Description of the thesis topic

The dynamics of sea ice is governed by a set of mechanical processes and complex interactions with the ocean and the atmosphere. The properties that characterize it have been established through the analysis of satellite observations over a scale range from 10km to approximately 1000km, and from the daily to seasonal scale. More specifically, scale invariance properties have been demonstrated across this entire spatio-temporal spectrum. However, it is not yet clear to what scale these properties extend. Indeed, particularly at kilometer/sub-kilometer scales, sea ice can no longer be considered a continuous object from a mechanical point of view. Rather, a granular state of the ice is observed, which is then composed of an assembly of ice fragments or "floes". As they drift, the floes interact mechanically with each other via contact dynamics, a process fundamentally different from the friction processes along shear faults that appear to control ice shelf movements on a larger scale. At small scales, the number of available observations remains too low for a robust study. A new generation of numerical ice shelf models has recently been developed to study, among other things, the realistic behaviour of the dynamics of a floe assembly, based on a granular approach.

The purpose of this thesis will therefore be to explore the properties of ice pack dynamics at kilometer/sub-kilometer and sub-daily scales based on these new modelling approaches, and more specifically the FloeDyn code developed in recent years at LJK/Grenoble and more recently at Sorbonne University/Paris as part of the SASIP project. It will be appropriate to verify whether a change in dynamic regime occurs at these scales, what are its characteristics, and its origin. This will be done within the framework of the concept of "solid turbulence" which seems to be quite relevant for characterizing ice pack dynamics across a very wide range of scales, from that of an assembly of floes to that of an ocean basin. In addition, a more detailed study on the importance of the mechanical coupling between the ice pack and the underlying oceanic boundary layer could be conducted.

This work will lead to a better understanding and characterization of sea ice dynamics and its interactions with the underlying ocean. It will potentially improve the parameterization of rheology integrated into current large-scale sea ice models, particularly those used for real-time forecasting and/or in the context of coupled climate simulations.

For the first two years, this thesis will be part of the international SASIP project (https://sasip-climate.github.io), for which Pierre Rampal is the principal investigator. SASIP is a research project funded by the Schmidt Sciences Foundation that aims, among other things, to develop a next-generation sea ice model for use in future climate models. It involves 11 partners from five different countries (France, the United States, Norway, Italy, and the United Kingdom). The project also aims to assess the impact of sea ice dynamics on its fate, as well as on upper ocean mixing and large-scale polar climate. The project proposes an innovative approach to model sea ice dynamics from the ice floe scale to the basin scale, leveraging hybrid data assimilation and machine learning methods to shape a physically robust parameterization and to calibrate the associated parameters.

Required Skills
The candidate must hold an engineering degree and/or a master's degree in geosciences, climate sciences, or applied mathematics. More specifically, the position requires solid knowledge of physical oceanography (ideally glaciology and solid/granular mechanics), as well as good oral and written communication skills (French and English required) to present at conferences and write articles in scientific journals. We are looking for a motivated and curious individual who will be committed to their project, who has a certain degree of autonomy and a strong motivation to develop interdisciplinary skills. In addition, the candidate must be able to work in a team and interact in an international environment.

Work Context

The thesis will be affiliated with the Doctoral School of Earth, Environmental, and Planetary Sciences (ED 105 STEP) and will be conducted at the Institute of Environmental Geosciences (IGE) in Grenoble. The Institute of Environmental Geosciences (IGE) is a public research laboratory under the supervision of the CNRS/INSU, the IRD, the Université Grenoble Alpes (UGA), the INRAE, and Grenoble-INP. It employs approximately 330 people, including 190 permanent staff members (researchers, lecturers, engineers) and approximately 140 doctoral students, postdoctoral fellows, and staff members on fixed-term contracts. The thesis will be supervised by Pierre Rampal (CNRS, IGE, Grenoble) and co-supervised by Mickael Bourgoin (CNRS, ENS, Lyon). In addition, two other researchers will also be part of the supervisory team: Quentin Jouet (Montagne bleue, lead developer of FloeDyn) and Dr Jérôme Weiss (CNRS, ISTERRE, Grenoble).

Constraints and risks

NTR