Glacier reconstruction and mass‐balance modelling as a geomorphic and palaeoclimatic tool     

Simon J. Carr  Sven Lukas  Stephanie C. Mills 《地球表面变化过程与地形》2010,35(9):1103-1115

The reconstruction of former mountain glaciers has long been used to examine the implications of rapid climate shifts, for example at the last glacial–interglacial transition, and for evaluating asynchronous behaviour of mountain glaciers compared with mid‐latitude ice sheets during the Late Quaternary. Glacier reconstruction has also been used as a source of palaeoclimatic information, based on the recognition of empirical relationships between glaciers and climate. This paper reviews the application and implications of a recently revised method of glacier reconstruction (Carr and Coleman, 2007 ), based around glaciological principles of mass‐balance. This study examines how this approach can be used to test geomorphological interpretations of former mountain glaciation and also to infer precipitation fields at sites of former glaciation. Sites of Younger Dryas niche and icefield glaciation in the British Isles demonstrate how this method can verify interpretations of marginal glaciation and begin to understand the different behaviour of outlet glaciers within the same environmental regime. Examination of a site of former niche glaciation in Southern Africa demonstrates how glacier reconstruction may be used to infer annual and seasonal precipitation values and strongly supports the idea that winter precipitation in Lesotho and SE South Africa was substantially greater than present‐day values during the last glacial cycle. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A multi-method approach for the identification and quantification of water balance components of two lentic small water bodies     

Lukas P. Loose  Jens Lange  Aaron Budde  Barbara Herbstritt  Nicola Fohrer  Uta Ulrich 《水文研究》2024,38(1):e15058

The protection of the globally widespread lentic small water bodies (LSWB) must be based on detailed knowledge about their hydrological connectivity and water balance. The study aimed to identify and quantify water balance components as well as surface-groundwater interaction of two LSWB in a characteristic lowland region with a combination of different methods. This includes the collection of hydrological data and the use of bromide and water stable isotopes (δ²H and δ¹⁸O) as tracers. With their help, mixing models were established, and daily water balances were assessed. The results show a strong bidirectional interaction of both LSWB systems with shallow groundwater. Bromide and stable isotope tracers allowed for the identification of the most relevant in- and outflow sources and pathways. Thereby, isotope data revealed isotopic enrichment typical for open-water bodies and only minor precipitation inputs mainly relevant at the end of the dry season. Water balance calculations suggested accentuated seasonal dynamics that were strongly influenced by shallow groundwater, which represented large inputs into both LSWB. By that, different phases could be identified, with high inflow rates in winter and spring and decreasing fluxes in summer. In one LSWB, a drainage system was found to have a major impact next to the shallow groundwater interaction. The findings of this research provide detailed insights into the influence and importance of shallow groundwater for LSWB in lowland regions. This impacts the diffuse input of agricultural pollutants into these ecologically important landscape features.  相似文献   

Interaction between warm Atlantic‐sourced waters and the East Greenland Current in northern Denmark Strait (68°N) during the last 10 600 cal a BP          下载免费PDF全文

Kerstin Perner  Anne E. Jennings  Matthias Moros  John T. Andrews  Lukas Wacker 《第四纪科学杂志》2016,31(5):472-483

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Statistically Extrapolated Nowcasting of Summertime Precipitation over the Eastern Alps     

Min CHEN  Benedikt BICA  Lukas TÜ  CHLER  Alexander KANN  Yong WANG 《大气科学进展》2017,34(7):925-938

This paper presents a new multiple linear regression(MLR) approach to updating the hourly, extrapolated precipitation forecasts generated by the INCA(Integrated Nowcasting through Comprehensive Analysis) system for the Eastern Alps.The generalized form of the model approximates the updated precipitation forecast as a linear response to combinations of predictors selected through a backward elimination algorithm from a pool of predictors. The predictors comprise the raw output of the extrapolated precipitation forecast, the latest radar observations, the convective analysis, and the precipitation analysis. For every MLR model, bias and distribution correction procedures are designed to further correct the systematic regression errors. Applications of the MLR models to a verification dataset containing two months of qualified samples,and to one-month gridded data, are performed and evaluated. Generally, MLR yields slight, but definite, improvements in the intensity accuracy of forecasts during the late evening to morning period, and significantly improves the forecasts for large thresholds. The structure–amplitude–location scores, used to evaluate the performance of the MLR approach,based on its simulation of morphological features, indicate that MLR typically reduces the overestimation of amplitudes and generates similar horizontal structures in precipitation patterns and slightly degraded location forecasts, when compared with the extrapolated nowcasting.  相似文献   

Component mobility at 900 °C and 18 kbar from experimentally grown coronas in a natural gabbro     

Lukas M. Keller  Bernd Wunder  Richard Wirth 《Geochimica et cosmochimica acta》2008,72(17):4307-4322

Several approximately 100-μm-wide reaction zones were grown under experimental conditions of 900 °C and 18 kbar along former olivine-plagioclase contacts in a natural gabbro. The reaction zone comprises two distinct domains: (i) an irregularly bounded zone with idiomorphic grains of zoisite and minor corundum and kyanite immersed in a melt developed at the plagioclase side and (ii) a well-defined reaction band comprising a succession of mineral layers forming a corona structure around olivine. Between the olivine and the plagioclase reactant phases we observe the following layer sequence: olivine|pyroxene|garnet|partially molten domain|plagioclase. Within the pyroxene layer two micro-structurally distinct layers comprising enstatite and clinopyroxene can be discerned. Chemical potential gradients persisted for the CaO, Al₂O₃, SiO₂, MgO and FeO components, which drove diffusion of Ca, Al and Si bearing species from the garnet-matrix interface to the pyroxene-olivine interface and diffusion of Mg- and Fe-bearing species in the opposite direction. The systematic mineralogical organization and chemical zoning across the corona suggest that the olivine corona was formed by a “diffusion-controlled” reaction. We estimate a set of diffusion coefficients and conclude that L_AlAl < L_CaCa < (L_SiSi, L_FeFe) < L_MgMg during reaction rim growth.  相似文献   

Estimation of a maximum Lu diffusion rate in a natural eclogite garnet     

Susanne Skora  Lukas P. Baumgartner  Nancy J. Mahlen  Thomas J. Lapen  Clark M. Johnson  François Bussy 《Swiss Journal of Geoscience》2008,101(3):637-650

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Ca2Mg(NO3)6×12H2O–structural investigations on a new compound retrieved from chimney deposits of a combined heat and power plant     

Volker Kahlenberg  Richard Tessadri  Martina Tribus  Daniela Schmidmair  Lukas Perfler  Udo Haefeker 《Mineralogy and Petrology》2014,108(5):633-643

Phase analysis of incrustations retrieved from chimney deposits of a combined heat and power plant in Malchow/Germany by X-ray powder diffraction gave evidence for the existence of a previously unknown hydrous calcium magnesium nitrate. Optical investigations of the sample showed the presence of colorless platy crystals with a maximum diameter of about 250 μm embedded in a partly polycrystalline and partly glassy matrix. Aided by EDX-analysis and Raman spectroscopy, a single-crystal diffraction study performed at ambient conditions demonstrated that the material represents a phase with composition Ca₂Mg(NO₃)₆×12H₂O. Basic crystallographic data are as follows: trigonal symmetry, space group type R \( \overline{3} \) , a?=?10.5583(5) Å, c?=?19.5351(10) Å, V?=?1885.97(16) ų, Z?=?3, (R(|F|) = 0.0248). The magnesium ions are coordinated by water molecules to form distorted Mg(H₂O)₆-octahedra. The calcium atoms are surrounded by nine ligands. The resulting CaO₉ tricapped trigonal prisms involve oxygen atoms from additional water moieties as well as from three different bidentate nitrate groups, respectively. Hydrogen bonds link one octahedron with two adjacent prisms into trimers. The trimers in turn are stacked in columns running parallel to [001]. Further hydrogen bonding between neighboring columns results in the formation of a three-dimensional network. To our best knowledge, Ca₂Mg(NO₃)₆×12H₂O represents a new structure type. However, column-like topologies with rods consisting of different types of polyhedra have been also observed in other trigonal hydrous nitrates. The structural relationships between these compounds are discussed. It is interesting to note that in previous phase equilibrium studies on the ternary system Ca(NO₃)₂-Mg(NO₃)₂-H₂O no other hydrous double salt has been described. Finally, the results of the structure analysis allowed a qualitative and quantitative phase analysis of the crystalline part of the chimney deposit by the Rietveld method.  相似文献   

Reaction rim growth in the system MgO-Al2O3-SiO2 under uniaxial stress     

Lutz Christoph Götze  Rainer Abart  Erik Rybacki  Lukas M. Keller  Elena Petrishcheva  Georg Dresen 《Mineralogy and Petrology》2010,99(3-4):263-277

We synthesize reaction rims between thermodynamically incompatible phases in the system MgO-Al₂O₃-SiO₂ applying uniaxial load using a creep apparatus. Synthesis experiments are done in the MgO-SiO₂ and in the MgO-Al₂O₃ subsystems at temperatures ranging from 1150 to 1350 °C imposing vertical stresses of 1.2 to 29 MPa at ambient pressure and under a constant flow of dry argon. Single crystals of synthetic and natural quartz and forsterite, synthetic periclase and synthetic corundum polycrystals are used as starting materials. We produce enstatite rims at forsterite-quartz contacts, enstatite-forsterite double rims at periclase-quartz contacts and spinel rims at periclase-corundum contacts. We find that rim growth under the “dry” conditions of our experiments is sluggish compared to what has been found previously in nominally “dry” piston cylinder experiments. We further observe that the nature of starting material, synthetic or natural, has a major influence on rim growth rates, where natural samples are more reactive than synthetic ones. At a given temperature the effect of stress variation is larger than what is anticipated from the modification of the thermodynamic driving force for reaction due to the storage of elastic strain energy in the reactant phases. We speculate that this may be due to modification of the physical properties of the polycrystals that constitute the reaction rims or by deformation under the imposed load. In our experiments rim growth is very sluggish at forsterite-quartz interfaces. Rim growth is more rapid at periclase-quartz contacts. The spinel rims that are produced at periclase-corundum interfaces show parabolic growth indicating that reaction rim growth is essentially diffusion controlled. From the analysis of time series done in the MgO-Al₂O₃ subsystem we derive effective diffusivities for the Al₂O₃ and the MgO components in a spinel polycrystal as ${\rm D}_{MgO} = 1.4 \pm 0.2 \cdot 10^{-15}$  m²/s and ${\rm D}_{Al_2O_3} = 3.7 \pm 0.6 \cdot 10^{-16}$  m²/s for T?=?1350 °C and a vertical stress of 2.9 MPa.  相似文献   

UNFCCC before and after Paris – what's necessary for an effective climate regime?     

Lukas Hermwille  Wolfgang Obergassel  Hermann E. Ott  Christiane Beuermann 《Climate Policy》2013,13(2):150-170

What can reasonably be expected from the UNFCCC process and the climate conference in Paris 2015? To achieve transformative change, prevailing unsustainable routines embedded in socio-economic systems have to be translated into new and sustainable ones. This article conceptualizes the UNFCCC and the associated policy processes as a catalyst for this translation by applying a structurational regime model. This model provides an analytical distinction of rules (norms and shared meaning) and resources (economic resources as well as authoritative and allocative power) and allows us to conceptualize agency on various levels, including beyond nation states. The analysis concludes that the UNFCCC's narrow focus on emission targets, which essentially is a focus on resources, has proven ineffective. In addition, the static division of industrialized and developing countries in the Convention's annexes and the consensus-based decision-making rules have impeded ambitious climate protection. The article concludes that the UNFCCC is much better equipped to provide rules for climate protection activities and should consciously expand this feature to improve its impact.

Policy relevance

The international community is negotiating a new global climate agreement, to be adopted at the Conference of the Parties (COP 21) in December 2015 in Paris and to be applicable from 2020. This article analyses the successes and limitations the UNFCCC has had so far in combating climate change and it develops recommendations on how to enhance efforts within and beyond the framework of the Convention. From our analysis we derive two main recommendations for an effective and structurationally balanced treaty: First, multidimensional mitigation contributions going beyond emission targets could strongly improve countries’ abilities to tailor their contributions around national political discourses. Second, the UNFCCC regime should be complemented with another treaty outside of the UNFCCC framework. This ‘Alliance of the Ambitious’ would allow the pioneers of climate protection to move ahead and enjoy the benefits of cooperation. The dynamics generated through such a club approach could be fed back into the UNFCCC, leading to increased ambition by others in future commitment cycles.  相似文献   

The behavior of Mg, Fe, and Ni during the replacement of olivine by orthopyroxene: experiments relevant to mantle metasomatism     

Ralf Milke  Rainer Abart  Lukas Keller  Dieter Rhede 《Mineralogy and Petrology》2011,103(1-4):1-8

Replacement of olivine by orthopyroxene is a frequently observed phenomenon in mantle metasomatism. In order to study element redistribution in SiO₂ metasomatism we synthesised orthopyroxene reaction rims at the contacts between forsterite-rich olivine and quartz. The orthopyroxene rims grew from the original quartz-olivine interface into both directions implying counterdiffusion of iron/magnesium and silicon. Following local equilibrium partitioning the X_Fe is lower in the orthopyroxene than in the reactant olivine at the olivine-orthopyroxene replacement front. The resulting local iron excess is compensated by formation of orthopyroxene with a higher X_Fe at the quartz-orthopyroxene interface, which is out of equilibrium with the reactant olivine. This is facilitated through short circuit diffusion along grain boundaries within the orthopyroxene rim. Due to the low capacity of orthopyroxene to accommodate Ni, this component is forced to diffuse back into the olivine producing a Ni enriched zone ahead of the replacement front. This leads to Ni contents in the orthopyroxene rim, which are higher than what is expected in equilibrium with the unaltered olivine. Taking quartz as a proxy for a silica rich fluid or liquid metasomatising agent, we conclude that the overall element fractionation between olivine and the silica rich phase may deviate from equilibrium partitioning so that the Fe and Ni concentrations in the orthopyroxene which is in contact with quartz are higher than in equilibrium with the reactant olivine. This indicates that kinetic fractionation is important for the chemical evolution of both the mantle rocks and the metasomatising agents.  相似文献