Holocene hydrological variability of Lake Ladoga,northwest Russia,as inferred from diatom oxygen isotopes

This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (δ¹⁸O_diatom) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8 cal. ka BP. The δ¹⁸O_diatom values range from +29.8 to +35.0‰, and relatively higher δ¹⁸O_diatom values around +34.7‰ between c. 7.1 and 5.7 cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in δ¹⁸O_diatom since c. 6.1 cal. ka BP accelerates after c. 4 cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8–0.2 cal. ka BP, corresponding to the Little Ice Age. Lake‐level rises result in lower δ¹⁸O_diatom values, whereas lower lake levels cause higher δ¹⁸O_diatom values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4–4.0 cal. ka BP. Generally, overall high δ¹⁸O_diatom values around +33.5‰ characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga δ¹⁸O_diatom record is roughly in line with the 60°N summer insolation, a linkage to broader‐scale climate change is likely.     

In-situ Gesteinsspannungen und Mechanismen der Kluftöffnung

Zusammenfassung Die Orientierung von post-orogenen Klüften in proterozoischen Sedimentgesteinen des Elliot Lake-Gebietes, Canada, läßt sich mit der meßbaren Gesteinsentspannung in Bohrlöchern in Beziehung bringen. Steile lokale und regionale Kluftscharen ohne Bewegungsspuren streichen in Richtung der elastischen Hauptentformungsachse, also in Richtung der größten in-situ-Kompressionsspannung.Die Klüfte lassen sich deshalb wahrscheinlich als Extensionsfugen erklären, und zwar als Resultat der Wechselwirkung zwischen Oberflächenabtrag des Gesteins und remanenter tektonischer Gesteinsspannung. Der vorgeschlagene Mechanismus sollte auch zum Verständnis von spät-orogenen (ac)-Klüften in gefaltetem Deckgebirge und oberflächenparallelen Klüften in massigen Gesteinen beitragen.

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Orientation of post-orogenic joints in Proterozoic sedimentary rocks of the Elliot Lake area (Canada) seems to be directly related to elastic-strain-recovery as measured in boreholes. Steep local and regional joint sets without displacement are parallel with the axis of maximum elastic-strain-recovery (i. e. the direction of the major principal in situ stress component). Consequently these joints are interpreted as extension joints forming as a result of the interaction between natural (or artificial) erosion of the rock mass and its remanent tectonic stresses. The proposed mechanism should also help to understand late-orogenic (ac)-joints in folded cover rocks and exfoliation joints in otherwise unjointed rocks.

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Résumé L'orientation des diaclases post-tectoniques dans des roches sédimentaires protérozoïques de la région du Lac d'Elliot, Canada, peut être mise en relation avec les tensions élastiques des roches telles qu'on peut les mesurer dans les trous de forage. Les systèmes de diaclases redressées, locales et régionales, sans traces de mouvement, sont dirigés parallèlement aux axes principaux de la déformation élastique, c'est-à-dire à la direction de la plus grande compression in situ mesurée par le changement de forme d'un trou de sonde. Par conséquent, les diaclases s'expliquent vraisemblablement comme joints d'extension, et en fait comme le résultat de l'action réciproque entre des tensions tectoniques rémanentes et l'érosion en surface. Le mécanisme proposé explique aussi les diaclase (ac) tardives dans les couvertures plissées et l'exfoliation parallèle à la surface dans les roches massives.

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Orogene Schollentektonik und granitoide Mobilisation im Westteil der Böhmischen Masse

Zusammenfassung Im vorwiegend bayerischen Westteil der Böhmischen Masse lassen sich Zusammenhänge zwischen dem Schollenbau und der orogen-tektonischen Verformung des saxothuringischen Varistikums erarbeiten. Dabei gewinnt die Schollentektonik im rigiden Rückland des Orogens, die Schollengruppe des moldanubischen Blockes als Kraton, ihre besondere Bedeutung durch die Ausbildung mächtiger, planarer Scherzonen im Grenzbereich zwischen Ober- und Unterkruste. Diese planaren Scherzonen vorwiegend migmatischer Ausbildung stellen den wichtigsten Bereich granitoider Mobilisation im kratonen Rückland von Orogenen dar. Als Ursache der granitoiden Mobilisation wird die Umsetzung von mechanischer Energie in Wärme bei der Scherung (Reibungswärme) angesehen. Am Beispiel der geotektonisch gut einstufbaren Verhältnisse in Scherzonen epizonalen Niveaus wird die Verbindung von planarer Schertektonik und granitoider Gesteinsbildung auf eine breitere Basis gestellt (Beispiel der Epigneise u. a. Orthogneise des Fichtelgebirges). Dabei läßt sich zeigen, daß mit der Tiefenlage einer planaren Scherzone das Ausmaß granitoider Mobilisation zunimmt. Von den mächtigen planaren Scherzonen kann eine regionale Thermometamorphose (Regionalmetamorphose) ausgehen.Die dargestellten Zusammenhänge zeichnen ein neues Modell für Orogene, deren Einengung auf den Tangentialschub angrenzender und von ihrer Unterlage abgescherter Kraton-Schollen beruht. Dieses Modell erlaubt nicht nur die Synthese von orogenen Einengungsbewegungen mit der kratonen Schollentektonik, sondern auch die Verknüpfung der Faltungsphasen mit den synorogenen granitoiden Prozessen weit im Rückland eines Orogens.

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In the western Bavarian part of the Bohemian Massif, block tectonics are genetically related to the orogenic folding of the Variscan Saxothuringicum. Within the rigid hinterland of the German Variscan (Moldanubicum) planar shearing zones occur, which coincide with the lower boundary of the crustal blocks moved. These planar shearing zones of predominantly migmatic development belong to the broad borderzone between upper and lower crust. They represent the most important realm of granitoid mobilization within the rigid hinterland of orogens. This type of anatectic mobilization is supposed to be caused by transformation of mechanical energy into heat by shearing (friction).An example of anatectic mobilization by friction is found in the so-called epigneisses of the Fichtelgebirge (north-eastern Bavaria). These rocks are identical with planar shearing zones in crustal levels of epizonal facies. Granitic orthogneisses of planar form and structure are supposed to be anatectic products of friction in some deeper crustal levels. The quantity of granitoid mobilization increases with depth and thickness of the shearing zones. Planar shearing zones of orthogneiss character may cause regional thermo-metamorphism (regional metamorphism). The relations demonstrated provide a new model for orogeny whose compression is caused by tangential movement of adjoining rigid crustal blocks. This model not only relates compressional tectonics of the orogen to block tectonics of the craton, but also explains the temporal coincidence of folding within the orogen and granitic magmatism far in the hinterland of an orogen.

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Résumé La partie ouest bavaroise du massif de Bohême présente une structure de glaçons en connexion avec la déformation orogène tectonique du «Varisticum» saxo-thuringique. La signification particulière de la tectonique des glaçons à l'arrière de l'orogène — groupe des glaçons du bouclier moldanoubique — repose sur la formation de vastes zones planes de cisaillement, régions limitrophes des croûtes, inférieure d'une part et supérieure d'autre part. Ces zones, en grande partie d'origine migmatique, représentent les plus importantes mobilisations granitiques à l'arrière de l'orogène. La mobilisation granitique aurait été causée par la transformation de l'énergie mécanique en énergie calorifique grâce aux forces de frottement.De par ses conditions géotectoniques bien classées dans des zones de cisaillement — au niveau de l'épizone — un exemple démontre le lien entre la tectonique des zones planes de cisaillement et la formation du granite (exemple de l'Epigneiss: Orthogneiss du «Fichtelgebirge»). L'auteur écrit que l'étendue de la mobilisation granitique augmente avec la profondeur de la zone plane de cisaillement. D'immenses zones de cisaillement peuvent donner naissance à un métamorphisme régional.La connexion décrite présente un nouveau modèle pour l'orogène dont le resserrement est dû à la poussée tangentielle des glaçons cratogènes limitrophes ayant glissé de leur socle.

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Modelling of the vertical fluxes of nitric acid,ammonia, and ammonium nitrate

Results from numerical investigations regarding the exchange of HNO₃, NH₃, and NH₄NO₃ between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with group concentrationsc ₁=[HNO₃]+[NH₄NO₃] (total nitrate),c ₂=[NH₃]+[NH₄NO₃] (total ammonia), andc ₃=[HNO₃]-[NH₃] as well as the fluxes of the individual nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified inferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO₃, NH₃, and NH₄NO₃) measured at a reference height by stations of a monitoring network.     

Optimal deflection of NEOs en route of collision with the Earth

Recently, a method for the n-body analysis of the velocity change required to deflect a hazardous near-Earth object (NEO) was presented by Carusi et al. [Carusi, A., Valsecchi, G.B., D'Abramo, G., Boattini A., 2002. Icarus 159, 417-422]. We extent this method in order to optimize the velocity change vector instead of its along-track magnitude. From an application of both methods to a fictitious NEO we find Carusi's parallel approach to be reasonable for phases of unperturbed two-body motion. But, for orbit phases inhering third-body perturbations, i.e., for planetary close approaches or prior to a collision, the results obtained from the new method show the radial component of deflection impulse to play a major role. We show that a fivefold greater efficiency can be achieved by a deflection impulse being non-parallel to orbital velocity. The new method is applied to two possible 99942 Apophis impact trajectories in order to provide constraints for future Apophis deflection mission analysis.     

Der Eiswinter 1983/84 im deutschen Küstengebiet zwischen Ems und Trave

Ohne Zusammenfassung     

The effect of bedform dynamics on computing suspended sediment fluxes using optical backscatter sensors and current meters

The sensitivity of the suspended sediment flux is tested with respect to rapid changes in bed-level across the surf zone of a sandy beach. The suspended flux was computed using a fixed instrument array, but bed-level changes due to ripple migration caused the instrument elevations to be significantly changed during the course of the experiment. The nominal elevations of the instruments were adjusted during data processing (using the MOBS array) to maintain a fixed elevation with respect to bed-level changes. The resultant suspended sediment concentrations and fluxes were significantly different from the unadjusted data, and for the present data set O(35%) less when averaged over the tide. The maximum difference between adjusted and unadjusted fluxes may be O(260%). The results indicate that changes in bed-level, particularly those due to bedform migration, must be accounted for when processing OBS data if reliable estimates of suspended sediment transport are to be obtained in the field.     

Synchronous pattern of moisture availability on the southern Tibetan Plateau since 17.5 cal. ka BP – the Tangra Yumco lake sediment record

A possible asynchronicity of the spatial and temporal moisture availability on the Tibetan Plateau has been a controversial subject of discussion in recent years. Here we present the first attempt to systematically investigate possible spatial and temporal variations in moisture availability by examining two lakes, Tangra Yumco and Nam Co, on an east–west transect on the southern Tibetan Plateau using identical proxies for palaeoenvironmental reconstruction. In this study, an independent record from Tangra Yumco was analysed applying a multi‐proxy approach to reconstruct variations in moisture availability since the Lateglacial. Results were subsequently compared with previously published records from Nam Co and additional records from Tso Moriri (northwestern Himalaya) and Naleng Co (southeastern Tibetan Plateau). Our results show that Tangra Yumco was at least partially ice covered prior to 17.1 cal. ka BP. A temperature rise after 17.1 cal. ka BP probably resulted in thawing of the permafrost. At 16.0 cal. ka BP moisture availability increased, representing an initial monsoonal intensification. Warmer conditions between 13.0 and 12.4 cal. ka BP and cooler conditions between 12.4 cal. ka BP and the onset of the Holocene reflect the Bølling‐Allerød and Younger Dryas. At the onset of the Holocene moisture availability rapidly increased, with moisture highest prior to 8.5 cal. ka BP when temperatures were also highest. After 8.5 cal. ka BP the moisture availability gradually decreased and showed only minor amplitude variations. These findings are consistent with the records from large lakes like Nam Co, Tso Moriri, and Naleng Co, revealing a synchronous pattern of moisture availability on the southern Tibetan Plateau.