Uenzelmann-Neben, Gabriele
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Uenzelmann-Neben, Gabriele
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Uenzelmann-Neben, Gabriele
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Item-typ:Veröffentlichung, Reconstruction of oceanic currents and climate change in the Transkei Basin, South African gateway(2007-11-09); ; ; The region south of South Africa has been a crucial gateway for large scale Thermohaline Circulations since late Eocene times. Here, three of the most important currents for maintaining the global heat exchange, namely the warm and surface related Agulhas Current (AC), and the cold and denser North Atlantic Deep Water (NADW) as well as the Atlantic Bottom Water (AABW), flow around South Africa. Due to the special tectonic and geologic situation, a huge amount of the deep and bottom water masses that flow around South Africa have to pass the narrow Agulhas Passage, located between the South African continental shelf and the submarine Agulhas Plateau. As a result, the sedimentary infill of the Transkei Basin, which is located east of the Agulhas Plateau, has been predominantly influenced by NADW and AABW activity since ~36 Ma. Via the analysis of this sedimentary infill, a palaeo current reconstruction of (proto-) NADW and (proto-) AABW revealed changing flow paths and flow strengths since then. These variations in current attributes were triggered by large scale effects, such as the opening of the Tasman Gateway and the Drake Passage in the Late Eocene, or the closure of the Isthmus of Panama in the Pliocene. A more detailed analysis of the Transkei Basin's depocentre locations and interface outlines resulted in a palaeo flow path reconstruction for this region.Moreover, palaeo climate conditions from the Late Cretaceous were partially reconstructed via the analysis of high amplitude seismic reflections, so called bright spots, from the central Transkei Basin. The evaluation of these bright spots provided indications for anoxic conditions for a period between ~90 Ma and ~80 Ma for the region south of South Africa, which could be related to worldwide Oceanic Anoxic Event 3.Dissertation574 1438 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Past interaction of ocean circulation and West Antarctic Ice Sheet dynamics in the Amundsen Sea SectorThe West Antarctic Ice Sheet is highly sensitive to ocean forcing and is currently experiencing grounding line retreat and ice shelf thinning. Since the response of the ice sheet to a warming world is unknown, it is important to analyze past warmer-than-present periods, e.g. the Pliocene, for comparison with possible future changes. Two drill sites, Site U1532 and Site U1533 of IODP Expedition 379, were linked to a large network of 2D high-resolution seismic reflection data to analyze changes of the West Antarctic Ice Sheet from the latest Miocene to the Pleistocene. During the Pliocene, between 4.2 to 3.2 Ma, a warm period was recognized with a highly dynamic West Antarctic Ice Sheet, correlating with reduced ocean bottom current activity. This period can be described as an overarching warm period with several advance and retreat phases of the West Antarctic Ice Sheet in the Amundsen Sea Sector.Dissertation209 177 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Cenozoic paleoceanographic changes of the South Pacific from seismic reflection data(2015-04-21); ; ; The Thermohaline Circulation (THC) in the world oceans is closely coupled with earth climate. With reconstructions of past oceanic conditions and comparisons with past climate conditions this coupling can be better understood. This in turn allows to provide better boundary conditions on ocean-climate coupling for forecasting models. However, the paleoceanographic setup is far from being completely revealed. One of the largest areas of the world oceans poorly surveyed is the South Pacific Ocean. The present ocean currents that transport deep cold water into the South Pacific are the Antarctic Circumpolar Current (ACC) and two northward setting flows directly influenced by the ACC, the Deep Western Boundary Current (DWBC) or western limb close to New Zealand and an eastern limb above the western flank of the East Pacific Rise (EPR). Understanding changes of this current system is important for reconstructions of past climates and the Antarctic Glaciation history. At present the reconstructed paleoceanographic history of the South Pacific is limited to ACC and DWBC at the western margin of the Southwest Pacific Basin and only reveals changes back to the Eocene/Oligocene boundary. This thesis presents new multichannel seismic reflection data surveying two regions at the eastern and western margin in the Southwest Pacific Basin. The objective is the identification and characterization of deep current derived sediment deposits in the South Pacific. The investigation covers the whole Cenozoic and thus provides indications for paleoceanographic changes due to East Antarctic Ice Sheet build-up prior to 34 Ma. Furthermore the study helps to fill a data gap in the open Pacific Ocean between New Zealand and South America and presents the first evidence for paleoceanographic changes in this poorly explored area. East of New Zealand at the Bounty Trough mouth a sediment drift indicates the onset of a deep cold current originating from the South Pacific Ocean around the Cretaceous/Palaeocene boundary. This current prevailed until the establishment of the ACC around the Eocene/Oligocene boundary. A second sediment drift indicates a current modification due to climate cooling around 44 - 42 Ma occurs contemporaneously with first indications of an East Antarctic Ice Sheet. These results are the first hints on a deep cold current in the South Pacific Ocean before the Opening of the Tasmanian Gateway and thus support the hypotheses that an Antarctic Ice Sheet was present at that time. Since ~19 Ma the history of the ACC has been recorded by the sedimentary deposits at the western flank of the EPR and east of the Bounty Trough mouth. Close to the EPR (45 deg. S) the sedimentary cover suggests a weak bottom current flow allowing deposition that is followed by a bottom current intensification around 9 Ma. The stronger bottom current flow has continued until today. East of New Zealand seismic data and drilling results reveal a current that created a sediment drift between 19.5 Ma and 10 Ma followed by a 5.4 Ma long hiatus in deposition caused by bottom current intensification due to West Antarctic Ice Sheet build-up. Thus, both limbs of bottom current flow into the South Pacific show intensification at the same time that was probably caused by an intensified ACC. Although deposition close to New Zealand starts again around 5 Ma, the flow of the DWBC remained strong, which is also evident at the eastern limb. A higher sediment load due to upstream erosion of the DWBC caused further deposition. The sediment deposits seen in seismic profiles also suggest that a limb of the DWBC enters the Bounty Trough, which until present was only inferred from erosional structures at the Bounty Trough mouth. A new approach based on spectral analysis of Parasound sub-bottom profiler data was used to further quantify the extent of the DWBC in the Bounty Trough. Under the assumption that the 41 kyr obliquity cycle is related to DWBC changes, mapping of this cyclicity in Parasound data is used to show that the extent of the DWBC into the Bounty Trough is limited to 178.2 deg. E.Dissertation409 168 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The Mozambique Ridge : Evolution of a Large Igneous Province and its implication for palaeocean circulationNew multi-channel seismic reflection data acquired in the southwest Indian Ocean is used to evaluate the basement structure and the origin of the southern Mozambique Ridge (MozR). Another objective of the interpretation of the data is to investigate the possible impact of the structure on palaeocean circulation in the evolving Southern Ocean. Investigation of the new geophysical data shows the occurrence of extensive lava flow sequences and a great number of extrusion centres. The observations suggest a Large Igneous Province origin of the southern MozR and its emplacement between 131 and 125 Ma. The sedimentary record in the area of the southern MozR acts as an archive for the water mass exchange between the Indian and South Atlantic Oceans through the African-Southern Ocean gateway. Characteristic sedimentary structures are deposited by current-controlled sedimentation and allow for an interpretation of the intensity, pathway and direction of the palaeocean circulation. The observations document the evolution from a restricted circulation during the Cretaceous towards an open marine circulation during Neogene and Quaternary times within the gateway.Dissertation374 164 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Cenozoic Palaeoceanographic evolution of the southwestern South Atlantic: indications from the Falkland/Malvinas PlateauDas Falkland/Malvinas-Plateau hat seinen Ursprung im südwestlichen Gondwana zwischen Südamerika, Afrika, der Antarktis und der Antarktischen Halbinsel hat und bildet heute ein submarines Plateau im südwestlichen Südatlantik. Seit der Aufspaltung Gondwanas in einzelne Kontinente dokumentiert das Falkland/Malvinas-Plateau die Entwicklung des Südatlantiks seit dem späten Mesozoikum und die Bildung der Drake Passage-Scotia See seit dem frühen Känozoikum. Diese tektonischen Ereignisse ermöglichten tiefe Verbindungen der Becken des Pazifiks und des Atlantiks, welche die Entwicklung der modernen ozeanischen Zirkulation erlaubten. Die Bildung des antarktischen Zirkumpolarstroms führte zur thermischen Isolierung der Antarktis, der Vereisung der Antarktis- und enormen klimatischen Veränderungen während des Känozoikums. Die ozeanographischen Modifikationen im südwestlichen Südatlantik sind in den Sedimentschichten des Falkland/Malvinas-Plateaus archiviert. Diese Arbeit untersucht die Entstehung und die Modifikationen in Pfaden und Intensitäten der südlichen Wassermassen des antarktischen Zirkumpolarstroms in Relation zu den tektonischen Bewegungen und klimatischen Veränderungen des Känozoikums. Zu diesem Zweck werden hochauflösende reflexionsseismischen Daten präsentiert, die 2019 vom Alfred-Wegener-Institut im Gebiet des Falklland/Malvinas-Plateaus akquiriert wurden. Die Definition eines seismostratigraphischen Modells durch die Integration von Bohrlochsinformation aus Deep Sea Drilling Project Leg 36 Sites 327, 329 und 330 und Leg 71 Site 511 ermöglichte mir die Interpretation der seismischen Daten. In dieser Studie werden die Sedimentstrukturen des Falkland/Malvinas-Plateaus untersucht, die auf die regionale tektonische Entwicklung und die entsprechenden ozeanographischen Veränderungen hinweisen. Insbesondere untersuche ich die bodenströmungsgesteuerten Ablagerungs- und Erosionsstrukturen von Sedimentdriftkörpern, die Spuren von Paläoströmungen in den Sektoren des Falkland/Malvinas-Plateaus, nämlich der Maurice Ewing Bank, dem Falkland/Malvinas-Becken und der -Rinne dokumentieren. Die Ergebnisse zeigen, dass das Falkland/Malvinas-Plateau seit dem Paläozän eine Barriere für die südlichen Tiefen- und Bodenwassermassen darstellt, die Richtung des Argentinischen Beckens fließen. Ein proto-zirkumpolares Tiefenwassers überfloß das Falkland/Malvinas-Plateau in einem hochdynamischen Zirkulationsregime bereits im späten Eozän/Oligozän, als die Öffnung der Drake Passage-Scotia See tiefozeanische Zirkulationen begünstigte. Die anhaltende Erosionwirkung dieser Bodenwassermassen initierten die heutige Morphologie des Meeresbodens des Falkland/Malvinas-Beckens. Erosion von Dutzenden von Metern an Sedimenten führte zur Fossilisierung/Arrestierung einer Silikat-Diagenesefront in Falkland/Malvinas-Becken und -Rinne. Seit dem mittleren Miozän, mit der vollständigen Öffnung der Drake Passage und der verstärkten Produktion von Bodenwassermassen unter den antarktischen Schelfeisen kann ein Proto-Weddellmeer-Tiefenwasser aus dem Georgia-Becken in die Falkland/Malvinas-Rinne fließen.Dissertation202 103 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, From early Miocene to present: Reconstruction of the deep Thermohaline Circulation at the Eirik Drift(2014-02-26); ; ; The Thermohaline Circulation (THC) distributes heat and freshwater around the global oceans, interacts with the atmosphere, and therefore is closely connected to the global climate. The deep branch of the North Atlantic THC mainly consists of deep-water formed by atmospheric cooling in the Nordic Seas, which overflows the Greenland-Scotland Ridge into the North Atlantic. The Eirik Drift south of Greenland is located closely downstream of the North Atlantic deep-water formation region and has been shaped by the Western Boundary Undercurrent (WBUC), which constitutes the main part of the deep North Atlantic THC. The sedimentary record of the Eirik Drift documents changes of the WBUC activity, which can be related to climate changes. The analysis of the sedimentary structure in combination with geological information from scientific drilling leads to a revised seismostratigraphic concept at the Eirik Drift and reveals particularly that the Eirik Drift has been influenced by the WBUC already since the early Miocene (~19 Ma). A more detailed structural analysis of the depocenter locations and their redistribution results in a temporal reconstruction of the deep paleocirculation at the Eirik Drift. The observed changes of pathways and intensity of the WBUC at the Eirik Drift were linked to the development of the Greenland-Scotland Ridge and climate changes. The onset of drift building at the Eirk Drift followed the formation of the Faroe Conduit in early Miocene, which allowed northern sourced deep-water to overflow the eastern part of the Greenland-Scotland Ridge. A separation of the WBUC at the Eirik Drift into two branches occurred contemporaneously with the onset of deep-water overflow at the Denmark Strait, the western part of the Greenland-Scotland Ridge (~7 Ma). At the Eirik Drift, strong WBUC activity is inferred to occur during warm climates and at the beginning of cooling phases, while cooling phases with enhanced ice extent are characterized by weak WBUC activity. Based on a combination of these observations with interpretations from other North Atlantic sediment drifts, a paleo flow path reconstruction for the northern North Atlantic is proposed. It is suggested that the deep-water formation regions and the main deep-water pathway shifted to the south during cold phases with enhanced ice-extent, i.e. Northern Hemisphere Glaciation. This implies that during these cool phases solely weak branches of the deep-water circulation overflowed the Eirik Drift and that the main North Atlantic deep-water route affected the Eirik Drift just during warm phases. Moreover, by applying the seismic oceanography method the present pathway and structure of the upper WBUC core at the Eirik Drift is imaged. For the first time, this method is successfully applied in water depth > 1500 m. The study confirms not only the improvement of oceanographic research by use of the seismic oceanography method but also supports the interpretation of the analysis of the sedimentary structure at the Eirik Drift.Dissertation390 187 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The Manihiki Plateau : Magmatic and tectonic evolution of a Large Igneous Province through time(2016-05-12); ; ; The Pacific Plate is highly engraved by volcanism that has formed oceanic plateaus and hotspot chains. The Manihiki Plateau (MP) is a large igneous province (LIP) located in the central Pacific that has an areal extent of 600000 km2. In 2006, Taylor proposed a joint emplacement of the MP with the Ontong Java Plateau, the Hikurangi Plateau and two missing fragments during the Cretaceous in a "Super-LIP" called Ontong Java Nui (OJN). The emplacement of OJN with an aerial extent of 1.1% of the earth's surface would have had major impacts on Earth's climate. An investigation of the initital volcanic emplacement history of the Manihiki Plateau and its break-up processes can contribute to a better understanding of LIP-impact on the paleo-climate. Analysis and interpretation of a new, high-resolution multi-channel seismic reflection dataset has provided a detailed and improved volcanic history of the Manihiki Plateau. The new model consists of three volcanic phases instead of the previously assumed two volcanic phases. It includes the initial formation phase (>125 Ma) that formed a spatially localized nucleus, which was extended to the East. The expansion phase (125-116 Ma) erupted massive tholeiitic basalts and break-up processes into the other LIP-fragments occurred. The third phase is a phase of secondary volcanism that leveled out the overall topography and was intense at the tectonically altered margins. Since the late Cretaceous/early Cenozoic, the morphology of the Manihiki Plateau was engraved by tectonic and volcanic features that were strongly related to the kinematics of the Pacific Plate. During the Pleistocene, a major Pacific plate-reorganization occurred that caused changes of inner-lithospheric stress fields. In this study, the origin of the Suvarov Trough has been investigated. Age and spatial extension point towards a cause that is in a good correlation to this major Pleistocene event. Strain within a LIP crust due to applied stress field changes appears to be similar to continental crust and different to the surrounding oceanic crust. During the Cenozoic, the seafloor morphology in the central Pacific is dominated by the formation of age-progressive hotspot seamount chains. Neogene igneous diapirs in the southwestern MP have been investigated within this study. Age and location characteristics support a hotspot origin, which might be related to the Society Islands Hotspot. The characteristic appearance of the diapirs is different to hotspot volcanism within oceanic lithosphere, which can probably be related to the anomalous thick crust of the Manihiki Plateau. The magmatic and tectonic history of the Manihiki Plateau reveals that this LIP acts similar to continental crust on applied external forces, although its chemical composition resembles thick oceanic crust.Dissertation368 149