Late Quaternary climatic history of the Chilean Channels based on fossil pollen and beetle analyses,with an analysis of the modern vegetation and pollen rain     

Allan C. Ashworth  Vera Markgraf  Carolina Villagran 《第四纪科学杂志》1991,6(4):279-291

Fossil beetles and pollen were examined from an intermorainal bog at Puerto Edén, Isla Wellington, Chile (latitude 49°08'S, longitude 74°25'W). Wood from near the base of the section has an age of 12 960 ± 150 yr BP. Occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia. The assumption that the Chilean Channels were entirely ice-covered is incorrect. Plants and insects that invaded the deglaciated terrain were those of an Empetrum heathland in which patches of Nothofagus forest were restricted to sheltered locations. The climate supporting the heathland is inferred to have been windier and probably drier than that of the present day. From 13 000 yr BP to 9500 yr BP Nothofagus forest expanded, possibly in response to less windiness and more available moisture. Neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr BP at the time of the Younger Dryas Stade. From 9500 to 5500 yr BP the climate was as wet as that of the present day, based on an increased representation of the pollen of moorland plants and of aquatic beetle species. From 5500 to 3000 yr BP the climate was drier, as indicated by the expansion of Empetrum heath and the reduction in mesic habitats. From 3000 yr BP to the present-day mesic habitats dominated as the climate returned to a wetter mode. The alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of Southern Westerlies.  相似文献   

Adakitic Dacites Formed by Intracrustal Crystal Fractionation of Water-rich Parent Magmas at Nevado de Longavi Volcano (36{middle dot}2{degrees}S; Andean Southern Volcanic Zone, Central Chile)     

RodrIguez  Carolina; Selles  Daniel; Dungan  Michael; Langmuir  Charles; Leeman  William 《Journal of Petrology》2007,48(11):2033-2061

The mid-Holocene eruptive products of Nevado de Longavívolcano (36·2°S, Chile) are the only reported occurrenceof adakitic volcanic rocks in the Quaternary Andean SouthernVolcanic Zone (33–46°S). Dacites of this volcano arechemically distinct from other evolved magmas of the regionin that they have high La/Yb (15–20) and Sr/Y (60–90)ratios and systematically lower incompatible element contents.An origin by partial melting of high-pressure crustal sourcesseems unlikely from isotopic and trace element considerations.Mafic enclaves quenched into one of the dacites, on the otherhand, constitute plausible parental magmas. Dacites and maficenclaves share several characteristics such as mineral chemistry,whole-rock isotope and trace element ratios, highly oxidizingconditions (NNO + 1·5 to >NNO + 2, where NNO is thenickel–nickel oxide buffer), and elevated boron contents.A two-stage mass-balance crystal fractionation model that matchesboth major and trace elements is proposed to explain magmaticevolution from the least evolved mafic enclave to the dacites.Amphibole is the main ferromagnesian phase in both stages ofthis model, in agreement with the mineralogy of the magmas.We also describe cumulate-textured xenoliths that correspondvery closely to the solid assemblages predicted by the model.We conclude that Nevado de Longaví adakitic dacites arethe products of polybaric fractional crystallization from exceptionallywater-rich parent magmas. These basaltic magmas are inferredto be related to an exceptionally high, but transient inputof slab-derived fluids released from serpentinite bodies hostedin the oceanic Mocha Fracture Zone, which projects beneath Nevadode Longaví. Fractional crystallization that is modallydominated by amphibole, with very minor garnet extraction, isa mechanism for generating adakitic magmas in cold subductionzones where a high flux of slab-derived fluids is present. KEY WORDS: adakite; amphibole; Andes; differentiation; Southern Volcanic Zone  相似文献   

The impact of land use change and check‐dams on catchment sediment yield     

Carolina Boix‐Fayos  Joris de Vente  María Martínez‐Mena  Gonzalo G. Barberá  Víctor Castillo 《水文研究》2008,22(25):4922-4935

Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check‐dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3‐fold and decreasing the agricultural land 2·5‐fold from 1956 to 1997. In addition 58 check‐dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM‐SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check‐dams. Calibration of the model provided a model efficiency of 0·84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check‐dams, about 77% of the sediment yield was retained behind the dams. Check‐dams can be efficient sediment control measures, but with a short‐lived effect. They have important side‐effects, such as inducing channel erosion downstream. While also having side‐effects, land use changes can have important long‐term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check‐dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Land use dynamics in Brazilian La Plata Basin and anthropogenic climate change     

Ana Carolina F. de Vasconcelos  Sandro L. Schlindwein  Marcos A. Lana  Alfredo C. Fantini  Michelle Bonatti  Luiz R. D’Agostini  Sergio R. Martins 《Climatic change》2014,127(1):73-81

The La Plata Basin (LPB) is one of the most important regions for agriculture and livestock production in South America, playing a central role in the world food production and food security. Within its borders is also located the whole Brazilian Pantanal region. Identifying the most important land use sectors in LPB as well as the changes observed in the past years is fundamental to recognize which areas of the basin might be more vulnerable to climate change in order to design adaptation strategies. A general characterization of land use and livestock production of Brazilian LPB was done by using the System of Automatic Retrieving (SIDRA) of Brazilian Institute of Geography and Statistics (IBGE) platform as the major source of data. It was observed expressive increases in land areas used for temporary crops, such as soybean, sugarcane, and maize, as well as increases in poultry and swine production. These important changes in agricultural land use and livestock production are currently associated to non-climatic drivers, but this dynamic might be strongly affected by the consequences of climate change and variability, with negative socio-economic impacts for the whole region.  相似文献   

Summer precipitation variability over South America on long and short intraseasonal timescales     

Paula L. M. Gonzalez  Carolina S. Vera 《Climate Dynamics》2014,43(7-8):1993-2007

A dipole pattern in convection between the South Atlantic convergence zone and the subtropical plains of southeastern South America characterizes summer intraseasonal variability over the region. The dipole pattern presents two main bands of temporal variability, with periods between 10 and 30 days, and 30 and 90 days; each influenced by different large-scale dynamical forcings. The dipole activity on the 30–90-day band is related to an eastward traveling wavenumber-1 structure in both OLR and circulation anomalies in the tropics, similar to that associated with the Madden–Julian oscillation. The dipole is also related to a teleconnection pattern extended along the South Pacific between Australia and South America. Conversely, the dipole activity on the 10–30-day band does not seem to be associated with tropical convection anomalies. The corresponding circulation anomalies exhibit, in the extratropics, the structure of Rossby-like wave trains, although their sources are not completely clear.  相似文献   

A concerted research effort to advance the hydrological understanding of tropical páramos     

Alicia Correa  Boris F Ochoa-Tocachi  Christian Birkel  Ana Ochoa-Sánchez  Charles Zogheib  Carolina Tovar  Wouter Buytaert 《水文研究》2020,34(24):4609-4627

Páramos, a neotropical alpine grassland-peatland biome of the northern Andes and Central America, play an essential role in regional and global cycles of water, carbon, and nutrients. They act as water towers, delivering water and ecosystem services from the high mountains down to the Pacific, Caribbean, and Amazon regions. Páramos are also widely recognized as a biodiversity and climate change hot spots, yet they are threatened by anthropogenic activities and environmental changes. Despite their importance for water security and carbon storage, and their vulnerability to human activities, only three decades ago, páramos were severely understudied. Increasing awareness of the need for hydrological evidence to guide sustainable management of páramos prompted action for generating data and for filling long-standing knowledge gaps. This has led to a remarkably successful increase in scientific knowledge, induced by a strong interaction between the scientific, policy, and (local) management communities. A combination of well-established and innovative approaches has been applied to data collection, processing, and analysis. In this review, we provide a short overview of the historical development of research and state of knowledge of the hydrometeorology, flux dynamics, anthropogenic impacts, and the influence of extreme events in páramos. We then present emerging technologies for hydrology and water resources research and management applied to páramos. We discuss how converging science and policy efforts have leveraged traditional and new observational techniques to generate an evidence base that can support the sustainable management of páramos. We conclude that this co-evolution of science and policy was able to successfully cover different spatial and temporal scales. Lastly, we outline future research directions to showcase how sustainable long-term data collection can foster the responsible conservation of páramos water towers.  相似文献   

Conflating Privilege and Vulnerability: A Reflexive Analysis of Emotions and Positionality in Postgraduate Fieldwork   总被引：1，自引：0，他引：1  

Martina Angela Caretta  Johanna Carolina Jokinen 《The Professional geographer》2017,69(2):275-283

Grounded in a self-reflexive, intersectional analysis of positionality, we examine emotions in fieldwork through the autobiographical accounts that we gathered during our postgraduate ethnographic research in the Global South. We show how we, two female early-career geographers, emotionally coped with instances that put us in a vulnerable position due to loneliness, commitment to the field, insistent questioning, violence, and violent threats. We argue that a culture of silence surrounding fieldwork difficulties and their emotional consequences tend to permeate our discipline. We contend that geography departments ought to provide mentorship that takes into account doctoral candidates' different positionalities, conflated vulnerability and privilege, and embodied intersectional axes. This renewed awareness will help not only to reveal possible risks and challenges connected with fieldwork but also ultimately to enrich the overall academic discussions within our discipline.  相似文献   

Stratigraphy, Chronology, and Paleoenvironmental Reconstruction of the Quaternary Sedimentary Infilling of a Volcanic Tube in Fuerteventura, Canary Islands     

Juan J. Coello  Carolina Castillo  Esther Martín Gonzlez 《Quaternary Research》1999,52(3):360

La Cueva del Llano is a volcanic tube of Pleistocene age on Fuerteventura Island, in the Canary Islands. Part of it is infilled with sediments of external origin. These deposits are exceptional in stratigraphic complexity and thickness compared with other known tube infillings, and they comprise nine stratigraphic units deposited in five phases. In Phase I, which has not been dated, sedimentation of cinder from a nearby cone occurred. Phase II began ca. 16,830 ± 900 ¹⁴C yr B.P., whereas phase IV dates to 9280 ± 370 ¹⁴C yr B.P. The interpretation of sedimentary features shows that phases III and V correspond to a dry climate, similar to the present one, whereas the climate was much wetter during phases II and IV. This paleoclimatic sequence agrees with those suggested by the study of deposits formed in other sedimentary environments, not only in Fuerteventura but on other islands of the Canary group and the Sud-Maroc region.  相似文献   

SlugIn 1.0: A Free Tool for Automated Slug Test Analysis          下载免费PDF全文

Sergio Martos‐Rosillo  Carolina Guardiola‐Albert  Alberto Padilla Benítez  Joaquín Delgado Pastor  Antonio Azcón González  Juan José Durán Valsero 《Ground water》2018,56(3):362-365

The correct characterization of aquifer parameters is essential for water‐supply and water‐quality investigations. Slug tests are widely used for these purposes. While free software is available to interpret slug tests, some codes are not user‐friendly, or do not include a wide range of methods to interpret the results, or do not include automatic, inverse solutions to the test data. The private sector has also generated several good programs to interpret slug test data, but they are not free of charge. The computer program SlugIn 1.0 is available online for free download, and is demonstrated to aid in the analysis of slug tests to estimate hydraulic parameters. The program provides an easy‐to‐use Graphical User Interface. SlugIn 1.0 incorporates automated parameter estimation and facilitates the visualization of several interpretations of the same test. It incorporates solutions for confined and unconfined aquifers, partially penetrating wells, skin effects, shape factor, anisotropy, high hydraulic conductivity formations and the Mace test for large‐diameter wells. It is available in English and Spanish and can be downloaded from the web site of the Geological Survey of Spain. Two field examples are presented to illustrate how the software operates.  相似文献   

Identification of factors influencing hydrologic model performance using a top-down approach in a large number of U.S. catchments     

Carolina Massmann 《水文研究》2020,34(1):4-20

Investigating the performance that can be achieved with different hydrological models across catchments with varying characteristics is a requirement for identifying an adequate model for any catchment, gauged or ungauged, just based on information about its climate and catchment properties. As parameter uncertainty increases with the number of model parameters, it is important not only to identify a model achieving good results but also to aim at the simplest model still able to provide acceptable results. The main objective of this study is to identify the climate and catchment properties determining the minimal required complexity of a hydrological model. As previous studies indicate that the required model complexity varies with the temporal scale, the study considers the performance at the daily, monthly, and annual timescales. In agreement with previous studies, the results show that catchments located in arid areas tend to be more difficult to model. They therefore require more complex models for achieving an acceptable performance. For determining which other factors influence model performance, an analysis was carried out for four catchment groups (snowy, arid, and eastern and western catchments). The results show that the baseflow and aridity indices are the most consistent predictors of model performance across catchment groups and timescales. Both properties are negatively correlated with model performance. Other relevant predictors are the fraction of snow in the annual precipitation (negative correlation with model performance), soil depth (negative correlation with model performance), and some other soil properties. It was observed that the sign of the correlation between the catchment characteristics and model performance varies between clusters in some cases, stressing the difficulties encountered in large sample analyses. Regarding the impact of the timescale, the study confirmed previous results indicating that more complex models are needed for shorter timescales.  相似文献