The main aim of this project was to consider the geochemical behaviour of a suite of radionuclides (137Cs, 241 Am, isotopes of Pu, Th and U and 234mpa)in the Ribble estuarine environment. Controls on the vertical distribution of radionuclides in sediment deposits were considered and the fluxes of sediment and radionuclides at sites close to the river channel were investigated. Vertical activity distributions were studied by taking cores from various intertidal sediment deposits. Sediment/activity fluxes were studied by installing sediment traps. All samples were analysed by gamma spectrometry. Selected samples were analysed for total organic carbon, mineralogy (XRD), major and trace-metals (XRF), grainsize distribution (laser granulometry) and alpha-emitting radionuclides (alpha spectrometry). The geochemical phase associations of radionuclides were investigated using sequential extraction experiments. Sellafield-derived radionuclides exhibited distinct subsurface maxima (up to 4 785 ± 42 Bq kg" 137Cs, 618 ± 14 Bq kg" 239,240pUand 868 ± Bq kg" 241Am) in mature saltmarsh sediment deposits. Thorium-230 exhibited more complex depth profiles (maximum = 2383 ± 36 Bq kg"). Variations in grain-size were low and therefore not important in controlling the specific activity variation with depth at these sites. The effects of early diagenesis on the specific activity profiles of 137Cs, 241 Am, 239,240pU and 230Th were small. The vertical distribution of Sellafield-derived radionuclides reflected the cumulative discharge pattern from Sellafield implicating a sediment transport mechanism that has involved the integration of contamination from previous discharge events. The vertical distribution of 230Th reflected the annual discharge pattern from BNFL Springfields implicating a transport pathway that involves little mixing of sediment. Levels of Springfields-derived 234mpaand 234Th were highly variable in time and space «0.5 - 495 kBq kg' recorded at Penwortham over the course of the study). The antecedent river discharge regime appears to be the dominant influence on the specific activity of these radionuclides at upstream sites.

Investigations into the effects of anthropogenic disturbance on greenhouse gas emissions from tropical peatlands are relatively well documented. However, the effects of such disturbance on fluvial carbon (C) losses has, thus far, been overlooked and remains unaccounted for in these ecosystem C budgets. Here, three land-cover classes in Central Kalimantan, Indonesia, were investigated in order to determine the effect of tropical peatland disturbance on fluvial organic C budgets. Intact peat swamp forest (IPSF), moderately disturbed and severely disturbed peat swamp forest (DPSF1 and 2) catchments were monitored for one year. Results demonstrate a trend of increasing annual total organic carbon (TOC) yields with increasing drainage severity, from 63 in IPSF to 105 and 131 g C m-2 y(1 in DPSF1 and 2, respectively. Including this routinely-ignored fluvial C loss component in the disturbed peatland ecosystem C budget increases the estimated total C loss by 30%. Radiocarbon analysis of dissolved organiC carbon (DOC) reveals that whilst DOC leaching from IPSF was derived from recent primary production, DOC leaching from the two disturbed sites was comprised of much older C, originating from deep within the peat column. The TOC flux from the Sebangau River basin was estimated to be 0.46 teragrams y(1, which upon regional extrapolation indicates that Indonesian rivers account for 10% of the global annual riverine DOC export to the ocean. There were no significant differences between sites in the quality of the organic C lost, but DOC lost from disturbed sites was generally less aromatic than from the intact site. It is recognized that a large portion of this labile C will be emitted to the atmosphere via biotic decomposition. Since 1990, peatland disturbance has resulted in a 53% increase in fluvial organic C export from Southeast Asia, an increase that alone approximates the entire annual fluvial organic C flux from European peatlands.

Speleothems are key archives of palaeoclimatic information, chronologies for which can be precisely derived by Uranium Series methods. This investigation uses stable isotopes, trace elements and petrography in speleothems from the Eastern Mediterranean to reconstruct palaeoclimatic parameters in the area over the last -100 ka. Speleothems were collected along a transect from North-East to South West Turkey to Greece. Five stalagmite samples were selected for detailed geochemical analysis which was anchored by - 30 Uranium-Series dates. Most notably, oxygen isotope ratios in a stalagmite from Karaca cave, northeast Turkey exhibit similar temporal patterns to the Greenland ice core oxygen isotope records and to Chinese speleothem records of East Asian Monsoon (EAM) fluctuations over the period 77 ka to 6 ka. Winter rainfall maxima in north-east Turkey coincide with periods of intensified EAM. The isotope curve is interpreted as an insolation (precession) forced record of rainfall seasonality on glacialinterglacial timescales, with periods of high Northern Hemisphere insolation giving rise to cool wet winters and hot dry summers. Millennial-scale variability is caused by shorter-term changes in seasonality of precipitation and/or switching of moisture source areas in response to the stadial-interstadial climatic oscillations originating in the North Atlantic Basin and widely recorded in both marine and terrestrial climate records. Oxygen isotope rations in a 21 ka to7 ka stalagmite from southern Greece are interpreted similarly to Karaca. Shifts in S13C values in the record are related to soil biogenic activity. An isotopic event at 21 ka is interpreted as a short term increase in winter rainfall in response to increased seasonality due to increased insolation (precession). In south-west Turkey the 110 ka to 68 ka KE- I record is characterised by several large shifts in &180 and 613C corresponding to MIS 4,5a, 5b and 5c. These variations are again related to changes in seasonality of rainfall and are correlative with the Hulu speleothem record and Greenland ice core oxygen isotope records.

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No description available.

Characterisation of three lava flow fields from the Columbia River Basalt Group (CRBG), USA, reveals compositional heterogeneity on all scales, from adjacent lava lobes to the intra-crystal scale. Simple flow fields can be traced from vent areas to distal reaches, but those with multiple-layered lobes present a degree of complexity that make lava pathways and eruption sequences difficult to identify. A 3-D model based on field investigation of a single flow field establishes a volcanological context for geochemical sampling. Compositional v.ariation within each flow field suggests that small-scale geochemical heterogeneity is common within and between lobes of these flood basalt lavas. Lobe cores emplaced during the latter stages of an eruption have less evolved compositions and more enriched incompatible elements, suggesting progressive variation of magma composition caused by either recharge or sequential tapping of compositionally zoned magma. Progressive crustal contamination of magma during a single eruption is indicated by Re-Os isotope ratios. Initial 1870s/1880s ratios range from 1.405 in the earlier emplaced lava crust to 0.128 in the latter emplaced lava core. These values are more radiogenic than any known enriched sources (normative mantle -0.127, HIMU -0.15) consistent with previous data that indicate that neither an enriched source nor sub-continental lithospheric mantle can be the source of CRBG magma. Os isotope signatures can be explained by different degrees' of contamination of two isotopically distinct lithologies represented by the North American craton and Jurassic accreted terranes underlying the province. Intra-crystal Sr isotope analyses within a flow field record variable histories in an open magmatic system. Results suggest crystal residences in an increasingly contaminated melt within the crust with several recharge events of less-contaminated more primitive basaltic melt. Assembly of melt and crystal cargo occurred immediately prior to eruption without significant residence times in the final host magma. The combined compositional evidence suggests that an extensive shallow-crustal network of dykes and sills supplied magma to the CRBG eruptions.

<i>In situ </i>produced cosmogenic ³He provides independent support for the existence of a stable hyper-arid polar climate within East Antarctica since the mid-Miocene. Cosmogenic ³He concentrations have been measured in over sixty boulders from glacial deposits in the Dry Valleys providing both age constraints for glacial events and quantitative erosion rate estimates for the region. Through these analyses, the processes that control cosmogenic ³He concentrations in moraine boulders are assessed. The interpretation of cosmogenic ³He exposure ages has been improved through, (a) the incorporation of erosion rate estimates, and (b) quantitative correction for non-cosmogenic ³He in Ferrar dolerite pyroxenes. Sub-glacial flood deposits in the northern Dry Valleys were exposed as the overriding ice retreated over the Transantarctic Mountains and out of the Dry Valleys, at approximately 15 Ma. The cosmogenic ³He concentrations suggest exposure ages of between 8.6 and 10.4 Ma approximately 25% lower than ⁴⁰Ar/³⁹Ar age estimates that have been used to constrain the retreat of the ice sheet. Applying an erosion rate correction of between 0.03 and 0.04 m Ma^-1 implies these samples were deposited 15 Ma as the ice retreated from the Dry Valleys. Nearby Ferrar dolerite bedrock surfaces confirm the occurrence of very low rates of erosion in the region, with surfaces eroding at an average rate of 0.17 m Ma^-1. Non-cosmogenic ³He, both derived from mantle and nucleogenic sources, can cause cosmogenic ³He analyses to overestimate the surface exposure age of magnetic rocks > 1 Ma. Ferrar dolerite from a mining drill core at a depth of over 600 m has never been exposed to cosmic rays. The 8.46 x 10⁶ at g^-1 measured in pyroxene from this sample is close to the theoretical production of nucleogenic ³He in the mineral based on measured U, Th and Li concentrations. This makes less than 1% difference to the majority of samples analysed within this work but becomes more important in Quaternary surfaces. Constraining erosion rates and estimating levels of non-cosmogenic ³He increases the accuracy with which cosmogenic ³He dating techniques can be applied to the glacial history the Dry Valleys. The existence of mid-Miocene aged flood deposits from the northern Dry Valleys confirm the antiquity of the landscape and support the existence of a stable hyper-arid polar climate and consequent limited geomorphic landscape evolution since this time. There must however be some flexibility within the stability model.

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No description available.

No description available.