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- Baykal, Yunus, et al.
(författare)
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Eurasian Ice Sheet derived meltwater pulses and their role in driving atmospheric dust activity: Late Quaternary loess sources in SE England
- 2022
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 296, s. 107804-107804
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Tidskriftsartikel (refereegranskat)abstract
- The role of Quaternary ice sheet fluctuations in driving meltwater pulses and ocean circulation perturbations is widely acknowledged. What is less clear is the role of these processes in driving changes in past atmospheric dust activity, and possible wider links between dust and climate. Terrestrial windblown dust (loess) deposits along the northern fringe of the European loess belt potentially record past atmospheric dust emission from regions close to the former Eurasian Ice Sheet (EIS) and provide a means to evaluate the role of ice sheet fluctuations in the past dust cycle. Numerical loess chronologies across this region generally agree on greatly enhanced dust deposition rates during MIS 2, when the EIS reached its maximum extent. Yet, uncertainties over the sources of this material prevent understanding of the precise causes of this greatly enhanced atmospheric dustiness, and any potential link to ice sheet fluctuations and climate. In southeast England, loess accumulation dominantly occurred in two phases centered on 25–23.5 ka and 20–19 ka, matching the timing of coalescence of the Fennoscandian and British-Irish ice sheets and specifically advances and retreats of nearby ice lobes in the western North Sea. As such, these deposits provide an ideal test of the role of ice sheet fluctuations in atmospheric dust dynamics. Here we undertake such a test through a detailed provenance study of loess in southeast England and potential dust source sediments across the North Sea region. We group extensive new and published data sets of detrital zircon U–Pb ages from basement rocks and Cenozoic sediments in the North Sea area, which not only provide new insight into both loess source, but also the nature of sediment transport over NW Europe into the North Sea basin more widely. Multi-proxy evidence allows us to unambiguously identify ice sheet derived sediments in the exposed North Sea basin as the dominant source of loess in southeast England, while fluvial sediments delivered by rivers draining Continental Europe possibly contributed additional source material to the first loess accumulation phase. We propose that sudden retreats of the North Sea Lobe released substantial amounts of sediment rich meltwater into the southern North Sea and Channel basins, driving accelerated dust emission, loess deposition and provenance variability in NW Europe during MIS 2. Moreover, we propose that this model of dust activity driven by proglacial sediment availability may be applicable for EIS marginal regions more widely, even where resultant loess cover is rarely preserved due to extensive erosion and reworking along the ice marginal spillway. This implies the role of ice sheets in controlling wider dust emission may be underestimated. In addition to driving changes in ocean circulation through meltwater pulses, ice sheet dynamics in the Quaternary may have also driven substantial and abrupt changes in atmospheric dust activity. This mechanism may in part explain the coupling between dust and climate events widely seen in Quaternary dust sediment records and suggests a possible major role of high latitude dust emission in MIS 2 dustiness across Europe and beyond.
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| 2. |
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| 3. |
- Sechi, Daniele, et al.
(författare)
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Age and significance of late Pleistocene Lithophyllum byssoides intertidal algal ridge, NW Sardinia, Italy
- 2020
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 400
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Tidskriftsartikel (refereegranskat)abstract
- Intertidal coralline red algal build-ups (Lithophyllum byssoides rims or ridges) are considered precise sea level markers and mostly used for Holocene sea level history. Several well-preserved patches of relict red algal ridges crop out along the north-west Sardinian coast (Mediterranean Sea, Italy) and have great potential in reconstructing the late Pleistocene sea level history of the western Mediterranean. The aim of this paper is to determine the sedimentary characteristics of the relict Lithophyllum byssoides build-ups cropping out along the Sardinian NW coast and to demonstrate how these can be used as past sea-level indicators. To establish a chronological framework for these deposits, luminescence dating (both quartz OSL and K-feldspar pIRIR290) has been applied and allows for the Lithophyllum byssoides ridge formation to be assigned to Marine Isotopic Stage (MIS) 5e (132–112 ka). The studied relict ridges confirmed that MIS 5e sea-level was at least at 4 m above present, well matching the widely accepted last interglacial global sea-level curves. Hence, fossil Lithophyllum byssoides ridges can be used as stratigraphic and chronologic indicators of late Pleistocene sea-level. Moreover, the study has underlined that Lithophyllum byssoides may grow: (1) in sheltered places along high cliffy coasts forming bench-like structures, and (2) in high-energy environments on wave cut platforms around fallen blocks or potholes, first as isolated mounds and then merging to form reef-like structures.
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| 4. |
- Stevens, Thomas, 1979-, et al.
(författare)
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Abrupt last glacial dust fall over southeast England associated with dynamics of the British-Irish ice sheet
- 2020
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Ingår i: Quaternary Science Reviews. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0277-3791 .- 1873-457X. ; 250
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Tidskriftsartikel (refereegranskat)abstract
- Loess deposits in southern Britain contain a record of dust, climate and landscape dynamics over the last glacial, yet their age and accumulation rate remain poorly known. Furthermore, the environmental controls on the loess-soil stratigraphy shown in the thickest deposits in southeast England are still debated. Here we apply the first high sampling resolution quartz optically stimulated luminescence study of dust accumulation and loess formation in Britain at the Pegwell Bay site in east Kent. We couple this to mineral magnetic, particle size and geochemical analyses to understand climate, environment and post depositional modification of the loess. The luminescence ages and Bayesian age modelling results suggest two phases of greatly enhanced dust accumulation at the site. Loess began to accumulate around c. 25-23.5 ka, coinciding with Heinrich event 2, and after subsequent lower accumulation rates, a second enhanced phase of deposition occurred at around 20-19 ka. We propose a model where the dynamics of the British-Irish and Fennoscandian Ice Sheets, associated glacial lake drainage, and linked reorganisations of atmospheric circulation, all controlled loess accumulation in southern Britain. Accumulation in the first phase was triggered by increased sediment supply from initial retreat of the North Sea ice lobe, and drainage of Dogger Lake. Loess accumulation during this phase was enhanced by easterly winds from Atlantic depressions tracking to the south of Britain, caused by the maximum extent of the Irish Sea Ice Stream at c. 25-24 ka. The subsequent retreat of the western part of the British Irish Ice Sheet then allowed storm tracking further north, which reduced effectiveness of dust transporting winds across southern Britain, while sediment supply and availability was reduced in North Sea source areas. A second retreat of the maximum extent of the North Sea Lobe of ice after c. 21-20 ka would have led to another abrupt input of sediment-rich ice dammed lake and meltwater from eastern England and the North Sea into the exposed southern North Sea area. This would have again dramatically increased sediment availability for transport and deposition as loess in SE England, resulting in the second dust accumulation phase. We also propose that the abrupt stratigraphic change from calcareous to non-calcareous loess up section at Pegwell Bay was driven, not by these changes in dust input, but rather deepening of the permafrost active layer after c. 21 ka. This deepening was associated with warmer and wetter conditions driven by Atlantic storms tracking further north following the regression of the Irish Sea Ice Stream and overall ice sheet retreat. As such, last glacial dust dynamics and loess accumulation in Britain is highly influenced by the interaction of the British Irish Ice Sheet the Fennoscandian Ice sheet, Atlantic storm tracks, and the topography and drainage of the exposed North Sea.
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| 5. |
- 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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