Littérature scientifique sur le sujet « Pinn, Ronnie »

AbstractWe describe a new tide model for the seas surrounding Antarctica, including the ocean cavities under the floating ice shelves. The model uses data assimilation to improve its fit to available data. Typical peak-to-peak tide ranges on ice shelves are 1–2 m but can exceed 3 m for the Filchner–Ronne and Larsen Ice Shelves in the Weddell Sea. Spring tidal ranges are about twice these values. Model performance is judged relative to the ~5–10 cm accuracy that is needed to fully utilize ice-shelf height data that will be collected with the Geoscience Laser Altimeter System, scheduled to be launched on the Ice, Cloud and land Elevation Satellite in late 2002. The model does not yet achieve this level of accuracy except very near the few high-quality tidal records that have been assimilated into the model. Some improvement in predictive skill is expected from increased sophistication of model physics, but we also require better definition of ice-shelf grounding lines and more accurate water-column thickness data in shelf seas and under the ice shelves. Long-duration tide measurements (bottom pressure gauge or global positioning system) in critical data-sparse areas, particularly near and on the Filchner–Ronne and Ross Ice Shelves and Pine Island Bay, are required to improve the performance of the data-assimilation model.

AbstractRutford Ice Stream, West Antarctica, drains a catchment of >45 000 km2 into the Ronne Ice Shelf through a 26 km wide, 2.4 km deep subglacial trough adjacent to the Ellsworth Mountains. Forty-two per cent of its catchment boundary is common with Pine Island Glacier, where rapid change to ice dynamics is currently underway. These changes may eventually affect adjacent catchments such as Rutford. Radar sounding data were acquired over the Rutford ice-drainage basin that show the internal structure. In particular, distinctive reflector groups were identified that mark the boundaries between four different flow elements. The flow-margin reflector groups include curvilinear events that cross-cut isochrones and are therefore likely to be post-depositional. These reflections may arise from crystal orientation fabrics generated by localized strain in a flow margin. One of the sectors of the ice-drainage basin supplies the largest share (38%) of the ice volume flux through the main trunk of Rutford Ice Stream. This sector may be preferentially affected by continuing surface lowering in the Pine Island Glacier catchment.

Abstract. Basal melting at the bottom of Antarctic ice shelves is a major control on glacier dynamics, as it modulates the amount of buttressing that floating ice shelves exert onto the ice streams feeding them. Three-dimensional ocean circulation numerical models provide reliable estimates of basal melt rates but remain too computationally expensive for century-scale projections. Ice sheet modelers therefore routinely rely on simplified parameterizations based on either ice shelf depth or more sophisticated box models. However, existing parameterizations do not accurately resolve the complex spatial patterns of sub-shelf melt rates that have been observed over Antarctica's ice shelves, especially in the vicinity of the grounding line, where basal melting is one of the primary drivers of grounding line migration. In this study, we couple the Potsdam Ice-shelf Cavity mOdel (PICO, Reese et al., 2018) to a buoyant plume melt rate parameterization (Lazeroms et al., 2018) to create PICOP, a novel basal melt rate parameterization that is easy to implement in transient ice sheet numerical models and produces a melt rate field that is in excellent agreement with the spatial distribution and magnitude of observations for several ocean basins. We test PICOP on the Amundsen Sea sector of West Antarctica, Totten, and Moscow University ice shelves in East Antarctica and the Filchner-Ronne Ice Shelf and compare the results to PICO. We find that PICOP is able to reproduce inferred high melt rates beneath Pine Island, Thwaites, and Totten glaciers (on the order of 100 m yr−1) and removes the “banding” pattern observed in melt rates produced by PICO over the Filchner-Ronne Ice Shelf. PICOP resolves many of the issues contemporary basal melt rate parameterizations face and is therefore a valuable tool for those looking to make future projections of Antarctic glaciers.

Abstract. Over the past decade, a wealth of research has been devoted to the detection of crevasses in glaciers and ice sheets via remote sensing and machine learning techniques. It is often argued that remotely sensed damage maps can function as early warning signals for shifts in ice shelf conditions from intact to damaged states and can serve as an important tool for ice sheet modellers to improve future sea level rise predictions. Here, we provide evidence for the Filchner–Ronne and Pine Island ice shelves that remotely sensed damage maps are only weakly related to the ice rate factor field A derived by an ice flow model when inverting for surface velocities. This technique is a common procedure in ice flow models, as it guarantees that any inferred changes in A relate to changes in ice flow measured through observations. The weak relationship found is improved when investigating heavily damaged shear margins, as observed on the Pine Island Ice Shelf; however, even in this setting, this association remains modest. Our findings suggest that many features identified as damage through remote sensing methods are not of direct relevance to present-day ice shelf flow. While damage can clearly play an important role in ice shelf processes and thus be relevant for ice sheet behaviour and sea level rise projections, our results imply that mapping ice damage directly from satellite observations may not directly help improve the representation of these processes in ice flow models.

Abstract: À partir des traumatismes, passés et présents, collectifs et individuels, Titaua Peu décrit une identité polynésienne traumatisée et fragmentée, loin du cliché paradisiaque hérité des récits des premiers explorateurs. Les récits de Mutismes et de Pina s’articulent autour du traumatisme des violences au sein de la société polynésienne: violence intrafamiliale et violence institutionnelle, violence héritée de la colonisation qui se mue en colère. Peu dépeint une société tahitienne fragmentée, rongée par des différends qui semblent irréconciliables. Face au traumatisme de la violence, le peuple polynésien s’est enfermé dans le silence: l’écriture de Peu vise ainsi à redonner au peuple polynésien les mots qu’il avait perdus, des mots qui semblent seuls capables d’apaiser un moi en quête de (re)construction. Se dessine finalement le portrait d’une identité polynésienne contemporaine née de la souffrance et de la douleur, mais forte aussi d’une résilience inébranlable, qui fait résonner l’expérience polynésienne comme une expérience universelle.

Abstract. Union Glacier (79°46' S/83°24' W) in the West Antarctic Ice Sheet (WAIS), has been used by the private company Antarctic Logistic and Expeditions (ALE) since 2007 for their landing and commercial operations, providing a unique logistic opportunity to perform glaciological research in a vast region, including the Ice divide between Institute and Pine Island glaciers and the Subglacial Lake Ellsworth. Union glacier is flowing into the Ronne Ice Shelf, where future migrations of the grounding line zone (GLZ) in response to continuing climate and oceanographic changes have been modelled. In order to analyse the potential impacts on Union glacier of this scenario, we installed an array of stakes, where ice elevation, mass balance and ice velocities have been measured since 2007, resulting in near equilibrium conditions with horizontal displacements between 10 and 33 m yr−1. GPS receivers and three radar systems have been also used to map the subglacial topography, the internal structure of the ice and the presence of crevasses along surveyed tracks. The resulting radar data showed a subglacial topography with a minimum of 858 m below sea level, much deeper than estimated before. The below sea level subglacial topography confirms the potential instability of the glacier in foreseen scenarios of GLZ upstream migration during the second half of the XXI century.

Abstract. Recent regional simulations and observations suggest a destabilization of the Amundsen Sea sector of West Antarctica. Whether the initiated ice drainage will be limited to Pine Island and Thwaites basin or extend to the Filchner–Ronne basin depends on the possibility of an interaction of the different drainage basins. Using a conceptional flow-line geometry, we investigate the possibility of whether a marine ice-sheet instability (MISI) can be triggered from the direction of the ice divide as opposed to coastal forcing and investigate the interaction between connected basins. We find that the initiation of a MISI in one basin can induce a destabilization in the other. The underlying mechanism of basin interaction is based on dynamic thinning and a consecutive motion of the ice divide which induces a thinning in the adjacent basin and a successive initiation of the instability. Our simplified and symmetric topographic set-up allows to scale both the geometry and the transition time between both instabilities. We find that the ice profile follows a universal shape that is scaled with the horizontal extent of the ice sheet and that the same exponent of 1/2 applies for the scaling relation between central surface elevation and horizontal extent as in the pure Shallow Ice Approximation (Vialov profile). Altering the central bed elevation we find that the extent of grounding line retreat in one basin determines the degree of interaction with the other. We conclude that for the three-dimensional case the possibility of such drainage basin interaction cannot be excluded and hence needs further investigation.

Abstract. Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional fields into a global data set. We use the S-2004 global 1-min bathymetry as the backbone and add an improved version of the BEDMAP topography (ALBMAP bedrock topography) for an area that roughly coincides with the Antarctic continental shelf. The position of the merging line is individually chosen in different sectors in order to get the best out of each data set. High-resolution gridded data for ice shelf topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier are carefully merged into the ambient ice and ocean topographies. Multibeam survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and blended into the existing bathymetry map. The resulting global 1-min topography data set (RTopo-1) contains maps for upper and lower ice surface heights, bedrock topography, and consistent masks for open ocean, grounded ice, floating ice, and bare land surface. The data set is available in NetCDF format from the PANGAEA database at doi:10.1594/pangaea.741917.

Abstract. Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic topography data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional surveys and maps into a global data set. We use the S-2004 global 1-min bathymetry as the backbone and add an improved version of the BEDMAP topography (ALBMAP bedrock topography) for an area that roughly coincides with the Antarctic continental shelf. The position of the merging line is individually chosen in different sectors in order to capture the best of both data sets. High-resolution gridded data for ice shelf topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier are carefully merged into the ambient ice and ocean topographies. Multibeam survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and blended into the existing bathymetry map. The resulting global 1-min Refined Topography data set (RTopo-1) contains self-consistent maps for upper and lower ice surface heights, bedrock topography, and surface type (open ocean, grounded ice, floating ice, bare land surface). The data set is available in NetCDF format from the PANGAEA database at doi:10.1594/pangaea.741917.

Abstract. The Antarctic firn layer provides pore space in which an estimated 94 % to 96 % of the surface melt refreezes or is retained as liquid water. Future depletion of firn pore space by increased surface melt, densification and formation of low-permeability ice slabs can potentially lead to meltwater ponding, hydrofracturing and ice-shelf disintegration. Here, we investigate the 21st-century evolution of total firn air content (FAC) and accessible FAC (i.e. the pore space that meltwater can reach) across Antarctic ice shelves. We use the semi-empirical IMAU Firn Densification Model (IMAU-FDM) with an updated dynamical densification expression to cope with changing climate forcing. The firn model is forced by general circulation model output of the Community Earth System Model version 2 (CESM2) for three climate emission scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5), dynamically downscaled to a 27 km horizontal resolution by the Regional Atmospheric Climate Model version 2.3p2 (RACMO2.3p2). To estimate accessible FAC, we prescribe a relationship between ice-slab thickness and permeability. In our simulations, ice shelves on the Antarctic Peninsula and the Roi Baudouin Ice Shelf in Dronning Maud Land are particularly vulnerable to total FAC depletion (> 50 % decrease by 2100), even for low-emission (SSP1-2.6) and intermediate-emission (SSP2-4.5) scenarios. In the high-emission (SSP5-8.5) scenario in particular, the formation of ice slabs further reduces accessible FAC on ice shelves with low accumulation rates (current rates of < 500 mmw.e.yr-1), including many East Antarctic ice shelves and the Filchner–Ronne, Ross, Pine Island and Larsen C ice shelves. These results underline the potentially large vulnerability of low-accumulation ice shelves to firn air depletion through ice-slab formation.

The rock shelter of the Roc-aux-Sorciers at Angles-sur-lAnglin (Vienne, France) is one of the archaeological reference sites for the Upper Paleolithic. The sculpted, painted and engraved frieze was gradually brought to light in its archaeological context by Susanne Cassou de Saint-Mathurin and Dorothy Garrod from 1949 onwards (Saint-Mathurin, Garrod, 1950). A wealth of archaeological material was discovered alongside the parietal art, comprising numerous works of portable art, tools made of animal bone, jewellery, etc. It was very rapidly observed that the portable art and the parietal art shared the same graphic and thematic conventions. For example, images of female bodies are rendered in high relief, in a monumental way, but also in the form of small statuettes. Our research has demonstrated the undeniable intra-site links between the portable art and the parietal art (Pinon, 2012). Here we propose to broaden this analysis within a well-identified culture of the Middle Magdalenian known as the Magdalenian of Lussac-Angles spearpoints. At the time of the discovery of the Magdalenian site of La Marche in 1937 (Vienne) (Lwoff, Pricard, 1940), some similarities had been identified between this site and that of Le Roc-aux-Sorciers, where the discoveries dated back to 1927 (Rousseau, 1933). These similarities are also perceptible in shared techniques (Chehmana, Beyries, 2010), as well as in the production of objects in hard organic materials such as the Lussac-Angles spearpoints (Pinon, 1988), the jewellery in fossil mammoth ivory (Dujardin, Pinon, 2000), the engraved horse incisors (Mazire, 2009) and the figurative art (Bourdier et al., 2016 Fuentes, 2016). We propose to further explore the links between these two sites through the analysis of the dynamic processes of reworking images. In particular we examine the engraved plaquettes of La Marche and the parietal art of Le Roc-aux-Sorciers to bring these links into perspective. This could shed light on some common ways of seeing the world in this Magdalenian group. Bourdier, C., Pinon, G., Bosselin, B. (2016). Norme et individualit au Rocaux-Sorciers (Vienne, France): approches des mains du registre animalier au travers de la forme. In M. Groenen, M.-Ch. Groenen (Eds.), Style, Techniques and Graphic expression in Rock Art (pp. 1735). BAR S2787. Chehmana, L., Beyries, S. (2010). Lindustrie lithique du Roc-aux-Sorciers (collection Rousseau). In J. Buisson-Catil, J. Primault (Eds.), Prhistoire entre Электронная библиотека ИА РАН: https://www.archaeolog.ru/ru/el-bib 16 Vienne et Charente. Hommes et socit du Palolithique (pp. 453460). Association des publications Chauvinoises, mmoire XXXVIII. Dujardin, V., Pinon, G. (2000). Le Magdalnien dans la Vienne et la Charente. In G. Pion (Dir.), Le Palolithique suprieur rcent: nouvelles donnes sur le peuplement et lenvironnement (pp. 213222). Actes de la table ronde de Chambry, 12-13 mars 1999, Mmoire de la Socit prhistorique franaise 28. Fuentes, O. (2016). The social dimension of human depiction in Magdalenian rock art (16,500 cal. BP 12.000 Cal. BP): the case of the Roc-aux-Sorciers rockshelter. Quaternary International, 430, 97113. https://doi.org/10.1016/ j.quaint.2016.06.023 Pericard, L., Lwoff, S. (1940). La Marche. Commune de Lussac-les-Chteaux (Vienne). Premier atelier de Magdalnien III dalles graves mobiles. Bulletin de la Socit Prhistorique franaise, 37(79), 155180. Pinon, G. (1988). Fiche sagaie de Lussac-Angles. In H. Camps Fabrer (Dir.), Fiches typologiques de lindustrie osseuse prhistorique. Commission de nomenclature sur lindustrie de los prhistorique. Cahier I: sagaies (fiche 3bis). Universit de Provence. Pinon, G. (2012). Art mobilier et art parital du Roc-aux-Sorciers (Angles-surlAnglin, Vienne, France): disparits ou sens communs In J. Clottes (Ed.), Lart plistocne dans le monde / Pleistocene art of the world / Arte pleistoceno en el mundo (pp. 15491558). Bulletin Socit Prhistorique Arige-Pyrnes. Mazire, G. (2009). Les incisives de chevaux graves. In G. Pinon (Dir.), Le Roc-aux-Sorciers: art et parure du Magdalnien. Runion des Muses Nationaux. http://www.catalogue-roc-aux-sorciers.fr Rousseau, L. (1933). Le Magdalnien dans la Vienne. Dcouverte et fouille dun gisement du Magdalnien, Angles-sur-lAnglin (Vienne). Bulletin de la Socit Prhistorique franaise, 30, 239256. Saint-Mathurin (de), S., Garrod, D. (1950). Une frise sculpte du Magdalnien ancien dcouverte Angles-sur-lAnglin, dans la Vienne. Acadmie des Inscriptions et Belles Lettres, 94(2), 123128.