Iceberg A-68 separated from the Larsen C Ice Shelf in July 2017 and the impact of this event on the local ocean circulation has yet to be assessed. Here, we conduct numerical simulations of ocean dynamics near and below the ice shelf pre- and post-calving. Results agree with in situ and remote observations of the area as they indicate that basal melt is primarily controlled by wintertime sea-ice formation, which in turn produces High Salinity Shelf Water (HSSW). After the calving event, we simulate a 50% increase in HSSW intrusion under the ice shelf, enhancing ocean heat delivery by 30%. This results in doubling of the melt rate under Gipps Ice Rise, suggesting a positive feedback for further retreat that could destabilize the Larsen C Ice Shelf. Assessing the impact of ice-front retreat on the heat delivery under the ice is crucial to better understand ice-shelf dynamics in a warming environment.

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Land ice discharge from the Antarctic continent into the ocean is restrained by ice shelves, floating extensions of grounded ice that buttress the glacier outflow. The ongoing thinning of these ice shelves – largely due to enhanced melting at their base in response to global warming – is known to accelerate the release of glacier meltwater into the world oceans, augmenting global sea level. Mechanisms of ocean heat intrusion under the ice base are therefore crucial to project the future of Antarctic ice shelves. Furthermore, ice shelves are weakened by the presence of kilometer-wide full-thickness ice rifts, which are observed all around Antarctica. However, their impact on ocean circulation around and below ice shelves has been largely unexplored as ocean models are commonly characterized by resolutions that are too coarse to resolve their presence. Here, we apply the Massachusetts Institute of Technology general circulation model at high resolution to investigate the sensitivity of sub-shelf ocean dynamics and ice-shelf melting to the presence of a kilometer-wide rift in proximity of the ice front. We find that (a) the rift curtails water and heat intrusion beneath the ice-shelf base and (b) the basal melting of a rifted ice shelf is on average 20 % lower than for an intact ice shelf under identical forcing. Notably, we calculate a significant reduction in melting rates of up to 30 % near the grounding line of a rifted ice shelf. We therefore posit that rifts and their impact on the sub-shelf dynamics are important to consider in order to accurately reproduce and project pathways of heat intrusion into the ice-shelf cavity.@en

Ice, a pervasive element across the Solar System, holds immense importance in understanding the response of the Earth to ongoing climate change as well as the dynamics of planetary bodies. This dissertation investigates ice fractures on terrestrial and planetary ice bodies, focusing on their impact on the melting of ice shelves in Antarctica and their dynamics on Europa, one of Jupiter’s moons. The urgency to understand the behavior of terrestrial ice shelves under environmental forcing is driven by the ongoing climate crisis. Antarctica is experiencing a rapid loss of mass, primarily due to increasing ocean-induced melting at the base of its ice shelves in response to global warming. The release of glacier meltwater into the world’s oceans contributes to arising the global sea level. However, the rate and magnitude of sea-level rise are highly uncertain and the potential ice mass-loss from Antarctica could significantly accelerate sea-level rise throughout this century due to the instability of its ice shelves. Thus, accurately projecting Antarctica’s contribution to global sea level necessitates a better understanding of the processes behind the loss of its ice shelves. In this dissertation, I examine the thinning of Antarctic ice shelves caused by enhanced melting at their base due to warming oceans. Intrusion of ocean heat beneath the ice shelves indeed plays a crucial role in projecting their future. Through idealized ocean modeling using the Massachussetts Institute of Technology general circulation model (MITgcm), I simulate ocean dynamics under the ice, investigating the impact of fractures and ice front retreat on the sub-shelf ocean circulation. Results indicate that fractures may act as barriers, inhibiting the intrusion of warm water towards the inland sections of the ice shelves, and thereby reducing basal melt. Furthermore, I examine the impact of the separation of iceberg A-68 from the Larsen C ice shelf in July 2017 on the sub-shelf ocean dynamics. This specific retreat event leads to the redistribution of heat under the ice, resulting in enhanced melting in specific sections of the ice shelf, suggesting future destabilisation of Larsen C. These findings highlight the importance of considering updated ice-shelf coastlines to accurately project ocean circulation and its implications for ice shelf stability. Furthermore, this dissertation explores the dynamics of specific lineament features observed on the surface of Europa, which are identified as ice fractures. Although limited observations restrict our understanding of ice fracturing events on this moon, insights from studying terrestrial ice sheets provide valuable knowledge. By extend ing an existing terrestrial-based numerical model of fracture propagation on ice shelves, I show that some lineaments on the surface of Europa exhibit a behavior that is similar to ice fractures on Antarctic ice shelves. The model depicts the evolution of these lineament features as bursts of fracture propagation events interspersed with periods of inactivity, which is a typical behavior of fractures on terrestrial ice shelves. Overall, this dissertation shows the potential for synergy between Earth and planetary science. By leveraging advances in our understanding of physical processes on Earth, terrestrial-based models and theories contribute to expanding our knowledge of physics on other celestial bodies. This interdisciplinary approach, supported and validated by remote sensing and in-situ missions, is fundamental in order to advance our understanding of ice fractures, their interaction with the surrounding environment and their dynamics throughout the Solar System. On Earth, a better understanding of the dynamics of Antarctic ice shelves is imperative to correctly project Antarctica’s contribution to global sea level.@en

The sudden propagation of a major preexisting rift (full-thickness crack) in late 2016 on the Larsen C Ice Shelf, Antarctica led to the calving of tabular iceberg A68 in July 2017, one of the largest icebergs on record, posing a threat for the stability of the remaining ice shelf. As with other ice shelves, the physical processes that led to the activation of the A68 rift and controlled its propagation have not been elucidated. Here, we model the response of the ice shelf stress balance to ice shelf thinning and thinning of the ice mélange encased in and around preexisting rifts. We find that ice shelf thinning does not reactivate the rifts, but heals them. In contrast, thinning of the mélange controls the opening rate of the rift, with an above-linear dependence on thinning. The simulations indicate that thinning of the ice mélange by 10 to 20 m is sufficient to reactivate the rifts and trigger a major calving event, thereby establishing a link between climate forcing and ice shelf retreat that has not been included in ice sheet models. Rift activation could initiate ice shelf retreat decades prior to hydrofracture caused by water ponding at the ice shelf surface.

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Existing lineaments on the surface of the Jovian moon Europa are thought to be the result of ongoing brittle crack formation in the elastic regime. Arcuate features are called cycloids and can be modeled using linear elastic fracture mechanics. Here, we build on existing terrestrial models of rift propagation and extend them to cycloids on the moon. We propose that these cracks tend to grow as a series of nearly instantaneous events, spaced by periods of inactivity. The behavior is similar to what is observed on Antarctic ice shelves, where rifts can remain dormant for years. We argue that dormant periods between growth events could explain the presence of cycloids on Europa even without invoking secular motion of the crust. Furthermore, being able to model propagation events and their timing should help future missions exploring the moon.

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