Dobeneck, Tilo von
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Dobeneck, Tilo von
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Dobeneck, Tilo von
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Item-typ:Veröffentlichung, How magnetics and granulometry of continental margin sediments reflect terrestrial and marine environments of South America and West Africa(2014-11-07); ; ; Continental margins are supplied by terrigenous clastic, as well as by biogenic marine sediments and, thus, act as natural archives for various environmental conditions. This thesis delineates sediment-distribution patterns off SE South America (20-55 deg. S) and NW Africa (14-17 deg. N) mainly based on rock-magnetic properties supplemented by clastic grain-size distributions, major-element concentrations, planktic and benthic foraminiferal assemblages, as well as stable-isotope signatures obtained from surface and down-core sediment samples. These investigations, spanning the last 19 kyr, reveal insights about prevalent climatic conditions on land (i.e., intensities of South American Monsoon System&Southern Westerly Wind Belt, or North-African Harmattan&trade winds) with impacts on major terrestrial sediment sources and transport paths. However, they also enable to draw conclusions about marine environmental conditions linked to ocean-current systems (i.e., Brazil&Malvinas Currents).Dissertation427 176 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, From shelf dynamics to shelf export: Evidence from sedimentologic and palaeoceanographic slope recordsThe continental shelf and slope are among the most dynamic sedimentary and oceanographic environments on Earth, strongly influenced by processes within the terrestrial and marine realm. The shelf break, geographically separating the two areas, marks one of the major physiographic transitions on Earth. The oceanographic and sedimentary processes that lead sediments across this boundary represent the dynamic link between both sedimentary systems. With a multi-proxy approach, this thesis tries to elucidate i) how strong sedimentary and (palae)oceanographic processes modify the primary shelf export signal, ii) if sedimentary records from the slope can be used as reliable archives for reconstructing sedimentary and paleoceanographic shelf dynamics, and iii) how important the local morphology is, in influencing shelf sediment export routes, transport process and/or the creation of depocentres on the slope. The key study areas of this thesis cover two different continental slope settings, the lower sloperegion (off Northwest Iberia) and the uppermost slope (off Uruguay). Off Northwest Iberia, based on high frequency sediment echo-sounding profiles and a large sediment core data set the late Pleistocene sedimentary history of the shelf system, as well as the detailed late Holocene evolution of fluviogenic depocentres on the middle shelf was revealed during the beginning of this thesis. Detailed knowledge of the late Pleistocene shelf sedimentary patterns enables the differentiation of local shelf export signals from over-regional palaeoceanographic signals within the sedimentary patterns at the Northwest Iberian slope. Applying this knowledge, multi-proxy investigation of three slope records off Northwest Iberia reveal the interplay of slope morphology as well as palaeoclimatic effects on shelf slope sediment dynamics and depositional patterns during the late Quaternary. At the uppermost slope off Uruguay a small morphologic terrace represents a further type of external archives for the effective and direct recording of shelf sediment export. Contrasting the regional morpho-sedimentary structure of the Southeast South American continental margin, the uppermost slope terrace off Uruguay is not influenced by contouritic sediment transport. Instead, sediment dynamics on the terrace are directly linked to the sedimentary shelf configuration, which is strongly controlled by sea-level rise during the Holocene. Very highsedimentation rates on the terrace (at least approx. 50 cm/kyr) enable the application of these sedimentary sequences for high-resolution palaeoceanographic reconstructions. Holocenelatitudinal shifts of the subtropical shelf front across the Southeast South American shelf and uppermost slope were primarily forced by palaeoclimatic variations (northward migration and extension of the Southern Westerlies; middle to late Holocene evolution of the El Niño Southern Oscillation). Moreover, for the most recent 200 years an anthropogenic forcing is suggested. Overall this thesis makes the attempt to study the complex interplay of palaeoceanographic and sedimentary processes within shelf sediment export and slope sedimentary patterns. It is shown that shelf sedimentary export signals can be recognized as far down-slope as the lower slope. Two different types of slope settings are presented as qualified external records of sedimentary and palaeoceanographic shelf dynamics and export archives. An uppermost slope terrace at the Southeast South American continental margin represents a reliable and direct archive for shelf dynamics, whereas off Northwest Iberia the linkage of middle to lower slope sedimentary patterns with the last deglacial to Holocene history of sediment dynamics on the shelf is more complex. Palaeoceanographic dynamics have little modifying effect on the Holocene shelf export patterns off Southeast South America shelf, off Northwest Iberia deglacial paleoceanographic changes on the outer shelf considerably foster export of shelf sands. Moreover, local margin morphology constitutes a crucial component for shelf slope linkage as well as in slope sedimentary patterns: At the uppermost slope, small morphologic steps might act as excellent off-shelf transport archives, whereas slope incisions might act as efficient sediment conduits. At the middle to lower slope, morphologic highs may deflect sediment transporting contour currents, which causes deposition on the stoss-side of these obstacles. The combined findings of this thesis demonstrate that slope records can serve as external archives for shelf sedimentary and palaeoceanographic dynamics, and doing so have great potential for contributing to our integral understanding of sedimentary shelf-slope linkage.Dissertation621 221 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Characterization of marine near-surface sediments by electromagnetic profiling(2010-01-28); ; ; This thesis investigates the theory, develops the technology and demonstrates the applicabilities for synchronous in-situ mapping of the magnetic and electric signatures of marine near-surface sediments. A marine electromagnetic profiler has been developed for coastal and shelf operations in 5 to 500 m water depths. The system was designed to resolve subtle and gradual variations in silt and clay content, porosity and diagenesis state of marine sediments at a sub-meter scale. An electromagnetic (EM) induction sensor (Geophex GEM 3) was modified for submarine operations and mounted into a special bottom-towed sled. Seafloor magnetic susceptibility and electric conductivity were calculated from the in-phase and quadrature component of the secondary electromagnetic field using a half-space inversion algorithm. Seawater conductivity was measured synchronously by an integrated conductivity-temperature-depth (CTD) probe. The electric conductivity depends on porosity, the grain-size distribution and conductivity of the pore fluid. Magnetic susceptibility was used in this study as a proxy for fine-grained terrigenous clay/silt content, diagenetically forced magnetite depletion, as well as anthropogenic contaminants.The three attached manuscripts address different applications of the modified EM profiler. The first manuscript develops the physical and technical principles of the method and presents first results regarding the facies, early diagenesis, transport, and deposition of near-surface sediments on the NW Iberian shelf. The second manuscript combines high-resolution acoustic, magnetometric, and electromagnetic profiling with sample-based rock magnetic and geochemical analyses related to submarine groundwater discharge in a Baltic Sea estuary. The third manuscript is an application of the EM profiler to study the contamination of coastal areas by ferrous objects, organic matter and heavy metal pollution for coastal zone management of the RÃ a de Vigo, a NW Iberian estuary.Dissertation578 389 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Petrology, rock magnetism and stratigraphy of late quaternary Ice-rafted detritus at the southeast Grand Banks slope of Newfoundland, Atlantic Canada(2024-06-11); ; ; The Quaternary sediments of the Atlantic Canada margin usually contain numerous evidences of paleoclimate oscillations. The short-lived, abrupt and episodic surges of sediment-laden armadas of icebergs calved from Laurentide Ice Sheet (LIS) into the North Atlantic Ocean via ice stream conduits has deposited ice-rafted detritus (IRD) all across the northern North Atlantic oceanic basin. Such events have had considerable impact on ocean water circulation system (i.e. Atlantic meridional overturning circulation – AMOC) and deep water formation owing to the huge influx of meltwater delivered by subglacial discharge and iceberg melting. This catastrophic instability of the LIS has resulted in a stratigraphic sequence of detrital-rich Heinrich Layers (HL) during the cold phases of the Late Quaternary period. As IRD fragments are the direct evidence of the interplay between ice sheets and the North Atlantic Ocean, we still lack understanding of their hidden information on ice sheet dynamics, location of ice margins, the provenance and spatial dispersion of distinct terrigenous materials and the petromagnetic properties and contributions of different IRD species to magnetic HL records. In this PhD thesis, I investigated a sediment core (GeoB 18530-1) acquired at the foot of Southeast Grand Banks Slope of Newfoundland, that represents a continuous Late Pleistocene stratigraphic sequence of Heinrich Event layers 1 - 6 (H1 – H6). Discrete sample sets were taken at a very high resolution of 2 cm for various analyses including digital light microscopy, thin section petrography, X-ray fluorescence, rock magnetics, and grain-size sieving. In a first step of the thesis project, a total of 8243 coarse-grained (>1 mm) IRD particles were petrologically identified and their lithologies petrographically classified into 22 microscopically distinguishable categories. The abundances of these IRD lithologies were determined by counting individual particles at a high resolution of 2 cm steps throughout the continuous stratigraphic sequence of HLs (H1 – H6). This revealed the temporal and spatial change in the deposition of each IRD lithology. It was found that dolomitic IRD predominates the mid-part of all HLs whilst muscovite-biotite granite was found in greater abundance at the top and bottom of the HLs. Additionally, the statistical investigation of the count records of the 22 IRD lithologies manifested three well-defined groups based on whether their deposition is higher within HLs or interlayers or similar in both. Compositionally, it was found that H1, H2, H4, and H5 are kindred to each other while H3 and H6 are individually distinct. The second step of the thesis was an advancement of the finding from the initial part where the petrological information that was gleaned is used for magnetic analysis of particularly HLs and individual IRD lithologies. The pronounced magnetic susceptibility signal of HLs is usually intriguing compared to the interlayer units thus, it is momentous to discern the IRD lithology that influences the signal. Though, the >1 mm IRD underrepresents the total amount of IRD where finer grains are much more abundant, a lithology-specific identification can only be conducted using the coarser IRD fractions. From the magnetic properties of the coarse IRD it was found that out of the 22 different lithologies, as many as 16 possess a relatively lower magnetic susceptibility than the background sediment. Only 6 IRD lithologies are typified by a higher susceptibility among which the muscovite-biotite granite is four-fold higher magnetic than the background. With the complementary XRF data is was revealed clearly that the viii susceptibility enhancement by the (K/Fe denoted) granite is partly compensated by the (Ca/Sr represented) dolomitic IRD. Therefore, with the muscovite-biotite granite being second in abundance to dolomitic IRD, it mainly controls the pronounced magnetic susceptibility signals of HLs. In modeling magnetic susceptibility based on coarse-grained IRD count data a misfit of the model was observed proposing that IRD sedimentation does not only occur through detritus rain-out from icebergs but rather through other transport processes like advection or gravitational flow, at least for the terminal part of the sediment’s trajectory. Lastly, traditional magnetic susceptibility measurements are obtained in ways, where the inhomogeneity of sediment records is mostly played down. This is because the sensor coils of whole-core magnetic susceptometers average signals over a large volume, thereby integrating the microscale susceptibility distribution over a considerable volume. Split-core susceptibility logs produced with a spot sensor at high resolution average the magnetic signal over a much smaller volume of a material. Using a novel protocol, this spot sensor technique provides the freedom to scan across an entire split core. By logging multiple parallel tracts at a high resolution of 1 cm along and between each tract, the derived contour plot reveals coarse IRD distribution, where the color spectrum denotes lateral variability in magnetic susceptibility.Dissertation69 73 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Electromagnetic Imaging of the marine subsurface : a novel approach to assess sediment patterns and dynamics on clastic shelf systems(2016-12-12); ; ; Electromagnetic (EM) imaging is a new approach to investigate marine near-surface sediments. The EM data provide information about electric conductivity and magnetic susceptibility of the sediments. Both are important physical parameters in exploration geophysics. Electric conductivity of marine sediments is a function of porosity, tortuosity and chemistry of the pore fluid. Magnetic susceptibility indicates the magnetic particle concentration and is hence related to the mineral composition of the sediment. In this thesis data processing, inversion and machine learning methods for a novel marine EM profiling system are developed, with the goal to explore the internal structure and spatial variability of sediment patterns in coastal and shelf regions. The investigated EM data were acquired on the NW Iberian shelf during the Meteor cruise M84/4b with the bottom towed electromagnetic profiler MARUM NERIDIS III. This non-conductive, non-magnetic fiberglass sled accommodates a controlled source electromagnetic system based on a frequency-domain concentric-loop EM induction sensor. In order to estimate quantitative seafloor sediment properties from the NERIDIS III EM data, the approach developed in this thesis follows three main steps: The first step is to calibrate the EM data such that instrument related bias is removed and the EM response is solely controlled by the frequency of the source signal, the system geometry, the electric conductivity and magnetic susceptibility of the seawater and the sediment. Calibration is necessary to make data from different measurements and surveys comparable and to enable solving of the ill-posed inverse problem for electric conductivity and magnetic susceptibility. This thesis shows that calibrating the primary EM field alone, by means of independently measured water conductivity and constant water susceptibility, is not sufficient. Therefore, a calibration methodology is developed which firstly calibrates the recorded EM data to compensate for bias in the primary EM field followed by a secondary EM field calibration by means of ground-truth data. The second step involves the inversion of the EM data, which can be subdivided into a half-space and 1-D inversion. The half-space inversion aims for the reconstruction of bulk sediment conductivity and susceptibility of the uppermost approximately 0.5 to 1 m. It is demonstrated that recovered half-space conductivity and susceptibility well reflect the main sediment patterns on the NW Iberian shelf and allow the reconstruction of sediment pathways. The 1-D inversion can be used to reconstruct the vertical conductivity structure of the subsurface. An algorithm is developed which employs the half-space susceptibility as a priori information and hence allows the utilisation of the in-phase component of the complex earth response increasing the depth of investigation. It is shown that vertical conductivity variations down to approximately 3 m below the seafloor can be reconstructed revealing the internal structure of the Galician Mud Belt. The third step covers the predictive modelling of grain-size from the electric conductivity and magnetic susceptibility of the sediment. Correlation analyses are carried out which reveal a strong relation between the electromagnetic and textural sediment properties. A radial basis function network is developed which predicts the entire grain-size distribution for each EM measurement location along shelf wide survey lines. The predicted grain-size distributions are used to identify the well-known sediment facies on the NW Iberian shelf and give new insights into their distribution and transitions.Dissertation337 177 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, On the Enrichment of Magnetic Heavy Minerals in a Coastal Environment : Exploration, Examination, Explanation(2016-11-10); ; ; In this thesis, an approach for the detailed assessment of magnetic heavy mineral enrichments in a coastal environment using integrated geophysical and sedimentological data is developed, the observed enrichment patterns are interpreted, and their formation mechanisms discussed. Used methods are electromagnetic profiling of the subsurface, close-up seafloor photography, various laboratory techniques to analyze bulk and magnetic grain sizes and mineralogy, and numerical modelling of bi-fractional sediment transport. The studies take place in an exemplary study area in the western Bay of Plenty (New Zealand) with dimensions of 60 km x 7 km in water depths from 2-35 m. Primary instrument is the benthic profiler MARUM NERIDIS III. Overall, the findings of this thesis demonstrate an innovative, effective way to approach an unmapped area and reach detailed results with conclusive interpretations in a relatively short time. It shows the conditions under which natural sorting patterns due to size and density develop along the coast. The basic formation mechanisms are applicable to other areas in similar coastal settings and for a diverse range of heavy minerals.Dissertation351 172 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Proxy based reconstructions of late Miocene climatic and tectonic driven changes in the Eastern Mediterranean(2008-11-07); ; ; Eastern Mediterranean sediments consist largely of terrigenous material originating from North Africa and Europe. Changes in provenance are traced in the sedimentary archive of the Metochia section, using a combination of geochemical and environmagnetic proxies. The different source areas and the complicated interplay of the proxy parameters are unravelled using fuzzy c-means cluster analysis combined with nonlinear mapping. The cluster solution clearly reveals a shift in the paleoenvironmental conditions in North Africa from arid to more humid conditions at ~8.2 Ma is also identified. The late Miocene palaeoenvironmental conditions in North Africa are traced in the sedimentary archive of the Monte Gibliscemi section using geochemical proxies. The terrigenous input in the section is dominated by material from North Africa. The proxy parameters indicate that the palaeoenvironmental conditions in North Africa were humid from 9.5 Ma with a comparatively high fluvial input to the Eastern Mediterranean. Tectonic reorganisations of the Mediterranean Atlantic gateways pertaining to the Betic and Rifian corridors occurred, initiated at ~8.4 Ma.Dissertation480 160 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Biogenic and hydrogenous magnetic mineral formation in upward oxygenated sediments of the East Pacific Rise(2025-09-04); 31 41 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Paleoenvironmental signatures of aeolian and fluvial sedimentary end-members off NW Africa(2012-03-22); ; ; This thesis presents a new approach to characterize properties of terrigenous sediments deposited off subtropical Africa. Grain-size distributions, geochemical compositions, and magnetic parameters of core material off the Gambia and Senegal rivers were analyzed. By end-member (EM) unmixing and least-square fitting, mixing coefficients and multi-parameters properties of fluvial and aeolian fractions were obtained. The properties are influenced by different factors and the joint characterization enables a three-level interpretation: (1) Grain-sizes reflect transport energy. (2) Geochemical composition differs in fluvial and aeolian sediments. (3) Magnetic mineralogy mirrors weathering and environmental conditions in the source areas. Volumetric EM representations enable to budget fluxes of aeolian and fluvial material. The highest dust accumulation occurred during Heinrich Stadial 1 and corresponds to a 100 times higher flux with respect to today. Such high values have not been reported yet off NW Africa and emphasize that disturbances of the meridional overturning circulation cause dramatic environmental changes also in low-latitudes.Dissertation562 182 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Rock magnetic and geochemical signals of late Quaternary climate variability over northwest Africa(2008-10-10); ; ; This thesis investigates the paleo- climatic and environmental changes over northwest Africa by focusing on the Senegal region and the Gulf of Guinea. Emphasis was placed on the timing of past climate changes, the frequency of occurrence, and regional impact. Possible shifts in the position of the intertropical conversion zone (ITCZ) were also investigated. A multi proxy approach integrating rock and environmental magnetic parameters diffuse reflectance spectrophotometry, scanning electron microscopy, color reflectance and climate modeling experiments was employed. The results show that a climatic boundary which certainly reflects the southward shift of the northern limit of summer position of the ITCZ existed between 13 and 12à �à °N during the last glacial. The West African monsoon varied at D O times-scales at 12à �à °N, demonstrating that drier conditions occurred further south of the Sahel than previously reported. A fresh water hosing experiment using coupled climate model experiment suggested that the North Atlantic sea surface temperature and West African climate are linked by shifts in the position of the monsoon trough and the mid tropospheric African Easterly jet. The cooling of the North Atlantic sea surface is directly linked to the weakening of the Atlantic Meridional Overturing Circulation. Further more, climate change regulated the influx of magnetic minerals and post depositional alteration in the Senegalese sediments. Interglacial showed lower concentrations of magnetic particles, with high concentration of euhedral and framboidal pyrite. Wind derived sediments dominated the glacial with hematite and goethite prominent at these intervals as a result of increase input of Saharan dust. This studies shows that climate over this region varies at different times scales and is interconnected with global climatic signals.Dissertation623 439