Core-mantle coupling and viscoelastic deformations     

Marianne Greff-Lefftz  Hilaire Legros 《Physics of the Earth and Planetary Interiors》1995,90(3-4)

Writing the angular momentum theorem for the Earth and for its fluid core, we show that there are couplings between the core and the mantle induced by viscomagnetic torque, by external active torque, by topographic torque acting at the core-mantle boundary (CMB) but also by viscoelastic deformations of the CMB which may perturb the axial rotations of the Earth and of the core. We compute these deformations at the CMB induced by the Pleistocenic deglaciation. The time-dependence of inertia tensor perturbations, i.e. the rheology of the mantle, is very important in the calculation of the coupling. Taking into account the passive viscomagnetic torque of tangential traction acting at the CMB, we investigate, for different values and various temporal evolutions of the topographic torque, the perturbations in the rotations of the Earth and of the core induced by the deglaciation, by the constant torque of tidal friction and by the 18.6 year tidal potential. We show that, for these excitation sources, the existence of a constant topographic torque involves the core oscillating with respect to the mantle and thus forbids any large drift of the core with respect to the mantle. However, it seems theoretically possible to have an excitation source with enough energy which involves a shift of the core with respect to the mantle. If the pressure within the fluid core varies with time, the motion of the core with respect to the mantle could be drastically different.  相似文献   

Variations in abundances and distributions of isoprenoid chromans and long-chain alkylbenzenes in sediments of the Mulhouse Basin: a molecular sedimentary record of palaeosalinity     

Jaap S. Sinninghe Damst  Brendan J. Keely  Susannah E. Betts  Marianne Baas  James R. Maxwell  Jan W. de Leeuw 《Organic Geochemistry》1993,20(8)

The abundances and distribution patterns of mono-, di- and trimethylated 2-methyl-2-(4,8,12-trimethyltridecyl) chromans (MTTCs) and long-chain alkylbenzenes in extracts of marl (66 samples), anhydrite (15) and halite (1) strata of the Salt IV Formation of the Oligocene Mulhouse Basin are reported. The distributions of the methylated MTTCs indicate salinity changes of the upper part of a density stratified water column of the basin. These variations are explained by a tectonically or climatically induced change in the supply of water of relative lower salinity to form a layer overlying the deeper water brine. Hence, it is suggested that mesohaline (3.5–15%) conditions in the surface waters were established as a result of periodic incursions of marine water and subsequent evaporation. Conversely, during periods when the surface water was derived mainly from fresh water from the hinterland, lower average salinity in the surface layer resulted. The distributions of long-chain alkylbenzenes also appear to record these changes.  相似文献   

Sedimentary iron inputs stimulate seagrass (Posidonia oceanica) population growth in carbonate sediments     

Núria Marbà  Carlos M. Duarte  Marianne Holmer  Maria Ll. Calleja  Elvira Álvarez  Elena Díaz-Almela  Neus Garcias-Bonet 《Estuarine, Coastal and Shelf Science》2008

The relationship between sedimentary Fe inputs and net seagrass population growth across a range of Posidonia oceanica meadows growing in carbonate Mediterranean sediments (Balearic Islands, Spain; SE Iberian Peninsula, Spain; Limassol, Cyprus; Sounion, Greece) was examined using comparative analysis. Sedimentary Fe inputs were measured using benthic sediment traps and the net population growth of P. oceanica meadows was assessed using direct census of tagged plants. The meadows examined ranged from meadows undergoing a severe decline to expanding meadows (specific net population growth, from −0.14 yr⁻¹ to 0.05 yr⁻¹). Similarly, Fe inputs to the meadows ranged almost an order of magnitude across meadows (8.6–69.1 mg Fe m⁻² d⁻¹). There was a significant, positive relationship between sedimentary iron inputs and seagrass net population growth, accounting for 36% of the variability in population growth across meadows. The relationship obtained suggested that seagrass meadows receiving Fe inputs below 43 mg Fe m⁻² d⁻¹ are vulnerable and in risk of decline, confirming the pivotal role of Fe in the control of growth and the stability of seagrass meadows in carbonate sediments.  相似文献   

Monitoring recovery after earthquakes through the integration of remote sensing,GIS, and ground observations: the case of L’Aquila (Italy)     

Diana Contreras  Thomas Blaschke  Dirk Tiede  Marianne Jilge 《制图学和地理信息科学》2016,43(2):115-133

The usefulness of remote sensing (RS), geographical information systems, and ground observations for monitoring changes in urban areas has been demonstrated through many examples over the last two decades. Research has generally focused on the relief phase following a disaster, but we have instead investigated the subsequent phases involving early recovery, recovery, and development. Our aim was to determine to what extent integration of the available tools, techniques, and methods can be used to efficiently monitor the progress of recovery following an earthquake. Changes in buildings within the Italian city of L’Aquila following the 2009 earthquake were identified from Earth observation data and are used as indicators of progress in the recovery process. These changes were identified through (1) visual analysis, (2) automated change detection using a set of decision rules formulated within an object-based image analysis framework, and (3) validation based on a combination of visual and semiautomated interpretations. An accuracy assessment of the automated analysis showed a producer accuracy of 81% (error of omission: 19%) and a user accuracy of 55% (error of commission: 45%). The use of RS made it possible for the identification of changes to be spatially exhaustive, and also to increase the number of categories used for a recovery index. In addition, using RS allowed the area requiring extensive fieldwork (to monitor the progress of the recovery process) to be reduced.  相似文献   

The Cariris Velhos tectonic event in Northeast Brazil     

Edilton José dos Santos  William Randall Van Schmus  Marianne Kozuch  Benjamim Bley de Brito Neves 《Journal of South American Earth Sciences》2010,29(1):61-76

The Borborema Province in northeastern South America is a typical Brasiliano-Pan-African branching system of Neoproterozoic orogens that forms part of the Western Gondwana assembly. The province is positioned between the São Luis-West Africa craton to the north and the São Francisco (Congo-Kasai) craton to the south. For this province the main characteristics are (a) its subdivision into five major tectonic domains, bounded mostly by long shear zones, as follows: Médio Coreaú, Ceará Central, Rio Grande do Norte, Transversal, and Southern; (b) the alternation of supracrustal belts with reworked basement inliers (Archean nuclei + Paleoproterozoic belts); and (c) the diversity of granitic plutonism, from Neoproterozoic to Early Cambrian ages, that affect supracrustal rocks as well as basement inliers. Recently, orogenic rock assemblages of early Tonian (1000–920 Ma) orogenic evolution have been recognized, which are restricted to the Transversal and Southern domains of the Province.Within the Transversal Zone, the Alto Pajeú terrane locally includes some remnants of oceanic crust along with island arc and continental arc rock assemblages, but the dominant supracrustal rocks are mature and immature pelitic metasedimentary and metavolcaniclastic rocks. Contiguous and parallel to the Alto Pajeú terrane, the Riacho Gravatá subterrane consists mainly of low-grade metamorphic successions of metarhythmites, some of which are clearly turbiditic in origin, metaconglomerates, and sporadic marbles, along with interbedded metarhyolitic and metadacitic volcanic or metavolcaniclastic rocks. Both terrane and subterrane are cut by syn-contractional intrusive sheets of dominantly peraluminous high-K calc-alkaline, granititic to granodioritic metaplutonic rocks. The geochemical patterns of both supracrustal and intrusive rocks show similarities with associations of mature continental arc volcano-sedimentary sequences, but some subordinate intra-plate characteristics are also found.In both the Alto Pajeú and Riacho Gravatá terranes, TIMS and SHRIMP U–Pb isotopic data from zircons from both metavolcanic and metaplutonic rocks yield ages between 1.0 and 0.92 Ga, which define the time span for an event of orogenic character, the Cariris Velhos event. Less extensive occurrences of rocks of Cariris Velhos age are recognized mainly in the southernmost domains of the Province, as for example in the Poço Redondo-Marancó terrane, where arc-affinity migmatite-granitic and meta-volcano-sedimentary rocks show U–Pb ages (SHRIMP data) around 0.98–0.97 Ga. For all these domains, Sm–Nd data exhibit T_DM model ages between 1.9 and 1.1 Ga with corresponding slightly negative to slightly positive ε_Nd(t) values. These domains, along with the Borborema Province as a whole, were significantly affected by tectonic and magmatic events of the Brasiliano Cycle (0.7–0.5 Ga), so that it is possible that there are some other early Tonian rock assemblages which were completely masked and hidden by these later Brasiliano events.Cariris Velhos processes are younger than the majority of orogenic systems at the end of Mesoproterozoic Era and beginning of Neoproterozoic throughout the world, e.g. Irumide belt, Kibaride belt and Namaqua-Natal belt, and considerably younger than those of the youngest orogenic process (Ottawan) in the Grenvillian System. Therefore, they were probably not associated with the proposed assembly of Rodinia. We suggest, instead, that Cariris Velhos magmatism and tectonism could have been related to a continental margin magmatic arc, with possible back-arc associations, and that this margin may have been a short-lived (<100 m.y.) leading edge of the newly assembled Rodinia supercontinent.  相似文献   

Source effects and the interpretation of geomagnetic sounding data at sub-auroral latitudes     

Marianne Mareschal 《Geophysical Journal International》1981,67(1):125-136

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Ergebnisse der limnologischen Untersuchungen der Oberengadiner Seen     

Frau Dr. Marianne Bosli-Pavoni 《Aquatic Sciences - Research Across Boundaries》1971,33(1):386-409

Ohne Zusammenfassung  相似文献   

Some remarks about the degree-one deformation of the Earth     

Marianne Greff-Lefftz  Hilaire Legros 《Geophysical Journal International》1997,131(3):699-723

The degree-one deformation of the Earth (and the induced discrepancy between the figure centre and the mass centre of the Earth) is computed using a theoretical approach (Love numbers formalism) at short timescales (where the Earth has an elastic behaviour) as well as at long timescales (where the Earth has a viscoelastic or quasi-fluid behaviour). For a Maxwell model of rheology, the degree-one relaxation modes associated with the viscoelastic Love numbers have been investigated: the M_o mode does not exist and there is only one transition mode (instead of two) generated by a viscosity discontinuity.
The translations at each interface of the incompressible layers of the earth model [surface, 670 km depth discontinuity, core-mantle boundary (CMB) and inner-core boundary (ICB)] are computed. They are elastic with an order of magnitude of about 1 mm when the excitation source is the atmospheric continental loading or a magnetic pressure acting at the CMB. They are viscoelastic when the earth is submitted to Pleistocene deglaciation, with an order of magnitude of about 1 m. In a quasi-fluid approximation (Newtonian fluid) because of the mantle density heterogeneity their order of magnitude is about 100 m (except for the ICB, which is in quasi-hydrostatic equilibrium at this timescale).  相似文献   

Dispersion of tailings in the Knabena—Kvina drainage basin, Norway, 1: Evaluation of overbank sediments as sampling medium for regional geochemical mapping     

Marianne Langedal 《Journal of Geochemical Exploration》1997,58(2-3)

Molybdenum mining in the Knabena—Kvina drainage basin (1918–1973) left more than eight million tons of tailings in two small lakes in the headwater area of the Knabena river. The piles, that reach above the water surface, were freely eroded until a dam was built to reduce the dispersion in 1976. Sampling of tailings and fluvial sediments took place almost 20 years later. Sampling media were natural sediment sources, 1-cm-thick slices of overbank sediments of various depths, material from the tailings pond, sandbars, stream sediments, fjord sediments, and integrated samples of floodplain surfaces (0–25 cm). In total 734 samples were collected. Chemical analysis (ICP-AES after aqua regia or HNO₃ extraction) showed that overbank sediments at a certain depth represent the pre-industrial trace metal concentrations within the drainage basin. The tailings and recent fluvial sediments were enriched in approximately the same element suite. The highest enrichment factors were obtained for Cu (8–53) and Mo (22–57). Fluvial processes in the tailings pond have probably selectively eroded fine-grained, low-density particles. Thus, coarse chalcopyrite may have been left behind, while molybdate associated with fine-grained particles may have been selectively entrained causing dilution of Cu and enrichment of Mo in the downstream fluvial sediments. In the sandbars, the highest Cu and Mo concentrations were found in fine-grained sediments downstream of a low-gradient reach that act as a bedload trap. On the floodplains, it is seen that the first areas to be inundated in a flood situation (proximal to the river and in depressions) have the highest metal concentrations. For regional geochemical mapping it is suggested that overbank sediment profiles along river reaches with a laterally stable or slowly migrating channel, should be sampled. In such floodplains, pre-industrial overbank sediments are usually preserved at depth. In case of laterally unstable reaches upstream of the sampling point, polluted and unpolluted sediments may be interlayered or mixed. Therefore, samples should be collected from various depths or sedimentary units in such profiles. A similar sampling strategy should probably be adopted to detect vertical migration of elements especially in areas with acid rain and low bedrock buffer capacity. To obtain high contrasts between polluted and unpolluted drainage basins, the overbank sediment profiles should be within the proximal part of the floodplain.  相似文献   

Spatial distribution of phytoplankton in Spring 2004 along a transect in the eastern part of the North Sea     

Pavel Škaloud  Magda Řezáčová  Marianne Ellegaard 《Journal of Oceanography》2006,62(5):717-729

We report the results from a 250 km long transect, from the Danish coast to the North Sea at 55°30′ N, which was sampled every 32 km in order to study the composition and distribution of phytoplankton, and their dependence on the distance from the coast, depth and other environmental factors. Altogether 144 species of algae were identified by light, epifluorescence and electron microscopy. Some ecological preferences were found on the basis of measured environmental parameters and compared with the literature. Possible controlling mechanisms for the distribution patterns of the plankton algae were analyzed by multivariate statistics. Only distance from the coast was found to be a significant factor for algal distribution along the transect. Three main areas of the transect were found: the coastal, middle and oceanic areas. Diatoms, mainly the centric ones, were the most abundant group of algae. The other less abundant groups were Dinophyceae, Dictyochophyceae, Prasinophyceae and Chlorophyceae. The pattern of distribution of diatoms and dinophytes along the transect was more or less similar, with larger numbers of cells found close to both the eastern and western parts of the transect, although the species composition was different. Some species were found to prefer coastal waters, other species were characterized as oceanic, and several species were found at all stations. Porosira glacialis showed an atypical distribution along the transect, with highest abundances at both coastal and oceanic stations.  相似文献