Numerical continuation methods for marine ice-sheet systems with various friction laws

Ice sheets are complex components of the climate system whose understanding is crucial in order to obtain robust predictions, in particular in context of the future sea-level rise. Marine regions, which are the areas in contact with the ocean, are of particular interest because they are non-linear systems. In particular, it has been previously shown that they exhibit turning-point bifurcations and hysteresis (Schoof, Ice sheet grounding line dynamics: Steady states, stability, and hysteresis, in J. Geophys. Res., vol. 112, 2007). Mathematically, marine regions can be formulated as obstacle problems, in which the “obstacle” is the underlying bedrock. Numerical continuation methods are great tools to study marine ice-sheet systems, as they allow to obtain the solutions associated with a range of parameter values, which naturally leads to bifurcation diagrams. In the glaciology literature, such methods have been used for a 1D geometry and with the so-called Weertman friction law (Mulder et al., Stochastic marine ice sheet variability, in J. Fluid Mech., vol. 843, pp. 748-777, 2018). However, there is an interest in applying this kind of methods to more general configurations, in particular to 2D geometries and to more complex friction laws. The main challenge for this extension is the presence of non-linear or non-smooth terms in the governing equations, which depends on the mathematical formulation of the contact problem and the friction laws used. In this presentation, we describe several continuation methods which can be applied to our problem, and we illustrate them on several configurations. Specifically, we introduce a novel constraint function that does not rely on the assumption that the solution curve is smooth, as opposed to the classical pseudo arc-length method. This constraint is based on variables that appear in a primal-dual formulation of the obstacle problem. We show that this continuation method is efficient and compatible with several friction laws which depend on both the velocity and the effective pressure between the ice and the bedrock

Extension of marine ice-sheet flux conditions to effective-pressure-dependent and hybrid friction laws

Marine ice sheets are complex systems with a highly non-linear behavior. There remains a large uncertainty about how various physical processes such as the basal friction and the subglacial hydrology affect the dynamics of the grounding line (GL). One possibility to better understand their mechanical behavior consists in adopting a boundary-layer analysis close to the GL. Specifically, one can derive a so-called flux condition, which is an analytical expression for the amount of ice that flows through this GL per unit time. In turn, this flux condition can provide useful information about the grounding-line dynamics, including the presence of hysteresis (Schoof, 2007b). Several studies have introduced hybrid friction laws to model friction between the grounded part of the ice sheet and the bedrock (Schoof, 2005, Gagliardini et al., 2007). These friction laws behave as power-law friction laws far from the GL and plastically closer to it. Recent experiments have shown that these models are more realistic than the usual power-law friction (Zoet and Iverson, 2020). In parallel, sophisticated models for the subglacial hydrology have been developed (Bueler and van Pelt, 2015). In this presentation, we show that the flux conditions previously derived for the Weertman friction law (Schoof, 2007a) and the Coulomb friction law (Tsai et al., 2015) can be extended to a flux condition for the general Budd friction law, with two different simple effective-pressure models for the subglacial hydrology. Using asymptotic developments, we provide a justification for the existence and uniqueness of a solution to the boundary-layer problem. Finally, we generalize our results to hybrid friction laws, based on a parametrization of the flux condition

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

Benchmark experiments for higher-order and full-Stokes ice sheet models (ISMIP-HOM)

We present the results of the first ice sheet model intercomparison project for higher-order and full-Stokes ice sheet models. These models are compared and verified in a series of six experiments of which one has an analytical solution obtained from a perturbation analysis. The experiments are applied to both 2-D and 3-D geometries; five experiments are steady-state diagnostic, and one has a time-dependent prognostic solution. All participating models give results that are in close agreement. A clear distinction can be made between higher-order models and those that solve the full system of equations. The full-Stokes models show a much smaller spread, hence are in better agreement with one another and with the analytical solution

Out FOXing Parkinson Disease: Where Development Meets Neurodegeneration

The central survival role of FOX proteins may allow a unified view of the genetic and environmental factors that cause Parkinson disease

Living on the edge: How to prepare for it?

IntroductionIsolated, confined, and extreme (ICE) environments such as found at Antarctic, Arctic, and other remote research stations are considered space-analogs to study the long duration isolation aspects of operational space mission conditions.MethodsWe interviewed 24 sojourners that participated in different short/long duration missions in an Antarctic (Concordia, Halley VI, Rothera, Neumayer II) or non-Antarctic (e.g., MDRS, HI-SEAS) station or in polar treks, offering a unique insight based on first-hand information on the nature of demands by ICE-personnel at multiple levels of functioning. We conducted a qualitative thematic analysis to explore how sojourners were trained, prepared, how they experienced the ICE-impact in function of varieties in environment, provided trainings, station-culture, and type of mission.ResultsThe ICE-environment shapes the impact of organizational, interpersonal, and individual working- and living systems, thus influencing the ICE-sojourners' functioning. Moreover, more specific training for operating in these settings would be beneficial. The identified pillars such as sensory deprivation, sleep, fatigue, group dynamics, displacement of negative emotions, gender-issues along with coping strategies such as positivity, salutogenic effects, job dedication and collectivistic thinking confirm previous literature. However, in this work, we applied a systemic perspective, assembling the multiple levels of functioning in ICE-environments.DiscussionA systemic approach could serve as a guide to develop future preparatory ICE-training programs, including all the involved parties of the crew system (e.g., family, on-ground crew) with attention for the impact of organization- and station-related subcultures and the risk of unawareness about the impact of poor sleep, fatigue, and isolation on operational safety that may occur on location

Ice flux divergence anomalies on 79north Glacier, Greenland

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