Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"biogenic silica"”.
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Biogenic silica dynamics of Arctic marine ecosystems
… silicon (Si) cycle through the formation of biogenic silica (bSiO2). Continental shelves account for half of the total marine area in the Arctic, yet our knowledge of the cycling of Si for this critically climate-impacted region is limited. The overall objective of this thesis was to improve …
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High Resolution Paleothermometry Using Biogenic Silica: A Feasibility Study
<p> Biogenic silica is produced by numerous organisms that include grasses, protozoa, and Chrysophyceae, as well as marine and freshwater diatoms and sponges (Simpson and Volcani, 1981). It is therefore not uncommon for biogenic silica to be found in environments subject to wildfires. Experimental …
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Using Silicon Isotopes to Trace the Biogenic Silica in the Southern Ocean
… as unicellular, eukaryotic organisms that form biogenic silica (bSi) frustules. The use of stable isotopes and physicochemical factors (temperature, light, and trace metal) provides a promising method for understanding how Si and C fluxes will change in response to future climate change. The Si …
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Using Silicon Isotopes to Trace the Biogenic Silica in the Southern Ocean
… as unicellular, eukaryotic organisms that form biogenic silica (bSi) frustules. The use of stable isotopes and physicochemical factors (temperature, light, and trace metal) provides a promising method for understanding how Si and C fluxes will change in response to future climate change. The Si …
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Investigating the ocean’s biological pump using thorium-235 and polonium-210
… biologically relevant elements such as POC and biogenic silica via the biological pump are radioisotopes – naturally-occurring clocks which allow us to look back in time to study oceanic processes. In this thesis, the two radioisotope pairs 234Th/238U and 210Po/210Pb are utilized. Chapter 2 is …
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Multiscale Structures and Mechanics of Biomineralized Lattices in Hexactinellid sponges and Echinoderms
… of the brittle nature of the constituents (e.g., biogenic silica and calcite). However, the quantitative explorations of the structure-mechanics relationships in multiscale of biomineralized lattices remain insufficient and hence hinder the leverage of the functional benefits to design architected …
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Characterisation of silica in Equisetum hyemale and its transformation into biomorphous ceramics
… wood during the past time due to its high silica encrustations in the epidermis. Equisetum hyemale (scouring rush) can accumulate silica up to 16% dry weight in its tissue, which makes this plant an interesting candidate as a renewable resource of silica for the synthesis of biomorphous …
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EFFECTS OF COMPLEXATION WITH THE SIDEROPHORE DESFERRIOXAMINE B ON TRANSITION METAL REMOVAL FROM SEAWATER
… Mn oxides, yet not significantly influenced by biogenic silica or calcite.
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Silica diagenesis and its pore-scale influence on the characteristics of the upper and lower Bakken shales, Williston Basin, North Dakota and Montana
… tracts and contain a significant portion of biogenic silica in the form of radiolaria. Biogenic silica dissolution and reprecipitation is known to contribute to the development and/or preservation of pore space, ultimately affecting source rock quality and reservoir recoverability. In …
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Biologically Controlled Mineralization and Demineralization of Amorphous Silica
… awaiting development upon a barren landscape. Silica biomineralization is one of these emerging frontiers. As new information about the chemical and structural nature of the macromolecules involved in biosilicification is revealed, the means these species employ to control the temporal and …
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Late Quaternary and Holocene Paleoecology of Interior Mesic Forests of Northern Idaho
… record of pollen and sediment composition (biogenic silica and inorganic and organic matter) over the last ca. 120,000 years provides evidence of a dynamic ecosystem. Over a long timescale, the slow shifts in vegetation are attributed to the changes in climate. During the last interglacial …
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Phytoplankton Dynamics in the Very Low Salinity Region of the James River Estuary, Virginia, U.S.A.
… by 23 um screen), exhaustion of dissolved silicate, relatively high ratio of particulate biogenic silica to particulate organic carbon, and relatively low ratio of particulate organic carbon to chlorophyll a in the very low salinity region indicate that diatoms are selectively trapped …
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Palaeoenvironmental reconstruction in South Africa's year-round rainfall zone using multiproxy geochemical analyses on lake sediments from Swartvlei
… from 3500 to 1400 cal BP. In addition, high biogenic silica concentrations indicate increased bio-productivity during the Little Ice Age (LIA) while increased sedimentation rates suggest that anthropogenic activity impacted the lake from 150 cal BP. This study adds insight to the geomorphic …
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Palaeoclimatology of the late Palaeocene to middle Eocene: geochemical records of stable and transient climate states
… indicate that a 3.5 million year period of high biogenic silica deposition during the Eocene was climatically relatively stable in the Arctic basin with only infrequent communication to the world's oceans outside. This period is correlated with high organic burial in the basin and global …
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Sequence Stratigraphy of Middle-Mississippian Carbonates of the Southern Appalachians: Tuscumbia Limestone, Tuscumbia, AL
… Additionally, possible sources of the silica (chert) found within these units (e.g., eolian dust, upwelling) are evaluated based upon thin section analysis. Four facies and one subfacies were identified: F1: echinoderm, bryozoan mudstone/wackestone facies and Fla: muddy echinoderm …
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The Ups and Downs of the Holocene: Exploring Relationships between Global CO2 and Climate Variability in the North Atlantic Region
… total carbon/nitrogen/sulphur determinations and biogenic silica), vegetational reconstruction (pollen analysis) and stomatal frequency based CO2 reconstructions. The stomatal frequency based reconstructions of CO2 provides decadal scale data, which complement ice core measurements. Lakes …
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Subarctic ecosystem responses to climate, catchment and permafrost dynamics in the Holocene
… stable isotopes, near infrared spectroscopy and biogenic silica. Results revealed that the structural development of the mire occurred during the later part of the Holocene. Peat inception was dated at 4700 cal BP and onset of organic sedimentation in two adjacent lake basins occurred at 3400 and …
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Microbial communities and their response to Pleistocene and Holocene climate variabilities in the Russian Arctic
… setting, as can be seen in the corresponding biogenic silica distribution. The availability of this algae-derived carbon is suggested to be a driver for the observed pattern in the microbial abundance. This work demonstrates the effect of climate changes on the community composition of …
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Investigations on rainfall variability during the late Quaternary based on geochemical analyses of lake sediments from tropical and subtropical southern Africa
… by parallel changes in the organic matter and biogenic silica content observed in the 22 m long profile recovered from Lake Challa. This covers the time of the last 25 kyr BP. It documents a transition around 16 kyr BP from relatively well-mixed conditions with high detrital input during …
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Phylogenetic and physiological characterization of deep-biosphere microorganisms in El’gygytgyn Crater Lake sediments
… while the extracellular DNA is dependent on the biogenic silica content. The different community-shaping parameters and the fact, that a redundancy analysis of the total DNA pool explains significantly less variance of the microbial community, indicate that the total DNA represents a mixture of …
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