11 research outputs found
Coordinates of cycloids on Europa
No full textSupporting information for: Poinelli, M., Larour, E., Castillo-Rogez, J., & Vermeersen, B. (2019). Crevasse propagation on brittle ice: Application to cycloids on Europa. Geophysical Research Letters, 46, 1–8. https://doi.org/10.1029/2019GL084033
The file called Cycloids.csv includes coordinates of 4 cycloids on the surface of the Jovian moon Europa.
Europa reference radius is 1562 km.
Latitude type is planetocentric. Longitude direction is positive west while longitude domain is: 0 to 360.</p
Toward a better Understanding of Europa Crevasses: Application of Linear Elastic Fracture Mechanics to Europa
No full textEuropa is one of the most interesting celestial world that has been ever observed. The habitability condition, met for the liquid water layer covering the moon, yields to astonishing speculations concerning what might exist in the interior of the tiniest moon of Jupiter. The Voyager and Galileo programs detected a frozen and brittle layer, deeply battered by lineament features. The observed crevasses on the moon's icy surface can be considered as results of a strong and variating stress field applied to the brittle icy shell that eventually reaches critical deformation conditions locally, and favors the process of crevasse propagation. The superimposition of secular widening to diurnal components is the source of stress that continuously deforms the brittle surface of Europa and induces the ice to crack, similarly to the processes observed with crevasses in large terrestrial ice sheets. The research's aim is to improve the existing models of fracture propagation for the Europa ice shell, dealing with analogs observed in Earth's crevasses on large ice shelves, by the implementation and the usage of linear elastic fracture mechanics (LEFM). Two different LEFM approaches are included in the document, one dealing with the estimation of global areas on the moon that are more favorable to host propagation and one dealing with the estimation of fractures' lengths for specific observed features. Results describe the existence of critical and non-critical areas centered in the equatorial zone which are respectively prone or not to host vertical propagation. Maximum critical depths for surface crevasses reach values of 120 meters, while critical heights for bottom crevasses show values up to 1.5 kilometers. Beside the outcomes of the vertical simulation, a mathematical manipulation of the LEFM analysis allowed the determination of horizontal cracks’ growth. Knowing the aspect of an observed lineament, the current model could calculate fracturing events’ intensity. These reach propagation rates of kilometers per second, namely almost instantaneous episodes. The outcomes of the current research are particularly interesting when seen in relation with the future exploration missions to Europa: ESA's JUICE, NASA Europa Clipper and its potential lander. Specific areas that are more prone to host propagation and the determination of growth rates are helpful elements in the preliminary description of target landing areas and the fracturing events’ detection possibility. The built model yields to a further and more accurate understanding of the dynamics for the interior of one of the most promising celestial object, in term of searching for a biosphere, hence extraterrestrial life.Aerospace Engineerin
MPoinelli/Poinelli2023b_GRL: version 0
No full text<p>Initial release for peer review.</p>
Ocean Dynamics and Ice Fractures: Insights from Earth and Beyond
No full textIce, 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.Physical and Space Geodes
Physical processes controlling the rifting of Larsen C Ice Shelf, Antarctica, prior to the calving of iceberg A68
No full textThe 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.Physical and Space Geodes
Basal channels affecting oceanic melting and freezing of a rifted Antarctic ice shelf
No full textFloating ice shelves regulate Antarctic ice sheet mass loss by buttressing land ice discharge toward the ocean. Next to basal melting, iceberg calving following the propagation of rifts has the potential to reduce this buttressing effect. However, rift propagation is largely unpredictable and generally not resolved in coarse climate models. The sub-shelf ocean circulation is believed to play an important role in rift propagation as it is closely related to ice shelf melting and freezing. Previous work suggests that the sub-shelf circulation of an intact ice shelf is altered by the presence of km-wide basal channels. As it could impact freezing and melting, the potential effect of basal channels on a rifted Antarctic ice shelf should be explored.In this study, the Massachusetts Institute of Technology general circulation model was applied to explore for the first time the potential effect of basal channels on the melting and freezing of a rifted Antarctic ice shelf. To this end, four simulations were performed with a high-resolution ocean model for the domain of an ice shelf cavity with idealized boundary conditions. These simulations correspond to a cavity with melt channels, a prominent rift close to the ice shelf front, both, and none of them. The effects of channels, a rift or the combination of both on melt, freezing and ocean circulation in the cavity were assessed through a comparison of these four simulations. Following previous research, results show that basal channels decrease ice shelf basal melting. We found that the addition of only a rift does not change the melt intensity or pattern. In addition, it was found that basal channels increase the freezing inside a rift. A sub-shelf boundary current on the Coriolis favoured side of the domain without channels is reformed to a clockwise circulation in each channel, resulting in an adjusted flow pattern inside the rift from one single large clockwise return flow to a smaller one behind each channel. Hence, buoyant cold shelf meltwater does not only enter the rift in the boundary current but after every topographic incision, and the thermal forcing is increased. Furthermore, the multiple return flow pattern enlarges the average frictional velocity inside the rift, which is positively related to the freezing rate intensity. In an offline calculation, it was found that the contribution of the thermal forcing to the total freezing amount is approximately three times larger than the friction velocity.From our simulations, we conclude that the presence of basal channels in a rifted ice shelf decreases basal melting at the grounding line and increases freezing inside rifts. Previous work on rift propagation suggests that these results imply that marine ice accretion inside the rift could increase, and fracture propagation could be reduced. Given these connections between ice shelf processes, this study stresses the importance of including basal channels and rifts in ice shelf cavity models to robustly reproduce Antarctic sub-shelf circulation and basal melt.Civil Engineerin
Ice-Front Retreat Controls on Ocean Dynamics Under Larsen C Ice Shelf, Antarctica
No full textIceberg 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.Physical and Space GeodesyGeoscience and Remote Sensin
Physical processes controlling the rifting of Larsen C Ice Shelf, Antarctica, prior to the calving of iceberg A68 in 2017
No full text
Can rifts alter ocean dynamics beneath ice shelves?
No full textLand 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
