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  • 1
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    Unknown
    Paleontological Society
    Publication Date: 2024-07-04
    Description: The underlying basis for Mg/Ca paleothermometry is that the amount of magnesium in calcite precipitated from seawater is dependent on temperature. Here we review the state of the art of the Mg/Ca seawater paleotemperature proxy, summarized by the following: 1) Calcite, whether formed abiotically or biologically as foraminifera and ostracode shells, incörporates variable amounts of magnesium into the crystal structure. 2) Uptake of Mg varies positively with temperature. 3) The relationship between temperature and the amount of Mg in calcite has been quantified by experiments on synthetic calcite growth and by culture, core top, and sediment trap experiments using living organisms. 4) The most careful calibrations of the Mg/Ca paleothermometer have been done for planktic foraminifera, then benthic foraminifera; there are species-specific variations in the amount of Mg incorporated into foraminifera shells. 5) The Mg/Ca ratio of calcite from planktic foraminifera in deep-sea cores has been widely used to interpret sea surface temperatures. 6) Measurement of both Mg/Ca and δ18O in planktic foraminifera have been used to calculate δ18O in seawater, and after correction for global ice volume, salinity could be inferred. 7) Mg/Ca from benthic foraminifera have been used to reconstruct deep-sea temperatures and cooling of ~12°C over the last 50 million years. 8) One problem with the Mg/Ca seawater temperature proxy is partial dissolution of. foraminifer shells, which lowers the Mg/Ca, and leads to an underestimation of ocean temperature. Benthic foraminifers appear to be more resistant to partial dissolution. 9) Past changes in the Mg/Ca ratio of seawater are an important factor in determining the amount of Mg in fossil skeletal calcite, and thus add another variable to the Mg/Ca temperature proxy. All Mg/Ca paleotemperature studies on fossil calcite older than Pleistocene should take into account the Mg/Ca of the seawater from which it precipitated.
    Type: Book chapter , PeerReviewed
    Format: text
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  • 2
    Publication Date: 2024-05-13
    Keywords: Course of study: MSc Biological Oceanography
    Type: Thesis , NonPeerReviewed
    Format: text
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  • 3
    Publication Date: 2024-04-08
    Description: Reconstructing the climate of mid-Cretaceous is a special challenge for climate modelling. High atmospheric C02 concentrations and a vastly different geography seem to have caused a global temperature increase. At the same time the geologic record provides ambiguous data about the strength and spatia.l distribution of this warming. In the following, 4 experiments with the new, fully coupled "Kiel Climate Model" (KCM) are realised to gain new insights into the mid-Cretaceous climatic conditions and to to investigate their influence on the ocean circulation. Furthermore, the changed boundary conditions (C02 =1200 ppmv, geography) and their respective impacts are examined independently. The experiments show a significant global warming in near surface temperatures of approximately 9°C and of about 6°C for sea surface temperatures, leading to ice free polar caps in the annual mean. Additionally they indicate that greatly increased trace gas concentrations are needed to reproduce distinct warming for tropical and subtropical regions. Changes in geography provide mainly high latitude warming. The ocean surface circulation is dominated by wind-driven gyre circulation comparable to present clay. A predominant westward flow through the Tethys Sea and a largely decreased southern circumpolar current are simulated. Changes in model geography lead to a clear decline in upper ocean salinities and a strong increase with depth for the deeper ocean. The warm, fresh surface layer prevents a deep mixing in the water column and there is no global meridional overturning circulation observable. As a result the model shows a strengthening in vertical ocean stratification for mid-Cretaceous contrarily to prior studies.
    Keywords: Course of study: BSc Physics of the Earth System
    Type: Thesis , NonPeerReviewed
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  • 4
    Publication Date: 2024-03-26
    Description: Mid-ocean ridges and volcanic passive continental margins are prime regions to explore active and extinct hydrothermal systems. In both settings, a large number of hydrothermal vents have already been discovered by direct observations and/or geophysical surveys. The growing interest in these systems results from their relevance for different fields of marine sciences. For example, commercially interesting ore deposits form as a byproduct of hydrothermal venting at the seafloor, unique ecosystems evolve around submarine vent sites, and hydrothermal systems driven by sill intrusions into organic sediments are related to hydrocarbon maturation and even venting of greenhouse gases into the atmosphere. Numerical simulations of hydrothermal fluid flow can help to gain a quantitative understanding of the subsurface physicochemical processes that control these systems. This thesis contributes to a better understanding of hydrothermalism in oceanic and continental settings by presenting a newly developed hydrothermal flow model and two case studies of hydrothermal flow at mid-ocean ridges and volcanic passive margins. To explore the effects of bathymetric relief on hydrothermal fluid flow in submarine settings, a systematic study has been carried out using 375 simulations. These simulations show that temperature-induced pressure variations in the subsurface result in the deviation of hydrothermal plumes towards bathymetric highs in submarine settings. The plume deviation from its origin is directly related to the surface slope and depth of the heat source. A case study for the fast-spreading East Pacific Rise at 9° 30’N shows that bathymetric effects help to focus venting directly onto the ridge axis – only if bathymetry is taken into account can across axis fluid flow be reconciled with exclusive on-axis venting. A second case study for the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge shows that also here venting is likely to occur at local bathymetric highs. The effects of hydrothermal convection triggered by sill intrusions in continental settings have been explored in a case-study for the Gjallar Ridge area on the Norwegian margin. This area is affected by a swarm of sill intrusions originated from North-Atlantic continental break-up during the Paleocene-Eocene transition as well as pre-break-up faults resulting from extensional tectonics. The structures are interpreted using 3D multichannel seismic data in combination with a structural and thermal reconstruction of the margin using TECMOD software. The reconstructed temperature is used as initial condition for sediments prior to sill injection and the detailed thermal history of sediments is modeled by a 2D fluid flow simulation. The simulation results show that high-temperature venting (〉200°C) occurs less than 1000 years following sill emplacement. The faults play strong roles for transferring the fluids to far-off regions. As a result of circulating hot fluids, the maturity of sedimentary rocks is greatly enhanced, especially where the hot fluids are trapped below impermeable sills during their ascent, thereby suggesting potential zones for future hydrocarbon explorations. Furthermore, solution strategies for modeling hydrothermal fluid flow by finite element, finite volume and semi-Lagrangian methods are explained in particular in order to find out how the temperature equation is solved. Different schemes of fully-implicit, Crank-Nicolson and exponential for temperature diffusion and finite volume and semi-Lagrangian for temperature advection are evaluated. The results suggest that the most accurate method for solving temperature diffusion is Crank-Nicolson. However, other methods such as fully implicit and exponential are still valid. The mass conserving finite volume method is the most accurate method for solving temperature advection; however, limited time-stepping is its major drawback and thus semi-Lagrangian method is usually preferred. Therefore, the definition of optimum method is linked to the accuracy of interest and complexity of the media.
    Type: Thesis , NonPeerReviewed
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  • 5
    Monograph available for loan
    Monograph available for loan
    Darmstadt : WBG (Wiss. Buchges.)
    Call number: M 24.95644
    Description / Table of Contents: Waldbrände, Flutkatastrophen, Erderwärmung - ein Phänomen des 21. Jahrhunderts? Oder bestimmt der Klimawandel nicht schon immer den Weg des Menschen? Mit dieser brandaktuellen Fragestellung befasst sich der Geowissenschaftler Frank Sirocko, doch nicht mit dem Ziel, die Zukunft vorherzusagen, sondern vielmehr um einen Blick weit zurück in die Vergangenheit zu werfen. Hochrangige archäologische Funde und historisch bedeutsame Ereignisse werden auf der Grundlage jüngster, bislang unveröffentlichter Forschungsergebnisse mit Wetter- und Klimaphänomenen in einen konkreten Zusammenhang gebracht. Ort der Forschung: Die Dauner Maare in der Vulkaneifel. Die Sedimente der Eifelmaare sind der einzige Ort in Mitteleuropa, der die letzten 40.000 Jahre vollständig dokumentiert. Mit Hilfe der Ablagerungen in den tiefen und sauerstoffarmen Seen können Geowissenschaftler erstmals die Klima- und Wetterbedingungen von den Neandertalern bis heute genau rekonstruieren. Extreme Hochwasser sind ebenso abzulesen wie kaltzeitliche Trockenphasen oder Vulkanausbrüche!   Biographische Informationen Frank Sirocko leitet das Institut für Geowissenschaften der Johannes Gutenberg-Universität Mainz.
    Description / Table of Contents: [Titelinformationen] -- Verzeichnis der Autoren -- [Impressum] -- [Menü] -- Zum Geleit -- Danksagung -- Einführung -- 1 Geologie und Entstehung der Maare -- 2 Limnologie der Maarseen und typische Sedimente -- Limnologie -- Seesedimente -- 3 Pollenanalyse als Grundlage der Rekonstruktion von Umwelt- und Vegetationsgeschichte -- Pollenanalyse -- Vegetationsgeschichte -- 4 Korngrößenanalyse und Sedimentgeochemie als Grundlage der Klima- und Wetterrekonstruktion -- Korngrößenanalysen -- Geochemische Analytik -- Transportprozesse -- Wellenerosion -- Windstaubsedimente -- Hochwasserlagen und fluviatile Sedimente -- Turbidite -- Rutschungen -- Vulkanite -- Schutt und Geröll -- 5 Bohrungen und Untersuchungsgebiete -- Schalkenmehrener Maar -- Ulmener Maar -- Holzmaar -- Dehner Maar -- 6 Datierung der Sedimente -- Die letzten 50 Jahre anhand von 137Cs -- Die letzten 100 Jahre anhand von 210Pb -- Die letzten 55.000 Jahre anhand von 14C -- Tephrochronologie -- Palynostratigraphie -- Freeze-Kerne der letzten 1000 Jahre -- Rammkerne der letzten 10.000 Jahre -- Holzmaar: Kern HM1 -- Ulmener Maar: Kern UM2 -- Seilkern der letzten 60.000 Jahre -- 7 Grundlagen des Klimas und extremer Wettersituationen -- Wettersysteme und Extremwetterereignisse -- Meteorologie von Extremwetterereignissen -- Kalt- und Warmereignisse -- Stürme -- Starkniederschläge -- Trockenperioden -- Regionalität -- 8 Ursachen von Klimavariabilität in der Vergangenheit -- Global Player Nummer 1: Die orbitale Konstellation zwischen Erde und Sonne -- Global Player Nummer 2: Veränderungen der Sonnenaktivität -- Global Player Nummer 3: Treibhausgase -- Global Player Nummer 4: Vulkanaktivität -- Interne Variabilität des Klimasystems als Global Player Nummer 5 -- 9 Archäologische Grabungen und Denkmäler -- 10 600.000-40.000 BP.
    Type of Medium: Monograph available for loan
    Pages: 208 Seiten , Illustrationen, Diagramme, Karten
    Edition: 3., durchgesehene Auflage
    ISBN: 978-3-534-25520-7
    Language: German
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 6
    Publication Date: 2023-12-18
    Description: Due to a steady increase of carbon dioxide concentrations in the atmosphere, the oceans take up more CO2 causing an increase in seawater pC02 and a decrease in seawater pH and calcite saturation state. Already today, especially in the late summer and autumn, low pHvalues can occur in the surface water of the Kiel Fjord due to the upwelling of CO2 rich bottom water. This is mainly caused by the degradation of phytoplankton blooms additionally increased by eutrophication of the oceans. Assuming that organisms from fluctuating habitats with respect to pCO2 and pH are adapted to - or at least able to cope with these conditions, their tolerance might be reduced when food - and thus energy - is limited. In the present study, freshly settled juvenile barnacles of the species Amphibalanus improvisus were reared for 5 months under experimental conditions. The combined effects of three pCOr (3 80, 1120 and 4000 ppm) and two feeding levels (high and low; 5: 1) on growth, reproduction and calcification, as well as the effects of the pCO2 stress on the settlement success of the offspring generation of the reared barnacles were investigated. Growth and reproduction were not affected by an increase of seawater pCO2, regardless of the diet. In the 4000 μatm pCO2 treatment with seawater undersaturated with respect to calcite, the external organic layer of the barnacle shell (epicuticle) peeled off under the long term exposure to the corrosive water with the underlying calcium carbonate layer starting to dissolve. Barnacles increased the calcification to compensate increasing CaCO3 dissolution. Since energy for successful compensatory calcification was possibly limited in the low food treatment, a decrease in shell strength was observed under the 4000 μatm pCO2 treatment. This reduction in shell strength could lead to an increased susceptibility of barnacles to crushing and drilling predators. The applied pCO2 and food treatments had furthermore no significant effects on the development and the settlement success of the offspring barnacle larvae. These results show that the barnacle Amphibalanus improvisus can cope with predicted future ocean acidification even under limited food conditions. A decrease in shell strength and thus a possible increase in susceptibility of barnacles towards their predators could nevertheless have negative effects on barnacle populations in the future. This highlights on the importance to investigate species interactions in response to multiple environmental stressors such as pC02 and food limitation.
    Type: Thesis , NonPeerReviewed
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  • 7
    Publication Date: 2023-12-14
    Type: Thesis , NonPeerReviewed
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  • 8
    Publication Date: 2023-12-12
    Type: Thesis , NonPeerReviewed
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  • 9
    Publication Date: 2023-12-11
    Description: Vorangegangene Studien deuten daraufhin, dass epibiontische Bakterien einen starken Einfluss auf den Bewuchs von Makroalgen durch groBere Epibionten, wie zum Beispiel Diatomeen und lnvertebratenlarven haben. Bakterien können induktiv oder inhibierend auf die Anheftung von Epibionten wirken und können somit nachteilig oder vorteilhaft für die Alge sein. Es ist wahrscheinlich, dass Makroalgen im Lauf der Evolution Mechanismen zur Förderung von Bakterien mit für sie positiven Eigenschaften entwickelt haben. Ziel meiner Arbeit war es, die Effekte von vier Bakterienstammen (Vibrio sp., ein α-Proteobakterium, Cellulophaga sp. und Pseudoa/teromonas sp.), die natürlicherweise im Biofilm von Fucus serratus und Fucus vesiculosus vorkommen, auf Diatomeenbewuchs zu analysieren. Dafür wurden Biofilme einzelner und kombinierter Bakterienstämme hergestellt, die danach mit Diatomeen besiedelt wurden. Die Diatomeendichten wurden über Chlorophyllfluoreszenz quantifiziert. Für alle vier untersuchten Stämme wurden unterschiedlich stark hemmende Effekte auf die Diatomeenart Stauroneis constricta gefunden. Vor allem das α-Proteobakterium und Pseudoa/teromonas sp. erwiesen sich als starke lnhibitoren, die bis zu 100 % der Diatomeenbesiedlung hemmten. Allerdings wiesen die Ergebnisse der Versuchsreihen groBe Variabilität auf. Die Kombination von α-Proteobakterium und Pseudoalteromonas sp. verstärkte die Hemmung der Diatomeenbesiedlung im Vergleich zu den Reinstämmen deutlich, wobei die Kombinationen mit den schwächeren lnhibitoren Vibrio sp. und Cellulophaga sp. sowohl stärkere Effekte erzielten, als auch Effekte, die zwischen denen der Reinstämme lagen.
    Type: Thesis , NonPeerReviewed
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  • 10
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    facet.materialart.12
    Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung
    Associated volumes
    Call number: ZSP-168-648
    In: Berichte zur Polar- und Meeresforschung
    Type of Medium: 12
    Pages: Online-Ressource
    Series Statement: Berichte zur Polar- und Meeresforschung 648
    Location: AWI Reading room
    Branch Library: AWI Library
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