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Atle Nesje Denise C. Rüther Jacob C. Yde 《Boreas: An International Journal of Quaternary Research》2023,52(2):194-205
This study presents the sedimentary succession of an outwash plain and an alluvial fan located along the valley Langedalen at the south-eastern side of the Jostedalsbreen ice cap in inner Sogn, western Norway. A newly exposed ~2.8-m-high section along the southern riverbank of Langedøla river shows alternating layers of minerogenic sediments and peat layers with tree logs, identified as Salix sp. The section is situated in the distal part of an alluvial fan built out from the southern slope of Langedalen. Six AMS radiocarbon dates of tree fragments indicate that the accumulation of the fine-grained sediments in the lower part of the section was initiated earlier than the basal radiocarbon date of 914–976 calibrated years CE (1σ age range). These basal, fine-grained sediments are interpreted as proglacial outwash deposited in a floodplain depression or abandoned river channel in a low-energy glaciofluvial environment. Periods of low glacier cover, low river discharge or low-water stands over the floodplain allowed peat formation and the growth of trees and shrubs in the valley. The radiocarbon dates further indicate relatively rapid sediment accretion (~2.7–3 cm a−1) between 190 and 125 cm below the sediment surface, equivalent to approximately 1220 to 1250 cal. a CE (1σ age range). At ~60 cm depth below the surface, dated to approximately 1590 to 1620 cal. a CE (1σ age range), a transition to more coarse-grained, sandy and gravelly sediments indicates increased sediment supply and distal expansion of the alluvial fan. This occurred most likely as a consequence of increased sediment yield from expanding glaciers along the southern valley side of Langedalen as a response to the initial Little Ice Age glacier growth. Based on these results, the accretion and progradation of glacier-fed alluvial fans mainly occur during periods of glacier advance rather than during glacier recession. 相似文献
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The consistent geographical and altitudinal distribution of autochthonous block fields (mantle of bedrock weathered in situ) and trimlines in southern Norway suggests a multi-domed and asymmetric Late Weichselian ice sheet. Low-gradient ice-sheet profiles in the southern Baltic region, in the North Sea, and along the outer fjord areas of southern Norway, are best explained by movement of ice on a bed of deforming sediment, although water lubricated sliding or a combination of the two, may not be excluded. The ice-thickness distribution of the Late Weichselian Scandinavian ice sheet is not in correspondence with the modern uplift pattern of Fennoscandia. Early Holocene crustal rebound was apparently determined by an exponential, glacio-isostatic rise. Later, however, crustal movements appear to have been dominated by large-scale tectonic uplift of the Fennoscandian Shield, centred on the Gulf of Bothnia, the region of maximum lithosphere thickness. 相似文献
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Radiocarbon dating of thin palaeopodsols buried beneath turf-banked gelifluction lobes at four localities in the low alpine mountain zone in the Jostedalsbreen region, western Norway, show that gelifluction processes were initiated subsequent to the late Subboreal Chronozone. Although large age-depth gradients have been demonstrated from buried palaeosols in southern Norway, evidence is presented that the palaeosols in this study show only moderate age-depth gradients. The age estimates from these buried palaeosols give maximum dates of burial, but the error is not thought to be large. Gelifluction processes were probably initiated close to the time of the climatic deterioration, which led to the formation of the present glaciers during the Subatlantic Chronozone. The processes may have been most active during the peak of the Little Ice Age, during which a periglacial climate was established to low levels in this mountainous region. 相似文献
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?yvind Breivik Tor Christian Bekkvik Cecilie Wettre Atle Ommundsen 《Ocean Dynamics》2012,62(2):239-252
The task of determining the origin of a drifting object after it has been located is highly complex due to the uncertainties
in drift properties and environmental forcing (wind, waves, and surface currents). Usually, the origin is inferred by running
a trajectory model (stochastic or deterministic) in reverse. However, this approach has some severe drawbacks, most notably
the fact that many drifting objects go through nonlinear state changes underway (e.g., evaporating oil or a capsizing lifeboat).
This makes it difficult to naively construct a reverse-time trajectory model which realistically predicts the earliest possible
time the object may have started drifting. We propose instead a different approach where the original (forward) trajectory
model is kept unaltered while an iterative seeding and selection process allows us to retain only those particles that end
up within a certain time–space radius of the observation. An iterative refinement process named BAKTRAK is employed where
those trajectories that do not make it to the goal are rejected, and new trajectories are spawned from successful trajectories.
This allows the model to be run in the forward direction to determine the point of origin of a drifting object. The method
is demonstrated using the leeway stochastic trajectory model for drifting objects due to its relative simplicity and the practical
importance of being able to identify the origin of drifting objects. However, the methodology is general and even more applicable
to oil drift trajectories, drifting ships, and hazardous material that exhibit nonlinear state changes such as evaporation,
chemical weathering, capsizing, or swamping. The backtracking method is tested against the drift trajectory of a life raft
and is shown to predict closely the initial release position of the raft and its subsequent trajectory. 相似文献
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Boundary-Layer Meteorology - Experimental results from a combined wind–wave tank are presented. Wind profiles and resulting wind–wave spectra are described, and an investigation of the... 相似文献
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Elisabeth Kastellet Atle Nesje & Einar Solheim Pedersen 《Geografiska Annaler: Series A, Physical Geography》1998,80(1):51-65
Documentary data provide long time series and sometimes high-resolution, detailed data from historical times to the present and can give valuable information about palaeoclimate, and for the prediction of future climates. In this paper, documentary data containing qualitative information on climate, in the form of a diary written by the farmer I.G. Grude, and two newspapers, were used for the reconstruction of the palaeoclimate at Jæren, in the county of Rogaland, in southwestern Norway, during the period 1821–50. An index method to quantify the qualitative climate data was developed and used for a low-resolution reconstruction of winter, summer and annual temperatures. A high-resolution climate reconstruction of temperature and precipitation for the winter of 1837/38 is also presented, making use of a method that keeps the climate data in a qualitative form. The climate reconstructions are compared to an instrumental temperature series from Bergen, for the same period. The two data sets are in good agreement except for summer temperature (annual temperature: r = 0.75, winter temperature: r = 0.77, summer temperature: r = 0.44). Compared to average temperatures during 1961–90, the instrumental data from Bergen during the 1821–50 period show slightly different temperatures: annual average was 0.3°C lower, winter 0.4°C lower, and summer 0.1°C lower than at present, implying conditions consistent with the "Little Ice Age" climate. 相似文献
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Berit Oline Hjelstuen Atle Nygård Hans Petter Sejrup Haflidi Haflidason 《Boreas: An International Journal of Quaternary Research》2012,41(3):379-390
Throughout the last 1.1 million years repeated glaciations have modified the southern Fennoscandian landscape and the neighbouring continental shelf into their present form. The glacigenic erosion products derived from the Fennoscandian landmasses were transported to the northern North Sea and the SE Nordic Seas continental margin. The prominent sub‐marine Norwegian Channel trough, along the south coast of Norway, was the main transport route for the erosion products between 1.1 and 0.0 Ma. Most of these erosion products were deposited in the North Sea Fan, which reaches a maximum thickness of 1500 m and has nearly 40 000 km3 of sediments. About 90% of the North Sea Fan sediments have been deposited during the last 500 000 years, in a time period when fast‐moving ice streams occupied the Norwegian Channel during each glacial stage. Back‐stripping the sediment volumes in the northern North Sea and SE Nordic Seas sink areas, including the North Sea Fan, to their assumed Fennoscandian source area gives an average vertical erosion of 164 m for the 1.1–0.0 Ma time period. The average 1.1–0.0 Ma erosion rate in the Fennoscandian source area is estimated to be 0.15 mm a?1. We suggest, however, that large variations in erosion rates have existed through time and that the most intense Fennoscandian landscape denudation occurred during the time period of repeated shelf edge ice advances, namely from Marine Isotope Stage 12 (c. 0.5 Ma) onwards. 相似文献
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Danielle M. Howlett Zhiyuan Ge Wojciech Nemec Rob L. Gawthorpe Atle Rotevatn Christopher A.‐L. Jackson 《Sedimentology》2019,66(6):2425-2454
Sea‐floor topography of deep‐water folds is widely considered to have a major impact on turbidity currents and their depositional systems, but understanding the flow response to such features was limited mainly to conceptual notions inspired by small‐scale laboratory experiments. High‐resolution three‐dimensional numerical experiments can compensate for the lack of natural‐scale flow observations. The present study combines numerical modelling of thrusts with fault‐propagation folds by Trishear3D software with computational fluid dynamics simulations of a natural‐scale unconfined turbidity current by MassFlow‐3D? software. The study reveals the hydraulic and depositional responses of a turbidity current (ca 50 m thick) to typical topographic features that it might encounter in an orthogonal incidence on a sea‐floor deep‐water fold and thrust belt. The supercritical current (ca 10 m sec?1) decelerated and thickened due to the hydraulic jump on the fold backlimb counter‐slope, where a reverse overflow formed through current self‐reflection and a reverse underflow was issued by backward squeezing of a dense near‐bed sediment load. The reverse flows were re‐feeding sediment to the parental current, reducing its waning rate and extending its runout. The low‐efficiency current, carrying sand and silt, outran a downslope distance of >17 km with only modest deposition (<0·2 m) beyond the fold. Most of the flow volume diverted sideways along the backlimb to surround the fold and spread further downslope, with some overspill across the fold and another hydraulic jump at the forelimb toe. In the case of a segmented fold, a large part of the flow went downslope through the segment boundary. Preferential deposition (0·2 to 1·8 m) occurred on the fold backlimb and directly upslope, and on the forelimb slope in the case of a smaller fold. The spatial patterns of sand entrapment revealed by the study may serve as guidelines for assessing the influence of substrate folds on turbiditic sedimentation in a basin. 相似文献