A NEW CHALLENGE FOR CLIMATE STUDIES IN GEOGRAPHY     

Brent Yarnal  Robert G. Crane  Andrew M. Carleton  Laurence S. Kalkstein 《The Professional geographer》1987,39(4):465-473

Greater emphasis is being placed on large-scale (synoptic and dynamic) climatology in geography. Concurrently, climatological research as a whole has evolved to view climate as a complex, integrated and interactive global system. In this context, we review new directions in large-scale climate studies in geography. We conclude that no matter at which climatic scale geographers are working, the new challenge is to integrate their research and teaching activities into a more holistic, global-systems approach while maintaining and improving their traditional strengths.  相似文献   

Multiple injected and natural conservative tracers quantify mixing in a stream confluence affected by acid mine drainage near Silverton,Colorado     

Laurence E. Schemel  Marisa H. Cox  Robert L. Runkel  Briant A. Kimball 《水文研究》2006,20(13):2727-2743

The acidic discharge from Cement Creek, containing elevated concentrations of dissolved metals and sulphate, mixed with the circumneutral‐pH Animas River over a several hundred metre reach (mixing zone) near Silverton, CO, during this study. Differences in concentrations of Ca, Mg, Si, Sr, and SO₄^2? between the creek and the river were sufficiently large for these analytes to be used as natural tracers in the mixing zone. In addition, a sodium chloride (NaCl) tracer was injected into Cement Creek, which provided a Cl^? ‘reference’ tracer in the mixing zone. Conservative transport of the dissolved metals and sulphate through the mixing zone was verified by mass balances and by linear mixing plots relative to the injected reference tracer. At each of seven sites in the mixing zone, five samples were collected at evenly spaced increments of the observed across‐channel gradients, as determined by specific conductance. This created sets of samples that adequately covered the ranges of mixtures (mixing ratios, in terms of the fraction of Animas River water, %AR). Concentratis measured in each mixing zone sample and in the upstream Animas River and Cement Creek were used to compute %AR for the reference and natural tracers. Values of %AR from natural tracers generally showed good agreement with values from the reference tracer, but variability in discharge and end‐member concentrations and analytical errors contributed to unexpected outlier values for both injected and natural tracers. The median value (MV) %AR (calculated from all of the tracers) reduced scatter in the mixing plots for the dissolved metals, indicating that the MV estimate reduced the effects of various potential errors that could affect any tracer. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Aspects of problematic acid-resistant,organic-walled microfossils (acritarchs) in the upper proterozoic of the north atlantic region     

G. Vidal 《Precambrian Research》1981,15(1):9-23

Proterozoic acritarchs are a heterogeneous group of acid-resistant, organic-walled microfossils of obscure biological affinities. The acritarch record is regarded as strongly baised by a combination of mechanisms, such as the character of the original ecosystems, depositional conditions, diagenetic history, and thermal and tectonic events.Three distinctive acritarch assemblages are recognized in Upper Proterozoic sequences in Scandinavia and Greenland. They can be compared with Upper Proterozoic (Upper Riphean and Vendian) assemblages previously reported from the Russian and Siberian platforms, China and elsewhere. Substantial taxonomic changes characterize these assemblages and are usually connected with the existence of major unconformities in the investigated rock sequences. The acritarch assemblages can be traced over vast areas and are considered as constituting a promising tool for the biostratigraphic correlation of the Upper Proterozoic and Lower Cambrian.  相似文献   

A palaeomagnetic and mineral magnetic study of the loess sequence at Liujiapo,Xian, China     

Laurence Thistlewood  Sun Jianzhong 《第四纪科学杂志》1991,6(1):13-26

Employing an average vertical sampling interval of 20 cm, oriented samples were collected from 26 m of the loess section at Liujiapo, near Xian, China in order to refine the existing magnetostratigraphic record. Palaeomagnetic results reveal two short reversed-polarity subzones within a profile of predominantly normally magnetised sediments, an interpretation that is at variance with previous results from this section and from other studies of Chinese loess. Investigation of sediment mineral-magnetic properties indicates a close correspondence between down-section variations in intensity of magnetisation, susceptibility and saturation isothermal Journal of Quaternary Science remanence (SIRM), and lithology. The ratios IRM_-100mT/SIRM and SIRM/ susceptibility appear to be particularly sensitive indicators of the degree of soil development and hence of palaeoclimate.  相似文献   

Using Wavelet Coherence to Characterize Surface Water Infiltration into a Low-Lying Karst Aquifer     

Philip Schuler  Èlia Cantoni  Léa Duran  Paul Johnston  Laurence Gill 《Ground water》2021,59(1):71-79

Karstified carbonate aquifers may receive significant recharge contributions from losing streams, hence, the knowledge about surface water-groundwater (SW-GW) interactions is crucial with regard to water management (e.g., source protection zone delineation). The dynamics of SW-GW interactions may depend on factors such as the relative water levels between streams and aquifers, resulting in a temporal variation of exchange, which imposes complexity to the understanding of such dynamics. This study highlights the use of high-resolution time series and multiresolution analysis to help to gain insights into such complex dynamics. Wavelet coherence is applied on hourly time series of rainfall, stream, and spring discharges of a low-lying karstified spring catchment to yield a correlation in the time-frequency domain. This analysis provides comprehensive information on the overall impact of the river on the spring, which is supported by the cross-correlation function, as well as by more detailed information, including time-variant influences such as a threshold level of influence. Field observations of turbidity sampling at the spring appear to support this interpretation. This innovative approach relies on basic hydrological parameters, water level, or discharge, and is therefore applicable to many other systems with such existing time series.  相似文献   

Long-term fluid circulation in extensional faults in the central Catalan Coastal Ranges: P–T constraints from neoformed chlorite and K-white mica     

Irene Cantarero  Pierre Lanari  Olivier Vidal  Gemma Alías  Anna Travé  Vinyet Baqués 《International Journal of Earth Sciences》2014,103(1):165-188

The neoformation of chlorite and K-white mica in fault rocks from two main faults of the central Catalan Coastal Ranges, the Vallès and the Hospital faults, has allowed us to constrain the P–T conditions during fault evolution using thermodynamic modeling. Crystallization of M1 and M2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton (290 °C > T > 370 °C) in the Permian. After that, three tectonic events have been distinguished. The first tectonic event, attributed to the Mesozoic rifting, is characterized by precipitation of M3 and M4 phengite together with chlorite and calcite C1 at temperatures between 190 and 310 °C. The second tectonic event attributed to the Paleogene compression has only been identified in the Hospital fault with precipitation of low-temperature calcite C2. The shortcut produced during inversion of the Vallès fault was probably the responsible for the lack of neoformed minerals within this fault. Finally, the third tectonic event, which is related to the Neogene extension, is characterized in the Vallès fault by a new generation of chlorite, associated with calcite C4 and laumontite, formed at temperatures between 125 and 190 °C in the absence of K-white mica. Differently, the Hospital fault is characterized by the precipitation of calcite C3 during the syn-rift stage at temperatures around 150 °C and by low-temperature fluids precipitating calcites C5, C6 and PC1 during the post-rift stage. During the two extensional events (Mesozoic and Neogene), faults acted as conduits for hot fluids producing anomalous high geothermal gradients (50 °C/km minimum).  相似文献   

Multistage growth of Fe–Mg–carpholite and Fe–Mg–chloritoid,from field evidence to thermodynamic modelling     

Amaury?PourteauEmail author  Romain?Bousquet  Olivier?Vidal  Alexis?Plunder  Erik?Duesterhoeft  Osman?Candan  Roland?Oberh?nsli 《Contributions to Mineralogy and Petrology》2014,168(6):1090

We provide new insights into the prograde evolution of HP/LT metasedimentary rocks on the basis of detailed petrologic examination, element-partitioning analysis, and thermodynamic modelling of well-preserved Fe–Mg–carpholite- and Fe–Mg–chloritoid-bearing rocks from the Afyon Zone (Anatolia). We document continuous and discontinuous compositional (ferromagnesian substitution) zoning of carpholite (overall X _Mg = 0.27–0.73) and chloritoid (overall X _Mg = 0.07–0.30), as well as clear equilibrium and disequilibrium (i.e., reaction-related) textures involving carpholite and chloritoid, which consistently account for the consistent enrichment in Mg of both minerals through time, and the progressive replacement of carpholite by chloritoid. Mg/Fe distribution coefficients calculated between carpholite and chloritoid vary widely within samples (2.2–20.0). Among this range, only values of 7–11 correlate with equilibrium textures, in agreement with data from the literature. Equilibrium phase diagrams for metapelitic compositions are calculated using a newly modified thermodynamic dataset, including most recent data for carpholite, chloritoid, chlorite, and white mica, as well as further refinements for Fe–carpholite, and both chloritoid end-members, as required to reproduce accurately petrologic observations (phase relations, experimental constraints, Mg/Fe partitioning). Modelling reveals that Mg/Fe partitioning between carpholite and chloritoid is greatly sensitive to temperature and calls for a future evaluation of possible use as a thermometer. In addition, calculations show significant effective bulk composition changes during prograde metamorphism due to the fractionation of chloritoid formed at the expense of carpholite. We retrieve P–T conditions for several carpholite and chloritoid growth stages (1) during prograde stages using unfractionated, bulk-rock XRF analyses, and (2) at peak conditions using compositions fractionated for chloritoid. The P–T paths reconstructed for the Kütahya and Afyon areas shed light on contrasting temperature conditions for these areas during prograde and peak stages.  相似文献   

Lipids and pigments in deep-sea surface sediments and interfacial particles from the Western Crozet Basin     

Laurence Pinturier-Geiss  Jeanne Laureillard  Catherine Riaux-Gobin  Joëlle Fillaux  Alain Saliot   《Marine Chemistry》2001,75(4)

Deep-sea sediment samples were collected in the Western Crozet Basin (Indian sector of the Southern Ocean) through Permanently Open Ocean Zone (POOZ), Polar Frontal Zone (PFZ) and Sub-Antarctic Zone (SAZ). Lipid class and fatty acid compositions were investigated to determine the sources and fate of organic matter in the first centimeter of sediment and, above this layer, in the fluff (when present) and particles in the overlying water. The total lipid content varied from 74 to 1033 μg l⁻¹ in the overlying particles and fluffs, and from 24 to 97 μg g⁻¹ dry mass (DM) in surficial sediments. Lipid composition was always dominated by phospholipids in the first centimeter of sediment and often in the overlying particles. The amount of phospholipids (labile compounds representative of fresh material) was compared to the amount of chlorophyll a (Chl a), another compound that is susceptible to rapid degradation. A strong N–S gradient was observed in the distribution of these two compounds, which was attributed to the contrasting hydrodynamic of the study area. The high sedimentation rate in POOZ resulted in better preservation of Chl a in this zone than in other zones of the Crozet Basin (PFZ and SAZ). Phospholipid fatty acids suggested the presence of viable as well as morphologically intact organisms, and these organisms consisted essentially of bacteria with some diatom cysts in the fluff of POOZ. These spores were able to grow in the culture, indicating that they were still viable. Despite the strong hydrodynamic variability, phospholipid fatty acids analysed from the deep-sea surficial sediments were never representative of plankton. This pointed to the extremely labile nature of the phospholipids originally present in planktonic material compared with Chl a, which was always found in overlying particles and surficial sediments.  相似文献   

Spatial restricted rhomboidal five-body problem and horizontal stability of its periodic solutions     

Marcelo Marchesin  Claudio Vidal 《Celestial Mechanics and Dynamical Astronomy》2013,115(3):261-279

The spatial restricted rhomboidal five-body problem, or shortly, SRRFBP, is a five body problem in which four positive masses, called the primaries, move two by two in coplanar circular motions with the center of mass fixed at the origin such that their configuration is always a rhombus, the fifth mass being negligible and not influencing the motion of the four primaries. The Hamiltonian function that governs the motion of the fifth mass is derived and has three degrees of freedom depending periodically on time. Using a synodical system of coordinates, we fix the primaries in order to eliminate the time dependence. With the help of the Hamiltonian structure, we characterize the regions of possible motion. The vertical $z$ axis is invariant and we study what we call the rhomboidal Sitnikov problem. Unlike the classical Sitnikov problem, no chaos exists and the behavior of the fifth mass is quite predictable, periodic solutions of arbitrary long periods are shown to exist and we study numerically their linear horizontal stability.  相似文献   

Organic sedimentary deposits in Titan’s dry lakebeds: Probable evaporite     

Jason W. Barnes  Jacob Bow  Jacob Schwartz  Robert H. Brown  Jason M. Soderblom  Alexander G. Hayes  Graham Vixie  Stéphane Le Mouélic  Sebastien Rodriguez  Christophe Sotin  Ralf Jaumann  Katrin Stephan  Laurence A. Soderblom  Roger N. Clark  Bonnie J. Buratti  Kevin H. Baines  Philip D. Nicholson 《Icarus》2011,216(1):136-140

We report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near Titan’s north pole in observations from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We show evidence that the deposits are evaporitic, making Titan just the third known planetary body with evaporitic processes after Earth and Mars, and is the first that uses a solvent other than water.  相似文献