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| 2. |
- Rasmussen, Christian F., et al.
(författare)
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High-resolution OSL dating of loess in Adventdalen, Svalbard : Late Holocene dust activity and permafrost development
- 2023
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Ingår i: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 310
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Tidskriftsartikel (refereegranskat)abstract
- There is considerable uncertainty over the nature and causes of Holocene dust activity in the Arctic, and its links to climatic changes. Loess deposits act as near-source archives of dust deposition and provide a means to address these uncertainties. Here we develop a fully independent age model for a loess core taken in Adventdalen, Svalbard, based on 136 quartz luminescence ages taken at 2 cm intervals. This represents the most detailed luminescence dating analysis undertaken to date on a sedimentary archive. Extensive laboratory tests and stratigraphic consistency indicate that the quartz luminescence ages are reliable. Together with grain size and cryostratigraphic analyses, as well as stratigraphic investigation of an adjacent loess exposure, the exceptional detail of the chronology combined with Bayesian age modelling uniquely allows changes in loess accumulation rates, particle size and permafrost development to be reconstructed over the last 3000 yrs on 101–103 yr timescales. The results show that loess deposition was mostly continuous over this interval, albeit with a short period of reworking or non-aeolian sedimentation during the Little Ice Age. Permafrost development in the loess is dominantly syngenetic, with ice contents increasing with depth. There is considerable variability in loess mass accumulation rate over the late Holocene, with peaks occurring during the last 250 yrs, as well as at 750–900, 1050–1200, 1400–1600, 1900–2450 and possibly 2700–3000 a. These peaks generally coincide with increased coarse silt deposition, potentially suggesting a link with greater wind activity. However, the peaks also seem to coincide with possible warm phases on Svalbard, which would rather imply that temperature-driven sediment availability in glaciofluvial source areas is the main control on dustiness in Adventdalen. In any case, the rates of loess deposition in the Adventdalen core are exceptionally high globally (up to 0.35 cm yr−1/2900 g m−2 yr−1 sedimentation and mass accumulation rates, respectively), and if representative of wider patterns across Svalbard, may suggest that the archipelago is a more important high latitude dust source than previously realised.
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| 3. |
- Schneider, Ramona A. A., et al.
(författare)
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Paleoglacial footprint and fluvial terraces of the Shaluli Shan, SE Tibetan Plateau
- 2021
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Ingår i: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 17:2, s. 439-452
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Tidskriftsartikel (refereegranskat)abstract
- This study provides mapping of glacial and fluvial geomorphology in the Shaluli Shan region on the eastern margin of the south-eastern Tibetan Plateau. Based on TanDEM-X 12 m elevation data and GoogleEarth imagery, glacial valleys, ice-marginal moraines, glacial lineations, scoured terrain and fluvial terraces were mapped. Covering around 11,000 km2, this map is the first for this region to display geomorphology at a spatial resolution of 0.4 arcsec (= c. 11 m) and to include fluvial terraces. Its glacial landform distribution is largely consistent with previous mapping. The substantially higher level of detail in this study is reflected in an approximately tenfold number and smaller median sizes of individual landforms such as moraines and glacial lineations. These results underscore the importance of high-resolution DEM data such as TanDEM-X for the identification of glacial and fluvial geomorphology. The map presented here will be used for detailed paleoglacial reconstructions and landscape evolution studies combining both glacial and fluvial landforms.
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| 4. |
- Stevens, Thomas, 1979-, et al.
(författare)
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Age, formation and significance of loess deposits in central Sweden
- 2022
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Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 47:14, s. 3276-3301
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Tidskriftsartikel (refereegranskat)abstract
- Loess deposits are common in the mid-latitudes and are excellent records of past climate, landscape change and dust. However, loess deposits are seldom reported from Fennoscandia. Here we investigate two former glaciofluvial areas in central Sweden, Brattforsheden and Bonäsheden, where post-glacial loess and sand dune activity have been documented previously. Based on detailed mapping, grain size, scanning electron microscopy and optically stimulated luminescence dating analyses, we confirm the presence of loess deposits at the sites and extend the known area of loess coverage. Our results suggest that loess deposits are more common than previously thought in Sweden. The results also demonstrate that basal parts of the loess are often mixed with underlying sediment, which may be a common feature of thin loess deposits close to former ice margins. Quartz luminescence is well suited for dating these deposits, but ages from the mixed basal loess layers are older than expected, while ages from undisturbed loess extend to c. 5 ka. The loess ages contrast with the timing of main dune activity in these areas, which is dominantly in the 1–3 kyr post-deglaciation (c. 10.9–10.5 cal kyr BP). We suggest that either sediment mixing during soil formation is responsible for the mid-Holocene loess ages, or that the loess deposits record periodic landscape destabilization into the mid-Holocene. Furthermore, there is a clear topographic control on aeolian sedimentary facies, with loess mantling high ground and dunes restricted to valleys. Loess deposits are also primarily found to the south and southwest of source areas, implying transport from the north and east. This pattern contrasts with evidence for NW winds inferred from associated sand dunes. At present, the reasons for this mismatch are unclear, although one possible explanation is that silts deposited at higher elevations were affected by Ekman flow deflection of NW surface winds.
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