Why Is the Climate Forcing of Sulfate Aerosols So Uncertain?

l. IntroductionAlthough the aerosol has been recognized as an important factor which has innuence onthe past, present and future climate for a long time, it still has much uncertainty in assessingits climate forcing. The direct radiative forcing of sulfate aerosols has been estimated rangingfrom --0.3 W/ m2 to --0.9 W/ m2 in recent publications (Charlson et al., l992, Kiehl andBriegleb l993; Taylor and Penner 1994, Boucher and Anderson l995, Kieh1 and Rodhe l995;Chuang et al., l997, Penne…     

A late Triassic 40Ar/39Ar age for the El Hammam high-REE fluorite deposit (Morocco): mineralization related to the Central Atlantic Magmatic Province?

El Hammam is the only fluorite mine in Morocco (production 100,000 t/year). The fluorite mineralization is in an array of fluorite–calcite veins and is characterized by unusually high REE content in carbonate minerals (1,400 ppm in calcite; up to 2,000 ppm in siderite) and in fluorite (about 600 ppm). Since the 1960s, the genesis of the deposit has been attributed to a mesothermal hydrothermal event connected with late-Variscan granitic intrusions. Precise ⁴⁰Ar/³⁹Ar dating of hydrothermal K-feldspar yields an age of formation of the El Hammam deposit at 205 ± 1 Ma. Its genesis is therefore associated in time and space with the development of the Triassic–Jurassic basins and the associated anorogenic continental flood basalts of the Moroccan Mesetian Middle Atlas. The source of the hydrothermal mineralization (magmatic and/or metamorphic) is discussed.     

Oxygen isotope systematics of gem corundum deposits in Madagascar: relevance for their geological origin

The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks). In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits (placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios (¹⁸O/¹⁶O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ¹⁸O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ¹⁸O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths contained in the alkali basalt of Soamiakatra have δ¹⁸O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ¹⁸O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo). The δ¹⁸O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ¹⁸O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ¹⁸O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety of colored sapphires and rubies, with δ¹⁸O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have a large variety of colored sapphires and rubies with a large variation in δ¹⁸O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire, syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire.     

Ba and Ni speciation in a nodule of binary Mn oxide phase composition from Lake Baikal

The partitioning and incorporation mechanism of Ni and Ba in a ferromanganese nodule from Lake Baikal were characterized by X-ray microfluorescence, microdiffraction, and absorption spectroscopy. Fe is speciated as goethite, and Mn as romanechite (psilomelane) and 10 Å-vernadite (turbostratic buserite) with minor 7 Å-vernadite (turbostratic birnessite). Barium is associated with romanechite and Ni with vernadite in distinct and irregularly distributed layers, and each type of Mn oxide is separated from the other type by goethite. The binary Mn oxide banding pattern is interpreted by a two-mode accretionary model, in which the variation in Ba flux induced by hydrothermal water pulses determines whether a tectomanganate (romanechite) or phyllomanganate (vernadite) is formed during the ferromanganese nodule accretion. Consistent with the dependence of Ni sorption on pH and the circumneutral pH of the lake water, nickel is mainly substituted isomorphically for Mn in the manganese layer, and is not sorbed at vacant Mn layer sites in the interlayer.     

Influence of Drying on the Stiffness and Strength of Cement-Stabilized Soils

Nowadays, improving the strength and deformation properties of soft soils by deep soil mixing is a commonly used technique. There is also an increasing interest in the use of this technique for foundation/structural elements and excavation retaining walls applications. The compressive strength and elastic modulus of the soil mix material are key parameters in the design of these structures. However, there is very limited information available on the impact of exposure to air drying (in the case of retaining wall) on the strength and stiffness of cement stabilized soils. The aim of this study is to investigate the effects of different curing conditions (immersion in water, cycles of wetting and drying, continuous air drying) on the mechanical properties of soils treated with cement in the laboratory. Free–free resonance tests and unconfined compression tests were performed on specimens of silt and sand treated with blastfurnace slag cement. Strength increases more rapidly than stiffness between 7 and 30 days. The strength of stabilized soils submitted to cyclic wetting and drying before the cement hydration process is complete continues to increase. As long as the periods of drying do not induce microcracks, the stiffness of the treated soil specimens also increases with time. However, the stiffness is lower than for the specimens cured in water indicating a disruptive effect of the imposed wetting–drying cycles on stiffness. Continuous exposure to air drying inhibits strength development due to insufficient water for hydration. Significant stiffness decreases were observed on specimens of stabilized silt and are attributed to microcracking.     

Tracing the emerald origin by oxygen isotope data: the case of Sandawana,Zimbabwe

Given the wide range of oxygen isotopic composition of emerald from all over the world (δ¹⁸O between +6.2 and +24.7‰), the δ¹⁸O_V-SMOW values of emeralds from the Sandawana mines in Zimbabwe (δ¹⁸O‰=+6.6 to +8.0), are relatively constant, among the lowest ever measured. These consistently low values can be explained by host-rock buffering in a very narrow emerald-bearing reaction zone between ultrabasic greenstones (metamorphosed komatiites) and albitised pegmatites. δ¹⁸O values of Sandawana emeralds overlap those of emeralds from Brazil, Austria, Australia and Madagascar, a fact indicating that, in these cases, oxygen isotope composition alone is not sufficient to determine the geographic origin of commercially available emeralds. However, stones with overlapping δ¹⁸O values may eventually be identified using a combination of physical properties, inclusion characteristics and chemical composition. To cite this article: J.C. Zwaan et al., C. R. Geoscience 336 (2004).     

Resazurin as an indicator of reducing capacity for analyzing the physiologic status of deep-sea bacterium Photobacterium phosphoreum ANT-2200

Resazurin(RZ)is a weakly fl uorescent blue dye and can be reduced irreversibly to highly fl uorescent pink resorufi n(RF)that is reduced reversibly to colorless dihydroresorufi n(hRF)by photodeoxygenation,chemical reaction and reductive organic compounds produced through cell metabolism.Because of the reliable and sensitive fl uorescence-color change and noninvasive features,RZ has been used widely as a redox indicator in cell viability/proliferation assays for bacteria,yeast,and mammalian cells.However,RZ is used rarely for physiological characterization of marine microorganisms.Here,we developed a custom-made irradiation and absorption-analysis device to assess the reducing capacity and physiologic status of marine bacterial cultures.We measured the absorption spectra of RZ,RF,and hRF in the presence of the reducing compound Na 2 S and under visible-light irradiation.After establishing appropriate parameters,we monitored the color changes of RZ and its reduced derivatives to evaluate the coherence between reducing capacity,bioluminescence and growth of the deep-sea bacterium Photobacterium phosphoreum strain ANT-2200 under various conditions.Emission of bioluminescence is an oxidation process dependent upon cellular reducing capacity.Growth and bioluminescence of ANT-2200 cell cultures were impeded progressively with increasing concentrations of RZ,which suggested competition for reducing molecules between RZ at high concentration with reductive metabolism.Therefore,caution should be applied upon direct addition of RZ to growth media to monitor redox reactions in cell cultures.Analyses of the instantaneous reduction velocity of RZ in ANT-2200 cell cultures showed a detrimental eff ect of high hydrostatic pressure and high coherence between the reducing capacity and bioluminescence of cultures.These data clearly demonstrate the potential of using RZ to characterize the microbial metabolism and physiology of marine bacteria.     

Stepwise palaeoclimate change across the Eocene–Oligocene transition recorded in continental NW Europe by mineralogical assemblages and δ15Norg (Rennes Basin,France)

The Eocene–Oligocene transition (EOT, ~34 Ma) is the largest global cooling of the Cenozoic Era and led the Earth's climatic system to change from a greenhouse to an icehouse mode. Although it is well documented in marine settings, the few studies focusing on continental environments have demonstrated regional heterogeneities. The study core CDB1, located in the Rennes Basin (Western France), is a unique terrestrial (lacustrine–palustrine) record comprising well‐preserved and terrestrial‐derived organic‐rich sediments encompassing the EOT. Clay minerals and the first organic nitrogen isotope record (δ¹⁵N_org) of terrestrial origin for this period are used to reconstruct palaeoclimate changes across this key interval. As suggested in worldwide marine and a few continental records, a stepwise transition from warm/humid conditions in the Late Eocene to cooler/drier conditions in the Early Oligocene is confirmed in the area. In addition, an episode of drier conditions in the Late Eocene and humid/dry cycles in the Early Oligocene are suggested.     

Jurassic penetrative deformation and Cenozoic uplift in the Central High Atlas (Morocco): A tectonic model. structural and orogenic inversions

The Central High Atlas is characterized by a relatively mild deformation, with a local development of a more or less penetrative cleavage in the axial part of the belt. Locally, this cleavage and the plutonic bodies which outcrop in the core of most of the north-east trending anticlines (ridges »with intrusions«) are overlain by a disconformable sequence that comprises red clastic deposits which are capped by Cenomano-Turonian limestones. The age of these red deposits are bracketted between Bathonian to Mid-Cretaceous. Therefore, the spatial relationship of the cleavage with mafic intrusions, in the axial part of the Central High Atlas, suggests that it developed contemporaneously with the emplacement of magmas, probably during Mid-Jurassic times. During this period, the structural inversion occurred, from a transtensional regime to a transpressive regime.There are few indications that an important shortening persisted within the axial part of the Central High Atlas after the end of the Jurassic. Along the northern and the southern borders of the belt, however, Cretaceous and Cenozoic strata were deposited. Their sedimentary facies bear witness of successive stages of the Atlas evolution. Especially, the rapidly coarsening up of the clastic deposits since the Oligocene in these marginal basins indicates the onset of the rising up of the belt, i. e. the orogenic inversion.

---

Zusammenfassung Der zentrale Hohe Atlas ist eine intrakontinentale Gebirgskette, die sich im Bereich der zwischen dem Sahara-Plateau und dem marokkanischen Variszikum gelegenen Trias- und Jurabecken herausbildete. Dieses junge Gebirge, dessen höchste Erhebungen über 4000 Meter hoch sind, ist durch einen relativ geringen Verkürzungsgrad gekennzeichnet. Axial tritt jedoch eine Schieferung auf im Bereich der N80° E ausgerichteten antiklinalen Hauptfalten sowie rund um die N45° E verlaufenden »Intrusions-Falten« und die Gangfelder. Die räumlichen Beziehungen dieser Schieferung zu den synsedimentären Faltungsstrukturen und den Gängen legen die Vermutung nahe, daß ihre Hausbildung während des Doggers mit dem Aufstieg und dem Eindringen der Plutone in das Sedimentgestein zeitlich zusammenfiel. In diesem Zeitraum erfolgte eine Strukturumkehrung, die das allmähliche Verschließen der Becken und das Zustandekommen der Schieferung bewirkte.Im Laufe des Tertiärs wurde nach und nach das gesamte Atlasgebiet einer etwa N-S gerichteten Einspannung ausgesetzt. Mit der Ablagerung immer gröberer Sedimente in den letzten Randbekken setzte schließlich im Oligozän die orogene Inversion ein, die das Gebirgsrelief bedingt hat.

---

Résumé Le Haut Atlas central est une chaîne intracontinentale qui s'est développée à l'emplacement de bassins subsidents triasiques et jurassiques installés en bordure de la plate-forme saharienne et de la chaîne hercynienne marocaine. Cette chaîne récente qui culmine à plus de 4000 mètres, est caractérisée par un taux de raccourcissement modeste. Cependant, dans son axe, une déformation pénétrative s'observe au droit des rides anticlinales majeures N 80° E, et autour des »rides avec intrusions« N 45° E et des champs filoniens. Les relations spatiales de cette schistosité avec les structures plicatives synsédimentaires et les intrusions nous conduisent à considérer son développement comme globalement contemporain de la mise en place des plutons dans la couverture sédimentaire. L'âge des dépôts détritiques, discordants sur les roches intrusives et sur le Lias schistosé, étant estimé callovien ou wealdien, la déformation synschisteuse est par conséquent d'âge postbathonien et antécrétacé. C'est pendant cette période que se manifeste, avec le passage d'un régime tectonique contrôlé par le jeu de décrochements senestres E-W à un autre dominé par le fonctionnement de décrochements senestres NE-SW en compression, une inversion structurale responsable de la fermeture progressive des bassins et du développement de la schistosité.Au cours du Tertiaire, une compression subméridienne a progressivement affecté tout le domaine atlasique. Et c'est à partir de l'Oligocène, avec l'arrivée de dépôts détritiques de plus en plus grossiers dans les bassins résiduels bordiers, que débute l'inversion orogénique, responsable du relief de la chaîne.

---

, , Map. , , , 4000 m., . N 80° N 45° » «, . , . , , , . , , N-S . , .

     

A novel methodology for radiative transfer in a planetary atmosphere

A novel methodology for evaluating the field of anisotropically scattered radiation within a homogeneous slab atmosphere of arbitrary optical thickness is provided. It departs from the traditional radiative transfer approach in first considering that the atmosphere is illuminated by an isotropic light source. From the solution of this problem, it subsequently proceeds to that for the more conventional case of monodirectional illumination. The azimuthal dependence of the field is separated in the usual manner by an harmonic expansion, leaving a problem in four dimensions (=optical depth, ₀=thickness, , =directions of incidence and scattering) which, as is well known, is numerically extremely inconvenient. Two auxiliary radiative transfer formulations of increasing dimensionality are considered: (i) a transfer equation for the newly introduced functionb ^m(,,₀) with Sobolev's function ^m(,₀) playing the role of a source-function. Because the incident direction does not intervene, ^m is simply expressed as a single integral term involvingb ^m. For bottom illumination, an analogous equation holds for the other new functionh ^m(,,₀). However, simple reciprocity relations link the two functions so that it is only necessary to considerb ^m; (ii) a transfer equation for the other new functiona ^m(,,,₀) with a source-function provided by Sobolev's functionD ^m(,,₀). For bottom illumination, another functionf ^m(,,,₀) is introduced; by a similar argument using reciprocity relations,f ^m is reduced toa ^m rendering necessary only the consideration ofa ^m. However, a fundamental decomposition formula is obtained which shows thata ^m is expressible algebraically in terms of functions of a single angular variable. The functions ^m andD ^m are shown to be the values in the horizontal plane ofb ^m anda ^m, respectively. The other auxiliary functionsX ^m andY ^m are also expressed algebraically in terms ofb ^m. These results enable one to proceed to the final step of evaluating the radiation field for monodirectional illumination. The above reductions toalgebraic relations involving only the functionb ^m appear to be more advantageous than Sobolev's (1972) recent approach; they also circumvent some basic numerical difficulties in it. We believe the present approach may likewise prove to be superior to most (if not all) other methods of solution known heretofore.This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory under Contract No. NAS-7-100 sponsored by the National Aeronautics and Space Administration.