Palaeoecological study on the Holocene valley development of the River Main, southern Germany   总被引：1，自引：0，他引：1  

BERND BECKER  WOLFGANG SCHIRMER 《Boreas: An International Journal of Quaternary Research》1977,6(4):303-321

Tree-ring studies carried out on subfossil oak trunk deposits within the Holocene valley fills of the River Main can reconstruct phases of increased fluvial activities. These phases have been dated on the base of two absolutely tree-ring dated chronologies and in addition by ¹¹C-datings of eleven floating tree-ring scries of subfossil oaks.
Geological-pedological investigations reveal an alternation between increased and reduced fluvial activity during the Holocene.
Periods of increased gravel redeposition are dated by dendrochronology, and by ¹⁴C and cultural findings. Increased fluvial activity becomes more frequent towards Modern Times with culminations in the Middle Atlantic, the Subboreal, the Iron-Roman Age, the Main Middle Ages till earliest Modern Times, and in the last century.
On the sequence of Holocene river deposits there developed specific soil types as indicators for the age of the river deposits since the Last Glacial.
Among other palaeoecological results an important finding is the correlation between tree-ring width, flood-loam sedimentation, and soil development.  相似文献   

PROBLEMS OF QUARTZ GRAIN MORPHOSCOPY     

HORST E. SCHNEIDER 《Sedimentology》1970,14(3-4):325-335

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The role of weathering and pedological processes for the development of sorted circles on Kvadehuksletta, Svalbard - a short report     

BERND ETZELMIILLER  JOHAN LUDVIG SOLLID 《Polar research》1991,9(2):181-191

The presence of silt-rich, fine-grained material at the center of the well-developed sorted circles on Kvadehuksletta, Svalbard, is a precondition for their development. Field work, laboratory work, and data from published studies indicate that the fine-grained material is a dissolution product of the dolomitic bedrock. The silt is accumulated in situ and by slope wash in terrain depressions. Chemical weathering and other pedogenetic processes, such as the translocation of silt, are of great importance in Arctic regions and can create the sedimentological prerequisites for cryogenetic processes, such as frost sorting and cryoturbation. Therefore, the bedrock composition and the composition of surficial material are considered to be important control factors for these processes.  相似文献   

Lake sediments from Store Koldewey, Northeast Greenland, as archive of Late Pleistocene and Holocene climatic and environmental changes     

MARTIN KLUG  STEFFI SCHMIDT  OLE BENNIKE  OLIVER HEIRI  MARTIN MELLES  BERND WAGNER 《Boreas: An International Journal of Quaternary Research》2009,38(1):59-71

A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25'N, 18°45'W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid-Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed.  相似文献   

Metastability of the 10- Phase in the System MgO-SiO2-H2O (MSH). What about Hydrous MSH Phases in Subduction Zones?     

WUNDER  BERND; SCHREYER  WERNER 《Journal of Petrology》1992,33(4):877-889

The so-called 10- phase of the MgO-SiO₂-H₂O (MSH) system wassynthesized with 100% yields from a 3: 4 MgO/SiO₂ gel at fluidpressure of 50 kb and 500 C, but only during runs of up to1 h and with total H₂O contents near 50 wt. % in the sealedcapsules. The water contents determined in the run productsindicate a chemical composition Mg₃Si₄O₁₀(OH)₂0.65 H₂O, whichis different from the composition reported by Bauer & Sclar(1981), which had 1 H2O molecule per talc formula. The 10-phase has a = 5.293(3) , b = 9.194(3) , c = 10.044(3) , ß=96.10(8)its calculated density is p_calc.= 2.672 g/cm³; the refractiveindices measured are n_x = 1.554. and n_x = 1.574. The compatibilityof mean refractive index, calculated density, and chemical compositionfalls within the category ‘excellent’ of Mandarino(1979). Runs of longer durations and with total H₂O again near 50 wt.%, seeded with the less hydrous phase talc with the same Mg/Siratio, show that the 10- phase breaks down in the range 30–70kb, 200–700 C to form more talc. Thus it is not the stablehydrous high-pressure equivalent of talc as reported by Yamamoto& Akimoto (1977), but a metastable phase, which cannot playany role as a natural mineral of the mantle or of subductionzones. If the tie-line forsterite-H₂O is stable in the MSH system,as it seems to be for the conditions of our experiments, mostof the hydrous, silica-poor, new high-pressure MSH phases maybe without significance for the Earth, except perhaps phaseA with as yet an ambiguous composition.  相似文献   

Turbidite system architecture and sedimentary processes along topographically complex slopes: the Makran convergent margin     

JULIEN BOURGET  SEBASTIEN ZARAGOSI  NADINE ELLOUZ‐ZIMMERMANN  NICOLAS MOUCHOT  THIERRY GARLAN  JEAN‐LUC SCHNEIDER  VALENTINE LANFUMEY  SIGFRIED LALLEMANT 《Sedimentology》2011,58(2):376-406

This study investigates the morphology and Late Quaternary sediment distribution of the Makran turbidite system (Makran subduction zone, north‐west Indian Ocean) from a nearly complete subsurface mapping of the Oman basin, two‐dimensional seismic and a large set of coring data in order to characterize turbidite system architecture across an active (fold and thrust belt) margin. The Makran turbidite system is composed of a dense network of canyons, which cut into high relief accreted ridges and intra‐slope piggyback basins, forming at some locations connected and variably tortuous paths down complex slopes. Turbidite activity and trench filling rates are high even during the Holocene sea‐level highstand conditions. In particular, basin‐wide, sheet‐like thick mud turbidites, probably related to major mass wasting events of low recurrence time, drape the flat and unchannellized Oman abyssal plain. Longitudinal depth profiles show that the Makran canyons are highly disrupted by numerous thrust‐related large‐scale knickpoints (with gradients up to 20° and walls up to 500 m high). At the deformation front, the strong break of slope can lead to the formation of canyon‐mouth ‘plunge pools’ of variable shapes and sizes. The plunge pools observed in the western Makran are considerably larger than those previously described in sub‐surface successions; the first insights into their internal architecture and sedimentary processes are presented here. Large plunge pools in the western Makran are associated with large scoured areas at the slope break and enhanced sediment deposition downstream: high‐amplitude reflectors are observed inside the plunge pools, while their flanks are composed of thin‐bedded, fine‐grained turbidites deposited by the uppermost part of the turbidity flows. Thus, these architectural elements are associated with strong sediment segregation leading to specific trench‐fill mechanisms, as only the finer‐grained component of the flows is transferred to the abyssal plain. However, the Makran accretionary prism is characterized by strong along‐strike variability in tectonics and fluvial input distribution that might directly influence the turbidite system architecture (i.e. canyon entrenchment, plunge pool formation or channel development at canyon mouths), the sedimentary dynamics and the resulting sediment distribution. Channel formation in the abyssal plain and trench‐fill characteristics depend on the theoretical ‘equilibrium’ conditions of the feeder system, which is related closely to the balance between erosion rates and tectonic regime. Thus, the Makran turbidite system constitutes an excellent modern analogue for deep‐water sedimentary systems with structurally complex depocentres, in convergent margin settings.  相似文献   

Regional Saharan dust modelling during the SAMUM 2006 campaign     

By BERND HEINOLD  INA TEGEN  MICHAEL ESSELBORN  KONRAD KANDLER  PETER KNIPPERTZ  DETLEF MÜLLER  ALEXANDER SCHLADITZ  MATTHIAS TESCHE  BERNADETT WEINZIERL  ALBERT ANSMANN  DIETRICH ALTHAUSEN  BENOIT LAURENT  REAS MASSLING  THOMAS MÜLLER  REAS PETZOLD  KERSTIN SCHEPANSKI  ALFRED WIEDENSOHLER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):307-324

The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006 SAMUM field campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry synoptic-scale dynamics, they are often misrepresented when dust emissions are caused by moist convection or influenced by small-scale topography that is not resolved by the model. In contrast to long-range dust transport, in the vicinity of source regions the model performance strongly depends on the correct prediction of the exact location of sources. Insufficiently resolved vertical grid spacing causes the absence of inversions in the model vertical profiles and likely explains the absence of the observed sharply defined dust layers.  相似文献   

Mass balance and changes of surface slope, crevasse and flow pattern of Erikbreen, northern Spitsbergen: an application of a geographical information system (GIS)     

BERND ETZELMULLER  GEIR VATNE  RUNE S. DEGARD  JOHAN LUDVIG SOLLID 《Polar research》1993,12(2):131-146

The polythcrmal valley glacier Erikbreen (79°40'N 12°30'E), northern Spitsbergen, was investigated in 1970 and 1990 using digital photogrammetry and digital elevation model (DEM) techniques. The bottom topography was derived from radio-echo soundings. Based on the DEM, mass balance and changes of surface slope, crevasse and flow pattern were evaluated, and internal ice deformation velocities were calculated. Calculations of the total mass balance show that Erikbreen has not been in equilibrium for the last 20 years. The average surface lowering was 0.38 m/a and the volume had decreased by 5% to 6% from 1970 to 1990 or on the average by 3.5 × 10⁻¹ water. The glacier surface subsided over the whole glacier area except in minor areas with northfacing slopes in the accumulation area. The surface slope and the crevasse pattern, however, did not change significantly during the 20-year-period, except in areas below 100 ma.s.l.  相似文献   

BRACKEN FERN INVASION IN SOUTHERN YUCATÁN: A CASE FOR LAND‐CHANGE SCIENCE*     

LAURA C. SCHNEIDER 《Geographical review》2004,94(2):229-241

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Seabirds and fronts: a brief overview   总被引：4，自引：0，他引：4  

DAVID C. SCHNEIDER 《Polar research》1990,8(1):17-21

Oceanographic fronts are the sites of enhanced physical and biological activity, including locally concentrated feeding by marine birds. Two general hypotheses relating marine birds to fronts have been developed. The first is that enhanced primary production at fronts increases prey supply through increased animal growth, reproduction, or immigration. The second is that prey patches develop at fronts either through behavioural responses of prey to thermal or salinity gradients, or through interaction between prey behaviour and circulatory patterns. Several recent studies support the second hypothesis. The first hypothesis, that birds benefit from enhanced primary production at fronts, has yet to be evaluated. We need a better understanding of trophic mechanisms at fronts in order to determine (1) the proportion of daily energy requirements extracted by predators at fronts; (2) the proportion of natural mortality of prey populations at fronts; and (3) the probability of contact between seabirds and point source pollutants.  相似文献