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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.

Tidewater glaciers are important conduits transporting ice from the land to the oceans. The two most important processes that remove mass from tidewater glaciers are iceberg calving and submarine melting. This dissertation seeks to use a novel finite element formulation of the ice dynamics to link iceberg calving to submarine melt. Increased calving and rapid retreat of glaciers can contribute significantly to sea level rise, but the processes controlling glacier retreat remain poorly understood. To improve our understanding of calving, a two-dimensional full Stokes finite element model was developed to calculate the stress field controlling tensile and shear failure. Using idealized rectangular geometries, we find that when rapidly sliding glaciers thin to near buoyancy, full thickness tensile failure occurs, similar to observations motivating height-above-buoyancy calving laws. In contrast, when glaciers are frozen to their beds, basal crevasse penetration is suppressed and calving is minimal. We also find shear stresses are largest when glaciers are thickest. Together, the tensile and shear failure criteria map out a stable envelope in an ice-thickness-water-depth diagram. The upper and lower bounds on cliff height can be incorporated into numerical ice sheet models as boundary conditions, thus bracketing the magnitude of calving rates in marine-terminating glaciers. Moreover, findings indicate that the combination of ice flow and erosion by submarine melt can affect the stress field as well. Our simulations show that for a range of melt rates and melt profiles, submarine melting can both increase and decrease calving rates with the magnitude and sign of the effect determined by the shape of the melt profile and the relative magnitude of average melt rate. Despite the fact that calving is suppressed in some circumstances, the addition of submarine melt almost always increases the total mass loss through the combination of calving and submarine melt. These results suggest that relatively small amounts of submarine melt can significantly increase calving rates and destabilize glaciers, but calving and frontal ablation are increasingly controlled by submarine melting as it continues to increase. Our model not only is able to provide explanations for existing 'calving laws' but is also consistent with observational data. These simulation results also prove that submarine melt can significantly alter the partitioning between calving and melting along with the total frontal ablation, improving our understanding of the interplay between submarine melting and iceberg calving.

Abstract: Time lapse imagery, an audio recorder and geophones were used to detect iceberg calving events on the Belcher Glacier, Devon Island, in the Canadian High Arctic, in order to identify the major controls on the rate and style of calving. Eleven calving events were identified between June 4th and August 14th 2009 which accounted for 44% of the annual calving flux. Several of the events recorded in the audio data were associated with debris avalanching and disintegration of large tabular bergs. The geophones did not identify calving events but did record hydro-fracturing when terminus water-filled crevasses drained into the glacier. None of the calving events were a direct response to an increase in ice velocity in the terminus region, break-up of the sea ice/mélange, tidal flexure of the terminus, or propagation of water-filled crevasses. The Belcher Glacier maintains a lightly grounded stable terminus position but develops a protrusion at the glacier centreline every few years. When this occurs, as it did in 2009, the meltwater plume is active in eroding the lateral stability of the protrusion by locally enhancing the calving rate. Further investigation is required to examine whether basal melt also undercuts the protrusion, eventually leading to its flotation. In 2009 the protrusion calved off as a series of tabular icebergs which strongly suggests it was floating, as do calculations of height-above-buoyancy and subglacial effective pressure. In general, calving was not driven by a single identifiable cause and its stochastic timing may reflect the progressive accumulation of damage to the ice as it is transported to the terminus. The interactions of ice flow with the ice and bed geometry, as well as ponding and hydro-fracturing of supraglacial meltwater, seemed to be the main contributors to this damage.