Universiẗat, Diss., 2002--Mainz.

Tierärztl. Hochsch., Diss., 2004--Hannover.

No description available.

Information on the concentration and distribution of dissolved methane (CH4), together with other geochemical tracers, in real time is of great value in detecting, monitoring, and understanding the functioning of hydrothermal plumes. Water column anomalies of light transmission, dissolved CH4, manganese (Mn), and iron (Fe) were located over segments 15 and 16 of the Central Indian Ridge (CIR 20ºS), in December 2006. Along segment 15, a hydrothermal plume was present at 19°33’S/65°50’E. The source might be located north of that position and dispersed along the western flank by NW-SE currents. Methane to manganese ratios suggest that methane is produced by magmatic processes. On Segment 16, evidence for 1 or 2 hydrothermal plumes were detected over a lava plain (18°20’S/65°18’E). These data suffered from uncertainties due to sampling issues, which demonstrate the need for a reliable in-situ methane sensing technology. Current in-situ methane sensing technology is based on gas partitioning across gas permeable membranes, which are poorly characterised and variable in terms of permeability and environmental pressures. Two optical techniques were laboratory tested for the measurement of dissolved methane; Near Infrared Fibre-optic Evanescent Wave Spectroscopy (FEWS) and Surface Plasmon Resonance (SPR). No detection (at the µM level) was possible with FEWS, but the second technique using SPR sensors associated with a methane specific binding chemically showed great promise. A limit of detection of 0.2 nM and a linear concentration range from 1 to 300 nM was demonstrated, under a range of temperature and salinity. In-situ deployments confirmed the suitability of the method for in-situ measurements. Values given by the sensor correlated well with the concentrations measured by traditional techniques. Future work is needed to decrease instrumental noise and to reduce the response time, and associated hysteresis effect.

The marine biogeochemistry of dissolved organic carbon (DOC) has come under increased scrutiny because of its involvement in the global carbon cycle and consequently climate change. Dissolved organic nitrogen (DON) and phosphorus (DOP), which have historically been ignored because of their suggested “biological unavailability”, have now received greater attention due to their importance in nutrient cycling, particularly in oligotrophic ecosystems. DOM, a byproduct of photosynthetic production, has important ecological significance as a substrate that supports heterotrophic bacterial growth, thereby causing oxygen consumption and regenerating inorganic nutrients. In the open ocean the net production of DOC is ultimately due to the decoupling of biological production and consumption processes. Concentrations of DOM in the surface oceans, therefore, are controlled by both physical and biological processes. This research investigates the biological factors that control the distributions of DOC, DON and DOP in surface waters, the importance of DOC degradation to oxygen consumption, the importance of DON and DOP degradation to remineralised dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP), and the C:N:P stoichiometry of DOM pool in the Atlantic Ocean. Samples were collected on Atlantic Meridional Transects (AMT) cruise 16 and 17, which crossed the southern temperate region, the southern subtropical gyre, the equatorial region, the northern subtropical gyre, and the northern temperate region. This work described here was performed as a component of the AMT programme. Concentrations of DOC and TDN were determined using a high-temperature catalytic combustion technique, and TDP concentrations were determined using a UV oxidation method. Concentrations of DON and DOP were estimated as the difference between the independent measurements of TDN and TDP. The results showed that the highest DOM concentrations were found in surface (0-30 m) waters, ranging from 70-80 µM DOC, 4.8-6.5 µM DON and 0.2-0.3 µM DOP, and decreased with increasing water depth to 45-55 µM DOC, 2.6-4.0 µM DON and 0.04-0.05 µM DOP at 300 m. The lowest DOM concentrations were observed in the deep (>1000 m) ocean, averaging 44 µM DOC, 2.3 µM DON and 0.02 µM DOP. In the upper 300 m, the concentrations of semilabile (and labile) DOC decreased by 45-95% from the surface values. DON and DOP were the dominant components of the total dissolved nutrient pools in the upper 50 m, accounting for up to 99% and 80% of the TDN and TDP pools, respectively. In the upper 300 m, semilabile (and labile) DON and DOP decreased by 50-65% and 90-95% from the surface values, respectively. The decoupled correlations between DOC/DON/DOP and chlorophyll-a and rates of carbon fixation suggested that phytoplankton biomass and rates of primary production were not the important controls of the cumulative DOC, DON and DOP. Zooplankton grazing was hypothesised to be an important factor in regulating the distributions of DOC, DON and DOP in surface waters. Poor correlations between DOC/DON/DOP and DIN/DIP suggested that inorganic nutrients were not the significant controls in DOC, DON and DOP distributions. N and P were probably retained mainly in the organic pool in the surface waters due to a hypothesised insufficient functioning of the microbial degradation. If the vertical migration of zooplankton was significant in bringing new nutrients into the surface waters, strong correlations between dissolved organic and inorganic nutrients should not be anticipated. Prochlorococcus spp. abundance was statistically linked with the concentrations of DOC, DON and DOP. The significant correlations may reflect the ability of Prochlorococcus to assimilate the labile forms of dissolved organic nutrients (including DOC), which may be quantitatively significant in surface waters of the Atlantic Ocean. The C:N, N:P and C:P stoichiometry of the bulk DOM pool deviated from the Redfield ratio of 6:1, 16:1 and 106:1, ranging from 12-18, 20-100 and 300-1400, respectively, in the upper 300 m, suggesting that the cumulative DOM was rich in C relative to N and P, and N relative to P compared to the Redfield trajectories. The offsets of the C:N:P stoichiometry relatively to the Redfield ratio were due to nutrient limitations that imposed on prokaryotic and eukaryotic microbial populations. The C:N:P stoichiometry of the bulk DOM pool showed an increased trend, with C:N = 12-16, N:P = 20-25, and C:P = 300-350 in the upper 30 m, C:N = 12-18, N:P = 50-100, and C:P = 700-1400 at 300 m, and C:N = 17-24, N:P = 79-132; C:P = 1791-2442 at 1000 m. The differences in the C:N:P stoichiometry of the bulk DOM pool between the upper and deep waters suggested preferential remineralisation of P relative to C and N, and N relative to C. A greater remineralisation length scale for DOC relative to DON and DOP produced a long-term, steady flux of C from the surface to the deep ocean. Therefore, CO2 fixed in the upper ocean during planktonic photosynthesis was continuously “pumped” into the ocean interior, and stored in the deep ocean up to thousands of years. The C:N, N:P and C:P stoichiometry of the semilabile (and labile) DOM pool generally agreed with the Redfield ratio (C:N = 6; N:P = 16; C:P = 106) in the upper 30 m. At 100 m C:N ratio was 5-12, C:P ratio was 20-30, and C:P ratio was 100-150. At 300 m, C:N ratio was 5-12, N:P ratio was 25-100, and C:P ratio was 150-500. The findings suggested that in the upper 300 m, there was no preferential remineralisation between the semilabile (and labile) DOC and DON, however, the semilabile (and labile) DOP seemed to be preferentially remineralised relative to the semilabile (and labile) DOC and DON. In the upper thermocline (i.e. above 300 m), DOC degradation was important with respect to oxygen consumption, contributing to as much as 25% of the apparent oxygen utilization (AOU). The remaining of 75% was attributable to POC decomposition. However, the AOU contributable to DOC showed a function of latitude, with 15-55% found in the central subtropical Atlantic gyres and 15-25% in the equatorial region. The most likely explanation for the variation of DOC relative to POC degradation with respect to AOU was the regional variability in the export of POC, which was suggested to be highest in the high nutrient regions of the equator and at the poleward margins of the subtropical gyres. As a result, DOC formed an important contribution to AOU in oligotrophic regions, while POC was the dominant control of AOU in upwelling regions. Some freshly-produced fractions of DON and DOP with turnover times of months to years were capable of escaping rapid microbial degradation in surface waters and became entrained into deep waters via diffusive mixing. Subsequent microbial degradation of these DON and DOP took place in the thermocline, regenerating inorganic nutrients. Statistically significant correlations were observed between the DON-to-DIN and DOP-to-DIP relationships. Calculations of the fluxes of dissolved organic nutrients relative to inorganic nutrients suggested that in the upper thermocline (i.e. above 300 m), the downward fluxes of DON and DOP contributed to a total of 4% and 5% of the upward fluxes of DIN and DIP, respectively, into the euphotic zone. The remaining of 95% of the upward dissolved inorganic nutrients fell out of the euphotic zone as particles in order to prevent nutrient accumulation and to maintain nutrient integrity of the pelagic ecosystem.

The behaviour of Tidal Stream Turbines (TST) in the dynamic flow field caused by waves and rotor misalignment to the incoming flow (yaw) is currently poorly understood. The dynamic loading applied to the turbine could drive the structural design of the power capture and support subsystems, device size and its proximity to the water surface and sea bed. In addition, the strongly bi directional nature of the flow encountered at many tidal energy sites may lead to devices omitting yaw drives; accepting the additional dynamic loading associated with rotor misalignment and reduced power production in return for a reduction in capital cost. For such a design strategy it is imperative to quantify potential unsteady rotor loads so that the TST device design accommodates the inflow conditions and avoids an unacceptable increase in maintenance action or, more seriously, suffers sudden structural failure. The experiments presented as part of this work were conducted using a 1:20th scale 3-bladed horizontal axis TST at a large towing tank facility. The turbine had the capability to measure rotor thrust and torque, blade root strain, azimuthal position and speed. The maximum outof- plane bending moment was found to be as much as 9.5 times the in-plane bending moment, within the range of experiments conducted. A maximum loading range of 175% of the median out-of-plane bending moment and 100% of the median in-plane bending moment was observed for a turbine test case with zero yaw, scaled wave height of 2m and intrinsic wave period of 12.8s. A Blade Element Momentum (BEM) numerical model has been developed and modified to account for wave motion and yawed flow effects. This model includes a new dynamic inflow correction which is shown to be in close agreement with the measured experimental loads. The gravitational component was significant to the experimental in-plane blade bending moment and was included in the BEM model. Steady yaw loading on an individual blade was found to be negligible in comparison to wave loading (for the range of experiments conducted), but becomes important for the turbine rotor as a whole, reducing power capture and rotor thrust.

This study investigates the preserved fluid contents of different generations of mineralised and unmineralised vein minerals from multiple different deposits across the Zambian Copperbelt to define the fluid physicochemical characteristics of the fluids and investigate the importance of fluid processes through the basin history. An investigation into REE and trace element and sulphur isotope signatures of sulphides was conducted to investigate sulphide formation mechanisms. Re-Os dating of sulphides from the Domes Region to provide temporal constraints on mineralisation processes in this area. A textural study on uranium mineralisation at the Lumwana deposit was undertaken to understand the relationships between uranium and sulphide mineralisation. Variable Cl/Br of fluids indicates they were derived from evaporation of seawater, deposition of evaporite sequences and the subsequent dissolution of these evaporite sequences, with bittern brines dominant earlier in the basin history, and dissolution of halite more important during compression and orogenesis. Cation contents of fluids record the development of alteration assemblages caused by the movement of these brines at temperatures typically >200C and salinities >30 wt% NaCl equiv. Stable isotope data records the role of organic reductants and fluid-host rock equilibration through basin history. Rare earth element signatures of sulphides further record the importance of the development of the alteration assemblage on the changing chemistry of the hydrothermal fluids, whilst trace element concentrations suggest the metal budget in the fluids reflects source rock variation. Sulphur isotope data suggests the main mechanism of sulphide formation was thermochemical sulphate reduction of seawater sulphate, consistent with the temperatures of the fluids reported here. Re-Os dating records the importance of orogenesis on the timing of mineralisation in the Domes Region, and are consistent with published Re-Os dating of sulphides and U-Pb dating of uranium minerals. Textural relationships indicate initial uranium mineralisation at the Lumwana deposit pre dates sulphide mineralisation, and final movement on the shear zone, but has undergone a remobilisation event later in the deposit history.

The results of laboratory experiments are described, relating to aspects of hydrodynamics and sediment dynamics under second-order Stokes type waves (or flows), of varying degrees of asymmetry. The majority of the measurements related to laminar and/or transitional flow conditions and were made using an oscillating trolley apparatus. The transition to turbulence over smooth beds has been reported previously in terms of a (single) critical flow amplitude Reynolds number, Recrit=U∞a/ν. On the basis of observations undertaken using sinusoidal flows (Li, 1954) and during the present study, this is found to be the case for wave periods of T>3.5s, where mean Recrit=1.66×105. However, for T<3.5s, it is shown that Recrit decreases in proportion to T. On the basis of the observations made by Li (1954), Manohar (1955) and during the present study, transition over rough (granular) beds is described by Recrit=c(a/D), where c is a coefficient that, for relatively fine sediment (D<275μm), is a linear function of T; for relatively coarse sediment (D>421μm), it is a linear function of D. At large values of Recrit, corresponding to longer wave periods together with relatively small bed roughness length-scales, the observed values deviate from the rough-bed relationship and tend towards the smooth-bed limiting value. Flow asymmetry acts to stabilise the boundary layer, increasing either the critical boundary Reynolds number RE 2ν /ω ν crit c =U (in the case of smooth beds), or Recrit (in the case of rough beds), following a non-linear relationship. Regulating mechanisms are proposed by which the transition to turbulence is governed over (relatively) smooth and/or rough beds. Of principle importance is the balance between the stabilising effect of fluid acceleration and the destabilising effects of vertical gradients in the horizontal velocity (thought to be important in regulating transition over a smooth-bed) and localised eddy formation around individual grains on the bed (similarly over rough beds). The threshold of motion for non-cohesive, sand-sized sediment is expressed typically as a critical bed shear stress amplitude, τo, relative to the resistant properties of individual grains (due to gravity). On this basis, numerous critical shear stress (e.g. the well known approach of Shields, 1936) and velocity amplitude relationships have been presented elsewhere. Previously, Voulgaris et al. (1995) have identified that a higher τo is required to cause threshold at smaller wave periods. On the basis of a large number of observations undertaken (elsewhere, and as part of the present study) using similar equipment, a negative linear relationship has been established between T and τo; this becomes progressively more significant, for threshold occurring under larger values of Re (into the transitional regime). Flow asymmetry has the effect of increasing τo crit; however, the critical orbital diameter for given conditions remains approximately constant, irrespective of the asymmetry. Using these data, in combination with detailed observations of the phase of the onset and the subsequent duration of sediment motion, it is suggested that (especially under (near) laminar flows) the threshold of motion is in response to a ‘time-‘ or ‘phase-mean’ shear stress, corresponding to some form of cumulative force. In addition, under turbulent or partially turbulent flow conditions, the stochastic distribution of the instantaneous shear stress is broader under waves of larger T and/or smaller R; this permits similarity in the occurrence of high-shear events, over a range of conditions. However, the mean τ0 crit decreases. Hence, an artefact or anomalous decrease is included, at longer wave periods, in the (time-mean) peak value of τo crit used to represent such flows.

The biological carbon pump (BCP) exports 5 - 12 Gt C yr−1 to the deep sea and is important for the distribution of carbon within the ocean. Previous studies proposed that the phytoplankton community structure and availability of dense biominerals are key in defining regional export. This thesis examines these factors and their influence on export in the Southern Ocean and the Arctic through the examination of upper ocean species composition, distribution and marine snow particles. In the Southern Ocean, the samples were collected from the high reflectance feature known as the Great Calcite Belt (GCB). The marine snow catcher was used to capture sinking particles and allowed the examination of both the large, fast sinking particles and the slow sinking fraction of particulate organic carbon (POC). The GCB was dominated by nanophytoplankton (<20μm), where the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, Fragilariopsis pseudonana and Pseudonitzschia sp. were the dominant species driving the variation in biogeography. The variation in biogeography was best described by a combination of temperature, nutrients and pCO2. E. huxleyi forms distinct features in the GCB on the Patagonian Shelf, near South Georgia and the Crozet Islands. A southwards progression of E. huxleyi occurs within High Nutrient Low Silica Low Chlorophyll waters in post-bloom conditions after silicic acid and iron drawdown by diatoms. When examined in terms of biomass, the diatoms dominate the GCB, although E. huxleyi was the single biggest contributor as a species. A statistical comparison of surface species and slow sinking material indicated that there was a degree of similarity between the surface and exported community but was regionally variable. Coccolithophores and diatoms contributed minimally (<10%) to upper ocean biomass and total carbon export. The results of this thesis indicate that even though the coccolithophores and diatoms are important phytoplankton for primary production, their direct contribution as cells to carbon export is low. POC flux correlated with opal flux but not calcite flux indicating that the opal was more important in driving POC flux in the GCB. Two types of sinking particles were examined, marine snow aggregates and faecal pellets and there was no significant difference between the sinking velocities. Marine snow sinking velocity was not dependent on size of the aggregate. The concentrations of biominerals and POC in the surface waters and the biominerals in the sinking particles did not influence the sinking velocity. This indicates that porosity and POC content could be more important in determining the sinking velocity and the carbon flux. The synthesis includes the species composition and biomass of the Arctic, which displayed similar trends to the GCB. The results from this thesis suggest that the slow sinking carbon export may not be significantly affected by potential changes in upper ocean biomineralising phytoplankton community structure and upper ocean chemistry. The effects of porosity and POC contents of the particles are here considered to be just as important for determining the export flux than upper ocean community structure and biomineral ballast availability. This implies that the impacts of ocean acidification will become more important deeper in the water column as biominerals become more important within sinking particles as POC is removed.

Phytoplankton growth is sustained by the supply of essential nutrients and balanced by mortality processes such as viral infection, both of which can give rise to stress. Remod- elling of cellular lipids in response to such stresses is common in unicellular organisms. Under phosphorus (P) stress, phytoplankton substitute glycerophospholipids with non- phosphorus analogues, reducing their demand for P. Reported herein, the model marine diatom Thalassiosira pseudonana degraded only a small proportion of its original glyc- erophospholipid. Most of the P remained incorporated in glycerophospholipids, but significant changes in the individual glycerolipid species were observed. Untargeted lipidomic screening highlighted diglycosylceramides, not previously ob- served in T. pseudonana, that increase with P stress and may be useful as biomarkers. The fatty acids comprising each individual diglyceride lipid were characterised filling a conspicuous gap in our knowledge. Preliminary results suggest partitioning of diacylglyc- erol lipids between subcellular compartments. Marine diatoms, rich in lipids such as triacylglycerols are potential feedstocks for bio- fuels, where nitrogen (N) starvation is common to increase lipid yield. Quantification of individual glycerolipid species under N stress revealed that polyunsaturated glycerophos- phatidylcholine species and the predominant chemotype of sulfoquinovosyldiacylglycerol displayed large increases. Total diacylglycerol increased 3 fold under N stress, comprised of increases in saturated/monounsaturated species. This appears to form part of the cell’s adaption to N limitation that ultimately leads to the accumulation of triacylglycerides. These findings provide insight on the diatom lipidic response to nutrient stress and their adaptations to life in low nutrient environments, with additional implications upon biofuel production. Marine viruses infect phytoplankton influencing host ecology and evolution. Emilia- nia huxleyi has a biphasic life cycle with a diploid and haploid phase. Diploid cells are susceptible to infection by specific coccolithoviruses, yet haploid cells are resistant. Anal- ysis of lipids from cultures of uninfected diploid, infected diploid and uninfected haploid E. huxleyi revealed that sialic-glycosphingolipid, previously linked with susceptibility to infection, was absent from the resistant haploid cultures. Additional untargeted analyses unveiled potential biomarkers furthering our understanding of E. huxleyi host/virus lipid dynamics and highlight potential novel biomarkers for infection, susceptibility and ploidy.