Reply to comment regarding the ICE-hypothesis     

S.B. Nielsen  K. Gallagher  D.L. Egholm  O.R. Clausen  M. Summerfield 《Journal of Geodynamics》2009,48(2):101-106

In this reply, we address the issues raise by the comment of Lidmar-Bergström and Bonow [Lidmar-Bergström, K., Bonow, J., 2009. Hypotheses and observations on the origin of the landscape of southern Norway – a reply regarding the isostasy–climate–erosion hypothesis by Nielsen et al., 2008. Journal of Geodynamics, in press]. We reject them and maintain all our suggestions regarding western Scandinavia unaltered.  相似文献   

Morphological records of storm floods exemplified by the impact of the 1872 Baltic storm on a sandy spit system in south‐eastern Denmark          下载免费PDF全文

Lars B. Clemmensen  Mette Bendixen  Mikkel U. Hede  Aart Kroon  Lars Nielsen  Andrew S. Murray 《地球表面变化过程与地形》2014,39(4):499-508

Beach‐ridge systems are important geo‐archives providing evidence for past wave climate including catastrophic storm flood events. This study investigates the morphological impacts of the 1872 Baltic storm flood on a beach‐ridge system (sandy spit) in south‐eastern Denmark and evaluates the frequency of extreme storm flood events in the area over a longer time perspective. This paper combines field studies of morphology and sedimentary deposits, studies of historical maps, digital terrain model, ground‐penetrating radar profiles, and luminescence dating. Sea water reached 2.8 m above mean sea level (amsl) during peak inundation and, based on studies of the morphological impacts of the 1872 storm flood, the event can be divided into four phases. Phase 1: increasing mean water levels and wave activity at the beach brought sediments from the beach (intertidal bars and normal berm) higher up in the profile and led to the formation of a storm‐berm. Phase 2: water levels further increased and sediment in the upper part of the profile continued to build up the storm‐berm. Phase 3: water levels now reached the top of the dune ridge and were well above the storm‐berm level. Sea water was breaching the dune ridge at several sites and wash‐over fans were generated until a level where the mean water level had dropped too much. Phase 4: the non‐vegetated wash‐over fans functioned as pathways for aeolian sand transport and relatively high dunes were formed in particular along the margins of the fan where aeolian sand was trapped by existing vegetation. The studied beach‐ridge system records about 4500 years of accumulation; the storm flood sediments described are unique suggesting that the 1872 Baltic storm flood event was an extreme event. Thus studies of beach‐ridge systems form a new source for understanding storm surge risk. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

An Evaluation of Internet Versus Paper‐based Methods for Public Participation Geographic Information Systems (PPGIS)     

Amy Pocewicz  Max Nielsen‐Pincus  Greg Brown  Russ Schnitzer 《Transactions in GIS》2012,16(1):39-53

Public participation geographic information systems (PPGIS) are an increasingly important tool for collecting spatial information about the social attributes of place. The availability of Internet‐based options for implementing PPGIS presents new opportunities for increased efficiency and new modes of access. Here we used a mixed‐mode approach to evaluate paper versus Internet mapping methods for the same PPGIS survey in Wyoming. We compared participant characteristics, mapping participation, and the spatial distribution of mapped attributes between participants who responded to the paper versus Internet option. The response rate for those who completed the paper version of the survey was nearly 2.5 times the response rate of the Internet version. Paper participants also mapped significantly more places than did Internet participants (43 vs. 18). Internet participants tended to be younger, more likely to have a college degree, and had lived in the region for less time than paper participants. For all but one attribute there was no difference in the spatial distribution of places mapped between Internet and paper methods. Using a paper‐based PPGIS survey resulted in a higher response rate, reduced participant bias, and greater mapping participation. However, survey mode did not influence the spatial distribution of the PPGIS data.  相似文献   

Sea‐level markers identified in ground‐penetrating radar data collected across a modern beach ridge system in a microtidal regime     

Lars Nielsen  Lars B. Clemmensen 《地学学报》2009,21(6):474-479

Sea‐level rise has been related to global warming. The modern system on the northern coast of Anholt, Denmark, may well be analogous to other beach ridge systems formed in microtidal regimes and our results should have impact on estimation of past sea‐level variation. Ground‐penetrating radar data collected across the modern (<30 years old) berm, beach ridge and swale deposits resolve downlapping reflections interpreted to mark sea level at the time of deposition. Existing time series of sea‐level data constrain actual sea‐level variation. Nineteen readings of sea‐level markers made along our profile fluctuate within ?0.42 and 0.57 m above present mean sea level, consistent with 95% of the sea‐level data. These fluctuations reflect tidal effects and meteorological conditions. Main data uncertainties are well‐known and the sea‐level markers may be identified with a high degree of confidence.  相似文献   

Adaptation to high light irradiances enhances the photosynthetic Cu resistance in Cu tolerant and non-tolerant populations of the brown macroalgae Fucus serratus     

Hanne Dalsgaard Nielsen 《Marine pollution bulletin》2010,60(5):710-717

The relationship between light acclimation and Cu²⁺ tolerance was studied in two populations of Fucus serratus known to be naturally non-tolerant and tolerant to Cu²⁺. Acclimation to high irradiances increased the photosynthetic tolerance to Cu²⁺. The xanthophyll cycle was apparently not involved in protecting the photosynthetic apparatus against Cu²⁺ toxicity, as results showed that Cu²⁺ did not induce dynamic photoinhibition. The higher photosynthetic Cu²⁺ resistance of high light algae did not result in increased growth. The excess energy acquired by high light-adapted algae appeared to be utilized in Cu²⁺ defense mechanisms in the Cu²⁺ non-tolerant population. The polyphenol content of the algae was reciprocal to the Cu_T content, suggesting that polyphenol may be the primary Cu²⁺ defense of non-tolerant low light algae, acting through secretion and extracellular chelating of Cu²⁺, while the compounds do not seem to be involved in the primary Cu²⁺ tolerance mechanism in Cu²⁺ tolerant algae.  相似文献   

Towards spatially distributed quantitative assessment of tsunami inundation models     

John Davis Jakeman  Ole M. Nielsen  Kristy Van Putten  Richard Mleczko  David Burbidge  Nick Horspool 《Ocean Dynamics》2010,60(5):1115-1138

This paper presents a framework and data for spatially distributed assessment of tsunami inundation models. Our associated validation test is based upon the 2004 Indian Ocean tsunami, which affords a uniquely large amount of observational data for events of this kind. Specifically, we use eyewitness accounts to assess onshore flow depths and speeds as well as a detailed inundation survey of Patong City, Thailand to compare modelled and observed inundation. Model predictions matched well the detailed inundation survey as well as altimetry data from the JASON satellite, eyewitness accounts of wave front arrival times and onshore flow speeds. Important buildings and other structures were incorporated into the underlying elevation model and are shown to have a large influence on inundation extent.  相似文献   

Investigation of sedimentary aquifers in Denmark using the magnetic resonance sounding method (MRS)     

Konstantinos Chalikakis  Mette Ryom Nielsen  Anatoli Legchenko  Tom Feldberg Hagensen 《Comptes Rendus Geoscience》2009,341(10-11):918-927

  相似文献   

Local and regional variation of MORB parent magmas: evidence from melt inclusions from the Endeavour Segment of the Juan de Fuca Ridge     

Rachel Sours-Page  Kevin T. M. Johnson  Roger L. Nielsen  Jill L. Karsten 《Contributions to Mineralogy and Petrology》1999,134(4):342-363

The development of petrogenetic models of igneous processes in the mantle is dependent on a detailed knowledge of the diversity of magmas produced in the melting regime. These primary magmas, however, undergo significant mixing and fractionation during transport to the surface, destroying much of the evidence of their primary diversity. To circumvent this problem and to determine the diversity of melts produced in the mantle, we used melt inclusions hosted in primitive plagioclase phenocrysts from eight mid-ocean ridge basalts from the axial and West Valleys of the Endeavour Segment, Juan de Fuca Ridge. This area was selected for study because of the demonstrated close association of enriched (E-MORB) lavas and incompatible element enriched depleted (N-MORB) lavas. Rehomogenized melt inclusions from E-MORB, T-MORB, and N-MORB lavas have been analyzed by electron and ion microprobe for major and trace elements. The depleted and enriched lavas, as well as their melt inclusions, have very similar compatible element concentrations (major elements, Sr, Ni and Cr). Inclusion compositions are more primitive than, yet collinear with, the host lava suites. In contrast, the minor and trace element characteristics of melt inclusions from depleted and enriched lavas are different both in range and absolute concentration. N-MORB lavas contain both depleted and enriched melt inclusions, and therefore exhibit the largest compositional range (K₂O: 0.01 to 0.4 oxide wt%, P₂O₅: <0.01 to 0.2 oxide wt%, La_N: 7 to 35, Yb_N: 1 to 13, and Ti/Zr: <100 to 1300). E-MORB lavas contain only enriched inclusions, and are therefore relatively homogeneous (K₂O: 0.32 to 0.9 oxide wt %, P₂O₅: 0.02 to 0.35 oxide wt%, La_N: 11 to 60, Yb_N: 4 to 21, and Ti/Zr: ∼100). In addition, the most primitive E-32 inclusions are similar in composition to the most enriched inclusions from the depleted hosts. Major element data for melt inclusions from both N-MORB and E-MORB lavas suggest that the magmas lie on a low pressure cotectic, consistent with a petrogenesis including fractional crystallization. However, the minor and trace element compositions in melt inclusions vary independently of the major element composition implying an alternative history. When fractionation-corrected, inclusion compositions correlate with their host glass composition. Hence, the degree of enrichment of the lavas is a function of the composition of aggregated melts, not of processing in the upper mantle or lower crust. Based on this fact, the lava suites are not produced from a single parent magma, but from a suite of primary magmas. The chemistry of the melt inclusions from the enriched lavas is consistent with a derivation from variable percentages of partial melting within the spinel stability field by a process of open system (continuous or critical) melting assuming a depleted lherzolite source veined with clinopyroxenite. The low percentage melts are dominantly enriched melts of the clinopyroxenite. In contrast, the depleted lavas were created by melting of a harzburgite source, possibly fluxed with a fluid enriched in K, Ba and the LREE. Such a source was likely melted up to or past the point at which all of its clinopyroxene was consumed. This set of characteristics is consistent with a scenario by which diverse melts produced at different depths travel through the melting regime to the base of the crust without homogenizing en route. The homogeneous major element characteristics are created in the lower crust by fractional crystallization and reaction with lower crustal gabbros. Therefore, the degree of decoupling between major and trace element characteristics of the melt inclusions (and lavas) is dictated by the reaction rate of the melts with the materials in the conduit walls, as well as the residence times and flux rate, in the upper mantle and lower crust. Received: 2 December 1997 / Accepted: 27 August 1998  相似文献   

On DDO 154 and cold dark matter halo profiles     

Sergio Gelato  Jesper Sommer-Larsen 《Monthly notices of the Royal Astronomical Society》1999,303(2):321-328

  相似文献   

The Vakkejokk Breccia: An Early Cambrian proximal impact ejecta layer in the North‐Swedish Caledonides          下载免费PDF全文

J. Ormö  A. T. Nielsen  C. Alwmark 《Meteoritics & planetary science》2017,52(4):623-645

The ≤27 m thick Vakkejokk Breccia is intercalated in autochthon Lower Cambrian along the Caledonian front north of Lake Torneträsk, Lapland, Sweden. The spectacular breccia is here interpreted as a proximal ejecta layer associated with an impact crater, probably ~2–3 km in size, located below Caledonian overthrusts immediately north of the main breccia section. The impact would have taken place in a shallow‐marine environment ~520 Ma ago. The breccia comprises i) a strongly disturbed lower polymict subunit with occasional, in themselves brecciated, crystalline mega‐clasts locally exceeding 50 m surrounded by contorted sediments; ii) a middle, commonly normally graded, crystalline‐rich, polymict subunit, in turn locally overlain by iii) a thin fine‐grained quartz sandstone, <30 cm thick. The upper sandstone is sporadically either overlain, or replaced, by a conglomerate. In progressively more distal parts of the ejecta layer, the lower subunit is better described as only slightly disturbed strata. The lower subunit is suggested to have formed by ejecta bombardment of the strata surrounding the impact crater, even causing some net outwards mobilization of the sediments. The middle subunit and the uppermost quartz sandstone are considered resurge deposits. The top conglomerate may be caused by subsequent wave reworking and slumping of material from the elevated rim. Quartz grains showing planar deformation features are present in the graded polymict subunit and the upper sandstone, that is, the inferred resurge deposits.  相似文献