Climate control on the evolution of Late Pleistocene alluvial‐fan and aeolian sand‐sheet systems in NW Germany     

Janine Meinsen  Jutta Winsemann  Julia Roskosch  Christian Brandes  Manfred Frechen  Stefan Dultz  Jürgen Böttcher 《Boreas: An International Journal of Quaternary Research》2014,43(1):42-66

The Late Pleistocene was characterized by rapid climate oscillations with alternation of warm and cold periods that lasted up to several thousand years. Although much work has been carried out on the palaeoclimate reconstruction, a direct correlation of ice‐core, marine and terrestrial records is still difficult. Here we present new data from late Middle Pleniglacial to Lateglacial alluvial‐fan and aeolian sand‐sheet deposits in northwestern Germany. Records of Late Pleniglacial alluvial fans in central Europe are very rare, and OSL dating is used to determine the timing of fan aggradation. In contrast to fluvial systems that commonly show a delay between climate change and incision/aggradation, the small alluvial‐fan systems of the Senne area responded rapidly to climatic changes and therefore act as important terrestrial climate archives for this time span. The onset of alluvial‐fan deposition correlates with the climate change from warm to cold at the end of MIS 3 (29.3±3.2 ka). Strong fan progradation started at 24.4±2.8 ka and may be related to a period of higher humidity. The vertical stacking pattern of sedimentary facies and channel styles indicate a subsequrent overall decrease in water and sediment supply, with less sustained discharges and more sporadic runoffs from the catchment area, corresponding to an increasing aridity in central Europe during the Late Pleniglacial. Major phases of channel incision and fan aggradation may have been controlled by millennial‐scale Dansgaard–Oeschger cycles. The incision of channel systems is attributed to unstable climate phases at cold–warm (dry–wet) or warm–cold (wet–dry) transitions. The alluvial‐fan deposits are bounded by an erosion surface and are overlain by aeolian sand‐sheets that were periodically affected by flash‐floods. This unconformity might be correlated with the Beuningen Gravel Bed, which is an important marker horizon in deposits of the Late Pleniglacial resulting from deflation under polar desert conditions. The deposition of aeolian sand‐sheet systems (19.6±2.1 to 13.1±1.5 ka) indicates a rapid increase in aridity at the end of the Late Pleniglacial. Intercalated flash‐floods deposits and palaeosols (Finow type) point to temporarily wet conditions during the Lateglacial. The formation of an ephemeral channel network probably marks the warm‐cold transition from the Allerød to the Younger Dryas.  相似文献   

The Požarevac loess–paleosol sequence: a record of increased aridity in the south-eastern margin of the Carpathian Basin during the last 350 ka     

Slobodan B. Marković  Eric A. Oches  Zoran M. Perić  Tivadar Gaudenyi  Mlađen Jovanović  Györgi Sipos  Christine Thiel  Jan-Pieter Buylaert  Stevan Savić  William D. McCoy  Milica G. Radaković  Rastko S. Marković  Milivoj B. Gavrilov 《第四纪科学杂志》2021,36(8):1436-1447

The loess sequence preserved in the Požarevac brickyard in north-eastern Serbia comprises eight loess units separated by seven paleosols. Geochronological investigation using amino acid racemization and luminescence dating support stratigraphic correlations of loess units L3, S2LL1 and L1 at the Požarevac section with loess of glacial cycles E [Marine Isotope Stage (MIS) 10], D (MIS 9–8), C (MIS 7–6) and B (MIS 5–2) across central Europe. Correlation with the marine oxygen-isotope stratigraphy and associated paleoclimatic inferences are further supported by magnetic susceptibility, particle size and carbonate content measured in Požarevac sediments. Malacological investigations at the Požarevac section reveal the continuous presence of the Chondrula tridens and Helicopsis striata faunal assemblages throughout the last 350 ka. The loess malacological fauna, which is characterized by the complete absence of cold-resistant and cold-preferring species, suggests a stable, dry and relatively warm glacial and interglacial climate, compared with other central European loess localities. Together these data suggest that the south-eastern part of the Carpathian (Pannonian, Middle Danube) Basin was a refugium for warm-preferring and xerophilous land-snails during the generally unfavorable glacial climates of the late Middle and Late Pleistocene.  相似文献   

Correlation between the energy supplied by reconnection and the magnetospheric energy consumption     

I.M. Stanisławska  G.W. Prölss 《Planetary and Space Science》1985,33(9):1091-1093

This study investigates the statistical correlation between the power input into the magnetosphere due to reconnection and the subsequent dissipation of this energy in the magnetosphere as measured by the U_T parameter (Perreault and Akasofu, 1978). It is found that of the three expressions for this energy input P_W, P_K (Gonzalez and Gonzalez, 1984) and ε (Perreault and Akasofu, 1975; Kan et al.,1980), P_W yields the highest correlation with the energy consumption of the magnetosphere.  相似文献   

A review of various factors influencing the stable carbon isotope ratio of organic lake sediments by the change from glacial to post-glacial environmental conditions     

Sören Håkansson 《Quaternary Science Reviews》1985,4(2):135-146

A survey is made of various factors influencing the ${}^{13}\text{C}{}^{12}\text{C}$ ratio of the organic component in lake sediments, focusing on the behaviour at the change from glacial to post-glacial environmental conditions.Increase in the ¹³C content of the organic sediment is caused by increase in temperature and the corresponding decrease of the supply of molecular CO₂ in the water of the lakes. An increase in the rate of organic production in the lakes may also, perhaps, cause a corresponding ¹³C increase. An increase of the fermentation of organic mud in the lakes may also have an effect in the same direction.Decrease in the ¹³C content of the organic sediment is caused by the change of the relative amounts of production of plankton and submersed macrophytes in the lakes from mainly submersed macrophytes to mainly plankton. A decrease towards almost complete absence of bicarbonate and CO₂ originating from carbonate rocks will also lead to a ¹³C decrease in the organic sediments. The same effect has the change of the terrestrial vegetation cover from almost complete absence to complete cover. A possible decrease of the ¹³C content in the atmospheric CO₂ has an effect in the same direction.  相似文献   

Book reviews     

T. Littmann  Rudolf Brázdil  Manfred Domrös  Mohammed A. Kishk  A. Wallner  Radan Květ  Andreas Grotewold 《GeoJournal》1992,26(4):547-549

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Pi 2 pulsations and the eastward electrojet: A case study     

Mark Lester  Karl-Heinz Glaßmeier  Jörg Behrens 《Planetary and Space Science》1985,33(3):351-364

We report the results of a case study of two Pi 2 pulsations observed near the eastward electrojet by the Scandinavian Magnetometer Array. The power of the two Pi 2 pulsations, calculated using a standard Fast Fourier Transform method, peaks near the centre of the eastward electrojet. For both events there is a strong latitudinal gradient in the power poleward of the equatorward border of the electrojet. The sense of polarisation is predominantly clockwise at the northern stations and anticlockwise at the southern stations although the reversal from clockwise to anticlockwise does not occur at a constant latitude. For the first event the polarisation reversal occurs at higher latitudes in the western half of the array; for the second the polarisation reversal occurs at higher latitudes at the edges of the array. The polarisation reversal does not appear to be related to the location of the eastward electrojet. Equivalent current vectors of the Pi 2 pulsations, obtained by rotating the band pass filtered data through 90°, exhibit clear vortex structures in both events. The vortices change sense of direction at half the period of the Pi 2 pulsation. A simple model for the ionospheric electric field in accord with the field line resonance theory reconstructs the basic features of the observed Pi 2 equivalent current system. We thus conclude that Pi 2 signatures in the region of the eastward electrojet and far away from the auroral break-up region are governed by the field line resonance mechanism.  相似文献   

Near-infrared imaging of H2 in molecular outflows from young stars     

C. J. Davis  R. Mundt  J. Eislöffel 《Astrophysics and Space Science》1995,224(1-2):121-124

In an attempt to identify the molecular shocks associated with the entrainment of ambient gas by collimated stellar winds from young stars, we have imaged a number of known molecular outflows in H₂ v=1-0 S(1) and wide-band K. In each flow, the observed H₂ features are closely associated with peaks in the CO outflow maps. We therefore suggest that the H₂ results from shocks associated with the acceleration or entrainment of ambient, molecular gas. This molecular material may be accelerated either in a bow shock at the head of the flow, or along the length of the flow through a turbulent mixing layer.  相似文献   

The relation between the synodic and sidereal rotation period of the Sun     

D. Roša  R. Brajša  B. Vršnak  H. Wöhl 《Solar physics》1995,159(2):393-398

The relation between the synodic and sidereal rotation period of the Sun for an arbitrary date of observation is derived taking into account details of the Earth's motion. The transformation procedure between the synodic (apparent) and sidereal rotation period presented here can be performed without using the annual ephemerides.  相似文献   

Bounds for mass and rotation of black holes in the observable universe     

A. De Vries  R. Böhme  Th. Schmidt-Kaler 《Astrophysics and Space Science》1995,225(2):221-226

The bounds for the energy change rate of a Maxwell field in the outer space of a rotating black hole, calculated by de Vries (1994) and de Vries (1995), enable us to deduce limits for the rotation and the mass of black holes. For this purpose we assume that a certain part of the anisotropies of the cosmic background radiation is due to absorption or superradiance of black holes (Teukolsky, 1973, Starobinskii and Churilov, 1973). The knowledge of these anisotropies yields bounds for rotation and mass of the black holes in the observable universe.  相似文献   

Nonlinear models of pulsation and mass loss     

S. Höfner  M. U. Feuchtinger 《Astrophysics and Space Science》1995,224(1-2):485-486

We briefly discuss the current status of our radiation-hydrodynamical models of pulsation in various stellar objects and of dust-driven mass loss in LPVs. We emphasize the importance of a future combined modelling of pulsation and mass loss in AGB stars which has to be based on reliable physical and numerical methods.  相似文献