Description of the thesis topic

Predicting the control of glacier morphology on subglacial hydrology and basal sliding: from the Alps to Greenland

By controlling the flux of ice towards the ocean, the flow of polar ice caps plays a key role in the fate of the cryosphere and subsequent sea-level rise in response to global warming. Glacier flow is set by both glacier internal deformation and glacier basal sliding, with the latter remaining particularly poorly understood despite being a dominant driver of dynamical changes. This lack of knowledge is primarily due to glacier basal friction being highly influenced by complex subglacial hydrology processes (Gilbert et al., 2022; Gimbert et al., 2021). Recent work conducted in our group has shown that spatial changes in basal friction are mainly controlled by changes in subglacial hydrology as driven by changes in glacier morphology, that is mainly surface slope (Maier et al., 2022), rather than by changes in melt rates as was commonly considered (Nienow et al., 2017; Tedstone et al., 2015). We suggested that the dependency of glacier bed friction on glacier morphology is primarily due to changes in water storage in weakly connected parts of the bed. Lower surface slopes are expected to drive lower subglacial water pressure gradients, which limits water drainage efficiency (through channels and/or connected cavities) and thus promotes water basal lubrication through increased storage in weakly connected cavities. These weakly-connectivity cavities, however, yet remain poorly documented by observations and undescribed in physical models of subglacial hydrology (e.g. Werder et al., 2013), such that the control of glacier morphology on basal friction cannot explicitly be described.
The overarching goal of this Ph.D. is to develop a modelling framework capable of representing the control of glacier morphology on basal friction through changes in subglacial hydrology characteristics and in particular cavity connectivity and channel evolution. First, we will explicitly represent weakly-connected high-water pressure cavities in subglacial hydrology models through describing the control of multi-scale bed roughness characteristics on cavity dynamics as well as on their interactions with drainage in connected cavities and/or channels. This work will be done using the software ELMER-Ice for the ice dynamics part, as well as using a dedicated software such as Comsole multi-physics for the water drainage part. This physical model will be tested against targeted observations from the literature as well as against novel seismically-based observations acquired in the context of the ERC project REASSESS (2024-2029), which the hired student will have the opportunity to acquire and analyze. Second, we will perform predictions under varying configurations in order to explore the range of model parameters that play a primary control, such that an empirical law may be proposed. Ultimately, we will incorporate this empirical law into large-scale ice-sheet models using Elmer-ICE and/or GRISLI in order to, for the first time, evaluate the control of glacier morphology onto long term friction changes in a context of deglaciation. This ultimate step will set the grounds for more reliable predictions of glacier evolution and thus contribution to sea-level rise over the coming decades to centuries.

Work Context

IGE is a public research laboratory under the auspices of CNRS, IRD, Université Grenoble Alpes (UGA) and Grenoble-INP, working on climate change and the anthropization of our planet in the polar, mountain and intertropical regions, which are particularly sensitive and have major societal implications.
The laboratory employs an average of 330 people, including 190 permanent members (researchers, teacher-researchers, engineers, technicians and administrative staff) and around 140 PhD students, post-docs and staff on fixed-term contracts. Each year, the laboratory welcomes around 120 trainees and visiting scientists. The IGE is housed in four buildings on the Grenoble university campus (Glaciology building, OSUG-B, Maison Climat Planète and INRAE-Grenoble Saint Martin d'Hères).
The successful candidate will work as part of the IGE's CyroDyn team, reporting to Florent Gimbert and Adrien Gilbert.

Constraints and risks

The person recruited may be required to carry out field missions in hostile environments.

Additional Information

Nothing to report