| 1. |
- Wolfe, Alexander P., et al.
(författare)
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Stratigraphic expressions of the Holocene-Anthropocene transition revealed in sediments from remote lakes
- 2013
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 1872-6828 .- 0012-8252. ; 116, s. 17-34
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Tidskriftsartikel (refereegranskat)abstract
- Stratigraphic boundaries are ideally defined by distinct lithological, geochemical, and palaeobiological signatures, to which a chronological framework can be applied. We present a range of observations that illustrate how the Holocene-Anthropocene transition meets these criteria in its expression in sediments from remote arctic and alpine lakes, removed from direct, catchment-scale, anthropogenic influences. In glaciated lake basins, the retreat of glaciers commonly leads to lithological successions from proglacial clastic sedimentation to non-glacial organic deposition. Sediments from the majority of lakes record marked depletions in the nitrogen stable isotopic composition of sediment organic matter, reflecting anthropogenic influences on the global nitrogen cycle. In all cases, siliceous microfossil assemblages (diatoms and chrysophytes) change markedly and directionally, with regional nuances. These stratigraphic fingerprints begin to appear in the sediment record after AD 1850, but accelerate in pulses between AD 1950 and 1970 and again after AD 1980. Our review indicates that recent environmental changes associated with humankind's dominance of key global biogeochemical cycles are sufficiently pervasive to be imprinted on the sediment record of remote lakes. Moreover, these changes are of sufficient magnitude to conclude that the Holocene has effectively ended, and that the concept of Anthropocene more aptly describes current planetary dynamics. The synthesis of these observations pertains directly to ongoing discussions concerning the eventual formalization of a new stratigraphic boundary. (c) 2012 Elsevier B.V. All rights reserved.
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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. |
- Hakansson, Lena, et al.
(författare)
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(10)Be data from meltwater channels suggest that Jameson Land, east Greenland, was ice-covered during the last glacial maximum
- 2011
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 76:3, s. 452-459
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Tidskriftsartikel (refereegranskat)abstract
- Along the northeast Greenland continental margin, bedrock on interfjord plateaus is highly weathered, whereas rock surfaces in fjord troughs are characterized by glacial scour. Based on the intense bedrock weathering and lack of glacial deposits from the last glaciation, interfjord plateaus have long been thought to be ice-free throughout the last glacial maximum (LGM). In recent years there is growing evidence from shelf and fjord settings that the northeast Greenland continental margin was more extensively glaciated during the LGM than previously thought. However, little is still known from interfjord settings. We present cosmogenic (10)Be data from meltwater channels and weathered sandstone outcrops on Jameson Land, an interfjord highland north of Scoresby Sund. The mean exposure age of samples from channel beds (n = 3) constrains on the onset of deglaciation on interior Jameson Land to 18.5 +/- 1.3-21.4 +/- 1.9 ka (for erosion conditions of 0-10 mm/ka, respectively). This finding adds to growing evidence that the northeast Greenland continental margin was more heavily glaciated during the LGM than previously thought.
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