Contrasting weathering and climate regimes in forested and cleared sandstone temples of the Angkor region

Comparative assessment of stone weathering intensities and bioclimatic conditions was conducted at four temples located in cleared and forested sites of the Angkor Park, based on similar protocols. Four thousand sculpted lotus petals carved in the same grey sandstone were categorized by using two customized scales of weathering intensity, and climate monitoring was conducted from December 2008 to November 2009. Whereas 70% of the sandstone lotus petals are almost completely destroyed by mechanical weathering in cleared areas, 74% of petals located in forested environments appear to be totally free of mechanical weathering and are only affected by superficial biochemical weathering. Ambient conditions are also contrasting, with the magnitude of the diurnal surface temperature and relative humidity ranges being three times higher at cleared sites than in wooded areas. As wetting–drying cycles are the driving force of sandstone decay at Angkor, causal links are suggested between weathering and climate regimes. In wooded areas, the microclimate is buffered by the forest and the associated lithobionts, which maintain constant humidity levels, reduce thermal stresses at the stone surface and induce a slow biochemical weathering regime. In cleared areas, direct exposure to sunshine and monsoon rains induces pronounced wetting–drying cycles conducive to swelling–shrinking movements and other potential processes, provoking the rapid mechanical decay of the sandstone. Even if local damage can be caused by tree roots, the forest cover and the associated lithobionts obviously play an overall protective role. Additionally, microtopographical factors related to architectural designs and post‐building events probably explain intra‐site and between site minor differences in the amount of sandstone decay, by influencing key factors such as the water residence time at the stone surface. Last, the contrasting weathering regimes in forested and cleared sites are but a trend, for besides overwhelming mechanical weathering, chemical weathering is also operative at cleared sites, as indicated by salt efflorescences and ferric oxidation. Copyright © 2012 John Wiley & Sons, Ltd.     

Exploration of the Outer Solar System by Stellar Occultations

Stellar occultations are a powerful method for exploring the outer solar system, where faintness and small angular diameters prevent us from exploring in details objects like satellites, rings, or Kuiper Belt Objects. Unique kilometric spatial resolutions or better can be reached through that method. Occultations usually observe identified objects whose trajectory is known, though the occultation events might be difficult to predict. It is also possible to explore populations of small objects populations whose density in the sky plane is large enough to search for serendipitous occultations. Various instrumental methods exist for both predicted and serendipitous occultation, both needing fast photometric recordings of target stars.     

Observations of the Earth's atmosphere: Introductory remarks

The Earth is surrounded by a layer of relatively thin gas, the mass of which is mainly concentrated in the first kilometres. With an exponential decrease of the density of the atmosphere as a function of altitude, 99.9% of this mass is located in the first 50 km. In addition, the composition of major species is homogeneous up to about 85 km, contrarily to what happens beyond. This is the homosphere. This layer of atmosphere, considered in this special issue, is also that which we breathe and which we unfortunately often pollute. All this justifies considering it as of vital importance, in the most basic sense of the word. However, in studying it, it is not possible to ignore what is happening beyond, from where comes, in particular, solar radiation, just as we cannot ignore what happens below the continents and the oceans, where solar radiation is absorbed, diffused and re-emitted to the top by the Earth's surface as infrared radiation. We must therefore keep in mind what are the layers that surround the homosphere, the importance of observing them and also give some examples of possible interactions which may exist with the surrounding layers; these are the objectives of these introductory remarks. Another general consideration must be made here, concerning the problems, which have existed until the middle of the 20th century, of how to observe the atmosphere in situ at all the altitudes. However, since then, the development of engineering involving balloons, rockets, aircrafts and artificial satellites has revolutionized our knowledge of this observational atmosphere; this is the second message of these remarks.     

Radiocarbon age inversions and progression: source and causes in Late Holocene sediments from Lake Chapala,western Mexico

The results of eight radiocarbon datings of Lake Chapala sediments (site T46) are presented, the age inversions (AI) observed and their age progression discussed. As deduced from some AIs and the ²¹⁰Pb activity (site CHP4), the bioturbation zone in the lake varies over a depth of 5–25 cm. The linear sedimentation rates (LSRs) calculated from ¹⁴C ages do not match the LSR calculated from unsupported ²¹⁰Pb activity for the upper sediments. This demonstrates the usefulness of dating sediments with complementary radiometric techniques such as short-lived isotope counting (SLIC), i.e., ²¹⁰Pb and ¹³⁷Cs. This approach leads to the following conclusions: (1) The incorporation of detrital particles with ancient carbon into the sedimentary column of the lake occurred by a combination of: (a) the presence of outcrops of hydrothermal petroleum with ages >40 ka (ka = thousands of years) in the lake, and (b) mass transport due to the presence of two elongated gyre circulation patterns integrated by cyclonic circulation (counterclockwise) in the north portion of the lake and anticyclonic circulation in the southern part. (2) Consequently, the ¹⁴C ages of shallow lake sediments have geologic ages one order of magnitude greater compared to their ages determined by the ²¹⁰Pb method. (3) A bioturbation mechanism is not necessary to explain the ¹⁴C AI in the top 70 cm and from 110 to 150 cm depth of the sediments. (4) According to the biological proxies data for the last 600 years B.P., the paleoclimate at Lake Chapala has changed from sub-humid to dry environmental conditions, and eutrophication has increased over the past 100 years due to local input from ongoing agricultural activities.     

The M<Subscript>W</Subscript> 4.5 Vallorcine (French Alps) earthquake of 8 September 2005 and its complex aftershock sequence

On 8 September 2005 a moderate M_W 4.5 earthquake occurred in the north-western Alps midway between Chamonix (France) and Martigny (Switzerland). The focal mechanism corresponds to a right-lateral strike-slip on a N60°E fault plane. The foreshock–mainshock–aftershock sequence is investigated on the basis of data recorded by a temporary network of 28 stations deployed for 1 month just after the mainshock, and data from permanent, regional seismic networks. Absolute and relative locations of more than 400 events are obtained with a mean uncertainty of approximately 0.2 km. Small foreshocks, the mainshock, and early and late aftershocks are located relative to the main aftershock set. The seismic sequence exhibits a surprisingly complex structure, with at least five clusters on distinct fault planes. The main elongated cluster agrees with the location of the mainshock, its hypocenter being 4.3 km below sea level. We discuss the relationship between the right-lateral fault beneath the Loriaz peak (the source of the Vallorcine event), the nearby normal Remuaz fault, and the regional seismotectonic stress field.     

Elimination des noeuds dans le probleme newtonien des quatre corps

Résumé Nous appliquons la méthode des transformations canoniques à variables imposées à la réduction du problème newtonien des quatre corps. L'élimination du centre de gravité étant supposée faite, le problème est ramené à celui des trois corps fictifs. Alors nous menons à bien la réduction dûe aux intégrales des aires explicitement sous forme Hamiltonienne en tenant compte de l'aspect géométrique d'élimination des noeuds préconisé par Jacobi.Nous nous imposons trois fonctions comme nouvelles variables: la troisième intégrale des aires et deux fonctions in variantes; ces deux dernières fonctions resteront nulles lorsque nous prendrons comme troisième axe de coordonnées l'axe défini par le moment cinétique des quatre corps; elles sont choisies en involution avec la troisième intégrale des aires et de crochet un entre elles. Cela nous conduit à déterminer un système de quatorze variables canoniques que nous interprétons géométriquement. Il y a effectivement élimination des moeuds: il s'introduit un pseudo-noeud commun aux deuxième et troisième corps fictifs qui concide avec le noeud du premier corps fictif; ces noeud et pseudo-noeud sont repérés par un paramètre ignorable.

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Elimination of nodes in the Newtonian four-body problem

We apply the method of canonical trasformations with imposed variables to the reduction of the Newtonian four-body problem. After the elimination of the center of gravity, the problem is reduced to that of three fictitious bodies. Then we proceed to the actual reduction using the integrals of angular momentum, in Hamiltonian formulation, and considering the geometrical aspects of the elimination of the nodes advocated by Jacobi.We impose three functions as new variables: the third integral of angular momentum and two invariant functions; these last two functions will remain null when we take as third coordinate axis the axis, defined by the momentum vector of the four bodies; they are chosen in involution with the third integral of momentum and so that their Poisson bracket is equal to one. Then we determine a system of fourteen canonical variables which have a simple geometrical interpretation. It is an actual elimination of the nodes: a pseudonode for the second and third fictitious bodies is introduced which coincides with the node of the first fictitious body; the node and the pseudo-node are referred to by an ignorable parameter.

     

Evaluation of the Risk of Marine Slope Instability: A Pseudo-3D Approach for Application to Large Areas

Abstract

This article presents a methodology developed to evaluate the instability of submarine slopes that extend over a large area. Special attention was paid to (1) the complex geometry (bathymetry) and the expanse of the slope, (2) the heterogeneity of the sediment, and (3) the distribution of the pore pressure. The safety factor was considered as a spatially varying quantity. The General Formulation (GLE, Fredlund and Krahn 1977), which fully satisfies equilibrium conditions, was used for evaluating the stability of the marine slope. The submarine slope failure, which occurred on 16 October 1979 during the construction of the new Nice airport, was studied in order to test the developed model. Geotechnical parameters were taken from experimental tests carried out by IFREMER on 19 cores extracted at different depths (from 27 m to 1300 m) (Cochonat, Bourillet, and Savoye, 1993; Mulder et al., 1994). Many scenarios were proposed in order to explain the cause of the Nice slope failure (Habib, 1994). In this article, two of those scenarios were tested. Simulation results are presented and discussed.     

A pilot study of genetic differentiation between two phenotypes of a Mediterranean population of the bivalve Cerastoderma glaucum and genetic discrimination with other Cerastoderma glaucum and Cerastoderma edule populations outside the Mediterranean

The internal transcribed spacer 1 (ITS1) region of 29 individuals of Cerastoderma glaucum (from the Mediterranean Sea, the Atlantic and the North Sea) and 18 individuals of Cerastoderma edule (from the Atlantic and the North Sea) and the cytochrome c oxidase subunit I (COI) region of 43 individuals of C. glaucum (from the Mediterranean Sea, the Atlantic and the North Sea) and 9 individuals of C. edule (from the Atlantic and the North Sea) were PCR amplified and sequenced. The ITS1 sequences led us to describe 27 genetic haplotypes, while 21 genetic haplotypes were determined via the COI sequences. The ITS1 and the COI sequences revealed an important genetic variability within the Mediterranean population of C. glaucum, which contained two different phenotypes: orange foot and yellow foot. A genetic differentiation between the two phenotypes was revealed by the nucleotide diversity index (π) and is strengthened by the AMOVA analysis. This result leads us to suspect the presence of two different groups in the same population of C. glaucum. Nevertheless to be confirmed this hypothesis requires further studies using more locations and a larger number of sample sizes.     

Partitioning Stakeholders for the Economic Valuation of Ecosystem Services: Examples of a Mangrove System

Although the importance of ecosystem services provided by natural forests, especially mangroves, is well known, the destruction of these environments is still ubiquitous and therefore protection measures are urgently needed. The present study compares the current approach of economic valuation of ecosystem services to a proposed one, using a study case of a mangrove system as an example. We suggest that a cost-benefit analysis for economically valuing environmental services should be performed with three additional modifications consisting of (i) a categorization of local stakeholders as demanders of particular ecosystem services, (ii) acknowledgement of the government as one of these demander groups, and (iii) the inclusion of opportunity costs in the valuation. The application of this approach to the mangrove area in the east portion of Great Abaco Island, the Bahamas, reveals that not only the ecosystem services received differ between demander groups, but the monetary benefits and costs are also specific to each of these groups. We show that the economic valuation of the ecosystem should be differentiated for each category, instead of being calculated as a net ‘societal value’ as it is currently. Applying this categorization of demanders enables a better understanding of the cost and benefit structure of the protection of a natural area. The present paper aims to facilitate discussions regarding benefit and cost sharing related to the protection of natural areas.