Medium-term effects of afforestation on sediment dynamics in a water supply catchment: A mineral magnetic interpretation of reservoir deposits in the macclesfield forest,N.W. England     

A. P. Stott 《地球表面变化过程与地形》1987,12(6):619-630

Short term increases in stream sediment loads during pre-afforestation ground preparation have often been followed by a return to low sediment loads. However, in the Macclesfield Forest in the southern Pennines, comparison of the magnetic characteristics of soils and downstream reservoir deposits suggest that significant changes in the processes of soil erosion occur later in the cycle of forest management at the time of canopy closure. A preliminary magnetic mixing model indicates that the proportion of reservoir sediments derived from the subsoil (below 0·3 m depth) has increased from 30 to 70 per cent between 1929 and 1981. Changes in hydraulic stresses subsequent to road construction and forest development, in association with unstable Pleistocene deposits, may provide an explanation for these events.  相似文献   

Comment on “late Wisconsinan glaciation models of northern Maine and adjacent Canada”     

Thomas V. Lowell  J.Steven Kite  Dale Becker  Harold W. Borns 《Quaternary Research》1983,19(1):136-137

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Detrital zircon provenance evidence for an early Permian longitudinal river flowing into the Midland Basin of west Texas     

Lowell Waite  Majie Fan  Dylan Collins  George Gehrels  Robert J. Stern 《International Geology Review》2020,62(9):1224-1244

ABSTRACT

Collision of Gondwana and Laurentia in the late Palaeozoic created new topography, drainages, and foreland basin systems that controlled sediment dispersal patterns on southern Laurentia. We utilize sedimentological and detrital zircon data from early Permian (Cisuralian/Leonardian) submarine-fan deposits in the Midland Basin of west Texas to reconstruct sediment dispersal pathways and palaeogeography. New sedimentological data and wire-line log correlation suggest a portion of the early Permian deposits have a southern entry point. A total of 3259 detrital zircon U-Pb and 357 εHf data from 12 samples show prominent groups of zircon grains derived from the Appalachian (500–270 Ma) and Grenville (1250–950 Ma) provinces in eastern Laurentia and the peri-Gondwana terranes (800–500 Ma) incorporated in the Alleghanian-Ouachita-Marathon orogen. Other common zircon groups of Mesoproterozoic-Archaean age are also present in the samples. The detrital zircon data suggest throughout the early Permian, Appalachia and Gondwana detritus was delivered by a longitudinal river system that flowed along the Appalachian-Ouachita-Marathon foreland into the Midland Basin. Tributary channels draining the uplifted Ouachita-Marathon hinterland brought Gondwana detritus into the longitudinal river with headwaters in the Appalachians or farther northeast. This drainage extended downstream westward and delivered sediments into the Permian Basin near the west terminus of the Laurentia-Gondwana suture. Estimated rates of deposition and proportions of zircons from more local (Grenville) versus more distal (Pan-African) sources indicate that river strength decreased throughout early Permian time. Primary sediment delivery pathway was augmented by minor input from the Ancestral Rocky Mountains and wind deflation of fluvial sediments north and east of the basin. Slope failure associated with early Permian deposition in the southeastern margin of the Midland Basin triggered gravity flows leading to submarine fan deposition.  相似文献   

Glacial deep-water properties in the west-equatorial Pacific: bathyal thermocline near a depth of 2000 m     

J. C. Herguera  L. D. Stott  W. H. Berger 《Marine Geology》1991,100(1-4):201-206

The stable isotope stratigraphy of Planulina wüllerstorfi in three box cores from Ontong Java Plateau in the western equatorial Pacific shows that there existed a bathyal thermocline near the depth of 2000 m during glacial time. Waters below the boundary were colder by about 1°C, those above were about the same as now. The deep waters were slightly enriched and the upper waters depleted in nutrients, compared with present values. The differences in δ¹³C to the present (after correcting for the global change) are of the order of 0.1‰ more positive (above 2000 m) and 0.1‰ more negative (below), corresponding to changes in phosphate of the order of 0.1 μmol/kg (less phosphate above, and more below the boundary).  相似文献   

Deep North Atlantic freshening simulated in a coupled climate model     

Peili Wu  Richard Wood  Peter Stott  Gareth S. Jones 《Progress in Oceanography》2007,73(3-4):370

The observed recent freshening trend in the deep North Atlantic and the Labrador Sea is investigated in three forced ensembles and a long control simulations using the HadCM3 coupled ocean–atmosphere–sea-ice climate model. The 40 yr freshening trend during the late half of the 20th century is captured in the all forcings ensemble that applies all major external (natural and anthropogenic) forcing factors. Each ensemble has four members with different initial conditions taking from the control run at a 100 yr interval. No similar freshening trend is found in each of the four corresponding periods of the control simulation. However, there are five large freshening events in a 1640 yr period of the control run, each following a sudden salinity increase. A process analysis revealed that the increase in salinity in the Labrador Sea is closely linked to deep convections while the following freshening trend is accompanied by a period of very weak convective activities.The fact that none of the five large freshening events appears in the four corresponding periods following the initial conditions of the four members of the all forcings ensemble suggest that external forcings may have contributed to triggering the events. Further analyses of two other ensemble simulations (natural forcings only and anthropogenic forcings only) have shown that natural rather than anthropogenic factors are responsible. Based on our model results, we can not attribute the simulated freshening to anthropogenic climate change.  相似文献   

Glacial Deposition Along an Ice-Contact Slope: An Example from the Southern Lake District, Chile   总被引：1，自引：0，他引：1  

Susan E. Turbek  & Thomas V. Lowell 《Geografiska Annaler: Series A, Physical Geography》1999,81(2):325-346

Glacially derived sediments and structures vary systematically with topographic position along ice-contact slopes near the margin of former temperate piedmont glaciers in the southern Lake District, Chile. Features along lower positions of the slopes include glaciolacustrine sediments and large-scalethrusting. Middle slope features include low-angle subglacial thrusting of thin slices of lacustrine sediment. Upper slope features include high-angle thrusting, and lodgement and flow till. Locally, the same ordering of these features occurs in vertical sequence.
A common theme that unifies the processes represented by these features is the distribution of hydrostatic pressure. Thicker ice (producing higher glacier overburden pressures) and aquicludes of fine-grained sediments toward the center of the basin result in high hydrostatic pressures, whereas thin ice and porous out-wash reduce these pressures at the top of the ice-contact slopes.However, such a distribution cannot completely explain the observed vertical sequences; hence, local variations in hydrostatic pressure because of lithologic contrasts probably play a role. Nowhere along the ice-contact slope are pervasively deformed glacial sediments observed; therefore they cannot be invoked to explain the low glacier profiles of these piedmont glacier lobes.  相似文献   

The United Nations'' department for policy coordination and sustainable development (DPCSD)     

Lowell Flanders 《Global Environmental Change》1997,7(4):391-394

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Highest rates of regional climate warming over the last decades and assessment of the role of natural and anthropogenic factors     

I. I. Mokhov  A. A. Karpenko  P. A. Stott 《Doklady Earth Sciences》2006,406(1):158-162

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Sensitivities of the equilibrium line altitude to temperature and precipitation changes along the Andes   总被引：1，自引：0，他引：1  

Esteban A. Sagredo  Summer Rupper  Thomas V. Lowell 《Quaternary Research》2014

Equilibrium line altitudes (ELAs) of alpine glaciers are sensitive indicators of climate change and have been commonly used to reconstruct paleoclimates at different temporal and spatial scales. However, accurate interpretations of ELA fluctuations rely on a quantitative understanding of the sensitivity of ELAs to changes in climate. We applied a full surface energy- and mass-balance model to quantify ELA sensitivity to temperature and precipitation changes across the range of climate conditions found in the Andes. Model results show that ELA response has a strong spatial variability across the glaciated regions of South America. This spatial variability correlates with the distribution of the present-day mean climate conditions observed along the Andes. We find that ELAs respond linearly to changes in temperature, with the magnitude of the response being prescribed by the local lapse rates. ELA sensitivities to precipitation changes are nearly linear and are inversely correlated with the emissivity of the atmosphere. Temperature sensitivities are greatest in the inner tropics; precipitation becomes more important in the subtropics and northernmost mid-latitudes. These results can be considered an important step towards developing a framework for understanding past episodes of glacial fluctuations and ultimately for predicting glacier response to future climate changes.  相似文献   

Three-dimensional reconstruction of fluvial surface sedimentology and topography using personal mobile laser scanning     

Richard David Williams  Marie-Lou Lamy  Georgios Maniatis  Eilidh Stott 《地球表面变化过程与地形》2020,45(1):251-261

High-resolution quantification of fluvial topography has been enabled by a number of geomatics technologies. Hyperscale surveys with spatial extents of <1 km² have been widely demonstrated by means of terrestrial laser scanning (TLS) and structure-from-motion (SfM) photogrammetry. Recent advances in the development and integration of global navigation satellite system (GNSS), inertial measurement unit (IMU) and lightweight laser scanning technologies are now resulting in the emergence of personal mobile laser scanners (MLS) that have the potential to increase data acquisition and processing rates by one to two orders of magnitude compared to TLS/SfM, and thus challenge the recent dominance of these technologies. This investigation compares a personal MLS survey using a Leica Pegasus Backpack that integrates Velodyne Puck VLP-16 sensors, and a multi-station static TLS survey using a Riegl VZ-1000 scanner, to produce digital elevation models (DEMs) and surface sedimentology maps. The assessment is undertaken on a 500 m long reach of the braided River Feshie. Comparison to 107 independent real-time kinematic (RTK)-GNSS check points resulted in similar mean error (ME) and standard deviation error (SDE) for TLS (ME = −0.025 m; SDE = 0.038 m) and personal MLS (ME = −0.014 m; SDE = 0.019 m). Direct cloud-to-cloud (C2C) comparison between a sample of TLS and personal MLS observations (2.8 million points) revealed that C2C distances follow a sharply decreasing Burr distribution (a = 2.35, b = 3.19, rate parameter s = 9.53). Empirical relationships between sub-metre topographic variability and median sediment grain size (10–100 mm) demonstrate that surface roughness from personal MLS can be used to map median grain size. Differences between TLS and personal MLS empirical relationships suggest such relationships are dependent on survey technique. Personal MLS offers distinct logistical advantages over SfM photogrammetry and TLS for particular survey situations and is likely to become a widely applied technique. © 2019 John Wiley & Sons, Ltd.  相似文献