26 documents found

Dissertation

Physical and geochemical controls on oxygen dynamics at continental margins...

In light of increasing anthropogenic influences on natural waters and climate change, it is important to advance our understanding of the intricate interactions between biological, geochemical and physical processes that control constituent dynamics within aquatic systems. Among those constituents, dissolved...
Dissertation

Phosphorus cycling in anoxic sediments

Worldwide oxygen minimum zones (OMZs) as well as coastal oxygen-deficient regions have been shown to be expanding during recent decades. When such oxygen minima impinge on the sea floor, the retention capacity of sediments for phosphate (TPO4), ferrous iron (Fe2+), as well as ammonium (NH4+) is strongly...
Dissertation

Modelling the marine biogeochemical implications of aeolian, sedimentary...

Iron is an important nutrient for marine phytoplankton and low concentrations of iron limit phytoplankton growth in around 40% of the surface area of the ocean. Due to the low solubility of iron in the sea, the concentrations of iron are largely dependent on external sources such as atmospheric deposition...
Dissertation

Production of greenhouse gases in organic-rich sediments

Methane (CH4) and nitrous oxide (N2O) are greenhouse gases, which atmospheric concentrations increased since preindustrial times by ~150 and ~20%, respectively, mainly due to the increase in anthropogenic emissions. The atmospheric increase of greenhouse gases (incl. carbon dioxide (CO2), CH4 and N2O)...
Dissertation

Regional and global scale modeling of the benthic marine nitrogen cycle

The benthic nitrogen (N) cycle is highly dynamic and diverse due to the strong redox gradients occurring in marine surface sediments and the variety of oxidation states accessible to nitrogen. Since N is a limiting nutrient for biological productivity, fluxes of nitrogenous species across the sediment-water...
Dissertation

The Phanerozoic δ(88/86)Sr Record of Marine Carbonates - Implications for...

In the light of increasing interest in the role of the world’s oceans in future global change, it is important to understand the underlying processes that were responsible for paleoceanographic changes in the geological past. Previous studies working on the geochemistry of ancient marine deposits agree...
Dissertation

Multiphase modeling of DNAPL seepage history as possible site investigation...

Modeling of the seepage history of DNAPLs is investigated as a new, non-invasive site investigation tool in order to elucidate the possible position of still unknown DNAPL source zone at many investigated industrial sites. Therefore, the spatio-temporal spreading behavior of the DNAPL TCE is studied...
Dissertation

Pore water expulsion at submarine cold seeps : geochemical evidence for...

Active pore water expulsion from marine sediments has been observed on continental margins worldwide and is therefore considered a potentially important link in global geochemical cycles. Understanding element recycling through submarine fluid discharge on a global scale requires a profound knowledge...
Dissertation

Mineralogical and isotope geochemical investigations of high Mg-calcites...

Within the framework of this thesis investigations on formation and dissolution processes of Mg-calcites have been carried out. Based on the results of mineralogical and isotope geochemical investigations it was possible to reconstruct the formation processes of authigenic high Mg-calcite concretions...
Dissertation

Quantification of methane fluxes and authigenic carbonate formation at...

This thesis represent stand-alone articles which have been published or will be submitted for publication in peer-reviewed scientific journals. Each of the Chapters II, III and IV contains a separate introduction, description of methods, presentation of data, results and discussion as well as a separate...
Dissertation

Box models of volatile cycles over the entire Phanerozoic

Three stand-alone geochemical box models have been developed to simulate globally coupled biogeochemical cycles. These models reflect the evolution of the participating biotic and abiotic constituents in marine and terrestrial environments, including the lower atmosphere. The single models focus on the...
Dissertation

Sulfidaufnahme von Calyptogena pacifica im Vergleich mit geochemischen...

Die Muschel Calyptogena pacifica (Fam. Vesicomyidae) lebt an den kalten Quellen, den Cold Seeps, der Subduktionszonen. Sie lebt mit sulfidreduzierenden Bakterien in ihrem Kiemengewebe in Symbiose. An zwei Muscheln aus den Cold Seeps aus dem Eel River Becken (östlicher Pazifik) wurden Sulphidaufnahmeraten...
Dissertation

Methane output from cold seep structures along the Central American continental...

Methane seepage from different geological structures was investigated along the convergent margin off the Pacific coast of Costa Rica in order to identify the fate and the amount of methane discharging into the ocean. Thus, the water column above four mud extrusions and one of several embayments caused...
Dissertation

Alteration of volcanic glasses in marine sediments : laboratory experiments...

Large volumes of mainly felsic volcanic ashes have been repeatedly released during explosive volcanic eruptions along the Central American Volcanic Arc. These ashes are found as up to several centimetres thick ash layers in marine sediments offshore Nicaragua and Costa Rica. Since volcanic ashes constitute...
Dissertation

Bacterial methane formation and distribution in marine environments : case...

(Keine Zusammenfassung in englischer Sprache vorhanden.) (No summary in English language.)
Dissertation

Benthic nitrogen fixation in oxygen minimum zones

The distribution and magnitude of benthic N2 fixation in OMZs, and its relevance for the community inhabiting these sediments was investigated. A possible coupling to sulfate reducers was determined by rate measurements of N2 fixation and sulfate reduction, as well as by molecular analysis in the respective...
Dissertation

Anthropogenic emissions of greenhouse gases from the seafloor into the...

The present thesis provides the first methane (CH4) emissions measurements from offshore abandoned wells in the North Sea and found that boreholes constitute unrecognized, but important conduits for the release of biogenic CH4 originating from shallow gas accumulations (<1,000 m sediment depth) in the...
Dissertation

Biodegradation of petroleum in marine seep sediments

This study presented for the first time the use of intact sediment cores in a continuous sediment-oil-flow-through (SOFT) system for investigating the degradation of petroleum under a simulated petroleum seepage.The biogeochemical response of sediments from hydrocarbon adapted sites like the Caspian...
Dissertation

Trace element and isotope measurement on artificially precipitated calcium...

Calcite and aragonite were precipitated by diffusing CO2 and NH3 gases into aqueous solutions containing Ca, Sr, Mg and ammonium ions at three different temperatures 12.5, 25 and 37.5 °C. Trace element incorporation and isotopic fractionation of Sr and Ca were measured as function of temperature and...
Dissertation

Experimental investigation of hydrogeochemical consequences of gas leakages...

The fluctuating energy production of renewable sources implies the necessity of energy storage. For the implementation of gas storage, a knowledge gap regarding gas-specific reactions to be expected in shallow aquifers following a leakage of compressed air, methane, or hydrogen existed. These reactions...