) to explain the observed trends.
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| 7. |
- Linge, Henriette, et al.
(författare)
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Stable isotope records for the last 10 000 years from Okshola cave (Fauske, northern Norway) and regional comparisons
- 2009
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Ingår i: Climate of the Past. - 1814-9324. ; 5:4, s. 667-682
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Tidskriftsartikel (refereegranskat)abstract
- The sensitivity of terrestrial environments to past changes in heat transport is expected to be manifested in Holocene climate proxy records on millennial to seasonal timescales. Stalagmite formation in the Okshola cave near Fauske (northern Norway) began at about 10.4 ka, soon after the valley was deglaciated. Past monitoring of the cave and surface has revealed stable modern conditions with uniform drip rates, relative humidity and temperature. Stable isotope records from two stalagmites provide time-series spanning from c. 10 380 yr to AD 1997; a banded, multi-coloured stalagmite (Oks82) was formed between 10 380 yr and 5050 yr, whereas a pristine, white stalagmite (FM3) covers the period from ~7500 yr to the present. The stable oxygen isotope (δ18Oc), stable carbon isotope (δ13Cc), and growth rate records are interpreted as showing i) a negative correlation between cave/surface temperature and δ18Oc, ii) a positive correlation between wetness and δ13Cc, and iii) a positive correlation between temperature and growth rate. Following this, the data from Okshola show that the Holocene was characterised by high-variability climate in the early part, low-variability climate in the middle part, and high-variability climate and shifts between two distinct modes in the late part.
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