Wood as a driver of past landscape change along river corridors     

Robert A. Francis  Geoff E. Petts  Angela M. Gurnell 《地球表面变化过程与地形》2008,33(10):1622-1626

The role of wood as a driver of landform development appears to have been overlooked in the interpretation of palaeo‐landscape change along river corridors. Deforested river corridors and wood‐free rivers characterize ‘modern’, managed landscapes, but along natural river corridors both driftwood dynamics and tree reproductive strategies can have a dramatic impact on the style and rate of channel and floodplain development. Therefore, we believe that interpretations of the post‐glacial history of river valleys across the northern temperate climatic zone could be usefully reassessed, incorporating the roles of riparian trees. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Potential impact of climate change on aquatic insects: A sensitivity analysis for European caddisflies (Trichoptera) based on distribution patterns and ecological preferences   总被引：1，自引：1，他引：0  

Daniel Hering  Astrid Schmidt-Kloiber  John Murphy  Sofie Lücke  Carmen Zamora-Muñoz  Manuel Jesús López-Rodríguez  Thomas Huber  Wolfram Graf 《Aquatic Sciences - Research Across Boundaries》2009,71(1):3-14

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The interannual variability of East Asian Winter Monsoon and its relation to the summer monsoon   总被引：76，自引：1，他引：75  

Chen Wen  Hans-F. Graf  Huang Ronghui 《大气科学进展》2000,17(1):48-60

1.IntroductionOvertheEastAsiaregion,themostprominentsurfacefeatureofthewintermonsoonisstrongnortheasterliesalongtheeastflankoftheSiberianhighandthecoastofEastAsia.At500hPathereisabroadtroughcenteredaboutatthelongitudesofJapan.Thedominantfea-tureat2O0hPaistheEastAsianjetwithitsmaximumlocatedatjustsoutheastofJapan.Thisktisassociatedwithintensebaroclinicity,largeverticalwindshearandstrongadvectionofcoldair(StaffmembersofAcademiaSinica,l957,LauandChang,1987;BoyleandChen,1987;Chenetal.,1991…  相似文献   

Secular Variability of the Coupled Tropospheric and Stratospheric Circulation in the GCM ECHAM 3/LSG     

F. Feser  H.-F. Graf  J. Perlwitz 《Theoretical and Applied Climatology》2000,65(1-2):1-15

Summary  Secular or multi-decadal variability is a widely observed phenomenon, apparent in instrumental and paleo climatic records. These long time oscillations are found in many variables of the climate system. The ocean especially experiences low frequency variations. But also atmospheric variables such as temperature, wind velocity and sea level pressure can show secular variability. The low frequency variability here is examined in the coupled atmosphere-ocean model ECHAM3/LSG T21. A coupled stratospheric and tropospheric mode is detected oscillating with a period of approximately 100 years. The atmospheric pressure system mainly involved in this oscillation is the northern hemispheric winter stratospheric polar vortex. The near surface temperature experiences variations of the same magnitude as the observed temperature trends of the last decades. Multi decadal variability is also shown in the North Atlantic Oscillation Index. A shift of the length of the oscillation period between longer and shorter time scales indicates that chaotic processes might be responsible for the variability. Received February 22, 1999/Revised August 5, 1999  相似文献   

Origin of transverse folds in an extensional growth-fault setting: Evidence from an extensive seismic volume in the western Gulf of Mexico     

Angela McDonnell  Martin P.A. JacksonMichael R. Hudec 《Marine and Petroleum Geology》2010

Growth faults in gravity-driven extensional provinces are dominated by coast-parallel trends, but coast-perpendicular (transverse) trends are far less documented. The Clemente–Tomas fault in the inner Texas shelf has corrugations that are transverse to the fault and that plunge downdip. A large (8500 km²), high-quality, 3D seismic survey allows a uniquely encompassing perspective into hanging-wall deformation above this corrugated fault surface. Synextensional strata in the hanging wall are folded into alternating transverse ridges and synclines, typically spaced 10 km apart. Forward modelling in dip profiles of an extensional fault having three ramps produces ramp basin-rollover pairs that compare with the seismically revealed ridges and synclines. As they translated down the undulose fault plane, ramp basins and rollovers were juxtaposed along strike, forming the hanging-wall ridges and synclines observed offshore Texas. Fault-surface corrugations correlate broadly with footwall structure. We infer that corrugations on the Clemente–Tomas fault formed by evacuation of an allochthonous salt canopy emplaced in the late Eocene to early Oligocene. Early salt evacuation (Oligocene) created an undulose topography that influenced incipient Clemente-Tomas fault segments as they merged to form an inherently undulose fault. Late salt evacuation (early Miocene) further deformed this fault surface.  相似文献   

Skeletal linear extension rates of the foliose scleractinian coral Merulina ampliata (Ellis & Solander, 1786) in a turbid environment     

Angela Dikou 《Marine Ecology》2009,30(4):405-415

Skeletal linear extension rates of a foliaceous, IndoPacific, skiophilous, heterotrophic, scleractinian Merulina ampliata (Ellis & Solander 1786) were obtained along a sediment/nutrient load gradient at the southern islands of Singapore. Measurements were made during November 1999– November 2000 using the alizarin red‐S staining technique. Suspended particulate matter concentration (r²_adj = 0.76), turbidity (r²_adj = 0.59), the organic content of suspended sediments (r² = 0.50), and nitrite‐nitrate concentration (r²_adj = 0.50) were significant predictors of the skeletal linear extension rate of M. ampliata. Maximum linear extension growth rates of M. ampliata (mean ± SD: 1.43 ± 0.67–3.26 ± 0.59 cm·year^?1) were comparable to 15‐year‐old accounts at the same research sites, indicating adaptation to low‐light, high‐sediment waters.  相似文献   

Discovery of Arundian and Holkerian faunas from a Dinantian platform succession in North Wales     

Ian D. Somerville  Angela R. E. Strank 《Geological Journal》1984,19(2):85-104

For the first time Arundian and Holkerian faunas have been recognized from the lower part of the Dinantian succession in North Wales. These limestones and sandstones, hitherto regarded as Asbian, have a macrofauna and microfauna confirming their older age, and this discovery' has necessitated a revision of the palaeogeography in the North Wales region. Biostratigraphical correlations have been made with contemporaneous platform successions in the Central, Northern, and Southwest Provinces of Britain. A new genus and species of foraminifer, Groessensella moldensis, is described.  相似文献   

Fifteenth Annual Geomorphology Symposium     

William L. Graf 《The Professional geographer》1985,37(1):98-98

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In situ arsenic removal in an alkaline clastic aquifer   总被引：1，自引：1，他引：0  

Alan H. Welch  Kenneth G. Stollenwerk  Angela P. Paul  Douglas K. Maurer  Keith J. Halford 《Applied Geochemistry》2008,23(8):2477-2495

In situ removal of As from ground water used for water supply has been accomplished elsewhere in circum-neutral ground water containing high dissolved Fe(II) concentrations. The objective of this study was to evaluate in situ As ground-water treatment approaches in alkaline ground-water (pH > 8) that contains low dissolved Fe (<a few tens of μg/L). The low dissolved Fe content limits development of significant Fe-oxide and the high-pH limits As adsorption onto Fe-oxide. The chemistries of ground water in the two aquifers studied are similar except for the inorganic As species. Although total inorganic As concentrations were similar, one aquifer has dominantly aqueous As(III) and the other has mostly As(V). Dissolved O₂, Fe(II), and HCl were added to water and injected into the two aquifers to form Fe-oxide and lower the pH to remove As. Cycles of injection and withdrawal involved varying Fe(II) concentrations in the injectate. The As concentrations in water withdrawn from the two aquifers were as low as 1 and 6 μg/L, with greater As removal from the aquifer containing As(V). However, Fe and Mn concentrations increased to levels greater than US drinking water standards during some of the withdrawal periods. A balance between As removal and maintenance of low Fe and Mn concentrations may be a design consideration if this approach is used for public-supply systems. The ability to lower As concentrations in situ in high-pH ground water should have broad applicability because similar high-As ground water is present in many parts of the world.  相似文献   

Arctic radiation deficit and climate variability     

Hans-F Graf 《Climate Dynamics》1992,7(1):19-28

One of the generally accepted climatic effects of stratospheric aerosol injection is the reduction of the global radiation in high latitudes by an order of 5% during El Chichon type eruptions. To test the effect of a high-latitude radiation deficit on global climate, a GCM experiment was performed with the ECMWF T21 atmosphere general circulation model (AGCM). The results provide physically-consistent evidence that this radiation deficit is a possible external forcing factor for severe climatic anomalies not only in the area directly affected by the reduced radiation, but also in the tropics. The most important factor is the creation of enhanced snow cover in regions of Asia that are distant from the location of the introduced radiation anomaly. The simulated results show certain features that are well known from observations in weak monsoon years, i.e. the weakened easterly jet in the upper troposphere over northern India, prolonged winter monsoon conditions, and prevailing anticyclonic vorticity anomalies over the entire Indian summer monsoon region. Over the western Pacific at the end of boreal winter (May), increased convective activity leads to a negative Walker circulation anomaly with westerly wind anomalies near the surface and easterly anomalies in the upper troposphere. This is known as one of the most important anomalies at the beginning of an El Niño/Southern Oscillation (ENSO) event.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil  相似文献