Mass balance calculations illustrate that the incorporation of silicate within sulphide analysis has a variable impact on the REE profiles, depending upon the degree of contamination and the REE characteristics of the silicate phases. Manganiferous Chert Deposits Manganiferous cherts are dominantly biogenic, produced from radiolarian tests, with only minor participation of hydrothermal and hydrogenous sources. Reduced detrital input is necessary for a thriving radiolarian population, and as the depositional basins were compartmentalised and separated by small ridges, this suggests that the surface area of sediment source areas was diminished. Absence of radiolarian tests is attributed to recrystallisation, as tests initially comprise amorphous silica. Chert REE and Nd-isotope geochemistry is variable and this is attributed to the presence or absence of detrital and/or volcanic material, which overprints the initial hydrothermal characteristics. This variation in signature is dominantly controlled by the spatial location of the chert, within the depositional basin., Genetically, both the massive sulphides and chert deposits are independent, the cherts being biogenic and sulphides being hydrothermal. Additionally, both may be precipitated concurrently. It has been previously suggested that sulphides were preserved and oxidation hindered, by the presence of siliceous gel cap. This is not necessary if bottom-hugging brines were present. This factor explains why sulphides are preserved in the absence of a capping horizon.

No description available.

The late Pliocene is marked by the end of an interval of warm, relatively stable global climate and a secular shift into a bipolar glaciated world. The intensification of northern hemisphere glaciation (iNHG) central to this climatic transition was accompanied by a decrease in atmospheric carbon dioxide concentrations and commenced around 3.5 million years ago. The climate forcing and response mechanisms involved in the iNHG are subjects of ongoing debate in the palaeoclimate literature. In this thesis, I reconstruct palaeoproductivity and suborbital climate fluctuations during this important interval, with particular focus on the first three consecutive, large, obliquity-paced glacial-interglacial cycles (marine isotope stages, MIS, 101-95), using proxy methods applied to deep-sea sediments in the equatorial oceans and the North Atlantic. In this way, I evaluate the forcing mechanisms, biogeochemical cycles and climate implications during the late Pliocene. In Chapter 2, palaeoproductivity is reconstructed in the western and eastern equatorial Pacific Ocean. Data reveal that productivity fluctuations are in phase between east and west and are obliquity-paced. This implicates high-latitude rather than local forcing of export productivity and no apparent role for east-west thermocline tilting on these timescales, as previously proposed. In Chapter 3, multi-proxy palaeoproductivity reconstructions in the eastern equatorial Pacific and Atlantic Ocean upwelling zones are considered in terms of proxy applicability and export productivity. Results suggest that alkenone accumulation may be a useful indicator of export productivity and that the late Pliocene biological pump was stronger during glacials than interglacials. In Chapter 4, an inferred secular productivity shift is investigated using calcareous nannofossil assemblages. Assemblage shifts at an equatorial Pacific and a North Atlantic Ocean site support the interpretation of an increase and a decrease in export productivity, respectively. Implications of a strengthened tropical biological pump at this time are considered. In Chapter 5, high-resolution climate records are used to investigate suborbital variability at North Atlantic Integrated Ocean Drilling Program Site U1313. Data indicate that only smallamplitude suborbital variability occurs during the late Pliocene, with no amplification within the boundary conditions and inferred ice-volume variations of MIS 103 to 95.

The geochemical significance of on-axis diffuse fluids, in addition to those formed during the waning phases of hydrothermal systems and off-axis crustal ageing processes, has been investigated through a comparison of the rare earth element (REE) systematics of hydrothermal materials from the ore-forming hydrothermal systems of the TAG vent field, 26 N Mid-Atlantic Ridge, and 90 Myr Troodos Ophiolite, Cyprus. Ophiolites integrate a long (c. 20 Myr) history of seafloor alteration, which reflects both , axial and off-axis hydrothermal processes. Spatially-resolved laser ablation inductively coupled plasma-mass spectrometric (LA ICP-MS) REE analyses of individual alteration phases within stockwork-mineralised Troodos lavas have been used to deconvolve the complex alteration processes associated with crustal generation at an oceanic spreading ridge. REE mobility was associated with the development of both high- (-200 to 350 C) and lowtemperature (<100 C) secondary phases which precipitated within contrasting alteration regimes (discharge- and recharge-dominated respectively). Low-temperature alteration phases are the major repository for the REEs in lavas which are depleted in the light REE Eu relative to pristine volcanic glass compositions. These data indicate that much of the REE signature of the alteration pipe is a post-mineralisation overprint acquired in the waning stages of hydrothermal activity and during the protracted alteration of the oceanic basement, rather than on-axis greenschist facies hydrothermal alteration. Submersible and drilling studies of the TAG mound have led to the development of models of mound growth and fluid evolution within an actively-forming seafloor sulphide deposit. The REEs have been used to test the applicability of these models to processes of sulphide mound and metalliferous sediment formation which occurred within the Troodos ophiolite. The REE patterns of umber, ochre and sulphide sampled from a section through the top of the Skouriotissa ore body clearly demonstrate extensive seawater ingress and circulation throughout the upper ore body during waning hydrothermalism and cooling of the mound, which has resulted in the overprinting of any original hydrothermal signatures in both mound sediments and sulphides. This study has demonstrated that the geochemistry of the sulphide mound deposits continues to evolve following the peak of hydrothermal activity, and that the seawater overprinting of the Skouriotissa deposit is the end product of a process which we only see the initiation of on the modern seafloor. At TAG, the origin of far-field Mn and Fe-rich oxide crusts has remained controversial over 25 years of investigations of the vent field. The REE and Nd isotope data presented in this thesis indicate these ferromanganese deposits are forming by a combination of sedimentation of Mn-rich particulates from the TAG hydrothermal plume, and direct precipitation from diffuse hydrothermal fluids seeping from the rift valley wall. The REE data reveal that the separation of manganese from other hydrothermally-derived metals at TAG is due to both plume processes and the spatial distribution of diffuse flow within the vent field. The studies presented in this dissertation have demonstrated the use ofREEs as tracers of chemical processes in ancient and modem hydrothermal systems on a wide range of temporal and spatial scales.

Amersham plc, now GE Healthcare, has discharged both organically bound tritium (OBT) and tritiated water (HTO) into the Severn estuary since 1981. The OBT component of these discharges results in elevated tritium (3H) activities in the sediments and biota of the estuary. A monthly sampling programme, covering February 2000 to May 2004, has provided the first detailed description of the spatial and temporal distribution of 3H activities in surface sediments from the estuary. Four sediment cores were also collected from salt marshes on the northern shore, to obtain longer term records of tritium accumulation. The spatial distribution of sediment 3H activities correlates well with predicted patterns of suspended sediment circulation, with higher activities (up to 3 Bq/g dry weight) in sediments from sites within 10 km of the Amersham plc discharge point and at a greater distance to the east. Temporal variations in the 3H activities of both surface and core sediments are predominantly controlled by the magnitude, composition and pre-discharge treatment of organic 3H discharges from Amersham plc, with secondary sediment composition effects; lower 3H activities are generally measured in sandy/gravelly sediments than in muddy sediments. The dated sediment 3H activity profile in one of the salt marsh cores corresponds to the Amersham plc OBT discharge record, indicating that 3H is persistent in sediments over a period of 25 years. Up to 60 % of the OBT in sediments could only be extracted with strong acids and bases, indicating that it may be composed of large, complex and hydrophobic compounds that are only extractable when lysed, such as humic compounds and/or large biomolecules. The sediment-bound fraction of OBT is predicted to be less than 2 % of the total organic tritium discharged from Amersham plc, however, these molecules do have the potential to remain in salt marsh and subtidal mud patch sediments for decades, unless the sediments are eroded and resuspended, until tritium activities decline by radioactive decay.

This dissertation introduces the habitat use and spatial-temporal distribution of Cuvier’s beaked whale (Ziphius cavirostris, Cuvier, 1823) in the Bay of Biscay, from surveys carried out by the Biscay Dolphin Research Programme between 1995 and 2007. I have analysed the spatio-temporal distribution of Cuvier’s beaked whale, using dedicated and opportunistic sightings and the interactions with fixed physical variables (depth, slope and aspect), non-fixed environmental variables (sea surface temperature) in the Bay of Biscay, northeast Atlantic. This study used a differing combination of environmental variables and modelling: GAM (General Additive Model), and ENFA (Ecological Niche Factor Analysis), and PCA (Principal Component Analysis). Geographical Information Systems (GIS) and Remote Sensing were used to achieve this. The habitat preferences of Cuvier’s beaked whale showed strong correlations with water depths >1000m and <4000m and steep slopes, associated with the Capbreton canyon, in the southeast Bay of Biscay and the continental shelf slopes in northern Biscay. Areas of high suitability for Cuvier’s beaked whale were predicted for the Bay of Biscay and predictions showed high habitat suitability areas over continental shelf slopes and submarine canyons. The variety of modelling techniques used to identify the habitat preferences and to predict areas of high suitability for Cuvier’s beaked whale in the Bay of Biscay all proved advantageous. On a global scale, techniques such as these could be applied to help research worldwide for future implementations of protected areas to conserve and maintain this species. The abundance and distribution of Cuvier’s beaked whales varied between years and seasons, with an increase in sightings over time and a seasonal distribution shifting north during spring and summer. Stranding records were also analyzed and compared with the sightings data, which identified regional patterns in seasonal distribution between France, the UK and Ireland. In addition to Cuvier’s beaked whale, this study investigated other deep-diving cetaceans (Northern bottlenose whale, Hyperoodon ampullatus, Sowerby’s beaked whale, Mesoplodon bidens, Sperm whale, Physalus macrocephalus, Pilot whale, Globicephala melas) and non-deep diving cetaceans (Fin whale, Balaenoptera physalus, and Common dolphin, Delphinus delphis) observed in the Bay of Biscay and the English Channel. The Bay of Biscay is the most northerly range of the Cuvier’s beaked whale in the eastern north Atlantic and with year round observations, it could be suggested the population may be resident. This raises the question, could Cuvier’s beaked whale act as a predictor of increasing water temperatures because of climate change by shifting their distribution further north.

The thesis describes the development of analytical procedures for the isolation and measurement of anthropogenic pure beta-emitting radioisotopes in low-level radioactive wastes and environmental samples. The research focussed on three key pure beta-emitting radioisotopes, namely 63Ni, 90Sr and 99Tc. Iron-55, which decays by electron capture, was also investigated. Source preparation and measurement techniques based on liquid scintillation counting were developed and optimised to permit the low-level measurement of all four radioisotopes. In particular, a technique was developed for increasing the amount of stable Fe that may be loaded into scintillant, reducing the limit of detection achievable for 55Fe measurement and increasing the sensitivity of analysis for 55Fe in Fe-rich materials such as sediments and steels. Chemistries for the isolation of the four radioisotopes were studied and optimised. Solvent extraction was chosen for the specificity offered by the technique. In most instances, improvements in separation efficiency were achieved by adsorbing the extractant onto an inert support producing an extraction chromatographic material. Key separation techniques were then combined to produce a sequential separation scheme that permitted a more rapid analysis of the four radioisotopes on a single sample. The sequential separation technique was then optimised for the analysis of 55Fe, 63Ni, 90Sr and 99Tc in both low-level wastes and environmental matrices (mainly sediments). Such separation schemes are crucial to the efficient analysis of samples in limited time spans and are vital when the amount of sample available is restricted. The optimised methods were used to investigate levels of anthropogenic pure beta-emitters in a saltmarsh sediment core collected from the Esk Estuary in Cumbria. Analysis of the four beta emitting radioisotopes was complemented by the analysis of major elements, trace elements and gamma emitting radioisotopes. This information was used to determine the behaviour of the beta emitters following deposition within the saltmarsh environment. Although all four beta emitters were detected in the core, only 90Sr and 99Tc were at sufficiently high levels to permit a more thorough investigation. The combination of geochemica! analysis and radiochemical analysis of this range of radioisotopes with widely varying chemistries has allowed a range of possible pre- and post-depositional processes to be investigated as well as providing data on the levels of previously unmeasured beta emitters in the saltmarsh environment. Such information is essential in assessing the long-term retention and potential re-release of these radioisotopes and their importance in radiological dose assessment. The information also has wider implications to the behaviour of inorganic pollutants in coastal waters.

The sediments of the eastern Mediterranean Sea contain Corg-rich layers, termed sapropels, interbedded with Corg-poor sediments which form by far the greater part of the sedimentary record. This research presents a high-resolution geochemical investigation on slowly- and rapidly-accumulated SI units. Mn, Fe, I and Se profiles in slowly-accumulated SI units (5-10 cm.kyr"1) have shown that these sapropels are affected by post-depositional oxidation following their formation which produces a much thinner sapropel than was originally deposited. In the slowly-accumulated examples investigated, up to 11.5 cm of the original sapropel has been lost through oxidation in as little as 6 kyr. Downward progression of the redox front causes the remobilisation and re-arrangement of redox-sensitive elements (As, Fe, I, Mn, Mo, Se, U and V) around the oxic/post-oxic boundary. Concentration-depth profiles of the redox-sensitive elements in SI have shown that these elements are immobilised in oxic and post-oxic conditions or both. It is noted that I and Se form well-defined peaks at the top of SI, and it is suggested that these two elements may be reliable markers for defining the location of an active oxidation front in the absence of pore water measurements. During this research, it was discovered that Hg behaves similarly to I and Se at the oxic/postoxic boundary, forming a well-defined peak in post-oxic conditions. In turbidite and sapropel examples, Hg is always closely associated with Se and it is suggested that Hg and Se become immobilised through the formation of the selenide mineral tiemannite (HgSe). The presence and persistence of Hg peaks in both recent and ancient sediments (up to 4 Ma) implies that Hg may be a useful diagnostic tool for defining the locations of both active and relict oxidation fronts. Investigation of two rapidly-accumulated Sis from the Adriatic (MD 90-917) and Aegean Seas (LC21) has shown that these cores have suffered negligible post-depositional oxidation due to rapid accumulation rates. The validity of the Ba/Al ratio as a more reliable and persistent productivity index has been confirmed in both LC21 and MD 90-917 where Ba/Al is directly related to Corg content over the entire visual SI units. In both cores SI appears as a doublet. This doublet is centred on 7.5 kyr BP and geochemical and micropalaeontological evidence indicates that this "saddle" is best interpreted as an episode of improved reventilation and increased deep-water O2 concentrations. A number of redox-sensitive elements are enriched (Cr, Mo, Ni, S, Se, U, V and Zn) in LC21 and MD 90-917, and exhibit double peaks in their concentrationdepth profiles. The principal routes by which SI develops high authigenie levels of redox-sensitive elements are: (i) pre-concentration in the water column by biological uptake followed by deposition at the sedimentwater interface and/or (ii) diffusion from seawater through pore waters into sediments followed by reduction and immobilisation under more reducing conditions. Under more reducing conditions, redox-sensitive elements are immobilised through associations with Corg, pyrite, sulphides or form insoluble solid phases (e.g. U is precipitated and immobilised as UO2(S)). Palaeoproductivity estimates based on Ba/Al weight ratios indicate that productivity was up to 5 times higher during SI formation compared with the present. It is suggested that high productivity was initiated by the formation of a deep chlorophyll maximum formed in response to an increased input of freshwater into the eastern Mediterranean. During SI formation, the flux of Corg greatly exceeded the supply of dissolved O2 to the bottom waters and so it is inferred that deposition of SI occurred under anoxic conditions. Interpretations of geochemical parameters such as S/C criteria, I/Corg and V/(V+Ni) ratios and framboidal pyrite sizes all indicate that bottom waters were anoxic-non sulphidic rather than anoxic-sulphidic during SI formation. The geochemical interpretation is in agreement with the benthic foraminiferal data, which show that the two S1 layers have an abundance of low-oxygen tolerant species. It is unclear whether anoxic conditions are induced by increased productivity alone or through a combination of increased productivity and reduction in deep-water formation. Evidence presented indicates that productivity and preservation are both necessary prerequisites for SI deposition. SI initiation and cessation was investigated by AMS 14C dating based upon the Ba/Al ratio criterion. AMS 14C ages for slowly-accumulated sapropels indicate that SI formation started at 10 kyr BP and ended by 5.3 kyr BP. For the rapidly-accumulated cores, the onset and termination of SI is more variable although SI was underway by 9.5kyr BP and complete by 6.0 kyr B.P. The offset in ages is attributed to bioturbation mixing artefacts affecting the Ba/Al signal in the slower-accumulated cores. Since rapidly-accumulated cores are not significantly affected by bioturbation, the best estimate for the duration of SI is 9.5-6.0 kyr B.P.

The diagenetic re-mineralisation of seafloor-sulphide deposits and the role of microbes in the metal-exchange processes were investigated in metalliferous sediments from the Alvin relict hydrothermal zone in the TAG area at 2608'N (Mid- Atlantic Ridge). The solid-phase and concomitant pore water concentrations of AI, Si, Ca, Clot, Corg, S, Fe, Mn, Cu, Zn, P, V, Co, U, Mo, Au, Ag and REE's were measured in a 230 cm long gravity core from the southern periphery of the relict vent field. These measurements were complemented by detailed analysis of bacterial abundance and specific activity. The altered sulphidic sediments are capped with a ~30cm thick layer of carbonate-rich (~60% CaCO3), Fe-stained sediments. Two distinct sulphide layers, interbedded with Fe-oxysilicates, and overlain by a thin layer of Fe/Mn oxyhydroxides, were found in this core. The dominant mineral-phase in both sulphide layers, which originate from mass-wasting of mound sediments, is pyrite with some goethite. Reaction of the exposed metal-sulphides in the upper sulphide layer with seawater has produced a thin layer of secondary atacamite, which is enriched in Au. Primary sphalerite is dissolved in the upper sulphide layer and re-precipitation as secondary sphalerite directly above and below. U continues to be scavenged from the porewater, producing marked enrichments on oxidised sulphide rims. The re-mineralisation processes identified in this core are in close analogy to the large-scale zone-refining that has been described for the active TAG mound and ancient ore-deposits. REE/Fe ratios clearly distinguish between plume derived sediments in the carbonate cap and slumped material from the hydrothermal mound. The REE signature of bulk sediments and clay phases imply multiple stages of alteration by diffuse fluids in the upper sulphide layer and intermediate layer, whereas the lower sulphide layer is not affected. Alteration by reactive low-temperature hydrothermal fluids is also inferred to be responsible for the observed diagenetic overprinting of trace-metal distributions in the upper sulphide layer. The intermediate layer is rich in nontronite, which has been precipitated in situ from diffuse fluids. The presence of Mn- and Fe-reducing bacteria coincide with elevated porewater concentrations of Mn and Fe, indicating direct involvement of bacteria in the cycling of these metals. Total counts of viable cells and general activity measurements show that although bacterial populations are relatively small, they are healthy and well adapted to this potentially toxic environment. The existence of active microbial communities in metalliferous sediments may therefore provide a continuum of bacterial populations between high and low temperature hydrothermal systems, thus representing an important transitional stage in the hydrothermal ecosystem. Microbial reduction and oxidation of S was observed throughout the core, indicating that microorganisms are particularly active in terms of S-cycling. For deep-sea sediments extremely high sulphate reduction rates (67 nmol/cm3/d) were measured in the ironstained carbonate cap. In the absence of significant organic carbon (~0.2 %) this strongly suggests the synthesis of alternative electron-donors by chemolithotrophic bacteria to support the observed high rates of heterothrophic activity in these sediments.

The aim of this thesis is to contribute to the observational database in order to address fundamental questions as to how dissolved organic nutrients influence N and P budgets, how they affect nutrient cycling and the sustainment of biological production within two major ocean oligotrophic gyres: the Southern Indian Ocean gyre and the subtropical North Atlantic gyre. A transect across the Indian ocean at 32°S conducted in March/April 2002 was sampled for dissolved oxygen, inorganic and organic nutrients and phytoplankton pigments concentrations. A second cruise was undertaken in April/May 2004 across the oligotrophic North Atlantic Ocean at 24oN. A similar set of samples were collected on the second cruise and in addition the stable nitrogen isotopic signature of particulate organic matter was determined plus surface enzymatic activity and primary production incubation measurements. The Indian ocean basin is characterized by low N:P ratios both in the inorganic and organic fractions with respect to phytoplankton nutrient requirements driven by an excess of denitrification over N2 fixation. The strongly non-Redfieldian TON:TOP ratio suggests a decoupling of TON and TOP remineralization processes and indicates a severe TON deficiency brought by the strong nitrate limitation that leads to a community demand for TON. TON and TOP Ekman meridional advection played a small but not trivial role in providing N and P into the gyre to support export production. It is estimated that the contribution of TON advection is of the same order as the new N supplied by N2 fixation into the gyre. In the Indian Ocean 40% of the net N transported by the overturning circulation across the boundary at 32°S, is attributable to organic nutrients. To close the N budget assuming the upper range estimates of denitrification to be correct, the inclusion of organic nutrient transport by the ITF is required. Hence, the Indian Ocean N budget conforms to a steady state where excess of denitrification over N2 fixation is compensated for by atmospheric, riverine and a hypothesized flux of DON in through the ITF. In the permanently stratified North Atlantic subtropical gyre, nutrient supply pathways for the growth of phytoplankton are unclear and appear inadequate for the maintenance of the observed export production. Here the significance of two mechanisms, N2 fixation and the bioavailability of organic nutrients, has been investigated. The computation of a new geochemical proxy, TNex, for the determination of N to P anomalies suggests that N2 fixation is more important than previously thought. The spatial distribution of the isotopic composition of particulate organic matter shows a N2 fixation signal across most of the basin with the exception of the coastal margins and a central region. Thus no latitudinal gradient in diazotrophy, as suggested by other workers, is apparent. TON and TOP represented not only the major component of the upper ocean N and P pools but were also bioavailable to the community through the release of extracellular enzymes. The cycling of TON and TOP was decoupled, with higher turnover rates of the TOP pool as compared to the TON pool. Both TON and TOP could potentially sustain a significant fraction of primary production and TOP could potentially provide nearly all the P needed by N2 fixers. In conclusion, in the permanently stratified North Atlantic subtropical gyre, N2 fixation and the bioavailability of organic N and P appear to be major mechanisms for supplying nutrients and sustaining phytoplankton growth.