| 1. |
- Graversen, Rune, et al.
(författare)
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Greenland’s contribution to global sea-level rise by the end of the 21st century
- 2011
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 37, s. 1427-1442
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Tidskriftsartikel (refereegranskat)abstract
- The Greenland ice sheet holds enough water to raise the global sea level with *7 m. Over the last few decades, observations manifest a substantial increase of the mass loss of this ice sheet. Both enhanced melting and increase of the dynamical discharge, associated with calving at the outlet-glacier fronts, are contributing to the mass imbalance. Using a dynamical and thermodynamical ice-sheet model, and taking into account speed up of outlet glaciers, we estimate Greenland’s contribution to the 21stcentury global sea-level rise and the uncertainty of this estimate. Boundary fields of temperature and precipitation extracted from coupled climate-model projections used for the IPCC Fourth Assessment Report, are applied to the icesheet model. We implement a simple parameterization for increased flow of outlet glaciers, which decreases the bias of the modeled present-day surface height. It also allows for taking into account the observed recent increase in dynamical discharge, and it can be used for future projections associated with outlet-glacier speed up. Greenland contributes 0–17 cm to global sea-level rise by the end of the 21st century. This range includes the uncertainties in climate-model projections, the uncertainty associated with scenarios of greenhouse-gas emissions, as well as the uncertainties in future outlet-glacier discharge. In addition, the range takes into account the uncertainty of the ice-sheet model and its boundary fields.
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| 2. |
- Goodfellow, Bradley, et al.
(författare)
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Vertically mixed and unmixed: Do surface features tell the whole story? An investigation of glacial regolith profiles using in-situ produced cosmogenic radionuclides
- 2007
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Ingår i: EOS.
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Konferensbidrag (refereegranskat)abstract
- Whether a regolith is unmixed or mixed is critical to determining its erosion rate or age from in situ-produced cosmogenic nuclides. We use in situ-produced 10Be and 26Al in quartzite clasts extracted from depth profiles to investigate mixing of a periglacially-sorted till blanketing a plateau in the northern Swedish mountains. Our data indicate significant intra-site variations from a completely unmixed to a fully mixed regolith. We conclude that caution must be exercised in assuming that an entire regolith is either unmixed or mixed from interspersed depth profiles and that the degree of mixing may differ significantly from that indicated by observation of surface features. From the difference between the surface isotope concentration of an unmixed profile and the average isotope concentration of a fully mixed profile, we confirm that the regolith is a glacial till and that it could have been emplaced in a single event. Incorporating isotope concentrations, 26Al/10Be ratios, and an isostasy and ice sheet burial model we date the till emplacement to the Saalian glaciation (~ 200 to 130 ka).
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| 3. |
- Goodfellow, Bradley W., et al.
(författare)
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Arctic-alpine blockfields in the northern Swedish Scandes : late Quaternary - not Neogene
- 2014
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Ingår i: Earth Surface Dynamics. - : Copernicus GmbH. - 2196-6311 .- 2196-632X. ; 2:2, s. 383-401
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Tidskriftsartikel (refereegranskat)abstract
- Autochthonous blockfield mantles may indicate alpine surfaces that have not been glacially eroded. These surfaces may therefore serve as markers against which to determine Quaternary erosion volumes in adjacent glacially eroded sectors. To explore these potential utilities, chemical weathering features, erosion rates, and regolith residence durations of mountain blockfields are investigated in the northern Swedish Scandes. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay / silt ratios, secondary mineral assemblages, and imaging of chemical etching of primary mineral grains in fine matrix are each used for this purpose. Secondly, erosion rates and regolith residence durations of two of the summits are inferred from concentrations of in situ-produced cosmogenic Be-10 and Al-26 in quartz at the blockfield surfaces. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite consistent variability according to slope position. In addition, average erosion rates of similar to 16.2 and similar to 6.7 mm ka(-1), calculated for the two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few metres in thickness, within a late Quaternary time frame. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. The persistence of autochthonous blockfields over multiple glacial-interglacial cycles confirms their importance as key markers of surfaces that were not glacially eroded through, at least, the late Quaternary. However, presently blockfield-mantled surfaces may potentially be subjected to large spatial variations in erosion rates, and their Neogene regolith mantles may have been comprehensively eroded during the late Pliocene and early Pleistocene. Their role as markers by which to estimate glacial erosion volumes in surrounding landscape elements therefore remains uncertain.
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| 4. |
- Stroeven, Arjen, et al.
(författare)
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Blockfields of Neogene origin: Challenging the paradigm
- 2007
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Ingår i: EOS.
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Konferensbidrag (refereegranskat)abstract
- The prevailing paradigm for cold-climate in situ blockfields is that they are remnants of Neogene deep weathering profiles. This opinion is frequently based on the presence of large quantities of interstitial silt and clay and/or the presence of clay minerals, such as gibbsite and kaolinite. Using in situ-produced cosmogenic isotopes 10Be and 26Al, XRD, and XRF to study blockfield regolith in the northern Swedish mountains, we challenge this paradigm. Incorporating surface burial by ice sheets, the isostatic response to ice sheet loading and unloading, and subaerial surface erosion, the cosmogenic data indicate that the regolith has been accumulating nuclides for up to 464.5 ka. The ubiquitous presence of chlorite makes it impossible to distinguish kaolinite according to standard XRD techniques. However, gibbsite is present in glacial till in addition to wet- location blockfield regolith. Coupled with the ubiquitous presence of poorly crystallized hydroxides, vermiculization in wet-locations, and an absence of smectite, incipient chemical weathering is indicated. Furthermore, XRF data indicate dominance of the interstitial fine matrix by a foreign component, likely of aeolian origin. All of our observations can be explained by processes operating within the Quaternary timeframe. Because we do not need to appeal to Neogene deep weathering to account for the characteristics of blockfields in the northern Swedish mountains we conclude that these blockfields may have Quaternary origins.
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