Supraglacial melt channel networks in the Jakobshavn Isbræ region during the 2007 melt season

Supraglacial channels are an important mechanism for surface water transport over the ablation zone of western Greenland. The first assessment of the spatio‐temporal distribution of surface melt channels and their relationship to supraglacial lakes over the Jakobshavn Isbræ region of Western Greenland was analysed using Landsat Enhanced Thematic Mapper Plus panchromatic images during the 2007 melt season. A total of 1188 melt channels were delineated and show an increase in the number of melt channels throughout the season, reaching a peak on 9 August. Water‐filled melt channels advanced to a maximum elevation of 1647 m on 9 August and attained a minimum average slope of 0.009 on 8 July. The ablation zone demonstrates two hydrologic modes, where crevasse and moulin terminating channels dominate at elevations <800 m and higher‐order channel networks >800 m. Development of higher‐order networks is interrupted by flow divergence due to partitioning of melt water into vertical infiltration through moulins and crevasse fields prevalent at lower elevations. Tributary and connector networks between 800 and 1200 m in elevation are correlated with fewer lake occurrences, lower surface velocities (~50 m a^?1), and ice flow dominated by internal deformation over basal sliding. High‐order channels are associated with lake basins that exceed melt water storage capacity. Evolution of channel networks is coupled to changes in melt water production, runoff, and ice dynamics with implication for the englacial and subglacial environments. © 2013 The Authors. Hydrological Processes Published by John Wiley & Sons, Ltd.     

Neoproterozoic events in the Tcholliré area: Pan-African crustal growth and geodynamics in central-northern Cameroon (Adamawa and North Provinces)

The Rei Bouba Group is a sedimentary and volcanic sequence (750–?650 Ma), regarded as a remnant of a Pan-African (back-arc?) orogenic basin that separated a remobilized Paleoproterozoic crust from an accretionary area (Poli Complex: 800-650 Ma). The latter was subjected to early deformation (D1) and intruded by calc-alkalic plutons (670 Ma). Transpressive tectonics and major thrusting, with emplacement of synkinematic granite, occurred at ca 630 Ma (D2-3) and a late compression (D4), with emplacement of calc-alkalic granite, occurred at ca 570 Ma. The Tcholliré Shear Zone is regarded as part of the major boundary between a recently accreted crust and the remobilized margin of the Congo Craton.     

Biochemical‐genetic and meristic evidence that blue and copper moki (Teleostei: Latridae: Latridopsis) are discrete species

Specimens of blue moki Latridopsis ciliaris (Forster in Bloch & Schneider, 1801) from New Zealand were shown to differ from specimens of copper moki Latridopsis forsteri (Castelnau, 1872) using two genetic methods—allozymes and muscle proteins. Allozyme techniques revealed fixed differences between blue and copper moki at 4 out of 15 loci. There was a genetic distance of 0.31–0.34 between population samples of the two colour morphs. The two morphs were also distinguished by iso‐electric focusing of muscle proteins. Meristic characters, counted in the specimens studied with genetic markers, revealed diagnostic markers in tubed lateral line scales and scales in the lower transverse series. It is concluded that specimens of blue moki from New Zealand and copper moki from New Zealand and Tasmania are valid species.     

A Practical Procedure for the Measurement of Fragmentation by Blasting by Image Analysis

Summary. The operation of a digital image analysis system in a limestone quarry is described. The calibration of the system, required in order to obtain moderately reliable fragmentation values, is done from muckpile sieving data by tuning the image analysis software settings so that the fragmentation curve obtained matches as close as possible the sieving. The sieving data have also been used to extend the fragment size distribution curves measured to sizes below the system’s optical resolution and to process the results in terms of fragmented rock, discounting the material coming from a loose overburden (natural fines) that is cast together with the fragmented rock. Automatic and manual operation modes of the image analysis are compared. The total fragmentation of a blast is obtained from the analysis of twenty photographs; a criterion for the elimination of outlier photographs has been adopted using a robust statistic. The limitations of the measurement system due to sampling, image processing and fines corrections are discussed and the errors estimated whenever possible. An analysis of consistency of the results based on the known amount of natural fines is made. Blasts with large differences in the amount of fines require a differentiated treatment, as the fine sizes tend to be the more underestimated in the image analysis as they become more abundant; this has been accomplished by means of a variable fines adjustment factor. Despite of the unavoidable errors and the large dispersion always associated with large-scale rock blasting data, the system is sensitive to relative changes in fragmentation.     

On the Use of Computational Fluid Dynamics to Investigate Aerosol Dispersion in an Industrial Environment: A Case Study

Aerosol dispersion in the area surrounding an existing biological treatment facility is investigated using large-eddy simulation, with the objective to investigate the applicability of computational fluid dynamics to complex real-life problems. The aerosol sources consist of two large aeration ponds that slowly diffuse aerosols into the atmosphere. These sources are modelled as dilute concentrations of a non-buoyant non-reacting pollutant diffusing from two horizontal surfaces. The time frame of the aerosol release is restricted to the order of minutes, justifying a statistically steady inlet boundary condition. The numerical results are compared to wind-tunnel experiments for validation. The wind-tunnel flow characteristics resemble neutral atmospheric conditions with a Reynolds number, based on the boundary-layer thickness, of Re _δ ≈ 2 × 10⁵. The numerical inflow conditions are based upon the wind-tunnel flow field. The predicted decay of both the mean and root-mean-square concentrations are in good agreement with experimental data; at 3 m from the ground, the plume mean concentration 200 m downwind of the source is approximately 2% of the source strength. The numerical data in the near-surface layer (0–50 m from the ground) correspond particularly well with the wind-tunnel data. Tentative deposition simulations suggest that there seems to be little difference in the deposition rates of large (1.8 × 10⁻⁵ m) and small (3 × 10⁻⁶ m) particles in the near-field under the flow conditions considered.     

An analysis of the components of the luminescence signals of selected polymineral and quartz samples from loess in western China and southern Tajikistan,and their suitability for optical dating

Previous luminescence dating studies on loess from China and Tajikistan have focused on the establishment of the regional chronology of the loess sequences. In order to improve the precision and accuracy of optical ages derived from the loess of the last glacial period in these regions, we have examined the components of luminescence signals in three loess samples from western China and southern Tajikistan. Our results show that the polymineral IRSL and post-IR OSL, and quartz OSL signals from loess of the two regions are represented by three components, which display different bleaching and growth characteristics. While the composition of the polymineral IRSL signals is similar between samples with the same age from the two regions, in the case of quartz there is significant discrepancy in the proportion of the fast and medium components of the OSL signals. Greater difference is observed in the composition of the polymineral post-IR OSL signals for the loess from the two regions. The three components of polymineral IRSL signals yield almost identical equivalent dose values as that derived from the total IRSL signal. An apparent agreement in equivalent dose is observed between the fast component of the polymineral post-IR OSL and the quartz OSL for the loess of western China but not in the loess of the same age from southern Tajikistan. The fast component of the quartz OSL yields an equivalent dose 25% higher than that based on the total signal for the sample from the base of the Late Pleistocene loess in southern Tajikistan. This demonstrates the importance of signal selection for an accurate luminescence dating of Central Asian loess.     

Provenance and accumulation rates of opaline silica,Al, Ti,Fe, Mn,Cu, Ni and Co in Pacific pelagic sediments

Accumulation rates and chemical compositions have been obtained for pelagic sediments for 73 locations in the Pacific and for 11 in the Indian Ocean. The data for the Pacific show that many elements accumulate rapidly close to the continents and slowly in the central part of the ocean. This pattern is interrupted by two major zones of relatively high accumulation rates, one along the Equator and one along the East Pacific Rise. Deposition of opaline silica is almost completely restricted to areas of known high biological productivities at the Equator and at very high latitudes. Cu and Ni show stronger tendencies than Fe and Mn to precipitate with opaline silica. The highest accumulation rates of Fe and Mn in the open Pacific occur along the East Pacific Rise, to some extent also Cu and Ni are enriched there due to volcanic processes. Al and Ti show high accumulation rates only close to the continents; these elements appear to be almost completely terrigenous.Provenance studies of minerogen fractions, using the relations between Fe, Ti, Al and Mn, show that significant quantities of basaltic matter (oceanic crust) are incorporated into the sediments only in areas of very low total sedimentation rates in the vicinity of oceanic island groups such as Polynesia and Hawaii, whereas hydrothermal processes act as a major sediment source only on the East Pacific Rise. Sediments in the north as well as in the southernmost part of the Pacific are nearly entirely terrigenous. A balance estimate of the minerogen fraction of the deep-sea sediments from the open Pacific suggests that between 75 and 95% of all sediments in the Pacific are terrigenous and that submarine weathering (and release of basaltic debris in general) and submarine exhalations each account for only a small fraction of the sediments.     

Deep dynamical processes in the central-southern Qinghai-Tibet Plateau—Receiver functions and travel-time residuals analysis of north Hi-Climb

Teleseismic receiver functions and travel-time residuals along the north Hi-Climb broadband seismic array in the central-southern Qinghai-Tibet Plateau show that the lithosphere structures in the central and western Qinghai-Tibet Plateau are different. In the central Qinghai-Tibet Plateau, the Indian Plate is northward subducted beneath the Qiangtang block and arrives at the greatest depth beneath the central-southern Qiangtang block. The delaminated Indian lithospheric slab remains beneath the central Lhasa block to a depth possibly greater than that of the upper interface of the mantle transform zone. In the western Qinghai-Tibet Plateau, the Indian lithospheric plate is gently northward subducted and may have arrived to the south of Tarim plate. Due to the resistance from the gently northward subduction of the Indian mantle lithosphere in the western Qinghai-Tibet Plateau, the upwelling mantle material be-neath the Qiangtang block moves mostly toward the east to bring about the lateral eastward flow of the deep mantle hot material in the central Qinghai-Tibet Plateau.     

“Basin scale” versus “localized” pore pressure/stress coupling - Implications for trap integrity evaluation

In petroleum industry, the difference between pore pressure (P_p) and minimum horizontal stress S_h (termed the seal or retention capacity) is of major consideration because it is often assumed to represent how close a system is to hydraulic failure and thus the maximum hydrocarbon column height that can be maintained. While S_h and P_p are often considered to be independent parameters, several studies in the last decade have demonstrated that S_h and P_p are in fact coupled. However, the nature of this coupling relationship remains poorly understood. In this paper, we explore the influences of the spatial pore pressure distribution on S_h/P_p coupling and then on failure pressure predictions and trap integrity evaluation. With analytical models, we predict the fluid pressure sustainable within a reservoir before failure of its overpressured shale cover. We verify our analytical predictions with experiments involving analogue materials and fluids. We show that hydraulic fracturing and seal breach occur for fluid pressure greater than it would be expected from conventional retention capacity. This can be explained by the impact of the fluid overpressure field in the overburden and the pressure diffusion around the reservoir on the principal stresses. We calculate that supralithostatic pressure could locally be reached in overpressured covers. We also define the retention capacity of a cover (RC) surrounding a fluid source or reservoir as the difference between the failure pressure and the fluid overpressure prevailing in shale at the same depth. In response to a localized fluid pressure rise, we show that the retention capacity does not only depend on the pore fluid overpressure of the overburden but also on the tensile strength of the cover, its Poisson’s ratio, and the depth and width of the fluid source.