This study addresses the influences on ridge basalt chemistry, through analysis of their major and trace element and isotopic composition at scales ranging from individual ridge segments to the entire length of the ridge system. Local-scale studies of basalts along the Mid-Atlantic Ridge shed light on crustal accretion at slow-spreading ridges, and on the nature of plume-ridge interaction in this region. We show that segments must have multiple supplies of magma delivered along their length, but with preferential delivery of magma to segment centers. Plume-ridge interaction near the Azores is not simple two- component mixing between “plume” mantle and “depleted” mantle as previously argued. The elevated highly incompatible trace element ratios possessed by basalts well south of the plume are the definitive sign of a low-degree melt, which can fractionate highly incompatible element ratios. We show that a low-degree melt of plume mantle acts to metasomatize ambient depleted mantle, creating a mixed source that melts to produce the enriched basalts south of the Azores. This metasomatized source is the enriched mixing component that produces the observed geochemical gradient, rather than bulk plume mantle. The latter half of this study is global in scope, involving a carefully compiled ridge basalt geochemical database. This database is unparalleled in size and coverage – including data from portions of the Gakkel and Southwest Indian Ridges and Lau basin that were unavailable in prior data compilations. It includes a catalog of 771 global ridge segments, enabling the calculation of mean MORB by averaging the “segment means”, including weighting on segment length and spreading rate and a quantitative treatment of errors. We show that the mean composition of ocean ridge basalts is more enriched than previously suggested, and argue for a re-definition of “normal MORB”. Segment basalt compositions are individually corrected for crystal fractionation, arriving at parental magma compositions that can be interpreted in terms of mantle processes. The fractionation-corrected mean segment compositions correlate with ridge depth, and with each other, in a manner that is consistent with control by mantle temperature variations. Mantle compositional heterogeneity is also seen, but appears to be a second-order effect. / Earth and Planetary Sciences

Various lines of evidence indicate that levels of anthropogenic pollutants, such as lead, mercury and cadmium, have increased in terrestrial and atmospheric environments since the early 19th century and the advent of industrialization. While the exposure to these three trace elements is a global concern, this study focused primarily on marine environments located throughout the Caribbean. Using ICP-MS, this study aimed to detect and quantify anthropogenic pollutants, specifically lead (Pb), mercury (Hg) and cadmium (Cd), using skeletonized remains of sea turtles as biological proxies for environmental quality. Archaeologically derived (n=5) and mid-late 20th century (n=6) Hawksbill and Green turtles were used to create a chronology of pollution exposure in Caribbean marine environments and establish a pre-industrial baseline for pollution exposure, useful for precisely gauging how human activities in the Caribbean, namely industrialization and tourism, have changed the concentration of these elements over time. Results from this study revealed that the industrial, modern sea turtle sample and the archaeological sample exhibit similar distributions of lead and cadmium ppm levels. Whereas, the mercury datasets revealed that the two samples share differing distributions of ppm levels, but that the archaeological sample yielded the higher mercury concentrations. Based on these results, this study was unable to verify whether skeletal sea turtle remains, specifically humeri, can be used as a biological proxy to reconstruct anthropogenic pollution in marine environments. Furthermore, it failed to quantify pre-industrial to mid-late 20th century anthropogenic lead, mercury, and cadmium pollution in Caribbean Marine Environments.

Identifying the natal origin of fish is important to understand connectivity among populations. Capelin, Mallotus villosus, is a key forage fish species that spawns at beach and deep-water habitats along the Newfoundland coast. I investigated the ability to identify the natal habitat of larval capelin using otolith chemical signatures quantified via LA ICP-MS. Otolith signatures of larvae reared under identical conditions were highly variable and classification into treatments was low (~50%). To investigate whether maternal investment was responsible for this variability, artificially fertilized eggs were reared under controlled treatments. Otolith signatures reliably classified individuals into families with high success (83.4%), suggesting maternal investment may confound our ability to identify natal origin. Eggs incubated in water enriched with 137Ba revealed trace elements from the environment are being incorporated into developing otoliths. These findings suggest moderate-high differences in water chemistry and environmental conditions are required to identify the natal origin of capelin. / October 2016

An investigation of heavy metal concentrations in sediments from Coxs River catchment, a tributary of the Hawkesbury-Nepean River system, has been undertaken. A number of digestion methods were assessed for the determination of Pb, Cu, Cd, Zn, Ni, Mn, Fe, Co and Cr in reference materials by flame AAS. The method that produced the best recovery is reverse aqua regia, HNO3-HC1 with ultrasonification followed by heating on a hotplate. Based on analysis of sediments from 133 sites, background concentrations were established. Elevated heavy metal concentrations were recorded in some samples. The three most polluted areas were investigated for heavy metal associations and distributions. Metal bioavailability was assessed from sediment samples by using selective extraction techniques. The association of heavy metals with different solid phases was assessed by a sequential extraction technique involving a series of extraction reagents. Pd, Cu, Fe and Cr were mainly associated with Fe/Mn oxides and organic matter plus sulphide phases. While Cd, Zn, Ni and Co which behave similarly were extracted from each step, the largest percentages of these metals were found in Fe/Mn oxides and organic matter phases. Mn was different to other metals, in that it predominantly associated with the ion exchangeable form. / Master of Science (Hons)

Abstract This study aims to understand the influence of weathering and human perturbation on spatial and temporal variability of major and trace element distributions in the Kaoping River basin. The collected data are used to elucidate the production, transport and export of major and trace elements from the Kaoping River basin. Experimental results show that the weathering index of the Kaoping River basin is rather high. The significant loss of major ions and enrichment of iron and aluminum from river suspended matter indicate the characteristic of high weathering rate in most tropical rivers. Particulate Si/Al mole ratios range from 1 to 2 showing that the distributions of dissolved and particulate matter are largely controlled by the weathering process of kaolinite and /or smectite formation. During the study period (2002), the physical and chemical weathering rates were estimated about 655.8 and 416.2 g/m2/yr, respectively. Both physical and chemical weathering rates are much lower than those estimated by Yang (2001) during the period of 1999-2000 [3601 g/m2/yr (physical weathering rate), 1146 g/m2/yr (chemical weathering rate)], due to significant difference in river discharge. However, the estimated physical and chemical weathering rates are still much higher than the world averages of physical (150 g/m2/yr) and chemical (33-40 g/m2/yr) weathering rates. The marked difference between this and Yang¡¦s estimates is caused from large difference in river discharge. Silicate weathering was estimated about 97.09 ¡Ó 2.41% of total chemical weathering in the Kaoping River basin. The temporal variations of enrichment factor (EF) for most particulate trace metals (Mn, Zn, Cu, Cr, Pb, Cd, and Hg) reveal a greater pollution status in the dry season than in the wet season. Spatial variations of EF also reveal a greater pollution in the downstream zone than in the upstream zone. Time-series observation showed that concentrations of particulate trace elements were inversely correlated with discharge. The significant correlation between the fluxes of dissolved and particulate trace elements and discharge suggesting that river discharge controlled largely the fluxes of major and trace elements. The annual variations of elemental fluxes were determined critically by the annual difference of river discharge. The distributions of particulate organic carbon (POC) and particulate nitrogen (PN) were similar between suspended matter in the Kaoping River and surface sediments in the Kaoping Canyon. The data of £_13Corg show that about 77.2% of organic matter derived from the Kaoping River basin deposit in the Kaoping Canyon. The Kaoping Canyon appears to play an important role on the transport and deposition of organic matter from the Kaoping River basin.

Abstract Isobaric (200 MPa) experiments have been performed to investigate the effects of H2O alone or in combination with P, S, F or Cl on the phase relations and elemental and oxygen isotopic partitioning between immiscible silicate melts in the systems Fe2SiO4-Fe3O4-KAlSi2O6-SiO2, Fe3O4-KAlSi2O6-SiO2 and Fe3O4-Fe2O3-KAlSi2O6-SiO2 +/- plagioclase (An50). Experiments were heated in a newly-designed rapid-quench internally-heated pressure vessel at 1075, 1150 or 1200 oC for 2 hours. Water alone or in combination with P, S, or F significantly increases the temperature and composition range of two-liquid fields at fO2= NNO and MH buffers. Water-induced suppression of liquidus temperatures, considered with the effects of pressure on two-liquid fields stability in silicate melts, suggests that liquid phase separation may occur in some volatile-rich silicate magmas at pressures up to 2GPa. Two-liquid partition coefficients for Fe, Si, P and S correlate well with the degree of polymerization of the SiO2-rich conjugate melts and the data can be applied to assess the involvement of liquid-phase separation in the genesis of coexisting volatile-rich magmas. The partitioning of trace concentrations of selected HFSE, REE and transition elements between immiscible experimental volatile-rich melts at 1200 oC, 200 MPa has been determined at QFM, NNO and MH oxygen buffers. Water generally increases the partitioning of HFSE, REE and transition elements into the Fe-rich melt. Water alone, or combined with P or S, produces nearly parallel partitioning trends for HFSE and REE. Absolute partitioning values of transition elements are strongly dependent on the network-modifier composition of the melt. 18O in experimental immiscible melts with H2O or H2O and P or S partitions preferentially into the felsic conjugate melt (δ18O felsic melt- δ18O mafic melt values range from 0.4 to 0.8 permil) consistent with observations in anhydrous immiscible silicate melts. The expansion of the P-T-X-fO2 stability ranges of two- or three-liquid fields observed in the experimental melts demonstrates that liquid-immiscibility may be an important process in the evolution of some volatile-rich natural magmas. The results support an immiscible petrogenetic origin for some iron-oxide dominated, Kiruna-type, ore-deposits. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2012-04-10 15:06:35.797

The aim of this thesis was to improve the properties of pressed and sintered aluminium powder alloys. This improvement was to be achieved using two methods. The first method involved the selection of an alloy system using binary aluminium phase diagrams and a knowledge of the phase diagram characteristics of ideal sintering systems. The second approach involved the judicious use of selected trace element additions to modify the sintering characteristics of aluminium and its alloys. A trace amount of magnesium was found to be critical to the sintering of aluminium powder due to its disrupting effect on the tenacious oxide layer covering the powder particles. The critical amount of Mg required to optimise both density and mechanical properties is dependent on the specific volume of oxide and the therefore particle size. The optimum concentration is 0.1-1.0wt% Mg. The Al-Sn phase diagram exhibits many of the characteristics of an ideal sintering system. Unsurprisingly, Sn was found to be an extremely efficient sintering aid, but only in the presence of Mg. Near full density parts were produced using an Al-8Sn-0.15Mg alloy in short sintering times (30 minutes). Additionally, as-sintered ductilities exceeding 20% were achieved using an Al-2Sn-0.15Mg alloy. Alloys based on the Al-Sn-Mg system lend themselves to sintering without compaction and therefore freeformed Al-Sn-Mg alloys have been produced and sintered to near full density from a starting density of ~50%. Trace amounts of Sn (Pb, In, Bi, or Sb) enhance the sintering response of an Al-4Cu-0.15Mg alloy via a vacancy binding mechanism. A similar mechanism suppresses natural ageing and stimulates artificial ageing when trace amounts of Sn are added to this alloy. A Sn-modified 2XXX series alloy has also been produced with mechanical properties nearly 20% above current commercial alloys. Along with the addition of 0.1wt%Sn, this improvement required an alteration to the solution treatment cycle which allowed the use of a higher sintering temperature without the formation of large amounts of boundary phase.

The aim of this thesis was to improve the properties of pressed and sintered aluminium powder alloys. This improvement was to be achieved using two methods. The first method involved the selection of an alloy system using binary aluminium phase diagrams and a knowledge of the phase diagram characteristics of ideal sintering systems. The second approach involved the judicious use of selected trace element additions to modify the sintering characteristics of aluminium and its alloys. A trace amount of magnesium was found to be critical to the sintering of aluminium powder due to its disrupting effect on the tenacious oxide layer covering the powder particles. The critical amount of Mg required to optimise both density and mechanical properties is dependent on the specific volume of oxide and the therefore particle size. The optimum concentration is 0.1-1.0wt% Mg. The Al-Sn phase diagram exhibits many of the characteristics of an ideal sintering system. Unsurprisingly, Sn was found to be an extremely efficient sintering aid, but only in the presence of Mg. Near full density parts were produced using an Al-8Sn-0.15Mg alloy in short sintering times (30 minutes). Additionally, as-sintered ductilities exceeding 20% were achieved using an Al-2Sn-0.15Mg alloy. Alloys based on the Al-Sn-Mg system lend themselves to sintering without compaction and therefore freeformed Al-Sn-Mg alloys have been produced and sintered to near full density from a starting density of ~50%. Trace amounts of Sn (Pb, In, Bi, or Sb) enhance the sintering response of an Al-4Cu-0.15Mg alloy via a vacancy binding mechanism. A similar mechanism suppresses natural ageing and stimulates artificial ageing when trace amounts of Sn are added to this alloy. A Sn-modified 2XXX series alloy has also been produced with mechanical properties nearly 20% above current commercial alloys. Along with the addition of 0.1wt%Sn, this improvement required an alteration to the solution treatment cycle which allowed the use of a higher sintering temperature without the formation of large amounts of boundary phase.

In rivers that shift in their natural or modified physical structure, it is expected that organisms alter their resource use with the shifts in physical changes. The Upper Mississippi River System (UMRS) is a modified river basin and stark contrasts in both the physical structure of habitat types and biological structure in the types of organisms present exist spatially. The upper reaches of the basin contain more complex habitat types than the lower reaches which suggests resource use of fishes likely differs at least between upper and lower reaches. To date, the resource use of some commercially important, invasive, and imperiled species has been studied. However, little information regarding resource use exists for most native fishes. Understanding resource use and how it differs across time and space would benefit managers of the UMRS as programs are underway to restore and manage the system. To determine how resource use of native fishes differs spatially and temporally in the UMRS, I quantified resource use of ten native fishes across six reaches of the UMRS using multiple techniques. At the largest spatial and temporal scale, I quantified the natal origins of six prey and two predatory fishes using trace element analysis. At a seasonal scale, I quantified the collective resource use of eight species using carbon and nitrogen isotopes to compare isotopic niche space, niche overlap, and community metrics. At the shortest scale, I quantified the diets of two predatory species that are thought to compete with one another. Both large scale similarities and nuances in resource use existed in the UMRS depending on the spatial and temporal contexts. At the longest scale, fishes consistently used network connectivity as tributaries and other mainstem river reaches contributed recruits to the mainstem river. However, the percentage of individuals resulting from network connectivity and the specific rivers that lent the recruits differed among species and reaches. Particularly, large tributaries like the Minnesota and Missouri rivers contributed relatively high numbers of recruits to nearby reaches compared to other tributaries, and the most downstream reaches had the greatest contributions from network connectivity. Prey fishes recruited more often from tributaries than predators whereas consumed prey and prey collected directly from the UMRS had similar origins which were consistent across years. At a seasonal scale, breadth of resource use of individual species and the assemblage and some community metrics increased whereas overlap decreased moving downstream in the UMRS. This shift in resource use metrics coincides with shifts in the physical structure of the system. At the shortest scale, diet compositions of the two predators were similar to one another and spatially among upper reaches in the UMRS. These two predators likely coexist in part due to diet plasticity and prey size allocations that differ between species. Additionally, the relative physical homogeneity of the upper reaches of the UMRS may have led to the spatial similarity in prey use. Together, these results suggest the physical structure of the system impacted the resource use of fishes, where trophic niches and use of network connectivity shifted with the shift in physical structure of the Mississippi River. At a minimum, spatial gradients in isotopic niches and percentage of individuals coming from network connectivity suggest the resource use of fishes in downstream reaches at seasonal and life-long scales differs from the upstream reaches within this system. These differences could stem from longitudinal or functional process zone shifts in the physical structure which cannot be determined given these data. In the context of management of the system, fishes use network connectivity to at least some degree across all species and sampling reaches, indicating that the connectivity in the system should at least be maintained if not improved. Additionally, fish move among reaches (i.e., through lock and dams) and tributaries, which highlights the need for interjurisdictional management not just in the UMRS but in nearby tributary systems like the Minnesota and Missouri River where fish originated.

The goal of this research was to devise a new analytical technique, using Accelerator Mass Spectrometry (AMS), to measure Platinum Group Element (PGE) concentrations to the sup-ppb levels in natural, insulating, samples. The challenges were threefold. First, a method of sputtering an insulating sample to successfully produce a stable beam of anions needed to be devised. Second, a suitable standard of known PGE concentrations had to be found and third, spectral analysis of the beam had to verify any claims of PGE abundance. The first challenge was met by employing a modified high intensity negative ion source flooded with neutral caesium that successfully sputtered insulators to produce a beam of negative ions. The second challenge, that of finding a suitable standard, was fraught with difficulties, as no synthesized standards available were found to be appropriate for this work. As a result, direction is provided for future production of standards by ion implantation. The third challenge, successful spectral analysis, was accomplished using a newly designed gas ionization detector which allowed for resolution of the interfering molecular fragment from the PGE ions. Coupled with the use of the SRIM computer programme, positive identification of all peaks in the spectra of the analyzed samples was accomplished. The success of the first and third challenges lead to the qualitative analyses of geological samples for sub-ppb levels of PGE by AMS. Quantitative analyses await only for the appropriate standards and with those will come a whole new range of research possibilities for measuring sub-ppb levels of PGE in insulating samples by AMS.