Seismic record of West Antarctic Ice Sheet dynamics during the late Oligocene to early Miocene in the Eastern Basin, Ross Sea

The Antarctic cryosphere is an important driver of global climate change and ocean circulation. The Antarctic Ice Sheet is comprised of the stable, terrestrially-based East Antarctic Ice Sheet (EAIS) and the marine-based West Antarctic Ice Sheet (WAIS) that may be prone to a collapse that would contribute over 3 m to global sea level rise. The Antarctic Ice Sheets have unique evolutionary histories and understanding how they have influenced and been influenced by global changes through the Cenozoic will yield a more robust understanding of their response to future climate change. 98% of Antarctica is currently covered in ice, posing challenges for investigators. Much of our understanding of the evolution of the Antarctic cryosphere has been developed from far field oxygen isotope records of global temperature and ice volume change; however, more direct records of Antarctic Ice Sheet dynamics from the continent and margin conflict with interpretations derived from these records. The Ross Sea embayment in Antarctic drains ~25% of the continent, receives input from both the EAIS and WAIS and contains a thick section of Cenozoic deposits, making it an important location to investigate the evolution of the Antarctic cryosphere. The Eastern Basin, Ross Sea contains a thick section of Cenozoic strata that records the evolution of the WAIS. This study reexamines legacy and recent seismic reflection data and uses spectral attribute analysis to enhance the resolution of the datasets. I document spectral decomposition techniques that enhance the temporal resolution of multi-channel seismic profiles. Using the spectral decomposition technique, I develop a higher resolution, third-order sequence stratigraphic model of late Oligocene to early Miocene sequences within the Eastern Basin to test hypotheses about the evolution of the WAIS. I identify evidence of an expanding late Oligocene WAIS and waning ice volumes during the early Miocene. Using seismic-stratigraphic stacking patterns, I correlated relative sea level fluctuations recorded in the Eastern Basin to global eustatic and oxygen isotope events and refined chronostratigraphic correlations of regional horizons and unconformities. These findings have important implications for the initiation and evolution of the West Antarctic Ice Sheet during the late Paleogene and early Neogene.Doctor of Philosoph

Investigation of geodesic acoustic mode flow oscillations using Doppler reflectometry in ASDEX Upgrade

Magnetic confinement fusion is a promising candidate for a future energy source. Its efficiency is limited by particle and heat transport due to plasma turbulence. A thorough understanding of the turbulence and turbulence moderation mechanisms, is therefore needed. The geodesic acoustic mode (GAM) is a radially localised plasma flow oscillation which contributes to the reduction of turbulent transport through velocity shearing. This thesis investigates the fundamental behaviour of the GAM through a systematic experimental study of its properties in the ASDEX Upgrade tokamak. In particular, the role of the plasma geometry on the scaling of the GAM frequency and amplitude, as well as the GAM radial structure are investigated in detail. The experimental data was obtained with the aid of the microwave Doppler reflectometry diagnostic. The GAM frequency scaling is compared with multiple models which reproduce the expected fundamental scaling behaviour, but do not give a satisfyingly accurate prediction. The GAM amplitude is studied in connection with damping rates predicted by models for collisional and collisionless Landau damping processes. It is found that finite orbit width effects need to be considered and that collisional damping effects cannot be neglected. In studying the GAM radial structure, three distinct states are identified for different plasma conditions. Transitions between these states are observed under variations of the plasma geometry

Simulating Hydrodynamics in Cosmology with CRK-HACC

We introduce CRK-HACC, an extension of the Hardware/Hybrid Accelerated Cosmology Code (HACC), to resolve gas hydrodynamics in large-scale structure formation simulations of the universe. The new framework couples the HACC gravitational N-body solver with a modern smoothed particle hydrodynamics (SPH) approach called CRKSPH. $\underline{\text{C}}$onservative $\underline{\text{R}}$eproducing $\underline{\text{K}}$ernel $\underline{\text{SPH}}$ utilizes smoothing functions that exactly interpolate linear fields while manifestly preserving conservation laws (momentum, mass, and energy). The CRKSPH method has been incorporated to accurately model baryonic effects in cosmology simulations - an important addition targeting the generation of precise synthetic sky predictions for upcoming observational surveys. CRK-HACC inherits the codesign strategies of the HACC solver and is built to run on modern GPU-accelerated supercomputers. In this work, we summarize the primary solver components and present a number of standard validation tests to demonstrate code accuracy, including idealized hydrodynamic and cosmological setups, as well as self-similarity measurements