Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
Search results
456 records were found.
Diatoms are one of the major groups of algae which originated relatively recently and evolved in the Late Jurassic/Cretaceous. This thesis presents the results of a comprehensive study of diatom lipids in cultures and in the environment and their applications in the age determination of petroleum and in palaeoenvironmental studies. Diatom DNA sequences were analyzed in order to relate the phylogenetic positions of diatoms to the lipid chemotaxonomy. Forty four different sterols were identified in diatoms, with 24-methylcholesta-5,24(28)-dien-3-beta-ol being most common. 24-Methylcholesta-5,22E-dien-3-beta-ol, previously described as a diatom biomarker, was only the fifth most common sterol and absent in some major diatom groups. All identified sterols have been reported in other algae, but within the diatoms, some sterols and sterol co...
Anammox, the anaerobic oxidation of ammonium to dinitrogen gas with nitrite as the electron acceptor, constitutes a novel route to convert biologically available (fixed) nitrogen to gaseous N2. This process is mediated by specific bacteria belonging to the Planctomycetes that were initially discovered in waste water systems. Within the nine years after their discovery, anammox bacteria have been identified as key players in the global nitrogen cycle. They have been found in different suboxic to anoxic environments, including oxygen minimum zones, marine and freshwater sediments, tropical lakes and even in sea ice. Anammox is now acknowledged as an important process for the removal of fixed inorganic nitrogen from the oceans, freshwater and wastewater treatment systems, which was so far solely attributed to heterotrophic denitrification...
The majority of planktonic species, including those that are informative in the reconstructions of past marine environmental conditions, do not produce diagnostic features (e.g., cysts, spores, or lipid biomarkers) and would therefore escape identification from the fossil record using traditional paleoecological tools (microscopy or lipid biomarker geochemistry). However, several studies have recently demonstrated that fossil DNA of planktonic species can be preserved for thousands of years and can be used for species-specific characterization using molecular biological techniques. The objectives of this thesis were to investigate the potential fate of fossil DNA and to what extent it can be used as a qualitative and quantitative biomarker for paleoecological and paleoenvironmental reconstructions. For this goal, fossil DNA of several ...
N₂ fixation adds bioavailable nitrogen to the global oceans and therewith drives modern-day marine primary productivity. The diazotrophs mainly responsible for the fixation of nitrogen are principally found in the cyanobacterial lineage with unicellular and filamentous non-heterocystous species dominating. There is evidence that diazotrophic cyanobacteria were of similar importance in the past nitrogen cycling, in particular during the formation of organic-rich deposits of the Phanerozoic (e.g. Pleistocene Mediterranean sapropels and Cretaceous black shales). However, the poor preservation potential and the lack of suitable geochemical tracers that are specific for N₂-fixing cyanobacteria have hampered their rigorous identification in the geological record. This thesis describes investigations aimed at a better understanding of the pre...
Ladderane lipids are membrane lipids produced exclusively by anaerobic ammonium oxidising (anammox) bacteria. Anammox bacteria are key players in the marine nitrogen cycle, performing the anammox reaction, converting equal parts of ammonium and nitrite into dinitrogen gas. This process is responsible for a significant loss of bio-available nitrogen from the ocean. Ladderanes can be used to trace present-day anammox activity. However, the fate of ladderane lipids as they undergo structural alterations during diagenesis and catagenesis is unknown, and the influence of these processes must be constrained before confidently applying these biomarkers to infer past anammox activity.
In this thesis, three novel environmental settings were investigated for the presence of ladderane lipids, and thus the anammox bacteria performing the anammox...
NW Africa and SE Australia are regions which are particularly vulnerable to climate change. In this thesis, organic proxies are used from marine sediment cores to reconstruct past environmental conditions from these areas.
In sediments from NW Africa, the UK'37 showed an efficient proxy for sea surface temperature (SST) reconstruction, while the TEXH86 reconstructed thermocline temperatures. The UK'37 and TEXH86 records for the last 192 ka showed that periods of reduced AMOC coincide with a reduction in the vertical temperature gradient. Thus, variations in AMOC strength is a driver of the thermocline structure in the tropical Atlantic. Three independent organic proxies (UK’37,TEXH86 and LDI) were used to reconstruct SSTs for the last 135 ka in sediments from offshore SE Australia. Comparison with SST estimates based on foraminiferal ...
In addition to the more acknowledged consequences of climate change, such as global warming, the current human-induced increase of CO2 into the atmosphere is also responsible for a change in the chemical composition of seawater. Since 1750, the initiation of the industrial revolution, approximately 50% of the emitted anthropogenic CO2 is taken up by the oceans. These enhanced concentrations of aquatic CO2 is responsible for an increase of the seawater acidity and thus a decrease in pH, leading to ocean acidification. The impact of present-day ocean acidification on the development of future climate change is still not entirely understood. Of key importance, in this matter, is the role of primary producers within the global carbon cycle and underlying feedback mechanisms. Studying past periods of ocean acidification that are characteriz...
For climate modelling in order to predict climate change scenarios, it is important to consider past climate conditions and their impacts. The study of past climates, paleoclimatology, makes frequent use of molecular fossils, molecules that are preserved over geological time scales. Ratios of different compounds can be used, for example, as paleothermometers in order to determine temperatures of air and sea millions of years ago. One of these paleothermometers is the so-called TEX86 which is based on compounds present in the membranes of microorganisms called Thaumarchaeota, that thrive in the ocean. Their membrane lipids are glycerol diether glycerol tetraethers with hydrophilic headgroups (IPL-GDGTs), which are degraded after cell death to core lipid (CL-) GDGTs by release of the head groups, and settle to the sea floor packaged in o...
Lacustrine sediments often contain relatively high amounts of organic matter because of limited bottom water oxygenation and relatively high sedimentation rates. The membrane lipids of Crenarchaeota, a major group of the domain Archaea, consist of isoprenoid glycerol dialkyl glycerol tetraether (GDGTs) containing cyclopentane moieties, a characteristic considered an adaptation mechanism to temperature of the membrane. Analyses of core top sediments showed that the distribution of isoprenoid GDGTs varies with sea surface temperature (SST), a relation expressed in the TetraEther indeX of lipids with 86 carbon atoms (TEX86). Branched GDGTs were detected in peat bogs, soils, and coastal marine and lacustrine sediments. Their abundance in marine sediments decreases relative to crenarchaeol (an isoprenoid GDGT) with increasing distance from ...
With the realization that the Arctic Ocean was covered with enormous quantities of the aquatic floating fern Azolla 49 Myrs ago, new questions regarding the Eocene conditions facilitating these blooms arose. This dissertation describes the reconstruction of paleo-environmental conditions facilitating the large-scale occurrence of the freshwater fern Azolla in the Early/Middle Eocene Arctic and how this bloom might have affected global climate. Comparison of organic geochemical analyses of Eocene Arctic sediments and extant Azolla filiculoides resulted in the discovery of unique biomarkers for both Azolla and its nitrogen fixating cyanobacterial symbiont Anabaena azollae. Lipids identified as 1,?20 C30–C36 diols and structurally related mid-chain hydroxy compounds can now serve as palaeo-environmental indicators for the Arctic Azolla in...
