The dual isotopes of deep nitrate as a constraint on the cycle and budget of oceanic fixed nitrogen   总被引：1，自引：0，他引：1  

Daniel M. Sigman  Peter J. DiFiore  Mathis P. Hain  Curtis Deutsch  Yi Wang  David M. Karl  Angela N. Knapp  Moritz F. Lehmann  Silvio Pantoja 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1419-1439

We compare the output of an 18-box geochemical model of the ocean with measurements to investigate the controls on both the mean values and variation of nitrate δ¹⁵N and δ¹⁸O in the ocean interior. The δ¹⁸O of nitrate is our focus because it has been explored less in previous work. Denitrification raises the δ¹⁵N and δ¹⁸O of mean ocean nitrate by equal amounts above their input values for N₂ fixation (for δ¹⁵N) and nitrification (for δ¹⁸O), generating parallel gradients in the δ¹⁵N and δ¹⁸O of deep ocean nitrate. Partial nitrate assimilation in the photic zone also causes equivalent increases in the δ¹⁵N and δ¹⁸O of the residual nitrate that can be transported into the interior. However, the regeneration and nitrification of sinking N can be said to decouple the N and O isotopes of deep ocean nitrate, especially when the sinking N is produced in a low latitude region, where nitrate consumption is effectively complete. The δ¹⁵N of the regenerated nitrate is equivalent to that originally consumed, whereas the regeneration replaces nitrate previously elevated in δ¹⁸O due to denitrification or nitrate assimilation with nitrate having the δ¹⁸O of nitrification. This lowers the δ¹⁸O of mean ocean nitrate and weakens nitrate δ¹⁸O gradients in the interior relative to those in δ¹⁵N. This decoupling is characterized and quantified in the box model, and agreement with data shows its clear importance in the real ocean. At the same time, the model appears to generate overly strong gradients in both δ¹⁸O and δ¹⁵N within the ocean interior and a mean ocean nitrate δ¹⁸O that is higher than measured. This may be due to, in the model, too strong an impact of partial nitrate assimilation in the Southern Ocean on the δ¹⁵N and δ¹⁸O of preformed nitrate and/or too little cycling of intermediate-depth nitrate through the low latitude photic zone.  相似文献   

Computation of Geometric Spreading of Seismic Body Waves in Laterally Inhomogeneous Media with Curved Interfaces     

V. &#;erven  J. Langer  I. P&#;en&#;ík 《Geophysical Journal International》1974,38(1):9-19

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Environmentalism and Natural Aggregate Mining     

Drew  Lawrence J.  Langer  William H.  Sachs  Janet S. 《Natural Resources Research》2002,11(1):19-28

Sustaining a developed economy and expanding a developing one require the use of large volumes of natural aggregate. Almost all human activity (commercial, recreational, or leisure) is transacted in or on facilities constructed from natural aggregate. In our urban and suburban worlds, we are almost totally dependent on supplies of water collected behind dams and transported through aqueducts made from concrete. Natural aggregate is essential to the facilities that produce energy—hydroelectric dams and coal-fired powerplants. Ironically, the utility created for mankind by the use of natural aggregate is rarely compared favorably with the environmental impacts of mining it. Instead, the empty quarries and pits are seen as large negative environmental consequences. At the root of this disassociation is the philosophy of environmentalism, which flavors our perceptions of the excavation, processing, and distribution of natural aggregate. The two end-member ideas in this philosophy are ecocentrism and anthropocentrism. Ecocentrism takes the position that the natural world is a organism whose arteries are the rivers—their flow must not be altered. The soil is another vital organ and must not be covered with concrete and asphalt. The motto of the ecocentrist is man must live more lightly on the land. The anthropocentrist wants clean water and air and an uncluttered landscape for human use. Mining is allowed and even encouraged, but dust and noise from quarry and pit operations must be minimized. The large volume of truck traffic is viewed as a real menace to human life and should be regulated and isolated. The environmental problems that the producers of natural aggregate (crushed stone and sand and gravel) face today are mostly difficult social and political concerns associated with the large holes dug in the ground and the large volume of heavy truck traffic associated with quarry and pit operations. These concerns have increased in recent years as society's demand for living space has encroached on the sites of production; in other words, the act of production has engendered condemnation. Many other environmental problems that are associated with dust and noise and blasting from quarry and pit operations have been reduced through the efficient use of technology. Recycling concrete in buildings, bridges, and roads and asphaltic pavements will ultimately reduce the demand for virgin natural aggregate. The impact created by the large holes in the ground required for the mining of natural aggregate can be greatly reduced by planning their reclamation before mining begins.  相似文献   

Relocation of microearthquake swarms in the Peloritani mountains – implications on the interpretation of seismotectonic patterns in NE Sicily, Italy     

L. Scarfî  H. Langer  A. Scaltrito 《Geophysical Journal International》2005,163(1):225-237

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Geodetic Reference System 1980   总被引：4，自引：3，他引：1  

H. Moritz 《Journal of Geodesy》2000,74(1):128-162

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Water level and atmospheric humidity history of Lake Ichkeul (northern Tunisia) during the last 3000 years     

Asma Ben Hamad  Finn A. Viehberg  Afef Khadraoui  Chahira Zaïbi  Yasser Trabelsi  Gloria H. Mouanga  Martin R. Langer  Habib Abida  Fekri Kamoun 《Arabian Journal of Geosciences》2018,11(12):316

Changes in paleoecology and climate of northern Tunisia during the last 3000 years were reconstructed based on the flood history interpreted from a 172-cm sediment core of Lake Ichkeul (NW Tunisia). Seven wet/dry episodes were identified based on biological (ostracods, foraminifera and mollusks) and biotic indices (H and E index, species richness and abundance). These proxy-based environmental changes were supported by correspondence analyses (CAs) and ecophenotypic responses of the brackish taxon Cyprideis torosa in addition to a grain-size study. Two dry episodes were identified in the lower (EP1) and upper (EP7) parts of the core. These were marked by the dominance of the brackish ostracod C. torosa. High water salinity was indicated by the presence of the brackish ostracod Loxoconcha elliptica, the foraminifer Ammonia sp. and lagoonal mollusks. The occurrence of the freshwater ostracods Ilyocypris sp., Herpetocypris sp., Dawinula stevensoni and Limnocythere inopinata was associated with high species richness and ecophenotypic changes of C. torosa valves indicating lower salinity during three major wet episodes (EP2, EP4, and EP6). The ecological and environmental changes, occurring between 3050 and 50 cal. year BP, are most likely linked to an increase of fluvial inputs which are also recognized in several other Mediterranean lakes. The humid episodes were interrupted by two saline periods (EP3 and EP5) during which freshwater ostracod assemblages declined, diversity indices dropped to the lowest values, and fine-grained sediments became dominant. The top of the core is characterized by the remarkable dominance of L. elliptica coupled with C. torosa, the absence of freshwater ostracods, and the changes in grain-size sediment parameters which are most likely the result of anthropogenic activities. The changes in hydrochemistry and sedimentology were attributed to the deepening of the Bizerte navigation canal, main wadis damming, and Tinja sluice construction which mostly occurred in the XX^th century.  相似文献   

Topographic signatures of progressive glacial landscape transformation     

Moritz Liebl  Jörg Robl  David Lundbek Egholm  Günther Prasicek  Kurt Stüwe  Gerit Gradwohl  Stefan Hergarten 《地球表面变化过程与地形》2021,46(10):1964-1980

The Pleistocene glaciations left a distinct topographic footprint in mountain ranges worldwide. The geometric signature of glacial topography has been quantified in various ways, but the temporal development of landscape metrics has not been traced in a landscape evolution model so far. However, such information is needed to interpret the degree of glacial imprint in terms of the integrated signal of temporal and spatial variations in erosion as a function of glacial occupation time. We apply a surface process model for cold-climate conditions to an initially fluvial mountain range. By exploring evolving topographic patterns in model time series, we determine locations where topographic changes reach a maximum and where the initial landscape persists. The signal of glacial erosion, expressed by the overdeepening of valleys and the steepening of valley flanks, develops first at the glacier front and migrates upstream with ongoing glacial erosion. This leads to an increase of mean channel slope and its variance. Above steep flanks and head-walls, however, the observed mean channel slope remains similar to the mean channel slope of the initial fluvial topography. This leads to a characteristic turning point in the channel slope–elevation distribution above the equilibrium line altitude, where a transition from increasing to decreasing channel slope with elevation occurs. We identify this turning point and a high channel slope variance as diagnostic features to quantify glacial imprint. Such features are abundant in glacially imprinted mid-latitude mountain ranges such as the Eastern Alps. By analysing differently glaciated parts of the mountain range, we observe a decreasing clarity of this diagnostic morphometric property with decreasing glacial occupation. However, catchments of the unglaciated eastern fringe of the Alps also feature turning points in their channel slope–elevation distributions, but in contrast to the glaciated domain, the variance of channel slope is small at all elevation levels.  相似文献   

“Failed” eruptions revealed by pattern classification analysis of gas emission and volcanic tremor data at Mt. Etna,Italy     

S. Falsaperla  B. Behncke  H. Langer  M. Neri  G. G. Salerno  S. Giammanco  E. Pecora  E. Biale 《International Journal of Earth Sciences》2014,103(1):297-313

During the spring of 2007, paroxysmal activity occurred at the Southeast Crater of Mt. Etna, always associated with sharp rises in the amplitude of the volcanic tremor. Activity ranged from strong Strombolian explosions to lava fountains coupled with copious emission of lava flows and tephra. During inter-eruptive periods, recurrent seismic unrest episodes were observed in the form of temporary enhancements of the volcanic tremor amplitude, but they did not culminate in eruptive activity. Here, we present the results of an analysis of these inter-eruptive periods by integrating seismic volcanic tremor, in-soil radon, plume SO₂ flux, and thermal data. SO₂ flux and thermal radiation are envisaged as the “smoking gun,” and certifying that changes in seismic or radon data can be considered as volcanogenic. Short-term changes were investigated by pattern classification based on Kohonen maps and fuzzy clustering on volcanic tremor, radon, and ambient parameters (pressure and temperature). Our results unveil “failed” eruptions between February and April 2007 that are explained as ascending magma batches, which triggered repeated episodes of gas pulses and rock fracturing, but that failed to reach the surface.  相似文献   

Friedmann universe as a limit of dust shell model     

A. Eid  J. Langer 《Astrophysics and Space Science》2012,337(2):747-752

We generalize the equations of motion of a shell for a sequence of thin shells and derive the general form of the expansion law of the dust shell model which represents the FRW universe when we take an appropriate limit. The three Friedmann model for the three possible values of k:0,±1 are satisfied.  相似文献   

Revisiting gateway cities: connecting hubs in global networks to their hinterlands     

Sören Scholvin  Moritz Breul  Javier Revilla Diez 《Urban geography》2013,34(9):1291-1309

Gateway cities have received much attention from urban geographers. In spite of outstanding contributions being made, we think that the concept needs to be revisited with regard to regional development implications. Bringing together research on global production networks (GPNs) and world cities, this article shows that gateway cities are critical for development in networks, generating impulses for peripheral locations by engaging them in processes of “strategic coupling.” Yet, gateway cities also concentrate segments of GPNs to the detriment of their hinterlands. We conceptualize gateway cities with the aid of five features: logistics and transport, industrial processing, corporate control, service provision and knowledge generation. Our concept allows for an understanding of cities in global and regional economic processes beyond corporate headquarters, corporate services and governance – that is, beyond the boundaries of existing research. It unsettles traditional understandings of strategic coupling and world cities, filling a lacuna on city–hinterland connections.  相似文献