| 1. |
- Anjar, Johanna, et al.
(författare)
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OSL dating of Weichselian ice-free periods at Skorgenes, western Norway
- 2018
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Ingår i: Norwegian Journal of Geology. - : Geological Society of Norway. - 2387-5852 .- 2387-5844. ; 98:3, s. 301-313
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Tidskriftsartikel (refereegranskat)abstract
- During recent years, many sites with sediments pre-dating the Last Glacial Maximum have been identified in formerly glaciated areas. As more and better dates are presented from these sites, the dynamic behaviour of the Scandinavian Ice Sheet is becoming increasingly clear. In this study, we revisited the site Skorgenes in western Norway. Here, sediments from two ice-free periods are found below and interbedded with glacial diamicts. We present an updated chronology for the site, based on ten new Optically Stimulated Luminescence (OSL) dates, and discuss possible correlations. The samples had poor OSL properties but still provide a substantial improvement of the existing chronology. The oldest sediments identified at Skorgenes were deposited in a proglacial subaqueous setting at some point between 21 and 42 ka. This period was followed by a glacial advance and, during the subsequent ice retreat, a delta or subaqueous fan formed at Skorgenes. OSL ages from the foreset beds indicate deposition at some point between 17 and 30 ka, implying that the ice-front retreated east of Skorgenes at least once during the Late Weichselian. A substantial ice advance followed this retreat. The youngest sediments, forming a proglacial delta succession, were deposited during the final deglaciation of the site.
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| 2. |
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| 3. |
- Björck, Svante, et al.
(författare)
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Nordlaguna – A unique lake basin at the foot of the Beerenberg volcano, Jan Mayen, containing partially enigmatic sediments
- 2022
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Ingår i: Quaternary Science Advances. - : Elsevier BV. - 2666-0334. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Sediments from the only permanent lake on the island of Jan Mayen (71°N, 08°30′W), Lake Nordlaguna (NL), were investigated. The lake, with an area of ∼1 km2, is situated at the foot of the world's northernmost active subaerial volcano and is separated from the sea by a 150–240 m wide beach barrier, which reaches 4–5 m above sea level. Most of the lake is deeper than 25 m, with the deepest part being 36 m. Altogether five coring sites, evenly spread out, were chosen and the sediment cores were retrieved from the lake ice with Uwitec and Nesje corers. After detailed descriptions of the very organic-poor and silt dominated sediments (of supposedly tephra-dominated origin), three sites were chosen for further analyses: macrofossils for 14C dating, tephra chemistry, C, S, grain-size, and XRF analyses. Based on 14C dates and the occurrence of the so-called Eggøya tephra (AD 1732), age models show variable bottom ages for the three sites: ∼3000, 600 and 400 cal yr BP. Due to the position of the core sites, with different sediment source areas, the elemental signals vary considerably between sites. An interesting feature of the lake is an isolated stock of Arctic char, which shows that the now land-locked lake has once been in contact with the sea. The almost total lack of organic material excluded any advanced paleo-ecologic investigations of the lake, and the study therefore focused on its marine-limnic history by different examinations of the XRF data with focus on the oldest and longest record. This development is based on elemental ratios (Br/Zn), PCA analyses of a center log ratio (clr) transformation of the original XRF data and magnetic susceptibility. It shows that the lake was isolated just before the time of the Eggøya tephra fall-out (∼220 cal yr BP), when the stock of Arctic char was most likely isolated from the sea. This was preceded by a ∼2200 yr long period of marine bay with a more or less open connection with the sea, and thus varying fresh-water impact. Between ∼2400 and 2600 cal yr BP the basin was more or less isolated, preceded by almost full marine conditions for at least the 300–400 preceding years we have data from, a period when relative sea level might have been higher.
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| 4. |
- Kjaer, Kurt, et al.
(författare)
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Eurasian ice-sheet interaction in northwestern Russia throughout the late Quaternary
- 2006
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 35:3, s. 444-475
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Tidskriftsartikel (refereegranskat)abstract
- Sediment successions from the Kanin Peninsula and Chyoshskaya Bay in northwestern Russia contain information on the marginal behaviour of all major ice sheets centred in Scandinavia, the Barents Sea and the Kara Sea during the Eemian - Weichselian. Extensive luminescence dating of regional lithostratigraphical units, supported by biostratigraphical evidence, identifies four major ice advances at 100 - 90, 70 - 65, 55 - 45 and 20 - 18 kyr ago interbedded with lacustrine, glaciolacustrine and marine sediments. The widespread occurrence of marine tidal sediments deposited c. 65 - 60 kyr ago allows a stratigraphical division of the Middle Weichselian Barents Sea and Kara Sea ice sheets into two shelf-based glaciations separated by almost complete deglaciation. The first ice dispersal centre was in the Barents Sea and thereafter in the Kara Sea. It is possible to extract both flow patterns from ice marginal landforms inside the southward termination. Accordingly, it is proposed that the Markhida line and its western continuation are asynchronous and originate from two separate glaciations before and after the marine transgression. The marine sedimentation occurred during a eustatic sea-level rise of up to 20 m/1000 yr, i. e. the Mezen Transgression. We speculate that the rapid eustatic sea-level rise triggered a collapse of the Barents Sea Ice Sheet at the MIS ( Marine Isotope Stage) 4 to 3 transition. This is motivated by lack of an early marine highstand, the timing of events, and the marginal position of Arkhangelsk relative to open marine conditions.
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| 5. |
- Kjær, Kurt H, et al.
(författare)
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Subglacial decoupling at the sediment/bedrock interface: a new mechanism for rapid flowing ice
- 2006
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 25:21-22, s. 2704-2712
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedOn millennial or even centennial time scales, the activity of rapid flowing ice can affect climate variability and global sea level through release of meltwater into the ocean and positive feedback loops to the climate system. At the surge-type glacier Bruarjokull, an outlet of the Vatnajokull ice cap, eastern Iceland, extremely rapid ice flow was sustained by overpressurized water causing decoupling beneath a thick sediment sequence that was coupled to the glacier. This newly discovered mechanism has far reaching consequences for our understanding of fast-flowing ice and its integration with sediment discharge and meltwater release. (c) 2006 Elsevier Ltd. All rights reserved.
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| 6. |
- Lambeck, Kurt, et al.
(författare)
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Constraints on the Late Saalian to early Middle Weichselian ice sheet of Eurasia from field data and rebound modelling
- 2006
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 35:3, s. 539-575
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Tidskriftsartikel (refereegranskat)abstract
- Using glacial rebound models we have inverted observations of crustal rebound and shoreline locations to estimate the ice thickness for the major glaciations over northern Eurasia and to predict the palaeo-topography from late MIS-6 ( the Late Saalian at c. 140 kyr BP) to MIS-4e ( early Middle Weichselian at c. 64 kyr BP). During the Late Saalian, the ice extended across northern Europe and Russia with a broad dome centred from the Kara Sea to Karelia that reached a maximum thickness of c. 4500 m and ice surface elevation of c. 3500 m above sea level. A secondary dome occurred over Finland with ice thickness and surface elevation of 4000 m and 3000 m, respectively. When ice retreat commenced, and before the onset of the warm phase of the early Eemian, extensive marine flooding occurred from the Atlantic to the Urals and, once the ice retreated from the Urals, to the Taymyr Peninsula. The Baltic - White Sea connection is predicted to have closed at about 129 kyr BP, although large areas of arctic Russia remained submerged until the end of the Eemian. During the stadials (MIS-5d, 5b, 4) the maximum ice was centred over the Kara - Barents Seas with a thickness not exceeding c. 1200 m. Ice-dammed lakes and the elevations of sills are predicted for the major glacial phases and used to test the ice models. Large lakes are predicted for west Siberia at the end of the Saalian and during MIS-5d, 5b and 4, with the lake levels, margin locations and outlets depending inter alia on ice thickness and isostatic adjustment. During the Saalian and MIS-5d, 5b these lakes overflowed through the Turgay pass into the Aral Sea, but during MIS-4 the overflow is predicted to have occurred north of the Urals. West of the Urals the palaeo-lake predictions are strongly controlled by whether the Kara Ice Sheet dammed the White Sea. If it did, then the lake levels are controlled by the topography of the Dvina basin with overflow directed into the Kama-Volga river system. Comparisons of predicted with observed MIS-5b lake levels of Komi Lake favour models in which the White Sea was in contact with the Barents Sea.
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| 7. |
- Larsen, Eiliv, et al.
(författare)
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A dated volcano-tectonic deformation event in Jan Mayen causing landlocking of Arctic charr
- 2021
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 36:2, s. 180-190
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Tidskriftsartikel (refereegranskat)abstract
- We provide the first documentation of tectonic deformation resulting from a volcanic eruption on the island of Jan Mayen. Vertical displacement of about 14 m southwest of the stratovolcano Beerenberg is associated with an eruption in ad 1732 on its southeastern flank. The age of the uplift event is bracketed by radiocarbon-dated driftwood buried by material deposited due to uplift, and by tephra from this eruption. Constraints, inferred from radiocarbon ages alone, allow for the possibility that uplift was completed prior to the ad 1732 eruption. However, the occurrence of tephra in the sediment column indicates that some displacement was ongoing during the eruption but ceased before the eruption terminated. We attribute the tectonic deformation to intrusion of shallow magma associated with the volcanic eruption. Our results complement previous studies of volcanic activity on Jan Mayan by providing precise age constraints for past volcanic activity. Also, it raises new hypotheses regarding the nature, timing and prevalence of precursor tectonic events to Jan Mayan eruptions. The uplift caused the complete isolation of a coastal lake by closing its outlet to the sea, thus landlocking the facultative migratory fish species Arctic charr (Salvelinus alpinus).
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| 8. |
- Larsen, Eiliv, et al.
(författare)
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Early Weichselian palaeoenvironments reconstructed from a mega-scale thrust-fault complex, Kanin Peninsula, northwestern Russia
- 2006
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 35:3, s. 476-492
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Tidskriftsartikel (refereegranskat)abstract
- A section, almost 20 km long and up to 80 m high, through alternating layers of diamict and sorted sediments is superbly exposed on the north coast of the Kanin Peninsula, northwestern Russia. The diamicts represent multiple glacial advances by the Barents Sea and the Kara Sea ice sheets during the Weichselian. The diamicts and stratigraphically older lacustrine, fluvial and shallow marine sediments have been thrust as nappes by the Barents Sea and Kara Sea ice sheets. Based on stratigraphic position, OSL dating, sea level information and pollen, it is evident that the sorted sediments were deposited in the Late Eemian-Early Weichselian. Sedimentation started in lake basins and continued in shallow marine embayments when the lakes opened to the sea. The observed transition from lacustrine to shallow marine sedimentation could represent coastal retreat during stable or rising sea level.
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| 9. |
- Larsen, Eiliv, et al.
(författare)
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Volcanical and surficial process constraints on the formation of a lake basin in Jan Mayen, Norway
- 2022
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Ingår i: Quaternary Science Advances. - : Elsevier BV. - 2666-0334. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The volcanic island of Jan Mayen, located in the Norwegian – Greenland Sea, has very few lake basins out of which only one, Lake Nordlaguna, holds a permanent lake throughout the year. The island is volcanic and has been glaciated, but the lake basin is not genetically typical for volcanic crater lakes or other common types of volcanic lakes. Nor is it typical for ice-scoured glacial lakes. Instead, the lake basin originated from a series of hydromagmatic and subglacial volcanic eruptions, which over time yielded an irregularly horseshoe-shaped chain of small mountains to form flanks of a bedrock basin. Potassium–Argon and Argon–Argon dates from these rock walls facing the lake yield ages ranging from about 564 to 21 ka. Subsequent glacier overriding only had a minor influence on the basin morphology, but contributed, as did other surface processes to its sediment infill. Following deglaciation, relative sea-level change led to the formation of a beach barrier that connects between the rock walls. Tectonic uplift recorded in sections and ground penetrating radar profiles around the lake perimeter and dated using radiocarbon and tephra geochemistry, is attributed to a historical eruption in 1732 CE that took place on the opposite side of the island, some 4–5 km away. The uplift blocked the last remaining passage between the basin and the ocean, leading to the present landlocked lacustrine environment.
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| 10. |
- Svendsen, John Inge, et al.
(författare)
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Maximum extent of the Eurasian ice sheets in the Barents and Kara Sea region during the Weichselian
- 1999
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Ingår i: Boreas. - : Wiley. - 1502-3885 .- 0300-9483. ; 28:1, s. 92-114
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Tidskriftsartikel (refereegranskat)abstract
- Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17000 calendar years ago. During the Late Weichselian (25 000–10000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation.
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