The gravitational potential due to uniform disks and rings

The gravitational potential due to thin uniform disks and rings is obtained in closed form in terms of complete elliptic integrals.     

Subbottom acoustic and sedimentary records of past surface water–groundwater exchange through sinkhole lakes in south Georgia,U.S.A

Lake Balboa is a deep sinkhole lake in south Georgia. Subbottom acoustic profiling and long sediment cores reveal four stratigraphic units within >20 m of lacustrine fill above acoustically stratified and faulted Miocene/Pliocene overburden and basement Eocene limestone which hosts the Floridan Aquifer system (FAS). Fill consists of thin, rhythmically bedded, peaty sediments (Unit I), indicative of slow sedimentation in a shallow swamp until 13,110–12,680 cal BP, a mix of desiccated and over-consolidated clay and silty sand (Unit II) implying periodic subaerial exposure of the lake bed until 9470–9025 cal BP, and gyttja associated with a rapid 8 m rise in water level by 9120–9020 cal BP (Unit III), as well as an additional rise of 10 m to modern lake levels (Unit IV). Accumulation of nearly 4.5 m of low permeability gyttja, and higher lake levels have fundamentally changed exchange between surface water and groundwater, reducing by 40% or more the rate of vertical leakage to the FAS and increasing shallow aquifer discharge to the lake.     

Processes affecting deposition of sediment in a small, morphologically complex lake

Devil Lake is morphologically complex as a result of Pleistocene glacial erosion of the Frontenac Axis of the Canadian Shield. In order to assess the processes causing highly variable sedimentation in the lake, we monitored currents, suspended sediment and temperature in the lake before and during autumn overturn in 2002. Strong summer thermal stratification (stability number to 0.11 s^–1 declining with the approach of overturn) was insufficient to prevent a dynamic response in the hypolimnion to wind forcing. Superimposed on a gradual increase in suspended sediment concentration in the last weeks of stratification from less than 2 g/l to about 30 g/l were shorter-term rises lasting up to several days. Associated with these events was an increase in particle size of the sediment from a mode of 40–50 to 150–200 m ascribed to flocculation from primary particles. These events culminated in rapid (<1 h) clearing of the water associated with strong, sustained winds over the lake, especially from the southwest. After overturn, the events were more frequent, and flocculation was unable to develop as well in the more vigorous circulation. However, currents in the hypolimnion occurred throughout the period before, during and after overturn with speed related to wind speed, but direction largely independent of wind direction. The results represent an approach to understanding the nature of sedimentary processes and thus to strengthening the use of sedimentary records as proxy in environmental and paleoenvironmental assessment.     

Petrologic and textural diversity among the PCA 02 howardite group,one of the largest pieces of the Vestan surface

Abstract— Nine howardites and two diogenites were recovered from the Pecora Escarpment Icefield (PCA) in 2002. Cosmogenic radionuclide abundances indicate that the samples are paired and that they constituted an approximately 1 m (diameter) meteoroid prior to atmospheric entry. At about 1 m in diameter, the PCA 02 HED group represents one of the largest single pre‐atmospheric pieces of the Vestan surface yet described. Mineral and textural variations were measured in six of the PCA 02 howardites to investigate meter‐scale diversity of the Vestan surface. Mineral compositions span the range of known eucrite and diogenite compositions. Additional non‐diogenitic groups of Mg‐ and Fe‐rich olivine are observed, and are interpreted to have been formed by exogenic contamination and impact melting, respectively. These howardites contain olivine‐rich impact melts that likely formed from dunite‐ and harzburgite‐rich target rocks. Containing the first recognized olivine‐rich HED impact melts, these samples provide meteoritic evidence that olivine‐rich lithologies have been exposed on the surface of Vesta. Finally, we present a new method for mapping distributions of lithologies in howardites using 8 elemental X‐ray maps. Proportions of diogenite and eucrite vary considerably among the PCA 02 howardites, suggesting they originated from a heterogeneous portion of the Vestan surface. While whole sample modes are dominated by diogenite, the finer grain size fractions are consistently more eucritic. This discrepancy has implications for near‐infrared spectral observations of portions of Vesta’s surface that are similar to the PCA 02 howardites, as the finer grained eucritic material will disproportionately dominate the spectra.     

Fractionated sulfur isotopes in sulfides of the Kaidun meteorite

Abstract— The Kaidun meteorite contains carbonaceous chondrite (CM1) clasts that have been highly altered by reactions with hydrothermal fluids. Pyrrhotite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate, and pentlandite forms veins that crosscut aggregates of phyllosilicate and garnet but not pyrrhotite. The isotopic compositions of S (δ³⁴S_CDT) in individual sulfide grains, measured by ion micro-probe, are fractionated compared to troilite in ordinary chondrites. The S in Kaidun sulfides is isotopically light (as much as ?4.2% for pyrrhotite and ?5.7%0 for pentlandite), unlike sulfides in other carbonaceous chondrites, which are enriched in ³⁴S. The unusual S-isotopic composition of these texturally unique sulfides supports the hypothesis that Kaidun CM1 clasts were pervasively altered under extreme thermal conditions, possibly by fluids that had lost isotopically heavy SO₂.     

Derivation of density and temperature from the Cassini–Huygens CAPS electron spectrometer

In this paper we present two methods to derive electron fluid parameters from the CAPS–ELS spectrometer on board the Cassini spacecraft currently in orbit around Saturn. In the first part of the paper we give a basic overview of the instrument and describe the challenges inherent in the derivation of density and temperature values using these techniques. We then describe a method to calculate electron moments by integrating the particle distribution function. We also describe a second technique in which we fit the electron energy spectrum with a Gaussian curve and use the peak energy of this curve to derive density and temperature values. We then compare the two methods with particular emphasis on their application to Cassini SOI observations in the saturnian environment and point out the limitations of the two techniques. We will show that results from the two very different methods are in agreement when the physical properties of the environment and of the observed electron populations have been inferred from inspection of the raw data. Finally we will suggest future developments that will remove these limitations.     

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long-term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 ( https://www.sno-tourbieres.cnrs.fr/ ). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available ( https://data-snot.cnrs.fr/data-access/ ). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution ( https://zenodo.org/communities/sno_tourbieres_data/ ).     

IN-SITU observations of irregular ionospheric structure associated with the plasmapause

Additional studies of the ion composition results obtained from the OGO-6 satellite support earlier observations of irregularities in the distribution of H⁺ and He⁺ within the light ion trough near L = 4, which has been associated with the plasmapause. These irregularities are in the form of sub-troughs superimposed upon the major mid latitude decrease of the light ions. In the sub-troughs, ionization depletions and recoveries of as much as an order of magnitude are observed within a few degrees of latitude, usually exhibited in a pattern which changes significantly with longitude as the Earth rotates beneath the relatively fixed satellite orbit. The location and properties exhibited by these sub-troughs appear to be consistent with the concept of a plasmasphere distortion in the form of “plasmatails” resulting from the combined effects of magnetospheric convection plus corotation. Like the light ion trough, the “plasmatail” irregularity in H⁺ may be obscured on the day side by the dominant topside distribution of O⁺. Consequently, these light ion irregularities are seen as an important factor for studies of plasmapause-trough relationships.     

Ein Verfahren zur Berechnung von Gezeitenstrom- und Gefällsellipsen

Zusammenfassung Bei der im Folgenden beschriebenen Methode zur Berechnung der Stromellipsenelemente werden die Summen und Differenzen der Hauptachsen bzw. ihrer Richtungen und Phasen als Beträge bzw. Richtungen zweier Vektoren bestimmt. Die Komponenten dieser Vektoren sind wieder Summen und Differenzen von vier Konstanten, die man bei der harmonischen Analyse der Stromkomponenten bezüglich der betreffenden Tide gewinnt. Eine andere Berechnungsmethode geht von den harmonischen Konstanten der Stromkomponenten aus und benutzt trigonometrische Funktionen komplexen Arguments. Zum Schluß werden Beziehungen zwischen den Elementen der Stromellipse und denen der Gefällsellipse aufgestellt unter der Voraussetzung, daß der Zusammenhang zwischen horizontalen und vertikalen Gezeiten sich durch die linearisierten hydrodynamischen Grundgleichungen darstellen läßt.

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A method of calculating tidal stream and gradient ellipses

Summary In the following paper a method of calculating the elements of tidal stream ellipses is described by which the sums and differences of the major axes or their directions and phases are determined as the scalar quantities or directions of two vectors. The components of these vectors, on their turn, are sums and differences of four constants obtained by the harmonic analysis of the stream components with regard to the respective tide. Another calculating method proceeds from the harmonic constants of the stream components and employs trigonometric functions of complex arguments. Finally, on the supposition that the relation between horizontal and vertical tides may be represented by the linearized fundamental hydrodynamic equations, relations are established between the elements of the tidal stream ellipse and those of the gradient ellipse.

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Mode de calcul des ellipses du courant de marée et du gradient

Résumé Le mode de calcul des éléments des ellipses du courant expliqué ci-dessous demande que les sommes et les différences des grandaxes ou leurs directions et leurs phases soient déterminées comme grandeurs scalaires ou comme directions de deux vecteurs. Les composantes de ces vecteurs sont, de leur part, les sommes ou les différences de quatre constantes qui résultent de l'analyse harmonique des composantes de courant de la marée en question. Une autre méthode de calcul part des constantes harmoniques des composantes de courant et emploie des fonctions trigonométriques à l'argument complexe. Enfin, pourvu que la relation entre les composantes horizontales et verticales puisse être représentée à l'aide des équations hydrodynamiques fondamentales linéarisées, des relations entre les éléments de l'ellipse du courant et ceux de l'ellipse du gradient sont établies.

     

Geochemistry of Flooded Underground Mine Workings Influenced by Bacterial Sulfate Reduction

Unlike the majority of the water in the flooded mine complex of Butte Montana, which includes the highly acidic Berkeley pit lake, groundwater in the flooded West Camp underground mine workings has a circum-neutral pH and contains at least 8 μM aqueous sulfide. This article examines the geochemistry and stable isotope composition of this unusual H₂S-rich mine water, and also discusses problems related to the colorimetric analysis of sulfide in waters that contain FeS_(aq) cluster compounds. The West Camp mine pool is maintained at a constant elevation by continuous pumping, with discharge water that contains elevated Mn (90 μM), Fe (16 μM), and As (1.3 μM) but otherwise low metal concentrations. Dissolved inorganic carbon in the mine water is in chemical and isotopic equilibrium with rhodochrosite in the mineralized veins. The mine water is under-saturated with mackinawite and amorphous FeS, but is supersaturated with Cu- and Zn-sulfides. However, voltammetry studies show that much of the dissolved sulfide and ferrous iron are present as FeS_(aq) cluster molecules: as a result, the free concentration of the West Camp water is poorly constrained. Concentrations of dissolved sulfide determined by colorimetry were lower than gravimetric assays obtained by AgNO₃ addition, implying that the FeS_(aq) clusters are not completely extracted by the Methylene Blue reagent. In contrast, the clusters are quantitatively extracted as Ag₂S after addition of AgNO₃. Isotopic analysis of co-existing aqueous sulfide and sulfate confirms that the sulfide was produced by sulfate-reducing bacteria (SRB). The H₂S-rich mine water is not confined to the immediate vicinity of the extraction well, but is also present in flooded mine shafts up to 3 km away, and in samples bailed from mine shafts at depths up to 300 m below static water level. This illustrates that SRB are well established throughout the southwestern portion of the extensive (>15 km³) Butte flooded mine complex.