Abstract: The microstructure and location of impurities in polar ice are of great relevance to ice core studies. We describe a reliable method to examine ice in the scanning electron microscope (SEM). Specimens were cut in a cold room and could have their surfaces altered by sublimation either before (pre-etching) or after (etching) introduction to the cryo-chamber of the SEM. Pre-etching was used to smooth surfaces, whilst etching stripped away layers from the specimen surface, aiding the location of particles in situ, and allowing embedded structures to be revealed. X-ray analysis was used to determine the composition of localized impurities, which in some cases had been concentrated on the surface by etching. Examining uncoated surfaces was found to be advantageous and did not detract from qualitative X-ray analysis. Imaging uncoated was performed at low accelerating voltages and probe currents to avoid problems of surface charging.

Abstract: The demographic variance of an age-structured population is defined. This parameter is further split into components generated by demographic stochasticity in each vital rate. The applicability of these parameters are investigated by checking how an age-structured population process can be approximated by a diffusion with only three parameters. These are the deterministic growth rate computed from the expected projection matrix and the environmental and demographic variances. We also consider age-structured populations where the fecundity at any stage is either zero or one, and there is neither environmental stochasticity nor dependence between individual fecundity and survival. In this case the demographic variance is uniquely determined by the vital rates defining the projection matrix. The demographic variance for a long-lived bird species, the wandering albatross in the southwestern part of the Indian Ocean, is estimated. We also compute estimates of the age-specific contributions to the total demographic variance from survival, fecundity and the covariance between survival and fecundity.

Abstract: L'article suivant aborde les paysages polaires à travers la production récente d'un cédérom consacré à l'analyse de paysages depuis le sol en milieu arctique. Après avoir rappelé brièvement l'ambiguïté des relations entre géographie et paysage, on évoque l'évolution des représentations des paysages et des zones polaires chez nos contemporains, avant de montrer comment les nouveaux médias autorisent une approche renouvelée des paysages. Le céderont, sur lequel on focalise progressivement le propos, sert de fil conducteur à cette réflexion sur le paysage polaire, considéré tout à la fois comme objet d'étude et comme espace expérimental.

Abstract: A new dating technique uses alpha-recoil tracks (ART), formed by the natural /?-decay of U, Th and their daughter products, to determine the formation age of Quaternary volcanic rocks (/<106 a). Visualization of etched ART by scanning force microscopy (SFM) enables to access track densities beyond 108cm-2 and thus extend the new ART-dating technique to an age range />106 a. In order to simulate natural radiation damage, samples of phlogopite, originating from Quaternary and Tertiary volcanic rocks of the Eifel (Germany) and Kerguelen Islands (Indian Ocean) were irradiated with U, Ni (11.4 MeV/u), Xe, Cr, Ne (1.4 MeV/u) and Bi (200 keV) ions. After irradiation and etching with HF at various etching times, phlogopite surfaces were visualized by SFM. Hexagonal etch pits are typical of U, Xe and Cr ion tracks, but the etch pits of Ni, Ne and Bi ion tracks are triangular. Surfaces irradiated with U, Xe, Cr and Ni ions do not show any significant difference between etch pit density and irradiation fluence, whereas the Ne-irradiated surface show /~14 times less etch pit density. The etching rate vH (parallel to cleavage) depends on the chemical composition of the phlogopite. The etching rate vT' (along the track) increases with energy loss.