Les tourbillons océaniques de subsurface sont des structures dynamiques qui peuplent l'océan global. Ils sont souvent générés à partir de courants d'échanges entre les bassins d'évaporation semi-fermés (comme la Mer Méditerranée, la Mer Rouge et le Golfe Persique) et l'océan ouvert ou pendant des processus de convection profonde. Ces tourbillons peuvent maintenir une géométrie cohérente sur des échelles de temps pluriannuelles et sont capables, du fait de leur migration, de transporter des quantités significatives de chaleur, sel et nutriments. Les tourbillons de subsurface contribuent donc à la redistribution tridimensionnelle des traceurs océaniques à échelle globale, d'où l'intérêt de connaître leurs positions et déplacements.En général, les tourbillons sont capables de modifier localement la surface de la mer, en générant des anomalies qui permettent leur suivi à travers des observations satellitaires. Notre étude se base sur l'utilisation de modèles analytiques et numériques pour caractériser les signatures induites à la surface par les tourbillons de subsurface; en particulier les anomalies de l'élévation (SSH), de température (SST) et de salinité (SSS) de la surface océanique.D'abord, nous avons étudié les signatures de surface (en SSH) dans un cadre idéalisé. Leurs propriétés ont été mises en relation avec la structure tridimensionnelle des tourbillons, nous permettant de déterminer que seulement les tourbillons de subsurface de meso-échelle océanique sont détectables via les observations altimétriques actuelles. En outre, en utilisant un modèle réaliste, nous avons étudié les signatures de surface des tourbillons d'eau méditerranéenne (MEDDIES) en termes de SSH, SST et SSS. L'étude a mis en évidence des différences entre les signatures en SSH et les signatures thermohalines: les premières montrent des intensités et des structures horizontales toujours liées aux changements structurels des Meddies, alors que les deuxièmes sont plutôt pilotées par la dynamique locale de surface.Enfin, nos résultats montrent que le suivi automatique des tourbillons de subsurface est plutôt envisageable à partir des techniques altimétriques, en valorisant aussi l'apport des futures missions satellitaires à haute résolution, comme SWOT. / Subsurface-intensified vortices are ubiquitous in the world ocean. They are often generated by water mass exchanges between semi-closed evaporation basins (e.g.: Mediterranean Sea, Red Sea, Persian Gulf) and the open ocean or during deep convection processes. These vortices can maintain a coherent geometry during inter-annual timescales and, due to their migration, they are able to carry large amounts of heat, salt and nutrients. Hence, the class of subsurface-intensified vortices participates to the redistribution of oceanic tracers along the three dimensions and at global scale, justifying the interest in determining their positions and mean pathways in the ocean. In general, vortices are able to locally modify the ocean surface generating anomalies that allow one to track them via satellite sensors. Our study, based on the use of analytical and numerical models, deals with the characterization of the sea-surface anomalies generated by subsurface-intensified vortices in terms of Sea-Surface Height (the elevation of the oceanic free-surface, SSH), Sea-Surface Temperature (SST) and Sea-Surface Salinity (SSS).In a first analysis, we have studied the SSH anomalies generated by subsurface vortices in an idealized context. Their properties have been related to the three-dimensional structure of the vortex, allowing us to state that only subsurface mesoscale vortices can be detected by the presentday altimetric observations. Furthermore, using a realistic model, we have studied the sea-surface expression of Mediterranean Water Eddies (MEDDIES) in SSH, SST and SSS. The study has evidenced the main differences between the Meddies-induced SSH anomalies and their thermohaline surface anomalies (i.e., SST and SSS): the first exhibit horizontal structures and intensities that can always be related to the Meddy structural changes at depth, while the second are mostly driven by the local surface dynamics.These studies show that the automatic tracking of subsurface-intensified vortices is mostly possible in an altimetric perspective, further confirming the importance of future high-resolution altimetric satellite missions, like SWOT.

Geologic sequestration of anthropogenic carbon dioxide (CO2) greenhouse gas emissions is an engineering solution that potentially reduces CO2 emissions released into the atmosphere thereby limiting their effect on climate change. This study focuses on Woodside field as a potential storage and sequestration site for CO2 emissions. The Woodside field is positioned on a doubly plunging, asymmetrical anticline on the northeast flank of the San Rafael Swell. Particular focus will be placed on the Permian White Rim Sandstone, Black Box Dolomite and Black Dragon Member of the Triassic Moenkopi Formation as the reservoir/seal system to store and sequester CO2 at Woodside field. The White Rim Sandstone, the primary target reservoir, is divided into three stratigraphic intervals based on facies analysis: a lower sand sheet facies (about 60 ft or 18 m), a thick middle eolian sandstone facies (about 390 ft or 119 m), and an upper marine reworked facies (about 70 ft or 21 m). Porosity and permeability analyses from the outcrop indicate good reservoir quality in the eolian sandstone and reworked facies. Porosity in the White Rim Sandstone ranges from 7.6 to 24.1% and permeability reaches up to 2.1 D. The maximum combined thickness of the three facies is 525 ft (160 m) at Woodside field providing a significant volume of porous and permeable rock in which to store CO2. The Black Box Dolomite is the secondary potential reservoir for CO2 storage at Woodside field and has a gross thickness up to 76 ft (23 m). The Black Box Dolomite is divided into four lithofacies: a basal nodular dolomudstone (8.2 -15 ft or 3.5-4.5 m), a dolowackestone (25-37 ft or 7.5-11 m), a dolomitic sandstone (0-8.2 ft or 0-2.5 m), and an upper sandy dolowackestone (0-16 ft or 0-4.9 m). Porosity and permeability analyses indicate reservoir potential in the dolowackestone, dolomitic sandstone, and sandy dolowackestone lithofacies. Porosity in the Black Box Dolomite ranges from 6.6 to 29.2% and permeability reaches up to 358 mD. The nodular dolomudstone lithofacies has relatively poor reservoir quality with porosity up to 9.4% and permeability up to 0.182 mD. This lithofacies could act as a baffle or barrier to fluid communication between the White Rim Sandstone and Black Box Dolomite. The Black Dragon Member of the Triassic Moenkopi Formation will serve as the seal rock for the relatively buoyant CO2 stored in the underlying formations. The Black Dragon Member is comprised of four lithofacies: a chert pebble conglomerate; an interbedded sandstone, siltstone, and shale; a trough cross-stratified sandstone, and an oolitic and algal limestone. The Black Dragon Member has a maximum thickness of 280 ft (85 m) at Woodside field. Mudstone beds contain from 0.16 to 0.47% porosity. QEMSCAN analysis indicates several minerals within shale beds that may react with a CO2-rich brine including calcite (18.73 to 23.43%), dolomite (7.56 to 7.89%), alkali feldspar (4.12 to 4.43 %), glauconite (0.04 to 0.05%), and plagioclase (0.03 to 0.04%). Silty mudstones comprise 75% of this member at Black Dragon Canyon. Volumetric estimates for Woodside field were calculated based on the 10th, 50th, and 90th percent probabilities (P10, P50, and P90). The White Rim Sandstone is the primary target reservoir and has capacity to hold 2.2, 8.8, or 23.7 million metric tonnes (P10, P50, and P90 respectively) of CO2 within the structural closure of Woodside field. The Black Box Dolomite may hold 0.5, 1.8, or 4.5 million metric tonnes, respectively of additional CO2 within the structural closure of Woodside field. These two formations combined have the capacity to store up to 28.3 million metric tonnes (P90) of CO2.

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No description available.

Master of Science / Department of Agronomy / Scott A. Staggenborg / In recent years, subsurface drip irrigation (SDI) acres have increased substantially. The use of SDI on corn (Zea Mays L.) in the Great Plains has increased due to increased land costs, reduced irrigation water availability, and higher commodity prices. Applying phosphorus (P) fertilizer through a SDI system becomes a major advantage, but further investigation of the interaction between water and fertilizer is needed. Sub-surface drip irrigation systems can be used to better improve the application efficiencies of fertilizers, applying in wet soil-root zones can lead to better uptake of soil applied materials. The objectives of this study were to determine how corn responds to P fertilizer applied via SDI and to create methodologies to simulate fertilizer and irrigation water compatibility tests for use in SDI systems. A plot sized SDI system was installed near Manhattan, KS to evaluate P treatments. Eight separate P fertilizers were applied via SDI mid-season at a rate of 34 kg P2O5 ha-1 and split-plots were created with 2x2 starter band at planting. Nitrogen was a non-limiting factor, with 180 kg N ha-1 applied as urea. Both starter fertilizer and injected fertilizer affected corn grain yield as indicated by the starter by treatment interaction. Split applying starter fertilizer at planting increased yield. A secondary laboratory study was conducted to evaluate the water and fertilizer interactions. A filtration system was used to simulate field conditions and each fertilizer/water mix was filtered through a 400 mesh filter paper to evaluate fertilizer precipitant formation. Sixteen common fertilizers were analyzed with different rates of Avail. Differences were observed between fertilizer treatments, visually and quantitatively. A secondary P soil movement field study was performed to quantify P concentrations around the SDI emitter. Soils were sampled in a 30.5 cm by 30.5 cm square adjacent to the emitter on a control treatment and a fertilized treatment, in both years of the study. Visual and quantitative differences were observed between the two treatments in both years of the study. When P fertilizers were added to the SDI system, higher P concentrations were found very close to the emitter orifice. Control treatments exhibited lower P concentrations around the emitter than fertilized treatments.

For most electromagnetic (EM) geophysical systems, the contamination of primary fields on secondary fields ultimately limits the capability of the controlled-source EM methods. Null coupling techniques were proposed to solve this problem. However, the small orientation errors in the null coupling systems greatly restrict the applications of these systems. Another problem encountered by most EM systems is the surface interference and geologic noise, which sometimes make the geophysical survey impossible to carry out. In order to solve these problems, the alternating target antenna coupling (ATAC) method was introduced, which greatly removed the influence of the primary field and reduced the surface interference. But this system has limitations on the maximum transmitter moment that can be used. The differential target antenna coupling (DTAC) method was proposed to allow much larger transmitter moments and at the same time maintain the advantages of the ATAC method. In this dissertation, first, the theoretical DTAC calculations were derived mathematically using Born and Wolf's complex magnetic vector. 1D layered and 2D blocked earth models were used to demonstrate that the DTAC method has no responses for 1D and 2D structures. Analytical studies of the plate model influenced by conductive and resistive backgrounds were presented to explain the physical phenomenology behind the DTAC method, which is the magnetic fields of the subsurface targets are required to be frequency dependent. Then, the advantages of the DTAC method, e.g., high-resolution, reducing the geologic noise and insensitive to surface interference, were analyzed using surface and subsurface numerical examples in the EMGIMA software. Next, the theoretical advantages, such as high resolution and insensitive to surface interference, were verified by designing and developing a low-power (moment of 50 Am²) vertical-array DTAC system and testing it on controlled targets and scaled target coils. At last, a high-power (moment of about 6800 Am²) vertical-array DTAC system was designed, developed and tested on controlled buried targets and surface interference to illustrate that the DTAC system was insensitive to surface interference even with a high-power transmitter and having higher resolution by using the large-moment transmitter. From the theoretical and practical analysis and tests, several characteristics of the DTAC method were found: (1) The DTAC method can null out the effect of 1D layered and 2D structures, because magnetic fields are orientation independent which lead to no difference among the null vector directions. This characteristic allows for the measurements of smaller subsurface targets; (2) The DTAC method is insensitive to the orientation errors. It is a robust EM null coupling method. Even large orientation errors do not affect the measured target responses, when a reference frequency and one or more data frequencies are used; (3) The vertical-array DTAC method is effective in reducing the geologic noise and insensitive to the surface interference, e.g., fences, vehicles, power line and buildings; (4) The DTAC method is a high-resolution EM sounding method. It can distinguish the depth and orientation of subsurface targets; (5) The vertical-array DTAC method can be adapted to a variety of rapidly moving survey applications. The transmitter moment can be scaled for effective study of near-surface targets (civil engineering, water resource, and environmental restoration) as well as deep targets (mining and other natural-resource exploration).

Reservoir heterogeneities exhibit a wide range of length scales, and their interaction with various transport mechanisms control the overall performance of subsurface flow and transport processes. Modeling these processes at large-scales requires proper scale-up of both heterogeneity and the underlying transport mechanisms. This research demonstrates a new reservoir modeling procedure to systematically quantify the scaling characteristics of transport processes by accounting for sub-scale heterogeneities and their interaction with various transport mechanisms based on the volume averaging approach. Although treatments of transport problems with the volume averaging technique have been published in the past, application to real geological systems exhibiting complex heterogeneity is lacking. A novel procedure, where results from a fine-scale numerical flow simulation reflecting the full physics of the transport process albeit over a small sub-volume of the reservoir, can be integrated with the volume averaging technique to provide effective description of transport at the coarse scale. In a volume averaging procedure, scaled up equations describing solute transport in single-phase flow are developed. Scaling characteristics of effective transport coefficient corresponding to different reservoir heterogeneity correlation lengths as well as different transport mechanisms including convection, dispersion, and diffusion are studied. The method is subsequently extended to describe transport in multiphase systems to study scaling characteristics of processes involving adsorption and inter-phase transport. Key conclusions drawn from this dissertation show that 1) variance of reservoir properties and flow responses generally decrease with scale; 2) scaling of recovery processes can be described by the scaling of effective mass transfer coefficient (Keff); in particular, mean and variance of Keff decrease with length scale, similar in the fashion of recovery statistics (e.g., variances in tracer breakthrough time and recovery); 3) the scaling of Keff depends on the underlying heterogeneity and is influenced by the dominant transport mechanisms. To show the versatility of the approach for studying scale-up of other transport mechanisms, it is also applied to derive scaled up formulations of non-Newtonian polymer flow to investigate the scaling characteristics of the apparent viscosity and effective shear rate in porous media. / text

The site-specific management of alfalfa has not been well-evaluated, despite the economic importance of this crop. The objectives of this work were to i) characterize the effects of soil moisture deficits on alfalfa and alfalfa yield components and ii) evaluate the use of canopy reflectance patterns in measuring treatment-induced differences in alfalfa yield. A randomized complete block design with five replicates of subsurface drip irrigation (SDI) and rainfed treatments of alfalfa was established at the University of Kentucky Animal Research Center in 2003. Potassium, as KCl, was broadcast on split-plots on 1 October 2004 at 0, 112, 336, and 448 kg K2O ha-1. In the drought year of 2005, five harvests (H1 - H5) were taken from each split-plot and from four locations within each SDI and rainfed plot. One day prior to each harvest, canopy reflectance was recorded in each plot. Alfalfa yield, yield components, and leaf area index (LAI) were determined. In 2005, dry matter yields in two harvests and for the seasonal total were increased (Pandlt;0.05) by SDI, but SDI did not affect crown density. Herbage yield was strongly associated with yield components but yields were most accurately estimated from LAI. Canopy reflectance within blue (450 nm), red (660 nm) and NIR bands were related to LAI, yield components, and yield of alfalfa and exhibited low variance (cv andlt; 15%) within narrow ( 0.125 Mg ha-1) yield ranges. Red-based Normalized Difference Vegetation Indices (NDVIs) and Wide Dynamic Range Vegetation Indices (WDRVIs) were better than blue-based VIs for the estimation of LAI, yield components, and yield. Decreasing the influence of NIR reflectance in VIs by use of a scalar (0.1, 0.05, or 0.01) expanded the range of WDRVI-alfalfa yield functions. These results indicate that VIs may be used to estimate LAI and dry matter yield of alfalfa within VI-specific boundaries.

Metabolically active microbial communities are present in a wide range of subsurface environments. Techniques like enumeration of microbial cells, activity measurements with radiotracer assays and the analysis of porewater constituents are currently being used to explore the subsurface biosphere, alongside with molecular biological analyses. However, many of these techniques reach their detection limits due to low microbial activity and abundance. Direct measurements of microbial turnover not just face issues of insufficient sensitivity, they only provide information about a single specific process but in sediments many different process can occur simultaneously. Therefore, the development of a new technique to measure total microbial activity would be a major improvement. A new tritium-based hydrogenase-enzyme assay appeared to be a promising tool to quantify total living biomass, even in low activity subsurface environments. In this PhD project total microbial biomass and microbial activity was quantified in different subsurface sediments using established techniques (cell enumeration and pore water geochemistry) as well as a new tritium-based hydrogenase enzyme assay. By using a large database of our own cell enumeration data from equatorial Pacific and north Pacific sediments and published data it was shown that the global geographic distribution of subseafloor sedimentary microbes varies between sites by 5 to 6 orders of magnitude and correlates with the sedimentation rate and distance from land. Based on these correlations, global subseafloor biomass was estimated to be 4.1 petagram-C and ~0.6 % of Earth's total living biomass, which is significantly lower than previous estimates. Despite the massive reduction in biomass the subseafloor biosphere is still an important player in global biogeochemical cycles. To understand the relationship between microbial activity, abundance and organic matter flux into the sediment an expedition to the equatorial Pacific upwelling area and the north Pacific Gyre was carried out. Oxygen respiration rates in subseafloor sediments from the north Pacific Gyre, which are deposited at sedimentation rates of 1 mm per 1000 years, showed that microbial communities could survive for millions of years without fresh supply of organic carbon. Contrary to the north Pacific Gyre oxygen was completely depleted within the upper few millimeters to centimeters in sediments of the equatorial upwelling region due to a higher supply of organic matter and higher metabolic activity. So occurrence and variability of electron acceptors over depth and sites make the subsurface a complex environment for the quantification of total microbial activity. Recent studies showed that electron acceptor processes, which were previously thought to thermodynamically exclude each other can occur simultaneously. So in many cases a simple measure of the total microbial activity would be a better and more robust solution than assays for several specific processes, for example sulfate reduction rates or methanogenesis. Enzyme or molecular assays provide a more general approach as they target key metabolic compounds. Since hydrogenase enzymes are ubiquitous in microbes, the recently developed tritium-based hydrogenase radiotracer assay is applied to quantify hydrogenase enzyme activity as a parameter of total living cell activity. Hydrogenase enzyme activity was measured in sediments from different locations (Lake Van, Barents Sea, Equatorial Pacific and Gulf of Mexico). In sediment samples that contained nitrate, we found the lowest cell specific enzyme activity around 10^(-5) nmol H_(2) cell^(-1) d^(-1). With decreasing energy yield of the electron acceptor used, cell-specific hydrogenase activity increased and maximum values of up to 1 nmol H_(2) cell^(-1) d^(-1) were found in samples with methane concentrations of >10 ppm. Although hydrogenase activity cannot be converted directly into a turnover rate of a specific process, cell-specific activity factors can be used to identify specific metabolism and to quantify the metabolically active microbial population. In another study on sediments from the Nankai Trough microbial abundance and hydrogenase activity data show that both the habitat and the activity of subseafloor sedimentary microbial communities have been impacted by seismic activities. An increase in hydrogenase activity near the fault zone revealed that the microbial community was supplied with hydrogen as an energy source and that the microbes were specialized to hydrogen metabolism. / Mikrobielle Gesellschaften und ihre aktiven Stoffwechselprozesse treten in einer Vielzahl von Sedimenten unterschiedlichster Herkunft auf. In der Erforschung dieser tiefen Biosphäre werden derzeit Techniken wie Zellzählungen, Aktivitätsmessungen mit Radiotracer-Versuchen und Analysen der Porenwasserzusammensetzung angewendet, darüber hinaus auch molekularbiologische Analysen. Viele dieser Methoden stoßen an ihre Nachweisgrenze, wenn Sedimente mit geringer Zelldichte und mikrobieller Aktivität untersucht werden. Bei der Untersuchung von Stoffwechselprozessen mit herkömmlichen Techniken kommt dazu, dass von mehreren Prozessen, die zeitgleich ablaufen können, jeweils nur einer erfasst wird. Deswegen wäre die Entwicklung einer neuartigen Messtechnik für die gesamte mikrobielle Aktivität ein wesentlicher Fortschritt für die Erforschung der tiefen Biosphäre. Ein vielversprechender Ansatz, um die gesamte lebende Biomasse auch in Proben mit geringer Aktivität zu bestimmen, ist eine Hydrogenase-Enzym-Versuchsanordnung mit Tritium als quantifizierbarer Messgröße. In dieser Doktorarbeit wurde die gesamte mikrobielle Biomasse und Aktivität von unterschiedlichen Sedimentproben einerseits mit herkömmlichen Methoden (Zellzählungen, Analyse der Porenwasserzusammensetzung) als auch mit einer neu entwickelten Hydrogenase-Enzym-Versuchsanordnung quantifiziert. Mit einer großen Anzahl eigener Zellzählungsdaten von Sedimenten aus dem Äquatorialpazifik und dem Nordpazifik und ergänzenden publizierten Daten konnte gezeigt werden, dass Zellzahlen sich in ihrer globalen geographischen Verteilung je nach Bohrlokation um 5 bis 6 Größenordnungen unterscheiden. Dabei bestehen Korrelationen zur Sedimentationsrate und zur Entfernung zum Land, mit deren Hilfe sich die Gesamtbiomasse in Tiefseesedimenten zu 4,1 Petagramm-C abschätzen lässt. Das entspricht ~0,6 % der Gesamtbiomasse der Erde und ist damit erheblich weniger als in früheren Schätzungen angegeben. Trotz der Korrektur auf diesen Wert spielt die Biomasse der tiefen Biosphäre weiterhin eine erhebliche Rolle in biogeochemischen Kreisläufen. Um die Zusammenhänge zwischen Aktivität der Mikroben, der Häufigkeit ihres Auftretens und Zustrom von organischem Material zu verstehen, wurde eine Expedition ins Auftriebsgebiet des Äquatorialpazifiks und zum nordpazifischen Wirbel durchgeführt. Daten der Sauerstoffaufnahme in Sedimenten des nordpazifischen Wirbels, die mit Sedimentationsraten von 1 mm pro 1000 Jahren abgelagert werden, zeigen, dass mikrobielle Gesellschaften über Millionen von Jahren ohne Zufuhr von frischem organischen Kohlenstoff überleben konnten. Im Gegensatz zum nordpazifischen Wirbel wird in Sedimenten des äquatorialpazifischen Auftriebsgebiets Sauerstoff bei höherer mikrobieller Aktivität und Verfügbarkeit organischer Verbindungen oberflächennah in den ersten Milli- bis Zentimetern komplett umgesetzt. Auftreten und Variabilität von Elektronenakzeptoren nach Tiefe und Bohrlokation machen die tiefe Biosphäre zu einer komplexen Umgebung für die Quantifizierung der gesamten mikrobiellen Aktivität. Aktuelle Studien zeigen das verschiedene Elektronenakzeptorprozesse gleichzeitig ablaufen können, obwohl man bisher davon ausgegangen war, dass diese sich thermodynamisch ausschließen. In vielen Fällen wäre also eine einfache Methode zur Messung der gesamten mikrobiellen Aktivität eine bessere und verlässlichere Lösung aktueller Analyseaufgaben als Messungen mehrerer Einzelprozesse wie beispielsweise Sulfatreduktion und Methanogenese. Enzym-oder Molekular-Versuchsanordnungen sind ein prozessumfassender Ansatz, weil hier Schlüsselkomponenten der Stoffwechselprozesse untersucht werden. Das Hydrogenase-Enzym ist eine solche Schlüsselkomponente und in Mikroben allgegenwärtig. Deshalb kann die Quantifizierung seiner Aktivität mit der neu entwickelten Hydrogenase-Enzym-Versuchsanordnung als Parameter für die gesamte mikrobielle Aktivität der lebenden Zellen verwendet werden. Hydrogenase-Aktivitäten wurden in Sedimenten unterschiedlicher Lokationen (Vansee, Barentssee, Äquatorialpazifik, und Golf von Mexico) gemessen. In Sedimentproben, die Nitrat enthielten, haben wir mit ca. 10^(-5) nmol H_(2) cell^(-1) d^(-1) die geringste zellspezifische Hydrogenase-Aktivität gefunden. Mit geringerem Energiegewinn des genutzten Elektronenakzeptors steigt die zellspezifische Hydrogenase-Aktivität. Maximalwerte von bis zu 1 nmol H_(2) cell^(-1) d^(-1) wurden in Sedimentproben mit >10 ppm Methankonzentration gefunden. Auch wenn die Hydrogenase-Aktivität nicht direkt in die Umsatzrate eines spezifischen Prozesses konvertierbar ist, können zellspezifische Aktivitätsfaktoren verwendet werden, um die metabolisch aktive Mikrobenpopulation zu quantifizieren. In einer weiteren Studie mit Sedimenten des Nankai-Grabens zeigen Daten der Zelldichte und der Hydrogenase-Aktivität einen Einfluss von seismischen Ereignissen auf Lebensraum und Aktivität der mikrobiellen Gesellschaften. Ein Anstieg der Hydrogenase-Aktivität nahe der Verwerfungszone machte deutlich, dass die mikrobiellen Gesellschaften mit Wasserstoff als Energiequelle versorgt wurden und dass die Mikroben auf einen Wasserstoff-Stoffwechsel spezialisiert waren.

Fretting phenomenon occurs when two bodies in contact undergo small repetitive relative motion such that the localized surface and subsurface material properties are altered leading to damage or failures. Fretting conditions are obtained by controlling externally applied parameters such as load, frequency of displacement, displacement amplitude. Material properties which influence fretting behavior include hardness, ductility, hardening behavior. External parameters like surface roughness, temperature also play a role in deciding the extent of damage. Based on fretting conditions and specimen geometry, various fretting modes can be classified. Rotational fretting is one such damage mode, observed in industrial applications such as cable ropes under tension used for support in construction industry and variable stator vanes (VSVs) in compressors of turbines. In spite of industrial and engineering relevance, rotational fretting has received little attention. In the present work, rotational fretting of self-mated AISI 4340 material pair was studied, with the objective of characterizing subsurface damage induced by fretting. AISI 4340 (EN 24) is a low alloy martensitic steel with an excellent combination of strength, ductility and toughness. It is widely used in high strength cyclic loading applications like gears, bearings, automobile pistons and aircraft landing gears as well as in low corrosion, high strength offshore applications. It can be readily machined and surface hardened which makes it useful for wear related applications. A novel rotational fretting test set up, capable of operating under various test loads, frequencies, displacement amplitudes and temperatures was used to perform experiments. Specimens were subjected to a combination of normal load and rotational displacement and caused to mutually contact on non-conformal curved surfaces which simulate a bearing or bushing geometry. Fretting results were primarily determined by the frictional torque versus angular displacement plots. The running condition response was linked to the fretting material response regime. Surface and subsurface characterization studies of fretted regions were conducted using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). TEM studies revealed varying levels of fretting induced plastic deformation within the fretted contact zone. Good correlation with available literature relating to formation of dislocation cells and presence of high dislocation density in the fretting damaged regions was established. Although quantifying the dislocation density as a damage indicator is a challenge, it is proposed that a microstructural feature based approach has the potential to be developed into a useful tool for life assessment and life prediction studies.