An ozone depletion event in the sub-arctic surface layer over Hudson Bay,Canada

During the Tropospheric Ozone Production about the Spring Equinox (TOPSE) program, aircraft flights during April 7–11, 2000 revealed a large area air mass capped below ∼500 m altitude over Hudson Bay, Canada in which ozone was reduced from normal levels of 30–40 ppbv to as low as 0.5 ppbv. From some of the in-situ aircraft measurements, back-trajectory calculations, the tropospheric column of BrO derived from GOME satellite measurements, and results from a regional model, we conclude that the event did not originate from triggering of reactive halogen release in the sub-Arctic region of Hudson Bay but resulted from such an event occurring at higher latitudes over the islands of the northern Canada Archipelago and nearby Arctic Ocean with subsequent transport over a distance of 1,000–1,500 km to Hudson Bay. BrO _x remained active during this transport despite considerable changes in the conditions of the underlying surface suggesting that chemical recycling during transport dominated any local halogen input from the surface. If all of the tropospheric column density of BrO is distributed uniformly within the surface layer, then the mixing ratio of BrO derived from the satellite measurements is at least a factor of 2–3 larger than derived indirectly from in situ aircraft measurements of the NO/NO₂ ratio.     

Sub-Milankovitch climatic cycles in Holocene stalagmites from Sauerland, Germany

Calcitic stalagmites from caves in the Sauerland, Germany, prove the existence of sub-Milankovitch cycles in precipitation during the last 6000 yr. The δ¹⁸O record dated with Th/U is interpreted as an indicator of paleohumidity. Spectral analysis of δ¹⁸O from 6000 a BP up to the recent top of a stalagmite from the Atta cave yields statistically significant peaks at 1450, 117, 64 and 57 a. Additionally we find a good correlation of the stalagmite’s δ¹⁸O and Δ¹⁴C from European tree rings. The 1450 a cycle in the stalagmite probably is analogous to the pervasive millennial scale climate cycle described by Bond et al. [Science 278 (1997) 1257-1266; 294 (2001) 2130-2136] derived from the amount of ice rafted debris in deep sediments from the North Atlantic. Our results suggest that the centennial to millennial shifts observed in the North Atlantic are accompanied by synchronous shifts of the climate in Northern and Central Europe, which most probably can be attributed to solar irradiation variations.     

The Effectiveness of Centre-Pivot Irrigation from Dolomitic Ground Water in the Northwest Province,South Africa

Because South Africa is situated in a semi-dry region, the limited water resources are placed under increasing pressure by consumers from different sectors. Irrigation consumes more than half of the available water resources in South Africa. In the Northwest Province large volumes of water are found in dolomitic aquifers. Since 1970 irrigation from these aquifers has resulted in an exponential growth in the withdrawal of groundwater. The purpose of this study is to evaluate the effectiveness of groundwater utilization with centre-pivot irrigation in the Northwest Province, as well as to identify the most important variables that influence this effectiveness. Factor Analysis and Multiple Regression Analysis were used to establish a model with which the probable effectiveness of groundwater utilization on a specific farm can be predicted. The results show that four variables have a significant effect on the net profit margin from centre-pivot irrigation in the study area, namely: • Knowledge regarding the water capacity of the soil • Adjusting irrigation according to precipitation • The use of a yield target for fertiliser application, and • Soil characteristics The above parameters were used to develop a model with which farmers in the study area can be ranked according to the effectiveness of their water usage for centre-pivot irrigation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isotope fractionation by chemical diffusion between molten basalt and rhyolite

Experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes. Diffusion couples were made by juxtaposing firmly packed powders of a natural basalt (SUNY MORB) and a natural rhyolite (Lake County Obsidian) and then annealing them in a piston cylinder apparatus for times ranging from 0.1 to 15.7 h, temperatures of 1350-1450°C, and pressures of 1.2-1.3 GPa. Profiles of the major elements and many trace elements were measured on the recovered quenched glasses. The diffusivities of all elements except lithium were found to be remarkably similar, while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured. Chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of ∼18 and produced a fractionation of ⁴⁴Ca from ⁴⁰Ca of about 6 ‰. Because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene (LiAlSi₂O₆) was added to the basalt in order to increase the concentration difference between basalt and rhyolite, which was expected to increase the magnitude of diffusive isotopic fractionation of lithium. The concentration ratio between Li-doped basalt and natural rhyolite was ∼15 and the resulting diffusion of lithium into the rhyolite fractionated ⁷Li from ⁶Li by about 40‰. We anticipate that several other major rock-forming elements such as magnesium, iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements.     

Injury and Environmental Epidemiology, a converging agenda

Reliance on motor vehicle travel and the internal combustion engine has provided mobility, but the public health costs are substantial: Road deaths, adverse deleterious health effects from air pollution and noise, reduction in physical exercise, and toxic hazards associated with the refining, transport, use and disposal of petrochemicals. For traumatic road injury, kinetic energy is the pathogen. Risks for injury and death rise with the second and fourth power of increases in velocity upon impact; emissions of many air pollutants also increase exponentially with speed. Models derived from vector transmission in infectious diseases have proven useful for defining risks and designing interventive strategies. These models predict the number of lives saved and injuries prevented from a package of low-cost, effective measures, which can be quickly implemented. Eradication of road deaths and elimination of air pollution emissions are achievable public health goals. Speed camera systems produce sustainable levels of detection deterring speeding, and thereby reducing human injury and environmental damage. “Education” and building more roads, part of the scenario “predict and provide,” have not been shown to reduce injury risks. Building more roads, which in the long run, promotes urban sprawl and congestion, does not reduce travel time. High speed toll roads and circular beltways, which involve trade-offs among time-saving, risk of injury, and diversion of traffic from population centers, need to be re-evaluated and compared to alternative strategies based on modal shifts. We suggest that revenues resulting from massive use of speed cameras can serve as the first step for funding the first steps of sustainable transportation policies based on developing alternatives to private vehicle use and trucking. Such alternatives could lead to even further reductions in injury and death and adverse effects of air pollution. More involvement by epidemiologists in overseeing and evaluating strategies can expedite progress towards the goal of eradication of deaths from road injury, and at the same time, reduce emissions of air pollutants. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the importance of advection in determining the local isotopic composition of the mantle

The equations for isotopic evolution in a deforming medium are derived and used to show that the local isotopic composition of the mantle depends primarily on the advection of heterogeneities by the flow field. Various examples of the role of advection are given using a two-scale model of mantle convection. The effect of small-scale flows, which have dimensions smaller than the plates themselves, is to convert any initially localized heterogeneity into thin spiral sheets. The isotopic properties of erupted lavas will depend on the relative size of the zone of partial melt to the spacing between such sheets. An idealized model for⁸⁷Sr/⁸⁶Sr variations from Pacific islands and the covariation of¹⁴³Nd/¹⁴⁴Nd-⁸⁷Sr/⁸⁶Sr is based on the combined effect of isotopic fluxes at subduction zones and advection by the return flow under the moving lithospheric plates.     

Sedimentology and facies of the meadfoot beds (Lower Devonian) in South-East Devon (England)

Summary The Lower Devonian Meadfoot Group on the east coast of South Devon represents a typical shallow-water facies, comprising a variable sequence of mudstones, siltstones and sandstones or sandy siltstones. Many features of the deposits indicate the influence of strong water movements: cross-lamination, ripple-drift lamination, erosion channels and other washout structures.Current directions have been measured for all the sedimentary structures. Most of the clastic material was carried by lateral transport in this part of the Variscan geosyncline in directions both from W to E and E to W; a polarity of flow which may be explained as due to tidal influence. The direction of slumping indicates a sea floor sloping towards the south or south-west.An interesting feature is the presence of ball-and-pillow structures which is explained as essentially due to a sagging process.Many trails of organisms in the form of burrows occur in pelitic or silty deposits.

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Zusammenfassung Die unterdevonischen Meadfoot Beds, die an der Ostküste von SE-Devonshire ausstreichen, sind in einer typischen Flachwasser-Fazies entwickelt. Sie bestehen aus einer Serie von Tonschiefern, Siltsteinen, Sandsteinen und Sand-Siltsteinen. Eine Reihe von Sedimentstrukturen beweist den Einfluß von stärkeren Wasserbewegungen auf das Ablagerungsbild, wie z. B. Schrägschichtung, Rippelstrukturen, Erosions-Rinnen und andere Auswaschungs-Strukturen.Die Strömungsrichtungen wurden an Hand der verschiedenen Sedimentstrukturen gemessen und ausgewertet. Sie zeigen, daß in diesem Teil des nördlichen Außenrandes der variszischen Geosynklinale der Transport des klastischen Materials vorwiegend durch E-W- oder W-E-Strömungen erfolgte. Diese Polarität wird durch Gezeiten-Wirkung erklärt. Subaquatische Rutschungen deuten auf einen Abfall des Meeresbodens während jener Zeit nach S oder SW.Ein interessantes Phänomen stellen ball-and-pillow-Strukturen dar, die auf komplizierte Sackungs-Bewegungen, vermutlich unter Mitwirkung thixotroper Vorgänge, zurückgehen und vielleicht durch Erdbeben ausgelöst wurden.Lebensspuren, wie Grab- und Borgänge, treten häufig auf, vorwiegend in pelitischem Material oder Siltsteinen.

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Résumé Les Meadfoot-Beds, d'âge éodévonien, qui affleurent sur la côte orientale du Devonshire sud-oriental, présentent un faciès néritique typique. Ces assises sont constituées de schistes, d'aleurites, de grès et de grès aleuritiques. Les structures sédimentaires font valoir une eau fortement agitée pendant le dépôt des sédiments; ainsi on note des stratifications obliques, des ripples-marks, des sillons d'érosion et d'autres indices de taraudage.Le sens des courants a été déterminé à l'aide de différentes structures sédimentaires. Il démontre que dans cette partie du bord septentrional du géosynclinal varisque le matériel clastique était transporté surtout par des courants EW et WE. Cette polarité se laisse expliquer par les effets de la marée. Les glissements subaquatiques suggèrent une pente du fond marin vers le S ou vers le SW.Les structures «ball and pillow» présentent un phénomène intéressant, qui se laisse ramener à des tassements, qui vont probablement de pair avec des procès de thixotropie, et qui sont peut-être occasionnés par des tremblements de terre.Les traces de vie, telles que des pistes d'excavation ou de fouissement, sont nombreuses surtout dans le matériel pélitique.

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The generalized Laplace condition

The Laplace condition relates conventionally disturbances of longitude-latitude and azimuth-horizon distance assuming parallelism of terrestrial and reference axes. Here the Laplace condition is generalized for non-parallel axes which coincide only after a three dimensional rotation.     

3. Das Alter des westnorwegischen Grundgebirges

Zusammenfassung Es wird der Nachweis erbracht, daß es sich bei dem ausgedehnten Kristallingebiet West- und Mittelnorwegens nicht um präkambrisches Grundgebirge handelt, sondern um kaledonisch umgewandeltes und teilweise migmatisiertes Kambrosilur der kaledonischen Geosynklinale. Damit entfällt in tektonischer Hinsicht die Drontheimer Mulde in der bisher angenommenen Form.Außerdem beteiligen sich noch Plutone am Aufbau des Grundgebirges, die jünger als die kaledonischen Hauptfaltungen, aber älter als das Downton sind.Die Faltungsgräben früherer Autoren werden abgelehnt. Zuletzt wird kurz darauf hingewiesen, daß Migmatisierung und die Metamorphose dieses Gebietes sich nicht in großer Tiefe abgespielt haben, sondern bis dicht unter die Faltungsoberfläche gereicht haben müssen.     

Das Überleiten von variscischer zu saxonischer Tektonik am nordwestlichen Thüringer Walde

Zusammenfassung Im Thüringer Walde sind zwischen Oberrotliegendem und Zechstein Bewegungen orogener Art nachweisbar. Die Diskordanz der noch zur variscischen Ära gehörenden Mosbacher Phase (nach Ort und Bach Mosbach) umfaßt auch vorzechsteinzeitliche Verwerfungen. Die bisher als primär angesehenen Grenzen der Oberrotliegendverbreitung sind infolge dieser sekundären Beeinflussung somit nicht mehr sicher festzulegen. Doch dürften die Störungen von mosbacher Alter hauptsächlich die unterpermischen Beckenränder betroffen haben. Am Nordrande des Thüringer Waldes ist die jüngere saxonische Tektonik einem solchen vorzechsteinzeitlichen Bruch gefolgt. Über der alten Narbe, die Gebiete grundsätzlich verschiedenen Baues trennt, entstand ein verwickelt gebauter — erst gezerrter, dann gepreßter — Grabenzug. Nach regionalen. Bohrergebnissen ist zu vermuten, daß auch benachbarte Gräben (z. B. Netra—Eisenach) auf einer solchen alten Naht zwischen hochliegendem Grundgebirge einerseits, permischem Beckenareal andererseits entstanden sind. Für spätere Zeiten mag sich die Hoffnung ergeben, daß aus dem saxonischen Bau einmal gewisse Rückschlüsse auf die Struktur des Untergrundes möglich werden könnten.