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51.
Factors controlling the magnitudes of, and short-term variations in, the potential temperatures of the snow surface and the
air at the height of 2 m θS and θ2 m over Arctic sea ice in winter are analysed. The study addresses the winters of 1986–1987 and 1987–1988, and is based on the
temperature, wind, and cloud observations made by Russian drifting ice stations. It also relies on the ERA40 re-analyses of
the European Centre for Medium-Range Weather Forecasts, which were utilised to calculate the lateral heat advection at the
sites of the ice stations. The cloud cover and wind speed were more important than the heat advection in controlling the magnitudes
of θ2 m and θS, while on a time scale of 24 h, during steady forcing conditions, the heat advection was the most important factor affecting
the changes in θS and θ2 m. During changing conditions, and considering individual factors separately, the monthly mean 24-h temperature changes were
less than ± 5 °C: the effect of the cloud cover was the largest, and that of the heat advection was the smallest. When simultaneous
changes in the three factors were analysed, the seasonal mean temperature changes were even of the order of ±15 °C, with the
strongest warming events exceeding 35 K in a single day. The difference θS − θ2 m reached its lowest seasonal mean values during conditions of clear skies (−1.3 °C), light winds (−1.3 °C) and warm-air advection
(−0.8 °C). θS and θ2 m followed each other closely, even during major synoptic-scale temperature variations. 相似文献
52.
In this paper, a study aimed to assess the rockfall hazard along a portion of the SS18 coastal road, located in the coastal area of Maratea (Basilicata Region, Southern Italy), is presented. The relevance of this study derives from the location of the study area, because the SS18 is a strategic roads in a touristic area, and, since the hazard assessment was performed in 2004 within a project financed by the Viability Regional Department of Autonomous National Company of Roads (ANAS), from the possibility to validate the results by using real rockfall events occurred after 2004. The procedure for assessing the rockfall hazard was composed of four sequential analyses: (i) geomechanical and kinematic characterization of rock mass, (ii) implementation of Romana’s (1985) Slope Mass Rating (SMR) method for identifying the potential boulder release areas (rockfall initiation areas), (iii) determination of rockfall trajectories by using a 3D numerical model (ROTOMAP), (iv) calculation and mapping of the hazard index by combining three factors, i.e., (a) lithological features of outcropping materials on rock faces, (b) kinematic compatibility defined by simulating the rockfall trajectories, and (c) spatial distribution of occurred rockfall events. Finally, the proposed methodology was validated by combining the distribution of the hazard levels along the road with the location on the SS18 of the rockfall events occurred from 2004 to 2014. 相似文献
53.
54.
Giovanni Monegato Sally E. Lowick Cesare Ravazzi Roberta Banino Marta Donegana Frank Preusser 《第四纪科学杂志》2010,25(5):617-632
The Middle–Late Pleistocene alluvial and lacustrine succession of Valeriano Creek (southeastern Alpine foothills, 190 m a.s.l.) documents the environmental evolution of the piedmont plain before the onset of the Last Glacial Maximum (LGM). The sedimentary record was investigated by multidisciplinary stratigraphical and sedimentological studies coupled with petrographic and palaeobotanical analysis. A chronology has been provided by luminescence, radiocarbon dating and pollen biochronology. The succession developed at the valley mouth of a small catchment and is confined in the piedmont plain by the alluvial fans of major rivers. The oldest deposits were formed during a cold phase during the late Middle Pleistocene. This part of the piedmont plain was generally stable until Termination II, when it was trenched more than 15 m deep by watercourses. The infilling succession of the trench, mostly by low‐energy alluvial sediments interbedded with mire and peat deposits, documents, for the first time on the southern side of the Alps, the relationships between fluvial activity, vegetation and climate change at the foothills piedmont plain during late Marine Isotope Stage (MIS) 5. The stadial–interstadial climate forcing implies a local reorganisation of fluvial dynamics and of forest composition, although substantial plant cover persisted even during cooler stadials. In accordance with coeval alluvial and speleothem records from the northern side of the Alps, this environmental evolution supports a very restricted Alpine glaciation of the main fluvial catchments of the southeastern Alps during MIS 5a–d. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
55.
Valentina Marin Francesca Palmisani Roberta Ivaldi Rosanna Dursi Mauro Fabiano 《Ocean & Coastal Management》2009,52(5):268-277
It is generally accepted that end-users’ perception is likely to play a pivotal role for planning and policy consideration. Beach user analysis is thus an important component defining beach management policies. In the framework of a wider project on beaches management, an investigation on residents and tourists was conducted. A survey conducted through questionnaires and interviews was carried out in six coastal municipalities. Results allowed obtaining a clear picture about user profile, perception of the beaches, awareness and attitude about themes related to beach management (i.e. Blue Flag award and beach nourishment practices). Their integration with the “expert knowledge” based analysis allowed to support the definition of beach management interventions. 相似文献
56.
Michele Zema Mark D. Welch Roberta Oberti 《Contributions to Mineralogy and Petrology》2012,163(5):923-937
The thermoelastic behaviour of a natural gedrite having the crystal-chemical formula ANa0.47
B(Na0.03 Mg1.05 Fe0.862+ Mn0.02 Ca0.04) C(Mg3.44 Fe0.362+ Al1.15 Ti0.054+) T(Si6.31 Al1.69)O22
W(OH)2 has been studied by single-crystal X-ray diffraction to 973 K (Stage 1). After data collection at 973 K, the crystal was heated to 1,173 K to induce dehydrogenation, which was registered by significant
changes in unit-cell parameters, M1–O3 and M3–O3 bond lengths and refined site-scattering values of M1 and M4 sites. These changes and the crystal-chemical formula calculated from structure refinement show that all Fe2+ originally at M4 migrates into the ribbon of octahedrally coordinated sites, where most of it oxidises to Fe3+, and there is a corresponding exchange of Mg from the ribbon into M4. The resulting composition is that of an oxo-gedrite with an inferred crystal-chemical formula ANa0.47
B(Na0.03 Mg1.93 Ca0.04) C(Mg2.56 Mn0.022+ Fe0.102+ Fe1.223+ Al1.15 Ti0.054+) T(Si6.31 Al1.69) O22
W[O1.122− (OH)0.88]. This marked redistribution of Mg and Fe is interpreted as being driven by rapid dehydrogenation at the H3A and H3B sites, such that all available Fe in the structure orders at M1 and M3 sites and is oxidised to Fe3+. Thermoelastic data are reported for gedrite and oxo-gedrite; the latter was measured during cooling from 1,173 to 298 K
(Stage 2) and checked after further heating to 1,273 K (Stage 3). The thermoelastic properties of gedrite and oxo-gedrite are compared with each other and those of anthophyllite. 相似文献
57.
Matthew R. M. IZAWA Roberta L. FLEMMING Neil R. BANERJEE Philip J. A. McCAUSLAND 《Meteoritics & planetary science》2011,46(5):638-651
Abstract– A new method for assessing the shock stage of enstatite chondrites has been developed, using in situ micro‐X‐ray diffraction (μXRD) to measure the full width at half maximum (FWHMχ) of peak intensity distributed along the direction of the Debye rings, or chi angle (χ), corresponding to individual lattice reflections in two‐dimensional XRD patterns. This μXRD technique differs from previous XRD shock characterization methods: it does not require single crystals or powders. In situ μXRD has been applied to polished thin sections and whole‐rock meteorite samples. Three frequently observed orthoenstatite reflections were measured: (020), (610), and (131); these were selected as they did not overlap with diffraction lines from other phases. Enstatite chondrites are commonly fine grained, stained or darkened by weathering, shock‐induced oxidation, and metal/sulfide inclusions; furthermore, most E chondrites have little olivine or plagioclase. These characteristics inhibit transmitted‐light petrography, nevertheless, shock stages have been assigned MacAlpine Hills (MAC) 02837 (EL3) S3, Pecora Escarpment (PCA) 91020 (EL3) S5, MAC 02747 (EL4) S4, Thiel Mountains (TIL) 91714 (EL5) S2, Allan Hills (ALHA) 81021 (EL6) S2, Elephant Moraine (EET) 87746 (EH3) S3, Meteorite Hills (MET) 00783 (EH4) S4, EET 96135 (EH4–5) S2, Lewis Cliff (LEW) 88180 (EH5) S2, Queen Alexandra Range (QUE) 94204 (EH7) S2, LaPaz Icefield (LAP) 02225 (EH impact melt) S1; for the six with published shock stages, there is agreement with the published classification. FWHMχ plotted against petrographic shock stage demonstrates positive linear correlation. FWHMχ ranges corresponding to shock stages were assigned as follows: S1 < 0.7°, S2 = 0.7–1.2°, S3 = 1.2–2.3°, S4 = 2.3–3.5°, S5 > 3.5°, S6—not measured. Slabs of Abee (EH impact‐melt breccia), and Northwest Africa (NWA) 2212 (EL6) were examined using μXRD alone; FWHMχ values place both in the S2 range, consistent with literature values. Micro‐XRD analysis may be applicable to other shocked orthopyroxene‐bearing rocks. 相似文献
58.
Wang-Ye Li Fang-Zhen Teng Shan Ke Roberta L. Rudnick Fu-Yuan Wu 《Geochimica et cosmochimica acta》2010,74(23):6867-6884
High-precision Mg isotopic data are reported for ∼100 well-characterized samples (granites, loess, shales and upper crustal composites) that were previously used to estimate the upper continental crust composition. Magnesium isotopic compositions display limited variation in eight I-type granites from southeastern Australia (δ26Mg = −0.25 to −0.15) and in 15 granitoid composites from eastern China (δ26Mg = −0.35 to −0.16) and do not correlate with SiO2 contents, indicating the absence of significant Mg isotope fractionation during differentiation of granitic magma. Similarly, the two S-type granites, which represent the two end-members of the S-type granite spectrum from southeastern Australia, have Mg isotopic composition (δ26Mg = −0.23 and −0.14) within the range of their potential source rocks (δ26Mg = −0.20 and +0.15) and I-type granites, suggesting that Mg isotope fractionation during crustal anatexis is also insignificant. By contrast, δ26Mg varies significantly in 19 A-type granites from northeastern China (−0.28 to +0.34) and may reflect source heterogeneity.Compared to I-type and S-type granites, sedimentary rocks have highly heterogeneous and, in most cases, heavier Mg isotopic compositions, with δ26Mg ranging from −0.32 to +0.05 in nine loess from New Zealand and the USA, from −0.27 to +0.49 in 20 post-Archean Australian shales (PAAS), and from −0.52 to +0.92 in 20 sedimentary composites from eastern China. With increasing chemical weathering, as measured by the chemical index of alternation (CIA), δ26Mg values show a larger dispersion in shales than loess. Furthermore, δ26Mg correlates negatively with δ7Li in loess. These characteristics suggest that chemical weathering significantly fractionates Mg isotopes and plays an important role in producing the highly variable Mg isotopic composition of sedimentary rocks.Based on the estimated proportions of major rock units within the upper continental crust and their average MgO contents, a weighted average δ26Mg value of −0.22 is derived for the average upper continental crust. Our studies indicate that Mg isotopic composition of the upper crust is, on average, mantle-like but highly heterogeneous, with δ26Mg ranging from −0.52 to +0.92. Such large isotopic variation mainly results from chemical weathering, during which light Mg isotopes are lost to the hydrosphere, leaving weathered products (e.g., sedimentary rocks) with heavy Mg isotopes. 相似文献
59.
60.
Roberta LasagnaMonica Montefalcone Giancarlo AlbertelliNicola Corradi Marco FerrariCarla Morri Carlo Nike Bianchi 《Estuarine, Coastal and Shelf Science》2011,94(3):255-262
While coastal management activities have long been known to exert a strong influence on the health of marine ecosystems, neither scientists nor administrators have realized that small interventions may lead to disproportionately larger impacts. This study investigated the broad and long-lasting environmental consequences of the construction of an ill-planned, although small (only 12 m long) jetty for pleasure crafts on the hydrodynamic conditions and on the meadow of the seagrass Posidonia oceanica of an embayed cove in the Ligurian Sea (NW Mediterranean). There, P. oceanica used to develop on a high (>1.5 m) matte (a lignified terrace causing seafloor elevation) in which the leaves reach the surface and form a compact natural barrier to waves in front of the beach. Such a so-called ‘fringing reef’ of P. oceanica is today recognized of high ecological value and specific conservation efforts are required. The construction of the jetty implied the cutting of the matte, which directly destroyed part of the fringing reef. In addition, meadow mapping and sedimentological analyses coupled with morphodynamic modelling showed that the ecosystem of the whole cove had been greatly altered by the jetty. We used the geometric planform approach, a proper tool in the study of headland-controlled embayment, both to characterise the present situation of Prelo cove and to simulate the original one, before the jetty was built. In the long term, such a small jetty completely altered the configuration and the hydrodynamic conditions of the whole cove, splitting the original pocket beach into two smaller ones and creating strong rip-currents flowing seaward along the jetty. These rip-currents enhanced erosion of residual shallow portions of the meadow and further modified the sedimentary fluxes in shallow waters. A century after the construction of the jetty, an irreversible environmental damage has occurred, as the slow growing rate of P. oceanica implies that the high matte terrace and the fringing reef will hardly form again, even after the removal of the jetty. The lesson learnt from this study is that even such small, and therefore reputed intrinsically ‘innocent’, interventions on the coastal zone require accurate planning based on interdisciplinary studies to understand and respect the delicate interplay among morphological, hydrodynamic and ecological components. 相似文献