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Chemical weathering of silicate rock consumes atmospheric CO2 and supplies the oceans with cations, thereby controlling both seawater chemistry and climate. The rate of CO2 consumption is closely linked to the rate of CO2 outgassing from the planetary interior, providing a negative feedback loop essential to maintaining an equable climate on Earth. Reconstruction of past global temperatures indicates that a pronounced episode of global cooling began ~50 million years ago, coincident with the collision of India and Asia, and the subsequent exhumation of the Himalayas and Tibet. This has drawn attention to the possible links between exhumation, erosion, changes in silicate weathering rates, and climate. However, many of the present-day weathering processes operating on the continents remain debated and poorly constrained, hampering our interpretations of marine geochemical archives and past climatic shifts. To constrain the controls on silicate weathering, this thesis investigates the lithium (Li) isotopic composition of river waters, suspended sediments and bed load sediments in the Alaknanda river basin, forming the headwaters of the Ganges. Due to the large fractionation of Li isotopes in the Earth’s surface environment, Li is sensitive to small changes in silicate weathering processes. As a consequence of the pronounced gradients in climate (rainfall and temperature) and erosion across the basin, the river waters show large variations in their Li isotopic composition (δ7Li), ranging from +7.4 to +35.4‰, covering much of the observed global variation. This allows a detailed investigation of the controls on Li isotope fractionation, and by extension silicate weathering. The Li isotopic composition is modelled using a one-dimensional reactive transport model. The model incorporates the continuous input of Li from rock dissolution, removal due to secondary mineral formation, and hydrology along subsurface flow paths. Modelling shows that the Li isotopic variations can be described by two dimensionless variables; (1) the Damköhler number, ND, which relates the silicate dissolution rate to the fluid transit time, and (2) the net partition coefficient of Li during weathering, kp, describing the partitioning of Li between secondary clay minerals and water, which is primarily controlled by the stoichiometry of the weathering reactions. The derived values of the controlling parameters ND and kp, are investigated over a range of climatic conditions and on a seasonal basis, shedding light onto variations in the silicate weathering cycle. In a kinetically limited weathering regime such as the Himalayan Mountains, both climate and erosion exert critical controls the weathering intensity (the fraction of eroded rock which is dissolved) and the weathering progression (which minerals that are being weathered), and consequently the fractionation of Li isotopes and silicate weathering in general. Modelling of the Li isotopic composition provides an independent estimate of the parameters which control silicate weathering. These estimates are then used to constrain variables such as subsurface fluid flux, silicate dissolution rates, fluid transit times and the fraction of rock which is weathered to form secondary clay minerals. The simple one-dimensional reactive transport model therefore provides a powerful tool to investigate the minimum controls on silicate weathering on the continents.

This research examines the relationship between the ways in which urban families engaged local landscapes and the development of shared identities at the prehispanic Maya city of Actuncan, Belize. Such shared identities would have created deep historical ties to specific urbanized spaces, which enabled and constrained political expansion during the Terminal Classic period (ca. A.D. 800–900), a time when the city experienced rapid population growth as surrounding centers declined. This research contributes to the understanding of urban processes of growth and decay in this region, and how they are linked to the behaviors of social factions in settlements. For communities, group identity can provide a sense of connection to place that integrates people at various social levels, provide an individual with social memories and meanings that can be applied to understanding and interpreting material life, and foster a common sense of self and awareness. Daily activities and their engagement with the material world entangle social meanings, values, and relationships. Further, spaces in which people reside and perform these tasks often affect the meanings and values associated with the activities themselves. The combination of shared practices and the spaces in which they occur is ultimately what helps to create and maintain group identity. To investigate household relationships, this research considers the nature and location of activity patterns in and around three commoner houses to infer shared practices and the shared identities that those activities both enabled and constrained. Importantly, this research investigates not only the architectural areas that each house comprises, but also the open areas surrounding them. The goal of this research is to determine similarities and differences in the use of space throughout the sample area. Were open spaces used in similar ways to residential groups? Did Terminal Classic residents of the Northern Settlement conduct similar activities in all of the residential groups? Alternatively, were these groups locations for different types of practices? To explore activity patterns, multiple methods were employed, including subsurface testing, soil chemical residue analysis, and macro– and microartifact analysis, to produce overlapping datasets of the sample area. Systematic testing using postholes was used to understand open spaces between architecture in addition to the architectural space itself. Through posthole sampling, macroartifacts, microartifacts, and soil samples were obtained for further examination. The aim of artifact analysis was to examine artifact diversity and density within the residential groups as well as between them to aid in the identification of activity loci. Additionally, soil chemical residue analysis was employed to investigate activities. Similarities and differences between artifact and chemical patterning can provide insight into shared practices. By creating multiple lines of evidence from independent datasets, inferences about activities can be more strongly supported. The artifact and chemical data were examined spatially using geostatistics as well as with quantitative assessment. The results suggest that Terminal Classic residents of Actuncan were extensively utilizing not only the formal patio spaces of residential groups but also the interstitial spaces in between. Additionally, it is argued that one group appears to have been a locus for affiliative ritual practices in connection with ancestor veneration.

Lakes and lake sediments from four areas around the Antarctic Peninsula are described. The concentrations of trace metals in sediment are found to be a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environment. A tephrochronology based on Deception Island tephra is developed, and used to cross date sediments from different lakes in order to overcome the radiocarbon dating problem of the area. The fluctuating concentrations of copper and phosphorus from penguin guano in the sediment of Lake Boeckella are used as a proxy for the penguin inpact on the sediment, and the size of the penguin rookery on the shores of the lake. Anthropogenic activities in the area, as well as climatic changes are discussed in relation to the rookery size. A radiocarbon dating model developed for the sediment of Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. The model is used to achieve more accurate radiocarbon dates of the Lake Boeckella sediment. This model, or a modified version, may contribute to a higher dating accuracy and a better understanding of the dating problems in Antarctica. Deglaciation dates, as well as data on the climatic and environmental history of Byers Peninsula on Livingston Island, South Shetland Islands, of Hope Bay, Antarctic Peninsula and of Hidden Lake area, James Ross Island are given. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 6 uppsatser.</p> / digitalisering@umu

The leakages of metals from acid sulfate soils and their potential toxicity to benthic invertebrates were studied in the sediment profiles of Lillkvasjön and Lövselefjärden - a lake and an estuary known to be affected by acid sulfate soils - in Västerbotten, northern Sweden. The concentrations of 25 different elements were analyzed throughout both sediment profiles through X-Ray Fluorescence (XRF) Spectrometer analysis. Organic matter was measured through loss-on-ignition (LOI). By performing correlation analysis and normalizations to LOI on all sediment variables, Cu, Fe, Ni, Pb, S and Zn were found to be leached from acid sulfate soils to both sites, while Mg and Mn were related to leakages from acid sulfate soils in Lövselefjärden. The concentrations of Cu (195 mg kg-1), Ni (55 mg kg-1), Pb (90 mg kg-1) and Zn (398 mg kg-1) in the surface sediment of Lövselefjärden were classified as potentially toxic to benthic invertebrates. In Lillkvasjön, Cu (210 mg kg-1) and Ni (87 mg kg-1) were classified to have an increased risk of negative impacts on benthic invertebrates, while the concentrations of Pb (121 mg kg-1) and Zn (329 mg kg-1) were likely to low to have any negative effects. These results strengthen previous finds of impacts from acid sulfate soils in the two catchment areas and elucidate the importance of further studies on the impact of acid sulfate soils on benthic invertebrates.

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