Markovian characteristics of dry spells over the Iberian Peninsula under present and future conditions using ESCENA ensemble of regional climate models     

Noelia López-Franca  Enrique Sánchez  Teresa Losada  Marta Domínguez  Raquel Romera  Miguel Ángel Gaertner 《Climate Dynamics》2015,45(3-4):661-677

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Timing and pace of ice-sheet withdrawal across the marine–terrestrial transition west of Ireland during the last glaciation     

Colm Ó Cofaigh  S. Louise Callard  David H. Roberts  Richard C. Chiverrell  C. K. Ballantyne  David J. A. Evans  Margot Saher  Katrien J. J. Van Landeghem  Rachel Smedley  Sara Benetti  Matthew Burke  Chris D. Clark  Geoff A. T. Duller  Derek Fabel  Stephen J. Livingstone  Stephen Mccarron  Alicia Medialdea  Steven G. Moreton  Fabio Sacchetti 《第四纪科学杂志》2021,36(5):805-832

Understanding the pace and drivers of marine-based ice-sheet retreat relies upon the integration of numerical ice-sheet models with observations from contemporary polar ice sheets and well-constrained palaeo-glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine-geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice-marginal landforms, to reconstruct the timing and rate of ice-sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine- to a terrestrially-based ice-sheet margin. Seafloor bathymetric data in the form of moraines and grounding-zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal bp with initial retreat underway by 25.9 ka cal bp. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal bp. The ice sheet thereafter retreated to the mid-shelf where it formed a large grounding-zone complex at ~23.7 ka cal bp. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice-free by ~19.5 ka bp and the ice sheet had become largely terrestrially based by 17.3 ka bp. This suggests that the Aran Islands acted to stabilize and slow overall ice-sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf west of Ireland to the period of minimum global eustatic sea level. Initial retreat was driven, at least in part, by glacio-isostatically induced, high relative sea level. Net rates of ice-sheet retreat across the shelf were slow (62–19 m a⁻¹) and reduced (8 m a⁻¹) as the ice sheet vacated the inner shelf and moved onshore. A picture therefore emerges of an extensive BIIS on the Atlantic shelf west of Ireland, in which early, oscillatory retreat was followed by slow episodic retreat which decelerated further as the ice margin became terrestrially based. More broadly, this demonstrates the importance of localized controls, in particular bed topography, on modulating the retreat of marine-based sectors of ice sheets.  相似文献   

Defining and detecting undesirable disturbance in the context of marine eutrophication   总被引：1，自引：0，他引：1  

Tett P  Gowen R  Mills D  Fernandes T  Gilpin L  Huxham M  Kennington K  Read P  Service M  Wilkinson M  Malcolm S 《Marine pollution bulletin》2007,55(1-6):282-297

An understanding of undesirable disturbance to the balance of organisms is needed to diagnose marine eutrophication as defined by EU Directives and OSPAR. This review summarizes the findings of the UK Defra-funded Undesirable Disturbance Study Team, which concluded that 'an undesirable disturbance is a perturbation of a marine ecosystem that appreciably degrades the health or threatens the sustainable human use of that ecosystem'. A methodology is proposed for detecting disturbance of temperate salt-water communities dominated by phytoplanktonic or phytobenthic primary producers. It relies on monitoring indicators of ecosystem structure and vigour, which are components of health. Undesirable disturbance can be diagnosed by accumulating evidence of ecohydrodynamic type-specific changes in: (i) bulk indicators; (ii) frequency statistics; (iii) flux measurements; (iv) structural indicators; and (v) indicator species. These are exemplified by (i) chlorophyll, transparency, dissolved oxygen, and opportunistic seaweed cover; (ii) HABs frequency; (iii) primary production; (iv) benthic and planktonic 'trophic indices'; (v) seagrasses and Nephrops norvegicus. Ecological Quality Objectives are proposed for some of these. Linking the diagnosis to eutrophication requires correlation of changes with nutrient enrichment. The methodology, which requires the development of a plankton community index and emphasizes the importance of primary production as an indicator of vigour, can be harmonized with the EU Water Framework Directive and OSPAR's Strategy to Combat Eutrophication.  相似文献   

The effect of the "Prestige" oil spill on the plankton of the N-NW Spanish coast     

Varela M  Bode A  Lorenzo J  Alvarez-Ossorio MT  Miranda A  Patrocinio T  Anadón R  Viesca L  Rodríguez N  Valdés L  Cabal J  Urrutia A  García-Soto C  Rodríguez M  Alvarez-Salgado XA  Groom S 《Marine pollution bulletin》2006,53(5-7):272-286

Chlorophyll, primary production, zooplankton biomass and the species composition of phytoplankton and zooplankton were studied in 2003, after the Prestige shipwreck. The information obtained was compared to previous data series available for the area affected by the spill. A large data series on plankton variables for the N-NW Spanish coast existed, and therefore a realistic evaluation of the effects by comparison with the range of natural variability could be carried out. We emphasized the evaluation of impact during the spring bloom, the first important biological event after the spill. Some minor changes were observed occasionally, but they did not show any clear pattern and were more related to the natural variability of the ecosystem than to effect of the spill. Plankton community structure did not undergo any changes. Only a few species were more abundant during spring 2003 than in previous years. No significant changes were detected in the planktonic community during productive periods, such as the spring bloom and the summer blooms related to intrusions of East North Atlantic Central Waters. The lack of evidence of the effects of the spill on planktonic communities is discussed in terms of the characteristics of the fuel, the high dynamics of the water masses, the biological mechanisms through which the fuel from the surface waters is transferred to the sea floor and, particularly, the influence of the natural variability by means of large and meso-scale hydrographic processes in the area under study. At the present time it is not possible to determine any minor effects the spill may have had on the plankton owing to the great variability of the planktonic cycles and the short-term impact of the oil from the Prestige on the pelagic system.  相似文献   

Probing the Earth’s Interior with the LENA Detector     

Kathrin A. Hochmuth  Franz V. Feilitzsch  Teresa Marrodán Undagoitia  Lothar Oberauer  Walter Potzel  Michael Wurm  Brian D. Fields 《Earth, Moon, and Planets》2006,99(1-4):253-264

A future large-volume liquid scintillator detector such as the proposed 50 kton LENA (Low Energy Neutrino Astronomy) detector would provide a high-statistics measurement of terrestrial antineutrinos originating from β-decays of the uranium and thorium chains. Additionally, the neutron is scattered in the forward direction in the detection reaction . Henceforth, we investigate to what extent LENA can distinguish between certain geophysical models on the basis of the angular dependence of the geoneutrino flux. Our analysis is based on a Monte-Carlo simulation with different levels of light yield, considering an unloaded PXE scintillator. We find that LENA is able to detect deviations from isotropy of the geoneutrino flux with high significance. However, if only the directional information is used, the time required to distinguish between different geophysical models is of the order of severals decades. Nonetheless, a high-statistics measurement of the total geoneutrino flux and its spectrum still provides an extremely useful glance at the Earth’s interior.  相似文献   

The Wild Life of Pesticides: urban agriculture,institutional responsibility,and the future of biodiversity in Sydney's Hawkesbury-Nepean River     

Roel Plant  Jeremy Walker  Scott Rayburg  Jacqueline Gothe  Teresa Leung 《The Australian geographer》2012,43(1):75-91

Agricultural chemicals are a notoriously intractable source of environmental pollution. Offering enhanced agricultural productivity, they simultaneously risk degrading the ecological basis upon which agriculture depends. This paper considers chemicalisation as a cause of the erosion of aquatic biodiversity and ecosystem resilience, focusing on the Hawkesbury-Nepean River and the small-scale horticulturalists who supply the city's fresh vegetable markets, working under the pressure of urbanisation, retail monopolies, indifferent land-use planning, and often without access to information about pesticide use in the languages they understand. Arguing that standard practices of ‘risk management’ are unable to adequately control chemical contamination, the paper presents findings from interviews with actors within the ‘assemblage’ of institutions with responsibility for agriculture, water quality, and environmental protection, in order to assess the effectiveness of pesticide governance in the Greater Sydney Basin. It appears that pesticide pollution is far from being tamed: it is rarely measured nor monitored, neither is it a priority of any particular agency. Arguing that public health, the long-term viability of local farming and the ecological well-being of the Hawkesbury-Nepean River are mutually consistent goals, we conclude that these vital elements of the common-weal are currently subject to a system of ‘organised irresponsibility’. The paper concludes by proposing several ways forward.  相似文献   

Mass segregation in young clusters: observational biases     

Joana Ascenso  João Alves  Maria Teresa V. T. Lago 《Astrophysics and Space Science》2009,324(2-4):113-119

We investigate the validity of the mass-segregation indicators most commonly used in the analysis of young stellar clusters. We construct and analyze synthetic massive clusters with a standard, fully sampled stellar initial mass function and a King density distribution function. We find that the commonly used indicators are highly sensitive to the effects of incompleteness in observational data, and that completeness determinations do not provide satisfactory corrections, leading to results that may be severely biased toward mass segregation.  相似文献   

Submicroscopic accessory minerals overprinting clay mineral REE patterns (celadonite–glauconite group examples)     

Erzsébet Tóth  Tamás G. Weiszburg  Teresa Jeffries  C. Terry Williams  András Bartha  Éva Bertalan  Ildikó Cora 《Chemical Geology》2010,269(3-4):312-328

Samples of glauconite, representing different stages of glauconitisation, as well as different formation environments, were analysed for rare earth elements (REE) and other trace elements using a combination of bulk sample and spatially-resolved in situ techniques. The results indicate that the high-sensitivity, spatially-resolved technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) produces values up to two orders of magnitude lower than the bulk sample analyses. This suggests that submicroscopic rare earth element-bearing phases are distributed within the glauconite aggregates comprising the bulk samples. Analytical scanning electron microscopy (ASEM) revealed the presence of micrometre-sized grains of apatite and pore filling precipitates of an unidentified (REE, Ca)-phosphate (approximate composition Ca_0.3–0.4(Ce_0.4La_0.1–0.2Nd_0.1)PO₄) in some glauconite grains.The inherent REE concentrations of the glauconite aggregates (i.e., glauconite crystallites without accidental mechanical inclusions or authigenic, not layer silicate mineral precipitates) was found to be relatively low (e.g., typically less than 100 ppm), and this value decreased with increasing glauconitisation (smectite–mica transformation through a series of recrystallisation processes). These results suggest that the REEs substitute for Ca in the interlayer space of the layer silicate structure and, therefore, the REE content decreases as Ca is progressively removed from the interlayer (smectite–mica transition).LA-ICP-MS, when combined with electron probe microanalysis (EPMA) or ASEM, offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses, and so produces reliable trace element data for the respective minerals which host those elements.These results illustrate that accessory minerals are difficult to eliminate from clay samples, and that care needs to be taken in the interpretation of clay mineral REE distributions, irrespective of the aggregation state of the studied clay (i.e., whether finely dispersed within the sedimentary rock, or forming millimetre-sized aggregates). Model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher REE content than “bioapatites”, the total REE content being above 10 000 ppm.  相似文献   

Spectral properties of volcanic materials from hyperspectral field and satellite data compared with LiDAR data at Mt. Etna     

Claudia Spinetti  Francesco Mazzarini  Ruggero Casacchia  Laura Colini  Marco Neri  Boris Behncke  Rosamaria Salvatori  Maria Fabrizia Buongiorno  Maria Teresa Pareschi 《International Journal of Applied Earth Observation and Geoinformation》2009

Spectral properties of volcanic materials in the optical region (350–2500 nm) of the electromagnetic spectrum are analyzed. The goal is to characterize air-fall deposits, recent lava flows, and old lava flows based on their spectral reflectance properties and on the textural characteristics (grain size) of pyroclastic deposits at an active basaltic volcano. Data were acquired during a spectroradiometric field survey at Mt. Etna (Italy) in summer 2003 and combined with hyperspectral satellite (Hyperion) and airborne LiDAR (Light Detection and Ranging) data. In addition, air-fall deposits produced by the highly explosive 2002–2003 eruption have been sampled and spectrally characterized at different distances from the new vents. The spectral analysis shows that air-fall deposits are characterized by low reflectance values besides variations in grain size. This distinguishes them from other surface materials. Old lava flows show highest reflectance values due to weathering and vegetation cover. The spectral data set derived from the field survey has been compared to corrected satellite hyperspectral data in order to investigate the Hyperion capabilities to differentiate the surface cover using the reflectance properties. This has allowed us to identify the 2002–2003 air-fall deposits in a thematic image just few months after their emplacement. Moreover, the observed differences in the field spectra of volcanic surfaces have been compared with differences in the signal intensity detected by airborne LiDAR survey showing the possibility to include information on the texture of volcanic surfaces at Mt. Etna. The approach presented here may be particularly useful for remote and inaccessible volcanic areas and also represents a potentially powerful tool for the exploration of extraterrestrial volcanic surfaces.  相似文献   

Can PAHs influence Cu accumulation by salt marsh plants?     

Almeida CM  Mucha AP  Delgado MF  Caçador MI  Bordalo AA  Vasconcelos MT 《Marine environmental research》2008,66(3):311-318

The presence of polycyclic aromatic hydrocarbons (PAHs) may change the mechanisms of metal uptake, thus influencing kinetics and extent of metal phytoextraction. Studies on the subject are scarce, particularly for salt marsh plants. The aim of this work was to investigate the effect of PAHs on the uptake of Cu by Halimione portulacoides, a plant commonly found in salt marshes. Experiments were carried out in the laboratory, either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, which were prepared with sediment and water from a salt marsh of the Cavado river estuary (NW Portugal). Groups of H. portulacoides (grown in a greenhouse) were exposed to those media during six days. Cu(2+) (as Cu(NO(3))(2)), 10(2) and 10(4)mugl(-1), was added to the media as well as 1.6mugl(-1) of the sixteen EPA priority PAHs (0.1mugl(-1) of each PAHs). Cu was assayed in solutions, sediments and different plant tissues before and after experiments. After exposure, photosynthetic efficiency and levels of chlorophylls were also measured, indicating that plant stress indicators were identical in all plants independently of the media to which the plants were exposed. PAHs influenced both the soluble Cu fraction and Cu uptake by plants. The amounts of metal accumulated in both roots and stems were significantly higher when the 10(4)mugl(-1) of Cu enriched elutriate was amended with PAHs. Thus, results suggest that PAHs may modify Cu solubility, the Cu sorption by plants and/or the passive penetration of Cu into the root cells. Therefore, the combined effects of different types of pollutants should be taken in consideration when studying the remediation potential of plants, namely in terms of phytoextraction.  相似文献