Cluster analysis applied to regional geochemical data: Problems and possibilities

Cluster analysis can be used to group samples and to develop ideas about the multivariate geochemistry of the data set at hand. Due to the complex nature of regional geochemical data (neither normal nor log-normal, strongly skewed, often multi-modal data distributions, data closure), cluster analysis results often strongly depend on the preparation of the data (e.g. choice of the transformation) and on the clustering algorithm selected. Different variants of cluster analysis can lead to surprisingly different cluster centroids, cluster sizes and classifications even when using exactly the same input data. Cluster analysis should not be misused as a statistical “proof” of certain relationships in the data. The use of cluster analysis as an exploratory data analysis tool requires a powerful program system to test different data preparation, processing and clustering methods, including the ability to present the results in a number of easy to grasp graphics. Such a tool has been developed as a package for the R statistical software. Two example data sets from geochemistry are used to demonstrate how the results change with different data preparation and clustering methods. A data set from S-Norway with a known number of clusters and cluster membership is used to test the performance of different clustering and data preparation techniques. For a complex data set from the Kola Peninsula, cluster analysis is applied to explore regional data structures.     

4D velocity of Strombolian eruptions and man-made explosions derived from multiple Doppler radar instruments

We used a novel system of three continuous wave Doppler radars to successfully record the directivity of i) Strombolian explosions from the active lava lake of Erebus volcano, Antarctica, ii) eruptions at Stromboli volcano, Italy, and iii) a man-made explosion in a quarry.     

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 2: comparison to other records

A new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42 ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on ¹⁴C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1 ka age difference between GICC05 and SFCP04 and a more than 0.5 ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on ¹⁴C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties.     

Cretaceous reactivation and intensified erosion in the Archean–Proterozoic Limpopo Belt,demonstrated by apatite fission track thermochronology

Cratons are generally assumed to be regions of long-lasting tectonic stability. In particular the study of the Phanerozoic exhumation history of cratons has been largely hampered by the scarcity of suitable stratigraphic controls onshore. This fact is even more pronounced in terranes lacking Mesozoic or younger penetrative structural fabrics and metamorphic overprinting. Our study in the Limpopo belt shows that modern apatite fission track thermochronology provides a hitherto unavailable perspective in the study of these rocks, and has profound implications for the crustal evolution of the Zimbabwe Craton.Apatite fission track data from 35 samples taken along two transects, in the southern edge of the Zimbabwe Craton and in the Central Zone of the Limpopo Belt, suggest that extensive regions experienced kilometer-scale exhumation in two discrete events, as recently as the Cretaceous. The first occurred at around 130 Ma, and the second at around 90 Ma. Basin subsidence and sedimentation loads on the Mozambique margin support the timing of these events and provide strong indications of the source and pathways for the eroded material. Further, the results indicate that young and old “surfaces” (in a geomorphological sense) may be structurally juxtaposed in regions of high elevation in Zimbabwe. This is contrary to early ideas of surface chronologies based on summit accordances or invoking pediplanation.     

Fate of bacterial biomass derived fatty acids in soil and their contribution to soil organic matter

Soil organic matter (SOM) is a major pool of the global C cycle and determines soil fertility. The stability of SOM strongly depends on the molecular precursors and structures. Plant residues have been regarded as the dominant precursors, but recent results showed a major contribution of microbial biomass. The fate of microbial biomass constituents has not yet been explored; therefore, we investigated the fate of fatty acids (FA) from ¹³C labeled Gram-negative bacteria (Escherichia coli) in a model soil study [Kindler, R., Miltner, A., Richnow, H.H., Kästner, M., 2006. Fate of gram negative bacterial biomass in soil—mineralization and contribution to SOM. Soil Biology & Biochemistry 38, 2860–2870]. After 224 days of incubation, the label in the total fatty acids (t-FA) in the soil decreased to 24% and in the phospholipid fatty acids (PLFA) of living microbes to 11% of the initially added amount. Since the bulk C decreased only to 44% in this period, the turnover of FA is clearly higher indicating that other compounds must have a lower turnover. The ¹³C label in the t-FA reached a stable level after 50 days but the label of the PLFA of the living microbial biomass declined until the end of the experiment. The isotopic enrichment of individual PLFA shows that the biomass derived C was spread across the microbial food web. Modelling of the C fluxes in this experiment indicated that microbial biomass is continuously mineralized after cell death and recycled by other organisms down to the 10% level, whereas the majority of biomass derived residual bulk C (～33%) was stabilized in the non-living SOM pool.     

Fully coupled simulation of fluid injection into geomaterials with focus on nonlinear near‐well behavior

An important part of our global wealth depends on the extraction of fluids from porous media. More recently, sequestration of carbon dioxide (rmCO₂) into deep geological layers as a possible measure to mitigate climate change has increased interest in fluid injection into porous media. Sophisticated numerical models play an important role in managing the uncertainties related to the subsurface, and finite element methods are the most versatile tool allowing the coupling of fluid flow, geomechanics and other physical processes. This paper gives insight into two important aspects of fluid injection/extraction in porous media: the correct modeling of the bore hole through specification of initial stresses, which together with a fully coupled strategy allows simulation of nonlinear poromechanics, and the imposition of appropriate boundary conditions that allow the controlled injection/extraction of a total specified amount of fluid in an anisotropic porous medium, without exceeding a safe operating pressure. Copyright © 2011 John Wiley & Sons, Ltd.     

Über den Einfluß fluktuierender Windfelder auf ein stetig geschichtetes Meer

Zusammenfassung Am geschichteten Meer werden die erzwungenen Schwingungen theoretisch untersucht, die ein an der Oberfl?che angreifender Wind hervorruft. Grunds?tzlich entsteht an der Oberfl?che eine Grenzschicht mit gro?er Horizontalgeschwindigkeit. Für den Fall, da? ihre Ausdehnung klein gegenüber der inneren Region ist, werden die erzwungenen Schwingungen (Abschnitt 2) analytisch berechnet. Interne Wellen oberhalb der Tr?gheitsperiode sind klein und auf sehr kleine Wellenzahlen beschr?nkt. Die physikalische Erl?uterung sowie die Tatsache, da? einige spezielle Windfelder keine internen Wellen anregen k?nnen, bringt Abschnitt 3, die numerische L?sung für beliebige Frequenzen und Wellenzahlen Abschnitt 4. Interne Wellen unterhalb der Tr?gheitsperiode werden haupts?chlich durch die Divergenz des Windfeldes hervorgerufen, solche oberhalb der Tr?gheitsperiode durch die Rotation des Windfeldes, und es ergeben sich unterschiedliche funktionale Zusammenh?nge zwischen Wind und internen Wellen. Die hier vorgelegten Ergebnisse k?nnen nur mit Hilfe einer tangential an der Oberfl?che angreifenden Kraft erhalten werden und weisen wesentliche Unterschiede gegenüber ?hnlichen Ergebnissen auf, die für den Windeinflu? eine Volumenkraft annehmen.

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On the influence of fluctuating winds on a continuously stratified ocean

Summary The model of a stratified ocean is used for a theoretical study of the forced oscillations caused by the wind acting upon the surface. A boundary layer with high horizontal velocity is principally generated at the surface. If it is narrow as compared with the inner region, the forced oscillations (section 2) are computed analytically. Internal waves above the inertia period are small and confined to very small wave numbers. The physical explanation and the fact that special wind fields cannot generate internal waves, are given in section 3; the numerical solution for arbitrary frequences and wave numbers is treated in section 4. Internal waves below the inertia period are mainly caused by the divergence of the wind field; those above the inertia period by the rotation of the wind field; and different functional connections between the wind and the internal waves are the results. The results presented here can be obtained only by means of a force acting tangentially upon the surface. They differ essentially from similar results based upon the assumption of a volume force for the wind effect.

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Influence de champs de vent fluctuants sur une mer contin?ment stratifiée

Résumé On étudie et on calcule analytiquement (paragraphe 2) pour une mer stratifiée, les oscillations provoquées par un vent s'attaquant à la surface. En principe, il se forme à la surface une couche-limite à grande vitesse horizontale. Les ondes internes au-dessus de la période d'inertie sont petites et se limitent à de très petits nombres d'ondes. Le paragraphe 3 donne l'explication physique et signale le fait que quelques champs de vent spéciaux ne peuvent pas provoquer d'ondes internes; le paragraphe 4 apporte une solution numérique pour des fréquences et des caractéristiques numériques d'ondes quelconques. Les ondes internes au-dessous de la période d'inertie sont dues principalement à la divergence du champ de vent, celles au-dessus de la période d'inertie, à la rotation de ce champ; et on trouve des rapports fonctionnels distincts entre le vent et les ondes internes. Les résultats exposés ici ne peuvent être obtenus qu'à l'aide d'une force attaquant tangentiellement la surface, ils diffèrent notablement des résultats correspondants obtenus en admettant que l'influence du vent s'exerce sous forme d'une force non tangentielle.

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Mit der — hier gekürzt — vorliegenden Arbeit promovierte der Verfasser bei der Mathematisch-Naturwissenschaftlichen Fakult?t der Christian-Albrechts-Universit?t Kiel.     

Results of Russian experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the EISCAT facilities

We present the results of complex experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the European Incoherent Scatter Scientific Association (EISCAT) facilities. During the ionospheric F-region heating by powerful extraordinary (X-mode) polarized HF radiowaves under the conditions of heating near the critical f _H frequency f _H ≈ f _x F2 of the extraordinary wave of the F2-layer, we were first to detect the excitation of intense artificial small-scale ionospheric irregularities (ASIs), accompanied by electron temperature increases by approximately 50%. The results of coordinated satellite and ground-based observations of the powerful HF radiowave impact on the high-latitude ionosphere are considered. During ionospheric F-region heating by powerful HF radiowaves of ordinary polarization (O-mode) during evening hours, the phenomenon of ion outflow accompanied by electron temperature increases and thermal plasma expansion was revealed. Concurrent DMSP-F15 satellite measurements at a height of about 850 km indicate an O⁺ ion density increase. The CHAMP satellite observations identified ULF emissions at the modulation frequency (3 Hz) of the powerful HF radiowave, generated during modulated emissions of the powerful HF radiowave of O-polarization and accompanied by a substantial increase in the electron temperature and ASI generation.