Quality assessment of COSMIC/FORMOSAT-3 GPS radio occultation data derived from single- and double-difference atmospheric excess phase processing

This study evaluates the quality of GPS radio occultation (RO) atmospheric excess phase data derived with single- and double-difference processing algorithms. A spectral analysis of 1 s GPS clock estimates indicates that a sampling interval of 1 s is necessary to adequately remove the GPS clock error with single-difference processing. One week (May 2–8, 2009) of COSMIC/FORMOSAT-3 data are analyzed in a post-processed mode with four different processing strategies: (1) double-differencing with 1 s GPS ground data, (2) single-differencing with 30 s GPS clock estimates (standard COSMIC Data Analysis and Archival Center product), (3) single-differencing with 5 s GPS clocks, and (4) single-differencing with 1 s GPS clocks. Analyses of a common set of 5,596 RO profiles show that the neutral atmospheric bending angles and refractivities derived from single-difference processing with 1 s GPS clocks are the highest quality. The random noise of neutral atmospheric bending angles between 60 and 80 km heights is about 1.50e−6 rad for the single-difference cases and 1.74e−6 rad for double-differencing. An analysis of pairs of collocated soundings also shows that bending angles derived from single-differencing with 1 s GPS clocks are more consistent than with the other processing strategies. Additionally, the standard deviation of the differences between RO and high-resolution European Center for Medium range Weather Forecasting (ECMWF) refractivity profiles at 30 km height is 0.60% for single-differencing with 1 and 5 s GPS clocks, 0.68% for single-differencing with 30 s clocks, and 0.66% for double-differencing. A GPS clock-sampling interval of 1 s or less is required for single- and zero-difference processing to achieve the highest quality excess atmospheric phase data for RO applications.     

Geochemistry of surface sediments in an acid stream estuary

Selective chemical attack has been used to separate recent surface marine sediments into organic, non-detrital and detrital components, and the concentrations of iron, manganese, copper and zinc in each fraction determined. The non-detrital fraction controlled the overall elemental concentrations and relationships apparent in the bulk sediment, particularly in the cases of copper, manganese and zinc. Copper was found associated with the organic fraction. The predominant processes of primary deposition are precipitation of hydrated ferric oxide and adsorption of copper and zinc onto this material.     

Diagenetic evolution of lower Jurassic platform carbonates flanking the Tazoult salt wall (Central High Atlas,Morocco)

Platform carbonates diagenesis in salt basins could be complex due to potential alterations of fluids related and non-related to diapirism. This paper presents the diagenetic history of the Hettangian to Pliensbachian platform carbonates from the Tazoult salt wall area (central High Atlas, Morocco). Low structural relief and outcrop conditions allowed to define the entire diagenetic evolution occurred in the High Atlas diapiric basins since early stages of the diapiric activity up to their tectonic inversion. Precipitation of dolomite and calcite from both warmed marine-derived and meteoric fluids characterised diagenetic stages during Pliensbachian, when the carbonate platforms were exposed and karstified. Burial diagenesis occurred from Toarcian to Middle Jurassic, due to changes of salt-induced dynamic related to increase in siliciclastic input, fast diapir rise and rapid burial of Pliensbachian platforms. During this stage, the diapir acted as a physical barrier for fluid circulation between the core and the flanking sediments. In the carbonates and breccias flanking the structures, dolomite and calcite precipitated from basinal brines, whereas carbonate slivers located in the core of the structure, were affected by the circulation of Mn-rich fluids. The final diagenetic event is characterised by the income of meteoric fluids into the system during uplift caused by Alpine orogeny. These results highlight the relevant influence of diapirism on the diagenetic modifications in salt-related basins in terms of diagenetic events and involved fluids.     

To what extent have laterites contributed to the geochemical,surface reflectance and magnetic properties of adjacent tropical soils? Evidence from Niger and Burkina Faso

The present study is based on a suite of surface samples from exposures of eroded laterite, considered to be Tertiary in age, and nearby soils in the Sahelian region of SW Niger and Burkina Faso. X‐ray fluorescence, X‐ray diffraction, computer‐controlled scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, diffuse UV–visible reflectance spectroscopy and a suite of magnetic measurements have been used to shed light on the origin of the soils and their possible derivation from the adjacent, eroded laterite outcrops. On the basis of the wide range of data obtained, we conclude that the mineralogy and magnetic properties of the soils preclude direct derivation from the laterites without further weathering and modification. Nor does the evidence support the view that the soils have evolved entirely independently, uninfluenced by input from the laterites. The only conclusion that is consistent with all the lines of evidence is that the erosion of the laterites provided at least a significant part of the material upon which soil formation took place. This must have occurred at a time early enough to permit a long period of subsequent soil development during which the iron oxides, specifically haematite and ferrimagnetic minerals, were significantly modified. From this, we infer that eroded material from discontinuous laterite exposures has contributed significantly to the remotely sensed, distinctive reflectance characteristics of the Sahel surfaces. The magnetic properties of the soils provide evidence for the in situ neo‐formation of fine, secondary, pedogenic magnetite/maghemite grains typical of those found in many soils across the Sahel region and elsewhere in both temperate and tropical environments. Copyright © 2017 John Wiley & Sons, Ltd.     

An examination of the steady‐state assumption in soil development models with application to landscape evolution

Soil depth and soil production are highly complicated phenomena, generated from a complex interaction of physical, biological and chemical processes. It has, nevertheless, become increasingly clear that soil formation rates are closely related to chemical weathering rates. Somewhat paradoxically, it is likewise becoming apparent that such biogeochemical reactions as slowly transform rock to soil are limited by physical processes, such as flowing water and the formation of fractures. We have formulated a theoretical approach that relates soil formation rates to chemical weathering rates, and those, likewise, to solute transport rates. For such a theoretical framework to be relevant, the solute transport rates cannot equal those of the flowing water, as is the case in Gaussian solute transport. Rather, solute transport must be slowed in accordance with heavy‐tailed solute arrival time distributions. The inference is that the traditional advection–dispersion equation formulation for solute transport is inadequate in the typically heterogeneous geological media that weather to form soils. Here we examine the implications of this soil production model on the assumption of the approach to steady state. Particularly at slow erosion rates we find that many soil columns are not in equilibrium. This tendency may be accentuated in dry climates. Copyright © 2017 John Wiley & Sons, Ltd.     

Sediment grain size measurements are affected by site-specific sediment characteristics and analysis methods: implications for environmental monitoring

Sediment grain size, and specifically changes in the percent mud content (i.e. the fraction <63?µm) over time is often used as an indicator of estuarine environmental health. Using sediment samples from three distinct estuarine systems, we determined that different analytical methods (laser diffraction and wet sieving) gave significantly different results in terms of percent mud content. These differences are also ecologically meaningful when considering the influence of mud on estuarine macrofauna. We propose an approach to measuring sediment grain size termed Environmentally Available Sediment (EAS), which advocates for the measurement of the sediment that biota are directly exposed to. For the purposes of environmental monitoring, it is also essential to monitor sediment grain size in a repeatable way which is likely to be achieved using consistent (or no) pre-treatment and the use of a measurement technique that is unlikely to change over time, e.g. wet sieving.     

A model for the statistical distribution of microlithotypes in coal

Microlithotype composition of a coal sample is often summarized by examining a large number (~500) of subsamples of a grain mount and estimating proportions of vitrite, intermediates, and inertite, where, for samples we have investigated, the proportion of intermediates is generally less than 0.4. This suggests that most subsamples are either greater than 95% vitrinite or greater than 95% inertinite, so that the statistical distribution of vitrinite has most of its weight in its tails. Two distributions which may have this shape are the beta and the logistic normal, and these have been fitted to the microlithotype distribution of some coal samples. Parameters of these fitted distributions are related to the proportion of vitrinite in the sample and thickness of microscopic bands in the coal. For coals in the Sydney Basin, at least, it was found that the parameter relating to band thickness is approximately constant over a coal seam; therefore, fitting one or other of these distributions to such data leads to directly interpretable parameters.     

Volatile C1C7 organic compounds in an anoxic sediment core from the Pettaquamscutt River (Rhode Island,U.S.A.)

Surface sediments from an anoxic marine environment, the Upper Basin of the Pettaquamscutt River, Rhode Island, were analyzed for volatile organic compounds in the C₁C₇ range. The compounds identified included methane, ethane, alkenes (C₂C₅), carbon disulfide, cyclopentane, 3-methylpentane, methylfuran, aldehydes and ketones. Ethane, methylfuran, and most of the aldehydes and ketones showed maxima at the sediment water interface. Methane levels were very high-10–100 times greater than observed in most other surface sediments examined in this laboratory.     

On solitary waves generated by a moving pressure field

Summary The waves generated by a steadily moving two-dimensional pressure distribution are examined using non-linear shallow water theory. The applied pressure is zero ahead of the disturbance, that is in the downstream direction, and is a constantP ₀ in the upstream direction, these regions being joined smoothly by a cubic function.We consider here only the case of supercritical flow in both regions, the solution representing an asymmetric solitary wave travelling with the disturbance. The wave profiles are determined by an iterative method previously employed for non-linear waves. Wave amplitudes and profiles, and the wave drag, associated with each system are computed for various values ofP ₀/Q g h, whereh is the undisturbed depth of water ahead of the wave.The solution obtained reduces to the classical solitary wave of finite amplitude when the applied pressure is everywhere zero.

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Résumé Nous avons calculé les expressions des profils d'ondes solitaires produites par une pression, qui se propagent sur la surface d'une couche d'eau peu profonde avec une vitesseU plus grande que (g h)^1/2. La pression appliquée est nulle en avant de l'onde, elle est une constanteP ₀ en arrière, et entre ces deux régions elle est representée par une fonction cubique. Les profils sont calculés par une methode iterative déjà employée pour des ondes non-linéaires. L'amplitude, le profil et la force ont été evalués pour diverses valeurs deP ₀/Q g h, ouh est la profondeur en avant de l'onde.

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Division of Numerical and Applied Mathematics, National Physical Laboratory.