35 documents found

Dissertation
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Evolving ocean basins in the Early Cretaceous greenhouse: A climate model-proxy...

Greenhouse climates with global mean temperatures significantly higher than today prevailed during large parts of the geological history. They provide direct evidence for the adaptation of the climate system to enhanced greenhouse gas forcing during the past and represent the only possibility to constrain...
Dissertation

Present and past changes in continental weathering and ocean circulation...

The past and present variability of ocean circulation and weathering inputs can be reconstructed from the geochemical composition of seawater and marine sediments. Among other proxies, the radiogenic isotope compositions of neodymium (Nd), hafnium (Hf) and lead (Pb) have been applied to reliably trace...
Dissertation

The Late Quaternary evolution of subsurface water masses in the Gulf of...

The area of this study has been under the influence of a monsoon-driven tropical climate and has experienced variable contributions from river systems in a near shelf area characterized by a complex hydrography. The goal of this study is to improve the understanding of the coupling mechanisms between...
Dissertation

The geochemical cycling and paleoceanographic application of combined oceanic...

Combined oceanic hafnium (Hf) and neodymium (Nd) isotope compositions are a geochemical tool developed over the past 15 years to study the present and past ocean circulation and continental weathering regimes. Since it is a relatively new proxy in marine research, a number of issues regarding the geochemistry...
Dissertation

Reconstructing the Plio – Pleistocene evolution of the water mass exchange...

Global climate of the Plio-Pleistocene has been largely impacted by changes of the Atlantic Meridional Overturning Circulation (AMOC), which has most likely to a large extent been controlled by the formation of North Atlantic Deep Water (NADW) ventilating the entire Atlantic Ocean. The main areas contributing...
Dissertation

Deep-water circulation and detrital provenance in the South Pacific, from...

Present and past climate of the Earth has strongly depended on oceanic circulation and marine biological productivity. The formation of deep and bottom waters in high latitudes as a consequence of density changes and their pathways through the global ocean, the so called thermohaline circulation (THC)...
Dissertation

Recent planktic foraminifera in the Fram Strait : ecology and biogeochemistry

This study describes the ecology (species abundances, depth habitat), the stable isotope compostion (carbon and oxygen isotopes) and the Mg/Ca ratios of recent planktic foraminifera in the Fram Strait.
Dissertation

Preservation of geochemical proxies in foraminifera during carbonate diagenesis...

The elemental and isotopic composition of calcitic foraminiferal tests, deposited in marine carbonate sediments, is widely used to reconstruct oceanic and climatic conditions of the geologic past. However, ancient tests are normally altered after deposition by recrystallisation, during which the original...
Dissertation

Benthic Foraminifera of the Peruvian and Ecuadorian Continental Margin

This study investigated the distribution of living (Rose Bengal stained) benthic foraminifera of the northwestern continental margin of South America with focus on the Peruvian oxygen minimum zone (OMZ) inhabiting species. Further, a new proxy for bottom water oxygen concentrations based on benthic...
Dissertation

Impacts of airborne volcanic ash on the surface ocean biogeochemistry and...

The availability of nutrients in the surface ocean affects the marine primary productivity (MPP), and the atmosphere represents an important source of nutrients to the euphotic zone of the in the global ocean. Volcanic eruptions, can through atmospheric transport, deposit volcanic ash into the ocean...
Dissertation

Late Quaternary Changes in Silicate Utilisation and Upwelling Intensity...

The Peruvian coastal upwelling region is characterised by one of the most pronounced oxygen minimum zones in the worlds ocean. The extension and strength of bottom water oxygen depletion has varied in the past as a function of surface water primary productivity and changes in circulation and upwelling...
Dissertation

Silicon and Neodymium Isotope Constraints on Biogeochemical Cycles and...

Stable and radiogenic isotope systems are powerful tools to investigate biogeochemical processes, nutrient cycling and water mass mixing in the ocean. Here a comprehensive study of the stable isotopes of silicon (Si) and the radiogenic isotope composition of the Rare Earth Element (REE) neodymium (Nd)...
Dissertation

Cretaceous to Quaternary Siliciclastic Sediments of the Tarfaya Basin,...

This dissertation is prepared to attain the doctorate under the title "Cretaceous to Quaternary Siliciclastic Sediments of the Tarfaya Basin, Marginal Atlantic, SW Morocco Petrography, Geochemistry, Provenance, Climate and Weathering".
Dissertation

Impact of elevated pCO2 on benthic foraminifera from the southwestern...

Increasing atmospheric CO2 concentrations have a strong impact on the marine carbonate chemistry leading to a phenomenon called ocean acidification. Excess CO2 dissolves in the surface water of the ocean, thereby the seawater pCO2 increases, whereas the [CO3 2-] and pH decrease. Reduced CO3 2- concentrations...
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

Variations in Mediterranean Outflow Water and its salt discharge versus...

Pliocene changes in Mediterranean Outflow Water (MOW) and its potential influence on northern North Atlantic thermohaline circulation prior and during the onset of Northern Hemisphere Glaciation (NHG; 3.7 – 2.6 Ma) were investigated at westernmost Mediterranean Site ODP 978 (1930 m w.d.) and along the...
Dissertation

Tracing water masses and continental weathering by neodymium and hafnium...

Radiogenic isotopes, such as the ones of hafnium (Hf) and neodymium (Nd), have been used to investigate present and past ocean circulation patterns, hydrothermal inputs and continental weathering regimes. This thesis presents a detailed study of the dissolved Hf and Nd isotope composition...
Dissertation

Late Quaternary variability of hydrography and weathering inputs on the...

The radiogenic isotope systems of neodymium (Nd), strontium (Sr) and lead (Pb) have been used in numerous studies throughout the last decades to investigate water mass circulations of the past and present oceans, and to trace changing contributions of detrital material from different source areas....
Dissertation

Benthic foraminifera as geochemical and micropaleontological proxies for...

Determination of the pore density in Bolivina spissa from the Peruvian oxygen minimum zone in respect to oxygen and nitrate availability. First applications of the pore dansity as an environmental proxy. Analysis of the redox sensitive elements manganese and iron in foraminiferal calcite from the Peruvian...
Dissertation

Holocene Variability of Surface and Deep Water Advection to the Arctic...

Micropaleontological, geochemical, and sedimentological parameters of two sediment cores from the eastern Fram Strait have been studied to reconstruct the variability of surface and deep water advection and related fluctuations of the marginal ice zone during the past ca ∼9,000 years with multidecadal...