Youth Mobility and Territorial Disparities: An Analysis of Urban and Rural Barcelona     

Xavier Delcls‐Ali  Carme Miralles‐Guasch 《Geographical review》2019,109(3):399-415

Travel behavior of the present generation of youths is being increasingly explored due to their relevance in shaping future accessibility needs and mobility habits. The present study offers an original perspective on this topic by identifying territorial disparities that emerge in youth mobility patterns in rural and urban areas. Unlike most previous research, we propose taking a global view on mobility by analyzing all trip purposes and transportation modes. This is conducted by analyzing a comprehensive mobility survey in the Barcelona Metropolitan Region, which provides data on mobility engagement, trip purposes, modal split, travel times and territorial differences. In general, youngsters account for larger daily travel times than older adults, present a higher attachment to public transportation and walk less on a daily basis. These differences are enhanced in rural territories, where while older adults overcome accessibility issues with higher use of the private vehicle, youngsters are more likely to invest larger travel times on transit.  相似文献   

8000 years of vegetation history in the northern Iberian Peninsula inferred from the palaeoenvironmental study of the Zalama ombrotrophic bog (Basque‐Cantabrian Mountains,Spain)          下载免费PDF全文

Sebastián Pérez‐Díaz  José Antonio López‐Sáez  Xabier Pontevedra‐Pombal  Martín Souto‐Souto  Didier Galop 《Boreas: An International Journal of Quaternary Research》2016,45(4):658-672

This paper focuses on pollen, spores, non‐pollen palynomorphs (NPPs) and certain geochemical elements from the ombrotrophic blanket bog of Zalama (Basque‐Cantabrian Mountains, northern Iberian Peninsula), with the support of a robust chronology based on 17 AMS ¹⁴C dates. The main results related to the last 8000 years show that, during the early middle Holocene, pines and deciduous forests were the most extensive tree formations. At the beginning of the succession, pines reach 44%, showing regional presence, whereas after 7600 cal. a BP, deciduous forests were particularly abundant. From c. 6500 cal. a BP the pollen diagram constructed from our samples shows the first anthropogenic evidence, linked with the new economic practices related to the Neolithic of the Basque‐Cantabrian Mountains. From 3300 cal. a BP the expansion of Fagus sylvatica is particularly clear, and has since then become one of the dominant forest species in this region. We also discuss the Holocene evolution of other noteworthy plant communities in southwestern Europe, such as Taxus baccata, Juglans and shrublands.  相似文献   

A gridded sea surface salinity data set for the tropical Pacific with sample applications (1950–2008)     

T. Delcroix  G. Alory  S. Cravatte  T. Corrège  M.J. McPhaden 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(1):38-48

We present a gridded data set of Sea Surface Salinity (SSS) for the tropical Pacific (120°E–70°W; 30°N–30°S), with a grid resolution of 1° longitude, 1° latitude and 1 month, from 1950 to 2008. The product, together with its associated error field, is derived from an objective analysis of about 10 million validated SSS records, with most of the data originating from Voluntary Observing Ships, TAO/TRITON moorings and Argo profilers (during the most recent period). We expect this product to benefit studies in oceanography, meteorology and paleoceanography. As examples of applications, we analyse: (a) the seasonal and ENSO (El Niño Southern Oscillation) modes of observed SSS variability, (b) the ability of 23 coupled models used in the Intergovernmental Panel for Climate Change 4th Assessment Report (IPCC AR4) to simulate the mean SSS and these two time varying modes, and (c) the usefulness of the SSS product and of its associated error field in calibrating and validating the paleo-salinity time series. We anticipate improvements and regular updates to our product, as more SSS data become available from in situ networks and from the ongoing and near-future satellite-derived observations by SMOS (Soil Moisture and Ocean Salinity) and Aquarius.  相似文献   

Internal erosion in granular media: direct numerical simulations and energy interpretation          下载免费PDF全文

Luc Sibille  Franck Lominé  Philippe Poullain  Yacine Sail  Didier Marot 《水文研究》2015,29(9):2149-2163

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Short‐ and long‐term evapotranspiration rates at ecological restoration sites along a large river receiving rare flow events          下载免费PDF全文

Margaret Shanafield  Hugo Gutiérrez‐Jurado  Jesús Eliana Rodríguez‐Burgueño  Jorge Ramírez‐Hernández  Christopher J. Jarchow  Pamela L. Nagler 《水文研究》2017,31(24):4328-4337

Many large rivers around the world no longer flow to their deltas, due to ever greater water withdrawals and diversions for human needs. However, the importance of riparian ecosystems is drawing increasing recognition, leading to the allocation of environmental flows to restore river processes. Accurate estimates of riparian plant evapotranspiration (ET) are needed to understand how the riverine system responds to these rare events and achieve the goals of environmental flows. In 2014, historic environmental flows were released into the Lower Colorado River at Morelos Dam (Mexico); this once perennial but now dry reach is the final stretch to the mighty Colorado River Delta. One of the primary goals was to supply native vegetation restoration sites along the reach with water to help seedlings establish and boost groundwater levels to foster the planted saplings. Patterns in ET before, during, and after the flows are useful for evaluating whether this goal was met and understanding the role that ET plays in this now ephemeral river system. Here, diurnal fluctuations in groundwater levels and Moderate Resolution Imaging Spectroradiometer (MODIS) data were used to compare estimates of ET specifically at 3 native vegetation restoration sites during 2014 planned flow events, and MODIS data were used to evaluate long‐term (2002–2016) ET responses to restoration efforts at these sites. Overall, ET was generally 0–10 mm d^?1 across sites, and although daily ET values from groundwater data were highly variable, weekly averaged estimates were highly correlated with MODIS‐derived estimates at most sites. The influence of the 2014 flow events was not immediately apparent in the results, although the process of clearing vegetation and planting native vegetation at the restoration sites was clearly visible in the results.  相似文献   

Comparing landslide susceptibility models in the Río El Estado watershed on the SW flank of Pico de Orizaba volcano,Mexico     

Gabriel Legorreta Paulín  Solène Pouget  Marcus Bursik  Fernando Aceves Quesada  Trevor Contreras 《Natural Hazards》2016,80(1):127-139

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Intra-interstadial environmental changes in Last Glacial loess revealed by molluscan assemblages from the Upper Palaeolithic site of Amiens-Renancourt 1 (Somme,France)     

Olivier Moine  Pierre Antoine  Sylvie Coutard  Gilles Guérin  Christine Hatté  Clément Paris  Ségolène Saulnier-Copard 《第四纪科学杂志》2021,36(8):1322-1340

The Amiens-Renancourt 1 site recently yielded one of the most important Upper Palaeolithic human occupations of northern France by the number of flint artefacts and especially by the presence of Venus figurines. All the material comes from a single archaeological layer located in a tundra gley bracketed by loess units. A multi-proxy study combining a detailed stratigraphy, luminescence and radiocarbon datings and high-resolution (5 cm per sample) grain size and molluscan analyses was therefore carried out to reconstruct and date the associated environmental changes and to determine the exact context of the human occupation. The chronological frame thus established supports the correlations of the archaeology-bearing tundra gley and of an underlying arctic brown soil with Greenland interstadials GI-4 and GI-3. Composition changes in the molluscan population enabled the identification of transitional and optimum phases and sub-phases within these two pedogenetic horizons. A conceptual correlation model linking molluscan phases with millennial-scale variations of Greenland ice-core and Sieben Hengste speleothem climate records is proposed. The Human occupation appears contemporaneous to the end of the stadial–interstadial transition of GI-3. Synchronous in Amiens-Renancourt 1 and Nussloch, subsequent micro-gleys may also result from a regional/global forcing. Such a level of detail is unprecedented in a loess sequence.  相似文献   

Carbon fluxes through major phytoplankton groups during the spring bloom and post-bloom in the Northwestern Mediterranean Sea     

Andrés Gutiérrez-Rodríguez  Mikel Latasa  Marta Estrada  Montserrat Vidal  Celia Marrasé 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):486-500

The carbon flux through major phytoplankton groups, defined by their pigment markers, was estimated in two contrasting conditions of the Northwestern Mediterranean open ocean ecosystem: the spring bloom and post-bloom situations (hereafter Bloom and Post-bloom, respectively). During Bloom, surface chlorophyll a (Chl a) concentration was higher and dominated by diatoms (53% of Chl a), while during Post-bloom Synechococcus (42%) and Prymnesiophyceae (29%) became dominant. The seawater dilution technique, coupled to high pressure liquid chromatography (HPLC) analysis of pigments and flow cytometry (FCM), was used to estimate growth and grazing rates of major phytoplankton groups in surface waters. Estimated growth rates were corrected for photoacclimation based on FCM-detected changes in red fluorescence per cell. Given the 30% average decrease in the pigment content per cell between the beginning and the end of the incubations, overlooking photoacclimation would have resulted in a 0.40 d^?1 underestimation of phytoplankton growth rates. Corrected average growth rates (μ_o) were 0.90±0.20 (SD) and 0.40±0.14 d^?1 for Bloom and Post-bloom phytoplankton, respectively. Diatoms, Cryptophyceae and Synechococcus were identified as fast-growing groups and Prymnesiophyceae and Prasinophyceae as slow-growing groups across Bloom and Post-bloom conditions. The higher growth rate during Bloom was due to dominance of phytoplankton groups with higher growth rates than those dominating in Post-bloom. Average grazing rates (m) were 0.58±0.20 d^?1 (SD) and 0.31±0.07 d^?1. The proportion of phytoplankton growth consumed by microzooplankton grazing (m/μ_o) tended to be lower in Bloom (0.69±0.34) than in Post-bloom (0.80±0.08). The intensity of nutrient limitation experienced by phytoplankton indicated by μ_o/μ_n (where μ_n is the nutrient-amended growth rate), was similar during Bloom (0.78) and Post-bloom (0.73). Primary production from surface water (PP) was estimated with ¹⁴C incubations. A combination of PP and Chl a synthesis rate yielded C/Chl a ratios of 34±21 and 168±75 (g:g) for Bloom and Post-bloom, respectively. Transformation of group-specific Chl a fluxes into carbon equivalents confirmed the dominant role of diatoms during Bloom and Synechococcus and Prymnesiophyceae during Post-bloom.  相似文献   

Coastal Occupations in Tierra del Fuego,Southernmost South America: A Late Holocene Hunter‐Gatherer Context at Marazzi 2     

Ivana L. Ozn  Charles French  Flavia Morello Repetto  Carlos A. Vsquez  Toms Luppo 《Geoarchaeology》2015,30(6):465-482

This paper focuses on the late Holocene occupation of hunter‐gatherers at the Marazzi 2 site located on the northwestern steppe of Tierra del Fuego, Chile. Our aim is to understand stratigraphy, formation processes, and pedogenesis with respect to human occupation over the last 3000 years. Based on archaeological excavations on a fluvial terrace of the Torcido River, we integrate soil micromorphology, mineralogy, geochemistry, magnetic susceptibility, and geomorphology, as well as the micro‐ and macrofrequency distributions of archaeological material. A micro‐taphonomical perspective is also applied to anthropogenic components recorded in sedimentary thin sections. We discuss various events in the interplay between soil development and human occupation through time. Marazzi 2 was witness to aggradation and pedogenesis with an episode of surface stability coincident with a phase of more intense human occupation at about 860 BC. Taphonomic analysis suggests that there are multiple occupation events mixed together, probably by biomechanical processes, resulting in a palimpsest with poor temporal resolution.  相似文献   

Subalpine fires: the roles of vegetation,climate and,ultimately, land uses     

Bérangère Leys  Christopher Carcaillet 《Climatic change》2016,135(3-4):683-697

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