PhD subject: Theoretical, experimental and numerical study of water and
energy transfers in superficial organic layers of permafrosts


To be started in october 2018 in Toulouse, France.
Duration: 3 years.

Laboratories:

Géosciences Environnement Toulouse (GET) - Geosciences Environment Toulouse
Institut de Mécanique des Fluides de Toulouse (IMFT) - Toulouse Institute of Fluid Mechanics

Supervisors:

Laurent Orgogozo (GET)
Manuel Marcoux (IMFT)

Other collaborations:

Yohan Davit (IMFT)
Michel Quintard (IMFT)
Oleg Pokrovsky (GET)
Christophe Grenier (Laboratoire des Sciences du Climat et de l'Environnement, LSCE - Laboratory of Environment and Climate Sciences)

Permafrosts cover about a quarter of the emerged lands of the northern hemisphere, and they thoroughly impact the hydro-bio-geochemical dynamics of the regions where they are present. Moreover, they are located in the areas that experience the strongest climate changes, the boreal areas. The hydrological regimes of the continental surfaces occupied by permafrosts are thus prone to be affected by fast changes, with consequences that may be important both on natural cycles (water, carbon, …) and on human activities (water supply, infrastructures stability, …). Therefore the development of relevant modeling tools is more necessary than ever in order to anticipate these changes. One of the major related difficulties is the quantification of transfers in the superficial organic layers that cover wide spaces in boreal areas (e.g. : peat layers in the plains of Arctic European Russia or of Western Siberia, moss and lichen layers in the taiga of Central Siberia). These layers act as thermal insulators and hydrological drains that play key roles in the active layer dynamics, and consequently in all the biogeochemical dynamics of the ecosystems of these regions. They thus exert strong controls on the responses of these ecosystems to anthropogenic perturbations. Due to the complex and highly porous structures of these media, the quantification of their thermal and hydrological properties for the whole range of water content (variably saturated media) and temperature (freeze/thaw of the poral water) conditions that may be encountered on boreal continental surfaces is challenging both theoretically and experimentally.

This PhD project aims to quantify the water and energy transfers in the superficial organic layers of the boreal regions through a theoretical upscaling approach coupled with experimental characterizations of natural samples in controlled cryogenic conditions. The considered samples are moss and peat samples from various sites of long term monitoring of thermo-hydrological dynamics of permafrosts (for example Khanimey in Western Siberia and Kulingdakan in Central Siberia). 3D tomographies of the samples will be used to obtain the relevant pore-scale geometry information needed for the numerical application of the theoretical upscaling study and also to interpret direct measurements of thermo-hydric properties. The results of the theoretical and experimental study of the thermo-hydric properties of the superifical organic layers of the boreal areas will then be used in order to parameterize mechanistic models of transfers in the studied sites with permaFoam, a high performance computing modeling tool for water and energy transfer in variably saturated porous media with freeze/thaw of the poral water developed in Toulouse (Orgogozo et al., 2016, 2017, in prep).

The considered transfer phenomena are highly non-linear and coupled, so that their numerical resolutions is difficult and requires the use of high performance computing techniques (CALMIP supercomputing center). This modeling work will be based on the very complete field data set acquired in the framework of the international research group GDRI CAR WET SIB since 2010.

The two main goals of this PhD project will thus be :

  • to theoretically and experimentally quantify the thermal and hydrodynamical transfer properties at Darcy scale of the superficial organic layers of the boreal areas at different water content and at different temperatures, based on the pore-scale transfer processes ;
  • to characterized on this basis the thermal and hydrological transfers in the active layers of various monitoring sites in permafrost affected areas along the seasonal freeze/thaw cycles, performing Darcy scale modeling with permaFoam.

The PhD student shall thus apply the method of volume averaging, realize experimental works of tomography of natural samples in controlled cryogenic conditions, and finally integrate the obtained results in simulations of transfers in the framework of the Computational Fluid Dynamics environment OpenFOAM® in which permaFoam is developed. Comparative analyses of the modeling results with permaFoam and the field observations available in the GDRI CAR WET SIB will finally be realized in order to improve our understanding of the processes that govern the water and energy fluxes in boreal environments.

The candidate shall have a solid background in applied mathematics for physics and in numerical methods for the resolution of partial differential equations. Knowledge in transfers in porous media and/or programming skills would also be appreciated, as well as a pronounced interest for experimental work.

In order to candidate, please send a curriculum vitae and a motivation letter, along with the notes obtained during the scholar year 2016-2017 to the address below.

Laurent Orgogozo
Maître de Conférences de l'Université Paul Sabatier - Toulouse III
Géosciences Environnement Toulouse UMR 5563 CNRS-IRD-UPS
Adresse : OMP - 14 avenue Edouard Belin, 31400 Toulouse, France.
Telephone : + 33 (0) 5 61 33 25 74
Courriel : toulouse18031@earthworks-jobs.com

published: 16 March 2018     Please mention EARTHWORKS when responding to this advertisement.