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Antarctica holds enough landlocked ice to raise the global sea level by nearly 60 m in the event of wholesale ice sheet collapse. In East Antarctica, the Aurora Subglacial Basin is drained by Totten Glacier and is one of the world’s largest and most rapidly-changing ice catchment systems. In recent decades, Totten Glacier has exhibited variability in its flow rate, mass balance, and ice thickness, each led by changes at the ice sheet margin. Totten Glacier dynamics are linked to processes in the Totten Ice Shelf, which buttresses the flow of grounded ice while being subjected to variable ocean forcing from below. Understanding the stability of the Aurora Subglacial Basin in a changing climate requires an understanding of how Totten Ice Shelf responds to changes in its environment. This dissertation investigates ice shelf processes on spatial scales of 1 km to 100 km, that act on sub-annual to decadal time scales. The independent roles of channelized basal melt and large-scale basal melt resulting from a variable supply of oceanic heat content are examined using surface elevation changes measured by airborne laser altimetry, satellite laser altimetry, and a new method of photometry applied to satellite images. A new method of satellite image template matching is also developed to understand ice shelf velocity response to several environmental forcing mechanisms. On the interannual time scale, Totten Ice Shelf is seen accelerating in response to nearby upwelling of warm circumpolar deep water that enhances basal melt rates. On the subannual time scale, Totten Ice Shelf exhibits winter slowdown as buttressing from seasonal landfast sea ice at the ice shelf front slows the flow of the glacier. These findings show that the Totten Glacier catchment is sensitive to changes in its environment, and may be susceptible to changes in the coastal wind stress projected for the 21st century.

Antarctica holds enough landlocked ice to raise the global sea level by nearly 60 m in the event of wholesale ice sheet collapse. In East Antarctica, the Aurora Subglacial Basin is drained by Totten Glacier and is one of the world’s largest and most rapidly-changing ice catchment systems. In recent decades, Totten Glacier has exhibited variability in its flow rate, mass balance, and ice thickness, each led by changes at the ice sheet margin. Totten Glacier dynamics are linked to processes in the Totten Ice Shelf, which buttresses the flow of grounded ice while being subjected to variable ocean forcing from below. Understanding the stability of the Aurora Subglacial Basin in a changing climate requires an understanding of how Totten Ice Shelf responds to changes in its environment. This dissertation investigates ice shelf processes on spatial scales of 1 km to 100 km, that act on sub-annual to decadal time scales. The independent roles of channelized basal melt and large-scale basal melt resulting from a variable supply of oceanic heat content are examined using surface elevation changes measured by airborne laser altimetry, satellite laser altimetry, and a new method of photometry applied to satellite images. A new method of satellite image template matching is also developed to understand ice shelf velocity response to several environmental forcing mechanisms. On the interannual time scale, Totten Ice Shelf is seen accelerating in response to nearby upwelling of warm circumpolar deep water that enhances basal melt rates. On the subannual time scale, Totten Ice Shelf exhibits winter slowdown as buttressing from seasonal landfast sea ice at the ice shelf front slows the flow of the glacier. These findings show that the Totten Glacier catchment is sensitive to changes in its environment, and may be susceptible to changes in the coastal wind stress projected for the 21st century.

Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps—plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings.

Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps—plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings.