Eocene fauna of Messel Pit Fossil Site, Germany

The paper reports sunthetically the Cocene fauna of the Messel Pit Fossil site of Germany, in detail, including its rich taxanomic composttions, geological and paleogeographic backgroud, and the studying and applying history.     

Variability and change in the Canadian cryosphere

During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing systems and retrieval algorithms for satellite measurements facilitated development of a snapshot of current cryospheric conditions, providing a baseline against which future change can be assessed. Key findings include: 1. surface air temperatures across the Canadian Arctic exhibit a warming trend in all seasons over the past 40?years. A consistent pan-cryospheric response to these warming temperatures is evident through the analysis of multi-decadal datasets; 2. in recent years (including the IPY period) a higher rate of change was observed compared to previous decades including warming permafrost, reduction in snow cover extent and duration, reduction in summer sea ice extent, increased mass loss from glaciers, and thinning and break-up of the remaining Canadian ice shelves. These changes illustrate both a reduction in the spatial extent and mass of the cryosphere and an increase in the temporal persistence of melt related parameters. The observed changes in the cryosphere have important implications for human activity including the close ties of northerners to the land, access to northern regions for natural resource development, and the integrity of northern infrastructure.     

The Canadian Meteorological Centre's Atmospheric Transport and Dispersion Modelling Suite

This paper describes the integrated suite of Lagrangian transport and dispersion models in operation at the Canadian Meteorological Centre. These models have been in use for several years and are applied to many types of environmental emergencies covering spatial scales from the very local to the global. The Modèle Lagrangien Courte Distance (MLCD) is used for atmospheric spills of the order of a few kilometres. The Modèle Lagrangien de dispersion de particules d'ordre 1 (MLDP1) is normally used for events affecting areas less than 100?km; Modèle Lagrangien dispersion de particules d'ordre zéro (MLDP0) is used for events of continental and global consequences. The Modèle Lagrangien dispersion de particules mode mixte (MLDPmm) alternates between first-order and zeroth-order depending on criteria specified by the user. The theoretical bases of the models are presented, and the main algorithms used in their implementation are discussed. Modelling of the diffusion processes is based on a stochastic differential equation with the assumption of quasi-stationary Gaussian turbulence, locally homogeneous in the horizontal. The practical aspects of the operational implementation are also described. Using these models, results from simulations of real cases on scales ranging from the very local, to a few kilometres, to regional (approximately 100?km) to continental (approximately 1000?km) and to global (approximately 10,000?km) are compared and validated with available observational data.     

Adaptation of the SNOWMAP algorithm for snow mapping over eastern Canada using Landsat-TM imagery

Abstract

The snow mapping algorithm SNOWMAP was adapted to Landsat-TM data and to the context of eastern Canada. Six Landsat-5 TM scenes were used. It was found that the original version of SNOWMAP greatly underestimates snow cover extent. The modification made to the original algorithm, by cancelling the minimum threshold of 0.1 on the NDVI value, allows gaps to be filled in. In addition, a spatial correction procedure applied to the modified SNOWMAP algorithm results improves snow detection under coniferous forests. Based on a limited data set of ground-based observations (only 40 sites were available), the modified SNOWMAP seems to perform better in snow detection than the original version of the algorithm. An application case is presented in order to demonstrate the relevance of the modified SNOWMAP results as a high spatial-resolution reference for the validation of historical snow maps derived from medium spatial-resolution satellite data.

Citation Chokmani, K., Dever, K., Bernier, M., Gauthier, Y. & Paquet, L.-M. (2010) Adaptation of the SNOWMAP algorithm for snow mapping over eastern Canada using Landsat-TM imagery. Hydrol. Sci. J. 55(4), 649–660.     

Microwave observations of the 4 January, 1973 solar eclipse

The eclipse was observed at two microwave frequencies, 7 GHz and 22.2 GHz, and has shown the presence of polarized regions, suggesting also excess of left-handed polarized radiation from the solar northern hemisphere. Difference in eclipsing times at the two frequencies for an active center near the limb is discussed.     

Ra or Ra/Ba dating of Holocene volcanic rocks: application to Mt. Etna and Merapi volcanoes

This paper shows how ²²⁶Ra–²³⁰Th disequilibria can be used to date Holocene volcanic rocks from some well selected volcanoes. A systematic study of these disequilibria on historical or well-dated volcanic samples is indeed first required to test the applicability of this method. Two examples are described here to illustrate its potential. In the case of Mt. Etna, the good correlation observed between (²²⁶Ra)₀ activities at the time of eruption and Th contents in lava flows from the last two millennia [M. Condomines, J.C. Tanguy, V. Michaud, Magma dynamics at Mt. Etna: constraints from U–Th–Ra–Pb radioactive disequilibria and Sr isotopes in historical lavas, Earth Planet. Sci. Lett. 132 (1995) 25–41] is used to infer the ages of several newly analysed lava flows. The calculated ages are in good agreement with those deduced from the archaeomagnetic curve describing the variation of the geomagnetic field direction in southern Italy [J.C. Tanguy, I. Bucur, J.F.C. Thompson, Geomagnetic secular variation in Sicily and revised ages of historic lavas from Mt. Etna, Nature 318 (1985) 453–455, J.C. Tanguy, M. Le Goff, V. Chillemi, A. Paiotti, C. Principe, S. La Delfa, G. Patane, Variation séculaire de la direction du champ géomagnétique enregistrée par les laves de l'Etna et du Vésuve pendant les deux derniers millénaires, C. R. Acad. Sci. Paris 329 (1999) 557–564, J.C. Tanguy, M. Le Goff, C. Principe, S. Arrighi, V. Chillemi, A. Paiotti, S. La Delfa, G. Patane, Archaeomagnetic dating of Mediterranean volcanics of the last 2100 years: validity and limits. Earth Planet. Sci. Lett. 211 (2003) 111–124]. We also present a whole set of new U-series data on historical, recent, and older samples from Merapi (Indonesia), and show that the (²²⁶Ra)/Ba ratio has probably maintained a quasi-steady state value during at least the past four millennia, and can be used to infer the (²²⁶Ra)₀/Ba ratio of old volcanics at the time of eruption, and thus their ages. Comparison with ¹⁴C ages available on three samples [R. Gertisser, J. Keller, Temporal variations in magma composition at Merapi volcano (Central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity, J. Volcanol. Geotherm. Res. 123 (2003) 1–23] shows an excellent agreement. These dating methods, based on the post-eruptive decrease of ²²⁶Ra excesses can be confidently used to date young rocks on both volcanoes, an important step to infer their recent eruptive history and magmatic evolution. It also opens the possibility to extend the geomagnetic field variation curve back into the past few millennia. The promising results obtained in this work should encourage new systematic U-series studies to test the applicability of such methods to other permanently active volcanoes showing ²²⁶Ra excesses.     

Biological interactions between microorganisms in the sea

Marine ecosystems, like terrestrial biological communities, are generally considered to depend, regarding their structure and functioning, upon the trophic and sexual relationships between organisms, either “horizontally”, between individuals at the same level, or “vertically”, all the way down the various levels of the food chains. Nevertheless, the functioning of biosystems is mostly governed by their structure, i.e., the qualitative and quantitative distribution of individuals within biocenoses, as well as the relationships with one another and with the environment. Therefore, it is vital to get to know how these connections work in order to outline the main causes of microbiological equilibrium in the sea. Actually, the major problem remains that of communication between individuals in biocenoses. This is a general problem as far as life is concerned, but it proves especially acute when it comes to microbial life because of its importance in the oceanic cycles.Data available in the literature, together with the results of our own studies in this field, led us to the assumption that some of the dissolved organic substances present in seawater might well be responsible for the control of the relationships between species. These substances would be active at various degrees of concentration, after they have been released into the medium by certain species. This theory, already adumbrated by Lucas (1938, 1947, 1955), Nigrelli (1958) and Fontaine (1970) concerning direct relationships between marine species or groups of organisms, was resumed and generalized by M. Aubert (1971) who called these substances “telemediators”.Such chemical communication plays a major role in a variety of fields including sexual behaviour, nutrition and predation, as well as defense mechanisms, mobility and migration.Remote connection of two organisms through a chemical mediation involves a sequence of actions and reactions which raises a number of problems of biochemical microecology. The organism that produces the telemediator must synthesize it — either spontaneously or in an induced way — and release it into the medium, during its active growth or after cell lysis. Next, the mediator is conveyed to the remote receiving organism, which it should reach without being degraded or chemically modified (or after such a modification. Its concentration must remain equal to or higher than its activity threshold. The receptor detects it, with or without absorption, and reacts by modifying its own metabolism or behaviour. This may go as far as causing the receptor the receptor to die. In even more complex situations, another mediator will be synthesized and released into the medium.Theoretical as it may be, such a pattern is a useful guide to explain the microbial interactions in a marine environment. It involves a number of complex microecological phenomena, some phases of which begin to be known. One specific problem is chemoreception in microorganisms, hence chemotaxis. Telemediator activity threshold and turnover in the natural environment must also be investigated.One should also take account of the physical context in which the phenomena take place. For instance, it is a known fact that an important fraction of the bacterial flora in the sea is adsorbed on solid or particulate substrates. Thus, the relationships with which they are concerned are much more probable in a sphere of a few fractions of a millimeter: this emphasizes the significance of the biochemical processes which cause the microorganisms to colonize substrates and to compete with one another in so doing. Another point of interest is how they modify the substrate until they are replaced by higher organisms.In the microbial field, communication between species has been described at various levels. Horizontally, it can take place between different bacteria or between various species of algae. Vertically, it may involve bacteria and planktonic algae, bacteria and protozoa, or algae and zooplanktonic organisms.Besides, the communication may be “positive”, if the mediator enhances the growth of the receiving organism — then, it is used as a source of carbon or nitrogen, or as a growth factor — or “negative” whenever the mediator is toxic (antibiotic, antiseptic or toxin) or induces a lethal metabolic modification in the receiver.In fact, there are various telemediation mechanisms, which correspond to increasing degrees of complexity in the biological systems: a primary mechanism, in which the mediator is synthetized by a species and controls (or modifies) the metabolism of another species in one step, and a secondary mechanism, where the mediator is synthetized by a species, and modifies the metabolism of another species; the latter, in turn, releases a primary mediator which controls the functions of a third species. This might be a longer sequence, involving a higher number of species.If the mechanism becomes cyclic, feedback may occur: as far as we know, such feedback may be either positive or negative ecologically, depending on whether it speeds up or slows down a biological process.A conception of a marine universe whose equilibrium would be controlled by the interaction of organisms within a more or less dense biotic network, with meshes made up of the relationship functions as a whole, is highly suggestive of an homology with cybernetic structures. Then, each marine organism can be considered as a separate functional unit characterized by some particular properties, its functions, which govern its activity. These units are involved in the functioning of complex and varying systems in which they intervene locally to channel up the flow of energy and matter to a given extent and in a given direction.The analogy is still more pronounced as there are feedbacks, which can control various sectors of the system. In a series of studies based on biological systems regulated by various chemical mediators, authors were able to demonstrate that the introduction of varied chemical pollutants into the marine environment entails modifications in the structure of the biological components of seawater and results in either the modification or the destruction of the mediating metabolites or “signals”. The result could be a more or less pronounced ecological drift, that varies according to the activity of the pollutant.