Quantifying rates and processes of landscape evolution     

Arjun M. Heimsath  Oliver Korup 《地球表面变化过程与地形》2012,37(2):249-251

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Seasonal temperatures for the past ∼400 years reconstructed from diatom and chironomid assemblages in a high-altitude lake (Lej da la Tscheppa,Switzerland)     

Lucien von Gunten  Oliver Heiri  Christian Bigler  Jacqueline van Leeuwen  Carlo Casty  André F. Lotter  Michael Sturm 《Journal of Paleolimnology》2008,39(3):283-299

We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established using ²¹⁰Pb analysis using a constant-rate-of-supply model, and validated with ¹³⁷Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and can be successfully used to track seasonal temperature trends.  相似文献   

500 years of trophic-state history of a hypertrophic Dutch dike-breach lake     

Emiliya P. Kirilova  Maarten van Hardenbroek  Oliver Heiri  Holger Cremer  André F. Lotter 《Journal of Paleolimnology》2010,43(4):829-842

We present a palaeolimnological study encompassing five centuries of trophic-state change of the dike-breach lake De Waay located on the Rhine-Meuse delta (the Netherlands). Diatom-inferred total phosphorus (TP) concentrations indicate hypertrophic epilimnetic conditions (>300 μg l⁻¹ TP) since the formation of the lake in the fifteenth century until the end of the eighteenth century. Cladocera data support the reconstructed trophic state and indicate turbid conditions in lake De Waay during this period. High inferred TP concentrations as well as the amount of Ti in the sediment reflect numerous flooding events. From the nineteenth century onwards reconstructed TP concentrations decreased to 40–150 μg l⁻¹ due to improvements in sewage and dike systems that considerably diminished direct river flooding and seepage-derived nutrients. As a consequence, the increased stability of littoral habitats led to an increased diversity of the Cladocera assemblages. The most significant decrease in TP concentrations to ~40 μg l⁻¹ occurred between about 1900 and 1930. This mesotrophic phase was a consequence of the isolation of the lake from catchment drainage and the introduction of a highly elaborate flood control during this period. However, since the mid twentieth century a eutrophication trend is preserved in the record, likely related to increased agricultural activity in the vicinity of the lake. Our results emphasize that land-use and trophic-state history must be taken into account when evaluating the ecological status of lakes for water management and protection actions, especially for lakes in landscapes that are strongly modified by human action.  相似文献   

Meteorology and oceanography of the Atlantic sector of the Southern Ocean—a review of German achievements from the last decade     

Hartmut H. Hellmer  Monika Rhein  Günther Heinemann  Janna Abalichin  Wafa Abouchami  Oliver Baars  Ulrich Cubasch  Klaus Dethloff  Lars Ebner  Eberhard Fahrbach  Martin Frank  Gereon Gollan  Richard J. Greatbatch  Jens Grieger  Vladimir M. Gryanik  Micha Gryschka  Judith Hauck  Mario Hoppema  Oliver Huhn  Torsten Kanzow  Boris P. Koch  Gert König-Langlo  Ulrike Langematz  Gregor C. Leckebusch  Christof Lüpkes  Stephan Paul  Annette Rinke  Bjoern Rost  Michiel Rutgers van der Loeff  Michael Schröder  Gunther Seckmeyer  Torben Stichel  Volker Strass  Ralph Timmermann  Scarlett Trimborn  Uwe Ulbrich  Celia Venchiarutti  Ulrike Wacker  Sascha Willmes  Dieter Wolf-Gladrow 《Ocean Dynamics》2016,66(11):1379-1413

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Special Issue on Applications of Wavelets in the Geosciences     

Margaret A. Oliver 《Mathematical Geosciences》2009,41(6):609-610

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Benchmarking spatial joins a la carte     

Oliver Gunther  Philippe Picouet  Jean-Marc Saglio  Michel Scholl  Vincent Oria 《International journal of geographical information science》2013,27(7):639-655

Spatial joins are join operations that involve spatial data types and operators. Spatial access methods are often used to speed up the computation of spatial joins. This paper addresses the issue of benchmarking spatial join operations. For this purpose, we first present a WWW-based benchmark generator to produce sets of rectangles. Using a Web browser, experimenters can specify the number of rectangles in a sample, as well as the statistical distributions of their sizes, shapes, and locations. Second, using the generator and a well-defined set of statistical models we define several tests to compare the performance of three spatial join algorithms: nested loop, scan-and-index, and synchronized tree traversal. We also added two real-life data sets from the Sequoia 2000 storage benchmark. Our results show that the relative performance of the different techniques mainly depends on the selectivity factor of the join predicate. All of the statistical models and algorithms are available on the Web, which allows for easy verification and modification of our experiments.  相似文献   

Generalized LSG models with spatially varying Coriolis parameter     

Marcel Oliver  Sergiy Vasylkevych 《地球物理与天体物理流体动力学》2013,107(3):259-276

In this paper, we derive and study approximate balance models for nearly geostrophic shallow water flow where the Coriolis parameter is permitted to vary across the domain as long as it remains nondegenerate. This situation includes, for example, the β-plane approximation to the shallow water equations at mid-latitudes. Our approach is based on changing configuration space coordinates in the underlying variational principle in such a way that consistent asymptotics in the transformed Lagrangian leads to a degenerate Lagrangian structure. In this paper, we restrict our attention to first-order models. We show that the resulting models can be formulated in terms of an advected potential vorticity with a nonlinear vorticity inversion relation. We study the associated solvability conditions and identify a subfamily of models for which these conditions are satisfied without additional restrictions on the data. Finally, we provide the link between our framework and the theory of constrained Hamiltonian systems.  相似文献   

A parcel formulation of Hamiltonian layer models     

O. Bokhove  M. Oliver 《地球物理与天体物理流体动力学》2013,107(6):423-442

Starting from the three-dimensional hydrostatic primitive equations, we derive Hamiltonian N-layer models with isentropic tropospheric and isentropic or isothermal stratospheric layers. Our construction employs a new parcel Hamiltonian formulation which describes the fluid as a continuum of Hamiltonian ordinary differential equations bound together by integral transport laws. In particular, we show that this parcel Hamiltonian structure is compatible with the stacking of layers under isentropic or isothermal constraints. The appeal of the parcel formulation is the simplification of various calculations, in particular the derivation of the continuum Poisson bracket and the proof of the Jacobi identity. A comparison and connection is made between the Hamiltonian dynamics of fluid parcels and the Hamiltonian system of partial differential equations. The parcel formulation can be seen as a precursor and tool for the study of Hamiltonian numerical schemes.  相似文献   

Mobile evaporite controls on the structural style and evolution of rift basins: Danish Central Graben,North Sea     

Oliver B. Duffy  Rob L. Gawthorpe  Matthew Docherty  Simon H. Brocklehurst 《Basin Research》2013,25(3):310-330

The Southern Tail‐End Graben, Danish Central Graben, is characterized by a lateral variation in the thickness and mobility of pre‐rift Zechstein Supergroup evaporites, allowing investigation of how supra‐basement evaporite variability influences rift structural style and tectono‐stratigraphy. The study area is divided into two structural domains based on interpretations of the depositional thickness and mobility of the Zechstein Supergroup. Within each domain, we examine the overall basin morphology and the structural styles in the pre‐Zechstein and supra‐Zechstein (cover) units. Furthermore, integration of two‐way travel‐time (TWT)‐structure and ‐thickness maps allows fault activity and evaporite migration maps to be generated for pre‐ and syn‐rift stratal units within the two domains, permitting constraints to be placed on: (i) the timing of activity on pre‐Zechstein and cover faults and (ii) the onset, duration and migration direction of mobile evaporites. The northern domain is interpreted to be free from evaporite‐influence, and has developed in a manner typical of brittle‐only, basement‐involved rifts. Syn‐rift basins display classical half‐graben geometries bounded by thick‐skinned faults. In contrast, the southern domain is interpreted to be evaporite‐influenced, and cover structure reflects a southward increase in the thickness and mobility of the Zechstein Supergroup evaporites. Fault‐related and evaporite‐related folding is prominent in the southern domain, together with variable degrees of decoupling of sub‐Zechstein and cover fault and fold systems. The addition of mobile evaporites to the rift results in: (i) complex and spatially variable modes of tectono‐stratigraphic evolution; (ii) syn‐rift stratal geometries which are condensed above evaporite swells and over‐thickened in areas of withdrawal; (iii) compartmentalized syn‐rift depocentres; and (iv) masking of rift‐related megasequence boundaries. Through demonstrating these deviations from the characteristics of rifts free from evaporite influence, we highlight the first order control evaporites may exert upon rift structural style and the distribution and thicknesses of syn‐rift units.  相似文献   

Location Based Social Networks – Definition,Current State of the Art and Research Agenda     

Oliver Roick  Susanne Heuser 《Transactions in GIS》2013,17(5):763-784

The growing penetration of GPS equipped smartphones allowing users to constantly share geographic information on their current whereabouts has led the way to an augmentation of existing Social Network Sites with location‐based features or the creation of new ones exclusively around geographic information. Within these Location Based Social Networks vast amounts of geographic information are allocated, which attracted the attention of researchers with various scientific backgrounds. This article presents a comprehensive definition of this special type of Social Network Site and an overview of research activities, which are currently conducted using the data. Finally, a research agenda for GIScience is drawn from existing research directions.  相似文献