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Trace elements sustain biological productivity, yet the significance of trace element mobilization and export in subglacial runoff from ice sheets is poorly constrained at present. Here, we present size-fractionated (0.02, 0.22, and 0.45 µm) concentrations of trace elements in subglacial waters from the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Concentrations of immobile trace elements (e.g., Al, Fe, Ti) far exceed global riverine and open ocean mean values and highlight the importance of subglacial aluminosilicate mineral weathering and lack of retention of these species in sediments. Concentrations are higher from the AIS than the GrIS, highlighting the geochemical consequences of prolonged water residence times and hydrological isolation that characterize the former. The enrichment of trace elements (e.g., Co, Fe, Mn, and Zn) in subglacial meltwaters compared with seawater and typical riverine systems, together with the likely sensitivity to future ice sheet melting, suggests that their export in glacial runoff is likely to be important for biological productivity. For example, our dissolved Fe concentration (20,900 nM) and associated flux values (1.4 Gmol y(−1)) from AIS to the Fe-deplete Southern Ocean exceed most previous estimates by an order of magnitude. The ultimate fate of these micronutrients will depend on the reactivity of the dominant colloidal size fraction (likely controlled by nanoparticulate Al and Fe oxyhydroxide minerals) and estuarine processing. We contend that ice sheets create highly geochemically reactive particulates in subglacial environments, which play a key role in trace elemental cycles, with potentially important consequences for global carbon cycling.

We present the results of a muon-spin spectroscopy investigation of GaV4S8−ySey with y = 0, 2, 4, and 8. Zero-field measurements suggest that GaV4Se8 and GaV4S8 have distinct magnetic ground states, with the latter material showing an anomalous temperature dependence of the local magnetic field. It is not possible to evolve the magnetic state continuously between these two systems, with the intermediate y = 2 and 4 materials showing glassy magnetic behavior at low temperature. The skyrmion lattice (SkL) phase is evident in the y = 0 and 8 materials through an enhanced response of the muon-spin relaxation to the emergent dynamics that accompany the SkL. For our polycrystalline samples of GaV4Se8, this enhanced dynamic response is confined to a smaller region of the magnetic field-temperature phase diagram than the previous reports of the SkL in single crystals.

The superconductivity in the rare-earth transition-metal ternary borides RRuB2 (where R = Lu and Y) has been investigated using muon-spin rotation and relaxation. Measurements made in zero field suggest that time-reversal symmetry is preserved upon entering the superconducting state in both materials; a small difference in depolarization is observed above and below the superconducting transition in both compounds, however, this has been attributed to quasistatic magnetic fluctuations. Transverse-field measurements of the flux-line lattice indicate that the superconductivity in both materials is fully gapped, with a conventional s-wave pairing symmetry and BCS-like magnitudes for the zero-temperature gap energies. The electronic properties of the charge carriers in the superconducting state have been calculated, with effective masses m∗/me = 9.8 ± 0.1 and 15.0 ± 0.1 in the Lu and Y compounds, respectively, with superconducting carrier densities ns = (2.73 ± 0.04) × 10^28 m^(−3) and (2.17 ± 0.02) × 10^28 m^(−3). The materials have been classified according to the Uemura scheme for superconductivity, with values for Tc/TF of 1/(414 ± 6) and 1/(304 ± 3), implying that the superconductivity may not be entirely conventional in nature.

The discovery of new families of unconventional superconductors is important both experimentally and theoretically, especially if it challenges current models and thinking. By using muon spin relaxation in zero field, time-reversal symmetry breaking has been observed in Re6Hf. Moreover, the temperature dependence of the superfluid density exhibits s-wave superconductivity with an enhanced electron-phonon coupling. This, coupled with the results from isostructural Re6Zr, shows that the Re6X family is indeed a new and important group of unconventional superconductors.

We systematically investigate the normal and superconducting properties of noncentrosymmetric Re6Zr using magnetization, heat capacity, and electrical resistivity measurements. Resistivity measurements indicate Re6Zr has poor metallic behavior and is dominated by disorder. Re6Zr undergoes a superconducting transition at Tc = (6.75 ± 0.05) K. Magnetization measurements give a lower critical field, μ0Hc1 = (10.3 ± 0.1) mT. The Werthamer-Helfand-Hohenberg model is used to approximate the upper critical field μ0Hc2 = (11.2 ± 0.2) T, which is close to the Pauli limiting field of 12.35 T and which could indicate singlet-triplet mixing. However, low-temperature specific-heat data suggest that Re6Zr is an isotropic, fully gapped s-wave superconductor with enhanced electron-phonon coupling. Unusual flux pinning resulting in a peak effect is observed in the magnetization data, indicating an unconventional vortex state.

The superconductivity of the noncentrosymmetric compound La7Ir3 has been investigated using muon spin rotation and relaxation (μSR). Zero-field measurements reveal the presence of spontaneous static or quasi-static magnetic fields below the superconducting transition temperature Tc = 2:25 K - a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic, and that the pairing symmetry of the superconducting electrons is predominantly s-wave with an enhanced binding strength. The results indicate that the superconductivity in La7Ir3 may be unconventional, and paves the way for further studies of this family of materials.

South East Asia is one of the fastest developing regions on Earth and has experienced a recent large increase in atmospheric pollution. Glaciers of the nearby Himalayan mountains represent a unique archive that provides the potential to be used to determine the strength and timing of the onset of anthropogenic atmospheric pollution in the region. Within the Third Pole Project several ice cores from the Tibetan Plateau and the Himalaya are analyzed for their trace element concentrations. Here we present results of a new trace element record from the Dasuopu ice core spanning 1790 - 1993 AD. The Dasuopu ice core was drilled in 1997 at 7200 m altitude in the Himalaya and provides the highest elevation ice core record ever obtained. Due to the high altitude this site has the potential to archive not only contamination records of regional significance, but possibly also long distant pollution from, for example, Europe and climatic signals influenced by the North Atlantic. This area is heavily influenced by the monsoon regime providing seasonally and highly variable snow accumulation rates. The upper 50 m of the core covering the time interval from 1950 to 1997 consist of Firn and is sampled non-continuously in a resolution of approximately one sample/year. The time interval between 1790 and 1950 is presented by a continuous record in subannual resolution. Crustal enrichment factors are used to discriminate between the terrigenous and the anthropogenic contributions. In this study we focus two research topics: (1) determine the onset of the earliest anthropogenic contamination from trace elements at this elevation (7200 m) Himalayan site and (2) determine intra-annual variations of atmospheric trace elements, with a focus on discriminating between pre-monsoon season (when the aerosol input is governed by the high dust input in spring) and the monsoon and dry season. We find trace element concentrations to be very low and very variable throughout the year with concentration changes of up to 2-3 orders of magnitude (e.g. Pb concentrations range from 0.1 ppt to 1000 ppt). Average concentration levels are comparable to those recorded at some polar sites. We find an increase in elements of crustal origin in the second half of the 20th century.

This dissertation examines Joel through the lens of rhetorical criticism and seeks to demonstrate that Joel is a unified work of prophetic literature that moves from scenes of devastation to promises of restoration through its persuasive evocation of divine and human responses in order to articulate the necessity of calling and relying upon YHWH in all circumstances. This study orients itself in the broader context ofJoel studies before examining rhetorical critical methodologies. This study discusses the model of George A. Kennedy and Karl Moller and proposes modifications so that it will better engage with the rhetoric of Joel. This dissertation then seeks to apply Kennedy's and Moller's model in a detailed study of Joel. The body of this study considers different text units within Joel, discussing how the text constructs the rhetorical situations into which it places its persuasive strategies. This dissertation then considers the potential effectiveness of these strategies in their situations. It traces how Joel uses a series of crises in order to persuade the text's implied audience that its only hope is found in crying out to YHWH amidst desperate circumstances. This leads to the consideration ofthe gap between Joel 2:17, 18, where the tenor of the text changes from devastation to restoration secured by the powerful actions ofYHWH. This study notes how the latter half ofJoel evokes restorative responses from YHWH culminating in the promise ofYHWH's protective presence in Zion, which should further persuade the implied audience that it ought to heed the text's appeal to cry out to YHWH. This dissertation concludes with a summary ofthe persuasive elements ofthe individual rhetorical units within Joel, while also considering the rhetorical trajectory of Joel as a literary whole. It then offers suggestions for further rhetorical study of prophetic literature. Thesis Doctor of Philosophy (PhD)

This thesis presents muon spin rotation and relaxation (μSR) studies of various superconducting materials. μSR studies have been complemented with laboratory measurements of heat capacity, resistivity, and magnetization. This work contributes to the body of work surrounding noncentrosymmetric superconductors (NCS) and unconventional superconductivity.\ud \ud The intermetallic compound La₇Ir₃ is found to break time-reversal symmetry upon transitioning into the superconducting state, elucidated by muon spin relaxation. The pairing symmetry appears fully gapped, and is well described by an isotropic s-wave model. Further theoretical analysis of the point group symmetry could investigate the allowed superconducting states potentially existing here.\ud \ud The physical properties of the NCS Re₃Ta are well described by the conventional BCS theory of superconductivity. μSR suggests unusual narrowing of the vortex lattice signal in a region close to Tc, interpreted as motional narrowing due to thermal motion of vortices. This is supported by irreversible magnetization in a sizable region in the phase diagram. Ginzburg number and quantum resistance calculations place Re₃Ta intermediate between the high-Tc and conventional low-Tc superconductors.\ud \ud LuRuB₂ and YRuB₂, superconducting members of the ternary boride family of materials, are studied using μSR. Zero-field measurements detect spin fluctuations exhibiting critical slowing down as the temperature is lowered, suggesting that these materials lie near a quantum phase transition. These weak fluctuations coexist with the superconductivity, which is well described by an isotropic, s-wave model for the pairing symmetry.\ud \ud The semi-metal Lu₃Os₄Ge₁₃ is investigated using transverse-field and zerofield μSR. The superfluid density is well described by a model containing two superconducting gaps, supporting previously reported heat capacity measurements. Zero-field measurements below Tc reveal a signal hinting at broken time-reversal symmetry, however, it does not coincide with the bulk superconducting transition. Further theoretical work could determine whether this is the first observation of a novel three-gap multiband superconducting ground state.