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611.
612.
Summary Rock magnetism and magnetostratigraphy of the lower part of the Hadar Formation (Afar, Ethiopia) is presented after analysis
of multiple new collection of samples from over 84 horizons. The Hadar Formation is composed of lacustrine, lake margin, fluvial
and flood plain sediments and known for important Pliocene vertebrate faunas including Australopithecus afarensis. Hysteresis
measurements, thermomagnetic analysis, growth and decay of isothermal remanent magnetisation are used to unravel the complex
magnetic mineralogy of the different representative lithologies. Ferrimagnetic minerals of magnetite or titanomagnetite in
composition, in the stable pseudo-single domain (PSD) size range are found to be the main carriers of the remanence. In most
sites the characteristic remanence was isolated using stepwise thermal demagnetisation. The overall mean direction for about
72 horizons (434 samples) is D=358·6°, I=7° (k=17·9, α95=4°) implying some 14° of inclination shallowing, related to sediment compaction due to the very rapid sedimentation history
of the site. Five successive polarity zones (N1-R1-N2-R2-N3) are identified and correlation with the lower Gauss chron of
the astronomically calibrated geomagnetic polarity time scale (GPTS) is proposed using the existing40Ar/39Ar ages. This implies the existence of a short normal polarity event (N2), identified on six different sites, within the reversed
Mammoth subchron, called the Kada-Hadar event. The age calculated for the Kada-Hadar event, using linear interpolation of
the dated horizons, assuming a constant rate of sedimentation is 3.246 Ma and its duration is about 8 kyr. 相似文献
613.
Phillip J. Clapham Simon Childerhouse Nicolas J. Gales Lorenzo Rojas-Bracho Michael F. Tillman Robert L. Brownell Jr. 《Marine Policy》2007
Morishita's “multiple analysis” of the whaling issue [Morishita J. Multiple analysis of the whaling issue: Understanding the dispute by a matrix. Marine Policy 2006;30:802–8] is essentially a restatement of the Government of Japan's whaling policy, which confuses the issue through selective use of data, unsubstantiated facts, and the vilification of opposing perspectives. Here, we deconstruct the major problems with Morishita's article and provide an alternative view of the whaling dispute. For many people in this debate, the issue is not that some whales are not abundant, but that the whaling industry cannot be trusted to regulate itself or to honestly assess the status of potentially exploitable populations. This suspicion has its origin in Japan's poor use of science, its often implausible stock assessments, its insistence that culling is an appropriate way to manage marine mammal populations, and its relatively recent falsification of whaling and fisheries catch data combined with a refusal to accept true transparency in catch and market monitoring. Japanese policy on whaling cannot be viewed in isolation, but is part of a larger framework involving a perceived right to secure unlimited access to global marine resources. Whaling is inextricably tied to the international fisheries agreements on which Japan is strongly dependent; thus, concessions made at the IWC would have potentially serious ramifications in other fora. 相似文献
614.
Michiel Rutgers van der Loeff Manmohan M. Sarin Mark Baskaran Claudia Benitez-Nelson Ken O. Buesseler Matt Charette Minhan Dai
rjan Gustafsson Pere Masque Paul J. Morris Kent Orlandini Alessia Rodriguez y Baena Nicolas Savoye Sabine Schmidt Robert Turnewitsch Ingrid Vge James T. Waples 《Marine Chemistry》2006,100(3-4):190
The short-lived thorium isotope 234Th (half-life 24.1 days) has been used as a tracer for a variety of transport processes in aquatic systems. Its use as a tracer of oceanic export via sinking particles has stimulated a rapidly increasing number of studies that require analyses of 234Th in both marine and freshwater systems. The original 234Th method is labor intensive. Thus, there has been a quest for simpler techniques that require smaller sample volumes. Here, we review current methodologies in the collection and analysis of 234Th from the water column, discuss their individual strengths and weaknesses, and provide an outlook on possible further improvements and future challenges. Also included in this review are recommendations on calibration procedures and the production of standard reference materials as well as a flow chart designed to help researchers find the most appropriate 234Th analytical technique for a specific aquatic regime and known sampling constraints. 相似文献
615.
With the advent of satellite altimetry it has become possible to determine the gravity field of the oceans on a global scale. This set of data can be used to predict the bathymetry of deep-seafloor features such as seamounts and ridges. During the last two decades, several algorithms which can be used to develop bathymetric predictions from satellite altimeter data have been published. The characteristics and quality of these algorithms are reviewed in this study. Based on this analysis, we suggest some guidelines for processing data towards the production of maps showing predicted bathymetry for economical purposes. 相似文献
616.
617.
A. Rigo A. Souriau H. Pauchet A. Grésillaud M. Nicolas C. Olivera S. Figueras 《Journal of Seismology》1997,1(1):3-14
An earthquake with local magnitude (ML) 5.2 occurred February 18, 1996 in the eastern Pyrenees (France) near the town of Saint-Paul de Fenouillet. This event is the first of this magnitude in France to be well recorded instrumentally. Less than 24 hours after the main shock, we installed a temporary network of 30 seismological stations in the epicentral area to record the aftershock sequence. In this paper, we analyse the main shock and present the 37 largest aftershocks (1.8 Ml 3.4) in the two months following the main shock. These events are located using data from the permanent Pyrenean seismological network and the temporary network when available. We also determined eight fault plane solutions using the P-wave first motions. The main shock and the aftershocks are located inside the small Agly massif. This Hercynian structure sits some 8 km north of the North Pyrenean Fault, which is usually considered to be the suture between the Iberian and Eurasian plates. The mechanism of the main shock is a left-lateral strike-slip on an E–W trending fault. The fault plane solutions of the aftershocks are mostly E–W striking reverse faults, in agreement with the general north-south shortening of the Pyrenees. The aftershocks located down to 11 km depth, indicating that the Agly massif is deeply fractured. The main interpretations of these results are: (i) The main shock involved an E–W trending fault inside the highly fractured Agly massif, relaying the North Pyrenean Fault which had, at least in the last 35 years, a poor seismic activity along this segment; (ii) The Saint-Paul de Fenouillet syncline to the north and the North Pyrenean Fault to the south delimit a 15 km wide senestral shear zone. Such a structure is also suggested by the highly fractured pattern of the Agly massif and by small en echelon faults and secondary folds in the Saint-Paul de Fenouillet syncline; (iii) we suggest that the North Pyrenean Frontal Thrust, located less than 10 km north of the Agly massif, has a ramp geometry at depth below the Agly massif. 相似文献
618.
619.
This paper investigates the equity implications of marketing ecosystem services in protected areas and rural communities. We use a three-tiered equity framework to analyse four distinct efforts to commercialise watershed recharge and carbon dioxide fixation by forests in Meso-America. We show that project development and participation are strongly mediated by organisational networks, as well as existing rights of access over land and forest resources. We demonstrate that procedural fairness diverges strongly when initiatives are implemented in protected areas or in rural communities. While in the former reserve managers and intermediaries concentrate all decision-making power, initiatives working with rural communities are able to integrate more significantly service providers in management decisions. Marketing ecosystem services in protected areas contributes to reduce expenditure rates for protected area management, but also results in less equitable outcomes, as rural communities and forest resource users become excluded from receiving sustained development benefits. When ecosystem services are commercialised by rural farmers, payments do not cover opportunity costs but act as a significant incentive for participation in most cases. Ecosystem service providers also benefit from complementary project activities, such as forest management training and agricultural extension support. We argue that limited economic impact and existing inequities in decision-making and outcomes can be explained by problems of institutional design, in particular the inability of markets and payments for ecosystem services to account for context-related factors, such as property rights. 相似文献
620.
Nicolas Gillet rew Jackson Christopher C. Finlay 《Geophysical Journal International》2007,171(3):1005-1016
We incorporate a maximum entropy image reconstruction technique into the process of modelling the time-dependent geomagnetic field at the core–mantle boundary (CMB). In order to deal with unconstrained small lengthscales in the process of inverting the data, some core field models are regularized using a priori quadratic norms in both space and time. This artificial damping leads to the underestimation of power at large wavenumbers, and to a loss of contrast in the reconstructed picture of the field at the CMB. The entropy norm, recently introduced to regularize magnetic field maps, provides models with better contrast, and involves a minimum of a priori information about the field structure. However, this technique was developed to build only snapshots of the magnetic field. Previously described in the spatial domain, we show here how to implement this technique in the spherical harmonic domain, and we extend it to the time-dependent problem where both spatial and temporal regularizations are required. We apply our method to model the field over the interval 1840–1990 from a compilation of historical observations. Applying the maximum entropy method in space—for a fit to the data similar to that obtained with a quadratic regularization—effectively reorganizes the magnetic field lines in order to have a map with better contrast. This is associated with a less rapidly decaying spectrum at large wavenumbers. Applying the maximum entropy method in time permits us to model sharper temporal changes, associated with larger spatial gradients in the secular variation, without producing spurious fluctuations on short timescales. This method avoids the smearing back in time of field features that are not constrained by the data. Perspectives concerning future applications of the method are also discussed. 相似文献