Amery Ice Shelf (AIS) in East Antarctica acts as the primary buttress for the largest reservoir of potential sea level rise in the region: the Lambert-Amery Basin. Iceberg calving is an important mass loss process for ice shelf systems and is one of the ways that an ice shelf loses mass. While calving events themselves are not inherently concerning for an ice shelf, changes from the steady state such as increased rifting and shortening calving cycles can indicate a mass imbalance. Therefore, it is crucial to understand calving processes to improve our ability to detect potential imbalances. Rifting is a precursor to all tabular iceberg calving events, yet there are many aspects of this process that remain unclear; for example, the disputed role of mélange (the ice mixture which congeals inside the rift at sea level) in rift propagation (Fricker, Young, et al., 2005; Larour et al., 2004). We use advances in satellite remote sensing to develop a metric for characterizing the propagation regime of ice rifts to indicate increased potential for calving events: the Rift Growth Metric (RGM). We determine the RGM from geometric observations derived from Landsat 8 imagery and ICESat-2 laser altimetry. ICESat-2 data enables us to characterize the status and behavior of mélange within each rift investigating its impacts on propagation of ice rifts on AIS. This method determines propagation shifts and assess mélange thickness spatiotemporally using geographic information systems software builds on established behavior of rift system dynamics before and after iceberg calving.

Ongoing increases in global sea level, projected to continue through the 21st century, have widespread impacts on coastal communities and infrastructure. Uncertainties in model projections of Antarctic Ice Sheet mass represent a major contribution to uncertainties in projected sea level rise. Many modelling studies have identified the important role of climate variability in driving ice sheet change; however, there have not been sufficient observational studies on the impact of this variability on the ice sheet.

The Antarctic Ice Sheet is vast, and remote; therefore, satellites are the only feasible instruments with which we can measure changes in ice mass. In particular, satellite radar and laser altimeter measurements of changes in ice sheet height are a valuable tool to monitor changes in mass of both grounded ice and floating ice shelves. In this dissertation, we use satellite altimetry together with other ancillary datasets to identify the influences of variability in atmospheric and oceanic conditions on ice sheet mass.

We demonstrate of how satellite radar altimetry data can be used to identify the climate drivers ice shelf change during 1994–2016 in the Antarctic Peninsula, a region that has changed rapidly during that period. In the western Antarctic Peninsula, the rates of ocean-driven basal melting exceeded values required to maintain constant mass. Extending this analysis to all Antarctic ice shelves, we find large interannual variability in the total volume flux of freshwater due to basal melting exported into the Southern Ocean, with the highest values occurring during the late 2000s from ice shelves in West Antarctica. Finally, we demonstrate how laser altimetry can be used to monitor large changes in snowfall at seasonal time scales over the grounded portion of the West Antarctic Ice Sheet during the 2019.

The results described in this dissertation together highlight the value of satellite altimetry in observing variability in ice sheet mass at seasonal to interannual time scales. We expect that they will help improve model projections of sea level rise through a better understanding of the processes driving ice sheet change, and by providing improved constraints on the current state of the atmosphere-ice-ocean system.

The Antarctic ice sheet has an extensive basal water system that lubricates the ice-bed interface and enables the fast flow of ice streams and outlet glaciers, which account for a majority of Antarctic ice discharge to the ocean. In the past decade, observational evidence has suggested that the subglacial hydrology of Antarctica can be non-steady, changing on sub-decadal timescales, but the effect of dynamic hydrology on ice flow remains uncertain. The Whillans Ice Plain (WIP), at the confluence of the Whillans and Mercer ice streams, West Antarctica, has been studied for over 50 years and has been identified as a region with extensive active subglacial hydrology. In this dissertation, we develop and implement methods using a combination of ground-based Global Positioning System (GPS) data and satellite-based radar and laser altimetry to observe the surface expression of water movement beneath WIP, quantify the dynamic ice-flow response to an evolving basal water system, and investigate processes driven by the interaction of WIP with ocean tides that may impact subglacial water flow near the grounding line. We find that the coupled subglacial-ice stream system can respond rapidly to basal perturbations on sub-annual timescales and in ways that are not captured by simple models. We demonstrate that the location where subglacial water enters the ocean is a complex interface that requires significant improvement to our measurement precision to better understand important time-varying processes. We also apply our method for observing dynamic ice-surface height changes to the inventory of known subglacial lakes in Antarctica to extend our observational record and assess variability of the subglacial hydrologic system in different physical settings. Through this continent-wide analysis of subglacial lakes, we suggest that our current knowledge of the characteristic spatial and temporal scales of hydrologic variability is still limited by our observational capacity. We conclude by proposing future studies that would address knowledge gaps currently preventing the inclusion of an evolving basal water system into large-scale predictive models of ice-sheet flow.

Increasing mass loss from the Antarctic Ice Sheet has contributed to recent acceleration in the rate of global mean sea-level rise (SLR). Its full SLR potential is ~58 m, and its future contribution remains highly uncertain. The flow of Antarctica’s grounded ice into the ocean, and thus its contribution to SLR, is regulated by buttressing from floating ice shelves. Ice-shelf mass loss can reduce this buttressing effect. In this dissertation, I used satellite and airborne remote sensing data to explore three processes by which the ocean drives mass change on Antarctica’s large Ross Ice Shelf (RIS).

First, I compared RIS thicknesses estimated from satellite laser altimetry and ROSETTA-Ice airborne radar data to identify a potential area of basal marine-ice accretion (i.e., local mass gain) in the ice-shelf interior. Large uncertainties prevent a definitive conclusion; reducing uncertainties will require additional measurements of ice-column density and firn properties. Second, I showed that airborne radar thickness profiles capture near-front thinning of RIS associated with basal melting by seasonally warmed upper-ocean water.

Finally, I investigated the bending of the RIS front due to buoyancy created by the melting-related development of a submerged bench of ice, a mechanism that may lead to mass loss by calving of small icebergs. Profiles of the ice-shelf surface height from two satellite laser altimetry missions (ICESat, 2003–2009; and ICESat-2, 2018–present) reveal that this bending is larger on the eastern section of the RIS front, reflecting along-front variability in near-front ice thickness and ocean conditions. I also found that the surface deformation increased overall between 2018 and 2022. Between the two satellite mission periods, these surface structures grew along sections of the RIS front that experienced large calving events in the early 2000s.

Taken together, these studies demonstrate that important mass-balance processes at the interface of ice shelf and ocean occur at small spatial scales that can only be resolved over large areas by high-resolution satellite and airborne sensors. Better understanding of these processes will require a combination of improved data density and models that correctly represent ocean properties and ice mechanical processes.

The salar de Uyuni in the Bolivian Andes is the largest salt flat on Earth, exhibiting less than 1 m of vertical relief over an area of 9000 km(2). We report on a kinematic Global Positioning System (GPS) survey of a 45-by-54 km area in the eastern salar, conducted in September 2002 to provide ground truth for the Ice Cloud and land Elevation Satellite (ICESat) mission. GPS post-processing included corrections for long-period GPS noise that significantly improved survey accuracy. We fit corrected GPS trajectories with 2-D Fourier basis functions, from which we created a digital elevation model (DEM) of the surface whose absolute accuracy we estimate to be at least 2.2 cm RMSE. With over two magnitudes better vertical resolution than the Shuttle Radar Topography Mission data, this DEM reveals decimetre-level topography that is completely absent in other topographic data sets. Longer wavelengths in the DEM correlate well with mapped gravity, suggesting a connection between broad-scale salar topography and the geoid similar to that seen over the oceans.