2-D modelling of fluid flow and heat transfer in the Paris basin, France: an assessment of the impact of permafrost during the last glacial/interglacial cycle.
Résumé
Periglacial areas are usually underlain by permafrost. Its geographic and depth distribution is mainly controlled by surface temperatures and therefore, has fluctuated according to climatic variations, especially during the last glacial/interglacial cycle. Today, permafrost extends predominantly accross the Arctic regions but was also present at mid-latitudes during glacial periods. Indeed, paleodata indicate its presence over most of the Paris basin, south of the Fennoscandian Ice Sheet in Europe. Freezing and thawing of permafrost may alter groundwater flow, recharge and discharge patterns in large sedimentary basins but their effect on hydrogeological processes are difficult to quantify. In particular, present-day hydrogeological conditions may still reflect the impact of the last glaciation. Here we investigate the response of the Paris basin groundwater system to permafrost formation and dissipation during the last glacial/interglacial cycle, by means of a numerical study. We use a newly developed coupled groundwater flow and heat transport model with integrated freezing and thawing processes to examine the interplay between groundwater flow and subsurface ice. It includes latent heat effects and modifications of hydraulic and thermal conductivities due to ice formation. A hydrogeological section across the Paris basin serves as the basis for our simulations. Time-varying boundary conditions are derived from a paleoclimatic scenario. Our model calculations allow us to estimate changes in groundwater movement over the last climatic cycle and to explore the influence of past permafrost on present-day hydrogeological conditions.