Subglacial hydrology modulates basal sliding response of the Antarctic ice sheet to climate forcing

Major uncertainties in the response of ice sheets to environmental forcing are due to subglacial processes. These processes pertain to the type of sliding or friction law as well as the spatial and temporal evolution of the effective pressure at the base of ice sheets. We evaluate the classic Weertman–Budd sliding law for different power exponents (viscous to near plastic) and for different representations of effective pressure at the base of the ice sheet, commonly used for hard and soft beds. The sensitivity of the above slip laws is evaluated for the Antarctic ice sheet in two types of experiments: (i) the ABUMIP experiments in which ice shelves are instantaneously removed, leading to rapid grounding-line retreat and ice sheet collapse, and (ii) the ISMIP6 experiments with realistic ocean and atmosphere forcings for different Representative Concentration Pathway (RCP) scenarios. Results confirm earlier work that the power in the sliding law is the most determining factor in the sensitivity of the ice sheet to climatic forcing, where a higher power in the sliding law leads to increased mass loss for a given forcing. Here we show that spatial and temporal changes in water pressure or water flux at the base modulate basal sliding for a given power, especially for high-end scenarios, such as ABUMIP. In particular, subglacial models depending on subglacial water pressure decrease effective pressure significantly near the grounding line, leading to an increased sensitivity to climatic forcing for a given power in the sliding law. This dependency is, however, less clear under realistic forcing scenarios (ISMIP6).</p

A new, fast and unified subglacial hydrological model applied to Thwaites Glacier, Antarctica

Subglacial hydrology is a crucial element for understanding the dynamics of marine ice sheets. Indeed, the presence of subglacial water modulates the ice basal motion, resulting in a modified ice flow across the entire ice sheet. Nonetheless, the subglacial environment is difficult to reach, which makes it necessary to develop models. Many efforts have recently been made in the glaciological and hydrological communities to improve their accuracy and efficiency. Even so, the models currently being developed are typically fairly costly in terms of computing time. As a consequence, conducting numerical simulations over long time scales or running ensemble simulations remains particularly challenging. Here, we propose a simplified approach for coupling subglacial hydrology with the motion of ice. First, we introduce a computationally efficient subglacial hydrology model that is suited for hard and soft bed types as well as efficient and inefficient drainage systems. Then, we show some numerical results based on our implementation of this model within the Kori-ULB ice-sheet code. We first study the impact of subglacial hydrology in the idealized MISMIP configuration. Subsequently, we show results of simulations conducted over Thwaites Glacier which suggest that the coupling of subglacial hydrology with ice flow could significantly increase the contribution of marine ice sheets to future sea-level rise

Modélisation analogique d'une inversion tectonique positive :exemple de la marge continentale de l'Ardenne.

info:eu-repo/semantics/publishe

Subglacial hydrology modulates basal sliding response to climate forcing of the Antarctic ice sheet

info:eu-repo/semantics/publishe

Coupling subglacial hydrology to basal friction in an Antarctic ice sheet model

info:eu-repo/semantics/publishe

The influence of subglacial hydrology on Antarctic ice sheet dynamics

Current observed mass loss of the Antarctic ice sheet is tightly linked to the loss of buttressing of ice shelves, leading to increased inland mass flux and concomitant grounding-line retreat. However, the rate of mass loss is also a function of the basal friction regime of the grounded ice sheet, exemplified by the type of sliding law governing basal sliding and/or sediment deformation. Recent studies (Ritz et al. 2015; Pattyn, 2017; Bulthuis et al. 2018) clearly advocate for higher mass losses with plastic sliding laws compared to viscous sliding. However, more elaborated processes leading to increased lubrication at the bed, such as subglacial hydrology, are often neglected.In this study we employ a basic subglacial hydrology model (Lebrocq et al. 2009) coupled to a thermomechanical ice-sheet model (f.ETISh; Pattyn, 2017) to investigate both the effect of sliding law power laws and subglacial water distribution on the sensitivity of Antarctic mass loss to ocean perturbations (represented by sub-shelf melting). Results show that while subglacial hydrology changes the sensitivity of the ice-sheet system, the choice of sliding law impacts sensitivity to a larger extent.info:eu-repo/semantics/publishe

Coupling subglacial hydrology to basal friction in an Antarctic ice sheet model

Due to the lack of direct observations, subglacial hydrology is still marginally considered in Antarctic ice sheet modelling studies, albeit that several approaches exist (e.g. LeBrocq, Bueler and Van Pelt). Subglacial hydrology impacts basal friction through a reduction in effective pressure and through changing properties of subglacial sediments, both factors influencing the lubrication at the bottom of the ice sheet. Several approaches exist to represent subglacial hydrology in ice sheet models (Bueler and Brown, 2009, Goeller et al. 2013) and are generally coupled to either a Coulomb or a Weertman friction law. However, the type of subglacial process determines to a large extent the sensitivity of Antarctic mass change (Sun et al, submitted).In this study we investigate the sensitivity of subglacial dynamics on the behaviour of the Antarctic ice sheet on centennial time scales. For this purpose we employ a subglacial hydrology model for subglacial water routing (Lebrocq et al. 2009) coupled to a thermomechanical ice-sheet model (f.ETISh; Pattyn, 2017). We consider different parametrizations and representations of effective pressure and till water content at the base. We also consider the combination of different friction laws and hydrological models (sheet flow, till deformation) depending on estimates of the subglacial conditions of the Antarctic ice sheet. Results show that the way of coupling subglacial hydrology influences the sensitivity of the ice-sheet system on centennial time scales. However, the type and power of the friction law (Coulomb versus Weertman) has the most dominant impact on ice sheet sensitivity.info:eu-repo/semantics/nonPublishe

Modélisation 3D par imagerie lidar et analyse structurale de la Salle du Dôme des Grottes de Han-sur-Lesse (Belgique, Ardenne)

La Salle du Dôme, au sein du réseau karstique des Grottes de Han-sur-Lesse, est la plus grande cavité reconnue en termes de volume souterrain en Belgique. Un pli-faille de grande ampleur affecte son plafond. En février 2016, un modèle 3D haute résolution de la Salle du Dôme a été réalisé par acquisition lasergrammétrique (lidar terrestre). Ce modèle a abouti à une représentation visuelle complète de la cavité. Pour une analyse structurale quantitative des fractures et discontinuités des roches dans une cavité karstique, l’imagerie lidar est un outil très efficace, car il permet de capturer avec acuité les morphologies des parois des grottes, objets souvent peu accessibles directement. L’acquisition topographique haute résolution a permis l’analyse de la fracturation de la Salle du Dôme dans les 3 dimensions de l’espace. Celle-ci est ensuite intégrée à l’histoire tectonique régionale. À partir du logiciel de rétro-ingénierie 3DReshaper©, la visualisation géométrique du pli-faille est obtenue par la mise en place d’une succession de plans créés à partir de minimum trois points sur les plans de stratification. La direction et le pendage de chaque plan sont déterminés par trigonométrie à partir des coordonnées des normales, calculées par le programme de visualisation. Sur la base du modèle 3D, un canevas structural du plafond est proposé. À terme, l’analyse structurale à partir d’une imagerie LIDAR aboutit à mieux cerner la géométrie et la dynamique d’une structure régionale qui joue un rôle indéniable dans l’évolution de la karstogenèse de la cavité.The “Salle du Dôme”, located in the middle of the karstic network of the Han-sur-Lesse Cave, is the biggest known cavity in terms of underground volume in Belgium. A large fold thrust can be seen across its roof. In February 2016 a high resolution 3D model of the “Salle du Dôme” was generated, using lasergrammetry acquisition (terrestrial Lidar). This model resulted in a complete visual representation of the cavity. Lidar images are very useful to perform structural quantitative analysis of the fractures and discontinuities of rocks in a karstic cavity, because the cave walls are usually difficult to access. The analysis of the fractures of the “Salle du Dôme” was then integrated into the regional tectonic history. Thanks to the reverse engineering software 3DReshaper©, it became possible to create a geometrical viewing of the fold thrust by a succession of planes created with at least three points on the stratification planes. The direction and dip of each plane are determined with trigonometric calculations, based on the coordinates of their normals, which are available thanks to the viewer software. On the basis of the 3D model, it is possible to present a structural pattern of the roof. Finally, the structural analysis based on Lidar images helps to better understand the geometry and dynamics of a regional structure which plays an undeniable role in the evolution of the karstogenesis of the cavity

Analogue modeling of passive-margin tectonic inversion: example from the Ardennes Variscan fold-and-thrust belt

International audienc

Modélisation analogique d’une inversion tectonique positive : exemple de la marge continentale de l’Ardenne

International audienc