Intercomparison of Formaldehyde Measurements in Clean and Polluted Atmospheres

Three different techniques used tomeasure atmospheric formaldehyde were compared duringa field campaign carried out at a clean maritime siteon the West coast of Ireland. Two spectroscopictechniques Differential Optical AbsorptionSpectroscopy (DOAS) and Tunable Diode Laser AbsorptionSpectroscopy (TDLAS), together with a glass coil/Hantzschreaction/fluorescence technique, wereemployed for measurements of atmospheric formaldehydeof the order of a few hundred pptv. The betteragreement was observed between the fluorescence andDOAS instruments.Two DOAS instruments were compared to the glasscoil/Hantzsch reaction/fluorescence technique at asemi-polluted site on the North Norfolk coast, U.K.,where concentrations of formaldehyde were observed atlevels up to 4 ppbv. A very good agreement wasobserved between the two instruments.The glass coil/Hantzsch reaction/fluorescence and theTDLAS instruments were also deployed simultaneously inorder to measure indoor air inside a mobile laboratorylocated at the Imperial College Silwood Park site nearAscot, U.K. The doors of the mobile laboratory wereleft open in order to obtain the backgroundformaldehyde concentrations. Closing them afterwardsallowed us to observe the increase in concentrationsas a result of indoor emissions. The agreement betweenthe two instruments was outstanding (correlationcoefficient was 99%).The results from this study showed that of the fourinstruments included in this intercomparison the glasscoil/Hantzsch reaction/fluorescence technique provedthe most suitable for continuous measurements offormaldehyde in the background atmosphere.     

Nepheline-bearing rocks from the Poohbah Lake complex,Ontario: Malignites and Malignites

Malignites from the Poohbah Lake complex of northwestern Ontario, Canada are melanocratic cumulates. Cumulus pyroxene and apatite are poikilitically enclosed in a groundmass of large plates of intercumulus orthoclase and nepheline. Nepheline-feldspar fingerprint-like intergrowths occur. Nephelines are commonly zeolitized and pyroxenes altered to aggregates of biotite and/or garnet by deuteric alteration. Pyroxenes are weakly zoned from Di₇₁ Hd¹⁸Ac₁₁ to Di₆₃Hd₂₂Ac₁₅, and are similar to the least evolved pyroxenes of other alkaline rocks. Nephelines all have compositions within the Morozewicz-Buerger convergence field and feldspars have a limited compositional range from Or⁸⁸ to Or⁹⁵. Perthites are absent.Inconsistancies in the usage of the terms malignite and juvite are discussed and it is considered that a non-genetic petrographic classification of nepheline syenites leads to the obscuration of a group of potassic nepheline syenites, characterized by the presence of nepheline plus orthoclase which are typically associated with saturated to over-saturated alkaline rocks, contain pseudo-leucite or nepheline-orthoclase intergrowths, are emplaced in mobile belts and are not associated with rocks of the ijolite-carbonatite suite.A genetic classification of nepheline syenites is suggested and it is proposed that; (1) mafic-rich nepheline syenites be referred to as mela-nepheline syenites (sensu lato) rather than as malignites; (2) the term malignite be used for magmatic potassic nepheline syenites characterised by the presence of nepheline plus a single potassium-rich feldspar (orthoclase or microcline) and devoid of exsolution perthite under subsolvus conditions; (3) the metasomatic malignites and juvites of ijolite-carbonatite complexes be referred to as varieties of fenites.     

Environmental controls on phytoplankton production in coastal ecosystems: A case study from Tokyo Bay

Phytoplankton biomass and primary production were examined in their environmental context, for a semi-enclosed bay (Tokyo Bay, Japan) using data from monthly samples collected over a three-year period. Heavy precipitation and high surface temperatures in the late spring and summer gave rise to a highly-stratified water-column and stimulated a series of phytoplankton blooms, whereas during the winter, a weakly-stratified and deeply-mixed water-column led to a rapid decline in phytoplankton biomass under light-limited growth conditions. By incorporating pigment, photophysiological and optical data into a primary production model we show that daily, water-column primary production ranges from ∼160 mg C m⁻² d⁻¹ to 7600 mg C m⁻² d⁻¹. High water turbidity and deep vertical mixing, both separately and in concert, limit the light available for algal growth over much of the year. Annual primary production varied from 370 to 580 g C m⁻² y⁻¹. The relative influences of nutrient limitation and light limitation are assessed. A model is developed that describes this in an explicit manner using photophysiological parameters.     

Balanced cross-sections and their implications for the deep structure of the northwest Alps: discussion

Field evidence around the southwestern termination of the Mont Blanc basement massif casts doubt on Butler's interpretation of the massif as a relatively thin thrust-sheet extending over the imbricated Dauphind cover. A thick-skinned model of basement faulting, analogous to Laramide faulting in the western U.S.A., seems more appropriate for the area.     

The mechanics of frontal imbrication: a first-order analysis

The detachment and imbrication of thrust slices at the front of a thrust wedge is one of the principle modes by which such wedges grow. Collapse of the frontal ramp under longitudinal compressional stress cannot explain the regular formation of new slices of finite length, unless there are regularly spaced heterogeneities in the footwall layer or the underlying basement surface. Advance of the thrust wedge over the frontal ramp, however, increases both the vertical load on the ramp and the traction on the upper flat. This will in general produce a peak deviatoric stress in the footwall layer below the leading edge of the thrust wedge. Failure will occur at this point when the thrust wedge has advanced a distance L such that the deviatoric stress in the footwall layer exceeds its strength. L is a function of (a) rock density, (b) ramp angle, (c) the resistances to motion on the basal detachment, the ramp, and the upper flat, and (d) the strength and thickness of the footwall layer. These mechanical parameters can therefore control the formation of new thrust slices of regular length in the absence of footwall heterogeneities.Continued accretion of thrust slices at the front of the wedge progressively diminishes its overall taper until it becomes mechanically unstable. Reactivation of previously formed thrusts is a likely response, and will alternate with or occur concurrently with frontal imbrication. Thrust reactivation occurs at a diminishing rate back from the wedge front and is the main cause of back-rotation of older thrust slices. Further back in the wedge, reactivation is not possible, because the thrusts are too steep and have strongly curved trajectories. Thickening of the wedge in this area must occur by out-of-sequence thrusting, backthrusting, or ductile deformation.

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Zusammenfassung Die Abscherung und Anstapelung von Schuppen an die Stirn eines Schuppenkeils stellt eine der wichtigsten Wachstumsarten von Schuppenkeilen dar. Der Verbrach einer frontalen Rampe wird durch die von ihr getragene longitudinale Normalspannung hervorgerufen. Die Entstehung neuer gleichförmiger Schuppen mit begrenzter Länge lä\t sich durch diesen Verbruch nicht erklären, ohne da\ man Heterogenitäten in gleichmä\igen Abständen in der liegenden Schicht oder dem Unterbau annimmt. Dennoch steigert der Vortrieb über die frontale Rampe eines Schuppenkeils sowohl die vertikale Last auf der Rampe als auch die Geschiebelast auf dem oberen der Schichtung parallelen Teil der überschiebung (upper flat). Infolgedessen ist es wahrscheinlich, da\ der Spannungsdeviator im Liegenden unter der Vorderkante des Schuppenkeils ein Maximum erreicht. Ein Bruch entsteht dann, wenn die Schubweite des Schuppenkeils einen WertL erreicht hat, von dem ab der Spannungsdeviator im Liegenden grö\er ist als dessen Bruchfestigkeit.L. ist von folgenden Variablen abhängig: (a) der Gesteinsdichte (b) dem Rampenwinkel (c) dem Geschiebewiderstand auf der basalen Abscherungsbahn, der Rampe und dem oberen der Schichtung parallelen Teil der überschiebung (d) der Bruchfestigkeit und Dicke der liegenden Schicht. Diese mechanischen Parameter haben also einen starken Einflu\ auf die Geometrie der neuen Schuppe.Durch fortlaufende Anstapelung von Schuppen an die Stirn des Schuppenkeils wird die Steigung des Keils progressiv reduziert, bis er mechanisch unstabil wird. Es ist wahrscheinlich, da\ dadurch frühere überschiebungsbahnen reaktiviert werden, und da\ dies entweder abwechselnd oder gleichzeitig mit der frontalen Anschuppung stattfindet. Die Wahrscheinlichkeit einer Reaktivierung von überschiebungsbahnen nimmt mit wachsender Entfernung von der Keilstirn ab. Das Reaktivieren ist die Hauptursache für die Rückrotation von älteren überschiebungen. Im hinteren Teil des Schuppenkeils ist das Reaktivieren nicht möglich, weil die überschiebungsbahnen zu steil und zu stark gekrümmt sind. Eine Verdickung des Keils in diesem Bereich mu\ durch eine — mehrere ältere überschiebungen durchschneidende — überschiebung (out of sequence thrust), durch eine Rücküberschiebung, oder durch eine duktile Verformung geschehen.

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Résumé Le décollement et l'imbrication des écailles au front d'un prisme de chevauchement constituent un des mécanismes principaux par lequel de tels prismes s'accroissent. La destruction de la rampe frontale par l'effet de contraintes compressives longitudinales ne peut expliquer la formation régulière de nouvelles tranches de longueur limitée, à moins que l'on n'admette l'existence d'hétérogénéités régulièrement espacées situées dans le mur ou à la surface du socle sousjacent. Cependant, l'avancée du prisme de chevauchement au-dessus de la rampe augmente la charge verticale supportée par celle-ci ainsi que la contrainte cisaillante dans la partie supérieure du substratum. Cette situation tend à produire un maximum de la contrainte déviatorique dans le substratum au-dessous du bord frontal du prisme de chevauchement.La rupture se produira à cet endroit lorsque le prisme se sera avencé d'une distance L telle que la contrainte déviatorique dans le substratum dépasse la résistance propre de celui-ci.La longueur L est fonction: (a) de la densité de la roche, (b) de l'angle de la rampe, (c) des résistances à l'avancement sur le décollement principal, la rampe et la surface supérieure de la partie sous-jacente. Ces paramètres mécaniques déterminent donc la géométrie de la nouvelle écaille.L'accrétion répétée d'écaillés à l'avant d'un prisme en coin diminue progressivement son angle frontal jusqu' à ce qu'il devienne mécaniquement instable. Il peut en résulter une réactivation des surfaces de chevauchement formés précédemment, soit alternativement, soit concurremment à l'imbrication frontale. Cette réactivation est de moins en moins active vers l'arrière du dispositif; elle constitue la cause principale de la rotation des écailles plus anciennes. Dans la partie du prisme située plus en arrière, cette réactivation n'est guère possible, car les chevauchements y sont trop pentés et ont des trajectoires fortement incurvées. Dans cette zone, l'épaississement du prisme peut se produire grâce à des chevauchements hors séquence (recoupant les surfaces antérieures), à des rétrochevauchements ou à une déformation ductile.

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The interpretation of baseline atmospheric turbidity measurements at Cape Grim,Tasmania

Five years of turbidity data at Cape Grim have been analysed. The turbidity at 500 nm in clean maritime airmasses from the South to the West shows a seasonal variation, with a minimum in winter. There is also a variation in turbidity with wind speed. The winter minimum can be explained partially by a minimum in wind strength in that season. On the assumption, based on observations at Cape Grim and at other locations, that the boundary layer turbidity is caused by seasalt haze, an attempt is made to interpret the observed turbidity values and their seasonal changes. Optical extinction coefficients at the surface deduced from the measured values of optical depth are compared with extinction coefficients calculated from Mie theory using particle size distributions measured at Cape Grim. Reasonable agreement is obtained when the growth of salt particles in the high maritime humidity is considered, using both theoretical models and previous experimental results together with the rapid increase in salt concentration with wind speed.     

Limnology of the Klutlan moraines,Yukon Territory,Canada

Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600–1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an “ultraoligotrophic” category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceran Daphnia pulex. Surface-sediment samples contained a total of 16 species of chydorid Cladocera. Of these, Alonella excisa and Alona barbulata are apparently the pioneer species in the youngest lakes. Chydorus sphaericus only appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age.