Geospatial analysis of controls on subglacial bedform morphometry in the New York Drumlin Field – implications for Laurentide Ice Sheet dynamics     

Dale P. Hess  Jason P. Briner 《地球表面变化过程与地形》2009,34(8):1126-1135

The outline and trend of 6566 subglacial bedforms in the New York Drumlin Field have been digitized from digital elevation data. A spatial predictive model has been used to extend values of bedform elongation over an area measuring 200 km × 110 km. The resulting surface is used in conjunction with depth‐to‐bedrock data and an assumed duration of ice residence to test three proposed controls on bedform elongation. Upon comparison, the resulting display of morphometry is best explained by differences in ice velocity across the field of study. The existence of multiple zones of fast‐moving ice located along the southern margin of the Laurentide Ice Sheet is implied by the observed patterns of bedform elongation and orientation. We present two interpretations that are consistent with the observations. First, enhanced basal sliding caused by decreasing effective pressure near a calving margin is suggested as a possible mechanism by which localized fast ice flow is initiated and maintained. Second, topographically controlled ice streams likely occupied the fjord‐like troughs of the Appalachian Upland northern rim. Contrary to previous understanding of the Laurentide southern margin in New York State, the resulting palaeoglaciological reconstruction illustrates a dynamic mosaic of ice stream and/or outlet glacier activity. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Sand–mud couplets deposited by spontaneous remobilization of subaqueous transitional flows     

Woong Mo Koo  David Mohrig  James Buttles  Daniel Sturmer  Anna Pontén  Thomas Hess 《Sedimentology》2020,67(1):78-95

Clean basal and capping argillaceous sandstone couplets in deep water settings have been previously interpreted as the result of spatially segregated turbidity currents and debris flows or spatio-temporal transitioning of a turbulent flow to a transitional/laminar state. However, this paper presents three-dimensional laboratory experiments demonstrating that a single sediment-gravity flow can develop sand–mud couplets by autogenic remobilization of sediments that are still in the process of being deposited. This remobilization appears common to flows composed of mixtures of sand and mud with viscosities and strengths measurably greater than water, but not so high as to fully suppress the settling of sand through the depositional current. Dewatering in the early sand deposit acts to lubricate the basal portion of the increasingly muddy upper division of the flow, causing it to accelerate downslope, triggering a secondary flow with a sediment composition distinct from the original mixture. Sediment deposition and remobilization processes in a single sediment-gravity flow and their resultant deposit were imaged acoustically and cored at representative locations within the deposit. The acoustic data and cores show sand–mud couplets that are qualitatively similar to interpreted turbidite–debrite-like couplets in natural systems.  相似文献   

Micro-climate influence on reference evapotranspiration estimates in wetlands     

J. Kelvin  R.J. Harding  T.M. Hess 《水文科学杂志》2017,62(3):378-388

Temperature and relative humidity measurements were made within and outside a lowland fen in eastern England during 2009 and 2010. Summer temperatures were found to be on average 0.24°C lower within the fen than outside, whilst summer vapour pressures were found to be on average 0.074 kPa higher within the fen. In contrast, winter temperatures were found to be higher within the fen by an average of 0.03°C. These differences may be expected to influence evapotranspiration estimates derived using data from each of the sites. The influence of the location of meteorological measurements on evapotranspiration estimates was therefore evaluated. The existence of a wetland microclimate results in up to a 7% reduction in annual reference evapotranspiration compared to a site surrounded by arable farmland only 5.5 km away.  相似文献   

A 15 000‐year record of climate change in northern New Mexico,USA, inferred from isotopic and elemental contents of bog sediments     

Luz M. Cisneros‐Dozal  Jeffrey M. Heikoop  Julianna Fessenden  R. Scott Anderson  Philip A. Meyers  Craig D. Allen  Marcey Hess  Toti Larson  George Perkins  Michael Rearick 《第四纪科学杂志》2010,25(6):1001-1007

Elemental (C, N, Pb) and isotopic (δ¹³C, δ¹⁵N) measurements of cored sediment from a small bog in northern New Mexico reveal changes in climate during the Late Pleistocene and Holocene. Abrupt increases in Pb concentration and δ¹³C values ca. 14 420 cal. YBP indicate significant runoff to the shallow lake that existed at that time. Weathering and transport of local volcanic rocks resulted in the delivery of Pb‐bearing minerals to the basin, while a ¹³C‐enriched terrestrial vegetation source increased the δ¹³C values of the sedimentary material. Wet conditions developed over a 300 a period and lasted for a few hundred years. The Younger Dryas period (ca. 12 700–11 500 cal. YBP) caused a reduction in terrestrial productivity reflected in decreasing C/N values, δ¹⁵N values consistently greater than 0‰ and low organic content. By contrast, aquatic productivity increased during the second half of this period, evidenced by increasing δ¹³C values at the time of highest abundance of algae. Dry conditions ca. 8 000–6 000 cal. YBP were characterised by low organic carbon content and high Pb concentrations, the latter suggesting enhanced erosion and aeolian transport of volcanic rock. The range in δ¹³C, δ¹⁵N and C/N values in the sedimentary record fall within the range of modern plants, except during the periods of runoff and drought. The sedimentary record provides evidence of natural climate variability in northern New Mexico, including short‐ (multi‐centennial) and long‐(millennial) term episodes during the Late Pleistocene and Holocene. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Estimating the impact of rural land management changes on catchment runoff generation in England and Wales     

T. M. Hess  I. P. Holman  S. C. Rose  Z. Rosolova  A. Parrott 《水文研究》2010,24(10):1357-1368

Although reviews of the scientific literature have failed to demonstrate conclusive evidence for the impact of rural land management on peak runoff rates, increasing emphasis is being placed by policy makers on its role in catchment‐scale flood risk management. Poor soil and field conditions can lead to higher rates of runoff from extreme rainfall events; however, the improvement of land condition will lead to differing runoff responses depending on land use, soil type and climatic regime. This study has evaluated the relative impact of improvement of field and soil conditions on peak daily runoff rates for a range of soils and vegetation cover types across England and Wales. It has shown that rural land management changes could be expected to make a positive contribution to sustainable flood risk management, especially for more frequent events. The greatest relative reduction in runoff can be achieved through the improvement of degraded permeable soils under managed grassland in drier regions. Taking a plausible scenario of land management improvement in arable and grassland systems, the relative reduction in peak runoff was estimated for 518 policy units as defined in the Environment Agency's Catchment Flood Management Plans. For the 1 in 100 year event, there were only a few policy units where the expected reduction in runoff exceeded 5%. Rural land management practices which are likely to be beneficial to flood risk management may afford some protection to areas where structural measures may not be implemented for cost–benefit reasons, and may help to offset some of the anticipated increases in flood risk associated with climate change. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The branch-cut quantum gravity with a self-coupling inflation scalar field: The wave function of the Universe     

Fridolin Weber  Peter O. Hess  Benno Bodmann  José de Freitas Pacheco  Dimiter Hadjimichef  Marcelo Netz-Marzola  Geovane Naysinger  Moisés Razeira  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230148

This paper focuses on the implications of a commutative formulation that integrates branch-cutting cosmology, the Wheeler–DeWitt equation, and Hořava–Lifshitz quantum gravity. Building on a mini-superspace structure, we explore the impact of an inflaton-type scalar field on the wave function of the Universe. Specifically analyzing the dynamical solutions of branch-cut gravity within a mini-superspace framework, we emphasize the scalar field's influence on the evolution of the evolution of the wave function of the Universe. Our research unveils a helix-like function that characterizes a topologically foliated spacetime structure. The starting point is the Hořava–Lifshitz action, which depends on the scalar curvature of the branched Universe and its derivatives, with running coupling constants denoted as $g_i$. The corresponding wave equations are derived and are resolved. The commutative quantum gravity approach preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner formalism. Additionally, we delve into a mini-superspace of variables, incorporating scalar-inflaton fields and exploring inflationary models, particularly chaotic and nonchaotic scenarios. We obtained solutions for the wave equations without recurring to numerical approximations.  相似文献   

The branch-cut quantum gravity with a self-coupling inflation scalar field: Dynamical equations     

Fridolin Weber  Peter O. Hess  Benno Bodmann  José de Freitas Pacheco  Dimiter Hadjimichef  Marcelo Marzola  Geovane Naysinger  Moisés Razeira  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230152

This article focuses on the implications of the recently developed commutative formulation based on branch-cutting cosmology, the Wheeler–DeWitt equation, and Hořava–Lifshitz quantum gravity. Assuming a mini-superspace of variables, we explore the impact of an inflaton-type scalar field $\varphi (t)$ on the dynamical equations that describe the trajectories evolution of the scale factor of the Universe, characterized by the dimensionless helix-like function ${\ln }^{-1}[\beta (t)]$. This scale factor characterizes a Riemannian foliated spacetime that topologically overcomes the big bang and big crunch singularities. Taking the Hořava–Lifshitz action as our starting point, which depends on the scalar curvature of the branched Universe and its derivatives, with running coupling constants denoted as $g_i$, the commutative quantum gravity approach preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner formalism. We investigate both chaotic and nonchaotic inflationary scenarios, demonstrating the sensitivity of the branch-cut Universe's dynamics to initial conditions and parameterizations of primordial matter content. The results suggest a continuous connection of Riemann surfaces, overcoming primordial singularities and exhibiting diverse evolutionary behaviors, from big crunch to moderate acceleration.  相似文献   

Noncommutative branch-cut quantum gravity with a self-coupling inflaton scalar field: The wave function of the Universe     

Peter O. Hess  Fridolin Weber  Benno Bodmann  José de Freitas Pacheco  Dimiter Hadjimichef  Marcelo Netz-Marzola  Geovane Naysinger  Moisés Razeira  César A. Zen Vasconcellos 《Astronomische Nachrichten》2024,345(2-3):e230162

This article focuses on the implications of a noncommutative formulation of branch-cut quantum gravity. Based on a mini-superspace structure that obeys the noncommutative Poisson algebra, combined with the Wheeler–DeWitt equation and Hořava–Lifshitz quantum gravity, we explore the impact of a scalar field of the inflaton-type in the evolution of the Universe's wave function. Taking as a starting point the Hořava–Lifshitz action, which depends on the scalar curvature of the branched Universe and its derivatives, the corresponding wave equations are derived and solved. The noncommutative quantum gravity approach adopted preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner Formalism. In this work we delve deeper into a mini-superspace of noncommutative variables, incorporating scalar inflaton fields and exploring inflationary models, particularly chaotic and nonchaotic scenarios. We obtained solutions to the wave equations without resorting to numerical approximations. The results indicate that the noncommutative algebraic space captures low and high spacetime scales, driving the exponential acceleration of the Universe.  相似文献   

The effects of a minimal length on the Kerr metric     

L. Maghlaoui  P. O. Hess 《Astronomische Nachrichten》2024,345(2-3):e230151

The effects of a minimal length on the Kerr metric are studied within the pseudo-complex General Relativity (pcGR), which has a minimal length parameter and also depends on a $r$-dependent metric, allowing for the accumulation of dark energy around a star. The relevant parameters are the rotational Kerr parameter $a$, the mass of a black hole, and a parameter measuring the amount of dark energy accumulated. It is found that the metric is modified by a factor, depending on $r$, resulting in a maximal acceleration. This factor shows several singularities. For small black holes, the corresponding effective potentials exhibit potential barriers, avoiding the increase of the black hole's mass. It is found that the effects of a minimal length are only of importance for very small mass black holes and vanish for macroscopic black holes.  相似文献   

Monte Carlo Simulations of Multiphase Flow Incorporating Spatial Variability of Hydraulic Properties   总被引：4，自引：0，他引：4  

Hedeff I. Essaid  Kathryn M. Hess 《Ground water》1993,31(1):123-134

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