Stochastic downscaling method: application to wind refinement

In this article, we propose a new stochastic downscaling method: provided a numerical prediction of wind at large scale, we aim to improve the approximation at small scales thanks to a local stochastic model. We first recall the framework of a Lagrangian stochastic model borrowed from Pope. Then, we adapt it to our meteorological framework, both from the theoretical and numerical viewpoints. Finally, we present some promising numerical results corresponding to the simulation of wind over the Mediterranean Sea.     

Last glacial–interglacial sea-ice cover in the SW Atlantic and its potential role in global deglaciation

Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 10⁶ km² to a maximum of 19 × 10⁶ km² during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ～61°S to ～52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ～30 ka and 22 ka that extended to ～59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation.     

Environment and landscape management during the Middle Neolithic in Southern France: Evidence for agro-sylvo-pastoral systems in the Middle Rhone Valley

Rescue excavations in the Middle Rhone Valley have provided opportunities to develop innovative strategies for the study of palaeoenvironments. These strategies involve sampling and analysis of botanical remains, recovered not only from archaeological sites but also in “off-site” pedosedimentary sequences thought to be poor in botanical remains. Thus, these remains (phytoliths, pedo-charcoal) give access to unexplored depositional contexts, such as alluvial plains. Moreover, off-site data are useful because they minimise the hazard of cultural bias (e.g., selection of species during wood gathering). Comparison of data collected in the alluvial plain with data obtained via anthracological analyses of karstic caves and rock-shelters in the hinterland suggests a complex agro-sylvo-pastoral management of the landscape during the Middle Neolithic. We propose a pattern that supposes considerable specialization in use of plains vs. slopes in the landscape, and a strong and continuous human pressure on the vegetation and soils between 4500 and 3500 cal BC. Nevertheless, these constraints are not sufficient to explain the persistence of such a system for more than a millennium. Favourable climatic conditions are thought to have been a determining factor in the persistence of an ecologically meta-stable relationship between human societies and their natural environment.     

Subduction initiation and ophiolite crust: new insights from IODP drilling

International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench recovered boninites and related rocks. Drilling in both areas ended in dolerites inferred to be sheeted intrusive rocks. The basalts apparently erupted immediately after subduction initiation and have compositions similar to those of the most depleted basalts generated by rapid sea-floor spreading at mid-ocean ridges, with little or no slab input. Subsequent melting to generate boninites involved more depleted mantle and hotter and deeper subducted components as subduction progressed and volcanism migrated away from the trench. This volcanic sequence is akin to that recorded by many ophiolites, supporting a direct link between subduction initiation, fore-arc spreading, and ophiolite genesis.     

Post‐excavation deterioration of the Copney Bronze Age Stone Circle Complex: A geomorphological perspective

Post‐excavation deterioration of stones from under blanket peat at the Copney Bronze Age Stone Circle Complex in County Tyrone, Northern Ireland, proceeded through widespread scaling, flaking, and splitting of stones. Investigation showed that prior to burial the porphyritic stones already possessed a complex legacy of geological weaknesses derived from hydrothermal alteration and tectonic deformation. Analysis indicated that significant alteration occurred during approximately 2000 years of burial under acidic peat cover, with development of a secondary porosity, alteration of primary minerals, and the opening of preexisting lines of weakness within the stones. Burial under peat also resulted in “bleaching” the stones so that they appeared white in color following excavation. These alterations during burial left the stones in a significantly weakened state and particularly susceptible to the effects of subaerial weathering processes. Data underline the potential fragility of excavated stonework and highlight the need to plan for its aftercare before complete excavation is undertaken. © 2010 Wiley Periodicals, Inc.     

The Léon Domain (French Massif Armoricain): a westward extension of the Mid-German Crystalline Rise? Structural and geochronological insights

The Léon Domain in the NW part of the French Massif Armoricain is a stack of synmetamorphic nappes displaced from south to north in ductile conditions. From bottom to top, an orthogneissic basement is overthrusted successively by (1) a Lower Nappe of gneiss including mafic eclogites, (2) an Intermediate Nappe of biotite–garnet–staurolite micaschists with mafic blocks, and (3) an upper nappe made up of Neoproterozoic phyllites covered by unmetamorphosed Paleozoic sedimentary series. This microstructural study documents a polyphase evolution with firstly a top-to-the-N shearing, secondly followed by upright folding of the stack of nappes coeval with migmatization, and lastly, a dextral wrenching along the North Armorican Shear Zone associated with emplacement of synkinematic plutons. New U–Th/Pb chemical dating of monazites from biotite–garnet–staurolite micaschists, migmatites, and granitoids argue for 340–335 Ma, 335–327 Ma, and about 320 Ma ages for synthrusting metamorphism, anatexis, and wrenching, respectively. A metagabbro from Le Conquet yields a zircon LA-ICP-MS age of 478 ± 4 Ma, which corresponds to magma emplacement time. The Léon Domain is interpreted as a microcontinent separated from Armorica by the Le Conquet-Penzé suture to the south and east, and from Laurussia by the Rheic suture to the north. A possible correlation with the Mid-German Crystalline Rise of Central Europe is discussed.     

High cadmium concentrations in Jurassic limestone as the cause for elevated cadmium levels in deriving soils: a case study in Lower Burgundy,France

Cadmium (Cd) is a highly toxic element and its presence in the environment needs to be closely monitored. Recent systematic surveys in French soils have revealed the existence of areas in eastern and central France, which show systematically high cadmium concentrations. It has been suggested that at least part of these anomalous levels are of natural origin. For the Lower Burgundy area in particular, a direct heritage from the Jurassic limestone bedrock is highly suspected. This potential relationship has been studied in several localities around Avallon and this study reports new evidence for a direct link between anomalously elevated cadmium contents of Bajocian and Oxfordian limestone and high cadmium concentrations in deriving soils. Soils in this area show cadmium concentrations generally above the average national population values, with contents frequently higher than the ‘upper whisker’ value of 0.8 μg g⁻¹ determined by statistical evaluation. In parallel, limestone rocks studied in the same area exhibit cadmium concentrations frequently exceeding the mean value of 0.030–0.065 μg g⁻¹ previously given for similar rocks by one order of magnitude, with a maximum of 2.6 μg g⁻¹. Mean ratios between the cadmium concentrations of limestone bedrock and deriving soils (Cd_soil/Cd_rock), calculated for different areas, range from 4.6 to 5.7. Calculations based on the analyses of both soils from a restricted area and fragments of bedrock sampled in the immediate vicinity of high-concentration soils are around 5.5–5.7. Cd_soil/Cd_rock is useful in determining the potential of soils in Lower Burgundy to reflect and exacerbate the high concentrations of cadmium present in parent bedrocks.     

Can Free (and Open Source) Software and Data be Used to Underpin a Self‐Paced Tutorial on Spatial Databases?

University College London's Department of Civil, Environmental and Geomatic Engineering (CEGE) offers a number of Masters programmes in topics related to Geomatics, including Surveying, Hydrographic Surveying, Remote Sensing and Geographical Information Science. Data management, and in particular the technology and applications of Spatial Databases, forms a key part of the curriculum on these courses. Interest in Spatial Databases is, however, more widespread – especially with the increasing understanding of the relevance of geospatial techniques to fields as diverse as anthropology and architecture. This article describes the development and evaluation of a self‐paced hands‐on course on Databases and Spatial Databases for CEGE students, presented to students to complement and enhance in‐class teaching. The article focuses on both pedagogical elements of self‐paced learning and the suitability of Free and Open Source Software and Open Data (PostgreSQL/PostGIS, Quantum GIS, Open Street Map) for the Spatial Databases curriculum. The resulting material was evaluated by a cohort of 25 students in 2010, and their feedback (very positive) and the overall results provide an interesting insight into suitable methods to employ when teaching technical subjects to a cohort having differing background skill levels.     

Système hydrogéologique d'un massif minier ultrabasique de Nouvelle-Calédonie

Ultramafic rocks outcrop over more than one third of New Caledonia's main island. Under tropical conditions, thick lateritic mantles with nickel concentrations developed on these rocks by geochemical weathering. Groundwater in ultramafic mined massifs represents a valuable resource, but also a severe constrain for mining engineering. Previous works describe several water tables in the various layers of the weathering mantle. From a hydrologic study of the Tiebaghi massif, the hydraulic continuity across the weathering layers down to the bedrock is proposed. To cite this article: J.-L. Join et al., C. R. Geoscience 337 (2005).