Considerada a maior ilha flúvio-marítima do mundo, com aproximadamente 48.000 km2, a Ilha de Marajó situa-se na zona equatorial brasileira, no litoral do Estado do Pará. Apresenta dois domínios distintos relacionados a geologia e vegetação. No setor oeste dominam solos desenvolvidos sobre os sedimentos Pós Barreiras (plio-pleistocênicos) recobertos pela Floresta Amazônica, enquanto no setor leste dominam sedimentos holocênicos derivados de ambiente fluvial/estuarino atualmente desativado. Neste setor encontram-se os extensos campos naturais marajoaras. O objetivo deste trabalho consistiu em aplicar os isótopos de carbono (12C, 13C e 14C) da matéria orgânica de solos e sedimentos com o intuito de avaliar possíveis modificações nos domínios da vegetação, em termos de plantas C3 e C4, durante o Quaternário Tardio e inferir sobre suas causas. Os resultados foram associados com observações de campo e análises petrográficas, sedimentológicas, químicas, de espículas de esponjas, isótopicas de nitrogênio e bibliográficas, sendo possível distinguir três mudanças ambientais relacionadas à geologia e vegetação, no setor leste da Ilha de Marajó durante o Pleistoceno Superior (aproximadamente 16.000 anos AP) ao Holoceno. No setor central da Ilha de Marajó foram obtidas as idades mais antigas da matéria orgânica em sedimentos de um paleocanal. Neste local, no intervalo Pleistoceno Superior-Holoceno Inferior, os dados isotópicos do carbono são característicos de plantas C3, com exceção de dois pontos correspondentes a 16.118 ± 60 anos AP e aproximadamente 13.000 anos AP, com valores de \'delta\' 13CPDB de -20,4 e -22,1 respectivamente. A relação entre os resultados isotópicos do carbono e nitrogênio indicam a presença de plantas terrestres (gramíneas C4) nesta região, atualmente ocupada por vegetação arbórea, provavelmente associada a clima mais seco. A presença de fragmentos vegetais carbonizados e minerais instáveis ao intemperismo químico como feldspato, hornblenda e biotita nos sedimentos, confirmam a hipótese. Nos demais pontos analisados, durante o Holoceno Médio/Superior (entre aproximadamente 5.000 a 3.000 anos AP) os dados isotópicos do carbono e de fragmentos vegetais carbonizados indicam que uma vegetação constituída por plantas C3 (arbóreas) no setor leste da ilha foi gradativamente substituída por gramíneas C4, iniciando a formação dos atuais campos na Ilha de Marajó, associados a um clima mais seco. Neste mesmo período os canais foram sendo abandonados, como indicado pela granodecrescência ascendente dos sedimentos de paleocanais e mudança da coloração (de cinza para marrom alaranjado) dos sedimentos argilosos da planície de inundação, associados à deposição em um ambiente redutor para um ambiente oxidante. No intervalo redutor, em alguns perfis houve a formação de pirita e jarosita. Estudos anteriores mostram que o processo de abandono de canais está associado a eventos de tectônica cenozóica na região. Os dados isotópicos de carbono mais enriquecidos observados no setor sudoeste da ilha, indicam no período de ~7000 a 3000 anos AP, uma abertura da vegetação arbórea e/ou a presença de plantas C4, associados a um período mais seco. Durante o Holoceno Superior os canais foram preenchidos e abandonados. O empobrecimento isotópico do carbono da matéria orgânica indica a implantação da vegetação arbórea sobre os mesmos, estabelecendo a condição atual observada no setor leste da Ilha com paleocanais com vegetação de cobertura arbórea (plantas C3) e planície de inundação com vegetação de campos (plantas C3 e C4). Aanálise de espículas de esponjas e isótopos de nitrogênio apontam o setor leste como um sistema deposicional transicional (estuarino) durante o Quaternário Tardio. / Considered the largest fluvial-marine island of the world, with approximately 48.000 km2, the Marajó Island is located in the Brazilian equatorial area, in the Pará State coast. It presents two different domains related to the geology and vegetation. In the west domain dominate soils developed on Pós Barreiras sediments (plio-pleistocenics) covered by the Amazonian Forest, while in the east domain dominate holocenic sediments derived of fluvial/estuarine environment, at present deactivated. In this sector are located the natural savanna. The objective of this work consisted of to apply the carbon isotopes (12C, 13C and 14C) of soil and sediment organic matter, in order to evaluate possible changes in the vegetation domains, in terms of C3 and C4 plants during the Late Quaternary, and inferences about their causes. The results were associated with field observations, petrographic, sedimentologic, chemical, sponge spicules and nitrogen isotope analyses and bibliography, being possible to distinguish three environmental changes related to the geology and vegetation in the eastern Marajó Island during Late Pleistocene (approximately 16.000 years BP) to the Holocene. In the central section of the Marajó Island were obtained the oldest ages of the sediment organic matter of a paleochannel. In this place, in the interval Late Pleistocene - Early Holocene, the carbon isotope data are characteristic of C3 plants, except for two points corresponding to 16.118 ± 60 years BP and approximately 13.000 years BP, with values of \'delta\' 13CPDB of -20,4 and -22,1 , respectively. The relation between the carbon and nitrogen isotopes data, indicate the presence of terrestrial plants (C4 grass) in this area, at present covered by arboreal vegetation, probably associated to a drier climate. The presence of charred wood fragments and unstable minerals to the chemical weathering as feldspar, hornblend and biotite in the sediments, confirm the hypothesis. In other points, during Middle/Late Holocene (between ~5.000 and 3.000 years BP) the carbon isotopes and charred wood fragments data, indicate that a vegetation constituted of C3 plants (trees) in the eastern sector of the island, was gradually substituted by C4 grasses, initiating the formation of savanna vegetation in the Marajó Island, associated to a drier climate. In this same period, the channels were abandoned, as indicated by the fining upward the paleochannel sediments and the color change (grey to brown orange) of the clayey sediments of the floodplain, associated to the deposition of a reducing environment to an oxidizing environment. In the reducing interval, in some profiles it was observed the formation of pirite and jarosite. Previous studies show that the channels abandonment processes is associated to tectonic Cenozoic events in the area. The more enriched isotope carbon data of soil organic matter observed in the Southwestern sector of the island, indicated in the period of ~7.000 and 3.000 years BP, an opening of the arboreal vegetation and/or the presence of C4 plants, probably associated to a drier climate. During the Late Holocene the channels were filled out and abandoned. More depleted carbon isotope data of the organic matter, indicates the implementation of the arboreal vegetation on the channels, establishing the modern conditions observed at the eastern section of the Island, with paleochannels covered by arboreal vegetation (C3 plants) and the floodplain covered by grassland vegetation (C3 and C4 plants). The sponge spicules and nitrogen isotope analysis, indicate the eastern section as a transitional deposition system (estuarine) during the Late Quaternary

No description available.

Hu Hong Bing. / "May 2004." / "13" in title is superscript. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

The purpose of this study was to use soil physical and chemical analyses to better understand the ancient agricultural landscape around the ancient Maya cities of Rio Amarillo and Piedras Negras, two tributary sites to Copan, Honduras. Our primary objective was to determine whether a mass erosion event around 800 A.D. occurred which could have caused crop failure and famine or if stable soil conditions persisted during the collapse of these city-states. Stable carbon isotope analysis of the humin fraction of the soils showed that much of this valley was used anciently for agriculture, including hillslopes and hilltops; however, there is no evidence of mass erosion in the soil profiles. Soil horizon development and texture is consistent with stable soil conditions in this area. The demise of these city-states was likely caused by a variety of factors including warfare and political unrest, and not solely by environmental degradation as postulated in previous studies of the valley.

Monthly δ18O and Sr/Ca records generated from modern and fossil corals from Southwestern Pacific Ocean sites in the Republic of Vanuatu are used to assess the differences in mean climate state, seasonality, and interannual variability between a glacial and interglacial period. The modern coral contains a well-defined annual signal in δ18O and Sr/Ca. The top 40 cm of the coral used in this study has a mean δ18O value of -4.99+/-0.13%VPDB (2σ) and a mean Sr/Ca value of 8.691+/-0.015mmol/mol (2σ). El Nino-Southern Oscillation (ENSO) events are characterized by positive δ18O and Sr/Ca anomalies, consistent with cooler temperatures and reduced rainfall that typifies ENSO at Vanuatu. The ~12cm long fossil coral is dated to 346 ka + 25, - 9, based on uranium-series analysis and stratigraphic forward modeling, indicating that the fossil coral grew during MIS10 - a glacial period. X-ray diffraction, petrographic inspection, SEM analysis, and geochemical considerations indicate excellent preservation. The mean δ18O value is enriched by 0.74%, and the mean Sr/Ca value is equivalent, compared to the modern coral. Mathematical modeling of Pleistocene mean SST and SSS results in temperature estimates up to ~2˚C warmer and salinity up to ~2 psu saltier than present-day conditions, if seawater Sr/Ca were 1-2% higher in MIS10. Our fossil coral data and modeling results preclude colder SST and lower SSS at Vanuatu during MIS10. Accurate estimates of past values of seawater Sr/Ca remain the largest obstacle to accurately reconstructing past tropical SST using pristine fossil corals. The fossil coral Sr/Ca annual range is similar to the modern range, indicating that seasonal SST ranges were similar, whereas the δ18O annual range is about half that of the modern coral, indicating weaker past seasonal salinity variations. The reduced seasonal SSS variations and increased SSTs near Vanuatu are interpreted as evidence that the SPCZ was displaced from its present location while the fossil coral lived. The geochemical response to El Niño events in the modern coral is observed twice in the fossil coral record, indicating that ENSO-like processes are not unique to interglacial time periods, but characterize the tropical Pacific at least back to MIS 10.

We test the fidelity of shallow-water gastropod skeletons as multi-proxy archives of seasonal paleo-environmental change by performing isotopic and trace-metal analyses on specimens of Conus ermineus from the Gulf of Mexico. Four adult specimens were collected from Stetson Bank in the Flower Garden Banks National Marine Sanctuary during the summer of 2002. Shell samples were milled along axes of growth to produce time-series profiles spanning up to eight years. We corrected the profiles for growth rate effects and compared the tuned results with in situ temperature and salinity records at the reef surface and temperature profiles from nearby surface buoys. Examination of sample densities in δ18O cycles shows that shell growth is faster during summers and slower during winters. Tuning the profiles versus time yields δ18O values that co-vary closely with seasonal temperatures to a high degree of coherency (R2 = 0.84). The δ13C profiles show cyclic variation modified by ontogenetic decreases in δ13C. These ontogenetic trends are attributable to decreasing metabolic efficiency, while seasonal cycles reflect hydrographic changes in the gastropods’ habitat. Salinity and δ13C of dissolved inorganic carbon show a strong correlation at Stetson Bank (R2 = 0.80), and early summer shell δ13C minima coincide with local salinity minima during times of peak river discharge. The terminations of these δ13C minima occur during annual upcoast reversals of shelf currents in this area. These effects are augmented by summer stratification and productivity minima that further decrease seawater δ13C. Sr/Ca ratios increase through ontogeny, most likely due to decreasing metabolic efficiency. However, seasonal variations in Sr/Ca profiles show strong similarity with δ18O profiles, confirming the temperature dependence of Sr/Ca and minimal influence of salinity on shell δ18O at Stetson Bank. The results of this study show that tuned δ18O and Sr/Ca profiles can be used to reconstruct seasonal paleotemperatures. Carbon isotope profiles and environmental data also demonstrate the utility of Conus δ13C as a proxy for freshwater flux and shelf circulation.

The objective of this thesis is to improve the understanding of what processes and mechanism affects the distribution of polychlorinated biphenyls (PCBs) and organic carbon in coastal sediments. Because of the strong association of hydrophobic organic contaminants (HOCs) such as PCBs with organic matter in the aquatic environment, these two entities are naturally linked. The coastal environment is the most complex and dynamic part of the ocean when it comes to both cycling of organic matter and HOCs. This environment is characterised by the largest fluxes and most diverse sources of both entities. A wide array of methods was used to study these processes throughout this thesis. In the field sites in the Stockholm archipelago of the Baltic proper, bottom sediments and settling particulate matter were retrieved using sediment coring devices and sediment traps from morphometrically and seismically well-characterized locations. In the laboratory, the samples have been analysed for PCBs, stable carbon isotope ratios, carbon-nitrogen atom ratios as well as standard sediment properties. From the fieldwork in the Stockholm Archipelago and the following laboratory work it was concluded that the inner Stockholm archipelago has a low (≈ 4%) trapping efficiency for freshwater-derived organic carbon. The corollary is a large potential for long-range waterborne transport of OC and OC-associated nutrients and hydrophobic organic pollutants from urban Stockholm to more pristine offshore Baltic Sea ecosystems. Theoretical work has been carried out using Geographical Information Systems (GIS) and statistical methods on a database of 4214 individual sediment samples, each with reported individual PCB congener concentrations. From this work it was concluded that the continental shelf sediments are key global inventories and ultimate sinks of PCBs. Depending on congener, 10-80% of the cumulative historical emissions to the environment are accounted for in continental shelf sediments. Further it was concluded that the many infamous and highly contaminated surface sediments of urban harbours and estuaries of contaminated rivers cannot be of importance as a secondary source to sustain the concentrations observed in remote sediments. Of the global shelf PCB inventory < 1% are in sediments near population centres while ≥ 90% is in remote areas (> 10 km from any dwellings). The remote sub-basin of the North Atlantic Ocean contains approximately half of the global shelf sediment inventory for most of the PCBs studied.

Atmospheric aerosols may be emitted directly as particles (primary) or formed from gaseous precursors (secondary) from different natural and anthropogenic sources. The highly populated South and East Asia regions are currently in a phase of rapid economic growth to which high emissions of carbonaceous aerosols are coupled. This leads to generally poor air quality and a substantial impact of anthropogenic aerosols on the regional climate. However, the emissions of different carbon aerosol components are still poorly constrained. Water-soluble organic carbon (WSOC) is a large (20-80%) component of carbonaceous aerosols that can absorb solar light and enhance cloud formation, influencing both the direct and indirect climate effects of the aerosols. A novel method for carbon isotope-based studies, including source apportionment, of the WSOC component of ambient aerosols was developed and tested for recovery efficiency and the risk of contamination using both synthetic test substances and ambient aerosols (paper I). The application of this method for the source apportionment of aerosols in South and East Asia shows that fossil fuel input to WSOC is significant in both South Asia (about 17-23%) highly impacted by biomass combustion practices and in East Asia (up to 50%) dominated by fossil energy sources (papers II, III, IV). Fossil fraction in WSOC in the outflow from northern China is considerably larger than what has been measured in South Asia, Europe and USA (paper IV). A trend of enrichment in heavy stable carbon isotopes in WSOC with distance the particles have been transported from the source is observed in the South Asian region (papers II, III). Dual-isotope (Δ14C and δ13C) analysis demonstrates that WSOC is highly influenced by atmospheric aging processes. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Submitted.</p>

Isotopic methods have been developed over the last 10 years as a method for determining chemical interactions of chlorinated solvents. These methods are especially promising for. This study attempts to employ and develop compound specific isotopic analyses of TCE and cDCE, along with chemical data, to characterize the degradation of TCE in a fractured bedrock aquifers. The Smithville site is a contaminated field site with extremely high levels of TCE contamination that is currently undergoing monitored remediation. From December 2008 until April 2010 extended samples were collected from the site to provide additional data analyses including isotopic data. The redox conditions at the site are anoxic to reducing, with sulfate reduction and methanogenesis as dominant terminal electron accepting processes. Redox data indicates that well electrochemical conditions are highly variable within the site, including areas near the source zone that not very reducing. Documented changes in groundwater conditions to much more reducing environments indicate that oxidation of organic matter is occurring at the Smithville site in select wells. Chemical analyses of TCE, DCE, VC, ethene and ethane are employed determine whether reductive dechlorination was occurring at the site. Results of field testing indicate that many wells on site, especially in the proximity of the source zone, dechlorination products were found. The isotopic data had a high range in both carbon and chlorine isotopes. Chlorine isotopic data ranges from a δ37Cl(TCE) of 1.39 to 4.69, a δ37Cl(cDCE) of 3.57 to 13.86, a δ13C(TCE) of -28.9 to -20.7, and a δ13C(cDCE) of -26.5 to -11.82. The range in values indicate varying degrees of degradation throughout the site, with the same wells grouping together. Combined chemical, redox and isotopic data shows that degradation seems to be a removal process for TCE at the Smithville site. Concentrations of chemicals created as a result of TCE degradation verify degradation, especially in wells 15S9, R7 and 17S9. Historically production of DCE in significant amounts, above 1.0 ppb, was observed to only occur after 2003. In addition to this, DCE data shows that the percentage of DCE made up of cDCE is above 96%. This indicates that microbes most likely mediate the processes that formed DCE from TCE. The linear regression of the delta-delta plot for isotopic TCE data shows line that is likely a direct function of the carbon and chlorine isotopic fractionation imparted upon the original TCE released. The slope found is consistent with data collected from other studies though cannot be applied to determining the process directly given the range of variability in isotopic field data.

Speleothems are considered a reliable proxy for paleoclimatic reconstructions and analysis of stable carbon isotopes in speleothems is used for paleoclimatic reconstructions. However, in temperate areas that lacks C4 vegetation there are uncertainties in how to interpret changes in the δ13C signal. The aim of this study is toincrease the understanding of how the δ13C signal in speleothems from temperateareas can be interpreted. The study was divided in two parts, first a literature studythat focused on interpretations of the δ13C signal in speleothems from temperate areasand a case study in which a comparison of seven 13C records from similarenvironments in the Scandes Mountains and the Alps are made. The results from the literature study were used in the case study to draw conclusions on tree line and vegetation changes during Holocene in central northern Scandinavia. The study showed that trends in interpretation of the δ13C signal in speleothems from temperateareas are that low δ13C values are interpreted as wetter, warmer conditions with higherbio productivity, and high δ13C values are interpreted as colder, drier conditions withlower bio productivity. Further it was found in the study that vegetation changes seen in Holocene pollen data are also seen in δ13C records from Scandinavia. The δ13Csignal in temperate speleothems therefore appears to be related to changes invegetation density and to tree-line changes.